Hyuk-Jun Kwon

Braille code display device with a PDMS membrane and thermopneumatic actuator

The Braille code display device with a PDMS (polydimethylsiloxane) membrane and thermopneumatic actuator is fabricated and tested. One dot (pixel) whose dimension is 3 mm x 3 mm among six dots in the Braille code is fabricated by using RIE (reactive ion etching), chemical wet etching, and E-beam evaporating. When applied input voltage is under 6 VPP, the deflections of the membranes occur under the thickness of the silicon substrate. On the other hand, when 8 Vpp and 10 Vpp are applied at 40 mum and 110 mum thickness membranes, the deflections happen about 1 mm, 0.4 mm, 1. 3 mm, and 1.4 mm over the substrate, respectively. The deflection of fabricated device is accomplished over 2 times larger than 600 mum standard height designated by Korea Blind Union.

Conceptual design of mniniature tunable stiffness display using MR fluids

Stiffness information is one of the important factors to naturally and intuitively interact with electronic devices and displays. For small-sized electronics, such as hand-held devices, the size of haptic modules is a key limiting factor, and it must be minimized. This paper proposes a concept of miniature and tunable stiffness display an aim to design a miniature device conveying stiffness information. The proposed device is based on Magneto-Rheological(MR) fluids, and its stiffness can be varied by activating the MR fluids with the magnetic field produced by the solenoid, . The proposed stiffness display is composed of three main parts such as an elastic returning part (providing elastic force), a stiffness tuning part (generating resistive force), and a PDMS membrane reservoir part (serving as a repository for the MR fluids). The use of MR fluids in the haptic display allows us to miniature it by eliminating bulky electrical and mechanical components in conventional haptic devices.

Transonic Flutter Prediction of Supersonic Jet Trainer with Various External Store Configurations

In this study, the aeroelastic analysis is performed to investigate the flutter characteristics of the aircraft model with external stores in the transonic and low supersonic regimes. The nonlinear aeroelastic analysis for the aircraft model is used using the TSD (Transonic Small Disturbance) theory in the transonic regime. A time-accurate AF (Approximate Factorization) algorithm is applied to solve the TSD equation. The aeroelastic analysis system is verified with the flight test data and the DLM results of the wing model. It is confirmed that the system is quite accurate. The mode shapes and natural frequencies of the aircraft model are obtained by the structural analysis with MSC/NASTRAN TM . This study shows that a flutter safety margin depends on store configurations in the transonic and low supersonic regimes.

Performance evaluation method of homogeneous stereo camera system for full-field structural deformation estimation

This study presents how we can evaluate stereo camera systems for the structural deformation monitoring. A stereo camera system, consisting of a set of stereo cameras and reflective markers attached on the structure, is introduced for the measurement and the stereo pattern recognition (SPR) method is utilized for the full-field structural deformation estimation. Performance of this measurement system depends on many parameters including types and specifications of the cameras, locations and orientations of them, and sizes and positions of markers; it is difficult to experimentally identify the effects of each parameter on the measurement performance. In this study, a simulation framework for evaluating performance of the stereo camera systems with various parameters has been developed. The maximum normalized root-mean-square (RMS) error is defined as a representative index of stereo camera system performance. A plate structure is chosen for an introductory example. Its several modal harmonic vibrations are generated and estimated in the simulation framework. Two cases of simulations are conducted to see the effects of camera locations and the resolutions of the cameras. An experimental validation is carried out for a few selected cases from the simulations. Using the simultaneous laser displacement sensor (LDS) measurements as the reference, the measurement errors are obtained and compared with the simulations.

Transonic Wing Flutter Analysis Using a Parallel Euler Solver

In this paper, a three-dimensional Euler aeroelastic analysis program is developed with a second-order staggered algorithm to reduce the lagging errors between the fluid and structural solvers. In the unsteady aerodynamic analysis, a dual-time stepping method based on the diagonalized-ADI algorithm is adopted to improve the time accuracy and a parallelized multi-grid method is used to save the computing time. The aeroelastic analyses of AGARD 445.6 wing model have been performed to verify the Euler aeroelastic analysis code. The analysis results are compared with the experimental data and other computational results. The results show comparatively good correlation when they are compared with other references.

Virtual Flutter Flight Test of a Full Configuration Aircraft with Pylon/External Stores

An advanced aeroelastic analysis using a computational structural dynamics (CSD), finite element method (FEM) and computational fluid dynamics (CFD) is presented in this Paper. A general aeroelastic analysis system is originally developed and applied to realistic design problems in the transonic flow region, where strong shock wave interactions exist. The present computational approach is based on the modal-based coupled nonlinear analysis with the matched-point concept and adopts the high-speed parallel processing technique on the low-cost network based PC-clustered machines. It can give very accurate and useful engineering data on the structural dynamic design of advanced flight vehicles. For the nonlinear unsteady aerodynamics in high transonic flow region, Euler equations using the unstructured grid system have been applied to easily consider complex configurations. It is typically shown that the advanced numerical approach can give very realistic and practical results for design engineers and safe flight tests. One can find that the present study conducts a virtual flutter flight test which are usually very dangerous in reality.

Nonlinear Simulation of Flutter Flight Test with the Forced Harmonic Motion of Control Surfaces

In this study, transonic/supersonic nonlinear flutter analysis system of a complete aircraft including forced harmonic motion pf control surfaces has been effectively developed using the modified transonic small disturbance (TSD) equation. To consider the nonlinear effects, the coupled time marching method (CTM) combining computational structural dynamics (CFD) has been directly applied for aeroelastic computations. The grid system for a complex full aircraft configuration is effectively generated by the developed inhouse code. Intransonic and supersonic flight regimes, the characteristics of static and dynamic aeroelastic effect has been investigated for a complete aircraft model. Also, nonlinear flutter flight simulations for the forced harmonic motion of control surfaces are practically presented in detail.

Transonic/Supersonic Nonlinear Aeroelastic Analysis of a Complete Aircraft Using High Speed Parallel Processing Technique

A nonlinear aeroelastic analysis system in transonic and supersonic flows has been developed using high speed parallel processing technique on the network based PC-clustered machines. This paper includes the coupling of advanced numerical techniques such as computational structural dynamics (CSD), finite element method (FEM) and computational fluid dynamics (CFD). The unsteady Euler solver on dynamic unstructured meshes is employed and coupled with computational aeroelastic solvers. Thus it can give very accurate engineering data in the structural and aeroelastic design of flight vehicles. To show the great potential of useful application, transonic and supersonic flutter analyses have been conducted for a complete aircraft model under developing in Korea.