bluuebunny/crossref_metadata_2025_split huggingface dataset:
Bragg Resonance of Surface Gravity Waves by Surface-Piercing Vertical Multi-Plate Breakwaters
Authors: Chang-Zhe Chen , Wu Jing-Ping , Pan Jun , Zou Zao-Jian 
Published: September 2023

Abstract
The interaction between surface gravity waves and surface-piercing vertical multi-plate breakwaters in finite water depth is investigated under the assumption of potential flow. The time-domain desingularized boundary integral equation method (DBIEM) is adopted to solve the boundary value problem. A decomposition method based on the superposition principle is used to obtain reflected waves. The effect of the vertical plates as a floating breakwater by making full use of Bragg resonance is analyzed. Firstly, the waveforms calculated without breakwaters are compared with the second-order Stokes regular waves to obtain the appropriate desingularization distance. Then, the interaction of surface gravity waves with the breakwaters of single plate, double and triple plates are analyzed. The transmission and reflection coefficients of the breakwater of single plate are verified with the analytical solutions in the literature. The transmission and reflection coefficients of the breakwaters of double and triple plates are verified with the experimental results. Finally, the transmission and reflection coefficients of surface-piercing vertical multi-plate breakwaters with different plate numbers and drafts are calculated. The occurring condition of Bragg resonance and its values affected by the plate number and the draft are analyzed. The present results have reference values for the optimal design of vertical plates as a floating breakwater for offshore and coastal engineering applications by fully using Bragg resonance.
Estimation for Efficiency of Offshore Installation Process of Floating Offshore Wind Turbines in Japan
Authors: Hasumi Tomohiro , Yokoi Takeshi , Haneda Ken , Chujo Toshiki , Fujiwara Toshifumi 
Published: September 2023

Abstract
In order to estimate the construction cost of floating offshore wind turbines (FOWTs) more precisely than before, it is necessary to calculate the installation time of FOWTs more precisely. Therefore, we proposed a model to estimate the installation time of FOWTs by dividing the offshore construction into major processes and quantitatively evaluating the efficiency of each installation process. On the basis of the Cost Breakdown Structure (CBS), the total offshore installation time can be formulated as the sum of the installation time of the following five processes: (1) pre-anchoring, (2) verification of anchor ultimate holding capacity, (3) towing, (4) mooring, and (5) other operational processes. This study introduces “installation time per mooring line” as a benchmark for measuring efficiency. First, the model proposed in this paper is applied to an FOWT demonstration project in Japan and the efficiency of the installation processes is analyzed. It is found that the installation time per mooring line for (2) verification of anchor ultimate holding capacity and (4) mooring were reduced by 69% and 95%, respectively, from the initial time. The proposed model is also applied to a large wind farm and the authors conduct a sensitivity analysis. It is concluded that the installation time for (1) pre-anchoring is the most strongly affected by the number of mooring lines per FOWTs. The installation time for (1) pre-anchoring was 1.6 times longer than that of (2) verification of anchor ultimate holding capacity and eight times longer than that of (4) mooring. This study revealed that (1)pre-anchoring and (2) verification of anchor ultimate holding capacity are expected to have a large impact on cost reduction and improve efficiency.
Linearized Model for Subsea Installation Based on Natural KC Number
Authors: Fernandes Antonio C. , Batista Soares Rodrigo , Martins de Andrade Emerson , Sena Sales Junior Joel 
Published: September 2023

Abstract
The behaviour of subsea equipment has been widely studied by companies to minimise risks during subsea installation, which bring huge costs on the operation. The prediction of equipment motions typically is accomplished utilizing either commercial software or recommended practices from Classification Societies to comply with the minimum requirements on launching operations. This paper analyzes subsea installation in time and frequency domains using experimental, numerical and analytical approaches. Experiments have been carried out at Instituto de Pesquisas Tecnológicas (IPT) to investigate the dependency of drag andadded mass coefficients on Keulegan-Carpenter number and at Laboratory of Waves and Currents (LOC-COPPE/UFRJ) to study equipment and cable responses on the installation. A numerical model is made in OrcaFlex® for determining the transmissibility of displacement and force in function of frequency ratio, and the time series of manifold responses. Linearized models from DNV [1] and the so-called natural KC (proposed in the present paper) are taken in the investigation and compared to previous methodologies. The natural KC approach arises as an innovative way of investigating subsea equipment as the literature only provides parametric analysis considering an arbitrary KC value (i.e., Pestana et al. [3]). The analyses notice a good agreement among experiments, OrcaFlex® model and natural KC model whereas the curves found by DNV method usually overpredict the response of subsea equipment specially around resonance region.
Uncertainty Analysis of the Safety Operating Envelope of a Subsea Shuttle Tanker
Authors: Yousef Hassan Hasan , Ma Yucong , Xing Yihan , Xu Xiaosen 
Published: September 2023

Abstract
The subsea shuttle tanker (SST) was proposed as a cost-effective alternative to pipelines and shuttle ships for transporting liquid CO2 from offshore/land facilities to marginal subsea wells for injection. When evaluating the safety of such a submarine, it is critical to study its survivability in the presence of serious failures. The safety operating envelope (SOE) is a depth-velocity graph that encloses the safe-to-operate region based on different malfunctions scenarios, including jam-to-rise, jam-to-dive, and partial flooding. The SOE typically considers only deterministic worst-case currents in its calculations. This may be over-conservative for a vessel like the SST that needs to maximise its payload by minimising structural and machinery weight. Motivated by this, this paper will extend the previous work on the SOE by determining the uncertainty band in the presence of a stochastic current for the jam-to-rise case. A 2D manoeuvring model that includes hydroplanes, propeller and environmental loads effect is used. Free-running simulations are carried out considering two current load cases of 0.5 and 1 m/s with 5 % and 10 % standard variations. Gumbel distribution is used to determine the extreme recovery depth values and, subsequently, the corresponding uncertainty band for each case. The simulations considered two current directions and load cases of 0.5 and 1 m/s with 5 % and 10 % standard variation that yielded results showing varying increase in the recovery depth from 1.6% to 20% compared to the deterministic case. Preliminary results show that the uncertainties in the SOE can be large under stochastic current loads.
CFD Simulations of the DeepCwind Semi-Submersible in Bichromatic Waves and Validation With the Experiments From OC6 Phase 1B
Authors: Zhang Yali , Santo Harrif 
Published: September 2023

Abstract
Second-order potential flow models were found to under-predict the low-frequency surge and pitch responses of the floating DeepCwind semi-submersible platform as concluded from the OC6 Phase 1A study. Subsequently, a component level approach was undertaken to examine the hydrodynamic loads on the individual parts of the semi-submersible in isolation using bichromatic wave in the OC6 Phase 1B study. Therefore, a direct assessment of the difference frequency wave loading could be obtained which further enabled numerical validation using the experimental dataset arising from the OC6 Phase 1B study. In this paper, a numerical approach based on Computational Fluid Dynamics (CFD) using StarCCM+ was used to simulate some of the OC6 Phase 1B experimental test cases. Fixed platform scenarios were simulated and compared with the experimental results in terms of surge force and pitch moment. Relatively good agreement could be achieved using the numerical model. Sensitivity studies such as the choice of laminar or turbulence flow model and domain length were carried out to establish robustness in the simulated results. The CFD results established the importance of considering up to 3rd order wave force/moment and viscous effects. The same semi-submersible platform was then made to be freely-floating with soft mooring, and additional bichromatic cases were simulated to analyse and compare the resultant low-frequency and wave-induced motion responses. Significant responses at the difference frequency could be excited due to non-linear interactions of the two wave frequency components.
Parameter Estimation for 1-eq./2-eq Turbulence Models by EnKF Data Assimilation: Twin Experiment With 2D Flat Plate
Authors: Sakamoto Nobuaki 
Published: September 2023

Abstract
Representative turbulence models typically used for viscous flow computation in the field of ship hydrodynamics include Spalart-Allmaras (SA), k-omega, explicit algebraic stress and detached eddy simulation. In these models, several model constants are introduced, yet they have rarely been changed from nominal values. Tuning of these constants to adapt ship flow simulations will be feasible using data assimilation technique together with available measurement data. As a very 1st step for such development, a data assimilation code using an Ensemble Kalman Filter (EnKF) is implemented and integrated to an in-house viscous flow solver for ship hydrodynamics developed at the National Maritime Research Institute. Twin experiments of parameter estimation for SA and k-omega shear stress transport (SST) turbulence models are carried out aiming to confirm fundamental functionality of the developed framework for data assimilation. A simple flow field around a two dimensional flat plate is of the interest. The assimilation results show different trends. When the SA model is adopted and 5 constants are assimilated, all the constants statistically converge to the nominal values within 80 filtering steps using 40 ensemble members. When the k-omega SST model is adopted and 1 to 4 constants are assimilated, two constants (one parameter associated with viscous diffusion term of turbulent kinetic energy, and the other parameter associated with the cross-diffusion term of specific frequency) show difficulty in statistical convergence even after 500 times of filtering with 40 ensemble members.
Numerical Analysis of Flexible Tube Wave Energy Convertor Using CFD-FEA Method
Authors: Huang Yang , Xiao Qing , Idarraga Guillermo , Yang Liu , Dai Saishuai , Abad Farhad , Brennan Feargal , Lotfian Saeid 
Published: September 2023

Abstract
To better understand the performance of flexible tube wave energy converters (WECs) in ocean waves, a coupled numerical analysis tool based on computational fluid dynamics and a finite element method is employed to perform numerical simulations for the well-known Anaconda WEC under given different regular wave conditions. The nonlinear behaviour of Natural Rubber is considered by using YEOH hyper-elastic model. Fluid-structure interaction responses of the Anaconda WEC are compared considering the impact of incident wave speed on the performance of the device. The free surface around the WEC, internal pressure and velocity in the flexible tube, structure deformation and stress distribution are fully explored. The results show that the proposed numerical analysis tool in this work is able to predict the complex fluid-structure interactions of flexible tube WEC in waves, including wave nonlinearity and inhomogeneous distribution of stress at cross-section. The typical resonant responses are also captured when the incident wave speed matches the bulge wave speed. The internal pressure amplitude, capture width, structural deformation and hoop stress all increase at resonance. Moreover, the deformed shape of the flexible tube is found to depend on the ratio of wavelength to tube length.
Determination of Mooring Load Levels on a Cage Designed for Exposed Aquaculture in Chile
Authors: Cifuentes Cristian , Tampier Gonzalo , Echevarría Alonso , Hurtado Carlos Felipe 
Published: September 2023

Abstract
The determination of mooring tension on a prototype cage for salmon production on exposed areas in southern Chile is obtained using experiments at laboratory scale, numerical simulations as well as on site measurements using a submersible load cell. The 40m diameter prototype cage used in this study is constructed out of HDPE pipe and has a ballast tank attached to the bottom to control the operational depth in case of high waves. The cage uses a copper nickel alloy net cancelling the need for a predatory net as in traditional systems. First, drag coefficients for the net were obtained at the Wave/Towing tank at Universidad Austral de Chile (UACh), plus the characterization of dynamic response and deformation of two cage models. These results were used as input for numerical simulations of the cage using the commercial software AquaSim. The last stage of the campaign was the measurement of tension on the prototype cage, using a load cell on a mooring line along with measurements of tides, wind, waves, and currents. The results are the base for a more complex analysis, since the net, due to its geometry, stiffness and wet weight, has a particular behavior when compared to traditional fiber-based nets.
Scaling Characteristics of the Unified Similarity Criterion for Geometrically Distorted Scale Models
Authors: Wang Yao , Wang Qinghu , Wang Deyu 
Published: September 2023

Abstract
Model test is the most common and important method to evaluate the performance of structures. For large and complex structures like hull structures, test objects need to be down-scaled and even simplified. The simplified and small-scale model is called the geometrically distorted scale model. A unified similarity criterion and a design method is proposed for the distorted scale model for ultimate strength model tests recently, which states that if the plate and stiffener slenderness of the scale model and the original model keep a certain relation, the similarity of the ultimate strength and collapse behavior of the two models are guaranteed. When designing the scale model, the designers need to decrease the count of stiffeners on every plate and increase their size to meet the criterion. Nevertheless, only a few examples are provided to prove the correctness of the criterion. The characteristics are still not clear, which means that the similarity of the scale model is unclear unless a numerical analysis is performed. In this paper, two typical hull structures, the stiffened plate, and the box girder are taken as examples to investigate the scaling characteristics. 23 scale models with different combinations of 8 length scale ratios (1, 1/2, 1/3, 1/4, 1/5, 1/6, 1/8, 1/10) and 4 thickness scale ratios (1, 2/3, 1/2, 1/3, 1/4) are designed and analyzed for both structures respectively. From the results, the influence of scale ratios is revealed. Several suggestions are proposed to guide the design of scale models to reduce the cost of trial and error.
Wakes of Surface-Piercing Cylinders
Authors: Potts Douglas , Leong Zhi , Binns Jonathan , Marcollo Hayden , Skvortsov Alex 
Published: September 2023

Abstract
The hydrodynamics of surface-piercing cylinders differ from fully submerged cylinders due to the generation of surface wakes and under increasing flow velocities the formation of a ventilated pocket in the lee of the cylinder, both of which grow with increasing velocity, with concomitant effects on the hydrodynamic loading. Laboratory testing of surface-piercing cylinders to date has predominantly been confined to characterising the wakes of a rigid cylinder cantilevered down into the water from a towing tank carriage, which under certain test conditions will exhibit significant Vortex-Induced-Vibration (VIV).
The wake characteristics of cylindrical structures such as those protruding through the free surface from a submerged platform do alter substantially depending on the structure, geometrical properties, and operating parameters. The relative length of submergence, or immersed aspect ratio (AR) and end conditions of the cylinder do also impact the wake formation. The wake characteristics can be described by two major regions: above and below the waterline. Where the above waterline wakes are derivatives of the bow wave run-up on the leading face of the cylinder, and the below waterline wakes are derivatives of the ventilation, which is the entrapment of air of the rear face of the cylinder.
This paper presents an experimental programme in a towing tank to characterise the wake of cylindrical structures of different diameters, submergence, and forward speeds. Conventional experiments have the model attached from above the surface, however, this method is not representative of some real-world applications such as structures that are bottom mounted. [To the best of our knowledge] The authors developed the novel design of a bottom mount test platform, where the model is cantilevered from a single connection pointed up through the water column. The experiments collected a range of results including the forces, motions and wakes of the models where this paper will focus on presenting and defining the different wakes and insights into these phenomena.
Creating a Realistic Piloted Simulation of Helicopter Recovery to an Offshore Platform
Authors: Watson Neale A. , Prior Mark , Owen Ieuan , White Mark D. 
Published: September 2023

Abstract
This paper describes the development of a realistic piloted simulation of helicopter recovery to an offshore platform, which has been used to assess the effect of turbulent air flow on a helicopter landing on a full-scale offshore platform. Time-accurate CFD was used to create the unsteady turbulent airwake generated by an offshore platform. The computed unsteady airwake velocities were integrated with a flight dynamics model representative of a Sikorsky SH-60B Seahawk helicopter in a six-degree-of-freedom motion flight simulator. A simulated flight trial was conducted in which a test pilot was instructed to perform a series of helideck landings to the platform for wind speeds of 20 to 50 kt and to give workload ratings for the difficulty of the task. The workload ratings, along with the corresponding pilot control activity and helicopter positional accuracy, are discussed in relation to the effect of the airwake on the helicopter and pilot workload. The results show that as the freestream wind speed increased, the vertical velocity fluctuations and pilot workload also increased. The paper demonstrates the potential for realistic piloted flight simulation to be used to support helicopter operations to offshore platforms.
Dynamic Response Analysis of an End-Anchored Floating Bridge With a Damaged Pontoon Under Repair Operation
Authors: Cui Minghao , Cheng Zhengshun , Chen Peng , Moan Torgeir 
Published: September 2023

Abstract
During the lifetime of floating bridges, the structural components are exposed to ship collision hazards. In the situation where a pontoon is damaged from a collision accident, an in-site repair operation is needed. If a significant damage has occurred, a floating drydock may be used to ensure that the pontoon can be repaired in a dry atmosphere and to compensate for the lost buoyancy. As the repair might take months, a main issue is then whether the bridge can be open for road traffic in the damaged condition and especially during the repair. The aim of this study is to investigate the feasibility of using a drydock for the repair. In this study, a comparative dynamic analysis of an intact end-anchored floating bridge and the bridge with a damaged pontoon under repair operation, is carried out under various combinations of environmental loads. Hydrodynamic analysis of the drydock indicates that the added mass and the wave excitation force can be multiple times of the original pontoon. Eigenvalue analysis is conducted and pendulum modes of oscillation are found with an eigen-period of around 15s. The dynamic responses are analyzed by conducting a series of fully-coupled time-domain simulations under various combinations of environmental conditions. It is found that the standard deviation of the moment about the girder weak axis increases significantly at the damaged pontoon axis due to the excitation of low-frequency resonant response. Swell wave loads can cause significant dynamic amplification with relatively small wave height. Actions to reduce the risk of a possible road traffic disruption in this connection are briefly discussed.
The Safety Assessment of Ship-Bridge Collision Based on a Simplified Dynamic Model
Authors: Zhang Wenzhe , Pan Jin , Li Na , Xu Mingcai 
Published: September 2023

Abstract
With the continued development of transportation, the risk of ship-bridge collision has been rising persistently. Meanwhile, a great mass of old bridges which were built decades ago can’t meet the anti-collision requirement nowadays. Many countries and regions noticed that problem and have been taking various measures to protect those bridges and provide a better navigable environment. For tabling reasonable protective proposals for each bridge, the first step is assessing the safety based on the design, current representative vessels, and so on. Hence, it is necessary to propose a simple, fast, and accurate method that can be widely used in practical engineering. Kinds of simplified formulae, e.g. AASHTO and IABSE, are used to calculate the ship collision force, however, the results are static forces that have errors. Consequently, the PRC Ministry of Transport (MOT) published the Specifications for Collision Design of Highway Bridges in 2020 which calculates the collision force as a simplified dynamic history. This paper compares the simplified dynamic histories with the numerical results obtained from LS-DYNA by using several ship models in different cases. Subsequently, a method of safety assessment for bridges against ship collisions based on Midas Civil is designed. The applicability and accuracy of this new specification in force calculations and safety assessments are discussed based on acceptable errors. The comparison indicates that for 500∼10000DWT ships, the simplified formula can calculate the momentum precisely with a certain error on the peak force and total time though. To expand the scope of the application, the specification still has relatively large errors and limitations in some cases.