梁柱简化模型在自立塔塔线体系动态响应中的适用性研究

对输电塔进行合理简化可以提高塔线体系动力学仿真的效率。本文给出自立塔梁柱简化模型的计算方法,并提出利用梁柱简化模型计算方法建立自立塔塔线体系整体模型,同时采用桁梁混合模型建立精细化塔线体系整体模型,对两种模型塔线体系静力特性及振型和固有频率等动力特性进行对比分析。以脱冰工况为例,采用生死单元技术将施加在输电线节点上的集中质量单元杀死来模拟脱冰,实现对塔线体系动力学响应的有限元模拟,研究塔线体系简化模型在动态响应中的适用性。结果表明,两种模型弯曲变形误差小,低阶的振型相同,固有频率值误差小,动力特性基本相同;脱冰工况下,自立塔节点位移和塔材内力时程曲线一致,在提高计算效率的情况下,能有效保证计算精度。     

Liquid droplets vaporization under free molecule gas beam conditions

Summary The present piece of research studies the vaporization of liquid droplets under rarefied gas beam conditions. The time dependent aspect of the phenomenon has been taken into account. In fact, during the vaporization, variations of the droplet's temperature, with influence upon the diameter's reduction rate, can occur. Numerical calculations relating to water droplets' vaporization have been made taking into account various values of the incident energy flux. The study should be considered as a theoretical approach to the analysis of the gas-liquid surface interaction phenomena. Moreover, according to C. S. Kurzius and F. H. Raab [1], the work can find its application in the study of the blackout suppressant methods in re-entry space vehicles.

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Sommario La presente ricerca studia l'evaporazione di gocce liquide investite da un fascio molecolare ipertermico, rarefatto. Il fenomeno è studiato da un punto di vista non stazionario; infatti, durante la vaporizzazione, si ha una forte variazione della temperatura media della goccia con conseguente influenza sulla velocità di riduzione del diametro. Sono stati eseguiti calcoli numerici relativi alla evaporazione di gocce d'acqua in flusso di gas ipertermico per fissati valori del flusso di energia incidente. Il presente lavoro è da considerarsi come premessa teorica allo studio del fenomeno fisico di interazione superficiale gas-liquido. Inoltre, secondo C. S. Kurzius ed F. H. Raab [1], trova la sua applicazione nello studio dei metodi di eliminazione del blackout nel rientro dei veicoli spaziali.

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This work, sponsored by the Centro Studi sulla Dinamica dei Fluidi of C.N.R., is a re-elaborated copy of a paper presented at the 6th Int. Symposium on Molecular Beams (9–12 July 1973, Cannes, France).     

On a model of structured medium fracture under compression conditions

Extension is necessary in order to initiate brittle fracture in a structured medium. One possible version of the fracture scenario under compression conditions is the development of extension near local concentrators. The dimensions of such regions depend on the level of hydrostatic compression (pressure). As the hydrostatic compression increases, these dimensions decrease approaching the dimension of individual structure elements of the medium (e.g., grains or pores). Under these conditions, the mechanisms of brittle fracture of the medium differ from those in ordinary structural materials. We consider mechanisms of brittle fracture in compression. It is assumed that the sources of the local extension required for the development of discontinuities are the response of the heterogeneous structure elements of the medium (pores) at which the external compressive stresses can transform into local extensions sufficient for crack propagation. In this case, a characteristic cell representing the scale of the leading process of local fracture is a volume containing two pores. The coalescence of these pores is an elementary fracture process. An increase in the pressure level increases the role of such fracture processes and leads to the development of ordered fracture structures. Several examples of fracture scenarios under loads that are combinations of homogeneous compression and a concentrated action are used to illustrate the conditions for the development of discontinuities, in whose end regions an elementary act of pore coalescence takes place, and to demonstrate the appearance of linear structures such as curtains or echelons of microcracks.     

A robust hyper-elastic beam model under bi-axial normal-shear loadings

In this paper, a simple and robust constitutive model is proposed to simulate mechanical behaviors of hyper-elastic materials under bi-axial normal-shear loadings in the finite strain regime. The Mooney–Rivlin strain energy function is adopted to develop a two-dimensional (2D) normal-shear constitutive model within the framework of continuum mechanics. A motion field is first proposed for combined normal and shear deformations. The deformation gradient of the proposed field is calculated and then substituted into right Cauchy–Green deformation tensor. Constitutive equations are then derived for normal and shear deformations. They are two explicit coupled equations with high-level polynomial non-linearity. In order to examine capabilities of the developed hyper-elastic model, uniaxial tensile responses and non-linear stability behaviors of moderately thick straight and curved beams undergoing normal axial and transverse shear deformations are simulated and compared with experiments. Fused deposition modeling technique as a 3D printing technology is implemented to fabricate hyper-elastic beam structures from soft poly-lactic acid filaments. The printed specimens are tested under tensile/compressive in-plane and compressive out-of-plane forces. A finite element formulation along with the Newton–Raphson and Riks techniques is also developed to trace non-linear equilibrium path of beam structures in large defamation regimes. It is shown that the model is capable of predicting non-linear equilibrium characteristics of hyper-elastic straight and curved beams. It is found that the modeling of shear deformation and finite strain is essential toward an accurate prediction of the non-linear equilibrium responses of moderately thick hyper-elastic beams. Due to simplicity and accuracy, the model can serve in the future studies dealing with the analysis of hyper-elastic structures in which two normal and shear stress components are dominant.     

从压杆的离散化模型看LS方法

通过压杆两自由度离散化模型形象地说明了 Lyapunov-Scbmidt方法的基本思想;用分岔理论的观点描述了压杆的失稳过程．     

Applicability of a one-dimensional model to the calculation of the properties of a plasma generator

Most engineering methods for calculating the properties of plasma generators use similarity theory to derive dimensionless equations to generalize experimental results [1]. Although their accuracy is acceptable for practical calculations, the equations cannot be used for a physical analysis of the local phenomena occurring in the working channel of a plasma generator. In the present paper the experimental data are compared with the results of a calculation of the local and integrated heat and gasdynamic properties of a dc plasma generator with a longitudinally injected arc. The basis of the computational method is a quasi-one-dimensional gasdynamic model of the flow of an electrically conducting gas in the channel of the plasma generator developed and studied in [2].Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 4, pp. 122–126, July–August, 1977.In conclusion, the authors thank G. A. Lyubimov for valuable remarks.     

Two-temperature model of a plasma under conditions of stationary blowing of a gas through a plasmotron

Results are given of a calculation conducted on the basis of a two-temperature plasma model for a cylindrical arc in a channel with the blowing through of a gas. It is shown that the gas venting leads to the appearance of a considerable separation between the electron and gas temperatures near the wall of the plasmotron and in the cathode zones. The possibilities of the two-temperature model are analyzed from the point of view of an approximate calculation of the electron temperature in arc and induction plasmotrons. It is shown that the electron temperature can be estimated from simple relationships with at least 10% accuracy for induction and 15–20% accuracy for arc plasmotrons.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 4, pp. 3–12, July–August, 1973.     

Hydrodynamic analysis of the displacement conditions of formation fluids using an axisymmetric model

The axisymmetric problem of the displacement of formation fluids by a drilling mud filtrate with filter cake formation is considered. An analysis is made of the distribution and variation of the main parameters of the process: filtrate volume, filter cake thickness, oil saturation, and pressure. The positions of the water-saturation and salt-concentration fronts are determined. The results are compared with the geophysical logging data for straight-hole drilling. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 49, No. 2, pp. 56–64, March–April, 2008.     

用悬臂梁法求解所有梁的变形

 针对求解梁变形的种种方法之不足，提出用悬臂梁结果分析所有梁的变形------悬臂梁及有限级 数法，将记忆转化为分析，用特殊而简单的结果求解一般而复杂的问题，并以各实例分析阐述其 要点.     

Chaotic vibrations of a beam with non-linear boundary conditions

Forced vibrations of an elastic beam with non-linear boundary conditions are shown to exhibit chaotic behavior of the strange attractor type for a sinusoidal input force. The beam is clamped at one end, and the other end is pinned for the tip displacement less than some fixed value and is free for displacements greater than this value. The stiffness of the beam has the properties of a bi-linear spring. The results may be typical of a class of mechanical oscillators with play or amplitude constraining stops. Subharmonic oscillations are found to be characteristic of these types of motions. For certain values of forcing frequency and amplitude the periodic motion becomes unstable and nonperiodic bounded vibrations result. These chaotic motions have a narrow band spectrum of frequency components near the subharmonic frequencies. Digital simulation of a single mode mathematical model of the beam using a Runge-Kutta algorithm is shown to give results qualitatively similar to experimental observations.     

火灾下混凝土结构破坏模拟的纤维梁单元模型

为分析和模拟结构构件在火灾下的失效破坏过程,本文基于建筑结构分析中常用的纤维梁单元模型,建立了钢筋混凝土梁、柱构件的火灾破坏数值模型.此模型将构件截面划分成多个纤维,从而可以模拟构件截面的不均匀温度场分布以及高温下混凝土材料的开裂、压碎和钢筋屈服等行为.并根据全拉格朗日描述方法,推导了纤维梁单元的切线刚度矩阵,建立了纤维梁单元的增量求解方程.最后,将本文模型的模拟结果和多个具体试验结果进行了分析比较,进一步验证了模型的可靠性.     

Effect of formation conditions on the motion of a cloud rising upward under the action of the force of buoyancy

The present article gives the results of an experimental investigation of the dependence of the angle of expansion of an ascending cloud on the conditions of its formation. When the cloud starts from a state of rest, 0.18. The greatest expansion corresponds to the presence of perturbations at the surface of the cloud. In this case, when the cloud has an initial velocity, the angle of expansion decreases with a rise in the value of the initial modified Froude number. Starting from Fr₀=1.5, at the initial moment of time the starting substance breaks away from the surface of the cloud. An experimental investigation was also made of the mechanism of the capture of the surrounding medium by the cloud.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 5, pp. 148–150, September–October, 1976.     

Applicability of the crack faces thermoelectric boundary conditions for thermopiezoelectric materials

The applicability and effect of the crack surfaces thermoelectric boundary conditions in thermopiezoelectric fracture mechanics problem are discussed by using the finite thickness notch approach. The stress and electric displacement intensity factors at the notch tips, and thermal flux and electric displacement inside the notch are derived in closed-form. The numerical results are compared with the ideal crack solutions. It is found that the electrically impermeable crack boundary condition assumption is reasonable if the flaw in the material is a notch with finite width, and the thermal conductivity of air or vacuum inside the crack must be considered.     

Solution of internal problems of aerodynamics under transitional conditions using a model kinetic equation

A method is developed based on the use of a model kinetic equation with a shock frequency = v/l (l is the mean length of the free flight path; v is the modulus of the molecular velocity). The method is tested on several classical problems.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 2, pp. 23–28, March–April, 1972.     

Stability analysis of a substructured model of the rotating beam

One of the most well-known situations in which nonlinear effects must be taken into account to obtain realistic results is the rotating beam problem. This problem has been extensively studied in the literature and has even become a benchmark problem for the validation of nonlinear formulations. Among other approaches, the substructuring technique was proven to be a valid strategy to account for this problem. Later, the similarities between the absolute nodal coordinate formulation and the substructuring technique were demonstrated. At the same time, it was found the existence of a critical angular velocity, beyond which the system becomes unstable that was dependent on the number of substructures. Since the dependence of the critical velocity was not so far clear, this paper tries to shed some light on it. Moreover, previous studies were focused on a constant angular velocity analysis where the effects of Coriolis forces were neglected. In this paper, the influence of the Coriolis force term is not neglected. The influence of the reference conditions of the element frame are also investigated in this paper.