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Seung Cho D.,Pusan National University | Hee Kim B.,Samsung | Kim J.-H.,Createch Co. | Vladimir N.,University of Zagreb | Muk Choi T.,Createch Co.
Thin-Walled Structures | Year: 2015

Abstract Numerical procedure for the forced vibration analysis of bottom and vertical rectangular plate structures in contact with fluid, subjected to internal point harmonic excitation force is developed. The procedure is based on the assumed mode method for free vibration calculation and mode superposition method for forced vibration analysis. Structural model covers Mindlin rectangular plates and stiffened panels. Lagrange's equation of motion is utilized to formulate the eigenvalue problem taking into account potential and kinetic energies of a plate and reinforcements, and fluid kinetic energy which is calculated according to potential flow theory, respectively. From the boundary conditions for the fluid and structure the fluid velocity potential is derived and it is utilized for the calculation of added mass using the assumed modes. The developed theoretical model and in-house code are verified with extensive numerical examples related to forced vibration of bare plates and stiffened panels in contact with different fluid domains. Comparisons of the results with those obtained by a general purpose finite element (FE) software confirmed high accuracy of the presented numerical procedure. © 2015 Elsevier Ltd.


Cho D.S.,Pusan National University | Kim B.H.,Samsung | Kim J.-H.,Createch Co. | Vladimir N.,University of Zagreb | Choi T.M.,Createch Co.
Thin-Walled Structures | Year: 2015

This paper deals with numerical procedure for the vibration analysis of rectangular plates and stiffened panels subjected to point excitation force and enforced displacement at boundaries. The procedure is based on the assumed mode method, where natural response is determined by solving an eigenvalue problem of a multi-degree-of-freedom system matrix equation derived by using Lagrange's equation of motion. Mode superposition method is applied to calculate plate/stiffened panel frequency response. The Mindlin plate theory is adopted for a plate, while the effect of stiffeners having the properties of Timoshenko beams is taken into account by adding their potential and kinetic energies to the corresponding plate energies. The accuracy of the proposed procedure is justified by several numerical examples which include forced vibration analysis of plates and stiffened panels with different dimensions and framing sizes and orientations, having various combinations of boundary conditions. The results obtained by the developed in-house code are compared to those obtained by the finite element method (FEM) and experimental results from the relevant literature. The presented procedure is confirmed to be highly accurate. © 2015 Elsevier Ltd All rights reserved.


Kim K.,Korea University | Kim B.-H.,Samsung | Choi T.-M.,Createch Co. | Cho D.-S.,Pusan National University
International Journal of Naval Architecture and Ocean Engineering | Year: 2012

An approximate method based on an assumed mode method has been presented for the free vibration analysis of a rectangular plate with arbitrary edge constraints. In the presented method, natural frequencies and their mode shapes of the plate are calculated by solving an eigenvalue problem of a multi-degree-of-freedom system matrix equation derived by using Lagrange's equations of motion. Characteristic orthogonal polynomials having the property of Timoshenko beam functions which satisfies edge constraints corresponding to those of the objective plate are used. In order to examine the accuracy of the proposed method, numerical examples of the rectangular plates with various thicknesses and edge constraints have been presented. The results have shown good agreement with those of other methods such as an analytic solution, an approximate solution, and a finite element analysis.


Cho D.S.,Pusan National University | Kim B.H.,Samsung | Kim J.-H.,Createch Co. | Choi T.M.,Createch Co. | Vladimir N.,University of Zagreb
Ocean Engineering | Year: 2016

Stiffened panels are basic constitutive members of ships and offshore structures, and in practice they often have different mass and stiffness attachments, which significantly influence their dynamic response. In this paper, a numerical procedure is presented for the free vibration analysis of stiffened panels with arbitrary sets of boundary conditions and carrying multiple lumped mass and stiffness attachments. It is based on the assumed mode method, where characteristic orthogonal polynomials having the properties of Timoshenko beam functions and satisfying the specified edge constraints are used as approximation functions. The Mindlin theory is applied for plate and the Timoshenko beam theory for stiffeners. The total potential and kinetic energies of the system are formulated in a convenient manner and further applied to derive an eigenvalue problem by means of Lagrange's equation of motion. Based on the developed numerical procedure, an in-house code is developed and is applied to a free vibration analysis of bare plates and stiffened panels carrying lumped masses and locally supported by pillars or springs. Comparisons of the results with those available in the literature and FEA solutions confirm the high accuracy and practical applicability of the presented procedure. © 2016


Kim K.,Korea University | Kim J.-H.,Createch Co. | Choi T.-M.,Createch Co. | Cho D.-S.,Pusan National University
International Journal of Naval Architecture and Ocean Engineering | Year: 2012

A software system for a complex object scattering analysis, named SYSCOS, has been developed for a systematic radar cross section (RCS) analysis and reduction design. The system is based on the high frequency analysis methods of physical optics, geometrical optics, and physical theory of diffraction, which are suitable for RCS analysis of electromagnetically large and complex targets as like naval ships. In addition, a direct scattering center analysis function has been included, which gives relatively simple and intuitive way to discriminate problem areas in design stage when comparing with conventional image-based approaches. In this paper, the theoretical background and the organization of the SYSCOS system are presented. To verify its accuracy and to demonstrate its applicability, numerical analyses for a square plate, a sphere and a cylinder, a weapon system and a virtual naval ship have been carried out, of which results have been compared with analytic solutions and those obtained by the other existing software.


Cho D.S.,Pusan National University | Vladimir N.,University of Zagreb | Choi T.M.,Createch Co.
Polish Maritime Research | Year: 2015

Thin and thick plates, plates with holes, stiffened panels and stiffened panels with holes are primary structural members in almost all fields of engineering: civil, mechanical, aerospace, naval, ocean etc. In this paper, a simple and efficient procedure for the free vibration analysis of such elements is presented. It is based on the assumed mode method and can handle different plate thickness, various shapes and sizes of holes, different framing sizes and types as well as different combinations of boundary conditions. Natural frequencies and modes are determined by solving an eigenvalue problem of a multi-degree-of-freedom system matrix equation derived by using Lagrange's equations. Mindlin theory is applied for a plate and Timoshenko beam theory for stiffeners. The applicability of the method in the design procedure is illustrated with several numerical examples obtained by the in-house developed code VAPS. Very good agreement with standard commercial finite element software is achieved. © 2015 Dae Seung Cho et al.


Cho D.-S.,Pusan National University | Vladimir N.,University of Zagreb | Choi T.-M.,Createch Co.
Proceedings of the International Conference on Offshore Mechanics and Arctic Engineering - OMAE | Year: 2014

Free vibration analysis of plates with openings represents an important issue in naval architecture and ocean engineering applications. Namely, they are often primary design members of complex structures and knowledge about their dynamic behavior becomes a prerogative for the proper structural design. This paper deals with application of assumed mode method to free vibration analysis of rectangular plates with multiple rectangular openings at arbitrary defined locations. Developed method can be applied to both thin and thick plates as well as to classical and non-classical edge constraints. In the assumed mode method natural frequencies and mode shapes of a corresponding plate are determined by solving an eigenvalue problem of a multi-degree-of-freedom system matrix equation derived by using Lagrange's equations of motion. The developed procedure actually represents an extension of a method for the natural vibration analysis of rectangular plates without openings, which has been recently presented in the relevant literature. The effect of an opening is taken into account in a simple and intuitive way, i.e. by subtracting its energy from the total plate energy without opening. Illustrative numerical examples include dynamic analysis of rectangular plates with single and multiple rectangular openings with various thicknesses and different combinations of boundary conditions. Also, the influence of the rectangular opening area on the plate dynamic response is analyzed. The comparisons of the results with those obtained using the finite element method (FEM) is also provided, and very good agreement is achieved. Finally, related conclusions are drawn and recommendations for future investigations are presented. Copyright © 2014 by ASME.


Cho D.S.,Pusan National University | Vladimir N.,University of Zagreb | Choi T.M.,Createch Co.
International Journal of Naval Architecture and Ocean Engineering | Year: 2013

Natural vibration analysis of plates with openings of different shape represents an important issue in naval architecture and ocean engineering applications. In this paper, a procedure for vibration analysis of plates with openings and arbitrary edge constraints is presented. It is based on the assumed mode method, where natural frequencies and modes are determined by solving an eigenvalue problem of a multi-degree-of-freedom system matrix equation derived by using Lagrange's equations of motion. The presented solution represents an extension of a procedure for natural vibration analysis of rectangular plates without openings, which has been recently presented in the literature. The effect of an opening is taken into account in an intuitive way, i.e. by subtracting its energy from the total plate energy without opening. Illustrative numerical examples include dynamic analysis of rectangular plates with rectangular, elliptic, circular as well as oval openings with various plate thicknesses and different combinations of boundary conditions. The results are compared with those obtained by the finite element method (FEM) as well as those available in the relevant literature, and very good agreement is achieved.


Cho D.-S.,Pusan National University | Choi T.-M.,Createch Co. | Kim J.-H.,Createch Co. | Vladimir N.,University of Zagreb
Thin-Walled Structures | Year: 2016

Stepped thickness rectangular plates are found in various engineering branches, and knowledge about their dynamic performance represents an important issue for rational structural design. The structural intensity analysis, assessing magnitude and direction of vibration energy flow provides information on dominant transmission paths, and vibratory energy distribution including sink positions. In this paper, vibration energy flow in stepped thickness rectangular plates is analysed by structural intensity technique employing the finite element method. An outline of structural intensity formulation for a plate element is given, and developed analysis system combining in-house code and commercial FE tools is described. Numerical examples include structural intensity analysis of stepped thickness rectangular plates subjected to harmonic excitation forces with different sets of boundary conditions, where special attention is paid to influence of plate thickness ratio variation on vibration energy flow. Moreover, different structural intensity components of a simply supported stepped thickness plate are separately quantified, to assess their contribution to the total intensity. © 2016 Elsevier Ltd


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