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A numerical procedure, with an exact strain-displacement relationship of twisted and curved cylindrical panels having variable thickness derived by considering the Green strain tensor on general shell theory, is presented using the principle of virtual work and the Rayleigh-Ritz method with algebraic polynomials as in-plane and transverse displacement functions. The accuracy and applicability of the procedure are verified by comparing the present results with previous experimental and theoretical results for several panels. The effects of variation ratio of thickness in chordwise and lengthwise directions, twist, and curvature both in two directions aforementioned on vibrations of cylindrical panels are studied in detail, and typical vibration mode shapes are plotted to demonstrate the effects. 相似文献
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本文提出一种新颖的轮廓曲面动态,实时,非接触光学测量方法,对飞机机翼,汽轮机叶片以及坦克,轿车等的轮廓曲面提供了一种有效的测量方法,该方法是利用激光测头扫描探测,CCD(电荷耦合器件)或PSD作为光电接收器件,利用微机控制的闭环测量方法,文中还给出了一种CCD的新探测驱动方法。 相似文献
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S.T. CHOI 《Journal of sound and vibration》2003,259(3):525-539
Free-vibration characteristics of cantilever non-circular curved panels are analyzed by using the differential quadrature method (DQM) in this paper. The equations of motion of a curved panel are based on the Love's hypothesis and are expressed in an orthogonal curvilinear co-ordinate system. By applying the differential quadrature formulation and the proposed modified relationships for specified boundary conditions, the free-vibration equations of motion of the curved panel are transformed to a set of algebraic equations. Natural frequencies of a cantilever flat plate and a circular curved panel are obtained for verifying the applicability of the present approach. Good convergent trend and accuracy are observed. Effects of shallowness, thickness and aspect ratios on the natural frequencies of a cantilever curved panel are also investigated. Furthermore, natural frequencies of parabolic curved panels are obtained. In all cases studied, the efficiency and convenience of the DQM are illustrated. 相似文献
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In this paper, the nonlinear dynamic stability of a rotating shaft-disk with a transverse crack is studied. The crack and the disk are located in arbitrary positions of the shaft respectively. Using the equivalent line-spring model, the deflections of the system with a crack are constructed by adding a deflection to the deflections of the uncracked system. The unstable regions are confirmed by Runge-Kutta method and the Floquet theory. The effects of crack depth, crack position, disk position, disk thickness and rotating speed on the principal unstable regions are discussed. The numerical results are compared with available data. 相似文献
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P. RUTA 《Journal of sound and vibration》2002,250(3):445-464
A dynamic stiffness matrix for a non-prismatic rod finite element resting on a two-parameter non-homogenous elastic foundation has been determined. To obtain the solution the shape function was approximated by Chebyshev series. This yielded closed analytical formulae for the coefficients of the matrices sought. The finite element obtained was used to solve the dynamic stability problem for a non-prismatic cantilever column. The results were compared with those reported by other authors. 相似文献
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《Journal of sound and vibration》2001,244(2):321-338
Randomness in the material properties is inherent in all engineering materials. Composites exhibit a greater scatter compared to conventional materials because of the larger number of parameters associated with its fabrication and manufacturing. For accurate prediction of its behavior, the composite material properties have been modelled as random variables in the present study. Higher order shear deformation theory including rotatory inertia effects has been employed in developing the system equations and first order perturbation technique has been adopted for the solution. An approach has been presented for obtaining the analytical solution for generalized eigenvalue problem associated with free vibrations. Mean and variance of the natural frequency have been obtained for cross-ply spherical laminates projected in rectangular plan form with different boundary conditions. 相似文献
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This paper proposes a new matrix method for calculating critical flow velocity of curved pipes conveying fluid, which have arbitrary centerline shape and spring supports. Its main advantage over other methods is that the corresponding characteristic equation can be reduced to a third order one, no matter how many elements are discretized in calculation. This will lead to saving computer time and obtaining a solution with good precision. 相似文献
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A.S. ALSUWAIYANS.W. SHAW 《Journal of sound and vibration》2002,252(5):791-815
Centrifugal pendulum vibration absorbers are a type of tuned dynamic absorber used for the attenuation of torsional vibrations in rotating and reciprocating machines. They consist of masses that are constrained to move along specific paths relative to the rotational axis of the machine. Previous analytical studies have considered the performance of single absorber systems with general paths and of multi-absorber systems with a specific path type. In this paper, we investigate the performance and dynamic stability of systems comprised of multiple, identical centrifugal pendulum vibration absorbers riding on quite general paths. The study is carried out by considering a scaling of the system parameters, based on physically realistic ranges of dimensionless parameters, which permits application of the method of averaging. It is found that the performance of these systems is limited by two distinct types of instabilities. In one type, the system of absorbers lose their synchronous character, while in the other a classical non-linear jump affects all absorbers identically, leading to highly undesirable system behavior. These results are used to evaluate two common types of absorber paths, namely circles and cycloids, including intentional mistuning of the absorber frequencies. The results are used to make some recommendations about the selection of paths to achieve design goals in terms of absorber performance and operating range. The analytical predictions are confirmed by numerical simulations. 相似文献
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Y.-B. YANGY.-S. WU 《Journal of sound and vibration》2002,258(1):65-94
The dynamic stability of trains moving over bridges shaken by earthquakes is studied. Unlike the seismic analysis of structures containing a single subsystem, the seismic analysis of a bridge sustaining a passing train requires not only information on acceleration, but also on velocity and displacement of the ground motion. Four typical earthquakes, including the 1999 Chi-Chi Earthquake, were adopted as the input excitations, each of which was normalized to have a moderate intensity. The results indicate that a train initially resting on the bridge can stay safely under the ground motions considered, if the bridge and track structures do not exhibit inelastic deformations during the earthquake. The type of the vertical component of ground motions can affect significantly the stability of the train-rail- bridge system. As a preliminary attempt, safety, possible instability and instability regions were established in a three-phase plot for the train running over the bridge for each of the earthquakes considered, from which the maximum allowable speed for the train to run safely under the specified ground acceleration can be obtained. 相似文献
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Ronchi线条法检验大非球面镜的理论计算 总被引:4,自引:0,他引:4
由光线追迹和三级像差理论计算大抛物面的Ronchi弯线条。分析这两种理论计算方法的结果和偏差,其偏差值随镜子的口径增大而增加,用所计算的结果制作的Ronchi弯线条检验可移动式平行光管的φ700mm口径的抛物面主镜。给出检验结果。 相似文献
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A linear stability analysis for a two-component Benard liquid with surface adsorption has revealed a dual role for the surface tension arising from the surfactant-it plays a stabilizing role in some cases and a destabilizing role in others.We have introduced a dimensionless parameter-surface excess number,proportional to the concentration gradient of solute and inversely proportional to the surface adsorption accumulation,to describe the dual effects of surface tension.We predict the existance of a critical surface excess number and calculate its value for two different boundary conditions.Our results have solved the seeming1y contrary results obtahed by Berg and Palmer and Velarde. 相似文献
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This paper presents an investigation into the dynamic stability of skew plates acted upon simultaneously by an aerodynamic force in the chordwise direction and a random in-plane force in the spanwise direction. Due to this random in-plane force, the plate may become unstable before the aerodynamic force reaches its critical value. In this work, the finite element formulation is applied to obtain the discretized system equations. The system equations are then partially uncoupled and reduced in size by the modal truncation method. Finally, the unsmoothed and the smoothed versions of the stochastic averaging are used to calculate the system response, and the second-moment stability criterion is utilized to determine the stability boundary of the system. Numerical results show that the stability boundary obtained by the smoothed stochastic averaging is less conservative than that obtained by the unsmoothed version, and the former is the tangent of the latter at zero spectral density of the random in-plane force. 相似文献
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三线圈超导磁体在脉冲电流下的动力稳定性分析 总被引:1,自引:1,他引:1
对于聚变反应堆中超导载流磁体在稳态电流基础上受到脉冲电流影响时的动力稳定性给出了定量分析方法。结合其超导载流磁体的实验结构,给出了超导磁体在不同稳态工作电流(即低于稳态的磁弹性人稳临界电流)作用下受到矩形脉冲电流作用 磁弹性动力响应的数值模拟结果。在此基础上,给出了关于稳态工作电流、脉冲电流强度和脉冲持续时间等参数的磁弹性动力稳定性参数范围。 相似文献