scispace - formally typeset
Search or ask a question
Author

Usik Lee

Bio: Usik Lee is an academic researcher from Inha University. The author has contributed to research in topics: Finite element method & Spectral element method. The author has an hindex of 28, co-authored 180 publications receiving 2717 citations. Previous affiliations of Usik Lee include Pennsylvania State University & Stanford University.


Papers
More filters
Book
Usik Lee1
17 Nov 2003
TL;DR: In this paper, the authors present a theoretical analysis of the Spectral Element Method and Spectral Analysis of Signals (SAM) in terms of the following: 1.1 Fourier Series. 2.2 Discrete Fourier Transform and FFT. 3.3 Aliasing. 4.4 Reduction from the Finite Models.
Abstract: Preface. Part One Introduction to the Spectral Element Method and Spectral Analysis of Signals. 1 Introduction. 1.1 Theoretical Background. 1.2 Historical Background. 2 Spectral Analysis of Signals. 2.1 Fourier Series. 2.2 Discrete Fourier Transform and the FFT. 2.3 Aliasing. 2.4 Leakage. 2.5 Picket-Fence Effect. 2.6 Zero Padding. 2.7 Gibbs Phenomenon. 2.8 General Procedure of DFT Processing. 2.9 DFTs of Typical Functions. Part Two Theory of Spectral Element Method. 3 Methods of Spectral Element Formulation. 3.1 Force-Displacement Relation Method. 3.2 Variational Method. 3.3 State-Vector Equation Method. 3.4 Reduction from the Finite Models. 4 Spectral Element Analysis Method. 4.1 Formulation of Spectral Element Equation. 4.2 Assembly and the Imposition of Boundary Conditions. 4.3 Eigenvalue Problem and Eigensolutions. 4.4 Dynamic Responses with Null Initial Conditions. 4.5 Dynamic Responses with Arbitrary Initial Conditions. 4.6 Dynamic Responses of Nonlinear Systems. Part Three Applications of Spectral Element Method. 5 Dynamics of Beams and Plates. 5.1 Beams. 5.2 Levy-Type Plates. 6 Flow-Induced Vibrations of Pipelines. 6.1 Theory of Pipe Dynamics. 6.2 Pipelines Conveying Internal Steady Fluid. 6.3 Pipelines Conveying Internal Unsteady Fluid. Appendix 6.A: Finite Element Matrices: Steady Fluid. Appendix 6.B: Finite Element Matrices: Unsteady Fluid. 7 Dynamics of Axially Moving Structures. 7.1 Axially Moving String. 7.2 Axially Moving Bernoulli-Euler Beam. 7.3 Axially Moving Timoshenko Beam. 7.4 Axially Moving Thin Plates. Appendix 7.A: Finite Element Matrices for Axially Moving String. Appendix 7.B: Finite Element Matrices for Axially Moving Bernoulli-Euler Beam. Appendix 7.C: Finite Element Matrices for Axially Moving Timoshenko Beam. Appendix 7.D: Finite Element Matrices for Axially Moving Plate. 8 Dynamics of Rotor Systems. 8.1 Governing Equations. 8.2 Spectral Element Modeling. 8.3 Finite Element Model. 8.4 Numerical Examples. Appendix 8.A: Finite Element Matrices for the Transverse Bending Vibration. 9 Dynamics of Multi-Layered Structures. 9.1 Elastic-Elastic Two-Layer Beams. 9.2 Elastic-Viscoelastic-elastic-Three-Layer (PCLD) Beams. Appendix 9.A: Finite Element Matrices for the Elastic-Elastic Two-Layer Beam. Appendix 9.B: Finite Element Matrices for the Elastic-VEM-Elastic Three-Layer Beam. 10 Dynamics of Smart Structures. 10.1 Elastic-Piezoelectric Two-Layer Beams. 10.2 Elastic-Viscoelastic-Piezoelctric Three-Layer (ACLD) Beams. 11 Dynamics of Composite Laminated Structures. 11.1 Theory of Composite Mechanics. 11.2 Equations of Motion for Composite Laminated Beams. 11.3 Dynamics of Axial-Bending-Shear Coupled Composite Beams. 11.4 Dynamics of Bending-Torsion-Shear Coupled Composite Beams. Appendix 11.A: Finite Element Matrices for Axial-Bending-Shear Coupled Composite Beams. Appendix 11.B: Finite Element Matrices for Bending-Torsion-Shear Coupled Composite Beams. 12 Dynamics of Periodic Lattice Structures. 12.1 Continuum Modeling Method. 12.2 Spectral Transfer Matrix Method. 13 Biomechanics: Blood Flow Analysis. 13.1 Governing Equations. 13.2 Spectral Element Modeling: I. Finite Element. 13.3 Spectral Element Modeling: II. Semi-Infinite Element. 13.4 Assembly of Spectral Elements. 13.5 Finite Element Model. 13.6 Numerical Examples. Appendix 13.A: Finite Element Model for the 1-D Blood Flow. 14 Identification of Structural Boundaries and Joints. 14.1 Identification of Non-Ideal Boundary Conditions. 14.2 Identification of Joints. 15 Identification of Structural Damage. 15.1 Spectral Element Modeling of a Damaged Structure. 15.2 Theory of Damage Identification. 15.3 Domain-Reduction Method. 16 Other Applications. 16.1 SEM-FEM Hybrid Method. 16.2 Identification of Impact Forces. 16.3 Other Applications. References. Index.

430 citations

Journal ArticleDOI
Usik Lee1, Jinho Shin1
TL;DR: In this paper, a frequency response function (FRF) based structural damage identification method (SDIM) for beam structures is introduced, where the damages within a beam structure are characterized by introducing a damage distribution function.

166 citations

Journal ArticleDOI
TL;DR: In this article, a finite element for planar beams with active constrained layer (ACL) damping treatments is presented, where a time-domain viscoelastic material model and the ability to readily accommodate segmented (i.e., non-continuous) constraining layers are discussed.
Abstract: A finite element for planar beams with active constrained layer (ACL) damping treatments is presented. Features of this non-shear locking element include a time-domain viscoelastic material model, and the ability to readily accommodate segmented (i.e. non-continuous) constraining layers. These features are potentially important in active control applications: the frequency-dependent stiffness and damping of the viscoelastic material directly affects system modal frequencies and damping; the high local damping of the viscoelastic layer can result in complex vibration modes and differences in the relative phase of vibration between points; and segmentation, an effective means of increasing passive damping in long- wavelength vibration modes, affords multiple control inputs and improved performance in an active constrained layer application. The anelastic displacement fields (ADF) method is used to implement the viscoelastic material model, enabling the straightforward development of time-domain finite elements. The performance of the finite element is verified through several sample modal analyses, including proportional-derivative control based on discrete strain sensing. Because of phasing associated with mode shapes, control using a single continuous ACL can be destabilizing. A segmented ACL is more robust than the continuous treatment, in that the damping of modes at least up to the number of independent patches is increased by control action.

136 citations

Journal ArticleDOI
TL;DR: The pulsatile flow of blood through mild stenosed artery is studied and it is found that the plug core radius, pressure drop and wall shear stress increase with the increase of yield stress or the stenosis height, and the effects of asymmetric of the stenotic on the flow quantities are brought out.

89 citations

Journal ArticleDOI
TL;DR: In this paper, the dynamics of a pipeline conveying one-dimensional unsteady flow is considered, which is represented by a set of partial differential equations which consists of the axial and transverse equations of motion of the pipeline and the equations of momentum and continuity of the internal flow.

71 citations


Cited by
More filters
Book ChapterDOI
01 Jan 1997
TL;DR: This chapter introduces the finite element method (FEM) as a tool for solution of classical electromagnetic problems and discusses the main points in the application to electromagnetic design, including formulation and implementation.
Abstract: This chapter introduces the finite element method (FEM) as a tool for solution of classical electromagnetic problems. Although we discuss the main points in the application of the finite element method to electromagnetic design, including formulation and implementation, those who seek deeper understanding of the finite element method should consult some of the works listed in the bibliography section.

1,820 citations

Journal ArticleDOI
TL;DR: In this article, the state of the art in vibration-based condition monitoring with particular emphasis on structural engineering applications is reviewed, focusing on the use of in situ non-destructive sensing and analysis of system characteristics for detecting changes, which may indicate damage or degradation.
Abstract: Vibration based condition monitoring refers to the use of in situ non-destructive sensing and analysis of system characteristics –in the time, frequency or modal domains –for the purpose of detecting changes, which may indicate damage or degradation. In the field of civil engineering, monitoring systems have the potential to facilitate the more economical management and maintenance of modern infrastructure. This paper reviews the state of the art in vibration based condition monitoring with particular emphasis on structural engineering applications.

1,394 citations

Journal ArticleDOI
TL;DR: In this paper, the advances and trends in the formulations and applications of the finite element modeling of adaptive structural elements are surveyed and discussed in a first attempt to survey and discuss the advances.

639 citations

Journal ArticleDOI
TL;DR: In this article, a review article provides an overview of the problems pertaining to structural dynamics with bolted joints, including energy dissipation, dynamic properties of the joints, parameter uncertainties and relaxation, and active control of the joint preload.

397 citations

30 Sep 1986
TL;DR: In this paper, the authors used the canonical M, K form of the undamped motion equations to model viscoelastic damping and used finite element analysis to model the damping factors.
Abstract: Mathematical models of elastic structures have become very sophisticated: given the crucial material properties (mass density and the several elastic moduli), computer-based techniques can be used to construct exotic finite element models. By contrast, the modeling of damping is usually very primitive, often consisting of no more than mere guesses at “modal damping factors.” The aim of this paper is to raise the modeling of viscoelastic structures to a level consistent with the modeling of elastic structures. Appropriate material properties are identified which permit the standard finite element formulations used for undamped structures to be extended to viscoelastic structures. Through the use of “dissipation” coordinates, the canonical “M , K ” form of the undamped motion equations is expanded to encompass viscoelastic damping. With this formulation finite element analysis can be used to model viscoelastic damping accurately.

339 citations