• Structural Engineering and Mechanics
• /
• v.72 no.2
• /
• pp.203-216
• /
• 2019

Reliability analysis of composite structures considering random variation of involved parameters is quite important as composite materials revealed large statistical variations in their mechanical properties. The reliability analysis of such structures by the first order reliability method (FORM) and Monte Carlo Simulation (MCS) based approach involves repetitive evaluations of performance function. The response surface method (RSM) based metamodeling technique has emerged as an effective solution to such problems. In the application of metamodeling for uncertainty quantification and reliability analysis of composite structures; the finite element model is usually formulated by either classical laminate theory or first order shear deformation theory. But such theories show significant error in calculating the structural responses of composite structures. The present study attempted to apply the RSM based MCS for reliability analysis of composite shell structures where the surrogate model is constructed using higher order shear deformation theory (HSDT) of composite structures considering the uncertainties in the material properties, load, ply thickness and radius of curvature of the shell structure. The sensitivity of responses of the shell is also obtained by RSM and finite element method based direct approach to elucidate the advantages of RSM for response sensitivity analysis. The reliability results obtained by the proposed RSM based MCS and FORM are compared with the accurate reliability analysis results obtained by the direct MCS by considering two numerical examples.

• Journal of Food Hygiene and Safety
• /
• v.28 no.3
• /
• pp.252-257
• /
• 2013

In this study the automated technique TEMPO STA method, a new automated enumeration based on MPN method, was compared to the direct plate count method by testing various ready-to-eat compound food products. Artificially inoculated food samples with Staphylococcus aureus - Bibimbap, Bibimnaengmyeon, Mulnaengmyeon, Kimmaki, Salad, Japchae, and Sushi- were tested. Statistical analysis of the results showed above 99% in agreement between the two enumeration methods. Also, we monitored 466 various ready-to-eat compound food products samples. The measure uncertainties of the two methods is also familiar, while TEMPO STA automated method is simpler, less time-consuming, more effective and more stable.

• Proceedings of the Korean Society of Agricultural Engineers Conference
• /
• 2000.10a
• /
• pp.144-150
• /
• 2000

A field case study was performed to investigate optimum cropping technique of direct seeded rice. In addition, an economic analysis was made to see the effect of this method. Field study was performed at a 2.1㏊ paddy field in Kimjae city, Chonbuk province from 1991 to 1999. Various direct seeding method such as dryland seeding, wetland seeding, and no-till wetland seeding were introduced. Optimum cropping techniques such as when and how to manage the rotary till, water supply, herbicide application, and ponding depth were developed for different cropping methods. Based on this study ￦640,000 per ㏊ can be saved by direct seeding due to no nursery cost, and ￦l,220,000 per ㏊ can be saved by no-till and no nursery cost. With further study these cropping techniques including the no-till direct deeding proves to be advantageous these can be adopted for the most of the paddy fields in Korea.

• Proceedings of the KIEE Conference
• /
• 1992.07b
• /
• pp.567-569
• /
• 1992

Design sensitivity analysis is proposed for the optimal shape design of three dimensional magnetostatic problems. The direct differentiation method is introduced for design sensitivity analysis and the boundary element method with reduced magnetic scalar potential as the state variable is used to analyze the magnetic characteristics. In the direct differentiation method, the design sensitivity, defined as the total derivative of the objective function with respect to the design variables, is calculated based on the variation of the state variable with respect to the design variable. And the variation of He state variable is calculated by differentiating the both sides of the system matrix equation obtained by applying boundary element method. Through the numerical example with simple electromagnet, the usefullness is proved.

• Proceedings of the KIEE Conference
• /
• 1995.11a
• /
• pp.195-198
• /
• 1995

Most of the theorems of nonlinear stability is based on the Lyapunov stability theory. The Lyapunov function method is the most well-known and provides precise and rigorous theoretical backgrounds. However, tile conventional approach to direct stability analysis has been performed without taking account of damping effects. For accurate stability analysis of nonlinear systems, it is required to consider the damping effects. This paper presents a new method to derive a group of Lyapunov functions to reflect the damping effects by considering the integral relationships of the system governing equations. This method tan be utilized as a powerful tool to determine the region of attraction.

• Proceedings of the Computational Structural Engineering Institute Conference
• /
• 2002.04a
• /
• pp.53-60
• /
• 2002

It has been recognized that damage control must become a more explicit design consideration. In an effort to develop design methods based on performance it is clear that the evaluation of the inelastic response is required. The methods available to the design engineer today are nonlinear time history analyses, or monotonic static nonlinear analyses, or equivalent static analyses with simulated inelastic influences. Some codes proposed the capacity spectrum method based on the nonlinear static(pushover) analysis to determine earthquake-induced demand given the structure pushover curve. This procedure is conceptually simple but iterative and time consuming with some errors. This paper presents a nonlinear direct spectrum method to evaluate seismic Performance of structure, without iterative computations, given the structural initial elastic period and yield strength from the pushover analysis, especially for multi degree of freedom structures. The purpose of this paper is to investigate accuracy and confidence of this method from a point of view of various earthquakes and unloading stiffness degradation parameters.

• Journal of the Korean Society for Precision Engineering
• /
• v.20 no.6
• /
• pp.145-150
• /
• 2003

This paper is on the study of flow force compensation for spool type valves. A simple method for flow force compensation using a stepped spool is presented in this paper. It is easy to manufacture the stepped spool of the presented method because the shape of it is simple. The method has another merit that the size of valve need not be increased. Actuating force required for driving the spool can be decreased through the compensation of flow force. The effect of presented method is predicted through CFD analysis. The results of the CFD analysis are also utilized for the optimization of step shape. The prototypes of flow force compensated Direct Drive Servo-Valve are manufactured, and the measurements of flow force are carried out. The measured effect of flow force compensation is very similar to that from the CFD analysis.

• The Transactions of the Korean Institute of Electrical Engineers
• /
• v.41 no.8
• /
• pp.850-857
• /
• 1992

Design sensitivity analysis is proposed for the optimal shape design of three-dimensional magnetostatic problems. The direct differentiation method is introduced for design sensitivity analysis and the boundary element method with reduced magnetic scalar potential as the state variable is used to analyze the magnetic characteristics. In the direct differentiation method, the design sensitivity, defined as the total derivative of the objective function with respect to the design variables, is calculated based on the variation of the state variable with respect to the design variable. And the variation of the state variable is calculated by differetiating the both sides of the system matrix equation obtained by applying boundary element method. Through the numerical example with simple electromagnet, the usefulness is proved.

• Korean Journal of Food Science and Technology
• /
• v.22 no.5
• /
• pp.562-568
• /
• 1990

The modified direct GLC method was evaluated for analysis of volatile compounds associated with WOF of cooked meat. This modified method was pertaining to collection of volatiles from the samples that contain quantities of water. The modification was appropriate for the studies of low molecular weight saturated aldehydes (C5-C15), unsaturated aldehydes (C5-C9), and saturated alcohols (C5-C9).

• Coupled systems mechanics
• /
• v.4 no.4
• /
• pp.317-336
• /
• 2015

The present paper deals with the analysis of water tank with elastic separator wall. Both fluid and structure are discretized and modeled by eight node-elements. In the governing equations, pressure for the fluid domain and displacement for the separator wall are considered as nodal variables. A method namely, direct coupled for the analysis of water tank has been carried out in this study. In direct coupled approach, the solution of the fluid-structure system is accomplished by considering these as a single system. The hydrodynamic pressure on tank wall is presented for different lengths of tank. The results show that the magnitude of hydrodynamic pressure is quite large when the distances between the separator wall and tank wall are relatively closer and this is due to higher rotating tendency of fluid and the higher sloshed displacement at free surface.