Measurement of rotational components of structures and machines

In this paper, the measuring methods of the rotational components, i. e. the free angular velocity and the moment mobility are presented. The performance of a moment actuator composed of two magnetostrictive rods (Tb_0.3 Dy_0.7 Fe_1.95) is discussed. Both theory and experiment show that the performance of the moment actuator does not influence the measurement results of the moment mobilities basically but affects the efficiency for exciting rotation. The efficiency for exciting rotation has also been calculated.     

Structural design of tension units for tracked vehicles, especially construction machines under the aspect of safety requirements

The commercial types of tension units for tracked vehicles which have been available so far consist of a spring which is in a permanent pretensioned condition. Although the probability of spring unit failures is very low, it cannot be guaranteed that springs in pretensioned condition will not break due to a potential material defect. This can mainly be explained by the fact that the special shape of the spring does not allow inspection and control. So to meet today's safety requirements in an improved way, a tension unit has been developed which is pretensioned only during assembly in the machine so that it does not involve any potential risk with regard to transport, storage or disposal of the component. This paper deals with some safety requirements for the use of tension units in construction machines under the aspect of an improved design of conventional tension units.     

Evolution of metastable quasi-regular structures in heated wavy liquid films

Formation and development of quasi-regular, metastable structures within laminar wavy falling films were studied using IR-thermography. These structures emerge within the residual layer between large waves. It is shown that the typical size of regular structures does not depend on the liquid flow rate and is in the order of magnitude of the critical length of the Rayleigh–Taylor instability. Also a model of thermal-capillary breakdown on the basis of a simplified force balance between the surface tension and the tangential stress as well as the energy balance in the residual layer is presented. Model predictions and experimental data are in good agreement.     

Evolution of vortex structures in an electromagnetically excited separated flow

Time periodic wall parallel Lorentz forces have been used to excite the separated flow on the suction side of an inclined flat plate. Experiments for a Reynolds number of 10⁴ and an angle of attack of α = 13° are reported. The controlled flow is characterised by a small number of relatively large scale vortices, which are related to the control mechanism. The influence of the main parameters, i.e. the excitation frequency, amplitude and wave form on the suction side flow structures was investigated by analysing time resolved particle image velocimetry (TR-PIV) measurements using continuous wavelet analysis for vortex detection and characterisation. Statistical analysis of the coherent structures of the flow was performed on a large amount of data samples.     

基于减基概念的凸集结构可靠性分析方法

针对椭球凸集参数域结构的可靠性分析问题,提出了一种基于减基概念的快速求解方法。首先,将椭球参数域进行坐标正交变换,获得标准的椭球域及其相应的矩形域,在矩形域采样且通过坐标逆向变换获得原椭球参数域的样本参数点集,并以此构建结构的减基空间及其相应的减基算法;随后,在标准椭球域产生均匀的等概率抽样点,并通过坐标逆向变换和相应的减基算法进行蒙特卡洛减基模拟来分析结构的可靠度及其可靠域。由于是在低维的逼近空间中进行椭球参数域结构的位移向量解分析,故而较之有限元法能够获得较高的计算效率。算例测试验证了本文方法的有效性。     

Upper and lower bounds for the average value and for the variance of the safety coefficients of structures with random resistance

Summary By going back to a theorem[1] [2] which gives an upper bound of the average plastic collapse load of a structure whose elements have random resistance, a method is demonstrated for supplying a lower bound.It will then be shown how it is possible to find an upper and a lower bound of the variance of collapse load of all structures conceivable in terms of random resistance.As far as limit analysis is concerned only a deterministic calculation is requested by the above methods.

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Sommario Richiamato un teorema[1] [2] che fornisce un maggiorante della media dei moltiplicatori di collasso plastico di una struttura dotata di elementi a resistenza aleatoria, si dimostra come sia possibile fornirne un minorante. Si dimostra poi come sia possibile fornire un minorante ed un maggiorante della varianza dei moltiplicatori di collasso.I limiti indicati sono, benchè basati su quantità fornite dalla elaborazione di variabili aleatorie, calcolati con criteri deterministici dal punto di vista dell'analisi limite.

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The results presented in this paper were obtained in the course of research sponsored by the C.N.R.     

Finding the operating point of Eulerian flow machines

Examples of Eulerian flow machines (EFM) are turbomachines, jet pumps and vortex amplifiers working with incompressible non-cavitating flow. They are ‘Eulerian’ in the sense used by Paynter² in his work on turbomachines subject primarily to dynamic flow forces. Efficient methods are specified in this paper for finding the operating point of an EFM from its characteristics and any two state-defining variables. A trivial example is to find the torque and pressure of a pump when the speed and flow are given. This is simple because the usual constant-speed characterisation favours the solution, but if other pairs of variables are given, the problem is less simple. For jet pumps or the many ‘power fluidic’ devices the variety of problems is much greater because of combinatorial aspects, although the fluid mechanics is analogous to that of the turbomachine. Solution procedures are specified first for turbomachines; there are six ‘algorithms’. For general ‘3-terminal’ EFM (jet-pumps etc) it is shown that there are 108 characterisation formats and that the 30 listed algorithms enable any of them to be solved given any possible variable-pair. Graphical and computational implementations are described     

Origin and development of the concept of wave

The modern notion of wave is the conclusion of a long intellectual process performed during two centuries. The first concept of wave was suggested by the configurations of a vibrating string, but later it was discovered that these configurations may admit singularities, opening, in this wave, the route to the theory of schock waves. The most recent results consist in the characterization of schock fronts in materials with memory.General Lecture presented (in Italian) at the 10th Italian National Congress of Theoretical and Applied Mechanics; AIMETA, Pisa, October 1990.     

Computational dynamics of soft machines

Soft machine refers to a kind of mechanical system made of soft materials to complete sophisticated mis-sions, such as handling a fragile object and crawling along a narrow tunnel corner, under low cost control and actuation. Hence, soft machines have raised great challenges to compu-tational dynamics. In this review article, recent studies of the authors on the dynamic modeling, numerical simulation, and experimental validation of soft machines are summarized in the framework of multibody system dynamics. The dynamic modeling approaches are presented first for the geometric nonlinearities of coupled overall motions and large deforma-tions of a soft component, the physical nonlinearities of a soft component made of hyperelastic or elastoplastic mate-rials, and the frictional contacts/impacts of soft components, respectively. Then the computation approach is outlined for the dynamic simulation of soft machines governed by a set of differential-algebraic equations of very high dimensions, with an emphasis on the efficient computations of the non-linear elastic force vector of finite elements. The validations of the proposed approaches are given via three case stud-ies, including the locomotion of a soft quadrupedal robot, the spinning deployment of a solar sail of a spacecraft, and the deployment of a mesh reflector of a satellite antenna, as well as the corresponding experimental studies. Finally, some remarks are made for future studies.     

Design features and results from fatigue-reliability-research machines

The design, fabrication, development, operation, calibration and results from reversed bending combined with steady-torque fatigue-research machines are presented. Fifteen-centimeter-long, notched, SAE 4340 steel specimens are subjected to various combinations of these stresses and cycled to failure. Failure occurs when the crack in the notch passes through the specimen automatically shutting down the test machine. These cycles-to-failure data are statistically analyzed to develop a probabilistic S-N diagram. These diagrams have many uses including the design of rotating components having minimum size and weight for a specified number of cycles and reliability.     

我怎样讲授边界层概念

本概述作在本科生流体力学课程中讲授边界层概念的体会：一方面通过实例反复阐明雷诺数极限下在物面附近引入边界层概念的必要性;另一方面通过反复练习培养学生掌握量阶分析方法。