Numerical Study of Propulsion Mechanism for Oscillating Rigid and Flexible Tuna-Tails

Numerical study on the unsteady hydrodynamic characteristics of oscillating rigid and flexible tuna-tails in viscous flow-field is performed. Investigations are conducted using Reynolds-Averaged Navier-Stokes （RANS） equations with a moving adaptive mesh. The effect of swimming speed, flapping amplitude, frequency and flexure amplitude on the propulsion performance of the rigid and flexible tuna-tails are investigated. Computational results reveal that a pair of leading edge vortices develop along the tail surface as it undergoes an oscillating motion. The propulsive efficiency has a strong correlation with various locomotive parameters. Peak propulsive efficiency can be obtained by adjusting these parameters. Particularly, when input power coeffcient is less than 2.8, the rigid tail generates larger thrust force and higher propulsive efficiency than flexible tail. However, when input power coefficient is larger than 2.8, flexible tail is superior to rigid tail.

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.

Over Modification Multi grid Method of Ship Propulsion Mechanism of Weis Fogh

The paper presents an over modification multi grid method of the ship propulsion mechanism of Weis Fogh, and obtains the complex potential integral formula by distributing vortices on the wing. The numerical formula is given on fine grid and coarse grid. The numerical results show that the algorithm is best when over modification factor is 1.5.

Burning surface formation mechanism of laser-controlled 5-aminotetrazole propellant

As an innovative propulsion technique, combustion mechanism of laser-augmented chemical propulsion has still to be ascertained. Benefiting from high nitrogen content and thermal stability, 5-aminotetrazole is a suitable ingredient for LACP. Under a flowing nitrogen environment, two kinds of unique burning surfaces were observed to occur for 5-ATZ, used as a single reacting propellant ingredient with the addition of carbon, under laser ablation. Both surfaces are hollow structures and differ by the possible presence of edges. Using micro computed tomography, the 3D perspective structures of both surfaces were revealed. Resorting to various characterization methods, a unified formation mechanism for both surfaces is proposed. This mechanism specifically applies to laser ablation, but could be crucial to common burning mechanisms in LACP.

Description of a Propulsion Unit Used in Guiding a Walking Machine by Recognizing a Three-point Bordered Path

A reconfigurable propulsion unit based on the Peaucellier-Lipkin mechanism has the ability to describe exact straight or curved paths depending on the selected ratio between the lengths of two of its links. The Peaucellier-Lipkin mechanism with one degree of freedom is transformed into a more sophisticated parallel kinematic chain by including four more degrees of freedom. The resulting propulsion unit is able to adapt its kinematic structure and reach instant centers of rotation, in accordance with the presence of three points that border a geometric path. A laser sensor mounted on the body of the machine detects each point. Once the machine has detected the exact location of the border of the road, it walks along a curve parallel to that border. Although the proposed research describes only one propulsion unit or leg, the methodology can be applied to all the legs of the walking machine. The novel 5-DOF leg is able to reach different centers of rotation, providing either the concave or convex arcs that satisfy the basic principle of displacement of walking machines.

Incentive Mechanism Model Design for Sharing of Information Resources in Rural Areas

In order to solve the issues concerning the cross-unit sharing of information resources in rural areas, we analyze the incentive problem of the sharing of information resources in rural areas using the incentive theory method; establish corresponding incentive mechanism model (It is divided into positive incentive model and negative incentive model, and only when the two models guarantee each other and are used at the same time can they be effective). Based on this, we put forward the institutional design for sharing of information resources in rural areas as follows: firstly, establishing an administrative agency of rural information resources sharing, above the authority of all units, responsible for related work on sharing of information resources in rural areas; secondly, establishing and improving the positive and negative incentive mechanisms, to ensure the realization of sharing of information resources in rural areas.

考虑动态接触电阻的电磁能推进装置运动和温度特性研究

在电磁能推进装置工作过程中,电枢与轨道间的接触电阻动态变化对系统性能有着重要影响。针对现有研究多依赖于Holm接触电阻理论并以电枢静止状态为基础的局限性,采用有限元和控制变量法研究实际推进情况下枢轨动态接触电阻对电磁能推进装置运动和温度特性的影响。首先,通过实验获取膛口电压、电流、电枢速度和位移等关键参数。其次,利用改进的完全自适应噪声集合经验模态分解(improved complete ensemble empirical mode decomposition with adaptive noise, ICEEMDAN)-小波阈值组合算法对所获得信号进行降噪处理,计算实际工况下的动态变化接触电阻。分别建立考虑枢轨动态接触电阻与不考虑接触电阻情况下的电磁热力耦合有限元模型,通过对比计算结果得到动态接触电阻对电枢运动和温度特性的影响。最后与实验结果进行对比,发现动态接触电阻是影响推进装置性能的重要因素,随着电枢位移的增加,接触电阻对运动特性的影响逐渐增加。另外,动态接触电阻的存在还会使电枢表面的温度迅速升高,电枢尾翼容易发生烧蚀,进而影响电枢的加速性能。该研究为进一步分析极端条件下动态接触电阻对电磁能推进装置的性能影响提供理论支持。

黄河流域生态保护与高质量发展耦合协调的协同推进机制

探索如何更好地实现黄河流域生态保护与高质量发展的耦合协调具有重大意义且迫在眉睫。推进黄河流域生态保护与高质量发展的耦合协调需要以协同学为理论基础,以黄河流域的客观现实为基本考量,寻求流域一体化的协同发展模式。推进黄河流域生态保护与高质量发展的耦合协调是一个涉及多个系统、多重目标、多个区域、多方利益、多元主体、多种关系、多个阶段的复杂系统性工程,需从功能协同、产业协同、空间协同和治理协同四大维度出发形成相应协同推进机制,并构建权责明晰的功能定位体系、优势互补的产业联动体系、统筹规划的区域治理体系和多元参与的全流域大治理体系,形成流域一体化发展的强大合力,以期早日实现黄河流域生态保护与高质量发展耦合协调水平的提档升级。

一种配置矢量调节机构的全电推卫星动力学模型

为建立全电推进卫星的精确模型、设计全电推卫星的姿轨控方法及提高卫星的控制精度,针对一种配置可展开矢量调节机构的全电推卫星开展动力学模型研究.建立四关节可展开矢量调节机构的模型,推导基于可展开式矢量调节机构构型的全电推卫星的电推力及力矩模型,在此基础上建立全电推卫星的姿态轨道动力学方程.利用此模型描述全电推进卫星的姿态运动状态及轨道变化,能够准确反映出卫星的运动性能,该模型已应用于我国亚太6E卫星研制中,应用该模型对卫星进行的动力学仿真结果符合测试及分析结果,且该卫星在轨控制效果与预期一致,验证了模型的有效性.

鱼类自主游动推进机理与游动性能二维数值模拟研究

推进机理及游动性能研究对鱼类洄游通道建设具有重要意义。利用计算流体动力学方法结合重叠网格技术,通过编译控制鱼体摆动的UDF程序,对二维鱼类自主游动进行模拟,分析鱼体压力场分布及反卡门涡街结构演化过程与参数变化情况,开展不同摆尾频率、摆尾幅度、鱼体体形及尾鳍尺寸等参数下鱼类游动性能及鱼体受力的变化情况,揭示鱼类自主游动过程中的游动机理。研究结果表明:(1)鱼体尾鳍周期性往复摆动下漩涡脱落形成反卡门涡街,是鱼体前进推力的主要来源,且随着摆尾频率、摆尾幅度的增加,鱼体尾部涡街长度、涡街强度逐渐增加,而摆尾幅度对涡街宽度的影响较大;(2)随着摆尾频率、摆尾幅度的增加,纵向平均合力系数和最大侧向力系数均增大,使得鱼类获得较大的游动速度,但摆尾频率改变时平均合力系数和游动速度的增加更为明显,摆尾幅度改变时最大侧向力系数的增加更为明显;(3)随着体宽指数的增加,纵向平均合力系数逐渐减小,需克服的游动阻力增加,使得鱼类游动速度逐渐减小,而最大侧向力系数逐渐增加;(4)随着尾鳍指数的增加,纵向平均合力系数和最大侧向力系数均增大,使得鱼类游动速度逐渐增大。研究成果可为鱼类生境恢复营造提供支撑。

离子液体电喷推力器工作机理研究进展

离子液体电喷推力器易于小型化,具有比冲高、推力精度高的特点,适用于微小卫星、太空引力波探测等领域,具有较大发展潜力。对电喷工作机理的认识与研究,不仅能够促进离子液体电喷推力器在工程中的应用,同时也为未来的进一步发展奠定基础。基于此,本文首先回顾了电喷推力器的发展历程及现状;其次以离子液体电喷推力器3个基础工作过程为出发点,对其锥射流形成及发射机理、束流模式及引出特性、羽流自中和机制进行了基础理论介绍与研究现状的总结;最后对离子液体电喷推力器未来的工作机理研究方向和工程应用发展方向提出展望。

基于仿生水母的水下机器人结构设计与试验研究

针对水下探测机器人隐蔽性好的需求,设计了一种仿生水母机器人。首先,进行了水母机器人的仿生设计,通过生物特征提取及功能耦合确定了机器人的功能设计要求,基于机构原理图,进行了三维模型设计;其次,对多杆推进机构进行了运动学求解,获得了两个闭环求解方程,并以此为依据,给定了一个尺寸设计案例;然后,采用ANSYS软件对设计案例进行了刚柔耦合分析和模态分析,对关键结构的强度和刚度进行了验证,获得了结构的低阶模态频率及振型,并为声学驱鱼装置的选择提供了依据;最后,根据设计模型制作了实物样机并进行了水下调试,获得了试验参数并验证了机器人的功能。研究结果表明:多杆推进机构在运动过程中最大等效应力约为4.92 MPa,最大变形量约为3.89 mm,该结构满足强度和刚度要求;通过实物样机制作与试验,实现了仿生水母机器人的水下游动和转向等功能,初步验证了方案的可行性;机器人在主驱动电机初设转速的驱动下,直线运动速度约为58.3 mm/s,转向速度约为22.5°/s。

Ignition processes and characteristics of charring conductive polymers with a cavity geometry in precombustion chamber for applications in micro/nano satellite hybrid rocket motors

The arc ignition system based on charring polymers has advantages of simple structure,low ignition power consumption and multiple ignitions,which bringing it broadly application prospect in hybrid propulsion system of micro/nano satellite.However,charring polymers alone need a relatively high input voltage to achieve pyrolysis and ignition,which increases the burden and cost of the power system of micro/nano satellite in practical application.Adding conductive substance into charring polymers can effectively decrease the conducting voltage which can realize low voltage and low power consumption repeated ignition of arc ignition system.In this paper,a charring conductive polymer ignition grain with a cavity geometry in precombustion chamber,which is composed of PLA and multiwall carbon nanotubes(MWCNT)was proposed.The detailed ignition processes were analyzed and two different ignition mechanisms in the cavity of charring conductive polymers were revealed.The ignition characteristics of charring conductive polymers were also investigated at different input voltages,ignition grain structures,ignition locations and injection schemes in a visual ignition combustor.The results demonstrated that the ignition delay and external energy required for ignition were inversely correlated with the voltages applied to ignition grain.Moreover,the incremental depth of cavity shortened the ignition delay and external energy required for ignition while accelerated the propagation of flame.As the depth of cavity increased from 2 to 6 mm(at 50 V),the time of flame propagating out of ignition grain changed from 235.6 to 108 ms,and values of mean ignition delay time and mean external energy required for ignition decreased from 462.8 to 320 ms and 16.2 to 10.75 J,respectively.The rear side of the cavity was the ideal ignition position which had a shorter ignition delay and a faster flame propagation speed in comparison to other ignition positions.Compared to direct injection scheme,swirling injection provided a more favorable flow field environment in the cavity,which was beneficial to ignition and initial flame propagation,but the ignition position needed to be away from the outlet of swirling injector.At last,the repeated ignition characteristic of charring conductive polymers was also investigated.The ignition delay time and external energy required for ignition decreased with repeated ignition times but the variation was decreasing gradually.

装填参数对水下新型气幕式发射内弹道性能的影响

为降低水下全淹没发射过程中射弹的附加质量,提高射弹初速,基于水下气幕式发射原理,提出了一种气幕的新型形成方式,即通过在发射管内壁开设沟槽,引导射弹后的火药燃气在发射管内汇聚形成气幕;建立了气幕式发射流体动力学模型,对该气幕形成方式下的发射过程进行了数值模拟,分析了装填参数对发射内弹道性能的影响。结果表明,与全淹没式发射相比,气幕式发射可将最大膛压降低89.4%,射弹初速提高53.3%;推进用包覆火药的包覆层燃速指数从0.75增大到0.78时,气幕排水时间缩短,弹丸启动时管内燃气体积分数大幅降低,弹丸初速降低,但内弹道全过程大幅缩短,发射频率提高;包覆层厚度的微小变化对内弹道性能影响较小。

凸导轨关键参数对电流密度分布的影响分析

电磁直线推进机构中导轨的形状密切影响着电流的分布,凸导轨在促进电流的均匀分布方面相对平导轨、凹导轨具有明显的优势。目前,尚未有文献分析研究凸导轨的弧面半径、覆层材料厚度等关键参数对电流分布的影响效果。因此,通过Maxwell有限元仿真软件,使用等效频率方法,针对25 mm小口径凸导轨电磁直线推进机构,计算了不同弧面半径、覆层材料厚度的电流密度与焦耳热功率的分布情况。结果表明:对于该口径直线推进机构,在弧面半径增大过程中,最大电流密度的位置会从弧顶向两侧边缘移动,最大值不断增加;钢覆层导轨有效降低了表面电流密度的最大值,但有更高的焦耳热功率;弧面半径为20 mm时,有最均匀的电流密度分布效果,1 mm厚度钢覆层可一定程度降低表面焦耳热功率。该研究结果对凸导轨的优化有一定指导作用。

稻田微型螺旋推进抑草机的设计与试验

为解决稻田机械除草作业中除草率低、伤苗率较高等问题,提出一种光学-机械复合除草方法,该方法通过提高水层浑浊度来抑制杂草光合作用,从而达到除草的目的。通过改进传统的螺旋推进装置,设计一种可适用于稻田土壤环境的微型螺旋推进抑草机。建立滚筒转速对螺旋滚筒工作阻力、运行转速的关系曲线;采用显式动力分析模块LS-DYNA对抑草机在稻田有水环境下的工作过程进行仿真分析,建立螺旋滚筒-土壤-水的耦合模型,进行流固耦合的仿真求解,取得抑草机在作业过程中的切削阻力及功率等参数;通过试验槽样机试验,探究水层深度对水层浑浊度影响的变化规律。结果表明:设计的微型螺旋推进抑草机最优转速为400 r/min;仿真阻力平均值较试验值大5.47%,仿真功率平均值较试验值大6.06%,仿真数据与试验数据的吻合度高,验证了仿真模型的可靠性;当试验槽中水层深度为20、40、60 mm时,浑浊度大于120 NTU的持续时间分别为5、8、8 h。

Initial Development of a Novel Amphibious Robot with Transformable Fin-Leg Composite Propulsion Mechanisms

Amphibious robots are very attractive for their broad applications in resource exploration, disaster rescue, and recon- naissance. However, it is very challenging to develop the robots for their complex, amphibious working environments. In the complex amphibious environment, amphibious robots should possess multi-capabilities to walk on rough ground, maneuver underwater, and pass through transitional zones such as sandy and muddy terrain. These capabilities require a high-performance propulsion mechanism for the robots. To tackle a complex task, a novel amphibious robot （AmphiHex-I） with,transformable fin-leg composite propulsion mechanisms is developed. With the fin-leg composite propulsions, AmphiHex-I can walk on rough and soft substrates and swim in water with many maneuvers. This paper presents the structural design of the transformable fin-leg propulsion mechanism and its driving module. A hybrid model is used to explore the dynamics between the trans- formable legs and transitional environment such as granular medium. The locomotion performances of legs with various ellip- tical shapes are analyzed, which is verified by the coincidence between the model predictions and the simulation results. Further, an orthogonal experiment is conducted to study the locomotion performance of a two-legged platform walking with an asyn- chronous gait in the sandy and muddy terrain. Finally, initial experiments of AmphiHex-I walking on various lands and swimming in water are implemented. These results verify that the transformable fin-leg mechanisms enable the amphibious robot to pass through a complex, amphibious working environment.

Relative position fitting based control strategy for thruster point assembly mechanism of electric propulsion

Purpose-Thruster point assembly mechanism(TPAM)of the electric propulsion system allows to adjust the thrust vector,sothat the thrust vectorisdirectedtothesatellitecenterof gravity(COG)during the satellite on-orbit working period.In this way the impact of disturbance torque caused by deviation of the thrust vector from the satellite COG during thruster ignition can be decreased.Therefore,the control accuracy of satellite is influenced directly by the control accuracy of TPAM.On the other hand,the on-orbit application of TPAM is restricted to the on-orbit computer resource.Therefore,the purpose of this paper is to design a control strategy for TPAM,and the strategy should not only be able to control the TPAM precisely but also be easily implemented by the on-board computer.Design/methodology/approach-First,the structure and work principle of TPAM are discussed,and the mathematical model based on D-H coordinate system is built for it.Then the fitting methods are utilized to design the control strategy of TPAM.Absolute position fitting-based control strategy and relative position fitting-based control strategy are designed,and the least squares algorithm is introduced for parameter selection.Findings-Simulations and tests are provided for the TPAM.Compared with the state-of-the-art PD controller,the proposed control strategy shows smaller overshoot and more simple realization.The experiment results are matched with the simulation results and both the experiment and simulation results show the validity of the proposed control strategies.Practical implications-The designed control strategies can be used for the TPAM of some satellite’s electric propulsion system.Originality/value-The mathematical model of the TPAM based on D-H coordinate system is given.The absolute position fitting-based control strategy and relative position fitting-based control strategy are proposed.Compared with existing methods,the two control strategies have more simple structure and smaller amount of computations.Furthermore,the relative position fitting-based control strategy achieves high precision with simple structure.

北京冬奥会背景下冰雪运动进社区:掣肘因素、推进机制与实现路径

为加速推广群众性冰雪运动,持续推进冰雪运动进社区,以供给侧结构性改革理论为学理依据对我国冰雪运动进社区的掣肘因素、推进机制与实现路径进行了深入探究。研究认为,当前我国冰雪运动进社区供需矛盾凸显。为破解难题,从供给主体、供给保障、供给质量、供给效率、需求主体5个方面剖析了冰雪运动进社区的掣肘因素;在厘定掣肘因素的基础上,提出完善统筹协调机制、市场保障机制、供给考核机制、需求监督机制等冰雪运动进社区的推进机制。为实现冰雪运动进社区的终极目标,从6个维度提出了冰雪运动进社区的实现路径:政府,加快冰雪运动进社区的政策调控;企业,提供社区居民参与冰雪运动的产品与服务;协会,充实冰雪运动进社区的发展模式;社区,筑牢冰雪运动进社区的思想阵地;学校,完善冰雪人才进社区的培养机制;家庭,转变观念成为冰雪运动的支持者与参与者。

喷水推进技术发展综述

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