Dae-Seung Cho

Bio: Dae-Seung Cho is an academic researcher from Pusan National University. The author has contributed to research in topics: Vibration & Finite element method. The author has an hindex of 14, co-authored 110 publications receiving 590 citations.

Prediction of ship fuel consumption by using an artificial neural network

Abstract: A smart ship collects various data with large volume, such as voyage, machinery, and weather data. Thus, big data analysis for smart ships is an important technology that can be widely applied to improve ship maintenance, operational efficiency, and equipment life management. In this study, an accurate regression model for the fuel consumption of the main engine by using an artificial neural network (ANN) was proposed by big data analysis including data collection, clustering, compression, and expansion. To obtain an accurate regression model, various numbers of hidden layers and neurons and different types of activation functions were tested in the ANN, and their effects on the accuracy and efficiency of the regression analysis were studied. The proposed regression model using ANN is a more accurate and efficient model to predict the fuel consumption of the main engine than polynomial regression and support vector machine.

Noise mapping using measured noise and GPS data

Abstract: In this paper, we introduce a system to easily produce a noise map using noise and GPS data measured simultaneously. The system consists of a sound level meter, a GPS receiver, a database program to manage the measured data, and a program to produce the noise map including a computer model of the target area. The GPS receiver interfaced to the sound level meter allows simultaneous measurement and storage of the noise level and the global position at a location. The database program directly imports one or more measured data stored in the sound level meter. Then, selected measurement results are exported to the noise mapping program for producing colour-coded or noise contour line maps using measured data at user-defined locations. The noise map produced can be exported to DXF and SHP files with other modeling items, for post-processing in GIS software. To demonstrate the capability of the developed system, we show a noise map for a university campus produced by the system.

Forced vibration analysis of arbitrarily constrained rectangular plates and stiffened panels using the assumed mode method

Abstract: 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.

Approximate natural vibration analysis of rectangular plates with openings using assumed mode method

Abstract: 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.

Natural vibration analysis of rectangular bottom plate structures in contact with fluid

Abstract: A simple and effective procedure for the natural vibration analysis of rectangular bottom plate structures in contact with fluid is presented. Structural part of the coupled hydroelastic problem covers thin and thick rectangular plates and stiffened panels with different framing types. The eigenvalue problem is formulated using Lagrange׳s equation of motion and taking into account potential and kinetic energies of a plate structure and fluid kinetic energy, respectively. Natural frequencies and modes are obtained applying the assumed mode method using the characteristic polynomials of a Timoshenko beam. Potential flow theory assumptions are adopted for the fluid and the effect of free surface waves is ignored. 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 is verified with several numerical examples dealing with the natural vibration of bare plates and stiffened panels in contact with different fluid domains. A comparison of the results with those obtained by a general purpose FEA software showed very good agreement, especially for the lowest natural frequencies that are actually most relevant for the structural design from the viewpoint of vibration.

Formulas For Natural Frequency And Mode Shape

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Flow-induced vibration

Abstract: Structural vibrations caused by a flowing fluid. Whenever a structure is exposed to a flowing fluid,…

A novel three-variable shear deformation plate formulation: Theory and Isogeometric implementation

Abstract: This study brings to readers the generalized formulation of three-variable plate theory and an efficient computational approach for analyzing plates. The theory not only has three degree of freedoms (DOFs) per node, which complies with three dimensional space of full plate model as classical plate theory (CPT) but also accounts for the effect of shear deformation without any requirement of shear correction factors (SCF). A complete set of strong forms, weak form as well as classical and non-classical boundary conditions (BCs) for linear and geometrically nonlinear analysis are consistently derived in this paper through a variational approach. The strong forms are sixth order differential equations, resulting in the symmetrical fourth order differential weak form. It is known that Isogeometric Analysis (IGA) arguably outweighs classical finite element method in terms of high continuity and high order differentiability. Thanks to its advantage, an IGA framework for the generalized three-variable plate theory is formulated with completely locking-free and only three DOFs per node. The classical BCs are strongly enforced to system equations as usual whilst the non-classical BCs are weakly imposed by a penalty approach. The new plate theory with only three-variable is thereafter used for static linear and nonlinear analysis of isotropic and functionally graded material (FGM) plates to demonstrate its ability. The reliability and accuracy of the present approach are ascertained by comparing the obtained results with other existing ones. Based on a robust formulation devoted in the paper, the proposed approach can be further extended for numerous problems related to the shear deformable effect in the literature.

Characterization of environmental noise based on noise measurements, noise mapping and interviews: A case study at a university campus in Brazil

Abstract: The purpose of this research was to characterize the environmental noise on the campus of the Polytechnic Center of the Federal University of Parana, Brazil. This research was divided into two parts: (1) Objective – in situ measurements of the equivalent continuous sound pressure level L Aeq followed by noise mapping of the whole campus area, using BK (2) Subjective – involving the preparation and application of a questionnaire to a sample of 389 people from the campus population to gather information about their reactions to noise. The L Aeq data were compared with the noise immission limits for outdoor environments in educational areas recommended by WHO – L Aeq = 55 dB(A). The results indicated that 89.65% of the 58 evaluated points exceeded the 55 dB(A) limit. Concentration difficulties and irritation were the most cited effects in all educational sectors evaluated. Together, these two effects were cited by 61% of the interviewed people in the Biological Science Sector, 81% in the Exact Science Sector, 69% in the Earth Science Sector and 74% in the Technological Sector. Further, there were strong positive correlations between measured noise levels and reports of annoyance from noise levels perceived by the interviewed campus population.

Free vibration analysis of porous plates with porosity distributions in the thickness and in-plane directions using isogeometric approach

Abstract: The main purpose of this paper is to study the free vibration of porous square plate, circular plate, and rectangle plate with a central circular hole in the framework of isogeometric analysis (IGA). Generally, the porosity distributions of plates are assumed to happen in the thickness direction. However, the graded distributions of porosity may occur through the in-plane direction of plates. Therefore, porosity distributions along both the thickness direction and in-plane direction are considered in this study. The displacement fields are described by the first order shear deformation theory (FSDT) and the exact geometric models are formulated wholly by non-uniform rational B-spline (NURBS) basis functions, which bear high-order continuity inherently. To ensure the versatility of IGA-FSDT, several numerical examples for isotropic and porous plates with different boundary conditions and various types of porosity distributions are presented. Moreover, some innovative results are presented and discussed, which can be the benchmark data for other algorithm researches. The effects of porosity coefficient, boundary conditions and geometric parameters on the free vibration of porous plates are investigated comprehensively.