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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 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.
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.
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.
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.
Smoothed Group-Sparsity Iterative Hard Thresholding Recovery for Compressive Sensing of Color Image
Viet Anh Nguyen,Khanh Quoc Dinh,Chien Van Trinh,Younghyeon Park(박영현),Byeungwoo Jeon(전병우) 대한전자공학회 2014 전자공학회논문지 Vol.51 No.4
압축센싱은 성긴(Sparse) 또는 압축가능한(Compressible) 신호에 대해 Nyquist rate 미만의 샘플링으로도 신호 복원이 가능하다는 것을 수학적으로 증명한 새로운 패러다임의 신호 획득 방법이다. 단순한 신호 획득 과정을 이용하면서도, 동시에 우수한 압축센싱 복원 영상을 얻기 위한 많은 연구들이 수행되고 있다. 그러나, 에너지 분포 및 인간 시각 시스템 등 컬러 영상에 대한 기본적인 특성을 복원 과정에 활용한 기존 압축센싱 관련 연구는 많이 부족하다. 이러한 문제를 해결하기 위해, 본 논문에서는 컬러영상의 압축센싱 복원을 위한 평활 그룹-희소성 기반 반복적 경성 임계 알고리즘을 제안한다. 제안하는 방법은 그룹-희소성에 기반한 경성 임계치 적용과 프레임 기반 필터의 사용을 통해 영상의 변환 영역에 대한 희소성을 증대시키는 동시에 화소 영역의 평활 정도를 복원 과정에 활용할 수 있도록 한다. 또한, 그룹-희소화 경성 임계 과정은 자연 영상의 에너지 분포 및 인간 시각 시스템 특성에 따라 중요하다고 판단되는 RGB-그룹 계수들을 보전하도록 설계하였다. 실험 결과 객관적 화질 측면에서 제안방법이 대표적인 그룹-희소화 평활 복원 기법 보다 평균 PSNR이 최대 2.7dB 높은 것을 확인하였다. Compressive sensing is a new signal acquisition paradigm that enables sparse/compressible signal to be sampled under the Nyquist-rate. To fully benefit from its much simplified acquisition process, huge efforts have been made on improving the performance of compressive sensing recovery. However, concerning color images, compressive sensing recovery lacks in addressing image characteristics like energy distribution or human visual system. In order to overcome the problem, this paper proposes a new group-sparsity hard thresholding process by preserving some RGB-grouped coefficients important in both terms of energy and perceptual sensitivity. Moreover, a smoothed group-sparsity iterative hard thresholding algorithm for compressive sensing of color images is proposed by incorporating a frame-based filter with group-sparsity hard thresholding process. In this way, our proposed method not only pursues sparsity of image in transform domain but also pursues smoothness of image in spatial domain. Experimental results show average PSNR gains up to 2.7dB over the state-of-the-art group-sparsity smoothed recovery method.