Vietnam Journal of Mechanics
http://vjs.ac.vn/index.php/vjmech
Publishing House for Science and Technologyen-USVietnam Journal of Mechanics0866-7136<span>1. We hereby assign copyright of our article (the Work) in all forms of media, whether now known or hereafter developed, to the Vietnam Journal of Mechanics (VJMech). We understand that the VJMech will act on my/our behalf to publish, reproduce, distribute and transmit the Work.</span><br /><span>2. This assignment of copyright to the VJMech is done so on the understanding that permission from the VJMech is not required for me/us to reproduce, republish or distribute copies of the Work in whole or in part. We will ensure that all such copies carry a notice of copyright ownership and reference to the original journal publication.</span><br /><span>3. We warrant that the Work is our results and has not been published before in its current or a substantially similar form and is not under consideration for another publication, does not contain any unlawful statements and does not infringe any existing copyright. </span><br /><span>4. We also warrant that We have obtained the necessary permission from the copyright holder/s to reproduce in the article any materials including tables, diagrams or photographs not owned by me/us.</span>Super cavity model with the coupling reaction of slender body motion and water flow
http://vjs.ac.vn/index.php/vjmech/article/view/8488
<p>On the imperfect water entry, a high-speed slender body moving in the forward direction, rotates inside the cavity. The body's motion makes super cavity phenomena in the water flow. The water velocity and pressure fields interact during the body's motion. In this paper, the coupling simulation model is a combination of two sub-models: In the first sub-model, the motion of slender body running very fast underwater is simulated. The equation system of this sub-model is solved by Runge-Kutta method; In the second sub-model, the water flow and pressure field under reaction of very fast slender body motion are simulated by Ansys-CFX. The simulation results of this coupled model are compared with experiments based on magnitudes of velocity U by x<sub>0</sub> direction and error percents for cavity diameter and length.</p>Tran Thu HaNguyen Duc ThuyenNguyen Thai DungDuong Ngoc Hai
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2018-01-012018-01-01DYNAMIC ANALYSIS OF STEPPED COMPOSITE CYLINDRICAL SHELLS RESTING ON PASTERNAK ELASTIC FOUNDATION BASED ON CONTINUOUS ELEMENT METHOD
http://vjs.ac.vn/index.php/vjmech/article/view/9832
<span lang="VI">This research presents a new continuous element model for solving vibration problems of stepped composite cylindrical shells resting on Winkler and Pasternak foundations with various boundary conditions. Based on the First Shear Deformation Theory (FSDT), the equations of motion of the circular cylindrical shell are introduced and the dynamic stiffness matrix is obtained for each segment of uniform shell. The interesting assembly procedure of continous element method (CEM) is adopted to analyze the dynamic behavior of the multi-stepped composite cylindrical shell on elastic foundation. Free vibrations and harmonic responses of different configurations of stepped composite cylindrical shells on elastic foundation are examined. Effects of structural parameters, stepped thickness and elastic foundations on the free vibration responses of stepped composite cylindrical shells are also presented. Comparisons with previously published results and finite element (FE) analyses show that the proposed technique saves data storage volume and calculating time, is accurate and efficient for studying medium and high frequencies. </span>Nam Bich LeCuong Manh NguyenThinh Ich Tran
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2018-01-112018-01-11Nonlinear dynamic response of ES-FGM plates under blast load
http://vjs.ac.vn/index.php/vjmech/article/view/9840
<p>The paper studies nonlinear dynamic response of an eccentrically stiffened FGM (ES-FGM) plates resting on the elastic foundations subjected to blast and thermal loads with temperature dependent material properties using the Reddy’s higher order shear deformation plate theory, stress function, the Galerkin and the fourth order Runge-Kutta methods. The plates are reinforced by outside stiffeners and both stiffeners and plate are deformed under temperature. The effects of material and geometrical properties, temperature-dependent material properties, elastic foundations and stiffeners on the nonlinear dynamic response of the ES FGM plate under blast and thermal loads in thermal environments are studied and discussed.</p>Nguyen Dinh DucCong Hong Pham
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2018-01-202018-01-20Buckling and postbuckling of carbon nanotube-reinforced composite cylindrical panels subjected to axial compression in thermal environments
http://vjs.ac.vn/index.php/vjmech/article/view/10088
<p>This paper presents an analytical investigation on the buckling and postbuckling behavior of thin composite cylindrical panels reinforced by single walled carbon nanotubes (SWCNTs), exposed to thermal environments and subjected to uniform axial compression. Material properties of isotropic matrix phase and carbon nanotubes are assumed to be temperature dependent, and effective properties of carbon nanotube-reinforced composite (CNTRC) are functionally graded in the thickness direction and estimated by extended rule of mixture. Governing equations are based on the classical thin shell theory taking von Karman-Donnell nonlinearity and initial geometrical imperfection into consideration. Approximate solutions are assumed to satisfy simply supported boundary conditions and Galerkin procedure is applied to derive explicit expressions of buckling loads and load-deflection relation. Effects of volume fraction and distribution type of carbon nanotubes, geometrical parameters, elevated temperature and initial imperfection on the nonlinear stability of CNTRC cylindrical panels are analyzed and discussed.</p>Hoang Van Tung
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2018-01-192018-01-19An approximate formula for the H/V ratio of Rayleigh waves in compressible pre-stressed elastic half-spaces coated with a thin layer
http://vjs.ac.vn/index.php/vjmech/article/view/10417
<span>This paper is concerned with the propagation of Rayleigh waves in a compressible pre-stressed elastic half-space coated with a thin compressible prestressed elastic layer. The main purpose of the paper is to establish an approximate formula for the H<span><em>/</em><span>V ratio (the ratio between the amplitudes of the <span>horizontal and vertical displacements of Rayleigh waves at the traction-free<br /><span>surface of the layer). First, the relations between the traction amplitude vector and the displacement amplitude one of Rayleigh waves at two sides of the <span>interface between the layer and the half-space are created. From the continuity condition at the interface and these relations the displacement amplitude <span>vector of Rayleigh waves at the interface is determined. Then, a third-order <span>approximate formula for the <span><em>H/V </em><span>ratio has been derived by expanding the<br /><span>layer displacement amplitude vector at its traction-free surface into Taylor<br /><span>series at the interface. It is shown numerically that the obtained formula is a<br /><span>good approximate one.</span></span></span></span></span></span></span></span><br /></span></span></span></span></span>Nguyen Thi Khanh Linh
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2018-01-102018-01-10FREE VIBRATION ANALYSIS OF 2-D FGM BEAMS IN THERMAL ENVIRONMENT BASED ON A NEW THIRD-ORDER SHEAR DEFORMATION THEORY
http://vjs.ac.vn/index.php/vjmech/article/view/10503
Free vibration analysis of two-directional functionally graded material (2-D FGM) beams in thermal environment based on a new third-order shear deformation theory is presented. The material properties are assumed to be graded in both the thickness and longitudinal directions by a power law distribution, and they are considered to be temperature-dependent. Equations of motion, in which the shear rotation rather than the cross-sectional rotation is considered to be an independent variable, are constructed from Hamilton's principle. A finite element formulation is derived and employed to compute the vibration characteristics of the beams. The numerical results reveal that the developed formulation is accurate, and it is capable to give accurate natural frequencies by using a small number of elements. A parametric study is carried out to highlight the effects of material composition, temperature rise on the vibration characteristics of the beams.Nguyen Dinh Kien
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2018-01-212018-01-21ROBUST CONTROL FOR A WHEELED MOBILE ROBOT TO TRACK A PREDEFINED TRAJECTORY IN THE PRESENCE OF UNKNOWN WHEEL SLIPS
http://vjs.ac.vn/index.php/vjmech/article/view/10564
<p>In this paper, a robust controller for a nonholonomic wheeled mobile robot (WMR) is proposed for tracking a predefined trajectory in the presence of unknown wheel slips, bounded external disturbances, and model uncertainties. The whole control system consists of two closed loops. Specifically, the outer one is employed to control the kinematics, and the inner one is used to control the dynamics. The output of kinematic controller is adopted as the input of the inner (dynamic) closed loop. Furthermore, two robust techniques were utilized to assure the robustness. In particular, one is used in the kinematic controller to compensate the harmful effects of the unknown wheel slips, and the other is used in the dynamic controller to overcome the model uncertainties and bounded external disturbances. Thanks to this proposed controller, a desired tracking performance in which tracking errors converge asymptotically to zero is obtained. According to Lyapunov theory and LaSalle extension, the desired tracking performance is guaranteed to be achieved. The results of computer simulation validated the validity and efficiency of the proposed controller.</p>Kiem NguyentienLinh LeDo Anh TuanNguyen Van TinhPham Minh Tuan
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2018-01-202018-01-20STUDY OF THE INFLUENCE OF SMALL DEFECTS NEAR A SINGULAR POINT IN ANTIPLANE ELASTICITY BY AN ASYMPTOTIC METHOD
http://vjs.ac.vn/index.php/vjmech/article/view/9341
We consider a domain made of a linear elastic material which contains an angular point. A small defect, like a cavity or a crack, is located in the neighborhood of the tip of the wedge. In order to study its inuence both on the local and global responses of the body, we use a matched asymptotic expansion method. After the general construction of the matched asymptotic expansions for an arbitrary defect, we develop the method in the particular case where the defect is a small crack. The numerical results obtained from the method are nally compared with those given by the classical nite element method. All the analysis is made in an antiplane setting in order to make easier the calculations.Dang Thi Bach TuyetLaurence HalpernJean-Jacques Marigo
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2018-01-242018-01-24Polarization versus Mori-Tanaka approximations for effective conductivity of isotropic composites
http://vjs.ac.vn/index.php/vjmech/article/view/10572
Our polarization approximations for the effective conductivity of isotropic multicomponent materials, constructed recently as approximate solutions to the minimum energy principles, are compared with the widely used Mori-Tanata approximation, derived as an approximate solution of the field equations. The similarities and differences, the advantages and disadvantages of both approaches are analysed with illustrating numerical examples.Kien Trung NguyenChinh Duc PhamDuyen Thi Hai Nguyen
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2018-01-072018-01-07Static and free vibration analyses of laminated composite shells by cell-based smoothed discrete shear gap method (CS-DSG3) using three-node triangular elements
http://vjs.ac.vn/index.php/vjmech/article/view/10579
A cell-based smoothed discrete shear gap method (CS-DSG3) using three-node triangular elements was recently proposed to improve the performance of the discrete shear gap method (DSG3) for static and free vibration analyses of isotropic Reissner-Mindlin plates and shells. In this paper, the CS-DSG3 is further extended for static and free vibration analyses of laminated composite shells. In the present method, the first-order shear deformation theory (FSDT) is used in the formulation due to the simplicity and computational efficiency The accuracy and reliability of the proposed method are verified by comparing its numerical solutions with those of others available numerical results.Pham Quoc HoaTran The VanPham Tien DatDang Trung HauNguyen Viet HaNguyen Manh HungNguyen Thoi Trung
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2018-01-242018-01-24Weighted averaging technique for the design of dynamic vibration absorber installed in damped primary structures
http://vjs.ac.vn/index.php/vjmech/article/view/10732
<p class="Abstract">The dynamic vibration absorber has been widely applied in various technical fields. In the case of using the tuned mass damper (TMD), the selection of optimum absorber parameters is extremely important. This paper presents a simple approach to determine a closed-form expression for the optimum tuning ratio of a TMD attachted to a damped primary structure. The result is obtained by using the equivalent linearization method based on the so-called weighted averaging technique proposed by the first author. The values of the optimum tuning ratio derived from the expression proposed in this paper is compared with those obtained numerically as well as the ones obtained from other authors. The comparison shows the reliability of the method given in this study.</p>Anh Dong NguyenHai Quang NinhNguyen Xuan NguyenTra My Thi Phan
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2018-01-242018-01-24REFLECTION AND TRANSMISSION OF QUASI-PWAVES THROUGH AN ORTHOTROPIC LAYER SANDWICHED BETWEEN TWO HALF-SPACES
http://vjs.ac.vn/index.php/vjmech/article/view/10807
<p>In this paper, the reflection and transmission of a qP wave through an orthotropic elastic layer sandwiched between two orthotropic elastic half-spaces is investigated. The main aim is to derive the expressions in closed-form of the reflection and transmission coefficients. These expressions have been obtained by using the transfer matrix for an orthotropic layer. Based on the obtained expressions, some numerical examples are carried out to examine the dependence of the reflection and transmission coefficients on the incident angle, the wave frequency and the ratio of mass densities.</p>Do Xuan TungNguyen Thi Kieu
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2018-01-242018-01-24