可着陆式水下机器人的多体动力学建模与仿真

可着陆式水下机器人由于变浮力机构的设计要求,其外形与结构较之传统的水下航行器更为复杂。在设计阶段对可着陆式水下机器人进行仿真和操纵性分析具有重要意义。文中采用多体系统动力学方法分析可着陆式水下机器人动力学特性,将作用在系统各组成部分上的流体动力、推进力以及其它作用力分别计算和考虑,建立了多体动力学模型,并进行了三维空间运动仿真。该方法为具有较复杂附体结构的水下机器人设计和动力学仿真提供了有效途径。     

基于水舱结构的UUV平衡液位算法研究

为了解决装配水舱的水下无人航行器在出航前,需人为通过调节水舱液位,使航行器处于零浮力状态的不便捷性问题,提出一种可以自动调整航行器平衡液位的方法。结合航行器自身水舱结构,通过 PID 算法将航行器的姿态信息和水舱液位信息进行整合,调节水舱水量实现航行器密度近似于当前水域密度,寻找满足航行器零浮力平衡姿态下的水舱液位。通过 MATLAB 仿真分析,该算法可以实现自主调节平衡液位的目的。     

高海况下无人水下航行器的横摇运动分析

为明确高海况下海况等级对无人水下航行器横摇运动的影响,得出满足某型无人水下航行器安全回收的海况条件,对高海况下无人水下航行器的横摇运动进行分析。运用频率响应法,分别在4级、5级和6级海况下，根据海浪谱密度函数和该型航行器的横摇频率响应函数,求得其横摇运动谱密度函数。再运用公式推导,得到其横摇运动的时域函数。使用MATLAB仿真软件对该型航行器进行横摇运动仿真,得到3种海况条件下，其横摇运动的时域函数图像,并验证仿真结果的准确性。仿真结论:高海况下的海况等级对无人水下航行器的横摇幅度有较大影响,满足其安全回收的海况条件为5级海况。     

基于MATLAB的自主水下航行器经典控制算法仿真分析

针对自主水下航行器在水下航行中的姿态控制问题,采用经典控制律的数学模型,依据总体参数和流体动力参数,代入到下航行器纵向运动微分方程组中,通过 MATLAB 自编程序运用龙格库塔法求解此微分方程组,并将经典控制方程(算法)引入到微分方程组的求解当中,其仿真分析结果验证和支持了自主水下航行器的湖上试验,为某自主水下航行器项目实航演示样机的研制提供理论支持,具有一定的工程参考价值。     

基于正交试验的水下航行器凸体涡流噪声优化

凸体作为水下航行器表面的一种常见附体结构,其产生的涡流噪声对搭载在水下航行器上的声学仪器的信号精度有非常重要的影响。在马赫数为0.004 8条件下,采用LES-Lighthill等效声源法对三维方形凸体的流场及声场进行仿真,形象地再现了凸体周围涡旋运动变化规律,分析了涡流流动机制及辐射噪声特征。通过正交试验设计,以噪声最小为目标,优化了三维方形凸体结构参数。研究成果为水下航行器附体结构的设计提供了依据。     

大深度潜航器水下空间运动建模与仿真

分析大深度潜航器水下空间运动特点，建立描述其空间运动的数学模型，并以数学模型为基础利用 MATLAB\Simulink 软件完成潜航器空间运动仿真模型的开发。在搭建的仿真模型基础上，通过数学仿真手段分析了潜航器在螺旋下潜、抛载过渡、定角爬升、稳定至水面航行状态下的水下运动全过程，给出了具有弧形翼板的潜航器外形设计方案的运动能力仿真评估，为后续潜航器运动能力优化设计提供仿真依据。     

水下滑翔机器人运动分析与载体设计

水下滑翔机器人是一种新型水下机器人,具有噪声低、航行距离远、续航时间长、成本低等特点。分析了水下滑翔机器人的驱动机理和运动实现,给出了水下滑翔机器人典型运动的仿真结果,并以正在设计的一水下滑翔机试验样机为研究对象,描述了样机的整体结构布局,详细研究了浮力调节机构、俯仰调节机构和横滚调节机构的实现方法,并就样机中各执行机构的设计实现进行了论述。     

水下滑翔器整体外形设计及水动力性能分析

对水下滑翔器的整体外形设计与水动力性能进行研究。在Slocum等几种典型水下滑翔器样机的基础上,对滑翔器的主体和附体进行一体化设计,得到阻力最小的新型水下滑翔器构型设计。利用CFD方法对水下滑翔器进行模拟仿真,通过分析对比五种主体构型,得到了比较合理的主体线型,然后用正交设计方法和曲线拟合法对附体进行了优选工作,最后得到了性能更优的整体载体外形。模拟仿真实验表明,滑翔器在8°左右攻角航行时,具有最大的升阻比;和Slocum等经典样机相比,新的载体具有更好的水动力性能。通过上述研究工作,也可以缩短水下滑翔器研制周期,降低设计成本,并为水下滑翔器的更优设计提供了有力的技术指导和参考。     

UUV定深控制模型参数优化设计方法

合适的控制模型参数能够保证被控对象在较快的响应时间和较小的超调量下达到控制目标,无人水下航行器定深控制模型参数的优化设计对提升水下航行器使用性能具有重要意义。首先,建立了水下航行器空间运动学方程,基于 Modelica 建模语言构建了航行器虚拟样机及其定深控制模型。然后,以响应时间和超调量最小为优化目标,采用非支配排序差分进化算法建立了水下航行器定深控制模型参数多目标优化流程,基于 OPTIMUS 平台构建了水下航行器定深控制模型参数优化设计工作流。以某水下航行器为对象的实验结果表明：所提方法可快速获得较优的 PID 控制模型参数,优化后的水下航行器定深运动控制特性显著改善。     

UUV应急处理策略构建推理研究

考虑水下无人航行器执行任务的安全性和时效性,需建立完善的应急处理体系。构建了分布式应急处理策略,实现快速故障诊断和应急响应,通过基于故障模式的反向推理和深度推理,利用故障分级诊断的推理策略,实现了针对不同故障采取相应的应急流程,并通过半实物仿真和实航测试,验证了 UUV 应急策略的正确性,提高了水下无人航行器任务执行的安全性。     

Hydrodynamic Analysis and Power Conversion for Point Absorber WEC with Two Degrees of Freedom Using CFD

Point absorber wave energy device with multiple degrees of freedom (DOF) is assumed to have a better absorption ability of mechanical energy from ocean waves. In this paper, a coaxial symmetric articulated point absorber wave energy converter with two degrees of freedom is presented. The mechanical equations of the oscillation buoy with power take-off mechanism (PTO) in regular waves are established. The three-dimensional numerical wave tank is built in consideration of the buoy motion based upon the CFD method. The appropriate simulation elements are selected for the buoy and wave parameters. The feasibility of the CFD method is verified through the contrast between the numerical simulation results of typical wave conditions and test results. In such case, the buoy with single DOF of heave, pitch and their coupling motion considering free (no PTO damping) and damped oscillations in regular waves are simulated by using the verified CFD method respectively. The hydrodynamic and wave energy conversion characteristics with typical wave conditions are analyzed. The numerical results show that the heave and pitch can affect each other in the buoy coupling motion, hydrodynamic loads, wave energy absorption and flow field. The total capture width ratio with two coupled DOF motion is higher than that with a single DOF motion. The wave energy conversion of a certain DOF motion may be higher than that of the single certain DOF motion even though the wave is at the resonance period. When the wave periods are high enough, the interaction between the coupled DOF motions can be neglected.     

Research on the unsteady hydrodynamic characteristics of vertical axis tidal turbine

The unsteady hydrodynamic characteristics of vertical axis tidal turbine are investigated by numerical simulation based on viscous CFD method. The starting mechanism of the turbine is revealed through analyzing the interaction of its motion and dynamics during starting process. The operating hydrodynamic characteristics of the turbine in wave-current condition are also explored by combining with the linear wave theory. According to possible magnification of the cyclic loads in the maximum power tracking control of vertical axis turbine, a novel torque control strategy is put forward, which can improve the structural characteristics significantly without effecting energy efficiency.     

Numerical and Experimental Investigation of Interactions Between Free-Surface Waves and A Floating Breakwater with Cylindrical-Dual/Rectangular-Single Pontoon

This paper investigates the hydrodynamic performance of a cylindrical-dual or rectangular-single pontoon floating breakwater using the numerical method and experimental study. The numerical simulation work is based on the multi-physics computational fluid dynamics (CFD) code and an innovative full-structured dynamic grid method applied to update the three-degree-of-freedom (3-DOF) rigid structure motions. As a time-marching scheme, the trapezoid analogue integral method is used to update the time integration combined with remeshing at each time step. The application of full-structured mesh elements can prevent grids distortion or deformation caused by large-scale movement and improve the stability of calculation. In movable regions, each moving zone is specified with particular motion modes (sway, heave and roll). A series of experimental studies are carried out to validate the performance of the floating body and verify the accuracy of the proposed numerical model. The results are systematically assessed in terms of wave coefficients, mooring line forces, velocity streamlines and the 3-DOF motions of the floating breakwater. When compared with the wave coefficient solutions, excellent agreements are achieved between the computed and experimental data, except in the vicinity of resonant frequency. The velocity streamlines and wave profile movement in the fluid field can also be reproduced using this numerical model.     

A Unified Computational Method for Simulating Dynamic Behavior of Planing Vessels

High speed planing hulls have complex hydrodynamic behaviors. The trim angle and drafts are very sensitive to speed and location of the center of gravity. Therefore, motion simulation for such vessels needs a strong coupling between rigid body motions and hydrodynamic analysis. In addition, free surface should be predicted with good accuracy for each time step. In this paper, velocity and pressure fields are coupled by use of the fractional step method. On the basis of integration of the two-phase viscous flow induced stresses over the hull, acting loads (forces and moments) are calculated. With the strategy of boundary-fitted body-attached mesh and calculation of 6-DoF motions in each time step, time history of ship motions including displacements, speeds and accelerations are evaluated. For the demonstration of the software capabilities, circular cylinder slamming is simulated as a simple type of water slamming. Then, a high-speed planing catamaran is investigated in the case of steady forward motion. All of the results are in good concordance with experimental data. The present method can be widely implemented in design as well as in performance prediction of high-speed vessels.     

Comparison of wave load effects on a TLP wind turbine by using computational fluid dynamics and potential flow theory approaches

Tension Leg Platform (TLP) is one of the concepts which shows promising results during initial studies to carry floating wind turbines. One of the concerns regarding tension leg platform wind turbines (TLPWTs) is the high natural frequencies of the structure that may be excited by nonlinear waves loads. Since Computational Fluid Dynamics (CFD) models are capable of capturing nonlinear wave loads, they can lead to better insight about this concern. In the current study, a CFD model based on immersed boundary method, in combination with a two-body structural model of TLPWT is developed to study wave induced responses of TLPWT in deep water. The results are compared with the results of a potential flow theory-finite element software, SIMO-RIFLEX (SR). First, the CFD based model is described and the potential flow theory based model is briefly introduced. Then, a grid sensitivity study is performed and free decay tests are simulated to determine the natural frequencies of different motion modes of the TLPWT. The responses of the TLPWT to regular waves are studied, and the effects of wave height are investigated. For the studied wave heights which vary from small to medium amplitude (wave height over wavelength less than 0.071), the results predicted by the CFD based model are generally in good agreement with the potential flow theory based model. The only considerable difference is the TLPWT mean surge motion which is predicted higher by the CFD model, possibly because of considering the nonlinear effects of the waves loads and applying these loads at the TLPWT instantaneous position in the CFD model. This difference does not considerably affect the important TLPWT design driving parameters such as tendons forces and tower base moment, since it only affects the mean dynamic position of TLPWT. In the current study, the incoming wave frequency is set such that third-harmonic wave frequency coincides with the first tower bending mode frequency. However, for the studied wave conditions a significant excitation of tower natural frequency is not observed. The high stiffness of tendons which results in linear pitch motion of TLPWT hull (less than 0.02 degrees) and tower (less than 0.25 degrees) can explain the limited excitement of the tower first bending mode. The good agreement between CFD and potential flow theory based results for small and medium amplitude waves gives confidence to the proposed CFD based model to be further used for hydrodynamic analysis of floating wind turbines in extreme ocean conditions.     

基于CFD船舶操纵性预报方法研究

基于CFD技术和重叠网格技术完成了黏性流场中KVLCC2船模的操纵性水动力导数的数值计算。为保证计算的精确性,进行了网格的收敛性分析,给出了合适的网格划分方法;通过数值模拟斜航运动、纯横荡运动和纯艏摇运动计算出的水动力与相应条件下的试验值对比,计算结果与试验值吻合良好,计算出的水动力导数准确度较高。基于MMG分离建模方法建立KVLCC2船模的操纵性数学模型,利用龙格-库塔算法求解微分方程组,对船舶操纵运动进行仿真。回转试验和Z形操舵试验的仿真结果与试验结果对比,其回转直径和轨迹都非常吻合,表明采用的船舶操纵性预报是可行的。     

风机基础TLP平台在波浪中运动性能的CFD数值分析

随着海上风能的开发向深水发展，支撑风机的载体平台越来越受到关注。在经济性与安全性、稳定性的多重要求下，张力腿平台（TLP）在海洋风能资源的开发中体现出了重要地位。采用基于开源平台OpenFOAM开发的计算流体动力学（CFD）水动力学求解器naoe-FOAM-SJTU对一座处于中等水深下的风机基础水下TLP（STLP）的运动响应进行了数值模拟与研究。文中使用弹簧锚链模型模拟STLP的垂向系泊锁链系统，模拟该平台在不同波浪环境下的运动响应情况。首先将STLP单自由度自由衰减CFD模拟结果与已有全耦合时域分析结果进行对比，验证了naoe-FOAM-SJTU求解器及使用弹簧模型模拟STLP系泊系统的准确性与可靠性。随后在考虑非线性波浪载荷的情况下研究极端海况下与一般作业海况下STLP的运动响应情况，计算工况中的风机基础所受弯矩及锚链受力情况，并详细展示流场、速度场信息，分析高阶波浪成分、不同海况等条件对于STLP运动性能的影响。研究结果表明，TLP在中等水深中具有良好的运动性能，naoe-FOAM-SJTU求解器可以有效模拟水中生产平台在波浪环境下的水动力问题，并可以对整个流场进行可视化展示与分析。     

液舱晃荡载荷计算与强度校核系统研究

随着薄膜型LNG运输船的需求量不断增加,晃荡载荷已成为船舶安全性研究的重要内容之一。本文结合中国船级社规范所推荐的公式,对薄膜型LNG船晃荡水平的载荷进行研究,提出载荷计算方法和流程,在MSC.patran的基础上结合二次开发语言PCL,设计了一套晃荡载荷计算与校核系统。该系统对有限元模型进行前后处理,设计了舱室识别算法来搜索晃荡载荷的作用域,实现薄膜型LNG船晃荡载荷的自动计算与施加,完成屈服强度评估。通过算例测试证明本系统自动计算结果的有效性和准确性,可以为工程设计人员大大节约工作量,大幅度提高工作效率。     

波浪作用下海床孔压累积过程离散元数值模拟

海床土层在波浪的循环荷载作用下会逐渐累积孔压,降低土层的稳定性,并威胁海上工程。为了研究孔隙水压力的累积机制,本文提出离散元孔隙密度流方法,并改进研发离散元分析软件MatDEM,实现了海床沉积物孔压的累积过程模拟。基于现场试验装置及土体力学参数建立离散元模型,通过对比试验和数值模拟结果发现:对海床沉积物施加波浪荷载后,表层土体中产生较高孔压,并逐渐向深层传递;在循环波浪荷载作用下,土颗粒间孔压累积范围逐渐增加;当孔压累积时间足够长时,土层中孔压收敛于所施加最大荷载与最小荷载的平均值,此时若孔压达到初始有效应力,土体将发生液化,内部土颗粒成为再悬浮沉积物;在周期性波浪荷载作用下,土颗粒液化悬浮后发生移动,浅层颗粒位移量大,土体整体表现为圆弧形移动。     

抛弃式探头下沉运动数值计算的网格划分方法研究

各类抛弃式探头下沉运动的数值计算研究都需要对探头表面和整个计算域进行网格划分的前处理过程,选择不同的网格划分方法和划分精度,会影响数值计算速度和计算精度,最终生成的网格质量决定了计算结果的收敛性和准确性。针对抛弃式探头的复杂结构,对比了两种网格划分方法、三种网格划分精度,完成探头计算区域的网格划分,采用k-ε湍流模型,进行抛弃式探头下沉运动的数值计算,并将计算结果与水箱和水库实验结果进行对比,验证了混合网格划分方法和普通精度网格对抛弃式探头下沉运动数值计算的适用性,研究结果对类似较为复杂结构的水下运动体的数值计算前处理过程具有一定的参考和借鉴意义。