Application of CFD and FEA Coupling to Predict Structural Dynamic Responses of A Trimaran in Uni-and Bi-Directional Waves

To predict the wave loads of a flexible trimaran in different wave fields,a one-way interaction numerical simulation method is proposed by integrating the fluid solver(Star-CCM+)and structural solver(Abaqus).Differing from the existing coupled CFD-FEA method for monohull ships in head waves,the presented method equates the mass and stiffness of the whole ship to the hull shell so that any transverse and longitudinal section stress of the hull in oblique waves can be obtained.Firstly,verification study and sensitivity analysis are carried out by comparing the trimaran motions using different mesh sizes and time step schemes.Discussion on the wave elevation of uni-and bi-directional waves is also carried out.Then a comprehensive analysis on the structural responses of the trimaran in different uni-directional regular wave and bi-directional cross sea conditions is carried out,respectively.Finally,the differences in structural response characteristics of trimaran in different wave fields are studied.The results show that the present method can reduce the computational burden of the two-way fluid-structure interaction simulations.

侧体尺度对小水线面三体船纵向运动影响研究

小水线面三体船主、侧体尺度相差较大,因此,理论上侧体尺度具有无数种方案。目前,多数学者侧重于对侧体位置的研究,而对小水线面三体船侧体尺度对其水动力性能影响的研究还不够广泛。采用基于势流理论的AQWA软件进行数值模拟计算。首先,为确保计算过程中参数设置的准确性,对AQWA软件计算船舶耐波性的可靠性进行验证;然后,研究系列傅汝德数Fr下侧体尺度变化对小水线面三体船的耐波性响应。结果显示,在波长船长比变化时,垂荡纵摇RAO随侧体尺度改变产生了非单调的变化。不同航速下,垂荡和纵摇性能最优的侧体尺度不一致。综合所有航速考虑,L_(c)/L为0.3和0.35的侧体方案耐波性能较好。研究结果可为小水线面三体船的设计提供借鉴。

基于Wasim的三体船耐波性能的敏感性分析

针对三体船舶在不同海况下的动力响应影响因素进行敏感性分析,并对三体船的主侧体布局进行优化设计。采用三维时域Rankine源法分析一艘典型三体船在不同分离比和不同侧体纵向位置时的耐波性响应特性。采用水动力分析软件Wasim针对3种航速、5个浪向、2个横向位置及5个纵向位置多次进行升沉、横摇和纵摇运动响应模拟,对不规则海域内的响应振幅算子(RAO)进行敏感性分析。布局分析结果表明,在船舶的耐波性能方面,对于所有的航速、浪向和模态周期下,侧体布局并没有保持一致的最佳位置,在常规迎浪条件下,主侧体横向间距小利于耐波性能;垂荡和纵摇运动性能的优劣主要取决于主侧体的纵向相对位置。

Resistance Analysis of Unsymmetrical Trimaran Model with Outboard Sidehulls Configuration

The application of multi-hull ship or trimaran vessel as a mode of transports in both river and sea environments have grown rapidly in recent years.Trimaran vessels are currently of interest for many new high speed ship projects due to the high levels of hydrodynamic efficiency that can be achieved,compared to the mono-hull and catamaran hull forms.The purpose of this study is to identify the possible effects of using an unsymmetrical trimaran ship model with configuration（S/L） 0.1-0.3 and R/L=0.1-0.2.Unsymmetrical trimaran ship model with main dimensions： L=2000mm,B=200 mm and T=45 mm.Experimental methods（towing tank） were performed in the study using speed variations at Froude number 0.1-0.6.The ship model was pulled by an electric motor whose speed could be varied and adjusted.The ship model resistance was measured precisely by using a load cell transducer.The comparison of ship resistance for each configuration with mono-hull was shown on the graph as a function of the total resistance coefficient and Froude number.The test results found that the effective drag reduction could be achieved up to 17% at Fr=0.35 with configuration S/L=0.1.

Numerical Research on Wave-making Resistance of Trimaran

A 3D rankine panel method was developed for calculating the linear wave-making resistance of a tri-maran with Wigley hulls. In order to calculate the normal vector and derivative of the body surface accurately, non-uniform rational B-spline (NURBS) was adopted to represent body surface and rankine source density. The radiation condition is satisfied using the numerical technology of staggered grids. Numerical results show that the linear wave-making resistance of the trimaran can be calculated effectively using this method.

Grid convergence study in the resistance calculation of a trimaran

As a new type of hull form,trimaran has remarkable excellent performances and has drawn more and more attention.When the viscous CFD technology now available is applied to the research of resistance performance of trimaran,the spatial discretization would usually result in the grid error and uncertainty,and thus the considerable discrepancy between the numerical results and the experimental data.In order to ascertain how much the grid would affect the calculation,the grid convergence should be studied.A mathematical trimaran was chosen as an example,with the commercial code CFX for the simulation,VOF for surface treatment,and the grid study was carried out based on two different turbulence models.It was concluded that carrying out grid study is helpful in estimating the grid error and uncertainty,and indicating the direction of improving the credibility of the numerical calculation, and,in addition to grid errors and uncertainties,the turbulence modeling errors and uncertainties contribute to the simulation errors.

An Experimental Study on the Effect of the Side Hull Symmetry on the Resistance Performance of a Wave‑Piercing Trimaran

This paper presented the results of an experimental investigation into the resistance performance of a wave-piercing trimaran with three alternative side hull forms,including asymmetric inboard,asymmetric outboard,and symmetric at various stagger/separation positions.Model tests were carried out at the National Iranian Marine Laboratory(NIMALA)towing tank using a scale model of a trimaran at the Froude numbers from 0.225 to 0.60.Results showed that by moving the side hulls to the forward of the main hull transom,the total resistance coefficient of trimaran decreased.Findings,furthermore,demonstrated that the symmetry shape of the side hull had the best performance on total resistance among three side hull forms.Results of this study are useful for selecting the side hull configuration from the resistance viewpoint.

Comparative Analysis of the Separation Variation Influence on the Hydrodynamic Performance of a High Speed Trimaran

This paper numerically investigates the influence of separation variation of the outriggers on the hydrodynamic performance of a high speed trimaran （HST） aiming at improving its applicability in diverse realistic disciplines. The present investigation was performed within the framework of the 2-D slender body method （SBM） by calculating the resistance of three symmetric trimaran series moving in a calm free surface of deep water. Each trimaran series comprises of 4681 configurations generated by considering 151 staggers （-50%≤a≤＋ 100%）, and 31 separations （100%≤β≤400%） for 81 Froude numbers （0.20≤Fn≤ 1.0）. In developing the three trimaran series, Wigley-st. AMECRC-09, and NPL-4a models were used separately for both the main and side hulls of each individu;d series models. A computer macro named Tri-PL was created using the Visual Basic for Applications~. Tri-PL~ sequentially interfaced Maxsurfe then Hullspeed to generate the models of the three trimaran series together with their detailed hydrostatic particulars, followed by their resistance components. The numerical results were partially validated against the available published numerical calculations and experimental results, to benchmark the Tri-PL macro and hence to rely on the analysis outcomes. A graph template was creaLed within the framework of SigmaPlot to visualize the significant results of the Tri-PL properlv.

Numerical Prediction of Form Factor and Wave Interference of A Trimaran for Different Outrigger Positions

Trimaran hydrodynamics have been an important research topic in recent years.Trimarans have even been chosen for naval surface combatants.In this case,investigation of a trimaran with different outrigger positions is important and necessary for better hydrodynamic performance.This paper focuses on the numerical investigation of trimaran hydrodynamics.The trimaran model used in this study is a 1/80 scale high-speed displacement frigate-type concept developed by the Center for Innovation in Ship Design(CISD)at Naval Surface Warfare Center,Carderock Division(NSWCCD).The numerical simulations were conducted for different outrigger positions at low and moderate Froude numbers by using commercial CFD software solving URANS equations.A verification and validation study was carried out for the numerical method in one configuration and one ship velocity.The existing experimental results for the trimaran resistance in the literature were used for validation.Five different outrigger positions were analyzed and the form factor of each configuration was calculated by the Prohaska method.The total resistance was decomposed to its components using the form factor.The interference factor was calculated for each configuration in terms of total resistance,residual resistance and wave resistance.Also,wave profiles using the longitudinal wave cuts in different locations were obtained both numerically and experimentally.It was concluded that the outrigger position had different effects on the interference,total resistance and wave profile at different Froude numbers.It was also shown that the CFD results were in good agreement with the experimental data in all configurations.In conclusion,this study presents the results of interference effects for different trimaran configurations in terms of wave resistance in addition to the total resistance and residual resistance.The numerical method was validated not only with the total resistance test data but also the longitudinal wave profiles along the hull.

An Experimental Study on Wind Loads Acting on a Trimaran PCC

In recent years,demands for car transportation by a ship have been increasing with favorable economic conditions in auto sector,and the need of a pure car carrier(PCC) has grown quickly.A PCC needs huge parking space but smaller displacement since a car is comparatively light for its volume.As a result,almost all PCCs have wide breadth,shallow draft and huge structure above the water surface.These features cause some technical issues of a PCC,like lack of stability,effect of strong winds on its resistance,difficulty of course keeping in rough seas,difficulty of berthing in strong winds,and so on.To overcome these technical issues,one of the authors has proposed a new concept for a PCC.This is a trimaran PCC which has very limited transverse bulkheads in the center hull by using two side hulls as fenders.In the present research,wind forces acting on a scale model of the trimaran PCC were measured in the towing tank with a wind generator at Osaka Prefecture University.Furthermore,in order to clarify the characteristics of wind pressure on the trimaran,height and width of tunnels which are between a main hull and side hulls were changed.And then,in order to imitate a real ship,we used wind reduction technology of corner-cut design for accommodation house of the ship.Moreover,the wind pressure acting on the trimaran was compared with that on a mono-hull PCC.Using these experimental and theoretical results,an estimation method of wind pressure acting on the trimaran PCC is deduced.

A Feasibility Study on a New Trimaran PCC in Medium Speed——Performance in Still Water and Strong Wind

In the present paper,a new trimaran Pure Car Carrier(PCC) is proposed and a feasibility study on the ship is carried out.In this study,first,the effective horse power(EHP)/car of the PCC running in still water is predicted.By comparing the predicted EHP/car with that of a conventional mono-hull PCC,it is found that the trimaran PCC is superior to the conventional mono-hull PCC at rather higher speed.As ship speed increases,the reduction of the resistance of the trimaran is bigger.It is also found that at common service speed of PCCs,the EHP/car of a small PCC is lower than that of a conventional PCC.Secondly,the optimal L/B of a main-hull of the trimaran PCC in still water is determined.The optimal L/B of the main-hull varies with ship speed and size because the wave resistance decreases but the frictional resistance increases as L/B of the hull increases.As ship size increases,the optimal L/B of the main-hull of the trimaran PCC decreases.Finally,the increase of the resistance of PCCs running in strong wind is predicted.The results show that drift angle and speed reduction of the trimaran PCC are much smaller than the conventional mono-hull PCC because of large side force created by three demi-hulls.

Experimental Study on the Configuration Hydrodynamics of Trimaran Ships

This paper presents experimental results on configuration hydrodynamics.Three models are used in the model tests,which are typical of hard,round,and soft chines.Although specific values are different,the influence patterns are similar in the three ship models.A set of different outrigger positions is investigated in calm water and regular waves.A variety of interesting phenomena are observed,among which the splash resistance is the dominant component for a trimaran at high speeds(with Froude number Fr>0.6).If two small outriggers are placed inside Kelvin’s wave systems of the main hull,a strong splash appears,resulting in a significant resistance increase.Moreover,short and long waves cannot be neglected,for they may excite the motions of much smaller outriggers.This condition leads to non-vanishing heaving at high-frequency and non-normalized pitches at low frequencies.Based on the tests,three spectra of optimum configurations for resistance,longitudinal motions,and transverse motions are presented.These results reveal the optimum configurations of a trimaran hull in terms of hydrodynamic performance,thus providing a very powerful tool for optimum design of trimaran ships.

Test Series Results of Varying Yaw and Roll Angles of Trimaran Amas

This paper illustrates the reasons behind the research strategy that has led to a new generation of trimaran hulls by minimizing the hull＇s drag-design approach. The objective of this study was to search for the optimal side-hull yaw and roll angle to minimize induced drag of trimarans a^d so to investigate the differences in the performance results of a trimaran hull. Specifically, this research has been based on a critical analysis of the diversity of ama yaw and roll angles and outriggers positioning. Then, the paper will be comparing the results of the test series of the yaw and roll angles of trimaran areas. Design and towing tank test of a scaled trimaran model will be illustrated and compared along with some key and relevant results. The term ＂ama＂ is a word in the Polynesian and Micronesian languages to describe the outrigger part of a canoe to provide stability.

基于CFD的三体船主侧体间流场干扰研究

三体船构型复杂,主侧体间相互干扰影响因素较多。为了研究三体船船体周围流场细节与主侧体间的流场干扰,运用计算流体力学(CFD)软件STAR-CCM+对三体船和主船体进行了不同航速的数值模拟,提取船体周围与主侧体间的流场信息,获得不同速度下的兴波、横截面垂向速度和横截面矢量流线演化。研究三体船与单体船的流场差异特性,分析三体船中侧体对单独主船体流场的扰动,获得了三体船船体兴波与流场流线随航速变化的规律,为三体船的阻力性能和整体布局的优化提供参考。

基于四自由度的三体船操纵运动数值模拟研究

文中针对某高速三体船的操纵运动预报,开展约束模型试验和横摇衰减试验.基于MMG模型,获取四自由度操纵水动力导数,进行三体船回转运动及Z形操纵运动预报.在数值计算过程中,进行了网格尺度及时间步长的收敛性分析,探讨了纵摇和垂荡运动对数值模拟结果的影响;数值模拟了斜拖、旋臂、横倾及横摇衰减试验.基于最小二乘法拟合计算结果并得到水动力导数,结合四自由度MMG模型进行了不同舵角下三体船的操纵性能预报,得到了三体船的操纵性能参数.

基于高速三体船阻力性能的压浪板参数敏感性分析

为了研究不同外形和安装位置的压浪板对高速三体船阻力的影响,选取了展长B、弦长L、安装角度θ、主体安装高度H及侧体安装高度h等5个代表性参数,通过正交试验设计出16种参数组合,采用基于雷诺时均方法的SST k-ω湍流模型对加装不同压浪板的三体船静水航行过程进行数值模拟并验证模拟的准确性,极差分析得出5个参数对总阻力系数的影响顺序为H>h>B>L>θ。对较优参数组合压浪板进行多航速模拟,并监测静水阻力、纵倾、艉下沉、自由液面及船底压力等数据,分析压浪板减阻和改变航行姿态的原因,发现减阻效果随着航速的增大而逐渐明显,傅汝德数Fr为0.598时减阻率可达12.69%。

基于CFD的排水型三体无人艇阻力优化研究

为预报某三体无人艇的静水航行阻力,利用STAR-CCM+软件对船体进行计算流体动力学仿真。基于船体的航速和排水量等设计参数,考虑侧体纵向位置和侧体船型2种因素,选取不同设计方案进行计算。结合后处理得到的流场特征对仿真结果进行分析,总结阻力变化规律,探讨船体水动力性能的变化机理。结果表明:侧体纵向位置后移可减小片体间兴波扰动,减阻率最大约6.7%;改变侧体型宽会小幅度降低船体压阻,其最大减阻率约4.5%。汇总多种船型方案的计算结果,为三体无人艇的后续研究提供参考。

三体船压浪板虚拟仿真系统

三体船压浪板作为完善船舶结构、降低船舶阻力的重要手段,在近年来得到了广泛的关注及应用,很好解决了船体航行中较大的纵向摇荡运动。本文通过对三体船的运动及受力进行分析,建立压浪板力学模型,采用数值计算与仿真技术相结合的方法,开发基于虚拟现实技术的三体船压浪板设计与分析系统。

船载波浪发电设备设计及其性能研究

为解决小型无人船由于船体空间紧凑,携带燃料较少导致的续航力差、航程短等问题,本文以三体船为平台,将摆式波浪能发电技术与多体船相结合,提出了一种新型船载波浪发电设备设计方案。该发电设备可由主侧船体之间的波浪运动响应差异驱动,在海上航行时捕获波浪能并转化为电能,以此来补充船上能源。通过数值软件对三体船进行性能预报,结果表明,在四级海况下迎浪航行时,三体船平均波浪能捕获功率可达3.57 kW,波浪能一级转换效率为7.32%,能够有效地补充船上能源。同时,安装船载波浪发电设备具备减摇减荡的效果,提升了三体船的航行稳定性,进一步体现了该装置的可行性和实用性。

三体船操纵性自航回转运动仿真预报分析

针对船舶操纵性自航回转试验成本较高,且现有成熟仿真方法效率低、分析要素单一等问题,本文提出了一种船舶自航回转运动数值模拟方法,并利用商用计算流体力学软件Star-CCM+对三体船模在满舵角30°和半舵角15°所受推力情况下的自航回转运动进行了数值模拟,将该模拟结果与较为成熟的基于数学模型方程组的约束模仿真回转运动结果进行了对比分析,通过对三体船在满舵角和半舵角时的纵距、横距、旋回初径和回转直径等操纵性回转要素值进行分析可知,其差值均在7%以内,验证了文中所提方法的可靠性。且采用文中所提方法对目标船模进行模拟计算时,不仅能够获得船模在平面运动内的回转性能要素,同时还能得到船模横摇、纵摇、升沉等多自由度运动响应要素,本文亦对三体船在满舵角和半舵角下做自航回转运动时的横摇、纵摇、升沉等响应要素进行了分析,从定性分析的角度看,模拟所得的各运动响应要素结果与实际船舶在做回转运动时产生的现象相符;从定量的角度分析,模拟目标船模所得各运动响应要素结果较好,不会对船模回转产生较大干扰。