Schedule for Presentation Meeting of Master-Degree Thesis in 2021
International Program of Maritime & Urban Engineering
Date :

July 28th (Wednesday) starting from 09:30

Venue :

S1- 312 Lecture Room
15 min. Oral presentation + 10 min. Q&A session

No.

Time

Name

Supervisor

Title of thesis

1

9:30-9:55

ALSHERFAWI ALJAZAERLY Alaa Kita

Urban morphological changes in the late modern era of Damascus city2

9:55-10:20

HUANG Ruoyi

Irie

Impacts of Yangtze river water transfer on water quality in Lake Taihu, China

3

10:20-10:45 SHI Kanbei

Doi

Investigating users’ acceptance on battery-swapping electric two-wheelers

4

10:50-11:15 HUANG Wenjia

Ma

Residual stress in wire and arc additive manufacturing using low transformation temperaturematerial 10Cr-10Ni

5

11:15-11:40 FUNDORA CAMPOS Sila Mercedes Aoki

Effect of horizontal plates on the sliding of breakwater caissons

Chairperson

Araki

Inui

Lunch breakNumerical study on derivation of hydrodynamic coefficients of AUV using CFD based on
N-S equation of non-inertial coordinate system
Development of automatic evaluation system of underwater vehicle's motion performancebased on OpenFOAM

6

13:00-13:25 CHAN Siyu

Suzuki7

13:25-13:50 LI Junjian

Suzuki8

13:50-14:15 LANGILANGI Colin Fatuimoana

Maki

Capsizing & survivability of ships based on safe basin’s fractals

9

14:20-14:45 LIN ShenChi

Toda

Microcomputer control of underwater vehicle with undulating side fins10

14:45-15:10 CHENG Yuxuan

Hirohata

An investigation on patch welding repair for thickness reduction of steel structural compressive
memberMeeting for Evaluation: From 15:30 at S1-312 Lecture Room
Members are Steering committee members and the supervisors

Inui

Irie

International Program of Maritime & Urban Engineering / Abstract of Master Thesis

July, 2021

Urban morphological changes in the late modern era of Damascus City
Alaa Alsherfawi Aljazaerly
Lab 03. Architectural and Urban Planning. Department of ArchitecturalEngineering
Key Words: Damascus, street system, Space Syntax, urban morphology

1. Introduction

3. Findings

Damascus, the capital of Syria, is among the oldest
continuously inhabited cities in the world. The long uninterrupted
history of Damascus dates back to 3000 BCE (UNESCO, 2009).
Through its long history, the city has been under different
rulership and has hosted multiple civilizations, from Aramaic
through Greeks, Romans, Islamic and finally Ottoman rule. It waslater colonized by the French until independence in 1946, when it
became the capital city of the Syrian Arab Republic (Burns, 2019;
Lababedi, 2008).
Since the early modern era— the end of the Ottoman empire in
Syria— Damascus has undergone different socio-spatial, political,
and economic changes. These multiple transformations, coupledwith rapid urbanization and urban expansion is exerting asignificant impact on the urban fabric, especially in the physicalconfiguration of space or urban morphological aspects. In order tocomprehend these morphological changes and associated patterns
since the late modern era this research aims to answer thefollowing questions:⁻ What is the spatial configuration of Damascus city urban
core between the French mandate and before the civil war?
⁻ What is the logic behind the street pattern of the spatialconfiguration?
⁻ What are differences between the street morphologies on thelocal level before the war?

The morphological transformation of Damascus City
According to the results, the city kept its traditional
morphology during the early years of the French mandate (1929).
The organic streets and hierarchy are visible on the axial map as
there is variance in the length of the axial lines. The syntactic corefollowed the shopping streets and commercial zones. As the city
was organically expanding, the strong integrated streets segments
correspond to the highly populated segments such as the "Haj"route, which had great spatial and also social and economic
relevance in the Ottoman era (Al Rahhal, 2015).
However, a new pattern of wide and straight (boulevards)
emerged after the first master plan directed by the French,creating a dual street morphology. This master plan was the firstcity-scale development plan for Damascus. It introduced a foreign
pattern to the street structure as the streets became primarily forvehicles rather than pedestrians. The city started to grow towards
the north. Consequently, syntactic core shifted towards the northand to the new city commercial center. The city's historic center,
which kept its traditional structure, consequently lost its position
as strong integration core.
With the second master plan, which had concentrated onzoning the city and link it with the surrounding suburbs, coupledwith population increase, new neighborhoods emerged in the city
towards the west and south. These new parts had different
morphological patterns than the French developed areas andneighborhoods. As the city grew southwards, the integration coreextended towards the north-south axis. By 2004 the density of thecity had increased, and informal settlements have grown to createa belt around the city. Hence, the integration core expanded in theradial direction with a center between the traditional and newcommercial areas.
Relationship between the parts and whole
The degree of consistency between the local and city-wide
analysis reflects how much the city is intelligible (Figure 2 and 3).
The areas with high local and city-wide integration values are themost visited parts known as the integration core, reflecting theimportance and performance of this area both locally and city
scale-wise. In contrast, areas with low values are segregated andgets less activity from the population as a whole. The commercial
area in Damascus is located in the geometric and integration
center of the city, which probably reflects socio-economic activity
in this part of the city.
Informal settlements located at the edge have less connection
with the city core. However, some informal settlements, despite
having a weak link with the city core, have a very strong local
core due to high street connectivity. This situation can beleveraged to potentially reduce the pressure on the integrationcore through the creation of multiple central poles and thus
decentralize the concentration from the city center towards thesouth.

2. Methodology
The study employed space syntax methodological tool toanalyze the morphological transformation of the Damascus(1929-2004). The timelines were according to major changes suchas economic, cultural, and political changes. However, 2004 was
set as the reference point to analyze the situation of the city on a
local scale. At the local scale, the city is analyzed according tostreet relational analysis. Based on the time of development andland use, eight cases were chosen for the microanalysis. By
comparing the eight cases with the results of the syntactic
analysis, it was possible to understand how different
morphologies are associated with the different syntactic
performances.

Figure 1: Research FrameworkLocal scale morphologies
The inner system of the areas has strong effect on the local
integration values. The results showed that different street
morphologies produced different patterns of syntactic
performance. The informal settlement which had uniformed street
system gave high integration value. However, this high local
integration with lack of connection to the city core may not bebeneficial on the activity level. Since all street have the same highvalue then relatively they have low activity as it will be equallydistributed on all the streets. Furthermore, the lack of accessibility
hierarchy can be translated as lack of privacy hierarchy. Whereas
the traditional systems showed less integration values, there ishierarchy in street morphological and syntactic system meaning
there is different scales from public to private. The hierarchy
gives underlying system to the distribution of function where
integrated areas used as commercial and shopping streets and theless integrated as housings.
Commercial areas on the other hand had the highest city-wide
integration meaning that these areas are accessible and have highactivity degree on the scale of the whole city.

future studies should employ human behavior analysis. More,there is the need to reference updated and recent maps after 2011
to comprehend the situation after the war.

4.

Figure (2): Global integration analysis of Damascus 2004 radii Rn

Conclusion and planning implication

Based on the findings from this study, the following three
implications for urban planning and policy are proffered:• City planners and urban policy makers need to maintain thestreet pattern of the historic centers to keep its present characterof balance between use and activity since it favors a pedestrianenvironment• Although the shift in core zones of street activity to the south
is necessary to reduce overconcentration, it needs to be managed
through integrated metropolitan planning that prioritize
connectivity between different areas to prevent segregation ofneighborhoods such as informal settlements• While southern area shows high integration, this is due to thearterial roads or planning street systems for cars. It is importantfor promote balance in street systems that improve connectivity atcity scale and the local scale especially in relation to thepedestrian or human environment.
• There should be the integration on informal neighborhoods
that show high integration but segregated from the larger cities.
Thy are potential news cores but need better connectivity to themain city to avoid segregation within the urban realm.
• Pos-war redevelopment should pay attention to the potentialof the street patterns in both historic and informal areas toencourage a more people-centered street design that promotes
human interaction, movement and diversity in the use of streets.
Overall, through space syntax-based analysis as showedvarieties in syntactic performance over different historical periods
and over local urban systems. Specifically, the study has
demonstrated a dual morphology of street pattern manifested inorganic street patterns concentrated in traditional and informal
areas, on one hand and preplanned streets in formally plannedneighborhoods.

5.

Future Studies

The major component of space syntax analysis is to undertake
empirical or field-based analysis integrate the human behavior
and the social dimension of street patterns. Due to the inherent
limitation of this study’s inability to engage in field analysis,

Figure (3): local integration analysis of Damascus 2004 radii 500

References
1) UNESCO(2009)

Ancient

City

https://whc.unesco.org/en/list/20/Hasemura

ofDamascus(retrievedon

20-1-2021)
2) Burns, R. (2019). Damascus: A history (Second edition).
Routledge.
3)

Lababedi, Z. (2008). The urban development of Damascus:
A study of its past, present and future Masters, (University
College London) https://discovery.ucl.ac.uk/id/eprint/14328/(retrieved on 01-02-2020)

4)

Al Rahhal, A. (2015). The Pilgrimage Route and its Service
Buildings in Syria during the Ottoman Period (Historical andcomparative study). Damascus University

International Program of Maritime & Urban Engineering / Abstract of Master Thesis

July, 2021

Impacts of Yangtze River Water Transfer on Water Quality
in Lake Taihu, China
Huang Ruoyi
Water Engineering Laboratory, Division of Global Architecture
Key Words: Lake Taihu, numerical simulation, water diversion, water quality, SCHISM

1. Introduction

2.2 Methodology

The rapid and extensive economic development of China inrecent decades has caused eutrophication of lakes. The water
quality deterioration of a lake not only affects the ecosystem of
the lake itself, but also the lives of local residents and thedevelopment of local economy. Therefore, improving the water
quality and ecological functions have become urgent tasks.1)
The Chinese government has carried out comprehensive
treatment of Lake Taihu near Shanghai. The main measures
include controlling external pollution, implementing ecologicaldredging, and scientific water diversion. Water diverted from the
Yangtze River into the lake could alleviate deterioration of thewater in the basin, improve the water environment, speed up theflow within the lake, improve the self-purification capacity, andshorten the water-change rate of the lake. 2)
In this study, the flow and water quality in the lake in 2013
were simulated. By varying the artificial water diversion from the
Yangtze River in the model, the effect of diversion on the water
quality of the lake, especially in the northern region, where
cyanobacteria outbreaks are severe, were studied. The purpose of
the study is to clarify the impact of the Yangtze River diversion
on the central and northern regions and propose an improvementof water diversion measures.

In this study, a three-dimensional flow model developed byZhang et al., semi-implicit cross-scale hydroscience integrated
system model (SCHISM), is used with an unstructured grid.
SCHISM solves the Reynolds averaged Navier–Stokes (RANS)
equations and uses the Boussinesq approximation to approximate
the transfer of heat, salt, and tracer in a hydrostatic form with
unstructured simulation grids.3) In the vertical direction, a simple
sigma grid was used in this study.
The water quality simulation in this study used the integrated
compartment model (ICM) module coupled to the SCHISM
model framework. It comprises 21 variables, including
zooplankton, phytoplankton, organic carbon, nitrogen,phosphorus, silica, chemical oxygen demand, and dissolved
oxygen (DO), etc.. The specific settings of the model andsimulation are shown in Table 1.

2. Materials and Methods
2.1 Description of the study area
Lake Taihu is the third largest freshwater lake in China. It is in
the southern part of Jiangsu Province, adjacent to Zhejiang. It has
an average water depth of 1.9 m, a maximum depth of 2.6 m, anda volume of 4.43 billion cubic meters. The average volume ofwater entering the lake annually is 5.72 billion cubic meters, andthe water is changed every 317 days. Fig. 1 shows the location of
the lake, and the river channels and water gates those used todivert water.

Fig. 1 Geographical location of Lake Taihu, river channels
and water gates.

Table 1 Setting and Conditions of the model.
Setting
Node spaceca. 500 m
Horizontal Grid
Number of grids
12690
Number of layers
5 layers
Vertical Gridσ coordinate
Coordinate systemsystemMeteorological
Data from Climate Forecast System
Data
Version 2 (CFSv2)
River Flow Data
Lake Taihu Basin Administration
Spin-up Period
2013.1.1–2013.5.31
Simulation Period
2013.6.1–2013.12.31
Timestep
120s

3. Results and Discussion
3.1 Model reproducibility
The reproducibility of the model is mainly achieved bycomparing the water temperature, ammonia nitrogen (NH4-N),
total nitrogen (TN), phosphate (PO4), total phosphorus (TP), DO,
cyanobacteria biomass and algae biomass ratio’s calculated
results of Case-R (using seasonal water diversion data same asreality) and observed values. The observation data are obtained
from the Lake Taihu monitoring dataset.4) Locations forvalidation are the observation stations of THL01 and THL08,
marked with red dots in Fig. 1. THL01 is in the northern Meiliang
Bay, an area prone to cyanobacteria, and THL08 is located in thecentral area of the lake. The reproducibility of these two points ishighly beneficial to the overall water quality research.
Fig. 2 shows the simulated TN, TP, DO, and cyanobacteria
biomass at THL01 and THL08. The model has good performance
during the study period when cyanobacteria blooms are prone tooccur.

Fig. 4 The ratio of the averaged concentration of each case to
Case-R from August to October.

Fig. 2 Simulated TN, TP, DO, and cyanobacteria biomass at
THL01 and THL08 of Case-R.
3.2 Impact of water diversion
Because Wangting and Taipu Watergates could be completely
controlled, it is possible to manually adjust the amount of water
drawn from the Yangtze River. This simulation varies the water
diversion volume of the Wangting Watergate in 2013 by factorsof 0, 0.25, 0.5, 0.75, 1.25, 1.5, 1.75, and 2 relatives to the reality
value to observe the impact on the lake water quality.
Fig. 3 shows the average flow of Case-0 (no diversion),
Case-R and Case-2 (2-fold volume) from Aug. to Sept. 2013. It
can be seen that the impact of water diversion on the flow
velocity is mainly concentrated in the northern part. It can be
expected that the water diversion will improve the water qualityof the northern part.

Fig. 3 The average flow of Case-0, Case-R and Case-2 from
August to September 2013.
At THL01 the cyanobacteria biomass decreased with theincrease of water diversion during August to October, and the gap
between the cases gradually increased over time. In THL08, thecyanobacteria biomass grows relatively smoothly in Case-0 andas the water diversion volume increases, the fluctuation increases.
Water diversion can reduce the TN concentration by about
0.3mg/L at most. This has a great impact on the lake, which has atarget TN content of 2mg/L. In different cases, the results of TP
and DO have not changed much and the results of TP and DO
met the target value in all cases.
Fig. 4 shows the ratio of the averaged concentrations of eachcase to Case-R. To evaluate the impact of water diversion volume,the calculation results were averaged during Aug. to Oct. for eachwater diversion case, and find the ratio to the averaged value of
Case-R.

At THL01, comparing Case-0.5 (0.5-fold volume) and Case-0,
the cyanobacteria biomass decreased by about 10%. When thewater volume rises to Case-2 level, it will be reduced by about
25%. In terms of TN and TP, water diversion can improve themslightly. A small amount of water diversion can increase the levelof DO, while continuing to increase the amount, the DO will
decrease. At THL08, the algae biomass in all cases was larger
than that of Case-0. However, when the water volume exceeds
Case-0.75, the biomass will fall again. Water diversion will
increase the TN and DO levels, but when the amount of water
conduction is larger than Case-R, the effect is no longer obvious.
In the calculation of the TN compliance rate from Aug. to Oct.,water diversion has a significant impact on the improvement of
TN in the northern part of the lake. Even a small amount of water
diversion, such as Case-0.25, can increase the compliance ratefrom 38% to about 47%. When the water conductivity exceeds
the Case-0.75 level, although the compliance rate has declined, it
can still be maintained at about 51%. In the lake center, water
diversion has little effect on the compliance rate, and thecompliance rate in each case is around 85%.

4. Conclusions(1) Seasonal water diversion is beneficial to improve thecyanobacteria outbreak in the northern part of Lake Taihu. (2)Even a small amount of water diversion can improve thecondition of cyanobacteria and TN in the northern part of the lake.
(3) Although DO and TP will deteriorate in central area due to thewater diversion, they can still meet the standards. (4) It is
possible improve the condition of cyanobacteria in the north byincreasing the amount of water diversion. Even doubled thevolume of diversion can still satisfy the water quality standards inthe central part of the lake.

References
1)

2)

3)
4)

Bai XH: Importation of wind driven drift of mat like algae bloom
into Meiliang Bay of Taihu Lake in 2004 Summer. J. Environ. Sci.,
26(6), 57–60, 2005. [In Chinese]
Hu WP: Study on the 3D numerical simulation of dynamics in Lake
Taihu, China. 1. Wind-driven and the up and down of water level
induced by wind. J. Lake Sci., 10(4), 18–25, 1998. [In Chinese]
Zhang YJ, Ye F: Seamless cross-scale modeling with SCHISM.
Ocean Model., 102, 64–81, 2016.
Min C, Qian R et al.: 2007–2015 Taihu water body physical andchemical monitoring dataset. China Scientific Database, 5(1), 2020.

International Course of Maritime & Urban Engineering / Abstract of Master Thesis

July 17, 2021

Numerical study on derivation of hydrodynamic coefficients of AUV
using CFD based on N-S equation of non-inertial coordinate system
Chan Siyu

Naval Architecture and Ocean Engineering
Key Words: AUV, Non -inertial coordinate system, Forced oscillation test, CFD, OpenFOAM

1. Introduction

2.2 Momentum Equation

In recent years, ocean exploration has gradually been paid
attention to by various countries, and some ocean exploration
technologies have also been well developed. For example,
Autonomous underwater vehicles, so known as AUV, are widelyused in this area such as ocean resource exploration and ocean
environment exploration.
To meet the requirements for different working conditions, theAUV design should take hydrodynamic performance as animportant target. So firstly, the force condition for a sailing AUV
should be studied. To know the force condition, computational
fluid dynamics (CFD) is a good choice because of the relatively
low cost and the feasibility. For example, GAO and PAN derived
hydrodynamic coefficients of a high-speed AUV by using
dynamic mesh tech. And Joung T., Sammut, K. did a study on thedesign optimization of an AUV by using computational fluid
dynamic analysis.
But the dynamic mesh tech has its own disadvantages. Firstly,
the efficiency is not good. The solving for mesh movement inevery time step consumes a lot of computing resources which
results in high time cost. Secondly, the numerical stability is not
good. Calculations are usually tended to diverge.
So in this work, a new method is developed to derivate theforce coefficients by describing the motion of the object in a
non-inertial coordinate system. When the coordinate system isfixed on the object, the deformation and the displacement of themesh system can be avoided fundamentally. By doing that, theefficiency of the simulation is greatly improved, and thenumerical stability is also greatly made better. Besides, theaccuracy is compared in this work. Two descriptions share thesame trend in time history.

2. Basic equations of fluid mechanics in non-inertial
coordinate system
To do the simulation in a non-inertial coordinate system, thebasic equations of fluid mechanics should be set up in a
non-inertial coordinate system. And firstly, the theorem for thecomposition of velocity and acceleration is known as:(1)

And also, the momentum equation can get as:(4)

Where the source term f is:(5)



The value of relative velocity u r is processed as the value of
it in the previous time step.

3. Solver process
Based on the basic equations of fluid mechanics in non-inertial
coordinate system, a solver is made by using PIMPLE algorithm.
And the process is shown in Fig 1.

Fig 1 relPimpleFoam Process
The translational and the angular velocity are included in the
additional source term contrubute in every step of the calculation.
So that the solving for the mesh motion is avoided.

4. Solver Correctness Verification
In order to compare the difference between the non-inertial
coordinate system and the inertial coordinate system for fluid
simulation. Two cases based on the same model, motion, fluid
properties and turbulence parameters will be tested. The only
difference is, motion is described in inertial coordinate system in
one case and in non-inertial coordinate system in the other case.

(2)

2.1 Continuity equation
Using relative velocity and acceleration instead of absolute
velocity and acceleration, the continuity equation in a non-inertial
coordinate system can get as:  ur  0(3)

Fig 2 Model
4.1 Case settings

Table 1 Case Parameters
Type of Fluid

Table 2 Efficiency Analysis
Water (20 ℃)

CPU

AMD RYZEN 5950X

Density

SMT

OFF

Kinematic Viscosity

Cores

10

Number of cells

280,391

Time cost in inertial system

3242s

Time cost in non-inertial system

663s

Dynamic Viscosity
Characteristic length of model
Reynolds Numberk

The calculation condition is shown in Table 2, by describing
the motion in a non-inertial coordinate system, the time cost was
reduced by 79.5 ％ . And as is shown in Fig 6, the numericalstability is much better in a non-inertial coordinate system.

εFig 6 Residuals for inertial coordinata system (left)& for non-inertial coordinate system (right)

5. hydrodynamic coefficients
Fig 3 Motion
4.2 Accuracy Analysis

Fig 4 Force Analysis

After the correntness verifivation, the hydrodynamic
coefficients is derivated. And the result is shown in Fig 7. Where
the lift (Cl), the drag (Cd) and the moment (Cm) coefficients ismeansured and shown.

Fig 7 Time history of hydrodanamic coefficients

6. Conclusion

Fig 5 Moment Analysis
The force condition of the two reference systems is shown in
Fig 3 and Fig 4. The motion is limited in the X-Z plane, so force
in the Y direction and moment in the X and Z direction are
ignored.
The force in the X and Z direction share the same trend in time
history. And the moment in the Y direction matched very well.
4.3 Efficiency Analysis

In this paper, a non-inertial system-based fluid mechanics
solution method is developed. And the accuracy and theefficiency of the method are analyzed. Two descriptions share thesame trend in the time history of force condition. Besides, theefficiency and the numerical stability are much better by using thenon-inertial system-based method.

References
1) Gao, F. D., Pan, C. Y., Xu, X. J., & Han, Y. Y. (2012).
Numerical computation and analysis of high-speed
autonomous underwater vehicle (AUV) moving in head sea
based on dynamic mesh. Journal of Central South University,
19(11), 3084-3093.
2) Joung, T., Sammut, K., He, F., & Lee, S. K. (2009, July). A
study on the design optimization of an AUV by using
computational fluid dynamic analysis. In The NineteenthInternational Offshore and Polar Engineering Conference.
OnePetro.

International Program of Maritime & Urban Engineering / Abstract of Master Thesis

July, 2021

An Investigation on Patch Welding Repair for Thickness Reductionof Steel Structural Compressive Member
CHENG Yuxuan
Structural Engineering Laboratory, Department of Civil Engineering
Key Words: Welding, Repair, Thickness reduction, Load-carrying capacity, Finite element method

2. Compressive Experiment
2.1 Size design of patch plate specimen
In this study, in order to clarify the influence of dimension ofpatch plate on the ultimate strength of patch-repaired specimen,
steel plate specimens with uniform thickness reduction were
fabricated.
The length of the thickness-reduced base plate is always 600
mm. The length of thickness reduction is 60 mm. The thickness
reduction of base plate is 50% [2] of the original thickness as 18 mm.
As shown in Table 1, the length of patch plate, L is 90 mm in A, B
and C specimens. That is 150 mm in D, E and F specimens. The
thickness of patch plate, tp and the weld bead size, s are different
in each group. The number of specimens in each group is 3.
Patch plate L
Base platetp

Thickness reduction
dc = 4.5
tb =18
Remaining t =9s
Weld bead
Throatthickness
r =60
tw = s / √2
Fig. 1 Shape and dimension of specimen (mm)Table 1 Detailed size information of specimens (mm)
Type
tb
t
L
tp
s
A
18
9
90
4.5
4.5
B
18
9
90
7.5
7.5
C
18
9
90
7.5
4.5
D
18
9
150
4.5
4.5
E
18
9
150
7.5
7.5
F
18
9
150
7.5
4.5
2.2 Experimental condition
After measuring and recording the detailed dimensions of eachspecimen, a universal testing machine was used for thecompressive loading experiment on the 6 sets of specimens. The

Load (kN)

When applying patch plate to thickness-reduced steel bridge
members due to corrosion, high-strength bolts are generally
selected as the joining method, and welding is rarely used [1]. In
this study, considering the adaptability of repair by patch weldingon thickness-reduced steel structural members, a basic experimentand its numerical simulation were conducted to examine the effectof patch welding in each different dimension. The changes incompressive behavior of thickness-reduced steel structuralmember repaired by different dimensions of patch plates were
examined.

specimens were fixed on both ends by steel blocks. Two
displacement transducers were set between the upper and lower
blocks for measuring the vertical displacement.
By the loading machine, the monotonic compressive load in a
vertical direction was slowly applied to the specimen. The
maximum load was confirmed and the vertical displacement
reached 2 mm, then the load was released. Fig. 2 shows therelationship between load and vertical displacement. In the figure,the result of one specimen per each group is shown.
200
Type t ps
180
A
4.5 4.5B
7.5 7.5
160
C
7.5 4.5
140
120
100
A
A ave max = 153.87
80
B ave max = 196.45
B60
C
C ave max = 180.45
40
A-s
A-s max = 172.18
B-s
B-s max = 189.81
20
C-s
C-s max = 177.44
0
0
0.3
0.6
0.9
1.2
1.5
Vertical displacement (mm)(a) Load and vertical displacement of A, B, C

Load (kN)

1. Introduction

200
180
160
140
120
100
80
60
40
20
0

Type t p
D
4.5
E
7.5
F
7.5

s
4.5
7.5
4.5

D ave max = 148.15
E ave max = 175.59
F ave max = 178.36
D-s max = 153.74
E-s max = 182.81
F-s max = 171.89

D
E
F
D-s
E-s
F-s

0

0.3
0.6
0.9
1.2
1.5
Vertical displacement (mm)(b) Load and vertical displacement of D, E, F
Fig. 2 Results of compressive loading experiments

3. Elastic Plastic Analysis
3.1 Analysis model information
As one of the highlights of this study, we performed an elasticplastic analysis to verify the results of the experiment. At the sametime, the compressive behaviors of the intact model, the corroded
thickness-reduced model, and the patch-repaired model arecompared.

In order to keep consistent with the experimental conditions, thesimple and easy-to-use models are used in this analysis, with auniform, constant thickness reduction and initial deformation ofmodel surface. Also due to the relatively slender and long size ofthe steel structure component and its symmetry, the deformation
under force is mainly bending deformation, we ignored its slight
deformation on the width direction, two-dimensional plane strain
condition simulation was chosen, as shown in Fig. 3. In theexperiment, materials of specimens did not experience significant
temperature changes so that we picked the curve is thecharacteristic of the steel material at 0 degrees Celsius [3].

Applied stress: 𝜎(Forced displacement)yy

4.2 Simulation results

Axial strain: 𝜀(Displacement / 600)

x

Fig. 3 Simulation model and mesh division.
3.2 Analysis simulation results

Bearing capacity (kN)

After analysis simulation, we got the maximum load value of theintact model was 185.13 kN. We take it as the target bearing
capacity on others patch-repaired models.
The simulation results for experiments are shown by continuouslines in Fig. 2, and we could think the simulation curves and results
are basically in line with the experimental curves and results.
In the A, B, C groups, the simulated maximum load of A is172.18 kN, which is 11.90% higher than the experimental average
result. The simulated maximum load of B and C are moreconsistent with the experiment. They are 3.38% and 1.66% smaller
than the average of the experimental results, respectively.
In the D, E, F groups, D specimens and the E specimens madewere unqualified, because holes are created in weld beadconnection part due to poor welding, which made the simulated
maximum load of D and E are much higher than the experimental
average results values. But when we added 4 holes in each model,
the simulation results are closer to the experimental results, whichwere only 3.78%, and 4.11% higher than the experimental averagevalues. And in E group, it is 3.63% lower than the experimental
average value. As shown in Fig. 4.

4.

more simulations to explore the recovery of the repaired patchplate load performance under different parameter conditions. We
selected materials and analysis condition which the same as theexperiment used and the previous simulations used.
This time, we simulated the specimens under 75 different
conditions to obtain the maximum load-bearing stress under thedifferent conditions. We still selected the test specimens with thecorrosion amount in the center part of the test specimens being 50%of the original thickness, and selected the weld bead size equal to
4.5 mm, 6.0 mm, 6.5 mm, 7.5 mm, 9.0 mm. After that, we selected
the thickness of the patch plate according to the bead size whichlarger than the bead size. Finally, we set the length of patch plate
to 60 mm, 90 mm, 120 mm, 150 mm, 180 mm.

When the weld bead size s were 4.5 mm and 6 mm, themaximum load stress did not reach the target load stress 185.13 kN.
When the weld bead size s=6.5 mm, the maximum load stressreached the target stress in some cases. It is considered that this isbecause the throat thickness tw (When s=6.5 mm, tw=4.6 mm) is
almost equal to the thickness reduction on one side of base plate dc(4.5 mm). When the weld bead size s were 7.5 mm and 9 mm, themaximum load stress was higher than the target stress except thesituation with patch plate length L=60 mm. At the same time, thepatch plate was longer the maximum load stress was higher.
Based on the deformation modes obtained by the simulation,
bending of patch plate occurs at the welded ends of the patch plate.
This bending deformation was restrained due to the contact
between the patch plate and the base plate when the patch plate
length was long enough. In this study, it was suggested that thepatch plate length should be longer by 30 mm than the thicknessreduced region.

5. Conclusions

Fig. 4 Analysis simulation results on different models(1) Whether in experiments or analysis simulations, the ultimate
compressive strength of thickness-reduced steel plates with patch
welding was influenced by the weld bead size and the thickness ofpatch plate.
(2) Under the limited conditions performed in this study, it is notthat the longer patch plate will provide greater ultimate strength,
the shorter patch plate provided the higher ultimate strength.
(3) In order to restore the load bearing performance to the target
stress level (the maximum load stress of the model without thebacking plate also without thickness reduction), we should ensurethat the throat thickness is greater than or equal to the base plate
thickness reduction, and set the length and thickness of the patch
plates corresponding to throat thickness. Throat thickness of beadsize was a dominant factor.
(4) Through many simulations, we can infer that the length ofthe patch plate should be set to be about 30 mm longer than the
thickness-reduced area.

Analytical study of patch welding repair on

References

thickness-reduced structural member subjected to1) Gheitasi, A., & Harris, D. K. (2015). Journal of Bridge
Engineering, 20(3), 05014012.
2) Tamakoshi, T., Yoshida, Y., Sakai, Y., & Fukunaga, S.
(2006). Public Work Research Institute of Japan.
3) 中川弘文, & 鈴木弘之. (1999). 鋼構造論文集, 6(22), 57-65.

200
185.13160

189.81
185.13182.81
177.44172.18171.89153.74120

s=4.5 s=7.5 s=4.5
tp=4.5 tp=7.5 tp=7.5

s=4.5 s=7.5 s=4.5
tp=4.5 tp=7.5 tp=7.5

80

L = 90

L = 150400Intact

A

B

C

D

E

F

compressive loads
4.1 Analysis model basic information
Because the analysis of the previous Chapter Three is only aimed
at six kinds of simulation analysis. In this part, we hope to conduct

International Program of Maritime & Urban Engineering / Abstract of Master Thesis

July, 2021

Investigating users’ acceptance on battery-swapping electric
two-wheelers
Kanbei Shi
Transportation and urban design, Civil engineering
Key Words: Battery sharing service, E2W, motivation, lifestyle, path analysis

1. Introduction
Transportation electrification [1] is proposed and regard as oneof significant opportunities to address harmful effects caused byoverreliance on mass motorization. However, even great efforts
have been taken in promoting electric vehicles and restrict
conventional vehicles by government worldwide, mass adoptionof electric vehicles has been hampered by many factors such as
limited driving range, insufficient charging infrastructure [2].
Battery swapping system was proposed and provided a solution
through providing battery share or subscription service instead of
selling. In Japan, E2W stays in low acceptance levels. After theoutbreak of Covid-19, battery swapping electric two-wheelers(BS-E2W), as a convenient eco-friendly mobility with hedonic
quality in usual days, offer a low-infection-risk means ofcommute and leisure activities in unusual days. On the other hand,
E2W is relatively vulnerable road participants, its promotion
needs careful consideration of emerging safety issues.
This study aims to finds factors that influence user’s
acceptance on BS-E2W, and to explore how those factors
influence consumers’ intentions switching between purchaseintention and intention to use battery sharing service.
The research structure is organized as follows. Chapter 1
describes the background and the aims of this research. Chapter 2
present a review of the literature on factors in relation to users’
acceptance of BS-E2W and proposed the research hypothesis,
Chapter 3 describes the details of survey context, questionnaire
design, and data analysis methods. Chapter 4 present the resultsof data analysis and the outcome of path analysis models. Chapter
5 discuss the findings and limitation of this research.

Fig. 1 Hypothesized conceptual model

3. Methods
3.1 Survey
The demonstration experiment “Eyan Osaka” is conducted by
the Japan Automobile Manufacturers Association in cooperation
with Osaka local government, Osaka University, and Lawson
convenience stores. In the project, experimental-use E2Ws (seeFig. 2) were rented to participants at a price of 1000 JPY permonth.12 battery swapping stations (1 in Suita campus, 1 in
Toyonaka campus, 10 in convenience stores, see Fig. 2 ) havebeen set up within the Hokusetsu area. The program last one year
from September 2020 to October 2021, four phases in total. The
10 battery swapping stations in convenience stores were put into
use in the second phase. Until the completion of this research, theproject has collected all data of 2 phases.

2. Literature review
2.1 Factors influencing acceptance of BS-E2W
Previous literature inspired us that instrumental, hedonic,
value-rational motivation, concerns may influent the user’s
lifestyle and further influent their usage intention to E2W.

Fig. 2 Electric two wheelers, swappable battery, battery swap
station, stations in convenience store (left to right)

2.2 Research hypotheses
Based on literature, an exploratory model (see Fig. 1) of factors
influencing usage intention was presented. First block of variables
that extracted from pre-questionnaire include instrumental,
hedonic, value-rational motivation, and concerns, working as
exogenous variables, which are also expected to have direct
effects on satisfaction and usage intention. Post perception andconcerns are expected to mediate the relationship between
motivation and usage experience and lifestyle change. The
Second block variables would directly predict satisfaction andusage intention, mediating the effects of motivation.

Fig. 3 Photos of safety training
3.2 Sample, procedure, data analysis
In this study, we focused on students and faculty in Osaka
university. In each phase of experiment, participants were asked
to fill 3 online questionnaires and attend online group interview(see Table.1) Subjective questionnaires and objective usage data
were collected to explore how hypothesized factors affected
respondents’ acceptance on BS-E2W. Demographic attributes
were collected from recruitment questionnaire, motivation-related
questions were asked in pre-questionnaire while questions ofperception, satisfaction, intention and usage behaviors were in thepost questionnaire. Except the questionnaire data, we collectedusage data from sensors on vehicles like origin-destination,monthly battery swapping times, trips, driving distance. The
responses from questionnaires and usage data from sensors wereanalyzed on statistical analysis software IBM SPSS 23.0 andAmos 24.0.
Table. 1 Summary of survey
SurveymethodThree online questionnaires(recruitment, pre, post);
Online group interview

Survey time

Phase Ⅰ: 2020.9.27- 2020.12.31
Phase Ⅱ: 2021.1.15- 2021.3.31※2021.1.11: C-BSS put into use

Target group

University students and faculty

Sample size

Phase Ⅰ: 21 (2 professors)
Phase Ⅱ: 11 (1 staff)
32 in total

4. Results
4.1 Descriptive statistics
32 participants were recruited in the study and completed all ofquestionnaires. 28 males and 4 females, with a mean age of 22.3.
65.5% were undergraduates, followed by 25.0% graduates and9.4% faculty. 53.1% of respondents’ commute mode were active
walking and cycling, 12.5% was powered two-wheelers (PTW),
31.1% was public transport. Except 34.4% experienced PTW
riders, the rest of participants were beginners not only E2W but
also PTW.
4.2 Difference analysis
T test results showed participants’ value-rational expectation(environmental and altruistic) increased and realized high-priceattribute of E2W after participation. Male participants were moreparticular about instrumental attributes of E2W, while female
respondents were easily satisfied and perceived higher
environmental awareness. Participants who had driven E2W for
last mile showed higher post instrumental satisfaction,
comprehensive changes in their lifestyle not only in weekday but
also in weekend activities. This group presented significantly
higher general satisfaction and higher usage level.
4.3 Correlation analysis
From the calculation of spearman’s rho correlation coefficientsmatrix, general satisfaction “BS-E2W fits my life”, werepositively correlated with hedonic perception, lifestyle items on“increased freedom of university-related activity” “expanded
range in weekday”, “increased communication with friends”,
monthly trips, while negatively correlated with post service
concerns “troublesome process of battery swapping”.
4.4 Path analysis
Path analysis is a powerful statistical technique that allows formore complicated models than multi-regression model, it can
examine “chains” of influence between exogenous variables andendogenous variables.
In this section, two path analysis models were constructed andestimated including all path coefficients, significance andgoodness-of fit. Considering the limited samples, the overallmodel fit was acceptable.
The results of 1st path model (CMIN/DF= 1.114, p = 0.281,
RMSEA= 0.077, GFI=0.714, CFI=0.923) shows people whoshow higher purchase intention (1) care much about hedonic

attributes of E2W, whereas instrumental dissatisfaction may
reduce the intention; were dissatisfied with the BSS location anddriving range in this experiment; (3) tend to drive for activities on
weekend instead of daily commute; (4) experienced motorcycles
have a relatively lower willingness to purchase possibly becauseof limited driving range of E2W.

p＜0.001***, p＜0.01**, p＜0.05*

Fig. 4 Path analysis on purchase intention N=20
The results of 2nd path model (CMIN/DF= 1.151, p = 0.143,
RMSEA= 0.070, GFI=0.728, CFI=0.907) indicates that people
who had higher intention to use share service (1) highly motived
by instrumental expectation/ satisfaction, interest about new BS
system; (2) did not expect to move in a wide range (narrowdriving range is enough) (3) tended to drive for university-related
activities in weekday. In addition, it is worth mentioning thatsafety training not only taught users safely-driving skills but also
positively correlated participants’ interests in the BS E2W anddirectly influenced users’ anticipation to swap system

p＜0.001***, p＜0.01**, p＜0.05*

Fig. 5 Path analysis on intention to use share service N=32

5. Conclusions
Value-rational (environmental and altruistic) expectation
increased after experiment. Different demographic attributes
groups and their usage purpose perceived different hedonic
perception, satisfaction level and ideal form of acceptance for
BS-E2W. Compatibility of participants’ lifestyle play asignificant role in this process. Extra information of service
allows people faster adaption to this new system. Operators andpolicymakers should take efforts to bridge the information gap
and actively address concerns of potential (but still hesitant) users
how E2W and BS service might fit their daily life.

References
1) Mingfei B, Jilai Y: G of EM, 44-54, 7(3), 20182) T. Eccarius, C.C. Lu.:J :J of ST, 215-231 14(3),2020

International Program of Maritime & Urban Engineering / Abstract of Master Thesis

July, 2021

Residual Stress in Wire and Arc Additive Manufacturing Using
Low Transformation Temperature Material 10Cr-10Ni
HUANG WENJIA
Mathematical Modeling and Computational Analysis Lab,
Naval Architecture and Ocean Engineering
Key Words: Wire and arc Additive Manufacturing, Low Temperature Transformation Material, Residual Stress, Contour Method,
Finite Element Method, Numerical Simulation

1. Introduction
Additive manufacturing(AM) is a technique which build up
objects layer by layer. Comparing to the conventional subtractive
manufacturing methods, additive manufacturing technologies
commonly apply wire or powder as a feedstock which is melted
by a focused heat source and consolidated in subsequent coolingto form a part [1]. During past thirty years, with the advantage ofsaving material and time as well as facilitating the manufacture ofcomplex assemblies formerly made of many subcomponents,
additive manufacturing has become a hot issue in forming filed[2]. Additive manufacturing methods can essentially be divided
into the nature and the aggregate state of the feedstock as well as
by the binding mechanism between the joined layers of material[3]. The most popular processes for AM of metals are Laser
Beam Melting (LBM), Electron Beam Melting (EBM), Laser
Metal Deposition (LMD) and Wire and Arc Additive
Manufacturing (WAAM).
Since additive manufacturing has been widely applied tofabricate functional metal parts in a variety of industries. The
requirements for component performance are also getting higher
and higher. Due to the unique thermal cycle of metal additive
manufacturing which is characterized by the rapid heating,cooling rates and re-melting of underlying previously solidified
layers, residual stress is generated. On one hand, parts’ fatigue
life will be reduced by tensile residual stress. On the other hand,steep residual stress gradients will cause deformation which will
decrease shape accuracy [4,5]. To solve these two points,
researchers in National Institute for Material Science applied aclassic low transformation temperature material 10Cr-10Ni as
deposition material [6,7].
In their research, it was clearly approved by experiment andnumerical simulation that the deformation can be efficiently
decreased through using low transformation material. However,for residual stress, only contour method measurement was
performed. At present, there is no effective explanation for thisproblem from the perspective of numerical simulation.

2.

Fig. 2.1 Heat source model and heating zone.
(2.1)
Where, the R and x, y, z are the radius of a hemisphere ofheating zone and moving local coordinates in which the origin is
the welding arc centre located on the plate surface.
2.2 Contour Method
The Contour Method theory is based on Bueckner’s elastic
superposition principle. The diagram in Fig.2.2 shows the initialresidual stress distribution acting in the horizontal direction in agiven structure (step A). The plate is cut into two parts along theplane of interest (step B). This causes the cut faces to deform
elastically due to the relaxation of residual stress. The resulting
deformations (the contours) are measured using a surface
profiling device with sufficient resolution (step C). After
processing the data (step D), the virtual stresses required to ‘force
back’ the deformed surfaces to their original shape are calculated(Step E). The results given in step F represent the initial stress
distribution from step A acting normal to the plane of interest.

Theory2.1 Thermal Elastic Plastic Analysis
Fig. 2.2 Diagram of contour method for residual stressmeasurement.

In this paper, a simplified hemisphere shape and Gaussianfunction given by Eq. (2.1) are employed. The heating zone isshown in Fig.2.1.

3.

Experiment

There are two different print shapes in this research. One iswall type which we call WAAM-I. The other one is pipe typewhich we call WAAM-O.

To use contour method, we need to use wire cutting to cut out
the section to be measured. In this process, broken wires will havea great impact on the accuracy of the measurement results, so theoperator must ensure the continuity of the cutting process asmuch as possible. The cut section can be directly used formeasurement without any processing. The cutting and measured
section of this experiment are shown in the Fig.3.2, and themeasured section is on the symmetry plane.

Fig. 3.1 Contour method measured section:(a) WAAM-I, (b) WAAM-O.

4.

Numerical Simulation Results and Analysis

4.1 WAAM-I
The stress and strain analysis is also carried out by
JWRIAN-HYBRID. Here we mainly discuss the residual stressalong the welding direction, which means component of residual
stress in Y direction in WAAM-I. Or we call it longitudinal
residual stress. The calculation results of SUS308 case, LTT caseand experiment measurement results are shown Fig.4.1-4.2.

Fig.4.1 The results of SUS308 case:(a) Contour methodmeasurement results, (b) Section surface simulation results.

measurement results, (b) Section surface simulation results.

5. Conclusions
The accuracy of the wire cutting experiment has a great
influence on the measurement of residual stress using contour
method. Measuring on a section that is partially damaged due tobroken wires will make the measurement result difficult to judge
and have large errors.
Through experiments, it is found that the first few layers in the
additive manufacturing process are mutually diluted with thesubstrate. The change of material composition caused by thisphenomenon will lead to the change of martensite transformation
temperature for LTT, which in turn changes the properties of LTT
material.
JWRIAN-HYBRID can accurately predict the residual stress
distribution of the non-transforming austenite stainless steel
SUS308 additive model WAAM-I and WAAM-O. For the phasetransformation material LTT-10Cr10Ni, JWRIAN-HYBRID canalso use the thermal expansion coefficient to perform a moreaccurate prediction of the phase transformation of the material.
Finally, the two models, WAAM-I and WAAM-O, are basicallyconsistent with the experiment measurements of residual stress
distribution.
Under the working condition of multiple decreasing thermal
cycles, LTT material cannot exert its characteristic of generating
compressive residual stress through martensitic transformation at
low temperature. Therefore, in multi-pass welding or multi-layer
additive manufacturing, only the top layers can generate residualcompressive stress. This is partly inconsistent with the original
intention of reducing residual stress by using LTT materials for
welding arc additive manufacturing. Therefore, the next work
should be to consider how to make the LTT still produce
compressive residual stress under the condition of multi-thermal
cycles to improve the fatigue performance.

References1)

2)
Fig.4.2 The results of LTT-10Cr10Ni case:(a) Contour methodmeasurement results, (b) Section surface simulation results.
4.2 WAAM-O
The stress analysis is also performed by JWRIAN-HYBRID.
The results of longitudinal residual stress and contour methodmeasurement results are shown in Fig.4.3-4.4.

3)

4)

5)

6)
Fig.4.3 The results of SUS308 case:(a) Contour methodmeasurement results, (b) Section surface simulation results.
7)

Fig.4.4 The results of LTT-10Cr10Ni case:(a) Contour method

Dirk Herzog, Vanessa Seyda, Eric Wycisk, Claus
Emmelmann,Additive manufacturing of metals, Acta
Materialia, Volume 117, 2016, Pages 371-392, ISSN
1359-6454.
Beaman Joseph J and Deckard Carl R, Selective Laser
Sintering With Assisted Powder Handling, 1990-07-03,
https://lens.org/119-984-865-808-739.
Kruth, J‐P., et al. "Binding mechanisms in selective laser
sintering and selective laser melting." Rapid prototyping
journal (2005).
Shiomi, M., et al. "Residual stress within metallic model
made by selective laser melting process." CIRP Annals 53.1
(2004): 195-198.
北野 萌一, 中村 照美, 低変態温度溶接材料を用いた溶融金属積層造形材の変形低減法に関する基礎的検討,
溶接学会論文集, 2018, 36 巻, 1 号, p. 31-38.
Mercelis, Peter, and Jean‐Pierre Kruth. "Residual stresses
in selective laser sintering and selective laser melting."
Rapid prototyping journal (2006).
S. W. Williams, F. Martina, A. C. Addison, J. Ding, G.
Pardal & P. Colegrove (2016) Wire + Arc Additive
Manufacturing, Materials Science and Technology, 32:7,
641-647.

International Program of Maritime & Urban Engineering / Abstract of Master Thesis

July, 2021

Effect of horizontal plates on the sliding of breakwater caissons
Sila Mercedes Fundora Campos
Coastal Engineering Laboratory, Department of Civil Engineering
Key Words: breakwater caisson, horizontal plate, sliding distance, performance design, BPS method

1. Introduction
Climate change is leading to an increase in frequency andintensity of natural disasters and a sea-level elevation, which
threatens the stability of coastal protection structures.
Furthermore, recent disasters have exposed the catastrophic
damage to the land and port facilities that the destruction of such
structures can cause. This fact implies that the loss of thestructure's functionality influences the extent of damage in thearea to be protected. Hence, evaluating the degree of functional
deterioration of the structure at the time of failure ("performanceat failure") is becoming essential.
Among coastal protection structures, vertical caisson
breakwaters have been widely utilized. Most cases of breakwater
damage involve sliding as a failure mode. Also, due to a
combination of increases in sea level and wave height, sliding
distances of caisson breakwaters are expected to become fivetimes greater than at present, according to Takagi et al. (2011).
Caisson (upright part of the breakwaters) can maintain theirfunctionality even if a limited amount of sliding occurs. Sliding is
not generally allowed under traditional breakwater design. Its
stability has been conventionally judged using safety factors,
balancing external and resisting forces. However, deformation
parameters such as the sliding distance directly indicate theirstability performance. Some researchers have been proposing"deformation-based reliability" design methods, such as Aoki etal. (1995)1)and Shimosako and Takahashi (2000), or developing
devices to extend such breakwaters functionality.
Present research pretends to contribute to the study of thecaisson breakwaters' performance during the failure process bydeveloping a reliable design method and describing theeffectiveness of introducing horizontal plates to reduce the sliding
motion of caissons. Such structure proposal is based on the
hypothesis that a horizontal plate will increase the water
constriction during the movement of the caisson, increasing theadded mass and, in consequence, decreasing the expected sliding
distance. The hypothesis was introduced and 'partially' proved in
Yoshihara (2017, 2019)2) with a 20% reduction of the sliding for aplate length l equal to the water depth h. However, it only
considered the horizontal force in the analysis. Therefore, thisstudy aims to evaluate the vertical forces introduced by the plate
addition determining its influence on the sliding reduction
accurately. Furthermore, to identify improvements and future
research opportunities in caisson shape optimization is also
pursued.

2. Methodology
The structure consists of a breakwater caisson with a horizontal
plate located at sea level. In the model representation (Fig. 1), thewater area is divided into three regions based on their different
boundary conditions. The acting forces are also represented,

where F is wave force, FR reaction forces, and Ff frictional force.

Fig. 1 Breakwater with a horizontal plate.
Model representation
Linear wave theory, wavemaker theory, and potential theory
are applied in the creation of a model which, after the
introduction of a "boundary-points selection" method3) todetermine velocity potentials, leads to the sliding calculation
following the method proposed by Aoki et al. (1995) 1).
Inputs: Model dimensions and properties (B, h, d, g, ρ, ρc)
Sections (z) and iterations (m, n)Frequency (ω) range
Input: Horizontal plate’s length (l)- Velocity Potential (Φ)

Repeat for eachfrequency ω*- Pressure (P)- Reaction Forces on the Breakwater's
Vertical Wall (Fxx)and Horizontal Plate (Fzx)- Added Mass (Mxx and Mzx) andDamping Coefficients (Nxx and Nzx)
- Constant Added Mass (Mxx∞ and Mzx∞) andMemory-effect Function (Rxx and Rzx)

Repeat fordifferent
plate lengthslInputs:Times series model of the wave force
Parameters related to sliding calculation (α, fs, tp)
Wave Force (Ft) and Friction Force (Ff, Fs)
Output: Sliding[Based on Aoki (1995)'s method considering Fzx]

Fig. 2 Sliding calculation flow.
2.1 Velocity Potential. Boundary-Point Selection Method.
After applying boundary conditions, velocity potential
solutions for regions I, II, III, are expressed by Eq.1, 2, and 3,
respectively. A+ and Bn+ are known coefficients, and C0, Cm, D0,
Dm, A- and Bn- unknowns. Eq.1 and Eq.3 are general expressions
for velocity potential, while Eq.2 is derived after somemathematical procedures (Fourier expansions and transforms).
Regions I and II share a boundary in x=l. In there, additional∞𝜙I (𝑥, 𝑧) = 𝐴+𝑐𝑜𝑠ℎ𝑘 (𝑧 + ℎ)𝑒 𝑖𝑘(𝑥+𝐵) +conditions∞

𝐵𝑛+𝑐𝑜𝑠𝑘𝑛 (𝑧 + ℎ)𝑒 𝑘 𝑛 (𝑥+𝐵)

a)

b)

𝑛=1
𝐵𝑛+𝑐𝑜𝑠𝑘𝑛 (𝑧 + ℎ)𝑒 𝑘 𝑛 (𝑥+𝐵)

1 (𝑧 + ℎ)𝑒 𝑖𝑘(𝑥+𝐵) +𝜙I (𝑥, 𝑧) = 𝐴+𝑐𝑜𝑠ℎ𝑘
𝜙II 𝑥, 𝑧 = 𝐶10 + 𝐷0 𝑥
(1)
𝑛=1
𝜙II 𝑥, 𝑧 ℎ= 𝐶0 + 𝐷0 𝑥
ℎ∞
2
𝑚𝜋
𝑚𝜋
𝑚𝜋
∞
+
𝐶𝑚 cosh𝑥 + 𝐷 sinh
𝑥 cos
(𝑧 + ℎ)ℎ+ 2ℎ 𝑚𝜋 𝑥𝑚+ 𝐷 sinhℎ 𝑚𝜋 𝑥 ℎ cos 𝑚𝜋 (𝑧 + ℎ)
𝐶
cosh
𝑚
𝑚
𝑚 =1
ℎ
ℎ
ℎ
ℎ
∞
𝑚 =1

(2)

𝜙III (𝑥, 𝑧) = 𝐴− cosh 𝑘(𝑧 + ℎ) 𝑒∞−𝑖𝑘(𝑥−𝑙) +𝐵𝑛− cos 𝑘𝑛 (𝑧 + ℎ) 𝑒−𝑘𝑛 (𝑥−𝑙)𝑛=1𝜙III (𝑥, 𝑧) = 𝐴− cosh 𝑘(𝑧 + ℎ) 𝑒−𝑖𝑘(𝑥−𝑙) +𝐵𝑛− cos 𝑘𝑛 (𝑧 + ℎ) 𝑒−𝑘𝑛 (𝑥−𝑙)

(3)

𝑛=1

conditions should be satisfied that grant the continuity of thevelocity potential and its derivative. A practical method in which
points at the shared boundary are selected and utilized to obtain
an equation system with an equal number of equations andunknowns is proposed. The method is called the boundary-point
selection method (BPSM), although it has been named in various
forms3). BPSM simplifies theoretical formulations and computer
programming. Its accuracy is examined by comparing the resultswith the conventional method for an RMSE inferior to 1.E-03 byselecting 20 points.
2.2 Sliding
The equation of motion is expressed as Eq.4, where Mxx∞ is theadded mass at an infinite frequency, and Rxx is the memory-effectfunction used in Cummings (1962). The wave force F(t) in thetime domain is determined by a triangle-shaped profile used in
Aoki et al. (1995)1).

Fig. 4 a) Dimensionless added mass (Mxx and Mzx)b) Dimensionless memory-effect function (Rxx and Rzx)
rises for larger plates. Similar relations are seen in thememory-effect functions (Fig.4b). The longer the plate, the moreequals become the parameters at the vertical wall and thehorizontal plate. Thus, the plate works as an equalizer forhorizontal and vertical directions, which is reflected in the sliding
calculations. In Fig.5a, the solutions to Eq.8 are displayed. For all
l/h>0, the maximum displacement is inferior to the case without aplate. However, the reduction of the sliding is insignificant, with amaximum of 2.1%. Comparing these with the sliding due to only
the horizontal force2) in Fig.5b, it is evident the importance ofconsidering the vertical force to represent the hydrodynamic
phenomena more accurately.
a)b)
Velocity

𝑡 𝑡
∞∞
𝑚𝑚
++𝑀𝑀
++ [𝑅[𝑅𝑡 −𝜏 𝜏𝑥 𝑥𝜏 𝜏𝑑𝜏𝑑𝜏==𝐹𝐹𝑡 𝑡−−𝐹𝑓𝐹𝑓 (4)𝑎𝑎𝑥𝑥𝑥𝑥𝑥 𝑥𝑥𝑥𝑥𝑥𝑡 −

Sliding

00

𝛼𝐹𝑠

𝐹 𝑡 =

𝑡 + 𝐹𝑠(0 ≤ 𝑡 ≤ 𝑡𝑝 )𝑡𝑝𝛼𝐹𝑠−
𝑡 + 1 + 2𝛼 𝐹𝑠 (𝑡𝑝 ≤ 𝑡)𝑡𝑝

(5)

𝐹𝑚𝑎𝑥 = 𝐹 𝑡𝑝 = (1 + 𝛼)𝐹𝑠

(6)Fig. 5 a) Dimensionless displacement/velocityb) Displacement reduction. Comparison without and with Fz.

4. Conclusions and recommendations

The following findings were obtained from this study:
1- The Boundary-Point Selection Method (BPSM) is applicable
Fig. 3 Wave force and sliding models.
with excellent results in finding solutions for boundary problems
With the addition of the plate, uplift forces are more influential
related to breakwaters with horizontal plates (as long as thein the system. Thus, the vertical added mass Mzx∞ and Rzx fromdivision regions are rectangular).
those forces are introduced in the motion equation as part of the2- The inclusion of the vertical force in the sliding analysis offriction force. Static frictional force Fs=fsW and dynamic
caisson with horizontal plates gives more accurate results. Not
frictional force Ff =f(W-V), where f=fs and the vertical force isincluding it leads to overestimating the horizontal plate's positive
expressed by Eq.7. Hence, the final equation of motion is defined
influence in reducing the sliding, especially for large l/h ratios.
by Eq.8.
3- Horizontal plates have a minimal influence on the overall𝑡∞(7)
𝑉 = −𝑀𝑥𝑥
𝑥 − 𝑅𝑧𝑥 (𝑡 − 𝜏)𝑥 𝜏 𝑑𝜏
slidingof breakwaters' caissons. (Sliding reduction ≤ 2%)
𝑡
0
𝛼 𝐹𝑠
(0 ≤
𝑡 For
≤ 𝑡𝑝 )the new shapes of caissons' design seeking to reduce
4𝑡
𝑝
𝑡
∞
∞
𝑚𝑎 + 𝑀𝑥𝑥+ 𝑓𝑠 𝑀𝑧𝑥
𝑥 + 0 [𝑅𝑥𝑥 𝑡 − 𝜏 + 𝑓𝑠 𝑅𝑧𝑥 (𝑡 − 𝜏)]𝑥 𝜏 𝑑𝜏 =𝑡sliding due to increments on the added mass because of water
𝛼 2 − 𝑡 𝐹𝑠 (𝑡𝑝 ≤ 𝑡)𝑡𝑝constriction, the new elements should induce an increment on the
𝛼 𝐹𝑠(0 ≤ 𝑡 ≤ 𝑡𝑝 )
𝑡𝑝
𝑡
∞
∞
𝑀𝑥𝑥
+ 𝑓𝑠 𝑀𝑧𝑥
𝑥 + 0 [𝑅𝑥𝑥 𝑡 − 𝜏 + 𝑓𝑠 𝑅𝑧𝑥 (𝑡 − 𝜏)]𝑥 𝜏 𝑑𝜏 =horizontal added mass but a reduced or no vertical added mass.
(8)𝑡

3. Results and Discussion

𝛼 2−𝑡

𝑝

𝐹𝑠 (𝑡𝑝 ≤ 𝑡)

The horizontal plate influence is analyzed by changing the ratioof plate length to water depth l/h = 0, 0.25, 0.5, 0.75, and 1.0;
been l/h = 0 the case of a caisson without a plate. For better
evaluation, dimensionless analysis is made. Horizontal andvertical parameters are analyzed at x=0 and z=0, respectively.
Added mass (Fig.4a) increases as the plate becomes larger, and
it is asymptotic to a particular value M (ω → ∞). The ratio Mzx / Mxx

References
1) Aoki, S. and Okube, A. Proceedings of Coastal Engineering,
Vol.42, pp.861-865, 1995. (in Japanese)
2) Yoshihara, M. Master thesis. Civil Engineering Department,
Osaka University, 2019. (in Japanese)3) Yoshida, A, Kojima, H and Tsurumoto, Y. JSCE Proceedings,
No.42/II-13, pp.265-274, 1990. (in Japanese)

International Program of Maritime & Urban Engineering / Abstract of Master Thesis

July, 2021

Capsizing & Survivability of Ships Based on Safe Basin’s Fractals
Colin Fatuimoana Langilangi
Ship Intelligentization Subarea, Naval Architecture and Ocean Engineering
Key Words: Safe basin, Flip bifurcation, Ship capsize, Chaos, Periodic solutions

1. Introduction
On August 5th 2009, the ferry MV Princess Ashika capsized andsank approximately 75 miles Northeast off the coast of the capital
Nuku’alofa, of Tonga. The tragedy claimed 74 lives mostly womenand children, thus highlighting the fact that capsizing is one of themost threatening events that a vessel could encounter at sea. As
evident from the consequence of the 2009 disaster, capsizing leads
to critical death tolls. Consequently, it is a vigorous commission to
obtain resolutions to avert the capsizing of ships at sea,
guaranteeing the safety and security of maritime transportation.
The term referred to as capsizing can be described as when a ship
encounters itself in a situation when it is turned on its side or isupside down in the water. A reasonable quantity of researches has
been carried out determining that the frequent reasons for thecapsizing of ships are due to determinants such as parametric rollresonance, broaching-to, water on deck, or the loss of stability at awave crest.
In courses of nonlinear dynamics, it is further recognised as ashift from a stable equilibrium point near the upright position intoa stable equilibrium point near the upside-down position. Yet,stemming from the 1980s advancements into nonlinear dynamics,
a significant number of enhanced computational capabilities
unlocked new possibilities in the investigation of such a complex
phenomenon. One of those studies is of what is known as the safe
basins, which was employed in an attempt to surmise themechanics behind capsizing.
In the study, the author focuses on the exact and approximationof boundaries of safe motion in the space of control parameters.
Based on the published investigation of vessel capsizing utilising
this method conducted by Kan and Taguchi 1) and others 2), theauthor implements the application of the method on a real-life shipin regular waves. The container ship of the ITTC Ship A1 has been
the subject ship of choice employed in this study. Due to therestoring term having a cubic polynomial in naval engineering,along with a simplified form of the GZ plotted curve of the ship,
the author proceeds with setting towards a 9th order polynomial.

Fig.1 ITTC Ship A1 GZ Curve
In past readings, manageable equations have been utilised tomodel the vessel’s equation of motion, where it is capable torepresent the roll motion using Newton’s second law and contain aquadratic or cubic polynomial term in the restoring moment.
Damping was then considered to be linear, while regular waves
were considered as external interference.
In this paper the following equation has been used to model the
ITTC Ship A1 in quartering regular waves:𝜙̈ + 𝛽! 𝜙̇ + 𝛽" 𝜙̇&𝜙̇& + 𝛽# 𝜙 #̇ + 𝛼! 𝜙 + 𝛼# 𝜙 # + 𝛼$ 𝜙 $+ 𝛼% 𝜙 % + 𝛼& 𝜙 & = 𝐵𝑐𝑜𝑠(𝜔𝑡)(1)where 𝛽! , 𝛽" , 𝛽# , 𝜔 and 𝐵 are constants representing thenormalized damping coefficient, the non-dimensional frequency
and amplitude of the exciting moment, respectively,
𝛼! , 𝛼# , 𝛼$ , 𝛼% , 𝛼& represents the restoring term through 9th orderpolynomial, and 𝜙 is the normalized angle of roll and 𝑡 is thenormalized time. The dots signify the differentiation with respect
to the normalized time. The equation (1) has produced a range ofdistinctive behaviors, including steady-state solutions and flip
bifurcation that eventually leads to chaos. The following sections
are descriptions of the safe basins, its concept and how it has been
applied for the case of the capsizing equation (1).

2. Safe Basin & Application
2.1 Safe Basin Concept
The safe basin primarily are sets of initial conditions within aphase plane (𝜙, 𝜙̇) which define the variance between capsizing
and non-capsizing regions and demonstrates the sensitivity ofcapsizing to the initial conditions. With the insertion of parameters(𝛽, 𝛼, 𝐵, 𝜔), the safe basin of attraction is formed by all initialconditions of (𝜙(0), 𝜙̇(0)) that does not capsize.
2.2 Safe Basin Application
The safe basin in the paper is generated numerically by course
grid-of-start method. The calculations are then run by theincreasing of the amplitude of excitation, which leads to a processof fractal erosion within the safe basin.
The capsizing equation (1) is then solved numerically andlopped through various initial conditions of 𝐵 using the RungeKutta method, implementing through Python. The system is thenrun for 100 cycles of forcing (period 𝑇 = 2𝜋/𝜔 ). The initialconditions ( 𝜙(0), 𝜙̇(0) ) were then tried against a vast set of641,601 = 801 x 801 points, and are obtained by also dividing theplane [-1.222, 1.222] x [-1.5, 1.5] into equally spaced divisions.
The points are then calculated against the criterion (vanishingangle), and sorted if capsizing occurs or not. When the calculation
return is safe, the program places a small black dot in the phaseplane (𝜙, 𝜙̇). If the return is not safe, then the plane maintains white.
Therefore, the safe basin is defined by the black area that ispresented by the phase plane. The fractal erosion observed by thesafe basin in this paper follows a different shape and routecompared to those from the previous studies, which are owed up to
the increasing of the excitation amplitude 𝐵 and the introduction
for a 9th order polynomial to the governing equation (1).

there are also cases of multiple points being observed, perhaps tobe signs of chaotic behavior present within those specific regionsof the safe basin.

Fig.3 Bifurcation Diagram of the safe basin of 𝐵 = 0.0, 𝐵 =0.033
3.2 Poincaré Bifurcation Diagram

Fig.4 Poincare Map Diagram showing behavior of points ofvarious 𝐵 values.
The assembly of the Poincaré map further supported the
behavior of the points return in the bifurcation diagram plots,showing a more comprehensible visual of the events occurring.

4. Conclusion

Fig.2 ITTC Ship A1 Safe Basin & erosion observed

3. Poincare Bifurcation Diagrams & Map
3.1 Bifurcation Diagrams
Now that the safe basin has been illustrated, further study wasthen carried out on the final safe state points of the system witheach given condition. In this case, the colors of the plots are alteredin order to easily distinguish the behavior of the points and whenbifurcation occurs. As observed, the system begins with a single
point of final safe state as expected when 𝐵 = 0.0 . Overtime
interesting cases arise with the observations of two points returned,
thus showing evidence of bifurcation at that point in time. However,In this study, the meticulous numerical analysis of the safe
basin’s fractal erosion was conducted on the ITTC A1 container
ship, adopting a revised symmetric capsizing equation to theequation utilized by Kan and Taguchi 1) and 2). Distinct erosions of
the safe basin were presented with bifurcation occurring. The paper
recognizes the correspondence of data that the safe basin and GZ
curves offer in setting measures that ships could operate within,
ensuring the safety and security of maritime transportation when
averting the case of capsizing.

References
1)2)Maki, A., Virgin, L., Umeda, N., Ueta, T., Miino, Y.,
Sakai, M., & Kawakami, H. (2019). On the loss ofstability of periodic oscillations and its relevance to ship
capsize. Journal of Marine Science and Technology , 846854.
Kan, M., & Taguchi, H. (1990). Capsizing of Ships in
Quatering Seas (Part 2. Chaos and Fractal in Capsizing
Phenomenon).

International Program of Maritime & Urban Engineering / Abstract of Master Thesis

July, 2021

Development of Automatic Evaluation System of Underwater Vehicle’s
Motion Performance Based on OpenFOAM
LI JUNJIAN

Marine hydro-science and engineering lab,
Naval Architecture & Ocean Engineering
Key Words: Underwater Vehicles, CFD, Python, openFOAM, Hydrodynamic Coefficients, Automatic Control System

1. Introduction
Nowadays, Computational Fluid Dynamic method (CFD) havebecome wildly used in the design of ships and underwater
vehicles. However, the operation of CFD requires a lot ofhydrodynamic learning and experience. And it is difficult for
beginners to evaluate the performance of ships or underwater
vehicles using CFD methods. Under these circumstances, open
source codes of CFD method are highly recommended to use.
Since most of open source codes of CFD method are free andthey are often used in the evaluation of the maneuverability ofunderwater vehicles with relatively small size, the development of
automatic evaluation system of underwater vehicle’s motion
performance is of great significance.
Nevertheless, as mentioned above, to use CFD method andderive convincing results, researchers need to accumulate acertain amount of CFD knowledge and experience. Therefore, inthis research, our laboratory aimed to develop a CFD-based
performance estimation tool for underwater vehicles which canobtain the results with reasonable accuracy if only the CAD dataof body shape of vehicles are given. Even relatively small
underwater vehicles’ manufacturers can use this estimation tool
for basic motion performance simulations.

2. Previous research
Automatic Change and Correction System (ACCS) was
developed by Mr. Takada who was a member of the lab. The wayof distinguishing between Work Type AUV and Cruise TypeAUV from triangle quality of CAD data has been founded. And
three degrees of freedom, which compose basic motion ofunderwater vehicles, is adopted. Analyzing the results from threetests with multiple regression analysis, Hydrodynamic
Coefficients can be obtained. The equations of Fluid forces acting
on the underwater vehicles and three tests for hydrodynamic
performance are shown in Fig. 1.

induced forces and moments due to fluid accelerating with anaccelerating body. When a body is accelerating in any direction, it
has to accelerate the surrounding fluid as it is moving through it
which requires additional forces and moments than if the vehicle
was moving in vacuum. It is important to note that there is no
distinct mass of fluid moving with a specific acceleration; it isjust a convenient way of describing the additional forces andmoments. In reality, all fluid particles surrounding the submerged
body will move with different acceleration. The hydrodynamic
forces caused by added mass can be derived as follow:(1)

Where Ma is the added mass matrix with a six degree of
freedom system, which also called 6DOF. The linear motions
surge, sway and heave and the angular motions roll, pitch andyaw are included in the six degree of freedom system, which arepresented in Table 1. And the notation used for these motions areaccording to SNAME (1950).
Table 1 Notation according to SNAME

After the expansion of added mass matrix, the hydrodynamic
forces can be defined as follow:(2)

Fig. 1 The calculations in ACCS

3. Hydrodynamic coefficients
Here, the added mass coefficient is described as an example ofthe hydrodynamic coefficient. Added mass is the pressure

Even with ACCS, many of these added mass components andother hydrodynamic force coefficients cannot be calculated, andin order to calculate them, it is necessary to perform simulations
such as forced oscillation. Therefore, in the new system, I decided
to aim at further automation of mesh generation and automatic
execution of forced oscillation test by CFD.

4. CFD method

4.1 Previous method
In order to estimate the motion performance of underwater
vehicles, four basic steps are needed, importing, meshing,calculating and analyzing. Using previous method, settings ofinitial values, meshing and calculation solver should be changed
manually according to different imported geometry, which takes
plenty blank time.
4.2 Proposed method
Automatic Grid Study System (AGSS) has been developed inthis research, which can conduct the studies of side walls and gridindependence. Referring to geometry information obtained from
CAD data, turbulence parameters, such as Turbulence kinetic
energy k and turbulence dissipation rate ε, can be calculated
automatically. Meanwhile, simulation results using different
mashing strategies can be obtained by this automatic estimation
system. After importing the CAD data of objective geometry, thissystem can execute the calculations for each case continually,
which can save a lot of time.

coefficients data can be obtained by two post-processing
commands. For visual analysis, ‘paraFoam’ will be used to checkpressure and velocity distribution.
5.5 AGSS 5th step (Motion Test)
Then the proper mesh strategy will be picked up for motion test.
Constant acceleration test was conducted in the previous research.
Assuming the speed resistance is negligible, the fluid force iscalculated immediately after 0.001 second, the object starts
accelerating. For motion oscillation test, dynamic mesh will be
used. Force oscillation test can also be conducted in this step. The
imported geometry will move with the oscillation in x-z plane.
Dynamic mesh and transient solver will be used. Calculated dragcoefficients with time history will be outputted. The map of thissystem is shown in Fig. 2.

5. Flow of proposed method
5.1 AGSS 1st step (Importing)
AGSS system inputs CAD file and processes CAD informationand outputs the processed CAD information, for example, length,
breadth, depth, center of masses and structure complexity. As theprevious research, it can also distinguish the cruise type or work
type of underwater vehicles by triangle quality. According to thetype of underwater vehicles, different strategies of simulations
will be adopted. And relative size or absolute size of boundary
layers will be added close to the geometry.
5.2 AGSS 2nd step (Pre-Calculation)
The hydrodynamic parameters will be automatically calculated,such as Reynolds number, turbulence kinetic energy andturbulence dissipation rate, etc. Then first layer thickness will becalculated by these 4 steps, skin friction, wall shear stress, friction
velocity and wall distance. The settings for initial values andboundary layers will be replaced by the calculated values.
5.3 AGSS 3rd step (Grid Study)
From the last step, the cad information after processing wasderived. Fig. 1 shows the calculation domain. Different meshstrategies will be created respectively. Using refinement ratio, 5meshes of different minimum size will be used.

Fig. 1 Calculation domain and boundary conditions
5.4 AGSS 4th step (Results Analysis)
After the calculations are finished, the forces and force

Fig. 2 The map of proposed method

6. Conclusion(a) Comparing with the previous estimation system ACCS,
new automatic estimation tool, which can conduct Side
Walls Study, Grid Independence Study and Force
Oscillation Test, has been developed.
(b) Different from ACCS system, and to get the results with acertain accuracy, parameters of turbulence model can becalculated according to the imported geometry. And thesettings of initial values will be changed automatically.
(c) Because of wall function used in k-ω SST model, AGSS
system can use y plus to calculate the first layer thickness
and add boundary layers with absolute size automatically.
References
1) Suzuki, H.; Sakaguchi, J.; Inoue, T.; Watanabe, Y.; Yoshida,
H. Evaluation of methods to estimate hydrodynamic force
coefficients of underwater vehicle based on CFD. IFAC Proc.
Vol. 2013, 46, 197-202.
2) SNAME. 1950. Nomenclature for treating the motion of asubmerged body through a fluid. Tech. rept. Technical andResearch Bulletin 1-5, Hydrodynamics Subcommittee of theTechnical and Research Committee, Society of Naval
Architecture and Marine Engineers.
3) Takada Yukihiro: “Development of Automatic Calculation
System for Hydrodynamics Analysis of AUV by using
Python Programs”, Osaka University (2020).
4) Josefine Severholt: “Generic 6-DOF Added Mass
Formulation for Arbitrary Underwater Vehicles based on
Existing Semi-Empirical Methods”, Royal Institute ofTechnology, 2017.

International Program of Maritime & Urban Engineering / Abstract of Master Thesis

July, 2021

Microcomputer Control of Underwater Vehicle with Undulating SideFins
Lin ShenChi
Sub-area of Marine Hydro-Science and Engineering, Department of Naval Architecture
and Ocean Engineering
Key Words: Squid-like underwater robot, Course keeping, Zig Zag test, Williamson Turn, Data analysis

1. Introduction

2.2 Manual Control

The propulsion system of squid-like body with undulating side
fins have been investigated in our laboratory for several years.
This propulsion system is designed the operation at a moderate
speed and can easily perform six degrees of freedom motion byadjusting direction and phase velocity of the side fins. It produces
propulsive force and control force for such as direction change bymoving the side fins in a traveling wave shape and create withlittle vertical movement and easy for seabed exploration.
The purpose of this study is to reduce the volume and control
system of model-7 correspond to model-5 by using smaller spaces
and microcomputers to control the motor rotation for the fins andto control the course keeping of the model. Also, with 360-degree
camera for complicated structure underwater exploring andreturning the images and videos.

Control systems using gyro sensor for course keeping, zig zag
test and Williamson turn in bigger model were conducted lastyear. For present study, the smaller system is designed by using
two Teensy 4.1 instead of stick PC and Arduino MEGA. But the
final installation could not be done due to time limitation, Manualcontrol using microcomputers were tested in towing tank.
Microcomputer, transmitter and receiver used for manual control
are shown in Fig.2 and Fig.3.

Fig. 2 Microcomputers

Fig. 3 Transmitter and Receiver

2. Experiment Overview
2.1 Overview of model-7
The traveling wave motion of side fins are produced byscotch-yokes and covered by rubber to increase its fluidity. A tailfin is designed behind the body to control the depth. Motors,
batteries, drivers and control system including various micro
computers are installed inside the watertight polyvinyl chloride(PVC) body. The vehicle model particulars are as shown in Table
1 and Fig.1 shows the body of model-7.
Table. 1 Principal particular
Length
57.0cmWidth
22.8cmHeight6.0cm
Weight
4.5kg
Fin Length
7.0cm
Number of fins
7(tot 14)
Length between each fin
5.0cm

In this study, two brushless motors were used for manualcontrol. The transmitter for proportional control as shown in Fig.3
controlled the slope of right- and left-hand control sticks to makethe forward and backward rotation of the left and right motors. By
the microcomputer, the signal for changing the rotation direction
by making short- circuited accordingly, and voltage for number of
revolutions was applied to the drivers to control the rotation speed.
By combining right and left sticks’ movement, the model could
move free and stable. The example of manual control is shown in
Fig.4. It shows the turning motion.

Fig. 4 Manual Control Running
2.3 360-degree camera

Fig. 1 Model-7

For the one of the sensors, 360-degree camera (Ricoh Theta
sc2) shown in Fig.5 was used in the free-running tests. The
camera can be used to discover the situation of underwater. Dueto the manipulate, such as course keeping, rotation and changing
depth by tail fin, clear surroundings could be found after sending
back the videos and images as shown in Fig.6. It can beconnected by Wi-Fi connection to the smart phone and can becontrolled and store the video images. To make the Wi-Fi
connection available in the water, the pipe should be installedfrom camera watertight case to the float. In this study, the control

was done when the vehicle was floating.

yaw angle of 30°, 60°, 90° and  f =0.3 were executed.
( f R = 1 f L = 0.7 or f L = 1 f R = 0.7) The zig zag motions withthree different transition angles are shown in Fig.9. The yaw
angle time histories for 30° is shown in Fig.10. psi is known as
yaw and df is known as the command value in the figure.

 T = 30
Fig. 5 camera

Fig. 6 surroundings underwater T = 60
2.4 Preliminary experiment of Gyro Sensor
The gyro sensor (BNO055) shown in Fig.7 would be used inmodel-7 for processing the data of yaw angle and yaw rate. For
the sensor, the switch signal by the transmitter could be sent toreset the yaw angle to 0 degree. The test using gyro system(BNO055 and Arduino Nano) was tested in laboratory forpreliminary test. The test time history is shown in Fig.8.

 T = 90

Fig. 9 Three Different Angles

Fig. 10 Simulation of 30°
Fig. 7 Gyro Sensor

Fig. 8 Preliminary test of Gyro

3. Simulation
The gyro censor data could be sent back to the main Arduino
for course keeping, zig zag test, Williamson turn maneuvers.
Some control strategies were simulated by 6DOF simulation
program by using equations of motion and hydrodynamic force
model. Here 3DOF results were shown.

3.3 Williamson Turn
The Williamson turn is a maneuver used to bring a vehicle
under power back to a point it previously passed through. In thismodel, after course keeping with the target angle of 0 ° for awhile, it turned right to the target Θ1, and started turning leftwhen it reached Θ2 and kept course keeping at the target angle-180 °. The proper trajectory angle of Williamson Turn in thismodel is 60 ° for Θ1 and 165 for Θ2 as shown in Fig.10. The
relation between turning circle and delta f is shown in Fig.11.

3.1 Course keeping maneuver
The course keeping maneuver simulation was done using PD
control. The equation for PD control is shown below.

f = − K p ( − t ) − K d
 f : Frequency difference between left and right fins
Kp: Proportional gain Kd: Differential gain

 : Yaw angle t : Target yaw angle  :Yaw rate
When Kd = 0, it becomes the equation for P control.
The computation was done for various initial angle and speed.
But the results are not shown here, because the course keeping
maneuver was used in the last stage of Williamson Turn.
3.2 Zig Zag Test
In the simulation of zig zag maneuver with transition absolute

Fig. 10 Williamson Turn in Three Different Frequencies

4. Conclusions
The manual control using microcomputers, transmitter andreceiver for model-7 could be performed and the model could becontrolled easily. Smaller model could be controlled easier thanthe big one. With a 360- degree camera, discovering even acomplicated structure underwater could be achieved. In addition,
gyro sensor simulations on this model were tested this year.