A QUASI-STATIC EQUIVALENT MECHANICAL MODEL FOR ROLL STABILITY OF PARTIALLY-FILLED TANKER TRUCKS

非满载液罐车转向行驶时,液体重心会发生偏移现象,对液罐车的侧倾稳定性造成不利影响。以椭圆形截面液罐车为例,分析了液罐车转向时发生侧翻的力学机理,将液面变化近似符合准静态过程,确定压力中心位置,计算液体对罐体壁的总压力,得到非满载液罐车转向侧倾稳定性准静态等效力学模型。研究结果表明,液罐车侧倾稳定性与罐体横截面形状、液体充装率等因素相关,为提高液罐车侧倾稳定性提供了理论分析依据。     

Dynamic analysis of turning performance of 4WD-4WS tractor on paved road

In this research, using a 4-wheel-driven, 4-wheel-steered tractor, two experiments and a computer simulation about its turning on paved ground are described. One experiment is on the relation between the wheel turning angle and the steering angle, and the other is a turning experiment to determine the path traced by the vehicle and to check the simulation. The computer simulation with equations of motion was conducted, and some effects, for example of the running speed, on the yaw angular velocity and on the side slip angle of the center of gravity of the tested tractor were analysed.     

Turning characteristics of multi-axle vehicles

This paper presents a mathematical model for multi-axle vehicles operating on level ground. Considering possible factors related to turning motion such as vehicle configuration and tire slip velocities, equations of motion were constructed to predict steerability and driving efficiency of such vehicles. Turning radius, slip angle at the mass center, and each wheel velocity were obtained by numerically solving the equations with steering angles and average wheel velocity as numerical inputs. To elucidate the turning characteristics of multi-axle vehicles, the effect of fundamental parameters such as vehicle speed, steering angles and type of driving system were examined for a sample of multi-axle vehicles. Additionally, field tests using full-scale vehicles were carried out to evaluate the basic turning characteristics on level ground.     

Development of a high-speed, half-tracked truck with metal-coreless rubber track

A high speed half-tracked truck using a new type of metal-coreless rubber track for traveling and load-carrying both on- and off-road was developed. In this application a conventional embedded-metal rubber track was examined in a first step, and was found to be unsuitable because of its chain-type structure. Then a new type of positive drive metal-coreless rubber track with endless spiral cable reinforcement was developed to meet all of the desired performance, i.e. low driving resistance, low heat build-up due to flexing, low noise, low vibration, light weight, good flexibility, low wear, etc. The development of this track, along with the use of properly matched undercarriage and suspension, has renewed interest in the use of half-tracked trucks. This truck is based on a conventional four-wheel-drive dump truck of two tonnes payload with its rear wheels converted into rubber tracks. Both high mobility off-road and traveling speed faster than 60 km/h on-road are obtained without detracking of the rubber tracks from the undercarriage. Therefore, the truck is capable of transporting its load between on- and off-road without transshipment. An identical driver's license for the same category as the original truck has been granted by the Japanese Ministry of Transportation since 1992. In this paper, the structure of the truck, the metal-coreless rubber track developed especially for high-speed traveling, the test results, and some market applications are reported.     

垂直湍流液-固流中大颗粒的相对速度

通过量纲分析和实验测量,对于垂直、局部均匀的湍流稀态液一固流中,大颗粒的相对速度,建立了无量纲参数表达式．用分析和实验相结合的方法,确定了表达式中无量纲参数的幂次及有关系数．实验中用激光多普勒分相测量技术,分别测出流体和颗粒的时均速度结果表明,大颗粒相对速度强烈依赖于流体雷诺数,当流体雷诺数较高时,其幂次渐近于1.5。     

The optimum height of application of force and eccentricity of a wheeled vehicle running on a loose sandy soil

In earthmoving sites, multi-wheeled vehicles are used to excavate a sandy soil or to pull other construction machinery. In this paper, the mechanism of a 5.88 kN weight, two-axle, four-wheel vehicle running on a loose sandy soil is theoretically analysed. For given terrain-wheel system constants, the combination of the effective braking force of the front wheel during pure rolling state and the effective driving force of the rear wheel during driving action will clarify the relation between effective effort of the vehicle and slip ratio and the relation between amounts of sinkage the front and rear wheels and slip ratio, etc. The maximum effective tractive effort of the vehicle varies with the height of application force and the position of the center of gravity of the vehicle. The optimum height of application of force and the eccentricity of the center of gravity to obtain the largest value of the maximum effective tractive effort can be explained with an analytical simulation program. Results of this study showed that the optimum height of application force should be 30 cm and the optimum eccentricity of the center of gravity is 0.05 for a vehicle considered for this study.     

大射电天文望远镜悬索馈源系统驱动力的研究

针对大射电天文望远镜馈源系统中悬索呈现出的柔性特征，在已知馈源舱的位置，姿态，速度和加速度的情况下，将悬索离散为柔性索杆单元，建立了系统的逆运动学及逆动力学模型。分析计算了悬索上各离散点的位置、速度、加速度和惯性力，推导了在重力和惯性力共同作用下悬索的空间挠曲线方程，研究了悬索的刚体位移和弹性变形。在此基础上，通过刚体-柔性的迭代计算，求出悬索馈源系统的驱动力，为高精度的大射电天文望远镜提供了必要的设计参数。     

Numerical simulation of a 4WD–4WS tractor turning in a rice field

For the steady-state circular turning of a 4WD–4WS (4 wheel driven–4 wheel steered) tractor in a rice field, a numerical simulation was achieved. Equations of motion of this tractor were developed in a vehicle fixed x–y coordinate system. By comparing the calculated and measured results of acting forces on the tractor tires, this simulation was evaluated. Then, the characteristic parameters of the turning vehicle, which are the side slip angle and the yaw angular velocity of the vehicle center of gravity, were simulated in several combinations of the steering wheel angle and the forward speed. Also the same simulation applied to a 4WD–2WS tractor which had the same body as the 4WD–4WS tractor. The simulated results showed a clear difference of turnability between 4WS and 2WS. ©     

Asymptotics of the Critical Regimes of Internal Gravity Wave Generation

The problem of constructing an asymptotic representation of the solution of the internal gravity wave field excited by a source moving at a velocity close to the maximum group velocity of the individual wave mode is considered. For the critical regimes of individual mode generation the asymptotic representation of the solution obtained is expressed in terms of a zero-order Macdonald function. The results of numerical calculations based on the exact and asymptotic formulas are given.     

Extremely large-amplitude oscillation of soft pipes conveying fluid under gravity

In this work, the nonlinear behaviors of soft cantilevered pipes containing internal fluid flow are studied based on a geometrically exact model, with particular focus on the mechanism of large-amplitude oscillations of the pipe under gravity. Four key parameters, including the flow velocity, the mass ratio, the gravity parameter, and the inclination angle between the pipe length and the gravity direction, are considered to affect the static and dynamic behaviors of the soft pipe. The stability analyses show that, provided that the inclination angle is not equal to π, the soft pipe is stable at a low flow velocity and becomes unstable via flutter once the flow velocity is beyond a critical value. As the inclination angle is equal to π, the pipe experiences, in turn,buckling instability, regaining stability, and flutter instability with the increase in the flow velocity. Interestingly, the stability of the pipe can be either enhanced or weakened by varying the gravity parameter, mainly dependent on the value of the inclination angle.In the nonlinear dynamic analysis, it is demonstrated that the post-flutter amplitude of the soft pipe can be extremely large in the form of limit-cycle oscillations. Besides,the oscillating shapes for various inclination angles are provided to display interesting dynamical behaviors of the inclined soft pipe conveying fluid.     

鲫鱼C形起动的运动学特征分析

快速起动是鱼类很重要的一种机动能力，有助于鱼类的逃逸和捕食。快速起动通常分为C形起动和S形起动两种模式。本文利用数字式高速摄像机定量地研究了鲫鱼为逃避危险从静止状态做逃逸反应的运动过程。观察发现所有的逃逸反应都是C形起动。仔细分析运动图像后，根据质心和尾鳍的运动，发现C形起动过程大体可以分解为三个阶段。第一阶段，质心保持不动，鱼体在极短的时间内绕质心弯曲呈C形，尾鳍同时迅速摆动；第二阶段，尾鳍作大幅度反向摆动，鱼头转动接近至最终方向；第三阶段，质心沿最终方向作直线运动。本文通过软件分析得到了各个阶段内鱼体躯干曲线的形状，进而给出了鱼体的速度和转动角速度分布，并从力学的角度定性地解释了机动过程。     

Turning behavior of articulated-frame-steering tractors—part 2. Motion of tractors with drawbar pull

The motion of an articulated-frame-steering tractor is analyzed by an equation of motion when the tractor is turned by an external force, which has an arbitrary direction. The turning path of the tractor is calculated and compared with test results. It is shown from this comparison that this analytical method will be adopted to clarify the turning behavior of vehicles with tires. Furthermore influences of some tractor parameters such as the position of the center of gravity, the position of the frame turning joint, the running speed on the tractor behavior are also shown by a simulation calculation.     

Practical method of reducing turning motion resistance of tracked vehicles

A practical method of reducing the resistance of a tracked vehicle to turning or steering motion is discussed. The torque of the sprocket shaft for driving the crawler was measured and used to evaluate how the resistance varied compared with the existing method to turning. There are two ways of reducing the turning resistance by decreasing the contact area of track; one is to decrease the width of the braked track and the other is to shorten its contact length during turning or steering motion. The former is practically impossible to control, but the latter is comparatively easy to do, even under that condition. Applying this mechanism, the resistant force (evaluated by measuring the driving torque of the sprocket shaft) could be reduced about 20% when the contact length of the braked track was shortened to form a small pivot area at its center. It was also reduced more than 50% when the contact length of both tracks was shortened to a pivot during turning motion.     

矩形弹性壳液耦合系统中的重力波分析

根据非线性动力学理论,建立了矩形壳液耦合系统的非线性振动方程组,通过数值求解,发现当激振频率为壳体固有频率与重力波频率之和,且激振力足够大时,会产生大幅低频重力波,通过实验验证,发现了壳液耦合系统中存在的大幅低频重力波现象,实验结果与理论结果基本吻合。     

Attitude dynamics of a cylinder floating in immiscible fluids

This study elaborates the attitude dynamics of a cylinder floating in two immiscible fluids. A cubic polyno- mial was derived based on the attitude angle, weight, center of gravity, and the density ratio of fluids. The numerical solution was validated by experimental data. Under prescribed constraints for the physical model, we have found that multiple solutions exist for cases with no radially biased center of gravity. When the center of gravity is biased, the attitude angles change abruptly around some critical values, which is related to the density ratio. Moreover, the attitude angles are less sensitive to the varying density ratios when the cylinder is heavier. The results also reveal that the cylinder tends to be vertical for nearly the whole range of density ratios when the center of gravity is slightly biased radially.     

一种新型后装式垃圾车结构优化设计

首先对后装式压缩垃圾车的车厢截面形状进行优化,设计出一种具有椭圆截面车厢的新型后装式垃圾车.给出椭圆截面车厢的自重、惯性、压缩、挤入、推出等压缩垃圾载荷的数学表达.而后对车厢与填科器结构进行多种危险工况的有限元分析,采用导重法对结构构件尺寸进行优化设计,在保证结构应力小于许用应力的前提下,本新型椭圆截面后装武垃圾车结构质量比原来的矩形截面压缩垃圾车减少了33.5%,是同类后装武压缩垃圾车中的最轻者.     

Experimental studies on dynamic plastic buckling of circular cylindrical shells under axial impact

In the present paper, experimental studies on dynamic plasticbuckling of circular cylindrical shells under axial impact are carried out. Hopkinson bar and drop hammer apparatus are used for dynamic loading. Three groups of circular cylindrical shells made of copper are tested under axial impact. From the experiments, the first critical velocity corresponding to the axi-symmetric buckling mode and the second critical velocity corresponding to the non-axisymmetric buckling mode are determined. The present results come close to those of second critical velocity given by Wang Ren^[4–6]. Two different kinds of non-axisymmetric buckling modes oval-shaped and triangle shaped are founded. The buckling modes under two loading cases, viz. with small mass but high velocity and with large mass and low velocity using Hopkinson bar and drop hammer, are different. Their critical energies are also discussed. The project is supported by the National Natural Science Foundation of China (19672039) and the Foundation for Returned Scholar from Abroad of Shanxi Province     

Turning behavior of articulated frame steering tractor — I. Motion of tractor without traction

The equation of motion is derived for the turning in a horizontal plane of a tractor with articulated frame steering when the tractor has no tractive force. Different from a standard tractor, the articulated tractor varies the position of its center of gravity according to the turning angle, so that the motion equation becomes very complex and difficult to solve. Side slip of the articulated tractor is obtained by the numerical analysis method, i.e. the Runge-Kutta-Gill method. Turning radii and ruts of tires are calculated for a running speed and a bending angle, and they are compared with experimental results.     

Theoretical study on the bifurcation of vortexes structure for flow in curved tube

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