柔性尾鳍推进装置的水动力计算

由于柔性尾鳍推进装置的水动力计算在理论和实际上涉及到许多复杂的问题,本文对装置的实验模型作了理论上的抽象和简化,并依据试验图谱,运用机翼理论和襟翼舵原理,建立了该装置的水动力数学模型     

仿生胸鳍的三维尾涡结构与参数影响分析

为研究仿胸鳍推进的机理和流体动力特性及缩小机器鱼与生物原型之间的性能差距,利用浸入边界法数值模拟了做耦合旋转运动胸鳍的非定常绕流问题。详细探讨胸鳍非定常运动的三维尾涡结构演化和推进机理,并开展胸鳍推进性能与尾涡结构的参数影响分析。结果表明:迎流面在背、腹侧边缘及鳍梢部显著涡旋结构的作用下所出现的低压力区,加之鳍表面和上游来流之间好的垂直度共同造成了在动力划水阶段的高推力;在恢复划水阶段的高升力与背侧边缘涡强度的持续增加,以及因鳍表面倾斜而引起的水动力被分解到竖直方向的比重提升有关;胸鳍尾流场被一个三维双环涡结构所支配;当前的模拟为仿胸鳍推进建立了一个最优的斯特劳哈尔数St范围(在0.55附近),在此之后平均推力仍随St的增大而增加,而推进效率则表现出一个缓慢降低的趋势;当前后拍动与纵倾运动之间的相位差为90度时,胸鳍同时取得最佳的推力和效率。     

基于连杆机构综合的水下仿生推进装置设计

海洋动物在长期的进化过程中形成了高超的游泳能力,科学家和工程师希望通过对海洋动物的运动机理分析研发新型的高性能仿生推进装置。本文利用海龟扑翼运动的机理,设计一种基于四杆机构的仿海龟推进装置,并进行了运动分析。通过对海龟的扑翼运动进行分析,获取了海龟水翼在游动过程中的运动规律;运用机构综合的轨迹创成和刚体导引方法,设计了四连杆机构,使固连在连杆上的翼片能够近似实现海龟水翼的运动轨迹和姿态。文中计算了该机构的运动轨迹、姿态和角速度等运动参数,进行了机构的运动学仿真,该研究对于仿海龟推进装置设计和分析有借鉴意义。     

柔性尾鳍推进装置的机构综合与优化设计

根据柔性尾鳍推进装置所需达到的性能特性要求，本文对该装置进行了机构综合与优化设计，以改善其水动力性能，提高其推进效率。     

基于磁力耦合器的载人潜水器电力推进装置研究

基于磁力耦合传动技术,对载人潜水器电力推进装置进行了系统设计与传动特性研究。采用电磁场有限元方法研究了永磁式磁力耦合器的运行机理和矩角特性,分析了其稳定传动区域和失步条件;分析了螺旋桨的负载特性,采用切比雪夫多项式研究了螺旋桨的四象限全工况动态模型;建立了水下无刷直流推进电机的数学模型和传递函数,设计了推进电机的转速闭环控制系统以抑制转速波动,提高输出推力的平稳度。完成了样机的设计与制造,通过水池试验验证了该推进装置在载人潜水器上的可行性与适用性。     

一种仿生波动鳍装置设计与实验研究

推进系统是自主水下航行器的重要组成部分,传统的螺旋桨推进器虽然推进效率高,但存在着低速状态下机动性不足、噪音以及水流扰动的问题,相比之下模仿鱼类的推进方式在推进效率与机动能力上具有极大优势。在模仿鱼类的推进方式中,仿生波动鳍推进方式具有高机动性与高稳定性的特点。影响仿生波动鳍推力大小的因素主要有幅值、频率及相位差等控制参数,此外还包括波动鳍自身结构的长度、材质等物理因素,探讨物理因素的影响对于指导仿生波动鳍的设计有着重要意义。本文通过对鳐鱼形态学的研究,设计了一套简化的仿生波动鳍推进装置,并设计了仿生波动鳍的实验平台以及软硬件系统,依托于此套系统重点研究了鳍条材质、鳍条间距、鳍面长宽比、鳍面安装的松紧程度等物理因素对于波动鳍推力的影响。研究结果揭示了物理因素对于波动鳍推力影响的规律,对于今后研制高性能的仿生波动鳍推进装置提供了理论与实践上的参考。     

基于构造矩阵零空间的动力定位系统推力分配方法

在动力定位系统中,推力分配方法是联系运动控制算法和执行机构的纽带,具有十分重要的意义。回顾目前用于海洋工程船舶动力定位系统的主要推力分配算法,针对动力定位系统中常见的过驱动推力分配问题提出了一种基于船舶推进器构造矩阵零空间的分配算法。该方法将构造矩阵分解为基空间和零空间,目标推力可以由基空间保证;零空间向量并不影响总的目标推力,但影响单台推进器的推力,目标函数可以在零空间上优化。并将这一算法应用于某一工程船的动力定位仿真模拟,对该算法进行了验证。     

一种三次多项式湍黏性底边界层的流场分布

本文通过假定底边界层湍黏性的三次多项式参数化形式,基于简化的Navier–Stokes方程,并利用超几何方程的性质,推导出了湍流粗糙底边界层的速度解析解。同时,得到了底边界层内其他的动力参数,如底剪应力、Ekman传输、Ekman抽吸及近底部速度分布场,从理论上讨论了均匀混合底边界层特征量分布特征。通过数值结果分析,进一步得出底边界层的总速度、亏损速度及其剪应力受平均流的角频率和地球自转影响比较大;而底边界层的动力结构对于底边界层顶部粗糙度不敏感。该涡黏性模式从理论上丰富了底边界层涡黏性的形式,为底边界层的动力系统研究提供了借鉴和理论参考。     

耙吸挖泥船导管可调桨设计及实验研究

某4 500 m3耙吸挖泥船,经多年使用后主机功率下降,挖泥作业时推力不足。对该船主机进行实测,了解并确认主机的工作状态,在不改变轴系和调距机构的前提下,首次采用JDC4-55可调桨配合高效导管替代原有可调桨的设计方案,并进行了新导管可调桨和原桨的敞水实验及自航实验。实验结果显示该改造设计方案能显著提高该船挖泥工况的推力,达到节能增效的目的。此外,对于尾部设置类似导流尾鳍的导流结构进行了相关实验,得到有益结论。     

一种新型单向步进传动棘爪的改进设计

介绍了一种新型的基于离合方式工作的、能够进行单向传动的棘爪机构,阐述了改进前后棘爪结构的不同之处,并详细介绍了该棘爪机构如何带动测量平台在水下垂直方向运动。该机械装置具有结构简单、工作可靠、易于加工、成本低廉外的特点,由棘爪机构等部件组成的测量平台在上浮下潜工作过程中不需要系统自身电能进行驱动,很好地解决了海上测量中的能量供应问题。可以应用到其他需要单方向传动的方面。     

波浪滑翔机推进装置翼片的启动阶段水动力学分析

波浪滑翔机直接利用波浪能实现大范围长距离的机动运动观测,在海洋环境观测中可以发挥重要的作用。本文对波浪滑翔机推进装置在启动阶段的翼片的水动力学行为进行了研究。以波浪滑翔机水下推进装置的翼片为研究对象,运用雷诺平均Navier-Stokes方程(RANS),对给定垂荡和摆动运动的翼片水动力学进行了水动力分析和仿真,模拟了单个翼片、纵向阵列多翼片的运动状况,得到推进装置翼片附近的压力分布和整体推进动力,分析翼片间距变化在启动阶段对推进力的影响作用。通过该研究工作为深入理解波浪滑翔机推进装置工作状态提供了理论依据。     

基于人工神经网络的半潜平台动力定位系统推力分配策略研究

针对带有禁止角的半潜平台动力定位系统推力分配算法功率较大的问题,提出了一种基于人工神经网络拟合桨—桨干扰推力损失函数的序列二次规划推力分配算法。该方法考虑了半潜平台桨—桨干扰造成的推力损失,引入推力系数来表达推力损失。利用人工神经网络拟合推力系数,将推力损失加入到推力分配的数学模型中,取消了禁止角。采用序列二次规划求解推力分配数学模型。最后以某半潜式钻井平台为例,选取三种浪向角工况进行推力分配仿真模拟,结果显示该算法在高效分配定位所需推力的同时有效减小了功率消耗,应用前景广泛。     

Accurate and practical thruster modeling for underwater vehicles

The thruster is the crucial factor of an underwater vehicle system, because it is the lowest layer in the control loop of the system. In this paper, we propose an accurate and practical thrust modeling for underwater vehicles which considers the effects of ambient flow velocity and angle. In this model, the axial flow velocity of the thruster, which is non-measurable, is represented by ambient flow velocity and propeller shaft velocity. Hence, contrary to previous models, the proposed model is practical since it uses only measurable states. Next, the whole thrust map is divided into three states according to the state of ambient flow and propeller shaft velocity, and one of the borders of the states is defined as critical advance ratio (CAR). This classification explains the physical phenomenon of conventional experimental thrust maps. In addition, the effect of the incoming angle of ambient flow is analyzed, and Critical Incoming Angle (CIA) is also defined to describe the thrust force states. The proposed model is evaluated by comparing experimental data with numerical model simulation data, and it accurately covers overall flow conditions within ±2 N force error. The comparison results show that the new model's matching performance is significantly better than conventional models'.     

Thrust Characterization of a Bioinspired Vortex Ring Thruster for Locomotion of Underwater Robots

A new type of thrusting technology, loosely inspired by the locomotion of cephalopods, offers promising low-speed maneuvering capabilities for a new generation of underwater vehicles and robots. The actuators consist of a small cavity with a moving wall on one side and an orifice on the other side. The net effect of periodic movement of the moving wall is the ingestion of low-momentum fluid inside the cavity and then the expulsion of the fluid as a pulsatile jet from the orifice, with no net mass flux. Continuous operation of the actuator results in a synthetic jet. The actuators provide a net positive momentum flux with zero net mass flux. They are compact with no extruding components to negatively impact the vehicle's drag at cruising speed. Parameters controlling the pulsatile jet and its thrust are identified. The thruster was empirically tested for a large range of frequencies and stroke ratios. The thrust characteristics of the device with respect to frequency was seen to converge to a single thrust coefficient. A model was developed to predict the thrust coefficient. The effect of the stroke ratios on the thrust coefficient is investigated. The model accurately predicts the observed thrust coefficient for stroke ratios up to five where the vortex ring pinchoff occurs. The accuracy of the model degrades for stroke ratios above the formation number where part of the expelled jet is pulled back into the cavity. Additionally, these devices have thrust tracking times faster than those reported for typical propellor-type thrusters, and deliver a fully quantized level of thrust.      

Dynamic Positioning Control of Surge-Pitch Coupled Motion for SmallWaterplane-Area Marine Structures

For general dynamic positioning systems, controllers are mainly based on the feedback of motions only in the horizontal plane. However, for marine structures with a small water plane area and low metacentric height,undesirable surge and pitch oscillations may be induced by the thruster actions. In this paper, three control laws are investigated to suppress the induced pitch motion by adding pitch rate, pitch angle or pitch acceleration into the feedback control loop. Extensive numerical simulations are conducted with a semi-submersible platform for each control law. The influences of additional terms on surge-pitch coupled motions are analyzed in both frequency and time domain. The mechanical constraints of the thrust allocation and the frequency characters of external forces are simultaneously considered. It is concluded that adding pitch angle or pitch acceleration into the feedback loop changes the natural frequency in pitch, and its performance is highly dependent on the frequency distribution of external forces, while adding pitch rate into the feedback loop is always effective in mitigating surge-pitch coupled motions.     

半潜式平台动力定位系统控制力动态约束分配法

半潜式平台动力定位推力分配系统通过计算每个推力器的推力和推力角,将控制力分配到推力系统的各推力器上。基于系统耗能最小模式,根据推力器之间的损失模型,通过动态设置推力可行域,将推力分配问题转化为求解二次型优化模型。考虑推力器的物理性能,以推力变化率和转角变化速率为控制参数,利用序列二次规划法得到数值计算结果。该方法充分考虑推力器的物理性能,降低推力器的机械磨损,且可以避免处理可行域为非凸集问题,有效地提高推力器的推力效率。     

Estimating basal friction and fluid pressure from the geometry and spacing of frontal faults in Naga fold thrust belt, India

Naga fold thrust belt is an emerging destination for petroleum exploration in eastern India. It is a thin skinned FTB where new initiatives are being taken after a long gap of initial discoveries. In absence of sufficient drilling or quality seismic data in the southern part of the fold thrust belt, fluid pressure regimes remain largely speculative. Using the concept and the formulation for efficient coefficient of basal friction, we have revisited the method and concept of pressure-dependent Coulomb wedge theory for thin skinned thrust belts for deriving the fluid pressure ratio in Naga fold thrust belt. The efficient coefficient of basal friction on the decollement and the fluid ratio of Naga fold thrust belt are estimated to be 0.22 and 0.85 respectively. This indicates an overpressure situation in the wedge. This method of estimating basal friction and fluid pressure is more case-specific and can be obtained from the data of thrust initiation angle and thrust spacing.     

Ship propulsion in waves by actively controlled flapping foils

Flapping wings located beneath or to the side of the hull of the ship are investigated as unsteady thrusters, augmenting ship propulsion in waves. The main arrangement consists of horizontal wing(s) in vertical oscillatory motion which is induced by ship heave and pitch, while rotation about the wing pivot axis is actively controlled. In this work we investigate the energy extraction by the system operating in irregular wave conditions and its performance concerning direct conversion to propulsive thrust. More specifically, we consider operation of the flapping foil in waves characterised by a spectrum, corresponding to specific sea state, taking into account the coupling between the hull and the flapping foil dynamics. The effect of the wavy free surface is accounted for through the satisfaction of the corresponding boundary conditions and the consideration of the wave velocity on the formation of the incident flow. Numerical results concerning thrust and power coefficients are presented, indicating that significant thrust can be produced under general operating conditions. The present work can be exploited for the design and optimum control of such systems extracting energy from sea waves for augmenting marine propulsion in rough seas, with simultaneous reduction of ship responses offering also dynamic stabilisation.     

基于南海波浪要素的波浪滑翔机翼板参数优化设计与仿真

针对南海不同波浪要素条件下波浪滑翔机翼板参数设计的问题进行研究。基于欧洲中尺度天气预报中心大气和海洋全球再分析数据集(ERA5), 对南海不同季节以及台风经过时的波高波周期进行统计。并利用FLUENT软件研究南海不同波浪要素条件下翼板最大偏转角度、转轴位置以及翼板间距对波浪滑翔机水下翼板平均推力的影响。仿真结果表明, 波高越大, 翼板最大偏转角度也应相应增大, 才能保证翼板获得更大的推力; 在南海波浪要素条件下, 翼板转轴位置选取在翼板前端1/5处较佳; 适当增加翼板间距能够提高翼板获得的推力。通过对翼板被动摆动进行仿真, 得到了翼板在不同参数设置下产生的推力, 为波浪滑翔机翼板设计提供参考。