• Interaction and multiscale mechanics
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• 제1권3호
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• pp.329-337
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• 2008

This paper presents the derivation of the generalized governing equations in theory of elasticity, their weak forms and the some applications in the numerical analysis of structural mechanics. Unlike the differential equations in classical elasticity theory, the generalized equations of the equilibrium and compatibility equations presented here take the form of integral equations, and the generalized equilibrium equations contain the classical differential equations and the boundary conditions in a single equation. By using appropriate test functions, the weak forms of these generalized governing equations can be established. It can be shown that various variational principles in structural analysis are merely the special cases of these weak forms of generalized governing equations in elasticity. The present weak forms of elasticity equations extend greatly the choices of the trial functions for approximate solutions in the numerical analysis of various engineering problems. Therefore, the weak forms of generalized governing equations in elasticity provide a powerful modeling tool in the computational structural mechanics.

• 지식경영연구
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• 제20권1호
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• pp.1-26
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• 2019

This tutorial introduces procedures and methods for performing structural equation modeling using R. For this, we present the whole process of analyzing the structural equations model from the confirmatory factor analysis to the path diagram generation using the lavaan package, which is relatively well evaluated among the R packages supporting the structural equation modeling, together with the R program codes. Considering that research applying structural equation modeling techniques is the mainstream in a variety of social sciences, including business administration, and that there is growing interest in open source R, this tutorial focuses on researchers who are looking for alternatives to traditional commercial statistical packages and is expected that it will be a useful guidebook for them.

• 지식경영연구
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• 제20권2호
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• pp.1-24
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• 2019

This tutorial introduces procedures and methods for performing structural equation modeling using R. To do this, we present advanced analysis methods based on structural equation model such as mediation effect analysis, moderation effect analysis, moderated mediation effect analysis, and multiple-group analysis with R program code using R lavaan package that supports structural equation modeling. R is flexible and scalable, unlike traditional commercial statistical packages. Therefore, new analytical techniques are likely to be implemented ahead of any other statistical package. From this point of view, R will be a very appropriate choice for applying new analytical techniques or advanced techniques that researchers need. Considering that various studies in the social sciences are applying structural equations modeling techniques and increasing interest in open source R, this tutorial is expected to be useful for researchers who are looking for alternatives to existing commercial statistical packages.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2003년도 봄 학술발표회 논문집
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• pp.269-278
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• 2003

In this study, the method of the finite element modeling for free vibration control of beam-type smart structures with bonded plate-type piezoelectric sensors and actuators is proposed. Constitutive equations for the direct piezoelectric effect and converse piezoelectric effect of piezoelectric materials are considered. By using the variational principle, the equations of motion for the smart beam finite element are derived, The proposed 2-node beam finite element is an isoparametric element based on Timoshenko beam theory. Therefore, by analyzing beam-type smart structures with smart beam finite elements, it is possible to simulate the control of the structural behavior by applying voltages to piezoelectric actuators and monitoring of the structural behavior by sensing voltages of piezoelectric sensors. By using the smart beam finite element and constant-gain feed back control scheme, the formulation of the free vibration control for the beam structures with bonded plate-type piezoelectric sensors and actuators is proposed.

• Korean Journal of Chemical Engineering
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• 제35권12호
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• pp.2327-2335
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• 2018

Fluid catalytic cracking (FCC) is an important chemical process that is widely used to produce valuable petrochemical products by cracking heavier components. However, many difficulties exist in modeling the FCC process due to its complexity. In this study, a dynamic process model of a FCC process is suggested and its structural observability is analyzed. In the process modeling, yield function for the kinetic model of the riser reactor was applied to explain the product distribution. Hydrodynamics, mass balance and energy balance equations of the riser reactor and the regenerator were used to complete the modeling. The process model was tested in steady-state simulation and dynamic simulation, which gives dynamic responses to the change of process variables. The result was compared with the measured data from operating plaint. In the structural analysis, the system was analyzed using the process model and the process design to identify the structural observability of the system. The reactor and regenerator unit in the system were divided into six nodes based on their functions and modeling relationship equations were built based on nodes and edges of the directed graph of the system. Output-set assignment algorithm was demonstrated on the occurrence matrix to find observable nodes and variables. Optimal locations for minimal addition of measurements could be found by completing the whole output-set assignment algorithm of the system. The result of this study can help predict the state more accurately and improve observability of a complex chemical process with minimal cost.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2000년도 가을 학술발표회논문집
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• pp.3-10
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• 2000

In this study, a new smart beam finite element is proposed for the finite element modeling of the beam-type smart structure with bonded plate-type piezoelectric sensors and actuators. Constitutive equations far the direct piezoelectric effect and converse piezoelectric effect of piezoelectric materials are considered. By using the variational principle, the equations of motion for the smart beam finite element are derived. The presented 2-node beam finite element is isoparametric element based on Timoshenko beam theory. The validity of the proposed beam element is shown through comparing the analysis results of the verification examples with those of other previous researches. Therefore, by analyzing smart structures with smart beam finite elements, it is possible to simulate the control of the structural behavior by piezoelectric actuators with applied voltages and the monitoring of the structure behavior by piezoelectric sensors with sensed voltages.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2003년도 가을 학술발표회 논문집
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• pp.444-451
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• 2003

In this study, a new three-dimensional finite element analysis model of high-speed railway bridges considering train-bridge interaction, in which various improved finite elements are used for modeling structural members, is proposed. The box-type bridge deck of a railway bridge is modeled by the NFS(Nonconforming Flat Shell) elements with 6 degrees of freedom. Track structures are idealized using the beam finite elements with the offset of beam nodes and those on Winkler foundation with two parameters. And, the vehicle model devised for a high-speed train is employed, which has an articulated bogie system. By Lagrange's equations of motion, the equations of motion of a bridge-train system can be formulated. Finally, by deriving the equations of the forces acting on a bridge considering bridge-train interaction the complete system matrices of total bridge-train system can be constructed. As numerical examples of this study, 2-span PC box-girder bridge is analyzed and results are compared with experimental results.

• 한국IT서비스학회지
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• 제18권4호
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• pp.115-134
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• 2019

The global music industry has been growing steadily every year. In particular, the proportion of music streaming services in the overall market are expanding. It shows same pattern in domestic market. Also, several companies are providing music streaming services competitively. It is clear that there is growing interest in effective operations of music streaming services. In this study, we examine the impact of customization and network effect on service quality and customer loyalty. We collect survey data and analyze relationships between latent variables using structural equations modeling. We find that customization and network effect of music streaming services positively affect service quality. However, the effect of customization on customer loyalty is not significant and there is a negative effect of network effect on customer loyalty. Finally, we find that service quality works as a mediator between customization and customer loyalty, and service quality also works as a mediator between network effect and customer loyalty.

• Smart Structures and Systems
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• 제8권3호
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• pp.275-302
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• 2011

This is a review paper on mathematical modeling of actively controlled piezo smart structures. Paper has four sections to discuss the techniques to: (i) write the equations of motion (ii) implement sensor-actuator design (iii) model real life environmental effects and, (iv) control structural vibrations. In section (i), methods of writing equations of motion using equilibrium relations, Hamilton's principle, finite element technique and modal testing are discussed. In section (ii), self-sensing actuators, extension-bending actuators, shear actuators and modal sensors/actuators are discussed. In section (iii), modeling of thermal, hygro and other non-linear effects is discussed. Finally in section (iv), various vibration control techniques and useful software are mentioned. This review has two objectives: (i) practicing engineers can pick the most suitable philosophy for their end application and, (ii) researchers can come to know how the field has evolved, how it can be extended to real life structures and what the potential gaps in the literature are.

• 한국전산구조공학회논문집
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• 제22권5호
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• pp.411-420
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• 2009

본 연구는 계면경계를 갖는 포텐셜 문제의 해석를 위한 이동최소제곱 기반의 확장된 유한차분법을 제시한다. 이동최소제곱법을 이용한 Taylor 전개로부터 얻어진 근사함수에 쐐기함수를 도입하여 계면경계의 특이성을 모사한다. 지배방정식은 요소나 그리드없이 절점만을 이용해 이산화한다. 계면경계의 특이성은 절점에서 구성되는 근사식에 매입되기 때문에 계면경계의 기하학적 모델링으로 발생하는 수치적인 어려움을 피할 수 있다. 계면경계 조건으로 인해 전체 계방정식에 추가되는 미지수는 없지만, 계방정식을 과결정 시스템으로 만드므로 강성도 행렬을 대칭화하여 미지수와 방정식의 개수를 일치시켰다. 이로 인한 계산량 증가는 계면경계 모델링의 간소화로 인한 수치적인 이득과 맞바꿀 수 있다. 다양한 수치적 검증을 통해 개발된 해석기법이 쐐기거동과 점프를 성공적으로 묘사할 뿐만 아니라 계면경계를 갖는 포텐셜 문제 효율적이고 정확하게 해석할 수 있음을 보였다.