Vietnam Journal of Mechanics

Calculation of transonic flows around profiles with blunt and angled leading edges

Hoang Thi Bich Ngoc — 2017-05-26

Transonic flow is a mixeđ flow of subsoníc and supersonic regions. Because of this míxture, the solution of transonic flow problems is obtained onlỵ when solving the diffeíentíal equations of motion with special treatments for the transition from subsonic re- gion to supersonic region and vice versa. VVebuilt codes solving the fulỉ potential equation and Euler equations by applying the íinite diííerence method and íinite volume method, and also associated with soítvvare Pluent to consider the viscous eííects. The analysis of resuits caỊculated for cases of transonic flow over proliỉes with blunt and angỉed ỉeading edges shows more dearly the physícal nature of the gas - solid interaction at leađing edges in the mixed flow and the optúnal applỉcation of each protìle in transonic flows.

An efficient numerical procedure for calculating periodic vibrations of elastic mechanisms

Nguyen Van Khang — 2017-05-30

This paper proposes a numerical procedure based on the well-known Newmark integration method to determine initial conditions for the periodic solution of a System of linear dilKerential equations with time-periodic coeffidents. Based on this, steady-state pe- riodic vibrations of mechanisms with elastic elements govemed by Imearixed differential equations with tữne-periođic coeííỉcients can be conveniently calculated. The proposed procedure is demonstĩated by a dynamic model of a planar four-bar mechanism with the flexible coupler.

The dispersion of Rayleigh waves in orthotropic layered half-space using matrix method

Tran Thanh Tuan — 2017-05-30

In this paper, the secular equation of Rayleigh suriface waves propagating in an orthotropic layered half-space is derived by the matrix method, AU the layers and the half- space are assumed to have identical prindple axes. The explicit form of the matrizant for each layer is obtained by the Sylvester's theorem. The derived secular equation takes only real values and depends only on the dimensionless variables and dimensionless material parameters. Hence, it is convenient in numerical calculation.

Reservoir optimization with differential evolution

Phan Thi Thu Huong — 2017-05-30

Reservoir optimization, is one of recent problems, which has been researched by several methods such as Unear Programming (LP), Non-linear Programming (NLP), Genetic Algorithm (GA), and Dynamic Programming (DP). Differential Evolution (DE), a method in GA group, is recently applied in many fields, especially water management. This method is an improved variant of GA to converge and reach to the optimal solution faster than the traditional GA. It is also capable to apply for a wide range space, to a problem with complex, discontmuous, undifferential optimal function. Furthermore, this method does not require the gradient information of the space but easily find the global solution by a simple algorithm. In this paper, we introduce DE, compare to LP which was considered mathematically decades ago to prove DE's accuracy, then apply DE to Pleikrong, a reservoir in Vietnam, then discuss about the results.

Vibration analysis of beams subjected to random excitation by the dual criterion of equivalent linearization

Nguyen Nhu Hieu — 2017-05-30

In this paper responses of beams subjected to random loading are analyzed by the dual approach of the equivalent linearization method. The extemal random loading is assumed to be a space-wise and time-wise white noise m which the exact solutions of the modal equations can be found. A system of nonlinear algebraic equations for linearization coeffidents of the modal lineramed system is obtained in a dosed form and is solved by the fixed-point iteration method. Results obtained from the proposed dual criterion are compared with the exact solution and those obtamed from other approaches including energy methods and conventional linearixation method. It is observed that the solution obtained by the dual criterion is in good agreement with the exact solution, especially, in the case of strong nonlinearity of beam.

Thermo-mechanical post-buckling of thick FGM plates resting on elastic foundations with tangential edge constraints

Hoang Van Tung — 2017-05-30

This paper investigates the effects of tangential edge consữaints and elastic foundations on the buckling and postbuckling behavior of thick PGM rectangular plates resting on elastic foundations and subjected to thermal and thermomechanical loading conditions. Material properties are assumed to be temperature dependent, and graded in (he thickness direction according to a simple power law distribution in terms of the volume fractions of constituents. Goveming equations are based on the higher order shear deformation plate theory incorporating the von Kannan geometrical nonlinearity, initial geometrical imperiection, tangential edge cọnstraints and Pastemak type elastic foundations. Approximate Solutions are assumed to satisfy simply supported bound- ary conditions and Galerkin procedure is applied to derive expressions of buckling loads and load-deflection relations. In thermal postbuckling analysis, an iteration algorithm is employed to determme critical buckling temperatures and postbuckling temperature- derection equilibrium paths. The separate and simultaneous effects of tangential edge resuaints, elastic foundations and temperature dependence of material propertles on the buckling and postbuckling responses of higher order shear deformable PGM plates are analyzed and discussed.