Jintai Chung

Bio: Jintai Chung is an academic researcher from Hanyang University. The author has contributed to research in topics: Equations of motion & Vibration. The author has an hindex of 28, co-authored 118 publications receiving 4249 citations. Previous affiliations of Jintai Chung include University of Michigan & Samsung.

A Time Integration Algorithm for Structural Dynamics With Improved Numerical Dissipation: The Generalized-α Method

Abstract: A new family of time integration algorithms is presented for solving structural dynamics problems. The new method, denoted as the generalized-α method, possesses numerical dissipation that can be controlled by the user. In particular, it is shown that the generalized-α method achieves high-frequency dissipation while minimizing unwanted low-frequency dissipation. Comparisons are given of the generalized-α method with other numerically dissipative time integration methods; these results highlight the improved performance of the new algorithm. The new algorithm can be easily implemented into programs that already include the Newmark and Hilber-Hughes-Taylor-α time integration methods.

Explicit time integration algorithms for structural dynamics with optimal numerical dissipation

Abstract: A new predictor-corrector explicit time integration algorithm is presented for solving structural dynamics problems. The basis of the algorithm is the implicit generalized-α method developed by the authors. Like its implicit parent, the explicit generalized-α method is a one-parameter family of algorithms in which the parameter defines the high-frequency numerical dissipation. For a given value of high-frequency dissipation, the explicit generalized-α method minimizes low-frequency dissipation. The algorithm can be utilized effectively for structural dynamics calculations in which numerical dissipation is needed to reduce spurious oscillations. Parameter values are given that enable physical damping to be treated explicitly while maintaining second-order accuracy without the need for an expensive second corrector pass.

Dynamic analysis of a rotating cantilever beam by using the finite element method

Abstract: A finite element analysis for a rotating cantilever beam is presented in this study Based on a dynamic modelling method using the stretch deformation instead of the conventional axial deformation, three linear partial differential equations are derived from Hamilton's principle Two of the linear differential equations are coupled through the stretch and chordwise deformations The other equation is an uncoupled one for the flapwise deformation From these partial differential equations and the associated boundary conditions, are derived two weak forms: one is for the chordwise motion and the other is for the flapwise motion The weak forms are spatially discretized with newly defined two-node beam elements With the discretized equations, the behaviours of the natural frequencies are investigated for the variation of the rotating speed In addition, the time responses and distributions of the deformations and stresses are computed when the rotating speed is prescribed The effects of the rotating speed profile on the vibrations of the beam are also investigated

A new family of explicit time integration methods for linear and non‐linear structural dynamics

Abstract: A new family of explicit single-step time integration methods with controllable high-frequency dissipation is presented for linear and non-linear structural dynamic analyses. The proposed methods are second-order accurate and completely explicit with a diagonal mass matrix, even when the damping matrix is not diagonal in the linear structural dynamics or the internal force vector is a function of velocities in the non-linear structural dynamics. Stability and accuracy of the new explicit methods are analysed for the linear undamped/damped cases. Furthermore, the new methods are compared with other explicit methods.

Nonlinear brake control for vehicle CW/CA systems

Abstract: A brake control law for vehicle collision warning/collision avoidance (CW/CA) systems has been proposed in the paper The control law has been designed for optimized safety and comfort A solenoid-valve-controlled hydraulic brake actuator system for the CW/CA systems has been investigated A nonlinear computer model and a linear model of the hydraulic brake actuator system have been developed Both models were found to represent the actual system with good accuracy Uncertainties in the brake actuator model have been considered in the design of the control law for the robustness of the controller The effects of brake control on CW/CA vehicle response has been investigated via simulations The simulations were performed using a complete nonlinear vehicle model The results indicate that the proposed brake control law can provide the CW/CA vehicles with an optimized compromise between safety and comfort

A phase-field description of dynamic brittle fracture

Abstract: In contrast to discrete descriptions of fracture, phase-field descriptions do not require numerical tracking of discontinuities in the displacement field. This greatly reduces implementation complexity. In this work, we extend a phase-field model for quasi-static brittle fracture to the dynamic case. We introduce a phase-field approximation to the Lagrangian for discrete fracture problems and derive the coupled system of equations that govern the motion of the body and evolution of the phase-field. We study the behavior of the model in one dimension and show how it influences material properties. For the temporal discretization of the equations of motion, we present both a monolithic and staggered time integration scheme. We study the behavior of the dynamic model by performing a number of two and three dimensional numerical experiments. We also introduce a local adaptive refinement strategy and study its performance in the context of locally refined T-splines. We show that the combination of the phase-field model and local adaptive refinement provides an effective method for simulating fracture in three dimensions.

Isogeometric Analysis of Structural Vibrations

Abstract: This paper begins with personal recollections of John H. Argyris. The geometrical spirit embodied in Argyris’s work is revived in the sequel in applying the newly developed concept of isogeometric analysis to structural vibration problems. After reviewing some fundamentals of isogeometric analysis, application is made to several structural models, including rods, thin beams, membranes, and thin plates. Rotationless beam and plate models are utilized as well as three-dimensional solid models. The concept of k-refinement is explored and shown to produce more accurate and robust results than corresponding finite elements. Through the use of nonlinear parameterization, “optical” branches of frequency spectra are eliminated for k-refined meshes. Optical branches have been identified as contributors to Gibbs phenomena in wave propagation problems and the cause of rapid degradation of higher modes in p-method finite elements. A geometrically exact model of the NASA Aluminum Testbed Cylinder is constructed and frequencies and mode shapes are computed and shown to compare favorably with experimental results.

Variational multiscale residual-based turbulence modeling for large eddy simulation of incompressible flows

Abstract: We present an LES-type variational multiscale theory of turbulence. Our approach derives completely from the incompressible Navier–Stokes equations and does not employ any ad hoc devices, such as eddy viscosities. We tested the formulation on forced homogeneous isotropic turbulence and turbulent channel flows. In the calculations, we employed linear, quadratic and cubic NURBS. A dispersion analysis of simple model problems revealed NURBS elements to be superior to classical finite elements in approximating advective and diffusive processes, which play a significant role in turbulence computations. The numerical results are very good and confirm the viability of the theoretical framework.

Isogeometric fluid-structure interaction: theory, algorithms, and computations

Abstract: We present a fully-coupled monolithic formulation of the fluid-structure interaction of an incompressible fluid on a moving domain with a nonlinear hyperelastic solid. The arbitrary Lagrangian–Eulerian description is utilized for the fluid subdomain and the Lagrangian description is utilized for the solid subdomain. Particular attention is paid to the derivation of various forms of the conservation equations; the conservation properties of the semi-discrete and fully discretized systems; a unified presentation of the generalized-α time integration method for fluid-structure interaction; and the derivation of the tangent matrix, including the calculation of shape derivatives. A NURBS-based isogeometric analysis methodology is used for the spatial discretization and three numerical examples are presented which demonstrate the good behavior of the methodology.

Research advances in intelligent collision avoidance and adaptive cruise control

Abstract: This paper looks into recent developments and research trends in collision avoidance/warning systems and automation of vehicle longitudinal/lateral control tasks. It is an attempt to provide a bigger picture of the very diverse, detailed and highly multidisciplinary research in this area. Based on diversely selected research, this paper explains the initiatives for automation in different levels of transportation system with a specific emphasis on the vehicle-level automation. Human factor studies and legal issues are analyzed as well as control algorithms. Drivers' comfort and well being, increased safety, and increased highway capacity are among the most important initiatives counted for automation. However, sometimes these are contradictory requirements. Relying on an analytical survey of the published research, we will try to provide a more clear understanding of the impact of automation/warning systems on each of the above-mentioned factors. The discussion of sensory issues requires a dedicated paper due to its broad range and is not addressed in this paper.