bluuebunny/crossref_metadata_2025 huggingface dataset:
Safety and Reliability Analysis of Composites Under Low Velocity Impact
Authors: Patel Shivdayal , Ahmad Suhail , Singh Manander
Published: October 2016

Low velocity impact on composite plates is studied taking material properties and initial velocity as random parameters. Graphite fiber reinforced composite plates are susceptible to damage due to impact by foreign objects and in plane loading. In order to assess the safe load carrying capacity and the probability of failure under impact, dynamic analysis of composite plate subjected to low velocity impact is carried out. Finite element method is used to study impact. During impact, the in-plane damage modes such as matrix cracking, fiber failure and shear cracking are modeled using a failure criterion. The out of plane de-lamination is modeled using cohesive surfaces. The uncertainties associated with the system properties due to the inherent scatter in the geometric and material properties and input loads are modeled in a probabilistic fashion. Random parameters represent various characteristics appearing in the limit state function. The probabilistic analysis and reliability prediction of the system is carried out using Gaussian response surface method and validity of method for the present problem is establish using Monte Carlo simulation (MCS) procedure. Sensitivity analysis of the probability of failure with respect to random parameters considered is an important study for design optimization. The safety level qualification is achieved in terms of reliability level targeted. The mean and standard deviations of random variables show an appreciable influence on the probabilistic failure. Systematic changes in the input parameters are governed by the probabilistic sensitivity tools to achieve target reliability.
Hydrodynamics of Side-by-Side Fixed Floating Bodies
Authors: Chua Kie Hian , Eatock Taylor Rodney , Choo Yoo Sang
Published: October 2016

Safety of cargo transfer operations between side-by-side vessels depends on accurate modelling of hydrodynamic behavior, especially in terms of predicting the gap free surface elevations between the two vessels. The common industry practice of using linear potential flow models to study these interactions over-predicts the free surface elevations, due to the fact that potential flow does not include viscous dissipation effects such as flow separation at hull corners and skin friction. This may result in inaccurate projections of the time-window when these operations can safely take place. This is an important aspect for developments such as Floating Liquefied Natural Gas (FLNG) platforms, where side-by-side cargo offloading is an essential operation.

In a recent research [1], an approach of splitting the amount of energy lost through viscous dissipation (calculated from three-dimensional viscous CFD simulations) into components representative of the flow phenomena has been proposed. Using the approach, referred to as component energy dissipation, the amount of energy lost due to vortex shedding and skin friction can be estimated. Modifications to linear potential flow were also proposed in the referenced research, such that the energy loss components can be converted into dissipative coefficients that are used in terms added to the free surface and body boundary conditions. By combining use of the component energy dissipation approach and the modified dissipative potential flow model, better predictions of gap hydrodynamic interaction can be obtained, compared to using conventional potential flow.

In this paper, results from viscous simulations of two identical fixed-floating side-by-side barges of 280m (length) × 46m (breadth) × 16.5m (draught) under excitation from regular incident waves are presented, and compared with corresponding results from the modified dissipative potential flow model. Two types of side-by-side hull configurations were investigated, the first using rectangular barges with sharp bilge corners at varying gap distances and the second using barges with rounded bilge corners of varying radii at a fixed gap distance. Estimation of the dissipative coefficients used in the modified potential flow model, calculated from the viscous results, will also be discussed. The comparison of results serves both as a validation of the modified potential flow model, and to highlight the importance of including viscous dissipation when analyzing hydrodynamic interactions.
Time Domain Analysis on Ship Maneuvering in Adverse Sea State
Authors: Guo Bingjie , Eivind Ruth , Austefjord Håvard , Bitner-Gregersen Elzbieta M. , Rognebakke Olav
Published: October 2016

Energy Efficiency Design Index (EEDI) introduced by the IMO Resolution MEPC.203 (62) has been the first initiative to regulate the greenhouse gas (GHG) emissions from ships. However, it has raised serious concerns that some ship designers might choose to lower the installed power to achieve EEDI requirements not accounting satisfactorily for ship safety. This has encouraged investigations addressing the ability of ship to maintain maneuverability in adverse sea states. The Interim Guidelines proposed in 2013, in IMO Res. MEPC.232 (65), recommend minimum propulsion power to maintain ship maneuvering ability in adverse weather conditions for bulk carriers and tankers. These guidelines are mainly based on statistical analysis and equilibrium analysis in a steady state. Today, most of the available tools and methods handle ship responses in waves by separating it into seakeeping and maneuvering. The present study investigates ship maneuverability by use of a recently developed time domain code which combines the sea-keeping and maneuvering equation to predict ship responses in waves. In this way, better insight into ship responses in adverse conditions is obtained. The numerical results presented in the study are validated by model tests. The limitations of the time-domain code are discussed and future research needs are pointed out.
Numerical Analysis of Added Resistance on Ship in Parametric Roll Motions
Authors: Lee Jae-Hoon , Kim Yonghwan , Seo Min-Guk
Published: October 2016

In the present study, the added resistance of a containership in parametric roll motion is investigated. The numerical simulation is carried out using a three dimensional Rankine panel method along with the weakly nonlinear formulation. The added resistance is evaluated by a near-field method, namely, the direct integration of the 2nd-order pressure on a body surface. To calculate the component resulting from the large-amplitude roll motion, the higher-order restoring and Froude-Krylov forces on wetted hull surfaces are taken into account. With or without parametric roll in regular waves, the components of added resistance classified with respect to integral terms are compared to figure out the important of each term. Through the investigation, the correlation between the added resistance and parametric roll is derived from coupling and decoupling the components of roll motion and vertical motions.
Experimental Investigation on Vortex-Induced Vibration of a Free-Hanging Riser Under Vessel Motion
Authors: Wang Jungao , Fu Shixiao , Ong Muk Chen , Li Huajun
Published: October 2016

A model test of a free-hanging riser under vessel motion was performed in the ocean basin at Shanghai Jiao Tong University to confirm whether vortex-induced vibration (VIV) can happen due to pure vessel motion, to investigate the equivalent current velocity and Keulegan–Carpenter (KC) number effect on the VIV responses and to obtain the correlations for free-hanging riser VIV under vessel motion with VIV for other compliant risers. Top end of the riser was forced to oscillate at given vessel motion trajectories. Fiber Brag Grating (FBG) strain sensors were used to measure the riser dynamic responses. Experimental results confirmed that the free-hanging riser would experience significant out-of-plane VIV. Meanwhile, VIV responses in terms of response amplitude, response frequency and cross-section trajectories under different test cases were further compared and discussed. Most importantly, the correlation among VIV response frequency, vortex shedding pairs and maximum KC number KCmax was revealed. The presented work is supposed to provide useful references for gaining a better understanding on VIV induced by vessel motion, and for the development of future prediction models.
A Calculation Method of Ultimate Torsional Strength for Subsea Collet Connector Based on Finite Element Method
Authors: Zhang Kang , Duan Menglan , Luo Xiaolan , Hong Yi
Published: October 2016

Subsea connector is an important connection facility in subsea production system. Once destroyed, it will cause sealing failure which could lead to leakage accident, so the connectors must have high degree of damage-resistance capacity. Ultimate bearing capacity is composed of a set of important parameters measuring subsea connectors’ damage-resistance capacity, such as ultimate bending strength, ultimate torsional strength, etc. However, these data are usually obtained by carrying out destructive tests, which will bring heavy cost to subsea connector products in order to obtain the required technical data. Considering reducing the cost of destructive testing, a theoretical calculation method is needed to be developed. In addition, during the stage of product design, it is also necessary to estimate ultimate bearing capacity to verify whether the structural design parameters meet the anticipated requirements. In this paper, only the ultimate torsional strength of subsea connectors was studied, and based on finite element analysis, a calculation method of ultimate torque was put forward, which consists of using finite element software to build the 3D subsea connector model, loading different pure torsional moment, analyzing the calculation results and establishing torsional failure criteria to determine ultimate torsional strength. The results show that sealing failure will be ahead of structural strength failure under the pure torsional loads, and traditional strength failure criterion is not suitable for determining ultimate torsional strength of subsea connectors; the numerical solution of ultimate torque is 60KN·m based on the sealing failure criterion in this paper. In the end, a simplified mechanical model of subsea connector was established, the limit state equation of sealing failure was built in the action of pure torsional load, and the analytical solution of ultimate torque was calculated. The calculation method of ultimate torsional strength established in this paper was verified through comparative analysis.
Numerical Study on Hydrodynamic Responses of a Two-Body System in Side-by-Side Operation
Authors: Ou Shaowu , Fu Shixiao , Wei Wei , Peng Tao , Wang Xuefeng
Published: October 2016

Typically, in some side-by-side offshore operations, the speed of vessels is very low or even 0 and the headings are manually maneuvered. In this paper, the hydrodynamic responses of a two-body system in such operations under irregular seas are investigated. The numerical model includes two identical PSVs (Platform Supply Vessel) as well as the fenders and connection lines between them. A horizontal mooring system constraining the low frequency motions is set on one of the ships to simulate maneuver system. Accounting for the hydrodynamic interactions between two bodies, 3D potential theory is applied for the analysis of their hydrodynamic coefficients. With wind and current effects included, these coefficients are further applied in the time domain simulations in irregular waves. The relevant coefficients are estimated by experiential formulas. Time-varying loads on fenders and connection lines are analyzed. Meanwhile, the relative motions as well as the effects of the hydrodynamic interactions between ships are further discussed, and finally an optimal operation scheme in which operation can be safely performed is summarized.
Hydrodynamic Behavior of Truss Pontoon Mobile Offshore Base Platform
Authors: Sakthivel Somansundar , Rajamanickam Panneer Selvam , Srinivasan Nagan
Published: October 2016

Very Large Floating Structures (VLFS) are highly specialized floating structures with variety of applications ranging from airport strips to floating motels offshore ports etc. Their economic design is based on their hydro-elastic behavior due to wave environmental forces. VLFS are extra large in size and mostly extra long in span and for that reason they are mostly modularized into several smaller structures and integrated. VLFSs may be classified into two broad categories, namely the semi-submersible type and the pontoon-type. The former type of VLFSs having their platform raised above the sea level and supported by columns resting on submerged pontoons and can minimize the effects of wave actions. In open sea, where the wave heights are relatively large, the semi-submersible VLFSs are preferred. On the other hand, the pontoon-type VLFS is a simple flat box structure floating on the sea surface. It is very flexible compared to other kinds of offshore structures, and so its elastic deformations are more important than their rigid body motions. The critical problem is the longitudinal bending moment of the long floating vessel in waves/current environment. Most of the present available VLFS designs are not economical for applications in hostile ocean. This paper presents hydrodynamic analysis carried out on an innovative VLFS called truss pontoon Mobile Offshore Base (MOB) platform concept proposed by Srinivasan [1]. The concept uses a strong deck with strong longitudinal beams to take care of the needed bending moment of the vessel for the survival, standby and operational conditions of the wave. At the submerged bottom just above the keel-tank top, a simple open-frame truss-structure is used instead of a heavy shell type pontoon. Thus the truss-pontoon provides the necessary flow transparency for the reduction of the wave exciting forces and consequently the heave motions and the vertical acceleration. Numerical analysis of truss pontoon MOB platform is carried out using HYDroelastic Response ANalysis (HYDRAN). Responses of the isolated scaled module in waves are obtained from these numerical tools and compared with published literature. Unconnected two modules and three modules are analysed using HYDRAN and the responses are compared with the isolated module. The proposed concept yielded lesser responses as compared to semisubmersible conventional MOB platform.
Assessment of Seasonal Wind Energy at Zhifudao Observation Station Based on Joint Wind Speed and Wind Direction
Authors: Lin Yifan , Dong Sheng
Published: October 2016

The joint distribution of wind speed and direction is of great importance to the assessment and layout of wind farm, however it is constructed under the condition that the meteorological data of the regime under research is abundant. Based on the continuous angular-linear distribution model, an approach is proposed in this paper to establish the joint probabilistic distribution of wind speed and direction just by using the data of wind rose. The method is taken to construct the seasonal statistical models of wind regime at Zhifudao Observation Station located in Yantai, and in order to assess the fitness of the joint probabilistic models to the original wind roses, two kinds of coefficients of determination are calculated. The results show that the presented statistical models have high reliability and strong correlation with their original wind roses. After the feasibility of the method is certified, the statistical models are used to survey the wind power pattern with wind power roses of different seasons. Furthermore, the wind power output of a 2 MW vertical-axis wind turbine assuming to assigned here is predicted.
Experimental Investigation of Water Exit Under Hydrophobic Effects
Authors: Guzel Bulent , Korkmaz Fatih C.
Published: October 2016

Prediction of hydrodynamic loads during water exit of a body is of a great importance in designing the marine vehicles that take off from the free water surface such as sea planes and wing-in-ground effect vehicles (WIG), and that pierce through the free surface like missiles and submarines. The results of an experimental investigation on water exit of two different geometries, sphere and flat plate, with hydrophobic surfaces are presented in this paper. With and without the hydrophobic effects present, different fluid dynamics phenomena like free surface evolution, deformation and break up of free surface, wave generation, splash, air entrapment and water detachment from the solid surfaces during a water exit event have been examined. The non-dimensional exit coefficient, Ce is a function of the total vertical hydrodynamic force which depends on the geometry of the object and the hydrodynamic conditions along with the water parameters. Our study is aimed at understanding and modeling the nonlinear free surface effects and the dynamics of water exit under an extended range of parameters including hydrophobic effects.

In this study, due to lack of the experimental data on the water exit problem in literature, water exit tests have been set up, first for initially partially immersed spheres and flat plates, with their center above the free surface, to be towed vertically from the water surface at various speeds. Secondly, buoyancy driven water exit of a fully immersed sphere is investigated. It is observed that when the sphere rises up, it first starts deforming the free surface, and then pierces into it. The thin water layer attached to the surface of the sphere is drawn back to the test tank as the sphere moves further upward. This causes breaking of the free surface, air entrapment and wave generation in the water tank.

From digital images captured using a high speed camera, free surface breakup and water detachment at different velocities are observed and the time evolution of the water detachment and the exit characteristics are measured during a water exit event. The position of the sphere and its velocity are plotted against time. A detailed measurement of the global loads on the test objects during exit is carried out by employing strain gauges.

We also showed the effects of water detachment on the test bodies during exit and after fully exited via strain gauges. All this data is also collected under the hydrophobic effects, to show how the change in surface characteristics would have significant impacts on the water exit phenomenon. Analyzing the difference in occurrence of water flow separation, the change in kinetic energy of the fluid and the free surface deformation under the hydrophobic effects may help give a better explanation of the phenomena observed during water exit and improve the design characteristics of marine structures for a water exit event.
Non-Linear Clay Soil Model for Lateral Pipe-Soil Interaction
Authors: Agusta Arifian , Ji Guomin , Sævik Svein
Published: October 2016

This paper describes implementation and application of nonlinear lateral soil models for pipeline lateral buckling analysis. Several lateral soil models have been developed in the past and the model developed by Verley is often referenced in pipeline on-bottom hydrodynamic stability analyses (see [11], [13]). The Verley’s model includes the build up of soil passive resistance as a function of small cyclic lateral motions and it is implemented in the PONDUS software (developed by MARINTEK) for on-bottom stability analysis as well as the DNV-RP-F109. However, the Verley model does not include the build up of additional soil berm resistance due to large cyclic in-place lateral motions applicable for lateral thermal buckling behaviors. The effect of additional soil berm resistance from large cyclic motions has been investigated by other research projects, such as the SAFEBUCK JIP [5]. In this paper, a complete non-linear lateral soil models with inherent soil berm resistance including both effects are formulated. The soil model combines the Verley model, the models described in DNV-RP-F109, and the berm model from SAFEBUCK’s results. The DNV and Verley’s model are used to model soil resistance in small amplitude cycle continued by the berm model after breakout achieved during large amplitude cycle. The new model is compared with PONDUS to validate the results of Verley and DNV model. The soil model is implemented inside SIMLA software [15] to enable finite element analysis. An example application of the model to pipeline global buckling analysis is then presented.
Practical Review on Fatigue Damage Estimation Under Combinations of Global and Local Loadings
Authors: Cho Tae Min , Chun Min Sung , Kim Hyun Joe , Lee Dong Yeon , Kim Boo Ki
Published: October 2016

In this paper, reviews on the fatigue damage estimation are presented in case that both the global and the local loadings are applied and two practical approaches are proposed if the statistical data of the local loading are not available. So far the fatigue damage has been estimated through Rules from Classification of Societies if the statistical data such as the standard deviation and the up-crossing rate of the stress processes are available. However, in many cases, it’s hard to prepare enough data for the fatigue damage estimation, which results in very severe design.

Hence two practical approaches are presented which can be applied if the statistical data of the local loading are not available. In practice, only the maximum stress range and the total cycles of the local loading are available very often. In the practical approach 1, it is assumed that the maximum stress range always occurs during the total cycles. Then, the local fatigue damage is very conservatively estimated and the total fatigue damage is obtained by the way of summation of the global fatigue damage and the local fatigue damage. In the practical approach 2, the local fatigue damage is estimated based on the assumption of the Weibull fitted local loading. And the use of the cube root summation is proposed between the global fatigue damage and the local fatigue damage. The presented two practical approaches are applied to the side appurtenances of a FPSO and the resultant fatigue damages are compared and discussed. The results of this study can be expected as practical and useful data for the fatigue analysis of the marine and offshore structures.
Rapid Assessment of Hull Girder Collapse for Corroded Double Hull Oil Tanker After Collision
Authors: Noh Sung Hwan , Seo Jung Kwan , Paik Jeom Kee , Youssef Samy A. M.
Published: October 2016

Corroded tankers might be subjected to a very serious structural damage if involved in collision accidents. For understanding or preventing the collision accidents, various studies are being proposed by researchers to improve the analysis method.

In this paper, four types of double hull oil tankers (Panamax, Aframax, Suezmax and VLCC) are used. Probabilistic approach is used to create ship-ship collision scenarios for each target structure and the ultimate longitudinal hull girder strength of the hypothetical oil tanker’s hull cross-section. The ALPS/HULL is used to simulate and is intelligent supersize finite element method (ISFEM) software. A relevant probability density function (PDF) is introduced using the results from finite element simulations of the ship-ship collisions, which is commonly used to predict residual strength.
Development of Dual-Lifting Technique for Installation of Topside Mega-Modules
Authors: Jung Dong Woo , Kim Hyun Joe , Ji Hae Sung , Jeong Hyoen Su , Nam Mihee , Lee Dong Yeon , Kim Booki , Jin Jong Dae
Published: October 2016

As many deep-sea oil and gas fields are being developed, floating platforms becomes larger with more complicated topsides. However, the construction time is demanded to be shorter to meet the overall project schedule. The use of very large topside modules is one of the effective ways to reduce the integration time and decrease the possibility of fabrication defects.

The Ichthys Project’s CPF (Central Process Facility) is currently being constructed at Samsung Heavy Industries (SHI). The CPF will be the world’s largest production semi-submersible platform. The hull is constructed on the Offshore Floating Dock and most of the topside modules are prepared at workshops and integrated by floating cranes on the hull.

To maximize production efficiency in terms of reduced integration time and reworks, several topside modules are assembled into a larger module weighing up to 7,400 tonne spanning 150m long. Such large module cannot be handled by a single 8,000 tonne F/C, the largest crane that SHI owns. This fact initiated the idea of dual-lifting with a combination of the two F/Cs (8,000 tonne and 3,600 tonne) which enables lifting, transportation and integration of the mega-modules properly and safely without building a larger capacity F/C. Using different sized F/Cs increases the flexibility of the operation of the F/Cs.

To ensure safety during the dual-lifting, the two F/Cs are synchronized to be controlled as a single crane unit. During hoisting, all the measured data such as loads and positions of the hooks, and rotation of the module, are monitored in real time basis and used to hoist the module automatically. All the systems are designed to be redundant. Additional engineering works are performed to check the safety such as 1) structural analysis to investigate the structural safety with out-of-phased motions at boom-tip 2) time-domain analysis and 3) model test in ocean basin with the operation scenarios in real environments to obtain the dynamic load factors and the guidance on the operation limits in terms of wave heights. The two crane barges are moored side-by-side using fenders and mooring lines, and tug operation conditions are planned not only to move but also to push the two barges from sideways to be moored tightly, which minimizes the possibility of relative motions between the two barges.

The developed system had been applied to the integration of all the modules successfully weighing from 4600 to 7400 tonne. It is expected to be applied to many other offshore projects to keep the construction schedule on time. This paper will address and share the technical experiences obtained during the dual lifting of the mega-modules for the Ichthys Project’s CPF.
Full Scale Reeling Simulation Tests of Girth Welded X60 HFW Linepipe
Authors: Sadasue Teruki , Igi Satoshi , Oi Kenji , Yabumoto Satoru
Published: October 2016

The reel-lay method is a fast and cost efficient installation process for offshore rigid steel pipelines. Pipelines installed by the reel-lay method are plastically deformed due to reeling, unreeling, aligning and straightening during pipeline installation. Therefore, local buckling is one of the major concerns from a view point of integrity in linepipes, especially around girth welds where strength mismatching arises due to adjacent pipes with different yield strength. One the other hand, the change in mechanical properties of linepipes during reel-lay, including coating process (e.g. 250°C) and long time exposure (e.g. 250°C aging) after installation is also important in order to guarantee safety of linepipes. Furthermore fracture toughness at girth weld Coarse-grain HAZ (CGHAZ) after reeling and aging should be clear to prevent brittle fracture of offshore linepipes in service.

In this study, full scale reeling simulation tests of girth welded X60 HFW (High Frequency electric resistance Welded) linepipes with OD; 323.9mm and WT;15.9mm after full body heat treatment (coating simulation) were conducted at 5cycles and 2cycles reeling and straightening situations when yield strength mismatches are present between adjacent pipes around girth welds. Localized strain concentration was observed near girth welds by strength mismatching of adjacent pipes. DNV ovality increased with increasing reeling and straightening cycles, however the ovality did not exceed 10%, which was a criterion value for local buckling, after 5cycles reeling simulation test. The change ratio of wall thickness after full scale reeling simulation tests were about ±2% (within DNV-OS-F101 tolerance) regardless of circumferential and longitudinal direction of pipes. Longitudinal tensile properties could be characterized by axial last introduced plastic strain. That is, in the positive number of last introduced plastic strain, YS and Y/T increased, while uEl decreased by work hardening effect. On the other hand YS and Y/T decreased, while uEl increased at the negative number of last introduced plastic strain by Bauschinger effect. Circumferential tensile properties could be also characterized by axial last introduced plastic strain. Yield strength and Y/T slightly increased while uniform elongation slightly decreased by aging at longitudinal and circumferential direction. Tensile properties did not change irrespective of the number of cycles of reeling simulation tests. After 5cycles reeling simulation test and aging, girth welded CGHAZ CTOD values were over 0.4mm at −20°C and Charpy absorbed energy were over 200J at −30°V, therefore, it was considered that the brittle fracture of the girth welded linepipe unlikely occur at reeling and aging situation in this study.
Parameter Sensitivity in Numerical Modelling of Ice-Structure Interaction With Cohesive Element Method
Authors: Feng Dianshi , Pang Sze Dai , Zhang Jin
Published: October 2016

The increasing marine activities in the Arctic has resulted in a growing demand for reliable structural designs in this region. Ice loads are a major concern to the designer of a marine structure in the arctic, and are often the principal factor that governs the structural design [Palmer and Croasdale, 2013]. With the rapid advancement in computational power, numerical method is becoming a useful tool for design of offshore structures subjected to ice actions.

Cohesive element method (CEM), a method which has been widely utilized to simulate fracture in various materials ranging from metals to ceramics and composites as well as bi-material systems, has been recently applied to predict ice-structure interactions. Although it shows promising future for further applications, there are also some challenging issues like high mesh dependency, large variation in cohesive properties etc., yet to be resolved.

In this study, a 3D finite element model with the use of CEM was developed in LS-DYNA for simulating ice-structure interaction. The stability of the model was investigated and a parameter sensitivity analysis was carried out for a better understanding of how each material parameter affects the simulation results.
Experimental and Numerical Studies on Nonlinear Impact Response of Deck Structures Subjected to Dropped Objects
Authors: Jung Bo Gyeong , Jo Sung Woo , Noh Sung Hwan , Paik Jeom Kee , Seo Jung Kwan , Kim Young Hun
Published: October 2016

Ships and offshore structures are exposed to various types of extreme and accidental events including fire, explosion, collision, dropped objects, etc. These events lead to nonlinear structural consequences. This paper focused on grated-steel deck structures subjected to dropped-objects. The aim of this paper is to confirm the nonlinear impact response of grated-steel deck structures. An experimental study was undertaken in a dropped object test facility and LS-DYNA nonlinear finite element computations were also performed for the corresponding test models. It is noted that nonlinear finite element analyses are useful in the analysis of the nonlinear impact structural responses as long as the modeling techniques are adequate. The conclusions developed in this paper will be informative in the safety design of ships and offshore structures.
Vortex-Induced Vibration of a Free-Hanging Riser Under Irregular Vessel Motion
Authors: Wang Jungao , Jaiman Rajeev Kumar , Adaikalaraj Peter Francis Bernad , Shen Linwei , Tan Sue Ben , Wang Wenping
Published: October 2016

In this paper, we focus on vortex-induced vibration (VIV) of a free-hanging riser attached to a vessel under irregular wave conditions. The global in-plane responses of the hanging riser are firstly studied numerically in order to generate the equivalent current profile under vessel motion, and a simplified irregular vessel motion-induced VIV prediction methodology is then proposed based on the understanding from previous experimental observations and literature review. Further comparison on irregular vessel motion-induced VIV and ocean current-induced VIV at the same operation site with the same return period is performed to emphasize the importance of vessel motion-induced VIV. Numerical results highlight that vessel motion-induced VIV can cause similar stresses, fatigue damage and drag amplification similar to the steady ocean current cases, especially to the operation site like Norwegian Sea where strong wave field exists with mild current condition. It should be mentioned that although the simplified methodology proposed in this paper requires further experimental validation, it is believed that the presented numerical pre-study would help the industry and the researchers to have initial understanding on the possible occurrence of vessel motion-induced VIV. We further show the similarities and differences of vessel motion-induced VIV with respect to the ocean current-induced VIV and its implications on riser design and operation.
Engineering Establishment of Living Quarters for Jack-Up Rig Structures
Authors: Ha Yeong Su , Park Joo Shin , Koo Jeong Bon , Cho Byung Jin , Ma Kuk Yeol , Jang Ki Bok
Published: October 2016

The Living-Quarters (hereafter referred to as ‘LQ’) is one of the major structures for ship and offshore structure. The LQ gives safe living conditions to crews on board. Until now the structural design of LQ structure is based on simplistic beam calculation to determine the initial scantling under design load. These days, safety for people is a raising issue. It is needed to meet the high oil company’s needs as well as technical specification throughout offshore project. But, the engineering procedure for LQ structure is not clearly defined by classification of society rules and international standards.

In this paper, the newly engineering procedure for LQ design is established considering LQ global loads with local loads for large equipment such as helideck structure, telecom mast and life saving appliances, and so on. To consider LQ global loads with local loads, the integrated three dimensional FE model and high technology engineering should be needed to require many kind of rules for equipment.

Recently, the damage of LQ structure is occasionally reported during towing condition for jack-up rig structure. The LQ of jack-up rig is encountered such as slamming pressure and greenwater produced by harsh wave loads during towing condition because of small height of freeboard comparing to the wave height. To verify the structural safety under towing condition, the detailed non-liner analysis is performed to verify the load-carrying capacity against greenwater pressure.

We newly propose a structural engineering procedure to improve the reliability of the LQ design in the jack-up rigs. From basis of this procedure, a more reasonable and optimized results are proposed as a practical manner as well as scientific approach.
Influence of the Skirt on the Seismic Response of Bucket Foundations for Offshore Wind Tower Using Dynamic Centrifuge Model Tests
Authors: Olalo Leonardo T. , Choo Yun Wook , Bae Kyung-Tae
Published: October 2016

The influence of skirt to the seismic behavior of the bucket foundation supporting offshore wind turbine was analyzed by performing dynamic centrifuge tests. Three types of bucket foundation with aspect ratios (length of the skirt/diameter of the foundation) of 0.50, 0.75 and 1.00 were tested. Kobe and El Centro earthquakes were used as excitation patterns. Clean sand was used to simulate the soil deposit. Peak acceleration, settlement and tilting of foundations on drained sand condition were analyzed and compared. The bucket foundation with the longest skirt accelerated the most at the platform level and experienced the least degree of tilting and normalized settlement. Obtained results were expected to contribute for a better understanding on the performance of bucket foundation during an earthquake.
A Study on Vertical Movement Model for Planktonic Larvae of Manila Clam in Tokyo Bay
Authors: Otsuka Fumikazu , Hironaka Mao , Kawanishi Toshimasa , Masuda Koichi
Published: October 2016

In this paper, the average growth rate and spawning date of Manila clam larvae in Tokyo Bay were estimated from their generation structure. A simplified model for the length and growth rate of the larvae was developed, along with a numerical model for their vertical movement in Tokyo Bay. The individual differences in the growth rate and length of the larvae for different spawning dates were considered in the vertical movement model. The three dimensional movement of Manila clam larvae was simulated using these models. The model was able to reproduce the main features of the larvae population at different depths.
Influence of the Draft Condition on Vortex-Induced Motions of a Semi-Submersible Platform With Four Square Columns
Authors: Liu Mingyue , Xiao Longfei , Lu Haining , Li Jun , Yu Xiaochuan
Published: October 2016

The vortex-induced motions (VIM) phenomenon of semi-submersibles has drawn increasing attention with the development (mainly increase of column size) of new semi-submersibles. Due to the elongated submerged columns and the enlarged projected area to current, deep-draft semi-submersible platforms are susceptible to higher in-line drag forces and transverse vortex-induced lift forces, resulting in considerable horizontal motions in a current environment. In order to check the influence of draft conditions on VIM of the semi-submersible platform with four square columns, experimental investigations with five draft ratios varying from 0.87 to 1.90 were carried out in a towing tank.

The 6-degree-of-freedom (6-DOF) motions of the model were recorded by the motion acquisition system, in synchronisation with restoring forces provided by four load cells, one for each horizontal mooring spring. This paper discusses the dynamic behavior of a semi-submersible platform in five different draft conditions, including coupled motions at the water surface plane, drag and lift forces, and spectral analysis. It is shown that the largest transverse amplitudes are around 75% of the column width in the range of 6.0 ≤ Ur ≤ 8.0 for the deep-draft semi-submersible (H/L = 1.90). With 50% of the immerged column height of the deep-draft model, a 30% decrease in the transverse motion amplitude can be seen. Furthermore, the effects of the draft condition on yaw responses and current loads are also addressed.
The Study of a Possible Strengthened Structure Implanting Into the Hoses in Umbilical for Deep Water Application
Authors: Zhou Chongyao , Zhang Liang , Kang Yongtian , Qu Yan , Huang Kevin , Zhang Dagang
Published: October 2016

Umbilical is the key actor connecting the subsea devices on the seabed to the platform, and acting like a neural line transforming the information from the central control system on platform to the subsea control elements.

Normally, according to the applied chemical reagent and hydraulics control fluid transmitting element, the umbilical is divided into two types for alternative depths, one consists with hoses for shallow water or medium water application, and the other utilizes the super duplex steel tubes for all depth water application. The main argument for using steel over thermoplastic hoses would be chemical resistance and hydraulic response time (where hose performance is poor).

However, the hose will have more flexibility than steel tube, which is also easier for manufacture. If the umbilical with hoses can be used in deeper water condition, the cost will decrease greatly.

In order to strengthen the hose structure for deep water use (up to 1000m twice the prior record), this paper will focus on the study of a possible strengthened structure implanting into the hoses to increase the outer pressure resistance capacity, which will increase the whole outer pressure resistance performance of umbilical finally. The thermoplastic hose with strengthened structure will enable the use of thermoplastic hoses in deeper water.
Study on Influence of Geometrical Dimensions of Floating Bodies on Cloaking Phenomenon
Authors: Zhang Zhigang , He Guanghua , Ju Xiaoqun , Yu Dong
Published: October 2016

Mooring offshore floating structures such as offshore platforms in large waves and winds, against the drift force and rotational moments are challenging in offshore engineering and ocean engineering. To investigate these kind of problems named positioning problems accurately, not only in hydrodynamic forces of first order but also in time-averaged steady forces of second order named wave drift force need to be taken into account. That arranging of several small cylinders regularly on a circle concentric with a fixed floating body is considered to reduce the wave drift force. Fortunately, a Cloaking phenomenon occurs at certain conditions with proper geometrical dimensions of floating bodies, which can reduce the wave drift force acting on bodies, perfectly even to zero. In this paper, with a combination of higher-order boundary element method (HOBEM) and wave-interaction theory, the influences of geometrical parameters of outer surrounding cylinders on the wave drift force of floating bodies are systematically investigated and discussed.
Loads and Dynamic Response of a Floating Wave Energy Converter due to Regular Waves From CFD Simulations
Authors: Büchner Anna , Knapp Thomas , Bednarz Martin , Sinn Philipp , Hildebrandt Arndt
Published: October 2016

The commercial CFD code ANSYS Fluent is used for the three-dimensional estimation of wave loads and the dynamic response of a floating single point wave energy converter of the SINN Power wave power plant due to non-breaking and unidirectional waves in coastal waters. The VoF method is used to model the free surface and wave theories to set up the boundary conditions at the inlet for regular waves. The wave induced vertical motions of the floating module are computed by a sixDoF solver. Preliminary 2D and 3D studies to set up boundary conditions, mesh densities and solver settings were performed. The numerical results were compared to analytical solutions in form of water surface elevations and wave kinematics which showed good agreement.

The paper presents the dynamic response of the floating module for different load cases in terms of non-breaking waves. The resulting horizontal and vertical forces at the floating module will be presented and explained by the flow dynamics. Time and space depending velocities and pressure distributions including details on vortex separation will be given, which reveal valuable insights on the contribution of inertia and drag forces leading to the dynamic structural response of the floating devices.
Coupled Mooring Analyses for the WEC-Sim Wave Energy Converter Design Tool
Authors: Sirnivas Senu , Yu Yi-Hsiang , Hall Matthew , Bosma Bret
Published: October 2016

A wave-energy-converter-specific time-domain modeling method (WEC-Sim) was coupled with a lumped-mass-based mooring model (MoorDyn) to improve its mooring dynamics modeling capability. This paper presents a verification and validation study on the coupled numerical method. First, a coupled model was built to simulate a 1/25 model scale floating power system connected to a traditional three-point catenary mooring with an angle of 120 between the lines. The body response and the tension force on the mooring lines at the fairlead in decay tests and under regular and irregular waves were examined. To validate and verify the coupled numerical method, the simulation results were compared to the measurements from a wave tank test and a commercial code (OrcaFlex). Second, a coupled model was built to simulate a two-body point absorber system with a chain-connected catenary system. The influence of the mooring connection on the point absorber was investigated. Overall, the study showed that the coupling of WEC-Sim and the MoorDyn model works reasonably well for simulating a floating system with practical mooring designs and predicting the corresponding dynamic loads on the mooring lines. Further analyses on improving coupling efficiency and the feasibility of applying the numerical method to simulate WEC systems with more complex mooring configuration are still needed.
Numerical Prediction of the Propulsion Characteristics of Ships in Waves
Authors: Sigmund Sebastian , el Moctar Ould
Published: October 2016

The influence of regular head waves on the propulsion characteristics of a twin screw cruise ship is investigated using RANS based flow-solver. Propeller open water characteristics are determined at first by computing the propeller forces in homogeneous inflow. Then, computations of the towed model without propeller and of the self-propelled model in calm water are performed to obtain the propulsion characteristics in calm water. Afterwards, the total resistance as well as the forces of the self-propelled model in regular head waves are computed. All computations are performed using a RANS based flow-solver coupled with the six-degrees-of-freedom equations of motion. The sliding interface method is used to allow the rotation of the geometrically modelled propeller, when needed. Computations are performed using the same numerical grids to keep errors originating on different spatial and temporal discretization as small as possible. Grid studies are performed to evaluate discretization errors of each mesh region, namely the hull region and the rotating propeller region, separately. The numerical results are compared with experimental results obtained from physical tests. It is shown, that RANS is capable of investigating the propulsion behavior of a ship in regular head waves, but to the cost of high computational effort. Fair agreement between numerical and experimental results is obtained. All results show that the propulsion characteristic change in waves. It is also found, that this is mainly caused by the change of the propeller efficiency due to a different propulsion point as a consequence of the added resistance in waves.
Potential Changes of the North Atlantic Wind and Wave Climate and Occurrence of Rogue Waves
Authors: Bitner-Gregersen Elzbieta M.
Published: October 2016

The present study investigates potential changes of wind and wave conditions in one North Atlantic location in the 21st century. The Fifth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC) uses four scenarios for future greenhouse gas concentrations in the atmosphere called Representative Concentration Pathways (RCP). Two of these scenarios with radiative forcing of 4.5 and 8.5 W/m2 by the end of the 21st century have been selected to project wind and wave conditions in the North Atlantic. The third generation (3G) wave model WAM, forced by winds obtained from GFDL-CM3, EC-Earth, HADGEM2, IPS-CM5A-MR, MRI-GCGCM3 and MIROC5 climate models, has been used to project waves for these two scenarios for the historical period 1971–2000 and the future period 2071–2100. Long-term probabilistic description of wind and waves is provided and deviations between the past and future wind and wave conditions are demonstrated, given attention to the projections obtained by use of the GFDL-CM3 and EC-Earth climate models. Changes in extreme wind and waves are shown and uncertainties associated with climate change projections discussed. Occurrence of rogue-prone crossing sea states which may trigger generation of rogue waves in the past and future climate is also investigated.