Dong-Pyo Hong

A new approach for the analysis solution of dynamic systems containing fractional derivative

Fractional derivative models, which are used to describe the viscoelastic behavior of material, have received considerable attention. Thus it is necessary to put forward the analysis solutions of dynamic systems containing a fractional derivative. Although previously reported such kind of fractional calculus-based constitutive models, it only handles the particularity of rational number in part, has great limitation by reason of only handling with particular rational number field. Simultaneously, the former study has great unreliability by reason of using the complementary error function which can’t ensure uniform real number. In this paper, a new approach is proposed for an analytical scheme for dynamic system of a spring-mass-damper system of single-degree of freedom under general forcing conditions, whose damping is described by a fractional derivative of the order 0< α< 1 which can be both irrational number and rational number. The new approach combines the fractional Green’s function and Laplace transform of fractional derivative. Analytical examples of dynamic system under general forcing conditions obtained by means of this approach verify the feasibility very well with much higher reliability and universality.

The Vibration Performance Experiment of Tuned Liquid Damper and Tuned Liquid Column Damper

Tuned Liquid damper and Tuned Liquid Column are kind of passive mechanical damper which relies on the sloshing of liquid in a rigid tank for suppressing structural vibrations. TLD and TLCD are attributable to several potential advantages —low costs; easy to install in existing structures; effective even for small-amplitude vibrations. In this paper, the shaking table experiments were conducted to investigate the characteristics of water sloshing motion in TLD (rectangular, circular) and TLCD. The parameter obtained from the experiments were wave height, base shear force and energy dissipation. The shaking table experiments show that the liquid sloshing relies on amplitude of shaking table and frequency of tank. The TLCD was more effective control vibration than TLD.

Design of decoupled dual servo stage with voice coil motor and linear motor for XY long stroke ultra-precision scanning system

A decoupled dual servo (DDS) stage for ultra-precision scanning system is introduced in this paper. The proposed DDS consists of a 3 axis fine stage for handling and carrying workpieces and a XY coarse stage. Especially, the DDS uses three voice coil motors (VCM) as a planar actuation system of the fine stage to reduce the disturbances due to any mechanical connections with its coarse stage. VCMs are governed by Lorentz law. According to the law and its structure, there are no mechanical connections between coils and magnetic circuits. Moreover, the VCM doesnt have force ripples due to imperfections of commutation components of linear motor systems - currents and flux densities. However, due to the VCMs mechanical constraints the working range of the fine is about 5mm2. To break that hurdle, the coarse stage with linear motors is used for the fine stage to move about 200mm2. Because of the above reasons, the proposed DDS can achieve higher precision scanning than other stages with only one servo. Using MATLABs Sequential Quadratic Programming (SQP), the VCMs are optimally designed for the highest force under conditions and constraints such as thermal dissipations due to its coil, its size, and so on. For linear motors, Halbach magnet linear motor is proposed and optimally designed in this paper. In addition, for their smooth movements without any frictions, guide systems of the DDS are composed of air bearings. And then, precisely to get their positions, linear scales with 0.1um resolution are used for the coarses XY motions and plane mirror laser interferometers with 20nm for the fines XYθz. On scanning, the two stages have same trajectories and are controlled. The control algorithm is Parallel method. The embodied ultra-precision scanning system has about 100nm tracking error and in-positioning stability.

Pure Nano-Rotation Scanner

We developed and tested a novel rotation scanner for nano resolution and accurate rotary motion about the rotation center. The scanner consists of circular hinges and leaf springs so that the parasitic error at the center of the scanner in the X and Y directions is minimized, and rotation performance is optimized. Each sector of the scanners system was devised to have nano resolution by minimizing the parasitic errors of the rotation center that arise due to displacements other than rotation. The analytic optimal design results of the proposed scanner were verified using finite element analyses. The piezoelectric actuators were used to attain nano-resolution performances, and a capacitive sensor was used to measure displacement. A feedback controller was used to minimize the rotation errors in the rotation scanner system under practical conditions. Finally, the performance evaluation test results showed that the resonance frequency was 542 Hz, the resolution was 0.09 μrad, and the rotation displacement was 497.2 μrad. Our test results revealed that the rotation scanner exhibited accurate rotation about the center of the scanner and had good nano precision.

DAMAGE DETECTION OF TRUSS-LIKE STRUCTURES USING WAVELET TRANSFORMS

This study deals with the application of wavelet transforms to the damage detection of truss-like structures. The principles of damage detection by using the wavelet transforms are interpreted and the damage detection capabilities of wave transforms for cracks are demonstrated by numerical and experimental methods. Numerical simulation in combination with the wavelet transforms provides reliable numerical results and the guided wave method using smart materials enables the experimental verification of the numerical results. The basic component elements of truss structures, i.e., beams, are studied first, and subsequently complex structures are considered. The information extracted from the simulation data by using the wavelet transforms shows considerably accurate signatures for localization of damages. In particular, the study considers the influence of structural discontinuities and loading points on damage detection of crack localization. The information extracted from the signal by using the numerical and experimental methods employing the wavelet transforms shows the robustness of the methods in detecting damages in simple and complex structures.

Estimation for Bolt Fastening Conditions of Thin Aluminum Structure Using PZT Sensors

This work presents a study on PZT impedance-based method, it is one of the NDT(Non-Destructive Technique). We study about assessment of the square-structure health condition by impedance-based technique using PZT patches, associated with longitudinal wave propagation. Health conditions of the square-structure controlled by bolt fastening condition is adjusted by torque wrench. In order to estimate the damage condition numerically, we suggest the evaluation method of impedance peak frequency shift.

Study on Uncertainty Factors of Head Vibration Measurements

This paper addresses uncertainty issues encountered recently in measuring head vibration using the conventional 6-axis or 9-axis bite-bar model. Those conventional bite-bar models are shown to present insufficient information to evaluate a generalized motion of head vibration. In order to overcome such limit, a new theoretical measurement model that consists of four 3-axis linear accelerometers is suggested. It is shown to enable the measurement of three angular acceleration components and six second-order angular velocity-dependent terms. Those nine angular motion-related ones, in addition to the three linear acceleration terms at the origin, are found to make it possible to evaluate the generalized head vibration for a given position. To examine the feasibility of the proposed method, a newly designed 12-axis bite-bar was developed. Detailed experimental results obtained from the developed 12-axis bite-bar are demonstrated in this paper. They illustrate that the popular 6-axis bite-bar model yield about relative measurement uncertainty for the pitch component of head vibration, and relative measurement uncertainty for the roll and yaw components of head vibration, respectively. Furthermore, this paper proposes other uncertainty factors to be considered in the future.

Quantitative Evaluation of a Crack Inside of Pressure Pipeline by Shearography and ESPI

Electronic Speckle Pattern Interferometry (ESPI) and Shearography for quantitative analysis of a crack inside of pipelines are described. Shearography is used widely for non‐destructive inspection because of less sensitivity to environmental disturbance and simple interferometer. However, it is difficult to determine the defect size quantitatively because there are so many effect factors‐ shearing distance, shearing direction, and induced load, which depend on operator’s skill and crack information. These effective factors in Shearography are optimized for quantitative analysis and the size of crack is determined. And also, ESPI is used for determination of crack size quantitatively. In ESPI only induced load play an important role and the effective factor is independent on information of a crack. The displacement of object surface is obtained three‐dimensionally and differentiated numerically, which is same to result of Shearography so that crack size can be determined quantitatively without any informat...

Design and modeling of XYθ H type stage using 1 rotational DOF flexure joint

It is important that high precision positioning system to cope with development of semiconductor and FPD nmanufacturing/inspection procedure. In this paper, the H type stage with flexure joint was proposed to compensate the yaw nerror in H type stage caused by manufacturing error, assembly error, and synchronous error. To implement the yaw motion nin H type stage, 1 rotational DOF flexure joint which has high stiffness and endurance was proposed. Conceptual design of nH type stage was performed to follow the criteria for precision machine design. The performance of H type stage was nverified by real time experiment.

BUMPER IMPACT PERCEPTION FOR PEDESTRIAN PROTECTION USING SMART SENSOR

In this paper, a pendulum system is constructed to perform the fundamental research which is concentrated on the various frequency pattern of impact-object simulation tests are presented. and we confirmed application possibility for the method of discriminable pattern recognition whether impact-object is human-like or not via frequency analysis using smart sensor. Therefore a specific experimental data are compared and analyzed with the above database within a short time period. The impact analysis system, which is based on the above processing, can be developed and then used to recognize the impact information measured by smart sensors.