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Trinh, Minh-Chien,Nguyen, Dinh-Duc,Kim, Seung-Eock Elsevier 2019 Aerospace science and technology Vol.87 No.-
<P><B>Résumé</B></P> <P>The fundamental frequencies and nonlinear dynamic responses of functionally graded sandwich shells with double curvature under the influence of thermomechanical loadings and porosities are investigated in this study. Two material models are considered. The continuity requirement of material properties throughout layers are fulfilled by newly introducing refined effects of two porosity types regarding the average of constituent properties weighted by the porosity volume fraction. The first-order shear deformation theory taking the out-of-plane shear deformation into account is employed to obtain the Lagrange equation of motions. The number of primary variables reduces from five to three after introducing the Airy stress function. The system of dynamic governing equations is obtained by utilizing the Bubnov–Galerkin procedure. The natural frequencies are analytically computed by solving eigenvalue problems, and the fundamental frequencies are acquired by further assumptions about the inertial force caused by the shell rotation variables. The nonlinear dynamic responses of the functionally graded spherical, cylindrical, and hyperbolic paraboloid shells under the influence of different geometry configurations, loading conditions, and porosity types and degrees are obtained by applying the fourth-order Runge–Kutta method. The numerical results are presented and verified with available studies in the literature. Although porosities are usually considered material defects weakening the structure performance, this study has proved clearly that porosities stiffen the shell structures to some extent.</P>
Nguyen, Dinh-Kien,Gan, Buntara S.,Trinh, Thanh-Huong Techno-Press 2014 Structural Engineering and Mechanics, An Int'l Jou Vol.49 No.6
Geometrically nonlinear analysis of planar beam and frame structures made of functionally graded material (FGM) by using the finite element method is presented. The material property of the structures is assumed to be graded in the thickness direction by a power law distribution. A nonlinear beam element based on Bernoulli beam theory, taking the shift of the neutral axis position into account, is formulated in the context of the co-rotational formulation. The nonlinear equilibrium equations are solved by using the incremental/iterative procedure in a combination with the arc-length control method. Numerical examples show that the formulated element is capable to give accurate results by using just several elements. The influence of the material inhomogeneity in the geometrically nonlinear behavior of the FGM beam and frame structures is examined and highlighted.
Dinh-Kien Nguyen,Buntara S. Gan,Thanh-Huong Trinh 국제구조공학회 2014 Structural Engineering and Mechanics, An Int'l Jou Vol.49 No.6
Geometrically nonlinear analysis of planar beam and frame structures made of functionally graded material (FGM) by using the finite element method is presented. The material property of the structures is assumed to be graded in the thickness direction by a power law distribution. A nonlinear beam element based on Bernoulli beam theory, taking the shift of the neutral axis position into account, is formulated in the context of the co-rotational formulation. The nonlinear equilibrium equations are solved by using the incremental/iterative procedure in a combination with the arc-length control method. Numerical examples show that the formulated element is capable to give accurate results by using just several elements. The influence of the material inhomogeneity in the geometrically nonlinear behavior of the FGM beam and frame structures is examined and highlighted.
Nguyen Dinh Tinh,Trinh Dang Khanh 대한전자공학회 2021 IEIE Transactions on Smart Processing & Computing Vol.10 No.4
This paper proposes a new imaging geometry model for multi-receiver synthetic aperture sonar (SAS). The model considers the change of the speed of sound in seawater, the effect of platform movement on the acoustic velocity vector (AVV), and the Doppler effect. Based on the proposed model, a solution to determine the phase distribution was generated to improve the SAS image quality. The simulation results demonstrate the merits of proposed model compared to the traditional models that consider the speed of sound in seawater as a fixed value, ignore the change of AVV during transmission, and suppress the Doppler effect.
New Solution Determining Optimal Amplitude Distribution for Sparse Cylindrical Sonar Arrays
Nguyen Dinh Tinh,Trinh Dang Khanh 대한전자공학회 2021 IEIE Transactions on Smart Processing & Computing Vol.10 No.1
This paper proposes a new solution to determine the optimal amplitude distribution reducing side-lobe level (SLL) to less than the required value and generate the narrowest half-power beamwidth (HPBW) in sparse cylindrical sonar arrays. The proposed solution was implemented based on the explicit expression of a beam pattern, separation of the amplitude distribution into the row and the column, and an analysis of the beam patterns from simulations. The merits of the proposed solution were evaluated by simulation in two cases with isotropic elements and directional elements.
Measurement Coding for Compressive Sensing of Color Images
Dinh, Khanh Quoc,Trinh, Chien Van,Nguyen, Viet Anh,Park, Younghyeon,Jeon, Byeungwoo The Institute of Electronics and Information Engin 2014 IEIE Transactions on Smart Processing & Computing Vol.3 No.1
From the perspective of reducing the sampling cost of color images at high resolution, block-based compressive sensing (CS) has attracted considerable attention as a promising alternative to conventional Nyquist/Shannon sampling. On the other hand, for storing/transmitting applications, CS requires a very efficient way of representing the measurement data in terms of data volume. This paper addresses this problem by developing a measurement-coding method with the proposed customized Huffman coding. In addition, by noting the difference in visual importance between the luma and chroma channels, this paper proposes measurement coding in YCbCr space rather than in conventional RGB color space for better rate allocation. Furthermore, as the proper use of the image property in pursuing smoothness improves the CS recovery, this paper proposes the integration of a low pass filter to the CS recovery of color images, which is the block-based ${\ell}_{20}$-norm minimization. The proposed coding scheme shows considerable gain compared to conventional measurement coding.