bluuebunny/crossref_metadata_2025 huggingface dataset:
Design, Fabrication, and Testing of a Flexible Three-Dimensional Printed Percutaneous Needle With Embedded Actuators
Authors: Varnamkhasti Zahra K. , Konh Bardia
Published: December 2020

Percutaneous needle-based procedures have replaced open surgeries in cancer treatments to perform the tasks with minimal invasiveness to the tissue. Precise placement of the needle at target positions in cancer diagnostic (e.g., breast biopsy) or therapeutic (e.g., prostate brachytherapy) procedures governs the success of such procedures. Also, in many needle insertion applications, it is desired to steer away from critical organs or to maneuver around anatomical obstacles in tissue. This work introduces a flexible three-dimensional (3D) printed percutaneous needle with embedded actuators for improved navigation inside the tissue toward the target. The needle is manipulated via a programmed portable motorized control unit to realize an average angular deflection of about 15 and 14 deg in air and a tissue-mimicking phantom, respectively. We demonstrated the needle's capability to reach the target, while avoiding obstacles. We also demonstrated that the flexible needle can be guided through a desired trajectory by controlling its angular deflection and axial movement. The 3D deflection of the needle is expected to assist in breast cancer lumpectomy for multiple extractions of tissue samples or in prostate brachytherapy via a curvilinear approach. The flexible needle may help reducing the complexity of current path planning algorithms, and thereby improve efficiency of closed-loop control systems in needle steering.
On the Effect of Various Heat Treatments on Microstructure of AISI 4130 Steel Used in Sour Service Pipes
Authors: Vysochinskiy Dmitry , Rybakov Dmitri
Published: December 2020

Nowadays welding is the most common way to connect metal parts and structures. One of the challenges connected to welding it that heat output from the welding alters the microstructure of the metal creating the heat affected zone (HAZ) near the weld. In steel welds HAZ is often harder and more brittle than the base material due to formation of martensite. This might cause hydrogen induced cracking and speed up the fatigue of the weld. To mitigate the martensite formation in the HAZ different heat treatments, like preheat, interpass and PWHT are often applied. However, for 4130 steel, preheat and interpass temperatures are not expected to restrict martensite formation due to materials slow transformation rate. Preheat and interpass temperatures are still important for hydrogen diffusion and reduction of tension in the weld.

This paper investigates the effect of different heat treatments on the microstructure of AISI 4130 steel used in sour service pipes. The welding and sample preparation were performed in accordance with ISO 15156 and ASME B31.3 standards. Two sample sets were produced: one with and one without preheating. The hardness tests of weld profiles were performed in accordance with ISO 15156-2 international standard. Comparison of hardness profiles indicated that preheat had virtually no effect on hardness of the steel in HAZ, although it affected hardness of fusion zone. Preheated samples were further heat treated in a furnace simulating PWHT effect. Three different PWHT condition were tested. The hardness profiles indicated that PWHT led to noticeable changes in steel microstructure. In order to understand those microstructure changes, the heat treatment of the steel during production process was reviewed and microscopic investigations of the weld profiles were performed.
LNG and Bulk Terminals: An Advanced Approach for Downtime Estimate and Layout Optimization
Authors: El Chahal Ghassan
Published: December 2020

Downtime related to excessive vessel motion and/or mooring line forces caused by environmental conditions is an important parameter for designing new terminals and ports in addition to planning offshore operations such as dredging, structure installations, etc. The present paper addresses an advanced approach using artificial intelligence in order to estimate the downtime in a more realistic manner. This approach is compared with conventional methods used in the industry and is applied for a number of terminal projects presented in this paper.

Operations at marine terminals are generally protected by a breakwater. These breakwaters whether are rubble mound type or caissons are expensive as constructed in deep waters in 20 m or greater. The conventional downtime methods result generally in a higher value which subsequently requires a longer breakwater once the downtime criteria is exceeded. The advanced approach for estimating downtime helps to optimize the terminal/breakwater layout and subsequently save on the CAPEX.

This approach estimates the downtime for the long term environmental time series using an inhouse Matlab code/program developed using neural network. In order to estimate the downtime, a set of specialized studies are conducted first illustrating the breadth and depth of port engineering. First, the wave climate for a long term time years is established at the project site using Spectral Wave Model MIKE 21 SW. The wave conditions are then transformed to the breakwater leeside (terminal side) using Boussinesq wave model MIKE 21 BW. Dynamic mooring study for the vessels at terminal is carried out using the time domain mooring analysis software MIKE 21 MA. Finally, an inhouse developed Matlab program calculates the downtime for the metocean time series based on the dynamic vessel response of the large set of selected environmental combinations.

Up to the author’s knowledge, this is the first published work highlighting limitations of conventional methods and the importance of implementing advanced techniques. This leads to a new thinking of how terminals are to be designed in the future.
Dynamic Simulation of a Mooring Catenary Based on the Lumped-Mass Approach: OpenModelica and Python Implementations
Authors: Viswanathan Savin , Holden Christian
Published: December 2020

In this paper, the theoretical background behind the formulation and solution of a discretized lumped-mass mathematical-model of the physically continuous and inelastic mooring catenary is re-visited. The drag term of the Morison equation is used to determine the fluid loads, and the sea-bed interaction is prescribed as vertical spring loads on the interacting nodes. Numerical solution to the equation of motion is sought through a finite-difference method. The initial conditions are determined using the catenary theory, the instantaneous boundary conditions are prescribed, and the in-elasticity of the mooring segments is specified as the constraint equation. The solution procedure is then implemented as both Python and Modelica code. Results of the Modelica simulation are then compared with those generated using the popular ocean-engineering software, Orcaflex. Finally, conclusions are drawn based on the analysis of simulation results. The codes and results are made available for download.
Measurement for the Hydrodynamic Coefficients of the Model of an Ultra-Deep Water Work-Class ROV in the O-Tube Facility
Authors: Meng Qingrui , An Hongwei , Kimiaei Mehrdad , Azarhoush Reza
Published: December 2020

Remotely-operated vehicles (ROVs) play an important role in offshore engineering, marine research, submarine rescue, etc., whose hydrodynamic coefficients are significant to their manoeuvrability and stability. The measurements for the hydrodynamic coefficients of an ultra-deep water work-class ROV were conducted using the O-tube facility. The O-tube has a test section with dimensions of 1 m × 1 m × 17.6 m, in which the current velocity up to 3 m/s can be generated. A 1/10 ROV model was held in the centre of the cross-section via a supporting bar with diameter 25 mm. The force signals were acquired from a load cell that could sense three-dimensional forces and moments simultaneously. The measurement strategy was validated via an alternative cuboid model. The three-dimensional forces and moments were obtained subsequently with respect to the bow, stern, top, bottom, and port faces of the ROV model under two steady incoming flow velocities. The results show that the drag coefficient varies within 0.8–1.2 for different faces and the bow face design has significant influence on the drag and pitch moment coefficients when piloting forward.
Extreme Value Estimation of Mooring Loads Based on Station-Keeping Trials in Ice
Authors: Sinsabvarodom Chana , Leira Bernt J. , Chai Wei , Naess Arvid
Published: December 2020

The purpose of this work is to perform an extreme value estimation of the mooring loads associated with station-keeping of a ship operating in ice. In general, the design of mooring lines is based on estimation of the extreme loading caused by environmental conditions within the relevant area. In March 2017, station-keeping trials (SKT) in drifting ice were performed as part of a project headed by Statoil in the Bay of Bothnia. The objective was to investigate the characteristics of the mooring loads for the supply vessel Magne Viking for different types of physical ice management schemes. Tor Viking was employed as an ice breaker as part of the physical ice management systems. The ice conditions (i.e. the ice drift velocity and the ice thickness) during the trials were monitored by using Ice Profiling Sensors (IPSs). Different patterns of ice-breaking manoeuvers were investigated as part of the physical ice management systems, such as square updrift, round circle, circle updrift and linear updrift pattern were studied as part of the field experiments. The peak values of the mooring loads for the supply vessel are determined by using the min peak prominence method. For the purpose of extreme value prediction, the peak over threshold method and block maxima method for a specific time window are applied to estimate the mooring loads that correspond to specific probabilities of exceedance (or equivalently: return periods). These loads can then be compared to the design loads that are being specified by relevant international standards.
Experimental Study of Laminar Displacement Flows in Narrow Horizontal Eccentric Annuli
Authors: Renteria Alondra , Liew Yee Voon , Frigaard Ian
Published: December 2020

Wells with poor cement jobs are prone to develop paths where the hydrocarbons might leak to the surface. Such events cause environmental risks and costly repairs. Even though horizontal wells have been drilled since the 1980s, studies on the dynamics of the fluid-fluid displacement under this configuration are scarce.

In this work, we present experiments on the displacement of two Newtonian fluids in laminar regime in a horizontal uniform annulus. The minimum non-dimensional parameters required to describe the flow under such conditions include a buoyancy number (b), viscosity ratio (μ2/μ1) and eccentricity (e).

We have designed and built a flow loop that mimics the annular displacement under controlled and dimensionlessly comparable conditions found in field. Within this apparatus we can set key process parameters: flow rate, eccentricity, fluid rheology and density. Data acquisition is through imaging with high sensitivity cameras and partially automated instrumentation.

Preliminary results of the experiments show that there is a subtle balance between eccentricity and buoyancy. Sufficiently high values of |b| will end up in stratification of the fluids. The secondary flows created in an eccentric annulus compete against a positive buoyancy, driving the flow to the wide side (top) at moderate values of b. The effect of the viscosity ratio is most relevant at small values of b.

The experimental data from this work can be compared against both mathematical model predictions and computational simulations used in the design of primary cementing jobs.
Research on Resonant Fluid Behaviors and Induced Violent Slamming Effects in a Stepped Moonpool Under Wave Excitations With Ship Forward Speed
Authors: Lyu Hongguan , Gu Jiayang , Tao Yanwu , Zhang Zhongyu
Published: December 2020

Moonpools on drilling vessels are structures located at the mid-ship position to facilitate drilling and other marine operations. The existence of the moonpools is prone to result in intense resonant fluid behaviors even other unexpected violent nonlinear impact on the flow system under external excitations, especially for those types with one or more recesses.

The present study focuses on the resonant fluid behaviors and the induced violent nonlinear effects so-called slamming in a moonpool with a recess within the frameworks of both theoretical and numerical investigations. The natural frequencies of the piston mode and the first-three modes of the studied moonpool are approximated based on the theoretical formulas extracted from the linear potential flow theory. Furthermore, the calculated frequency of piston mode are carried out as the external wave excitations combined with varying current velocity to investigate the slamming effects at the typical locations such as the wall of the moonpool and the bottom of the recess. Finally, the characteristics of the slamming pressure both in space and time are discussed in detail based on the RANS-based numerical simulations.

The result shows that the resonant fluid behaviors under the wave-current interactions are greatly different from the wave-only excitations. Moreover, intense slamming occur in a moon-pool with a recess under some particular wave-current interactions due to the shallow water effects in the recess region and the phenomenon of energy transfer. The phenomenon of slamming must be treated with special cautions in practical engineering because of the fact that some induced adverse effects could weaken the hydrodynamic performance of the drilling vessel, as well as the structural strength of the moonpool.
Analysis of a FOWT Model in Bichromatic Waves: An Investigation on the Effect of Combined Wave-Frequency and Slow Motions on the Calibration of Drag and Inertial Force Coefficients
Authors: do Carmo Lucas H. S. , de Mello Pedro C. , Malta Edgard B. , Franzini Guilherme R. , Simos Alexandre N. , Gonçalves Rodolfo T. , Suzuki Hideyuki
Published: December 2020

The choice of drag and inertia coefficients are critical for the evaluation of hydrodynamic loads in slender cylinders using either Morison’s equation or an approach where viscous forces are simply added to the results of potential theory. Many studies available in the literature have considered fixed cylinders under the action of (two dimensional) sinusoidal currents, showing that the average values of drag and added mass coefficients can be correlated with the Keulegan-Carpenter and Reynolds numbers. However, when the semi-empirical models are used for the analysis of Floating Offshore Wind Turbines (FOWTs), many other aspects of the flow may play an important role, such as the spatial variations of the wave flow over the hull, three-dimensional flow effects associated with the floater motions, the presence of heave plates, among others. The present work is based on a case-study involving a simplified version of the floater of a semi-submersible FOWT and deals with cases where the incoming flow is composed of more than one frequency and body motions are a combination of periodic components with very different frequencies (wave frequency and slow-drift motions). In this case, the choice of proper coefficients for the Morison’s approach becomes somewhat puzzling, to say the least. The objective is to understand how the more complex flow and the coexistence of different frequencies affect the hydrodynamic forces and whether proper values of force coefficients can indeed be obtained from simplified model tests performed in the absence of incoming waves, such as forced oscillations and decay tests. For doing so, the paper analyses the results of an experimental campaign performed with the model scale floater (1:80) composed of four vertical circular columns. Three sets of tests are taken into account: forced oscillations of the hull, free decays of the moored model, and motions under the action of waves (monochromatic and bichromatic). The first two are used to assess the values of added mass and drag coefficients (and also for obtaining linearized damping levels), while the third group of tests helps to evaluate the accuracy of the motions predicted when using these coefficients in frequency-domain computations.
Numerical Simulation of Dynamic Response of Foam Aluminum Sandwich Panel Under Impact Load
Authors: Wan Wenchao , Li Xiaobin , Jiang Li , Li Pu
Published: December 2020

The impact resistance of protective structure directly affects the vitality of the ship. Since the excellent energy absorption characteristics and lightweight structural forms, foamed aluminum sandwich panels have gradually replaced stiffened panels and are widely used in local structures and components of vessels. In order to improve the protective ability of the ship structure, the impact resistance of the foam aluminum sandwich panel is studied in this paper. The deformation mechanism of the foam aluminum sandwich panel under the impact of the foam aluminum projectile is simulated by the finite element analysis, and the effect of different core thickness and core strength on the dynamic response of the sandwich panel is studied. An optimized structural form is proposed for the shear failure of foam aluminum sandwich panels. The results show that the optimized structure improves the impact resistance of foam aluminum sandwich panel and the shear resistance of the intermediate core layer. The research of this paper provides reference for the optimization of foam metal sandwich structure and its application in ship protection structure.
Numerical Investigate of Penetration Resistance of Bucket Foundation With Internal Cylindrical and Cruciform Skirts
Authors: Xiao Zhong , Ma Teng , Liu Haixiao , Zhang Wei , Rafique Muhammad Akbar
Published: December 2020

Bucket foundation has broad application prospects in marine engineering as a competitive foundation. By providing internal cylindrical and cruciform skirts inside the bucket foundation,. the performance of the bucket foundation can be improved . But penetration resistance will also increase. However, few large deformation numerical analysis is carried out to simulate the penetration process of the bucket foundation with internal skirts.

In this paper, three-dimensional large deformation finite element (LDFE) models for bucket foundations with and without internal cylindrical and cruciform skirts considering strain softening effect of soft soil were established using the coupled Eulerian-Lagrangian (CEL) approach. It was found that the elevation of the soil surface inside the bucket is higher than that of initial soil surface when the penetration depth ratio is relatively small for the bucket foundation with internal cylindrical and cruciform skirts. However, with increase of the penetration depth ratio, the increased frictions on the cylindrical and cruciform skirts drive the soil inside the inner cylinder downward, and the elevation of the soil surface inside the inner cylinder is lower than that of initial soil surface. It is also lower than that of soil surface between outer and inner cylinders. The average lateral friction per unit area on each skirt decreases from outer to inner skirt. The soil flow can explain well for the evolution of the penetration resistance.
Projection and Detection Procedures for Long-Term Wave Climate Change Impact on Fatigue Damage of Offshore Floating Structures
Authors: Zou Tao , Kaminski Miroslaw Lech , Li Hang , Tao Longbin
Published: December 2020

The climate change may affect the long-term wave statistics and consequently affect the cumulative fatigue damage. This paper aims to project the trend of annual fatigue damage of offshore floating structures and to detect the climate change impact on the future fatigue damage by coupling a conventional fatigue design method with climate and wave models. Firstly, climate scenarios are selected to project the global radiative forcing level over decadal or century time scales. Secondly, climate models are used to simulate atmosphere circulations and to obtain the wind field data. Thirdly, wave conditions are simulated by coupling wind driven wave models to climate models. Fourthly, stress analysis and fatigue assessments are conducted to project the annual fatigue damage. At last, control simulations are carried out in order to identify the range of natural variability and to detect the human-induced change. A case study is presented in the Sable field offshore South Africa. The results indicate that the significant wave height is considerably influenced by the human-induced climate change. However, this change induced by human activities is still partially masked by the dominant natural variability. In addition, both the significant wave height and the annual fatigue damage increase over century time-scales.
Pipeline Walking due to Temperature Transient: Enhanced Analytical Calculations
Authors: Carneiro Daniel , Carvalhal Renata
Published: December 2020

Pipeline walking induced by transient temperature profiles as the pipeline heats up is assessed. Firstly, an integrated, closed-form solution is given for a problem for which only an ‘incremental’ solution was available [1]. This involves a short pipeline unrestrained at both ends subject to a linearly ramping temperature front.

Secondly, the range of validity of this solution is significantly extended, whilst still presenting it in closed-form. Results are compared with previously published FEA results, presenting remarkable agreement.

The closed-form analytical solution is then compared with FEA of more realistic transients (non-linear temperature front). Results show that the linear simplification can introduce excessive conservatism.

The FEA results are then examined, and the reason for the excessive conservatism is found to be associated to early expansion of the cold end, which is not observed with the simplified linear front. A simplified incremental solution for non-linear transients is proposed. This is shown to be simple and effective in improving prediction for the range over which where the closed form solution is most conservative.
Spectral Fatigue Analysis of Plate Surface Hot-Spots: A Practical Solution to the Stress Direction Issue
Authors: Bigot Fabien , Mougin Stéphanie
Published: December 2020

Spectral Fatigue Analysis using coupled hydrodynamics and finite element models has now become a common practice for the fatigue strength assessment of offshore units, with established procedures given in Classification Rules. However, users are facing a practical issue that is almost never mentioned in the procedures. Indeed, many fatigue hot-spots are located on a plate surface, as opposed to plate edges. For such hot-spots, the finite element model results are the three components of the plane-stress stress tensor. Therefore, the outcome of the Spectral Fatigue Analysis is a set of three transfer functions (RAOs). On the other hand, our industry’s practice regarding the fatigue strength model is still the proven « design S-N curve » approach in combination with the Palmgren-Miner’s damage summation. As a consequence, today the engineer is left with no clear instruction about the proper way how to close this gap between the three stress RAOs on the one hand, and the single stress S-N curve on the other hand. If any advice is given, it is most often to consider the principal stresses, tentatively extending to spectral analysis the classification rule load cases approach. However, principal stress determination is a non-linear procedure that is not compatible with spectral analysis in frequency domain. Turning the spectral results into time domain to overcome this limitation is extremely costly and is not straightforward. Of course, a rational solution to this issue would be the adoption of a multiaxial fatigue damage criteria in lieu of the uniaxial S-N curve. But until such a multiaxial fatigue criteria is widely accepted in our industry, users have to square the circle, and force their stress tensor RAOs into the existing rule criteria. In this paper, a practical solution to reconcile plane stress results and conventional S-N curve criterion in spectral fatigue is proposed: the “facet approach “.
A Fluid-Structure Coupled Computational Model for the Certification of Shock-Resistant Elastomer Coatings
Authors: Ma Wentao , Zhao Xuning , Wang Kevin
Published: December 2020

Shock waves from underwater and air explosions are significant threats to surface and underwater vehicles and structures. Recent studies on the mechanical and thermal properties of various phase-separated elastomers indicate the possibility of applying these materials as a coating to mitigate shock-induced structural failures. To demonstrate this approach and investigate its efficacy, this paper presents a fluid-structure coupled computational model capable of predicting the dynamic response of air-backed bilayer (i.e. elastomer coating – metal substrate) structures submerged in water to hydrostatic and underwater explosion loads. The model couples a three-dimensional multiphase finite volume computational fluid dynamics model with a nonlinear finite element computational solid dynamics model using the FIVER (FInite Volume method with Exact multi-material Riemann solvers) method. The kinematic boundary condition at the fluid-structure interface is enforced using an embedded boundary method that is capable of handling large structural deformation and topological changes. The dynamic interface condition is enforced by formulating and solving local, one-dimensional fluid-solid Riemann problems, which is well-suited for transferring shock and impulsive loads. The capability of this computational model is demonstrated through a numerical investigation of hydrostatic and shock-induced collapse of aluminum tubes with polyurea coating on its inner surface. The thickness of the structure is resolved explicitly by the finite element mesh. The nonlinear material behavior of polyurea is accounted for using a hyper-viscoelastic constitutive model featuring a modified Mooney-Rivlin equation and a stress relaxation function in the form of prony series. Three numerical experiments are conducted to simulate and compare the collapse of the structure in different loading conditions, including a constant pressure, a fluid environment initially in hydrostatic equilibrium, and a two-phase fluid flow created by a near-field underwater explosion.
An Improved SPH Model for Simulating Hydrodynamic Consequences Induced by Reef Degradation
Authors: Zhao Yinlin , Wen Hongjie , Ren Bing , Wang Guoyu , Wang Yongxue
Published: December 2020

Coral reefs degradation accelerates in recent decades due to the natural disturbance and anthropogenic activities. It is important to predict and evaluate reasonably the hydrodynamic consequences of reef degradation. An improved weakly compressible smoothed particle hydrodynamic (WCSPH) porous model is developed based on the standard two-phase mixture theory. The developed WCSPH mixture model is validated by comparing the predicted results with the corresponding available data. The model is then adopted to predict the effects of reef degradation on the spatial distributions of wave setup, wave-induced current and low frequency wave energy over the reef-flat under the reef resonance conditions.
Design of Water Hammer Protection for FPSO Domestic Water System Based on AFT-Impulse
Authors: Huan Zhang , Qipeng Zhang , Chao Wang , Jiangguo Xu , Weiwen Kong
Published: December 2020

Due to the limitation of cabin space, FPSO domestic water pipe network system has the characteristics of long water delivery distance, more bending of pipeline and frequent opening and closing of valves, etc. The above characteristics are very likely to cause water hammer in the pipeline, resulting in increased risk of safe operation of pipe network system. In this paper, a FPSO domestic water system was taken as the research object. In view of the water hammer problem in the pipe network system, the model of FPSO domestic water system was established by using dynamic fluid analysis software AFT-Impulse, combined with the factors affecting the water hammer phenomenon (such as pipe diameter, velocity of wave, pipe length, pipeline roughness and valve closing time), the steady state analysis and transient analysis of multi-working conditions and multi-scenarios were realized to determine the main control factors. Based on the influence of main control factors, a comparison scheme of water hammer protection in FPSO domestic water system was proposed. Through the transient analysis of AFT-Impulse software under multi-working conditions, the optimal scheme of water hammer protection for FPSO domestic water system was obtained, which provided guarantee for the safe operation of the system.
Numerical Design Study of Duct and Stator for a Pump-Jet Propulsor
Authors: Ji Xue-Qin , Yang Chen-Jun , Dong Xiao-Qian
Published: December 2020

The pump-jet propulsor consists of a duct, a rotor and stators which are installed upstream of the rotor to provide pre-swirl flow or downstream of rotor to absorb the kinetic energy in the flow. The strong interactions between the three components and the vehicle are closely related to their design and exert great effect on noise and hydrodynamic performance. This paper attempts to develop an effective and efficient method for the optimal design of the duct and the pre-swirl stators under the influence of vehicle and rotor via viscous flow CFD simulations. In this paper, the two key parameters, attack angle of the duct and pitch angle of pre-swirl stators, are investigated.

The numerical simulations are based on the solution of the Reynolds-Averaged Navier-Stokes (RANS) equations using a two-layer realizable k-ε model for turbulence closure. The computational domain is discretized into mixed unstructured cells. The software package STAR-CCM+ is used for both grid generations and flow simulations.

The rotor is replaced by the body-force model which is proposed according to the load distribution of the rotor in pump-jet propulsor. Total thrust of body force balances the resistance of a fully-appended underwater vehicle and its propulsor in the self-propulsion simulations and torque is determined by assuming that the propulsive efficiency is 80%. To the end of the optimal design, the total resistance, as the main consideration, and detailed flow field, such as pressure distribution, are numerically investigated for varied attack angles of the duct and pitch angles of pre-swirl stator. It is shown that the two parameters have significant impact on the performance of the propulsor and the recommended design is given.
A New Methodology for Generation of Solitary Water Waves in Laboratory
Authors: Liu Xiao , Liu Yong
Published: December 2020

In this article, a very simple system based on the enhanced dam-break flows was proposed and implemented to generate solitary wave with larger relative wave height (the ratio of wave height to water depth) in a laboratory flume. The experimental results showed that stable waves with the solitary wave profiles were successfully generated in the wave flume. The wave surface elevations were recorded by a series of wave gauges, and the fluid velocity field of the solitary wave was measured by Particle Image Velocimetry (PIV) system. The measurements of solitary wave profile, celerity and horizontal fluid velocity were also compared with the predictions by three different solitary wave theories. Results demonstrated that the present simple system was reliable and effective for the generation of solitary waves in laboratory.
Droplet Size Distributions and Pressure Control in the Gas-Liquid Cylindrical Cyclone
Authors: Yang Lele , Wang Jing , Zou Li
Published: December 2020

The gas–liquid cylindrical cyclone (GLCC) employs gravitational and centrifugal forces to realize gas-liquid separation. The aim of this study is to understand the droplet size distribution and pressure control in the GLCC via experiment and numerical analysis. The droplet size and pressure distributions were measured using Malvern RTsizer and pressure transmitters, respectively. The Discrete Phase Model was used to numerically analyze the swirling hydrodynamics of the GLCC. The results showed that the increase in the gas superficial velocity decreased the droplet size distribution at the inlet as a whole due to the shear effect and flow instability. The increase in the liquid superficial velocity only increased the small droplet size distribution at the inlet for the limitation of the gas’s carrying capacity. The pressure loss mainly occurred at the inlet and the overflow outlet. When the liquid level was remained below the inlet and above the liquid outlet, the liquid level and the liquid outlet section approximately met the Bernoulli equation for a finite large flow beam. With the increase in the pressure at the gas outlet, the liquid film fell back and the separation efficiency increased gradually. These results are helpful for further spreading applications of the GLCC in industry.
Investigations Into Fatigue of OPB Loaded Offshore Mooring Chains
Authors: Farrow Gary H. , Dimopoulos Simon , Kilner Andrew A.
Published: December 2020

The Chain FEARS (Finite Element Analysis of Residual Strength) JIP developed a correlated FEA method for determining fatigue life of Tension-Tension (T-T) loaded offshore mooring chain. The developed first principles method incorporated the non-linear effects of proof loading, accounted for mean chain tension, accounted for material grade, employed a multi-axial fatigue method to account for complex stress fields within the chain, and was based on a parent material S-N curve. It was anticipated that this high fidelity approach could be applied more universally to successfully address a broader spectrum of emergent factors experienced in-field which have caused chain fatigue life reduction and adversely impacted mooring system integrity. These emergent factors include an array of chain degradation modes including; uniform, pitting and mega pitting corrosion; preferential butt weld corrosion; abrasive, contact and interlink wear; and load duties other than Tension-Tension (TT) such as Out-Of-Plane Bending (OPB), In-Plane-Bending (IPB) and Bending-Tension (BT). The objective of the investigations conducted by AMOG Consulting following completion of the Chain FEARS JIP research was to explore the extent to which the developed fatigue method could be applied more universally to address these emergent factors as they pertained to residual fatigue life. Application of the method identified a number of trends in fatigue performance for links subject to hawse pipe and fairlead interaction, and demonstrated good correlation against available guidance on fairlead performance and against OPB fatigue test data. The investigation confirms that the first principles FEA fatigue method can be applied more universally to successfully address a broader spectrum of emergent factors experienced in-field relating to fatigue life reduction.
Simplified Analytical Calculation and Modification of the Crushing Forces of Intersection Units in Vessel-Bridge Collisions
Authors: Faqiang Yin , Jin Pan , Shiwen Huang , Mingcai Xu
Published: December 2020

Because of the increasingly busy maritime trade, the number of bridges damaged by ship-bridge collision also increases. In order to reduce the serious losses caused by ship-bridge collision incidents, it is necessary to make a rapid estimation of ship collision forces. The simplified analytical formulas can be used to rapidly evaluate the collision force in ship collision accidents, but it is found that the existing simplified formulas are only applicable to bulb structures including small-angle inclined elements and not suitable for large-angle inclined elements which exist in ship-bridge collision. In this paper, the quasi-static crushing simulation of the bulbous structure with small-angle inclined angle elements is carried out, and the applicability of the simplified analytical formula of the intersection unit to the typical structure is verified. By comparing the simplified analytical results of the bow with the quasi-static simulation results and the ratio of the strength reduction factor to the effective crushing distance, it is found that the inclined angle of the inclined element will affect the impact force of the simplified analytical calculation. Then, finite element analysis of the truncated-type intersection structure with different element inclination angles are carried out, and the results show that the existing simplified analytical formula is no longer suitable for the calculation of collision force when the inclined angle is greater than 40°. For this reason, the existing simplified analytical formulas are modified for the large-angle inclined elements, and it can provide a certain reference calculation value for the collision force of vessel-bridge collision which includes large-angle inclined elements.
Benchmark Case Study of Scale Effect in Self-Propelled Container Ship Squat
Authors: Kok Zhen , Duffy Jonathan , Chai Shuhong , Jin Yuting
Published: December 2020

A URANS CFD-based study has been undertaken to investigate scale effect in container ship squat. Initially, CFD studies were carried out for the model scale benchmarking squat cases of a self-propelled DTC container ship. In this study, a quasi-static modelling approach was adopted where the hull was fixed from sinking and trimming which is computationally more efficient than dynamic mesh methods that models actual motion directly. Instead, the quasi-static approach allows estimation of the squat base on the recorded hydrodynamic forces and moments. Propulsion of the vessel was modelled by the body-force actuator disc method. Upon successful verification and validation of the model scale self-propelled CFD model against benchmark data, full scale investigations were then undertaken. Validation of the full scale set-up was demonstrated by computing the full scale bare hull resistance in deep, laterally unrestricted water and comparing against the extrapolated resistance of model scale benchmark resistance data. Upon validating the setup, it was used to predict full scale ship squat in confined waters. The credibility of the full scale confined water model was checked by comparing vessel resistance in confined water against the Landweber empirical prediction. To quantify scale effect in ship squat predicitons, the benchmarking squat cases were computed by adopting the validated full scale CFD model with body-force propulsion. Comparison between the full scale CFD, model scale CFD and model scale benchmark EFD squat results demonstrates that scale effect is negligible.
System-Based Modelling of KCS Manoeuvring in Calm Water, Current and Waves
Authors: Jin Yuting , Yiew Lucas J. , Magee Allan R. , Zheng Yingying
Published: December 2020

Maritime autonomous surface ships (MASS) require accurate future state projection to initiate collision-avoidance manoeuvres. Forecasts of the vessels’ trajectories and motions are fundamentally based on the mathematical manoeuvring model, which is an essential component of their hydrodynamic digital twin nowadays. Using the benchmark container ship KCS as an object of study, this paper adopts a 4-DOF modular-type manoeuvring (MMG) model to predict the vessel trajectories in calm water and under the presence of steady current and regular waves. The current effects are treated as additional ship over water speed, while the wave effects are considered by superimposing the second-order mean wave drift loads to the calm water hull hydrodynamics. The wave drift loads are solved using the potential flow solver WASIM, which is based on Rankine panel method. The computed vessel trajectories and motions are compared with available literature results and show good correlation.
The Effects of Hydrodynamic Forces on Maneuvrability Coefficients for Wind-Assisted Ships
Authors: Giovannetti L. Marimon , Olsson F. , Alexandersson M. , Werner S. , Finnsgård C.
Published: December 2020

Assessing the manoeuvring performances of a ship at a design stage is becoming more important, especially when trying to improve shipping efficiency to reduce fuel consumption.

When designing a hull with appendages, it is necessary to balance hydrodynamic efficiency with manoeuvrability. Therefore, the possibility of simulating a captive test at a design stage will increase the chances of understanding the behaviour of a ship from an early stage in the design process. The current research is based on the evaluation of hydrodynamic efficiency of a hull and appendages in a pure resistance, self-propulsion and in a wind-assisted mode.

The forces and moments acting on the hull and appendages are then analysed and used as inputs for a Virtual Captive Test (VCT) [1]. In order to correctly perform a VCT and further analyse the performances of a ship with a Velocity Prediction Programme (VPP), particular care has been put in correctly capturing the manoeuvrability coefficients. Those are derived with polynomial fittings once the forces and moments acting on the ship are extracted from the Computational Fluid Dynamics (CFD) simulations.

Many CFD simulations were performed to assess the hydrodynamic characteristics of the hull and appendages in a range of flow directions, rudder angles and rotating flow. Those simulations encompass the whole range of datapoints needed to describe a wind-assisted ship during manoeuvring.

Taking into consideration both hydrodynamic characteristics and manoeuvrability effects at an early design stage can reduce model tests costs and will allow to inspect a larger number of hull-appendages scenarios when analysing the final VPP results.
Assessing Climate Change in the North Atlantic Wave Regimes
Authors: Bernardino M. , Gonçalves M. , Guedes Soares C.
Published: December 2020

An improved understanding of the present and future marine climatology is necessary for numerous activities, such as operation of offshore structures, optimization of ship routes and the evaluation of wave energy resources.

To produce global wave information, the WW3 wave model was forced with wind and ice-cover data from an RCP8.5 EC-Earth system integration for two 30-year time slices. The first covering the periods from 1980 to 2009 represents the present climate and the second, covering the periods from 2070–2099, represents the climate in the end of the 21st century.

Descriptive statistics of wind and wave parameters are obtained for different 30-year time slices. Regarding wind, magnitude and direction will be used. For wave, significant wave height (of total sea and swell), mean wave period, peak period, mean wave direction and energy will be investigated. Changes from present to future climate are evaluated, regarding both mean and extreme events. Maps of the theses statistics are presented.

The long-term monthly joint distribution of significant wave heights and peak periods is generated. Changes from present to future climate are assessed, comparing the statistics between time slices.
Time-Domain Hydrodynamic Model for Mooring Analysis of a Spread Moored FPSO With Calibration of Wave Drift Forces
Authors: Zhang Min , Wang Junrong , Du Junfeng , Fonseca Nuno , Tahchiev Galin , Engebretsen Espen
Published: December 2020

The paper presents calibration and validation of a time domain numerical model for mooring analysis of a spread moored FPSO in moderate seastates with and without current. The equations of motion are solved in the time domain with a fully coupled method, accounting for linear wave frequency (WF) radiation and diffraction, second order wave drift forces and nonlinear low frequency (LF) damping. The mooring system dynamics is solved by a FEM. Uncalibrated numerical models are based on input from the mooring system, vessel mass, radiation/diffraction analysis, decay tests and current coefficients. WF responses are very well predicted by standard radiation/diffraction linear analysis, therefore the focus is on the LF responses. LF motions are underpredicted by the uncalibrated numerical model.

Calibration is performed by comparing simulations with model test data and adjusting hydrodynamic coefficients known to be affected by uncertainty. These include wave drift force coefficients and LF damping. Correction of the drift coefficients is based on empirical quadratic transfer functions (QTFs) identified from the test data by a nonlinear data analysis technique known as “cross-bi-spectral analysis”. The LF damping coefficients are then adjusted by matching low frequency surge and sway spectra from the model tests and from the simulations.
3-D Simulation of Iceberg Towing Operations: Cable Modeling and Frictional Contact Formulation Using Finite Element Analysis
Authors: O’Rourke Brian J. , Fuglem Mark K. , King Tony
Published: December 2020

Ice management in regions of offshore development with icebergs present includes re-direction of icebergs by means of towing. The prevention of tow-rope slippage and iceberg rolling due to hydrostatic instability are essential for an effective and safe operation. The ability to simulate any particular towing operation in the field, prior to attempting it, would provide some measure of assurance of its feasibility. In addition, such a model will allow optimization of towing configuration and application by showing optimal tow direction, maximum force and rate of force application; selection of single tow line or net; and optimum net configuration. The objective of the described work is to develop a simulation tool that can be used for such application.

A previous project funded by Hibernia Management and Development Company Ltd. (HMDC) gathered 3-dimensional profile data on 29 icebergs off the East coast of Canada; and further data collection has been ongoing. The present project utilizes these profiles as valuable input in the development of the model for simulating single-line and net tows.

This paper presents the first phase of development of a 3-D dynamic iceberg towing model that evolved from an earlier 2-D static version. The current iteration applies the ‘Total Lagrangian’ Finite-Element Method (FEM) to model the cable-and-rope structure between the towing vessel and iceberg, and a contact model that includes sticking and sliding friction between the rope/net and iceberg. The iceberg is modeled as a rigid surface mesh and is fully constrained against motion during the current phase of development, while the cables and ropes are modeled as elastic bar elements with translational inertia and velocity-squared fluid drag. The contact elements consist of penalty springs with proportional damping, and appropriate values of these are found to be critical for numerical stability of the solution. As well, due to the large difference in stiffness values between the heavy tow cable and buoyant ropes, special attention is given to obtaining the initial tangent stiffness matrix of the cable-and-rope structure. The FE dynamic equations of motion are solved implicitly in the time domain using a combination of full and modified Newton-Raphson iteration.

Simulations of contact initiation between the rope and iceberg for single-loop and net configurations are presented, as well as slipping during particular single-loop tows. Current challenges and opportunities for further development are discussed, including improving computational speed, implementing iceberg motion, adding wind and wave forces, and validating rope-ice friction characteristics through small-scale iceberg towing response in a laboratory.