Search results

As structural members, circular helicoidal bars are frequently used in the construction industry for a variety of practical and/or aesthetical reasons. While these bars (curvilinear beams) might represent the most practical alternative for carrying loads in a specified structural configuration, the three dimensional structural response has been found to be superior compared to that of other forms of structural members under a general state of loading. Presents the results of a study that has been designed to investigate the free vibration characteristics of this type of bar. The study reported is limited to the analysis of free vibrations utilizing the method of dynamic transport matrix (DTM), and the finite elements method (FEM). A comparative study of the results provided by the DTM is presented to assess the vibration characteristics of circular helicoidal bars and circular bars. The results indicate: the inherent structural superiority of the three dimensional behaviour of circular helicoidal bars; and the computational efficiency of the DTM as compared to the FEM.

Gives a bibliographical review of the finite element methods (FEMs) applied for the linear and nonlinear, static and dynamic analyses of basic structural elements from the theoretical as well as practical points of view. The range of applications of FEMs in this area is wide and cannot be presented in a single paper; therefore aims to give the reader an encyclopaedic view on the subject. The bibliography at the end of the paper contains 2,025 references to papers, conference proceedings and theses/dissertations dealing with the analysis of beams, columns, rods, bars, cables, discs, blades, shafts, membranes, plates and shells that were published in 1992‐1995.

The purpose of this paper is to propose and analyze the free vibration response of the spatial curved beams with variable curvature, torsion and cross section, in which all the effects of rotary inertia, shear and axial deformations can be considered.

The governing equations for free vibration response of the spatial curved beams are derived in matrix formats, considering the variable curvature, torsion and cross section. Frobenius’ scheme and the dynamic stiffness method are applied to solve these equations. A computer program is coded in Mathematica according to the proposed method.

To assess the validity of the proposed solution, a convergence study is carried out on a cylindrical helical spring with a variable circular cross section, and a comparison is made with the finite element method (FEM) results in ABAQUS. Further, the present model is used for reciprocal spiral rods with variable circular cross section in different boundary conditions, and the comparison with FEM results shows that only a limited number of terms in the results provide a relatively accurate solution.

The numerical results show that only a limited number of terms are needed in series solutions and in the Taylor expansion series to ensure an accurate solution. In addition, with a simple modification, the present formulation is easy to extend to analyze a more complicated model by combining with finite element solutions or analyze the transient responses and stochastic responses of spatial curved beams by Laplace transformation or Fourier transformation.

The purpose of this paper is to address the practically important problem of the load dependence of transverse vibrations for helical springs. At the beginning, the author develops the equations for transverse vibrations of the axially loaded helical springs. The method is based on the concept of an equivalent column. Second, the author reveals the effect of axial load on the fundamental frequency of transverse vibrations and derive the explicit formulas for this frequency. The fundamental natural frequency of the transverse vibrations of the spring depends on the variable length of the spring. The reduction of frequency with the load is demonstrated. Finally, when the frequency nullifies, the side buckling spring occurs.

Helical springs constitute an integral part of many mechanical systems. A coil spring is a special form of spatially curved column. The center of each cross-section is located on a helix. The helix is a curve that winds around with a constant slope of the surface of a cylinder. An exact stability analysis based on the theory of spatially curved bars is complicated and difficult for further applications. Hence, in most engineering applications a concept of an equivalent column is introduced. The spring is substituted for the simplification of the basic equations by an equivalent column. Such a column must account for compressibility of axis and shear effects. The transverse vibration is represented by a differential equation of fourth order in place and second order in time. The solution of the undamped model equation could be obtained by separation of variables. The fundamental natural frequency of the transverse vibrations depends on the current length of the spring. Natural frequency is the function of the deflection and slenderness ratio. Is the fundamental natural frequency of transverse oscillations nullifies, the lateral buckling of the spring with the natural form occurs. The mode shape corresponds to the buckling of the spring with moment-free, simply supported ends. The mode corresponds to the buckling of the spring with clamped ends. The author finds the critical spring compression.

Buckling refers to the loss of stability up to the sudden and violent failure of seed straight bars or beams under the action of pressure forces, whose line of action is the column axis. The known results for the buckling of axially overloaded coil springs were found using the static stability criterion. The author uses an alternative approach method for studying the stability of the spring. This method is based on dynamic equations. In this paper, the author derives the equations for transverse vibrations of the pressure-loaded coil springs. The fundamental natural frequency of the transverse vibrations of the column is proved to be the certain function of the axial force, as well as the variable length of the spring. Is the fundamental natural frequency of transverse oscillations turns to be to zero, is the lateral buckling of the spring occurs.

The spring is substituted for the simplification of the basic equations by an equivalent column. Such a column must account for compressibility of axis and shear effects. The more accurate model is based on the equations of motion of loaded helical Timoshenko beams. The dimensionless for beams of circular cross-section and the number of parameters governing the problem is reduced to four (helix angle, helix index, Poisson coefficient, and axial strain) is to be derived. Unfortunately, that for the spatial beam models only numerical results could be obtained.

The closed form analytical formulas for fundamental natural frequency of the transverse vibrations of the column as function of the axial force, as well as the variable length of the spring are derived. The practically important formulas for lateral buckling of the spring are obtained.

In this paper, the author derives the new equations for transverse vibrations of the pressure-loaded coil springs. The author demonstrates that the fundamental natural frequency of the transverse vibrations of the column is the function of the axial force. For study of the stability of the spring the author uses an alternative approach method. This method is based on dynamic equations. The new, original expressions for lateral buckling of the spring are also obtained.

The paper's aim is to focus on the utilization of the GRID distributed computing environment in order to reduce simulation time for parameter studies of travelling wave tube (TWT) electron guns and helix slow‐wave structures.

Two TWT finite‐element analysis modules were adapted to be run on the GRID, for this purpose scripts were written to submit a collection of independent jobs (the parameter study) to the GRID and collect the results.

A 25‐job electron gun parameter study runs on the GRID in 30‐40 min instead of 7 h locally. A 16‐job slow‐wave structure parameter study runs in 1 h on the GRID instead of 8 h locally. Turnaround time on the GRID was limited by priority levels presently set by GRID management for the various jobs submitted.

The procedures guarantee a remarkable reduction of the computing time.

For heavy‐computational cost tasks such as the above finite element electromagnetic calculations, the effective use of a heterogeneous, distributed, computing platform (the GRID computing platform) is very advantageous. The paper shows the development of new generation collaborative tools.

This paper aims to present a new iterative procedure for the 3D representation of focusing magnetic fields in TWTs generated by PPMs, by using equivalent sources and optimisation algorithms.

In the integrated optimisation strategy general models for magnetic sources are employed and local and global inverse problems are iteratively solved for the minimization of the representation error.

The results obtained show that the target accuracy is reached with a low computational effort, employing a minimum number of equivalent sources.

The procedure is robust and converges for all the examined magnetic field configurations.

Different from other approaches, the procedure presented here can be directly applied to a variety of different models for magnetic sources.

A bibliographical review of the finite element methods (FEMs) applied for the linear and nonlinear, static and dynamic analyses of basic structural elements from the theoretical as well as practical points of view is given. The bibliography at the end of the paper contains 1,726 references to papers, conference proceedings and theses/dissertations dealing with the analysis of beams, columns, rods, bars, cables, discs, blades, shafts, membranes, plates and shells that were published in 1996‐1999.

Under this heading are published regularly abstracts of all Reports and Memoranda of the Aeronautical Research Council, Reports and Technical Memoranda of the United States National Advisory Committee for Aeronautics and publications of other similar Research Bodies as issued

THE Fourth International Congress for Applied Mechanics was held this year at Cambridge from July 3rd to July 9th, under the Presidency of Professor C. E. Inglis, O.B.E., F.R.S. At a conversazione at the Engineering Laboratory, by invitation of Professor Inglis and the staff of the University Engineering Department, members of the Congress were enabled to exhibit their own apparatus. A visit to the Cavendish Laboratory was also arranged for those especially interested in Atomic Physics.

Under this heading are published regularly abstracts of all Reports and Memoranda of the Aeronautical Research Council, Reports and Technical Notes of the United States National Advisory Committee for Aeronautics and publications of other similar Research Bodies as issued