Numerical computation of motions and structural loads for large containership using 3D Rankine panel method

In this paper, we present the results of our numerical seakeeping analyses of a 6750-TEU containership, which were subjected to the benchmark test of the 2 nd ITTC–ISSC Joint Workshop held in 2014. We performed the seakeeping analyses using three different methods based on a 3D Rankine panel method, including 1) a rigid-body solver, 2) a flexible-body solver using a beam model, and 3) a flexible-body solver using the eigenvectors of a 3D Finite Element Model(FEM). The flexible-body solvers adopt a fully coupled approach between the fluid and structure. We consider the nonlinear Froude–Krylov and restoring forces using a weakly nonlinear approach. In addition, we calculate the slamming loads on the bow flare and stern using a 2D generalized Wagner model. We compare the numerical and experimental results in terms of the linear response, the time series of the nonlinear response, and the longitudinal distribution of the sagging and hogging moments. The flexible-body solvers show good agreement with the experimental model with respect to both the linear and nonlinear results, including the high-frequency oscillations due to springing and whipping vibrations. The rigid-body solver gives similar results except for the springing and whipping.     

Dynamic coupled analysis of the floating platform using the asynchronous coupling algorithm

This paper discusses the numerical modeling of the dynamic coupled analysis of the floating platform and mooring/risers using the asynchronous coupling algorithm with the purpose to improve the computational efficiency when multiple lines are connected to the platform. The numerical model of the platform motion simulation in wave is presented. Additionally, how the asynchronous coupling algorithm is implemented during the dynamic coupling analysis is introduced. Through a comparison of the numerical results of our developed model with commercial software for a SPAR platform, the developed numerical model is checked and validated.     

Three-dimensional fluid-structure interaction case study on cubical fluid cavity with flexible bottom

In this paper, we report our study on a numerical fluid-structure interaction problem originally presented by Mok et al.(2001) in two dimensions and later studied in three dimensions by Valdés Vazquez(2007), Lombardi(2012), and Trimarchi(2012). We focus on a 3D test case in which we evaluated the sensitivity of several input parameters on the fluid and structural results. In particular, this analysis provides a starting point from which we can look deeper into specific aspects of these simulations and analyze more realistic cases, e.g., in sails design. In this study, using the commercial software ADINATM, we addressed a well-known unsteadiness problem comprising a square box representing the fluid domain with a flexible bottom modeled with structural shell elements. We compared data from previously published work whose authors used the same numerical approach, i.e., a partitioned approach coupling a finite volume solver(for the fluid domain) and a finite element solver(for the solid domain). Specifically, we established several benchmarks and made comparisons with respect to fluid and solid meshes, structural element types, and structural damping, as well as solution algorithms. Moreover, we compared our method with a monolithic finite element solution method. Our comparisons of new and old results provide an outline of best practices for such simulations.     

采用基于雷诺平均的N-S方程和势流方法进行散货船阻力和运动的预报研究（英文）

Resistance prediction of ships using computational fluid dynamics has gained popularity over the years because of its high accuracy and low cost. This paper conducts numerical estimations of the ship resistance and motion of a Japan bulk carrier model using SHIP_Motion, a Reynolds-averaged Navier–Stokes(RaNS)-based solver, and HydroSTAR, a commercial potential flow(PF)-based solver. The RaNS solver uses an overset-structured mesh and discretizes the flow field using the finite volume method, while the PF-based solver applies the three-dimensional panel method. In the calm water test, the total drag coefficient,sinkage, and trim were predicted using the RaNS solver following mesh dependency analysis, and the results were compared with the available experimental data. Next, calm water resistance was investigated for a range of Froude numbers. The added resistance in short-wave cases was simulated using both Ra NS and PF solvers, and the results were compared. The PF solver showed better agreement with the RaNS solver for predicting motion responses than for predicting added resistance. While the added resistance results could not be directly validated because of the absence of experimental data, considering the previous accuracy of the RaNS solver in added resistance prediction and general added resistance profile of similar hull forms(bulk carriers), the prediction results could be concluded to be reliable.     

开源环境下的高精确度船舶水动力学仿真(英文)

The numerical simulation of wake and free-surface flow around ships is a complex topic that involves multiple tasks: the generation of an optimal computational grid and the development of numerical algorithms capable to predict the flow field around a hull. In this paper, a numerical framework is developed aimed at high-resolution CFD simulations of turbulent, free-surface flows around ship hulls. The framework consists in the concatenation of "tools", partly available in the open-source finite volume library Open FOAM. A novel, flexible mesh-generation algorithm is presented, capable of producing high-quality computational grids for free-surface ship hydrodynamics. The numerical frame work is used to solve some benchmark problems, providing results that are in excellent agreement with the experimental measures.     

海床对海洋管道涡旋脱落和受力系数的影响（英文）

The effect of rigid bed proximity on flow parameters and hydrodynamic loads in offshore pipelines exposed to turbulent flow is investigated numerically. The Galerkin finite volume method is employed to solve the unsteady incompressible 2 D Navier–Stokes equations. The large eddy simulation turbulence model is solved using the artificial compressibility method and dual time-stepping approach. The proposed algorithm is developed for a wide range of turbulent flows with Reynolds numbers of 9500 to 1.5×104. Evaluation of the developed numerical model shows that the proposed technique is capable of properly predicting hydrodynamic forces and simulating the flow pattern. The obtained results show that the lift and drag coefficients are strongly affected by the gap ratio. The mean drag coefficient slightly increases as the gap ratio increases, although the mean lift coefficient rapidly decreases. The vortex shedding suppression happen at the gap ratio of less than 0.2.     

High Resolution Ship Hydrodynamics Simulations in Open Source Environment

The numerical simulation of wake and flee-surface flow around ships is a complex topic that involves multiple tasks： the generation of an optimal computational grid and the development of numerical algorithms capable to predict the flow field around a hull. In this paper, a numerical framework is developed aimed at high-resolution CFD simulations of turbulent, free-surface flows around ship hulls. The framework consists in the concatenation of ＂tools＂, partly available in the open-source finite volume library OpenFOAM. A novel, flexible mesh-generation algorithm is presented, capable of producing high-quality computational grids for free-surface ship hydrodynamics. The numerical frame work is used to solve some benchmark problems, providing results that are in excellent agreement with the experimental measures.     

二维冲箱式造波机的间隙和形状效应数值研究（英文）

The installation of plunger-type wave makers in experimental tanks will generally include a gap between the back of the wedge and the wall of the tank. In this study, we analyze the influence of this gap on the wave making performance of the plunger using two-dimensional(2 D) CFD calculations for a range of nearly linear wave conditions and compare the results with both experimental measurements and linear potential flow theory. Three wedge-shaped profiles, all with the same submerged volume, are considered. Moreover, the generated waves are compared with the predictions of linear potential flow theory. The calculations are made using the commercial ANSYS FLUENT finite-volume code with dynamic meshes to solve the Navier–Stokes equations and the volume of fluid scheme to capture the air–water interface. Furthermore, the linear potential flow solution of Wu(J Hydraul Res 26:481–493, 1988) is extended to consider an arbitrary profile and serve as a reference solution. The amplitude ratios of the generated waves predicted by the CFD calculations compare well with the predictions of linear potential flow theory for a simple wedge, indicating that viscous effects do not influence this ratio for small-amplitude motions in 2 D. By contrast,significant higher harmonic components are produced by larger amplitude motions. Also, the simple wedge is found to produce the smallest spurious higher harmonic content in the far-field wave.     

Mathematical modelling of response amplitude operator for roll motion of a floating body: Analysis in frequency domain with numerical validation

This paper investigates mathematical modelling of response amplitude operator （RAO） or transfer function using the frequency-based analysis for uncoupled roll motion of a floating body under the influence of small amplitude regular waves. The hydrodynamic coefficients are computed using strip theory formulation by integrating over the length of the floating body. Considering sinusoidal wave with frequency （ω ） varying between 0.3 rad/s and 1.2 rad/s acts on beam to the floating body for zero forward speed, analytical expressions of RAO in frequency domain is obtained. Using the normalization procedure and frequency based analysis, group based classifications are obtained and accordingly governing equations are formulated for each case. After applying the fourth order Runge-Kutta method numerical solutions are obtained and relative importance of the hydrodynamic coefficients is analyzed. To illustrate the roll amplitude effects numerical experiments have been carried out for a Panamax container ship under the action of sinusoidal wave with a fixed wave height. The effect of viscous damping on RAO is evaluated and the model is validated using convergence, consistency and stability analysis. This modelling approach could be useful to model floating body dynamics for higher degrees of freedom and to validate the result.     

浮体横摇运动传递函数数学建模的频域分析研究及相关数值验证(英文)

This paper investigates mathematical modelling of response amplitude operator(RAO) or transfer function using the frequency-based analysis for uncoupled roll motion of a floating body under the influence of small amplitude regular waves. The hydrodynamic coefficients are computed using strip theory formulation by integrating over the length of the floating body. Considering sinusoidal wave with frequency( ω) varying between 0.3 rad/s and 1.2 rad/s acts on beam to the floating body for zero forward speed, analytical expressions of RAO in frequency domain is obtained. Using the normalization procedure and frequency based analysis, group based classifications are obtained and accordingly governing equations are formulated for each case. After applying the fourth order Runge-Kutta method numerical solutions are obtained and relative importance of the hydrodynamic coefficients is analyzed. To illustrate the roll amplitude effects numerical experiments have been carried out for a Panamax container ship under the action of sinusoidal wave with a fixed wave height. The effect of viscous damping on RAO is evaluated and the model is validated using convergence, consistency and stability analysis. This modelling approach could be useful to model floating body dynamics for higher degrees of freedom and to validate the result.     

迎浪规则波中波浪增阻和船体垂向运动的数值预报(英文)

The numerical prediction of added resistance and vertical ship motions of one ITTC (International Towing Tank Conference) S-175 containership in regular head waves by our own in-house unsteady RANS solver naoe-FOAM-SL JTU is presented in this paper. The development of the solver naoe-FOAM-SJTU is based on the open source CFD tool, OpenFOAM. Numerical analysis is focused on the added resistance and vertical ship motions (heave and pitch motions) with four very different wavelengths (0.8Lpp≤λ≤1.5Lpp) in regular head waves. Once the wavelength is near the length of the ship model, the responses of the resistance and ship motions become strongly influenced by nonlinear factors, as a result difficulties within simulations occur. In the paper, a comparison of the experimental results and the nonlinear strip theory was reviewed and based on the findings, the RANS simulations by the solver naoe-FOAM-SJTU were considered competent with the prediction of added resistance and vertical ship motions in a wide range of wave lengths.     

纵向弯矩下材料随机特性对复合材料船体可靠性的影响

The effects of stochastic characteristics of materials on the reliability of ship hulls made of composite materials under longitudinal moment were extensively studied using reliability and sensitivity calculations of a composite ship hull which was sagging.The reliability indices and failure probabilities of the ship in three kinds of failure modes (buckling,material failure,and ultimate collapse) were calculated by the surface response method and JC method.The importance factors of random variables in stochastic models,such as the model errors in predicting the ultimate longitudinal strength of ship and the longitudinal bending moment that the ship withstands,as well as the stochastic characteristics of materials in the models used,were calculated.Then,the effects of these random variables,including the stochastic characteristics of materials on the reliability index and the failure probability of ships which were sagging,were discussed with their importance factors.The results show that the effects of stochastic characteristics of materials on the reliability of ship hulls made of composite materials should be considered during the reliability assessment of composite ships.Finally,some conclusions and recommendations were given for high-speed ship design and safety assessment.     

Interaction of two three-dimensional explosion bubbles

The interaction of two underwater explosion bubbles was mathematically analyzed in this paper. Based on the assumption of potential flow, high-order curved elements were used to discretize the boundary integral equation and solve it. Assuming that gas inside the bubble follows the isentropic rule, the Euler-Lagrange method was used to trace the evolution of the bubble, and when calculating the singular integral, the singularity of the double-layer singular integral was eliminated by reconstructing a principal-value integral of double-layer potential so that a more precise result could be obtained. Elastic mesh technique (EMT) was also used when tracing the evolution of the bubble interface, and numerical smoothing wasn't needed. A comparison of calculations using this three-dimensional model with results of the Reyleigh-Plesset bubble model shows that the three-dimensional model and calculation method in this paper is practical. This three-dimensional model was applied to simulate the interaction of two bubbles under the action of gravity, and the dynamic characteristics of two bubbles near the surface was also analyzed. Bubbles influenced by surface effects and gravity present severe non-linearity. This paper provides a reference for research into the dynamics of multi-bubbles.     

双隔板矩形液舱内抑制晃荡的优化研究（英文）

A dual-baffled rectangular tank with different configurations is proposed to reduce the sloshing effect, and design optimization is conducted through numerical simulations with open-source software, namely Open FOAM, based on the computational fluid dynamic model. A series of physical experiments in the dual-baffled rectangular tank is performed for model validation and design optimization with the measured water surface elevation distributions along the tank. The optimization uses the calculate...     

驱逐舰烟气排放过程数值仿真及同模型试验比较研究(英文)

The exhaust smoke dispersion for a generic frigate is investigated numerically through the numerical solution of the governing fluid flow, energy, species and turbulence equations. The main objective of this work is to obtain the effects of the yaw angle, velocity ratio and buoyancy on the dispersion of the exhaust smoke. The numerical method is based on the fully conserved control-volume representation of the fully elliptic Navier-Stokes equations. Turbulence is modeled using a two-equation(k-ε) model. The flow visualization tests using a 1/100 scale model of the frigate in the wind tunnel were also carried out to determine the exhaust plume path and to validate the computational results. The results show that down wash phenomena occurs for the yaw angles between ψ =10° and 20°. The results with different exhaust gas temperatures show that the buoyancy effect increases with the increasing of the exhaust gas temperature. However, its effect on the plume rise is less significant in comparison with its momentum. A good agreement between the predictions and experiment results is obtained.     

液舱晃荡与浮体非线性耦合运动分析(英文)

Nonlinear interactions among incident wave, tank-sloshing and floating body coupling motion are investigated. The fully nonlinear sloshing and body-surface nonlinear free surface hydrodynamics is simulated using a Non-Uniform Rational B-Spline (NURBS) higher-order panel method in time domain based on the potential theory. A robust and stable improved iterative procedure (Yan and Ma, 2007) for floating bodies is used for calculating the time derivative of velocity potential and floating body motion. An energy dissipation condition based on linear theory adopted by Huang (2011) is developed to consider flow viscosity effects of sloshing flow in nonlinear model. A two-dimensional tank model test was performed to identify its validity. The present nonlinear coupling sway motion results are subsequently compared with the corresponding Rognebakke and Faltinsen (2003)’s experimental results, showing fair agreement. Thus, the numerical approach presented in this paper is expected to be very efficient and realistic in evaluating the coupling effects of nonlinear sloshing and body motion.     

硬帆辅助推进散货船的稳定性和动力性能综合分析（英文）

The wind-assisted propulsion system is becoming one of the most popular and efficient ways to reduce both fuel consumption and carbon dioxide emission from the ships.In this study,several analyses have been carried out on a model of bulk carrier fitted with five rigid sails with a 180° rotating mechanism for maximum usage of wind power and a telescopic reefing mechanism for folding it during berthing.The stability of the ship has been verified through the calculations of initial stability,static stability,and dynamic stability through the fulfillment of the weather criterion using MAXSURF software.The structural analysis of the sail was carried out in ANSYS static structural module.Several flow simulations were carried out in ANSYS fluent module to predict the thrusts produced by the sails at different apparent wind angles,which would in turn reduce the thrust required from the propeller.In this way,the brake horse powers required for different sail arrangements were analyzed to find out a guideline for this wind propulsion system to generate better powering performances.To consider drift and yaw effect on propulsion system,an MMG mathematical model-based simulation was carried out for different drift angles of motion of the ship considering hard sail-based wind loads.Through these analyses,it has been found out that the hard sail-based wind-assisted propulsion system in some cases have produced a reduction of more than 30% brake power in straight ahead motion and around 20% reduction in case of drifting ships compared to the model having no sails.     

机翼在接近地面的起飞模拟数学模型（英文）

Aircraft flying close to the ground benefit from enhanced efficiency owing to decreased induced drag and increased lift. In this study, a mathematical model is developed to simulate the takeoff of a wing near the ground using an Iterative Boundary Element Method(IBEM) and the finite difference scheme. Two stand-alone sub-codes and a mother code, which enables communication between the sub-codes, are developed to solve for the self-excitation of the Wing-In-Ground(WIG) effect. The aerodynamic force exerted on the wing is calculated by the first sub-code using the IBEM, and the vertical displacement of the wing is calculated by the second sub-code using the finite difference scheme. The mother code commands the two sub-codes and can solve for the aerodynamics of the wing and operating height within seconds. The developed code system is used to solve for the force, velocity, and displacement of an NACA6409 wing at a 4° Angle of Attack(AoA) which has various numerical and experimental studies in the literature. The effects of thickness and AoA are then investigated and conclusions were drawn with respect to generated results. The proposed model provides a practical method for understanding the flight dynamics and it is specifically beneficial at the pre-design stages of a WIG effect craft.     

Numerical modeling of exhaust smoke dispersion for a generic frigate and comparisons with experiments

The exhaust smoke dispersion for a generic frigate is investigated numerically through the numerical solution of the governing fluid flow, energy, species and turbulence equations. The main objective of this work is to obtain the effects of the yaw angle velocity ratio and buoyancy on the dispersion of the exhaust smoke The numerical method is based on the fully conserved control-volume representation of the fully elliptic Navier-Stokes equations. Turbulence is modeled using a two-equation （k-ε） model The flow visualization tests using a 1/100 scale model of the frigate in the wind tunnel were also carried out to determine the exhaust plume path and to validatc the computational results. The results show that down wash phenomena occurs for the yaw angles between ψ=10° and 20°. The results with different exhaust gas temperatures show that the buoyancy effect increases with the increasing of the exhaust gas temperature. However, its effect on the plume rise is less significant in comparison with its momentum. A good agreement between the predictions and experiment results is obtained.