自适应半主动悬架系统机械硬件在环试验研究

车辆处于加速、制动或转向工况时,运动惯性会导致车身发生俯仰、侧倾运动,如果幅值过大将使乘员产生紧张、眩晕等不舒适感。为解决此问题,提出一种基于车身姿态补偿控制与天棚加速度控制相结合的算法,建立自适应阻尼控制系统,不仅可使车辆垂向运动的振动效果得到改善,还能兼顾车身俯仰、侧倾控制,使其控制效果更加接近主动悬架。另外,搭建一种新型的减振器机械硬件在环试验台,可以对车辆垂向、俯仰及侧倾运动进行控制算法有效性验证,能克服四分之一减振器台架仅能验证车辆垂向运动的局限性。试验结果表明,与被动悬架相比,该算法在不同车速工况下B级路面和C级路面质心加速度幅值平均降幅达21.16%和13.21%,不同减速度和加速度工况下俯仰角波动峰峰值平均降幅达25.50%和28.82%,蛇形工况下不同车速的侧倾角幅值也均有降低。     

Joint kinematics and kinetics of overground accelerated running versus running on an accelerated treadmill

Literature shows that running on an accelerated motorized treadmill is mechanically different from accelerated running overground. Overground, the subject has to enlarge the net anterior–posterior force impulse proportional to acceleration in order to overcome linear whole body inertia, whereas on a treadmill, this force impulse remains zero, regardless of belt acceleration. Therefore, it can be expected that changes in kinematics and joint kinetics of the human body also are proportional to acceleration overground, whereas no changes according to belt acceleration are expected on a treadmill. This study documents kinematics and joint kinetics of accelerated running overground and running on an accelerated motorized treadmill belt for 10 young healthy subjects. When accelerating overground, ground reaction forces are characterized by less braking and more propulsion, generating a more forward-oriented ground reaction force vector and a more forwardly inclined body compared with steady-state running. This change in body orientation as such is partly responsible for the changed force direction. Besides this, more pronounced hip and knee flexion at initial contact, a larger hip extension velocity, smaller knee flexion velocity and smaller initial plantarflexion velocity are associated with less braking. A larger knee extension and plantarflexion velocity result in larger propulsion. Altogether, during stance, joint moments are not significantly influenced by acceleration overground. Therefore, we suggest that the overall behaviour of the musculoskeletal system (in terms of kinematics and joint moments) during acceleration at a certain speed remains essentially identical to steady-state running at the same speed, yet acting in a different orientation. However, because acceleration implies extra mechanical work to increase the running speed, muscular effort done (in terms of power output) must be larger. This is confirmed by larger joint power generation at the level of the hip and lower power absorption at the knee as the result of subtle differences in joint velocity. On a treadmill, ground reaction forces are not influenced by acceleration and, compared with overground, virtually no kinesiological adaptations to an accelerating belt are observed. Consequently, adaptations to acceleration during running differ from treadmill to overground and should be studied in the condition of interest.     

Knee extension moment arm variations relate to mechanical function in walking and running

The patellofemoral joint plays a crucial mechanical role during walking and running. It increases the knee extensor mechanism''s moment arm and reduces the knee extension muscle forces required to generate the extension moment that supports body weight, prevents knee buckling and propels the centre of mass. However, the mechanical implications of moment arm variation caused by patellofemoral and tibiofemoral motion remain unclear. We used a data-driven musculoskeletal model with a 12-degree-of-freedom knee to simulate the knee extension moment arm during walking and running. Using a geometric method to calculate the moment arm, we found smaller moment arms during running than during walking in the swing phase. Overall, knee flexion causes differences between running and walking moment arms as increased flexion causes a posterior shift in the tibiofemoral rotation axis and patella articulation with the distal femur. Moment arms were also affected by knee motion direction and best predicted by separating by direction instead of across the entire gait cycle. Furthermore, we found high inter-subject variation in the moment arm that was largely explained by out-of-plane motion. Our results are consistent with the concept that shorter moment arms increase the effective mechanical advantage of the knee and may contribute to increased running velocity.     

A collisional perspective on quadrupedal gait dynamics

The analysis of terrestrial locomotion over the past half century has focused largely on strategies of mechanical energy recovery used during walking and running. In contrast, we describe the underlying mechanics of legged locomotion as a collision-like interaction that redirects the centre of mass (CoM). We introduce the collision angle, determined by the angle between the CoM force and velocity vectors, and show by computing the collision fraction, a ratio of actual to potential collision, that the quadrupedal walk and gallop employ collision-reduction strategies while the trot permits greater collisions. We provide the first experimental evidence that a collision-based approach can differentiate quadrupedal gaits and quantify interspecific differences. Furthermore, we show that this approach explains the physical basis of a commonly used locomotion metric, the mechanical cost of transport. Collision angle and collision fraction provide a unifying analysis of legged locomotion which can be applied broadly across animal size, leg number and gait.     

大型刚体惯性参数识别的三线扭摆系统实验方法改进研究

精确获取汽车动力总成刚体惯性参数是发动机悬置系统设计的重要前提之一。利用三线扭摆法测量刚体单轴转动惯量精度较高的特点,基于表面固定点确定刚体方位的三点定位方法和测量6个~9个不同方位的多次测量原理,发展了一套适合于大型复杂刚体的惯性参数识别方法。关键技术有:(1)选取刚体表面三个定位点定义一个刚体随动坐标系以描述刚体方位;(2)通过测量刚体定位点至托盘表面参考点(定义一个整体坐标系)的距离,计算出定位点在整体坐标系下的坐标和两个坐标系之间的转换关系;(3)求出各组实验中在动坐标系下的刚体转轴方位和转动惯量;(4)运用最小二乘原理,求解多个转轴的最优交点得到动坐标系下的刚体质心坐标,求解由转动惯量转轴定理导出的线性方程组得到刚体惯性矩阵。实验方法中容易引起误差的环节较多,但是可以根据最小二乘原理进行逐级误差估计和控制。通过误差分析、长方体质量块实验验证和大量的汽车动力总成惯量参数识别实验,证明了该方法的实用性和可靠性。     

Constructing predictive models of human running

Running is an essential mode of human locomotion, during which ballistic aerial phases alternate with phases when a single foot contacts the ground. The spring-loaded inverted pendulum (SLIP) provides a starting point for modelling running, and generates ground reaction forces that resemble those of the centre of mass (CoM) of a human runner. Here, we show that while SLIP reproduces within-step kinematics of the CoM in three dimensions, it fails to reproduce stability and predict future motions. We construct SLIP control models using data-driven Floquet analysis, and show how these models may be used to obtain predictive models of human running with six additional states comprising the position and velocity of the swing-leg ankle. Our methods are general, and may be applied to any rhythmic physical system. We provide an approach for identifying an event-driven linear controller that approximates an observed stabilization strategy, and for producing a reduced-state model which closely recovers the observed dynamics.     

测量物体转动惯量的新方法研究

利用刚体绕定轴转动的动能定理,在建立了单轴气浮台绕定轴转动的转动惯量与时间关系的基础上,提出了一种基于单轴气浮台利用能量衰减测量物体转动惯量的新方法。通过理论推导得出了测量物体转动惯量的实验计算式,并进行了实验验证,实验测量结果与理论计算结果的相对误差均在±0.5%以内。     

转动惯量测量系统的研制

介绍了一种新的利用三线摆测量转动惯量的系统及方法,该方法采用传感器和数据采集装置采集计算转动惯量所需的周期信号和力信号;并通过开发出专门的软件,最终计算出待测物体的转动惯量。该方法将机械装置与电子部件和计算机相结合,与原有的传统测量方法相比,避免了手动操作和人工计算,方便实用,能够对大型刚体进行测量;整个过程趋于自动化,提高了测量精度和效率。     

White noise excitation of road vehicle structures

Heave and pitch motions of road vehicle structures affect the comfort and the safety of passengers. Excitation of these vertical vibrations is due to road surface roughness. Road vehicle structures are modelled as mechanical systems characterized by their inertia, damping and stiffness, and represented as state equations. This paper deals with the influence of random road profiles on the vertical dynamics of road vehicles characterized by stochastic processes. Switching from road profile displacement to road profile velocity results in white noise excitation facilitating mathematical analysis. Some fundamentals of power spectral density analysis and covariance analysis are reviewed. A quarter car model is used to show the advantages of the covariance analysis resulting immediately in standard variations characterizing the vehicle’s performance. A list of symbols is given at the end of the paper This paper is dedicated to Prof R N Iyengar of the Indian Institute of Science on the occasion of his formal retirement.     

The effect of graphite addition on the mechanical and tribological properties of pitch-based granular carbon composites

The present work deals with the effect of graphite addition on selected mechanical and tribological properties of pitch-based granular carbon composites. Three pitches (a commercial impregnating coal tar pitch, an air-blown pitch and a thermally treated coal tar pitch) and anthracite particles as reinforcing material were used to prepare carbon composites to be tested as carbon brake pads. These carbon composites show good compression strength (from 25.8 to 94.2 MPa) but unstable and high friction coefficients (>0.5). Experimental results have showed that small amounts of graphite addition (2.5 and 5.0 wt%) lead to carbon materials with more stable and lower friction coefficient (<0.3). So, graphite addition promoted the reduction in the wear rate. Finally, compressive strength of carbon composites prepared with modified pitches significantly increases after addition of small amounts of graphite with values from 94 to 128.8 MPa.     

金属托盘面板弯曲力学性能研究及有限元分析

目的确认以镀锌钢为材质的面板是否适合物流金属托盘包装,并对其弯曲变形力学性能进行研究。方法通过SolidWorks软件对金属面板进行建模,利用力学相关知识建立面板的形心位置模型及惯性矩求解方法。同时在Ansys Workbench中对长度为600~1200 mm之间的面板进行位移弯曲变形仿真,及对面板的最大挠度理论计算过程进行推导。结果得到了面板的精确形心位置y_p=10.334 mm,惯性矩I_(zp)=1.372×10~(-8) m~4,以及不同长度面板的最大位移变形理论与仿真数值。结论提供了金属托盘面板弯曲变形的理论计算方法,进一步确认了金属托盘面板在物流包装中的耐用性、实用性,该研究为金属托盘力学性能探讨、结构优化提供依据。     

Characterising heave,pitch, and roll motion of road vehicles with principal component and frequency analysis

For the great majority of transport vehicles, the magnitude of the heave vibration is generally more severe than pitch and roll. Consequently, the measurement, analysis, and simulation of the vehicle vibrations have been focused on vertical vibration. Despite this, it is now being increasingly recognised that the combination of heave, pitch, and roll vibratory motion can induce more severe damage to shipments than vertical vibration alone. Although the pitch and roll motion of road vehicles can now be readily measured, there is little information on how to analyse the data to produce meaningful statistical relationships between the three variables. This paper builds upon previous work that showed that there is some correlation between pitch, roll, and heave motion and that these relationships are dependent on vehicle geometry, including payload mass, centre of mass, vehicle roll centre, and moments of inertia as well as vehicle speed and the road surface. In this paper, data from a range of quasi‐controlled experiments, which involved driving vehicles at constant‐speed on selected roads, were analysed using principal component analysis as well as frequency domain analysis to reveal the relationship between heave, pitch, and roll motion. This was undertaken for a variety of vehicle speeds and routes in order to establish if they influence pitch and roll response. Results are presented in the form of distribution functions, statistical coefficients, and frequency response functions, all of which are useful for helping to define parameters for the simulation of complete, three‐axis vibrations using multi‐axis vibration test systems.     

葵花型索穹顶结构力学性能及拉索破断试验研究

通过对一直径6m的葵花型索穹顶试验模型,进行竖向对称加载、非对称加载以及拉索瞬间破断试验,研究了该结构的受力特点以及单根拉索瞬间破断时结构的响应特征。应用非线性有限元数值计算方法建立索穹顶计算模型,对葵花型索穹顶结构的力学性能进行了分析,并与试验结果进行比较。结果表明：在各加载阶段,节点竖向位移实测值普遍较计算结果偏大,拉索索力实测值与计算结果总体吻合较好;对称加载过程,结构的荷 载-位移关系具有较好的线性规律;与对称加载比较,非对称加载的荷载-位移关系则表现出非线性,节点位移也较大,非对称荷载对结构竖向刚度的设计起控制作用;单根拉索瞬间破断时,结构会有微幅振动,不同位置拉索的失效对结构的影响程度不尽相同。     

The human foot and heel–sole–toe walking strategy: a mechanism enabling an inverted pendular gait with low isometric muscle force?

Mechanically, the most economical gait for slow bipedal locomotion requires walking as an ‘inverted pendulum’, with: I, an impulsive, energy-dissipating leg compression at the beginning of stance; II, a stiff-limbed vault; and III, an impulsive, powering push-off at the end of stance. The characteristic ‘M’-shaped vertical ground reaction forces of walking in humans reflect this impulse–vault–impulse strategy. Humans achieve this gait by dissipating energy during the heel-to-sole transition in early stance, approximately stiff-limbed, flat-footed vaulting over midstance and ankle plantarflexion (powering the toes down) in late stance. Here, we show that the ‘M’-shaped walking ground reaction force profile does not require the plantigrade human foot or heel–sole–toe stance; it is maintained in tip–toe and high-heel walking as well as in ostriches. However, the unusual, stiff, human foot structure—with ground-contacting heel behind ankle and toes in front—enables both mechanically economical inverted pendular walking and physiologically economical muscle loading, by producing extreme changes in mechanical advantage between muscles and ground reaction forces. With a human foot, and heel–sole–toe strategy during stance, the shin muscles that dissipate energy, or calf muscles that power the push-off, need not be loaded at all—largely avoiding the ‘cost of muscle force’—during the passive vaulting phase.     

车用电涡流缓速器试验台组合飞轮系设计及优化

  飞轮系是车用电涡流缓速器试验台用来模拟车辆惯性的关键部件。根据能量守恒理论,给出了汽车质量的表达形式,建立了所模拟汽车的质量相对应的转动惯量与汽车参数（车身重量G、车轮半径r、前后车轮制动力分配比β）之间的关系。设计了一种结构新颖的组合飞轮系。在考虑实际应用要求的前提下,总结出一套可行的飞轮系转动惯量优化组合方案。利用有限元模态分析方法,对组合优化后的飞轮系进行模态分析,得到了飞轮系固有频率和振型,为试验台运行时避免共振提供了依据。     

舰载电视跟踪仪鲁棒自稳定控制

船体在海面上受风、浪、流的影响而发生周期性的横摇、纵摇和艏摇运动, 直接安装在甲板上的电视跟踪仪将跟随船体发生同样幅度的摇摆运动, 从而使视轴摆动, 造成电视图像模糊, 甚至丢失目标. 为了保证电视跟踪仪海上跟踪测量的平稳性和准确性, 基于惯性导航系统给出的横摇和纵摇位置数据, 建立了包含艏摇的完整的三自由度船摇自稳定数学模型, 并且在 Matlab 仿真环境中采用闭环增益成形控制算法进行了三自由度船摇自稳定系统的数字仿真, 结果表明所设计方法能够提高舰载电视跟踪仪的跟踪精度并使电视图像清晰.     

火箭炮交流位置伺服系统的鲁棒最优控制

为了实现某火箭炮交流伺服系统的高速、高精度位置控制,针对实际系统中存在的转动惯量和负载力矩变化大、冲击力矩强等各种不确定因素,提出了一种鲁棒最优控制方法。实验结果表明,该控制器鲁棒性强,而且具有较好的动态性能及稳态精度。     

Response probability structure of a structurally nonlinear fluttering airfoil in turbulent flow

The stationary probability structure for the aeroelastic response of a structurally nonlinear fluttering airfoil subject to random turbulent flow is examined numerically. The airfoil is modelled as a two-dimensional flat plate with degrees of freedom in torsion and heave (vertical displacement). The nonlinearity is a hardening cubic stiffness force in the torsional direction. The aerodynamic force and moment are assumed to be linear, thus limiting the analysis to small oscillations; unsteady effects are retained. Furthermore, both parametric and external random coloured excitations are considered. It is found that depending on the value of turbulence variance and nonlinear cubic stiffness coefficient, the pitch marginal probability density functions (PDF) exhibits uni-, bi- or double bi-modality; the nature of the bi-modality is not unique. An explanation of the behaviour is provided via an analysis of the joint PDF in pitch and pitch rate for which both the deterministic and random responses are examined. More generally, it is found that the random excitation effectively ‘decouples’ the nonlinear responses such that the pitch, pitch rate, heave and heave rate marginal PDFs transition from uni- to bi-modality at different airspeeds. It is argued that a fundamental cause of the observed behaviour is the synergy between the nonlinearity and the random external excitation.     

A direct derivation of the equations of motion for 3D-flexible mechanical systems

Equations of motion for rigid bodies with the body-fixed co-ordinate system placed at or away from the centre of mass are derived in a clear and direct way by making use of the two basic equations of mechanics (Newton's second law and the corresponding law of angular momentum). The dynamic equations for flexible mechanical systems are derived using the principle of virtual work, which introduces inertia in a straightforward manner, because this principle treats inertia as a force. The flexible formulation is exemplified by the use of circular beam elements and some basic matrices are derived in a direct way using skew-symmetric matrices. The capabilities of the formulation are demonstrated through examples. Results are compared with and verified by examples from the literature. Derivations throughout the paper are simplified by means of skew-symmetric matrices. © 1998 John Wiley & Sons, Ltd.