High speed on/off valve control hydraulic propeller

The work-class remotely-operated-underwater-vehicles(ROVs) are mainly driven by hydraulic propulsion system,and the effeciency of hydraulic propulsion system is an important performance index of ROVs.However,the efficiency of traditional hydraulic propulsion system controlled by throttle valves is too low.Therefore,in this paper,for small and medium ROVs,a novel propulsion system with higher efficiency based on high speed on/off valve control hydraulic propeller is proposed.To solve the conflict between large flow rate and high frequency response performance,a two-stage high speed on/off valve-motor unit with large flow rate and high response speed simultaneously is developed.Through theoretical analysis,an effective fluctuation control method and a novel pulse-width-pulse-frequency-modulation(PWPFM) are introduced to solve the conflict among inherently fluctuation,valve dynamic performance and system efficiency.A simulation model is established to evaluate the system performance.To prove the advantage of system in energy saving,and test the dynamic control performance of high speed on/off valve control propeller,a test setup is developed and a series of comparative experiments is completed.The smimulation and experiment results show that the two-stage high speed on/off valve has an excellent dynamic response performance,and can be used to realize high accuracy speed control.The experiment results prove that the new propulsion system has much more advantages than the traditional throttle speed regulation system in energy saving.The lowest efficiency is more than 40%.The application results on a ROV indicate that the high speed on/off valve control propeller system has good dynamic and steady-state control performances.Its transient time is only about 1 s-1.5 s,and steady-state error is less than 5%.Meanwhile,the speed fluctuation is small,and the smooth propeller speed control effect is obtained.On the premise of good propeller speed control performance,the proposed high speed on/off valve control propeller can improve the effeciency of ROV propulsion system significantly,and provides another attractive ROV propulsion system choice for engineers.     

I-beam Crack Identification Based on Study of Local Flexibility due to Crack

Local flexibility of crack plays an important role in crack identification of structures.Analytical methods on local flexibility in a cracked beam with simple geometric crossing sections,such as rectangle,circle,have been made,but there are some difficulties in calculating local flexibility in a cracked beam with complex crossing section,such as pipe and I-beam.In this paper,an analytical method to calculate the local flexibility and rotational spring stiffness due to crack in I-beam is proposed.The local flexibility with respect to various crack depths can be calculated by dividing a cracked I-beam into a series of thin rectangles.The forward and inverse problems in crack detection of I-beam are studied.The forward problem comprises the construction of crack model exclusively for crack section and the construction of a numerically I-beam model to gain crack detection database.The inverse problem consists of the measurement of modal parameters and the detection of crack parameters.Two experiments including measurement of rotational spring stiffness and prediction of cracks in I-beam are conducted.Experimental results based on the current methods indicate that relative error of crack location is less than 3%,while the error of crack depth identification is less than 6%.Crack identification of I-beam is expected to contribute to the development of automated crack detection techniques for railway lines and building skeletons.     

Dynamic analysis of propulsion mechanism directly driven by wave energy for marine mobile buoy

Marine mobile buoy(MMB) have many potential applications in the maritime industry and ocean science. Great progress has been made, however the technology in this area is far from maturity in theory and faced with many difficulties in application. A dynamic model of the propulsion mechanism is very necessary for optimizing the parameters of the MMB, especially with consideration of hydrodynamic force. The principle of wave-driven propulsion mechanism is briefly introduced. To set a theory foundation for study on the MMB, a dynamic model of the propulsion mechanism of the MMB is obtained. The responses of the motion of the platform and the hydrofoil are obtained by using a numerical integration method to solve the ordinary differential equations. A simplified form of the motion equations is reached by omitting terms with high order small values. The relationship among the heave motion of the buoy, stiffness of the elastic components, and the forward speed can be obtained by using these simplified equations. The dynamic analysis show the following:The angle of displacement of foil is fairly small with the biggest value around 0.3 rad;The speed of mobile buoy and the angle of hydrofoil increased gradually with the increase of heave motion of buoy; The relationship among heaven motion, stiffness and attack angle is that heave motion leads to the angle change of foil whereas the item of speed or push function is determined by vertical velocity and angle, therefore, the heave motion and stiffness can affect the motion of buoy significantly if the size of hydrofoil is kept constant. The proposed model is provided to optimize the parameters of the MMB and a foundation is laid for improving the performance of the MMB.     

MODELING AND ROBUST DESIGN OF REMANUFACTURING LOGISTICS NETWORKS BASED ON DESIGN OF EXPERIMENT

The uncertainty of time, quantity and quality of recycling products leads to the bad stability and flexibility of remanufacturing logistics networks, and general design only covered the minimizing logistics cost, thus, robust design is presented here to solve the uncertainty. The mathematical model of remanufacturing logistics networks is built based on stochastic distribution of uncontrollable factors, and robust objectives are presented. The integration of mathematical simulation and design of experiment method is performed to do sensitive analysis. The influence of each factor and level on the system is investigated, and the main factors and optimum combination are studied. The numbers of factors, level of each factor and design process of experiment are investigated as well. Finally, the process of robust design based on design of experiment is demonstrated by a detailed example.     

Contents and Abstracts of Journal of Mechanical Engineering

Vol.47,No.3,2011 DOI:10.3901/JME.2011.03.001 Effect of Kinematic Behavior of Caudal Fin on Fishlike Robot Propulsion during Steady Swimming CHEN Weishan XIA Dan LIU Junkao SHI Shengjun (State Key Laboratory of Robotics and System,Harbin Institute of Technology,Harbin 150080,China) The speed convergence algorithm is applied in the numerical simulation of a fishlike robot in self-propelled swimming.All simulations are started with the body at rest,the swimming speed is dynamically modified to converge to the steady value by verifying the fluid forces during the swimming process.The effects of kinematic behavior of caudal fin on fishlike robot propulsion are numerical investigated in the converged steady speed,while the propulsive mechanism and flow field structure are revealed. The results show that the steady speed can be predicted validly by using the     

Optimal Dimensional Synthesis of a Symmetrical Five-Bar Planar Upper-Extremity Neuromotor Device

Individuals with hemiplegia suffer from impaired arm movements that appear as a marked change in arm stiffness. A quantitative measure of arm stiffness would characterize rehabilitation therapy effectively, while little mechanism is designed to implement the function. A symmetrical five-bar linkage consisting of two revolute joints and three prismatic joints is presented. Inverse kinematics and forward kinematics are obtained first. Then inverse singularities and direct singularities of the mechanism are gained. The global stiffness index is defined based on the results of kinematics analysis. Finally, optimal dimensional synthesis of the mechanism in terms of maximum stiffness is conducted by genetic algorithms. The calculation results show that with the length of both the two linkage a=830 mm, the interacting angle of the two guides 2δ=4.48 radian, and the maximum range of displacement of the two carriers dmax=940 mm, the mechanism achieves highest rigidity and its workspace is singularity-free, which covers the human left and right arm range of motion. The proposed novel mechanism featuring high rigidity and a singularity-free workspace can provide rehabilitation training, also solve the problem of quantitative measure of arm stiffness.     

Dynamic bending of bionic flexible body driven by pneumatic artificial muscles(PAMs) for spinning gait of quadruped robot

The body of quadruped robot is generally developed with the rigid structure. The mobility of quadruped robot depends on the mechanical properties of the body mechanism. It is difficult for quadruped robot with rigid structure to achieve better mobility walking or running in the unstructured environment. A kind of bionic flexible body mechanism for quadruped robot is proposed, which is composed of one bionic spine and four pneumatic artificial muscles(PAMs). This kind of body imitates the four-legged creatures' kinematical structure and physical properties, which has the characteristic of changeable stiffness, lightweight, flexible and better bionics. The kinematics of body bending is derived, and the coordinated movement between the flexible body and legs is analyzed. The relationship between the body bending angle and the PAM length is obtained. The dynamics of the body bending is derived by the floating coordinate method and Lagrangian method, and the driving force of PAM is determined. The experiment of body bending is conducted, and the dynamic bending characteristic of bionic flexible body is evaluated. Experimental results show that the bending angle of the bionic flexible body can reach 18°. An innovation body mechanism for quadruped robot is proposed, which has the characteristic of flexibility and achieve bending by changing gas pressure of PAMs. The coordinated movement of the body and legs can achieve spinning gait in order to improve the mobility of quadruped robot.     

ADAPTIVE MEASUREMENT METHOD BASED ON CHANGING-CURVATURE FOR UNKNOWN FREE-FORM SURFACE

Current measurement method for unknown free-form surface has low efficiency. To acquire given precision, a lot of null points are measured. Based on change surface curvature, a new measurement planning is put forward. Sample step is evaluated from the change curvature and the locally-bounded character of extrapolating curve. Two coefficients, maximum error coefficient and local camber coefficient, are used to optimize sampling step. The first coefficient is computed to avoid sampling-point exceeding the measurement range and the second control sampling precision. Compared with the other methods, the proposed planning method can reduce the number of the measuring-point efficiently for the given precision. Measuring point distributes adaptively by the change surface curvature. The method can be applied to improve measurement efficiency and accuracy.     

Synthetical efficiency-based optimization for the power distribution of power-split hybrid electric vehicles

Now the optimization strategies for power distribution are researched widely, and most of them are aiming to the optimal fuel economy and the driving cycle must be preknown. Thus if the actual driving condition deviates from the scheduled driving cycle, the effect of optimal results will be declined greatly. Therefore, the instantaneous optimization strategy carried out on-line is studied in this paper. The power split path and the transmission efficiency are analyzed based on a special power-split scheme and the efficiency models of the power transmitting components are established. The synthetical efficiency optimization model is established for enhancing the transmission efficiency and the fuel economy. The identification of the synthetical efficiency as the optimization objective and the constrain group are discussed emphatically. The optimization is calculated by the adaptive simulated annealing （ASA） algorithm and realized on-line by the radial basis function （RBF）-based similar models. The optimization for power distribution of the hybrid vehicle in an actual driving condition is carried out and the road test results are presented. The test results indicate that the synthetical efficiency optimization method can enhance the transmission efficiency and the fuel economy of the power-split hybrid electric vehicle （HEV） observably. Compared to the rules-based strategy the optimization strategy is optimal and achieves the approximate global optimization solution for the power distribution. The synthetical efficiency optimization solved by ASA algorithm can give attentions to both optimization quality and calculation efficiency, thus it has good application foreground for the power distribution of power-split HEV.     

Effect of magnetic field on forced convection between two nanofluid laminar flows in a channel

This paper provides a numerical study of forced convection between hot and cold nanofluid laminar flows that are separated by a thin membrane, in a horizontal channel. Outer surface of channels' walls are thermally insulated and divide into two parts; namely NMP and MP. NMP is the channel's wall from the entrance section to the middle section of channel that is not influenced by magnetic field. MP is the channel's wall from the middle section to the exit section of channel which is influenced by a uniform-strength transverse magnetic field.The governing equations for both hot and cold flows are solved together using the SIMPLE algorithm. The effects of pertinent parameters, such as Reynolds number(10≤Re≤500), Hartman number(0≤Ha≤60) and the solid volume fraction of copper nano-particles(0≤?≤0.05), are studied. The results are reported in terms of streamlines, isotherms, velocity and temperature profiles and local and average Nusseltnumber.The results of the numerical simulation indicate that the increase in Reynolds number and the solid volume fraction lead to increase in Nusselt number. Meanwhile, the results also show that the rate of heat transfer between the flows increases as the Hartmann number increases, especially at higher values of the Reynolds number.     

咽颌运动模式仿生胸鳍的建模及试验研究

从咽颌运动模式鱼类胸鳍的骨骼结构和神经肌肉控制机理出发,充分发挥导边鳍条和后缘边鳍条的引导作用,设计一套新型的柔性仿生胸鳍,建立此仿生胸鳍的样机及其运动学和动力学模型。并对仿生胸鳍的推进运动进行了仿真分析和试验研究。将上述仿生胸鳍推进运动的仿真结果、试验结果以及实际胸鳍推进运动的观测结果进行了比较研究可以看出,所建立的仿生胸鳍数学模型是合理、有效的,能够较好地仿真仿生胸鳍的推进运动,同时从中也可以看出,所建立的胸鳍仿生机构能够较好地模拟鱼类胸鳍的推进运动。     

仿蝠鲼机器鱼软体胸鳍建模与仿真

介绍一种仿蝠鲼机器鱼上使用的软体胸鳍推进器，具有三维立体翼型并集成多个软体致动单元，具备更高形态及运动仿生度。分析提取了生物原型翼缘曲线并建立扑翼运动学模型，解耦描述胸鳍俯仰-摆转复合运动模式；对比了不同致动器数量的软体胸鳍运动特性与控制策略，并通过样机静态加载试验验证了有限元模型可靠性；基于格子-玻尔兹曼方法实现复杂曲面动态边界的流固耦合，在仿真环境中分析了单/多自由度软体胸鳍在不同工况下的扑翼推升力特性；数据对比表明多自由度胸鳍平均推力为单自由度的7.2倍，性能优势显著，为进一步水动力试验研究与机器鱼平台整合提供了数据预测与方向指导。     

咽颌运动模式鱼类胸鳍的运动学建模及仿真

针对实际鱼类胸鳍运动的随机性、不确定性和复杂性等问题给胸鳍推进机理和推进性能研究带来的挑战与困难,以及柔性胸鳍仿生研究所存在的问题,在对太阳鱼胸鳍的结构和运动特征进行大量观测研究的基础上,分阶段建立柔性胸鳍推进运动的运动学模型,并对其运动形态的变化过程进行仿真分析。仿真结果表明,所建立的运动学模型能够较好地描述胸鳍推进运动的运动规律和运动形态。此研究可为柔性胸鳍推进机理、推进性能和仿生等方面的深入研究提供理论依据。     

欠驱动柔性胸鳍仿生设计及仿真

为了进一步提高咽颌运动模式鱼类胸鳍仿生机构的性能,以实际鱼类胸鳍的结构和驱动控制机理为基础,采用欠驱动技术设计了一套新型的柔性胸鳍仿生机构,建立其运动学和动力学模型,并采用Matlab对其性能进行了仿真分析。从仿真结果来看,所建立的新型柔性胸鳍仿生机构及其运动学、动力学模型是合理、有效的。它不但能够较好的模拟胸鳍的各种操纵运动,而且减少了驱动装置的数量,降低了系统的复杂性。从而为深入研究鱼类胸鳍的推进机理和新型水下操纵工具的设计提供了一定的基础和保障。     

基于遗传算法的胸鳍推进性能优化研究

由于鱼类胸鳍的推进性能是和其运动学参数直接相关的,为了进一步提高胸鳍的推进性能,建立了胸鳍推进运动的运动学模型,对在推进运动过程中胸鳍所受到的水动力进行了计算,并建立了对其推进性能进行优化的数学模型,然后,采用MATLAB编写了相应的遗传优化算法,以对胸鳍推进性能进行了优化设计。最后,对优化结果和胸鳍的推进性能进行了仿真分析,从仿真结果可以看出,所建立的优化模型以及所采用的优化算法能够较好的对胸鳍的性能进行优化,提高了胸鳍在推进过程中的推进力。因此,所进行的优化分析是合理、有效的,为进一步提高胸鳍的推进性能提供了一定的理论依据。     

胸鳍摆动推进模式仿生鱼研究进展

胸鳍摆动推进模式鱼类兼具高机动性、高效率和较高运动速度等优势特征,以此种鱼类为自然原型构建仿生机器鱼成为水下机器人研究领域的一个热点问题。通过对牛鼻鲼生物学研究成果的总结和实地观测分析,得出胸鳍摆动推进模式鱼类的典型身体结构特征和运动变形规律。系统总结胸鳍摆动推进模式仿生鱼研究领域中摆动胸鳍功能单元理论和试验研究情况以及仿生鱼样机构建的国内外研究现状。着重介绍研究小组在胸鳍摆动推进仿生鱼研究中所取得的阶段性成果,并在游动速度方面与本领域内的其他样机进行对比。通过对当前胸鳍摆动推进仿生鱼研究成果进行分析,得出现有仿生样机与自然原型存在差距的主要原因。随着研究的不断深入,胸鳍摆动推进仿生鱼样机性能与自然原型之间的差距必将逐渐缩小,实际应用前景广阔。     

面向水下无声推进的形状记忆合金丝驱动柔性鳍单元

水下无声推进是潜器追求的理想目标,但几乎所有成熟的潜器都应用螺旋桨推进,噪声较大,推进效率随航度变化波动大,限制了潜器的应用.基于大多数鱼类和鳍波动推进时的乌贼的游动基本动作为柔性弯曲这一事实,从软体动物乌贼的鳍结构获得启发,借鉴其肌肉性静水骨骼原理,提出并研制嵌入形状记忆合金丝驱动的仿生柔性鳍单元,对柔性鳍单元进行转角理论分析及水中弯曲、回复试验,研制并试验基于柔性鳍单元的微型机器鱼.柔性鳍单元通过电流驱动,以模块化形式安装,实现身体/尾鳍推进、胸鳍波动推进等功能.柔性鳍单元为动作无噪声,转角大,无相对移动的机械部件,具有足够的输出力,结构简单,隐蔽性好,可实现水下无声仿生推进,在微小型水下机器人上应用具有优势.     

仿鳐鱼水下机器人自主游动建模与仿真

随着探索海洋的呼声越来越高,仿鱼机器人的研究热潮也随之而来。在众多鱼类中,以鳐鱼为代表的胸鳍推进式鱼类具有良好的机动性,能适应复杂的海底环境。然而目前国内外对仿鳐鱼机器人的研究很少,特别是对其动力学模型和自主游动方面的研究更是不足,因而建立了仿鳐鱼机器人的物理模型,提出了一种动力学模型,并在此基础上仿真实现了仿鳐鱼机器人的自主游动,获得了与真实鳐鱼游动十分接近的速度和相同的运动规律,证明了模型和仿真的正确性。     

压电纤维致动的仿鲤鱼尾鳍式小型推进器的摆动特性及流固耦合机理

宏压电纤维复合材料（Macro fiber composite,MFC）克服了传统压电材料在韧性和脆性方面的不足,具有驱动变形大、柔韧性好且防水性好的优点,在仿生变形驱动领域具有广泛的应用前景。模仿锦鲤鱼类的形态特征和身体/尾鳍（Body or caudal fin,BCF）游动推进模式,提出了一种MFC致动的仿鲤鱼尾鳍式小型水下推进器。在峰值1 000 V、频率7.5 Hz的简谐激励电压下,试验测得推进器末端水下最大摆速154.5 mm/s。采用计算流体力学（Computational fluid dynamics,CFD）分析了推进器摆动过程中周围流场分布及变化情况。仿真结果表明,推进器在稳定推进阶段产生的瞬时最大推进力和平均推进力分别为9.8 mN和4.22 mN,与Lighthill细长体理论一致;同时从推进器周围的周期平均流场结构中观察到了一片流速约为推进器结构最大摆速2倍的高速流场区域,且始终存在着一对对称分布、旋向相反的涡环结构沿着推进器顺流而下,因此产生一股高速水流从推进器尾部喷射而出,而推进器在高速水流的反作用力下向前推进,从而揭示了仿鲤鱼尾鳍式小型水下推进器的流固耦合特性和推进机理。     

基于理想推进器理论的尾鳍推力与效率估算

鱼类尾鳍的动力学问题已经得到广泛研究,但是在进行尾鳍推进器的设计时,还缺乏一种简单有效的设计和估算方法,将尾鳍的运动参数与推力、效率联系起来;在观测和分析尾鳍流场的基础上,研究了2自由度尾鳍推进器的流场结构和推力形成原因;将理想推进器理论应用于尾鳍推进器的推力和效率计算,提出了射流及其诱导速度的量化假设,建立了推力、效率与运动参数、斯特劳哈尔数之间的函数关系;运用该函数对海洋动物的典型运动状态进行了估算,估算结果与动物观测现象基本吻合,该方法在机器鱼模型设计中得到了应用和验证。