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>Reservoirs optimization with dynamic programming
http://vjs.ac.vn/index.php/vjmech/article/view/8334
Differential Evolution (DE) and Dynamic Programming (DP) are important optimal methods in reservoir regulation. In the previous work [1], we presented the outline of DE, and applied it into Pleikrong reservoir, a big one in the Highland of Vietnam for dry season of 2010 year. Continuing from that, in this work, we present the outline of DP and then <span> </span>again, apply it to Pleikrong reservoir; and also apply it to Ialy, the biggest reservoir in Sesan cascade in the Highland of Vietnam; to reach optimal regulation for the maximum power production in the dry season of two years: 2010 and 2012. The results getting from DP are compared to the results by using DE. The results by these two methods have the same trend of releases which is storing the water at the beginning and significantly releasing at the end of the calculation time.<br />Phan Thi Thu PhuongDao Thi Ngoc HanHoang Van LaiBui Minh Tri2017-09-232017-09-2339Theoretical and experimental studies for crack detection of a beam-like structure using element stiffness index distribution method
http://vjs.ac.vn/index.php/vjmech/article/view/8422
<p>In this paper, theoretical and experimental studies for crack detection of structures using ‘‘element stiffness index distribution’’ are presented. The element stiffness index distribution is defined as a vector of norms of sub-matrices corresponding to element stiffness matrices calculated from the reconstructed global stiffness matrix of the beam. When there is a crack at an element, the element stiffness index of that element will be changed. By inspecting the change in the element stiffness index distribution, the crack can be detected. A significant peak in the element stiffness index distribution is the indicator of the crack existence. The crack location is determined by the location of the peak and the crack depth can be determined from the height of the peak. The global stiffness matrix is calculated from the measured frequency response functions instead of mode shapes to avoid limitations of the mode shape-based methods for crack detection. Numerical simulation results for the cases of beam-like structures are provided. The experiment is carried out to justify the efficiency of the proposed method.</p>Khoa Viet NguyenQuang Van Nguyen2017-09-232017-09-2339Mode shape analysis of multiple cracked functionally graded Timoshenko beams
http://vjs.ac.vn/index.php/vjmech/article/view/8631
In this paper based on Timoshenko beam theory, rotational spring model of crack and dynamic stiffness method the authors analyzed mode shapes of multiple cracked functionally graded material (FGM) beam. Material properties vary continuously throughout the thickness direction according to the volume fraction constituent deﬁned by power law function. Consistent theory of vibration is formulated for multiple cracked FGM Timoshenko beam taking into account the actual position of neutral axis that is a useful tool for analysis of coupled vibration in the beam. The frequency and mode shape equation obtained provides an efficient method for modal analysis of multiple cracked FGM Timoshenko beam. The theoretical development has been illustrated and validated by numerical examples.Tran Van LienNguyen Tien KhiemNgo Trong Duc2017-09-232017-09-2339A CELL-BASED SMOOTHED THREE-NODE PLATE FINITE ELEMENT WITH A BUBBLE NODE FOR STATIC ANALYSES OF BOTH THIN AND THICK PLATES
http://vjs.ac.vn/index.php/vjmech/article/view/8809
This paper develops the cell-based (CS) smoothed finite element method for a three-node plate finite element with a bubble node at the centroid of the element. Based on the first-order shear deformation theory, the in-plane strains are smoothed on three non-overlapped subdomains of the element to transform the numerical integration of the element stiffness matrix from the surfaces into the lines of the subdomains. The shear-locking phenomenon, which occurs when the plate’s thickness becomes small, is removed by employing the mixed interpolation of tensorial components (MITC). The present element, namely CS-MITC3+, passes the patch test and behaves independently from the sequence of node numbers of the element. Numerical results given by the CS-MITC3+ elements are better than the MITC3+ elements. As compared to other smoothed three-node plate finite elements, the CS-MITC3+ is a good competitor.Thanh Chau-Dinh2017-09-232017-09-2339NONLINEAR VIBRATION OF SANDWICH DOUBLY CURVED SHALLOW SHELLS REINFORCED BY FGM STIFFENERS. PART 1: GOVERNING EQUATIONS
http://vjs.ac.vn/index.php/vjmech/article/view/9692
This paper focus on highlights as follows: the shells are reinforced by FGM stiffeners; four models of the shells with general Sigmoid and Power laws distribution are considered; expressions of force and moment resultants depend on the stiffeners and the temperature. Nonlinear vibration of sandwich doubly curved shallow shells<strong> </strong>subjected to<strong> </strong>mechanical and thermal loading are investigated based on the first order shear deformation theory (FSDT) with von Kármán- type nonlinearity, taking into account initial geometrical imperfection and smeared stiffener technique. By Galerkin method, the explicit expressions for determining natural frequencies, nonlinear frequency–amplitude relation, and time – deflection curves of the sandwich shallow shells are derived.Dang Thuy DongDao Van Dung2017-09-232017-09-2339Vibrations of Fractional Half- and Single-Degree of Freedom Systems
http://vjs.ac.vn/index.php/vjmech/article/view/9772
<p>In this paper we study vibrations of fractional oscillators by two methods: the triangular strip matrix approach, based on the Grünwald-Letnikov discretization of the fractional term, and the state variable analysis, which is suitable for systems with fractional derivatives of rational order. Some examples are solved in order to compare the two approaches and to conduct comparison with benchmark problems.</p>Isaac ElishakoffValentina CiaschettiAlessandro Marzani2017-09-232017-09-2339A one dimensional variational model of superelasticity for shape memory alloys
http://vjs.ac.vn/index.php/vjmech/article/view/10750
In this paper we propose a variational framework for the modeling of superelasticity in shape memory alloys with softening behavior. This model is valid for a class of standard rate-independent materials with a single internal variable. The quasi-static evolution is based on two physical principles: a stability criterion which selects the local minima of the total energy and an energy balance condition which ensures the absolute continuity of the total energy. The stability criterion allows to bypass non-uniqueness issues associated to softening behaviour while the energy balance condition accounts for brutal evolutions at the local levels. We investigate properties of homogeneous and non-homogenous solutions towards this variational evolution problem. Specifically, we show how softening behaviour can lead to instability of the homogeneous states. In this latter case, we show that a stable solution would consist in following the Maxwell line given by the softening behaviour, then resulting in a non-homogeneous evolution.Kim Pham2017-09-232017-09-2339