Assessment of gas thermodynamic characteristics on fluidic thrust vectoring performance: Analytical,experimental and numerical study

The cross injection in a supersonic flow is an issue encountered in several aerodynamic applications such as fuel injection in scramjet combustor, missile control, drag reduction and thrust vector control. In a recent work, an analytical model has been presented to calculate the fluidic thrust vectoring performance for a supersonic axisymmetric nozzle. The model is able to take into account both the injected gas thermodynamic properties and the geometrical nozzle characteristics. The analytical model has been successfully validated following the cold air flow experimental analysis, in the case of fluidic thrust vectoring applied to conical nozzle. The aim of this work is to show how far the injected gas thermodynamic properties, different from that of the nozzle main flow, could influence the fluidic thrust vectorization parameters.In this work, the experimental performance of the fluidic thrust vectoring concept, using numbers of gases as injectant, has been qualitatively and quantitatively analyzed. Schlieren visualization, force balance and wall pressure measurements were used in the case of a truncated ideal contour nozzle. The experimental results are compared to the numerical and analytical findings.Performance analysis are conducted and basic conclusions are drawn in terms of thermodynamic gas properties effect on the fluidic thrust vector system. The primary effect was related to the gas molecular weight and its specific heat ratio product. It is observed that for fixed injection conditions, the vectoring angle is higher when the injected gas molecular weight and specific heat ratio product is less than that of the primary gas. For a given mission of the launcher, it can be concluded that the mass of the embedded gas, used for the fluidic vectorization system, can be significantly reduced, depending on its molecular weight and specific heat ratio.     

Measurement on Friction Coefficients of Tire Grounding Surface in Arbitrary Directions under High-Load

In order to measure friction coefficients of tire grounding surfaces in car running, a simple cantilever-type tactile sensor that can detect the vertical load and friction force applied to the sensing part as well as direction of the friction force, simultaneously, has been proposed. The present study equips the proposed sensor to a tire and confirms that the sensor can measure the friction coefficient of the tire grounding surface. For this purpose, measurements in this study were conducted using a sensor under a similar load as that of a common automobile travelling in an arbitrary direction. In order to perform the experiments under a high load in an arbitrary direction, we developed a parallel mechanism-type tire-driving device. The developed device can apply a high load to the tire in an arbitrary direction and can measure the vertical load, friction force, and the direction of the friction force applied to the tire involving the sensor. Thus, the measurement accuracy of the proposed sensor can be verified by comparing the output of the sensor to that of the driving device. As a result of this study, we clarified that the measurement values of the sensor are affected by the deformation of the tire, and proposed a method for correcting the effect of the tire deformation. By introducing the proposed correction method to the measurement of the sensor, it was confirmed that the friction coefficients of various surfaces can be measured with sufficient accuracy under a practical high-load condition.     

An instrumented vehicle for offroad dynamics testing

The paper presents an instrumented vehicle that was equipped with measuring systems to perform complete dynamics tests, especially in off-road conditions. The equipment consists of four wheel dynamometers, a steering robot, and a differential GPS system together with an inertial platform, a non-contact vehicle speed sensor, and an on-board computer with software to control the devices and collect experimental data. The four wheel dynamometers measure six elements; based on strain gage force transducers, it measures three orthogonal forces and three moments. The steering robot can control the steering wheel of the vehicle at a variety of excitation modes; it can carry out typical vehicle dynamics tests (ISO 7401, ISO 4138, ISO/TR3888, etc.) as well as custom engineered tests at a wide range of setting parameters (steer angle rate up to 1600 deg/s). The differential GPS system gives true time vehicle kinematics data (velocities, accelerations, angles, etc.) at 10-ns sample rate and 20-mm accuracy. The base vehicle, a Suzuki Vitara 4 × 4, required no special modifications or changes to install the measuring equipment. The paper also describes typical tests performed with the use of the instrumented vehicle together with sample results.     

A hybrid multi-degree-of-freedom vibration isolation platform for spacecrafts by the linear active disturbance rejection control

The hybrid vibration isolation, which takes advantages of both the passive and active approaches, has been an important solution for space missions. The objective of this paper is to design a vibration isolation platform for payloads on spacecrafts with the robust, wide bandwidth, and multi-degree-of-freedom(MDOF). The proposed solution is based on a parallel mechanism with six voice-coil motors(VCMs) as the actuators. The linear active disturbance resistance control(LADRC) algorithm is used for the active control. Numerical simulation results show that the vibration isolation platform performs effectively over a wide bandwidth, and the resonance introduced by the passive isolation is eliminated. The system robustness to the uncertainties of the structure is also verified by simulation.     

Disturbance compensation of a dual-arm underwater robot via redundant parallel mechanism theory

Disturbance compensation is one of the major issues for underwater robots to hover as a mobile platform and to manipulate an object in an underwater environment. This paper presents a new strategy of disturbance compensation for a mobile dual-arm underwater robot using internal torques derived from redundant parallel mechanism theory. A model of the robot was analyzed by redundant serial and parallel mechanisms at the same time. The joint torque to operate the robot is obtained from a redundant serial mechanism model with null-space projection due to redundancy. The joint torque derived from the redundant parallel kinematic model is calculated to perfectly compensate for disturbances to the mobile platform and is included in the solution of the joint torque based on the serial redundant model. The resultant joint torque can generate force on the end-effector for required tasks and forces for disturbance compensation simultaneously . A simulation shows the performance of this disturbance compensation strategy. The joint torque based on the algorithm generates the desired task force and the disturbance compensation force together, and a little additional joint torque can generate a large internal force effectively due to the characteristics of a redundant parallel mechanism. The proposed method is more effective than compensation methods using thrusting force on the mobile platform.     

On human–robot interaction of a 3-DOF decoupled parallel mechanism based on the design and construction of a novel and low-cost 3-DOF force sensor

This paper addresses the extension of a 3-degrees-of-freedom (3-DOF) decoupled parallel mechanism for human–robot interaction purposes. To this end, a low-cost 3-DOF force sensor for human–robot interaction applications is proposed, designed and constructed. In the latter force sensor, five load cells are placed in order to identify the amount of the applied force along each Cartesian direction. In addition, an experimental identification procedure based on least square method is carried out in order to obtain the first and third degree polynomial models of the sensor output model. From the practical tests it has been reveled that the force sensor has a reasonable precision of 0.1 N in both x and y-axes and 0.2 N in z-axis, within a range of 5 N which is suitable for human–robot interaction applications. Then, using the proposed force sensor, two control methods, namely “position control” and “speed control” are applied for human–robot interaction purposes and their performances are compared.     

Global multistability and analog circuit implementation of an adapting synapse-based neuron model

This paper proposes a MEMS resonant pressure sensor through implementing an out-of-plane repulsive (levitation) force to enhance the sensor detection threshold and consequently widen its sensing range. 2D and 3D finite-element simulations are conducted and compared to some available experimental data. The simulated results show an increase in the generated levitation force as outstanding merit owing to the added side upper electrodes. The levitation force is then further increased by lateral spacing optimization in association with the assumed applied voltage, which decreases the overall size (footprint) as well. The dynamical behavior around the static equilibrium is first numerically solved using the so-called shooting technique and then compared with an available online simulation tool: the “Matcont” package. The simulated results prove the capability of the online simulator to capture the dynamic response of the resonant micro-sensor when approaching its respective bifurcation points where the stable and unstable branches collide, when in contrary, the shooting technique failed to get the dynamic responses when passing by these bifurcations. Thanks to the fast converging outcomes of the “Matcont” online simulation equipped with simultaneous stability analysis, a comprehensive analysis of the micro-sensor dynamical response is conducted. Three sensing mechanisms as: measurements of frequency shift, amplitude alternation, and amplitude rise/fall near a bifurcation region are evaluated and characterized. Along with enumerating the strengths of the proposed sensor over the conventional capacitive pressure sensors, the advantage of measuring the amplitude rise/fall near the corresponding bifurcation region comparing to the two other sensing mechanisms is detailed, and its possible failure for performance repeatability is resolved by means of the slow-varying frequency sweep. Unlike the traditional parallel-plate configuration in which only one-side frequency shift is observed, in this proposed design, two-sides frequency shift is detected, and accordingly, the reinitialization is categorized based on that. As compared to the conventional MEMS pressure sensor, this revisited design equipped with the suggested sensing mechanism offers wider tunability and sensing range, resolution power enhancement, and simplification of the signal processing circuit.

     

Open and closed-loop control of transonic buffet on 3D turbulent wings using fluidic devices

This paper presents an overview of the work performed recently at ONERA on the control of the buffet phenomenon. This aerodynamic instability induces strong wall pressure fluctuations and as such limits aircraft envelope; consequently, it is interesting to try to delay its onset, in order to enlarge aircraft flight envelop, but also to provide more flexibility during the design phase. Several types of flow control have been investigated, either passive (mechanical vortex generators) or active (fluidic VGs, fluidic trailing-edge device (TED)). It is shown than mechanical and fluidic VGs are able to delay buffet onset in the angle-of-attack domain by suppressing the separation downstream of the shock. The effect of the fluidic TED is different, the separation is not suppressed, but the rear wing loading is increased and consequently the buffet onset is not delayed to higher angles of attack, but only to higher lift coefficient. Then, a closed loop control methodology based on a quasi-static approach is defined and several architectures are tested for various parameters such as the input signal, the objective function or, the tuning of the feedback gain. All closed loop methods are implemented on a dSPACE device calculating in real time the fluidic actuators command from the unsteady pressure sensors data.     

Development of co-current air–water flow in a vertical pipe

Measurements of the cross-sectional distribution of the gas fraction and bubble size distributions were conducted in a vertical pipe with an inner diameter of 51.2 mm and a length of about 3 m for air/water bubbly and slug flow regimes. The use of a wire-mesh sensor obtained a high resolution of the gas fraction data in space as well as in time. From this data, time averaged values for the two-dimensional gas fraction profiles were decomposed into a large number of bubble size classes. This allowed the extraction of the radial gas fraction profiles for a given range of bubble sizes as well as data for local bubble size distributions. The structure of the flow can be characterized by such data. The measurements were performed for up to 10 different inlet lengths and for about 100 combinations of gas and liquid volume flow rates. The data is very useful for the development and validation of meso-scale models to account for the forces acting on a bubble in a shear liquid flow and models for bubble coalescence and break-up. Such models are necessary for the validation of CFD codes for the simulation of bubbly flows.     

微重力下Stewart平台的主动减振系统研究分析

Stewart平台是一种并联减振机构,因其具有承载能力强、刚度大、结构稳定、精度高等优点,广泛应用于航天航空和精密仪器领域。采用Cubic构型Stewart平台并对压电陶瓷的力一位移关系线性化后,可简化成单自由度的线性主动控制系统,对六自由度的Stewart平台分散控制,在随机平稳白噪声的激励下考虑时滞影响,并对其解耦后的Stewart平台进行LQR数值分析,用Adams预测公式进行时滞补偿。分析结果表明：Stewart平台具有较好的减振性能,能有效减小平台在微重力干扰下引起的位移反应;时滞因素会降低LOR的控制作用;可通过Adams预测公式对时滞影响进行较好地补偿。     

Surface plasmon resonance reflectance imaging technique for near-field (~100 nm) fluidic characterization

Surface plasmon resonance (SPR) reflectance imaging technique is devised as a label-free visualization tools to characterize near-field (100 nm) fluidic transport properties. The key idea is that the SPR reflectance intensity varies with the near-field refractive index (RI) of the test fluid, which in turn depends on the micro/nano-fluidic scalar properties, such as concentrations, temperatures, and phases. The SPR sensor techniques have been widely used in many different areas, particularly in the biomedical and biophysical societies. While flow visualization techniques based on RI detection have been extensively well documented (Merzkirch 1987), the use of SPR imaging for fluidic applications has been introduced only recently since the author’s group presented a series of related studies in the past few years. The primary goal of this review article is two-fold: (1) Introduction of the working principles of the SPR imaging as a fluidic sensor, and (2) Presentation of example measurement applications for various fluidic scalar properties using the SPR imaging sensor technique. Section 1 summarizes the history and the basic principle of SPR by focusing on the Kretschmann’s theory and Sect. 2 describes the laboratory SPR imaging system specifically designed for fluidic applications. Section 3 presents the optical and material properties that affect the SPR measurement capabilities and sensitivity. Section 4 presents example applications of the implemented SPR for different near-field characterization problems, including (1) micromixing concentration field, (2) convective/diffusion of salinity distributions, (3) full-field thermometry, and (4) fingerprinting of crystallized nanofluidic self assembly. Sections 5 and 6 discuss the spatial measurement resolutions of the SPR imaging technique and the overall measurement sensitivities, respectively. Section 7 presents a few suggestions to further enhance the SPR measurement accuracy particularly for near-field fluidic characterization.     

STABILITY ANALYSIS OF REUSABLE LAUNCH VEHICLE LANDING STRUCTURE$^{\bf 1)}$

近年来,包括中国在内的诸多国家相继开展垂直起降重复使用火箭的研究,运载火箭在平台上垂直着陆时的着陆稳定性为实现运载火箭重复使用的关键问题. 由于在运载火箭设计初期结构设计尚未完成,不具有供着陆稳定性分析的详细的动力学模型,难以开展着陆过程动力学仿真,故对运载火箭着陆稳定性评估方法的研究尤为必要. 本文基于广义碰撞定律,对二维运动模式下运载火箭与着陆平台的多点碰撞过程进行了分析,切向采用库伦摩擦模型给出了切向运动学恢复系数的表达式. 本文首先通过机械能约束和接触碰撞中的单边约束给出了一般运动形式下广义运动学恢复系数的值域,再对两种典型运动模式,给出了该两种典型运动模式下广义运动学恢复系数的值域. 然后考虑着陆腿中缓冲器的作用,将运载火箭与平台的碰撞近似为完全非弹性碰撞,得到了其广义运动学恢复系数,并结合运动学分析和能量法提出了一种基于碰撞后速度的着陆稳定性的判别方法. 最后以某型运载火箭着陆样机的参数为例,分析了碰撞前速度、着陆腿跨距、摩擦系数对着陆稳定性的影响,结果表明,本文提出的稳定性判别方法较能量法更为精确,可以考虑触地速度、角速度、摩擦系数等参数间的耦合关系.     

Foot force distribution of walking machine with consideration of terrain properties

Determination of foot force distribution during walking is important to the simulation and control of the vehicle. This problem was often considered as an indeterminate problem and several optimization methods were proposed. The indeterminancy, which was due to the assumption of rigid bodies, can, however, be removed by incorporating the compliance equations into the equations of equilibrium. Based on such a compliant model, a s stiffness matrix method was developed to determine the foot force distribution. However, due to the complexity of the problem, the compliance of terrain in the stiffness matrix method was considered either negligible or as a linear spring model. In this paper, two realistic terrain models are incorporated into the stiffness matrix method to study the effect of terrain properties on foot force distribution during walking. These two terrain models are the three-parameter solid model and the four-parameter Burgers model. The former is a model of clay terrain while the latter is a model of a paddy field. These models are extended to three dimensions and then combined with the leg compliances to form the stiffness matrix of the system. The simulation results show that the terrain compliance has significant effect on foot force distribution. For example, it is observed that this compliance helps to distribute the foot forces evenly and to minimize the frictional angles.     

重复使用火箭着陆结构稳定性分析

近年来,包括中国在内的诸多国家相继开展垂直起降重复使用火箭的研究,运载火箭在平台上垂直着陆时的着陆稳定性为实现运载火箭重复使用的关键问题. 由于在运载火箭设计初期结构设计尚未完成,不具有供着陆稳定性分析的详细的动力学模型,难以开展着陆过程动力学仿真,故对运载火箭着陆稳定性评估方法的研究尤为必要. 本文基于广义碰撞定律,对二维运动模式下运载火箭与着陆平台的多点碰撞过程进行了分析,切向采用库伦摩擦模型给出了切向运动学恢复系数的表达式. 本文首先通过机械能约束和接触碰撞中的单边约束给出了一般运动形式下广义运动学恢复系数的值域,再对两种典型运动模式,给出了该两种典型运动模式下广义运动学恢复系数的值域. 然后考虑着陆腿中缓冲器的作用,将运载火箭与平台的碰撞近似为完全非弹性碰撞,得到了其广义运动学恢复系数,并结合运动学分析和能量法提出了一种基于碰撞后速度的着陆稳定性的判别方法. 最后以某型运载火箭着陆样机的参数为例,分析了碰撞前速度、着陆腿跨距、摩擦系数对着陆稳定性的影响,结果表明,本文提出的稳定性判别方法较能量法更为精确,可以考虑触地速度、角速度、摩擦系数等参数间的耦合关系.      

Pure delayed non-fragile control for offshore steel jacket platforms subject to non-linear self-excited wave force

This paper is concerned with pure delayed non-fragile control for an offshore steel jacket platform subject to non-linear self-excited wave force. By purposefully introducing a proper time-delay into control channel, a pure delayed non-fragile controller (DNFC) is proposed to improve performance of the offshore steel jacket platform. The positive effects of time-delays on non-fragile stabilization control for the system are investigated. It is shown through simulation results that (i) the DNFC and the delay-free non-fragile controller are capable of attenuating the vibration of the offshore platform to almost the same level, while the required control force under the DNFC is less than that under the delay-free one; and (ii) both the oscillation amplitudes of the offshore platform and the ranges of the control force under the pure delayed state feedback controller (DSFC) are smaller than the ones under the non-linear controller and the dynamic output feedback controller; and (iii) the oscillation amplitudes of the offshore platform under the DSFC are almost the same as the ones under integral sliding mode controller and the delayed dynamic output feedback controller, while the control force required by the former is less than the one by the latter.     

Closed-loop bluff-body wake stabilization via fluidic excitation

This article describes an experimental study aimed at stabilizing the wake of a shedding bluff-body by means of closed-loop active flow control at low Reynolds numbers. A D-shaped (6.5?mm thick) cylinder was used to allow a direct wake interaction rather than mixed wake-boundary-layer separation control. The fluidic actuators, installed inside the thin body, were ideally located at the separation locations, i.e., the trailing edges?? upper and lower corners. The wake unsteadiness was monitored by a pair of hot wires (HWs), while a single surface-mounted hot-film (HF) sensor was used as a frequency and phase reference for closed-loop control. The HF signal was contaminated by noise. Hence, a technique for real-time tracking of a low signal-to-noise ratio (SNR) signal was necessary. This was achieved by means of a Phase-Locked Loop (PLL), common in communications systems. The closed-loop scheme was based on real-time measurement of the wake-state, using the surface-mounted HF sensor, and control authority imposed by the fluidic actuators. By using opposition control at frequencies close to the natural vortex shedding frequency (VSF), it was possible to significantly reduce the wake unsteadiness. Applying the same approach, but sensing the wake HW signal, rather than the surface-mounted HF signal, as the controller input did not result in wake stabilization. On the contrary, the unsteadiness increased at all the tested conditions. It is expected that a similar approach would work at much higher Reynolds numbers as well, as long as a clearly identifiable and nominally 2D vortex shedding occurs, even when the background flow is fully turbulent.     

Hybrid approach for dynamic model identification of an electro-hydraulic parallel platform

In this paper, a hybrid optimization algorithm is proposed to identify the dynamic parameters of a 6-DOF electro-hydraulic parallel platform. The dynamic model of a parallel platform with arbitrary geometry, inertia distribution and frictions is obtained based on a structured Boltzmann–Hamel–d’Alembert formulation, and then the estimation equations are explicitly expressed in terms of a linear form with respect to the identified inertial and the friction coefficients in accordance with a linear friction model. However, when nonlinear friction models are considered, the parameter identification of the electro-hydraulic parallel platform is considered as an optimization process with an objective function minimizing the errors between the measurement and identification, and then an effective combination of the particle swarm optimization (PSO) method and the local quasi-Newton method is proposed to solve the identification problem. Experimental identification processes are carried out for the identified parameters, and the identified models are compared by the predicted forces between the LS method and the optimization technique as well as between the linear and nonlinear friction models.     

Inverse dynamics of a 3-PRC parallel kinematic machine

Recursive matrix relations for kinematics and dynamics analysis of a three-prismatic-revolute-cylindrical (3-PRC) parallel kinematic machine (PKM) are performed in this paper. Knowing the translational motion of the platform, we develop first the inverse kinematical problem and determine the positions, velocities and accelerations of the robot’s elements. Further, the inverse dynamic problem is solved using an approach based on the principle of virtual work and the results in the framework of the Lagrange equations with their multipliers can be verified. Finally, compact matrix equations and graphs of simulation for input force and power of each of three actuators are obtained. The investigation of the dynamics of this parallel mechanism is made mainly to solve successfully the control of the motion of such robotic system.     

Kinematic analysis of a 5-R SP parallel mechanism with?centralized motion

The paper presents a kinematic analysis of a parallel mechanism, referred to here as a mechanism with centralized motion. The paper includes a proof, based on the geometry of the mechanism, that the platform exhibits centralized motion. An interesting feature of this parallel mechanism is that it is partially collapsible which may be beneficial in practical applications where storage space is limited. The platform is connected to a base, regarded as fixed in this paper, by five identical legs where each leg is a three-link chain connected by a revolute joint, a spherical joint, and a prismatic joint. The result is that the platform has a screw motion about an axis which is perpendicular to the base and passes through the centroids of the base and the platform, for all positions of the platform. The pitch of the instantaneous screw depends on the platform assembly configuration and is a function of the platform position and orientation. To complete the kinematic study, the paper includes closed-form solutions to the inverse and forward position and velocity problems. Finally, the paper includes several numerical examples to illustrate some of the key features of this novel parallel mechanism.     

关节混合空间控制下的冗余绳驱并联机器人绳力分布特性分析

绳驱并联机器人是由绳索代替刚性杆件的一类特殊机器人,其中绳索具有只能承受拉力而不能承受压力的特点,冗余绳驱并联机器人的绳力分配问题是一个难点.在关节混合空间控制中,将冗余的绳索组合采用绳力控制,而其余绳索进行绳长控制.因为不同的绳索组合可能导致不同的控制效果,本研究旨在解决关节混合空间控制条件下,力控绳索组合的选择问题.以二冗余绳驱并联机器人为例,通过向量空间基变换方法,实现了冗余绳驱系统绳力在拉力索张力空间的表达.基于拉力索张力空间,计算了绳力控制绳索组合的对称最大误差带,用于找到合适的绳索组合用于力控.使用多体动力学仿真手段,对关节混合空间的控制效果和对称最大误差带解析解计算方法的正确性进行了模拟验证.在同时考虑绳长和绳力控制误差的条件下,发现当选择不合适的绳索组合时,绳力误差会被显著放大,说明了本文针对绳力分布特性分析的意义.本文提出的对称最大误差带概念同时也为关节混合空间控制策略下的绳力控制器设计提供指导.