共查询到19条相似文献，搜索用时 250 毫秒
1.
Dynamic tests of three bonded and two unbonded full-prestressed concrete beams were carried out.The purpose was to seek the relation between prestressing force and natural frequency.Test results indicate that the frequency of prestressed concrete(PSC)beam increases with the increase in prestressing force approximately.The results are different from the dynamic characteristics of isotropic material beam subjected to compressive axial force which were put forward by Clough et al.The reason is that the beams were considered as isotropic,homogeneous,linear elastic material in the traditional analysis method.However,more accurate results are required in the analysis of frequency of PSC beam.The constitutive mode of PSC member is analyzed based on microstructure of concrete in this paper.The orthotropic linear elastic mode is used to analyze the relation between dynamic frequency and prestressing force of concrete beam,at the same time the equivalent stiffness of prestressed tendon relating to the prestressing force is added to the bending deformation stiffness of the beam.The analytical value agrees well with the test result,indicating that the current analysis method in this paper is feasible to full-prestressed concrete beam. 相似文献
2.
Arrangement strategy of ground heat exchanger with groundwater 总被引：2，自引：2，他引：0
The orientation strategy of side pipe and the heat transfer performance of six ground heat exchangers(GHEs) were optimized by numerical simulation,with soil being treated as a porous medium.An experiment on the heat transfer of four GHEs was carried out in 2010.Results indicate that the velocity field is disturbed by GHEs.The optimal orientation strategy of side pipe is that the upward pipe is located upstream and the downward pipe downstream.The space between GHEs should be appropriately adjusted,depending on the direction and flow velocity.Groups of GHEs should be installed perpendicular to the mainstream in a single row,but if the acreage does not meet the requirements,GHEs should be installed in staggered multiple rows.Fewer GHEs parallel to the mainstream strengthen the heat transfer.Moreover,numerical results agree well with the test data,with the maximum relative error being less than 7.7%. 相似文献
3.
The dynamic response of an infinite beam placed on a Pasternak foundation when the system was subjected to a moving load was investigated. We used the double Fourier transform and its inversion to solve the formulations of the problem. A closed form analytic solution of the beam was obtained by the theorem of residues. We selected a numerical example to illustrate the dynamic response of the beam on Pasternak and Winkler foundations, respectively. We discuss the effect of the moving load velocity on the dynamic displacement response of the beam. The maximum deflection of the beam increases slightly with increased load velocity but increases significantly with reduced shear modulus of subgrade at a given velocity. The maximum deflection of a beam resting on a Pasternak foundation is much smaller than that of a beam on a Winkler foundation. 相似文献
4.
We proposed an optimal design method to expand the bandwidth for the control of large hydraulic Stewart platform. The method is based on generalized natural frequency and takes hydraulic oil into consideration. A Lagrangian formulation which considers the whole leg inertia is presented to obtain the accurate equivalent mass matrix. Using the model, the effect of leg inertia and the influence of design parameters on the generalized natural frequency are investigated. Finally, numerical examples are presented to validate and confirm the efficiency of the mathematical model. The results show that the leg inertia, especially the piston part plays an important role in the dynamics. The optimum diameter ratio of the base to the moving platform is between 2 and 3, and the optimum joint angle ratio of the base to the moving platform is about 1. The smaller joint angles and a longer leg stroke are favorable for raising system frequencies. The system oil should be preprocessed for large platforms with a requirement for good dynamic performance. 相似文献
5.
The indirect boundary element method (IBEM) is used to study the surface motion of an alluvial valley in layered half-space for incident plane P-waves based on Wolf’s theory. Firstly, the free field response can be solved by the direct stiffness method, and the scattering wave response is calculated by Green’s functions of distributed loads acting on inclined lines in a layered half-space. The method is verified by comparing its results with literature and numerical analyses are performed by taking the amplification of incident plane P-waves by an alluvial valley in one soil layer resting on bedrock as an example. The results show that there exist distinct differences between the wave amplification by an alluvial valley embedded in layered half-space and that in homogeneous half-space and there is interaction between the valley and the soil layer. The amplitudes are relatively large when incident frequencies are close to the soil layer’s resonant frequencies. 相似文献
6.
The dynamic response of moored crane-ship is studied. Governing equations for the dynamic response of a crane-ship coupled with the pendulum motion of the payload are derived based on Lagrange＇s equations. The boom is modeled based on finite element method, while the payload is modeled as a planar pendulum of point mass. The dynamic response was studied using numerical method. The calculation results show that the large-amplitude responses occur at wave periods near the natural period of the payload. Load swing angle is smaller for crane-ship with flexible boom, in comparison with rigid boom. The ship surge motions have large vibrations for crane-ship with flexible boom, which were not observed for a rigid boom. The analysis identifies the significance of key parameters and reveals how the system design can be adjusted to avoid critical conditions. 相似文献
7.
A measurement model based on torsion pendulum was established,in which nonlinear damping and nonlinear restoring force were considered.The calculation method of the moment of inertia was based on Hilbert transform.The motion of torsion pendulum showed the time-frequency characteristics due to the nonlinear factors,which were validated by the experimental data.The analytical signal was formed by Hilbert transform of the angular displacement signal of the test object.The moment of inertia can be computed by the instantaneous undamped natural frequency with Hilbert transform.Prior to the implementation of Hilbert transform,the empirical mode decomposition was used to filter the experimental signal.The moment of inertia of the test object was measured by the torsion pendulum system.The experimental results show that the relative measurement error of the moment of inertia was within 0.7%,which indicated the validity of the measurement method. 相似文献
8.
In the application of active magnetic bearings(AMB),one of the key problems to be solved is the safety and stabiltiy in the sense of rotor dynamics,The project related to the present paper deals with the method for analyzing bearing rotor systems with high rotation speed and specially supported by active magnetic bearings,and studies its rotor dynamics performance,including calculation of the natural frequencies with their distribution characteristics,and the critical speeds of the system.one of the targets of this project is to formulate a theory and method valid for the analysis of the dynamic performance of the active magntic bearing-rotor systemby combining the traditional theory and method of rotor dynamics with the analytical theory and design method based on modern control theory of the AMB system. 相似文献
9.
MALIK Pravin KADOLI Ravikiran GANESAN N. 《浙江大学学报(A卷英文版)》2007,8(7):1044-1052
Numerical exercises are presented on the thermally induced motion of internally heated beams under various heat transfer and structural boundary conditions. The dynamic displacement and dynamic thermal moment of the beam are analyzed taking into consideration that the temperature gradient is independent as well as dependent on the beam displacement. The effect of length to thickness ratio of the beam on the thermally induced vibration is also investigated. The type of boundary conditions has its influence on the magnitude of dynamic displacement and dynamic thermal moment. A sustained thermally induced motion is observed with progress of time when the temperature gradient being evaluated is dependent on the forced convection generated due to beam motion. A finite element method (FEM) is used to solve the structural equation of motion as well as the heat transfer equation. 相似文献
10.
Xue-ping LI Wei-qiu ZHU Zu-guang YING 《浙江大学学报(A卷英文版)》2008,9(3):330-337
An optimization method for time-delayed feedback control of partially observable linear building structures subjected to seismic excitation is proposed. A time-delayed control problem of partially observable linear building structure under horizontal ground acceleration excitation is formulated and converted into that of completely observable linear structure by using separation principle. The time-delayed control forces are approximately expressed in terms of control forces without time delay. The control system is then governed by Itoe stochastic differential equations for the conditional means of system states and then transformed into those for the conditional means of modal energies by using the stochastic averaging method for quasi-Hamiltonian systems. The control law is assumed to be modal velocity feedback control with time delay and the unknown control gains are determined by the modal performance indices. A three-storey building structure is taken as example to illustrate the proposal method and the numerical results are confirmed by using Monte Carlo simulation. 相似文献
11.
根据动力学分析和边界条件推导出轴向运动梁的系统特征方程,利用微分求积法对本征方程离散,计算出梁横向振动的固有频率,并数值模拟了梁运动速度和刚度对固有频率的影响。 相似文献
12.
基于非局部理论,建立了受初始拉力的纳米梁的横向自由振动的力学模型。考虑了非局部效应对于固有频率和振动模态的影响,并以两端简支纳米梁为例,运用分离变量法和多尺度分析法考察了梁的线性振动特征。分别讨论了振动模态与无量纲化轴坐标,以及固有频率与非局部参量的关系。两种方法求得结果非常接近,这证明了新建纳米梁横向振动模型的有效性。 相似文献
13.
研究了Galerkin截断方法在不同支承条件下轴向运动梁振动问题中的应用．利用离散化后的微分方程在u-vf平面上的失稳区域随离散维数的变化情况，验证了两端铰支的轴向运动梁取正弦函数做Galerkin截断方法时所得结果的正确性，对于两端固支的轴向运动梁，选取不同的特征函数，分别应用Galerkin截断方法并比较所得结果，最后得到适用于此种支承条件下的离散方法． 相似文献
14.
NomenclatureV-Relative velocity vectorV′-Absolute velocity vectorω-Relative vorticity vectorω′-Absolute vorticity vectorR-Pipe radiusa-Radius of cylinder for helical vortex filament2πl-Pitch of i mage helical vortex filamentQ-Flowrate in pipe with an arbitrary cross-sectionΓ-Circulation of each helical vortex filamentV0-Constant transferal velocity of vortex filaments along thez-axisΩ-Constant angular velocity of vortex filaments around thez-axis(a,χ1) ,(a,χ2) -Relative helical … 相似文献
15.
研究基于有限元模型的梁结构损伤识别的正反问题,即正问题采用有限元模型求解包含损伤位置和程度参数的结构前三阶固有频率,经曲面拟合技术拟合得到解曲面;反问题将实际损伤结构前三阶固有频率作为输入,绘制损伤梁结构位置和程度的等高线,根据曲线的交点识别出损伤梁结构损伤位置和程度。数值仿真算例表明:该方法具有足够的辨识精度,为梁类结构损伤识别提供了新方法。 相似文献
16.
罗运文 《宁德师专学报(自然科学版)》2012,24(4):366-367
超流关键的物理量就是临界速度,MIT（麻省理工学院）实验组用激光来同扫描凝聚体的方法测出BEC超流体的临界速度,但是与理论值相比小得多．考虑到非凝聚态粒子的影响,发现MIT组测得的实验值并不是临界速度,而是玻色气体获得能量的最小速度,实际临界速度比测得的速度要大．通过修正玻色气体获得能量的速率公式从而得出临界速度与实验测量数据的关系,并发现修正后的临界速度的实验值符合理论值． 相似文献
17.
ZHU Bin LEUNG A.Y.T. 《浙江大学学报(A卷英文版)》2006,7(8):1351-1357
INTRODUCTION Thin-walled structures have considerable tech-nological importance in many situations of engi-neering practice. The rotary and warping inertia terms should be considered in the analyses of thin-walled structures (Alwis and Wang, 1996), although it is difficult to obtain the analytical solutions of govern-ing differential equations, especially of thin-walled frame and spatial twisted structure. The finite element method (FEM) is widely used for vibration and sta-bility analy… 相似文献
18.
INTRODUCTION Vibrations of cylindrical shells are of consider-able importance as they are extensively used in in-dustry,flight structures and marine crafts.The naturalfrequencies and mode shapes are important sources ofinformation for understanding and controlling thevibration of these structures,so many papers on theprediction of the natural frequencies of cylindricalshells have been published over the past years.Many shell theories have been developed andvarious solution methods have bee… 相似文献