Vietnam Journal of Mechanics

Xem 1-20 trên 451 kết quả Vietnam Journal of Mechanics
  • A further illustration of the interest shown in the 1950's for dynamic problems involving stationary cracks is given by the occurrence of a doctor's thesis in the California Institute of Technology by D.D.Ang, who considered the same problem as Maue and used the Wiener-Hopt technique after solution of dual integral equations.

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  • In the present paper it is introduced the method for determining the reactions of mechanical constraints ( holonomic and nonholonomic constraints).

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  • This paper presents results of numerical simulation for a wave energy converter using linear permanent magnet generator. The use of linear permanent generator has advantages of simple structure, minimizing mechanical loose... On the base of mechanics model, a system of equations describing the operation of the device under linear potential wave was obtained. The magnetic field in generator was calculated by FlexPDE software.

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  • In the paper a new method for mechanical systems with non-ideal constraints is presented. It is proved that a mechanical system subjected to physical non-ideal constraints cannot be determined purely by theoretical analysis because the reaction forces depend on the physical parameters of interactive environment, which are identified only by measurement. The principle of compatibility is shown to be an effective tool in combination with experience to investigate such a problem. For illustration the dynamics of a digging machine is investigated.

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  • Let us consider a vibrating system with n degrees of freedom which consists of a weightless cantilever beam carrying n concentrated masses m1, m2, ... , mn (Fig. 1). The elastic elements of the vibrating system have stiffness ki, k2, ... , kn.

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  • The paper presents the results of theoretical and experimntal studies of the aerodynamic characteristics of a wing-in-surface-effect ship (WISES), which was made under coordination of the Institute of Mechanics, Vietnamese Academy of Science and Tech nology.

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  • The analysis of the dissipation shows that the thermodynamical force associated with the evolution of a crack is an energy release rate, form of which depends on the presence or not of mechanical discontinuities. This energy release rate is given as an integral based on free or complementary energy. We analyse the invariance of such integrals and we discuss the obtained results in elastoplasticity.

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  • The dynamic analysis of mechanisms with joints friction is complex since the frictional force depends nonlinearly on the resultant reactive force between the two mating surfaces of the joint. In this paper a non-iterative approximate method is used for determining the joint reaction forces and the driving torque of mechanisms is considered. By using the computing program MATLAB the dynamic forces of a six-link planar mechanism are cakulated with this method.

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  • In the paper it is introduced a method of determining internal forces at any cross section of the links of mechanisms. As known, so far it is used the method of D'Alembert, which consists of two steps, the determination of the acceleration states of links and the establishment of the equilibrium equations for the set of forces including the forces of inertia and the internal forces at the cross section. A. I. Lurie proposed a method of analytical mechanics for this problem.

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  • This paper will present a method to identify flow patterns (bubble & slug flow) in vertical air-water two-phase flow by void fraction measurement (using an impedance probe) at Inst. of Mechanics Hanoi.

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  • The article deals with the form of equations of motion of mechanical system with constraints. For holonomic systems the number of differential equation is equal to the degrees of freedom, without regard to the number of chosen coordinates. The possibilities of computer processing (symbolical and numerical) are shown. Two simple examples demonstrate the described technique.

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  • This paper presents an experimental facility conducted in Hanoi Institute of Mechanics to investigate multiphase How pattern in the pipes. First and foremost, it ts used to define the conditions of water layer formation in the horizontal pipe.

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  • The determination of reaction forces at kinematical joints of mechanism plays an important role in dynamics of machines. In the paper a method of determining the reaction at kinematical joints is presented. It is established a set of equations that are divided into two groups. The one describes the motion of the system and the other allows to calculate the reaction at kinematical joints.

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  • In this paper, the finite element for cohesive crack for quasi-brittle materials is constructed by XFEM, which allows incorporation of the displacement discontinuities in the element. The algorithm of construction and procedures for involving this finite element into code Cast3M are presented. The numerical calculations in fracture mechanics are presented to demonstrate the benefits of the proposed implementation.

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  • In the study an extension of the Bubnov-Galerkin method in terms of the equivalent linearization method is presented. It is combined with sequential linearization and nonlinear procedure to yield a new method for solving nonlinear equations which can improve the accuracy when the nonlinearity is strong. For illustration the Duffing oscillator is considered to show the effectiveness of the proposed method.

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  • The dynamic behavior of nonuniform Euler-Bernoulli beams made of transversely functionally graded material under multiple moving forces is studied by the finite element method. The beam cross-section is assumed to vary in the width direction by two different types. A simple finite element formulation, accounting for variation of the material properties through the beam thickness and the shift in the physically neutral surface, is derived and employed in the study.

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  • In the paper the bifurcation theorem on the problem of thermal convection and contaminant transport in underground water is proven.

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  • This paper presents the influence coefficient method of determining the locations of unbalances on a flexible rotor system and the correction weights. A computer software for calculating the at-the-site balancing of a flexible rotor systern was created using c++ language at the Hanoi University of Technology. This software can be used by balancing flexible rotors in Vietnam.

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  • In the present article the author advances a diagnosis method of structures ditl'erent from the above, we expect that the advanced method could avoid some difficult inherent with the solution of inverse problem.

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  • This paper presents a displacement - based finite element formulation for nonlinear analysis of steel - concrete composite planar frames subjected to combined action of gravity and lateral loads. A 6DOF super element is proposed for modelling composite beam, allowing for partial interaction between the steel beam and the concrete slab, semi - rigid nature of beam to column composite connection and material nonlinearity.

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