• Wind and Structures
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• v.30 no.5
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• pp.475-483
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• 2020

This work investigates Reynolds number Re (= 50 - 200) effects on the flows around a single cylinder and the two tandem (center-to-center spacing L^⁎= L/D = 4) cylinders, each of a diameter D. Vorticity structures, Strouhal numbers, and time-mean and fluctuating forces are presented and discussed. For the single cylinder, with increasing Re in the range examined, the vorticity magnitude, Strouhal number and fluctuating lift all monotonically rise but time-mean drag, vortex formation length, and lateral distance between the two rows of vortices all shrink. For the two tandem cylinders, the increase in Re leads to the formation of three distinct flows, namely reattachment flow (50 ≤ Re ≤ 75), transition flow (75 < Re < 100), and coshedding flow (100 ≤ Re ≤ 200). The reattachment flow at Re = 50 is steady. When Re is increased from 75 to 200, the Strouhal number of the two cylinders, jumping from 0.113 to 0.15 in the transition flow regime, swells to 0.188. The two-cylinder flow is more sensitive to Re than the single cylinder flow. Fluctuating lift is greater for the downstream cylinder than the upstream cylinder while time-mean drag is higher for the upstream cylinder than for the other. The time-mean drags of the upstream cylinder and single cylinder behaves similar to each other, both declining with increasing Re.

• Journal of Institute of Control, Robotics and Systems
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• v.7 no.10
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• pp.812-818
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• 2001

This paper proposes an optimum design method of structural and control systems, taking a 2-D truss structure as an example. The structure is supposed to be subjected to initial static loads and disturbances. For the structure, a FEM model is formed, and using modal transformation, the equation of motion is transformed into that of modal coordinates in order to reduce the D.O.F. of the FEM model. The structure is controlled by an output feedback $H^$\infty$$ controller to suppress the effect of the disturbances. The design variables of the simultaneous optimal design of control-structure systems are the cross sectional areas of truss members. The structural objective function is the structural weight. The control objective function is the $H^$\infty$$ norm, that is, the performance index of control. The second structural objective function is the energy of the response related to the initial state, which is derived from the time integration of the quadratic form of the state in the closed-loop system. In a numerical example, simulations have been carried out. Through the consideration of structural weight and $H^$\infty$$ norm, an advantage of the simultaneous optimum design of structural and control systems is shown. Moreover, while the optimized performance index of control is almost kept, we can acquire better design of structural strength.

• Journal of rehabilitation welfare engineering & assistive technology
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• v.11 no.3
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• pp.271-277
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• 2017

The purpose of this study was to develop a balance chair for improving pelvic correction and postural balance through postural balance training using tactile feedback by a vibration motor provided in real time according to the user's attitude. We built a body frame using mono cast(MC) Nylon, Touch thin film transistor(TFT) for user interface, a main control module using Arduino, a 9-axis acceleration sensor for user's posture determination, and a vibration module for tactile feedback. The prototype of the Balance Chair which surrounds the outside was made with cushion for sitting conformability. In order to verify the effectiveness of the postural balance training system using the built prototype, the muscle activity (% MVIC) of the left and right iliocostalis lumborum those are the main muscles of the spinal movement was measured with ten female subjects. And the balance ability before and after training was measured using Spine Balance 3D, a posture balance ability evaluation device. The muscular activities of the left and right iliocostalis lumborum showed the balance activation according to vibration feedback during exercise protocol and postural balance improved after balance exercise training using balance chair. This study could be apply to use the fundamental research for developing the various postural balance product.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.31 no.5
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• pp.227-234
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• 2018

Researches regarding measurement and control of the dynamic behavior of liquid such as sloshing have been actively on undertaken in various engineering fields. Liquid vibration is being measured in the study of tuned liquid dampers(TLDs), which attenuates wind motion of buildings even in building structures. To overcome the limitations of existing wave height measurement sensors, a method of measuring liquid vibration in a TLD using a laser Doppler vibrometer(LDV) and galvanometer scanner is proposed in this paper: the principle of measuring speed and displacement is discussed; a system of multi-point measurement with a single point of LDV according to the operating principles of the galvanometer scanner is established. 4-point liquid vibration on the TLD is measured, and the time domain data of each point is compared with the conventional video sensing data. It was confirmed that the waveform is transformed into the traveling wave and the standing wave. In addition, the data with measurement delay are cross-correlated to perform singular value decomposition. The natural frequencies and mode shapes are compared using theoretical and video sensing results.

• Wind and Structures
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• v.38 no.1
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• pp.15-42
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• 2024

A flexible-base coupled-two-beam (CTB) discrete model with equivalent tuned mass dampers is used to assess the effect of soil-structure interaction (SSI) and different types of lateral resisting systems on the design of passive dynamic absorbers (PDAs) under the action of along-wind and across-wind loads due to vortex shedding. A total of five different PDAs are considered in this study: (1) tuned mass damper (TMD), (2) circular tuned sloshing damper (C-TSD), (3) rectangular tuned sloshing damper (R-TSD), (4) two-way liquid damper (TWLD) and (5) pendulum tuned mass damper (PTMD). By modifying the non-dimensional lateral stiffness ratio, the CTB model can consider lateral deformations varying from those of a flexural cantilever beam to those of a shear cantilever beam. The Monte Carlo simulation method was used to generate along-wind and across-wind loads correlated along the height of a real shear wall-frame building, which has similar fundamental periods of vibration and different modes of lateral deformation in the xz and yz planes, respectively. Ambient vibration tests were conducted on the building to identify its real lateral behavior and thus choose the most suitable parameters for the CTB model. Both alongwind and across-wind responses of the 144-meter-tall building were computed considering four soil types (hard rock, dense soil, stiff soil and soft soil) and a single PDA on its top, that is, 96 time-history analyses were carried out to assess the effect of SSI and lateral resisting system on the PDAs design. Based on the parametric analyses, the response significantly increases as the soil flexibility increases for both type of lateral wind loads, particularly for flexural-type deformations. The results show a great effectiveness of PDAs in controlling across-wind peak displacements and both along-wind and across-wind RMS accelerations, on the contrary, PDAs were ineffective in controlling along-wind peak displacements on all soil types and different kind of lateral deformation. Generally speaking, the maximum possible value of the PDA mass efficiency index increases as the soil flexibility increases, on the contrary, it decreases as the non-dimensional lateral stiffness ratio of the building increases; therefore, there is a significant increase of the vibration control effectiveness of PDAs for lateral flexural-type deformations on soft soils.

• 제어로봇시스템학회:학술대회논문집
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• 1992.10b
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• pp.265-271
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• 1992

It is the purpose of this paper to present a dialogical designing method for control system using a rough grasp of the unknown process property. We deal with a single-input single-output feedback control system with a fuzzy controller. The process property is roughly estimated by the step response, and the fuzzy controller is interactively modified according to the operator's requests. The modifying rules mainly derived from computer simulation are useful for almost every process, such as an unstable process and a non-minimum phase process. The fuzzy controller is tuned by taking notice of four characteristics of the step response: (1) rising time, (2) overshoot, (3) amplitude and (4) period of vibration. The tuning position of the controller is fourfold: (1) antecedent gain factor GE or GCE, (2) consequent gain factor GDU, (3) arrangement of the antecedent fuzzy labels and (4) arrangement of the control rules. The rules give an instance to the respective items of the controller in an effective order. The modified fuzzy PI controller realizes a good response of a stable process. However, because the GDU tuning becomes difficult for the unstable process, it is necessary to evaluate the stability of the process from the initial step response. The fuzzy PI controller is applied to the process whose initial step response converges with GDU tuning. The fuzzy PI controller with modified sampling time is applied to the process whose step response converges under the repeated application of the GDU tuning. The fuzzy PD controller is applied to the process whose step response never converges by the GDU tuning.

• Wind and Structures
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• v.10 no.3
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• pp.233-247
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• 2007

The insertion of steel braces has become a common technique to limit the deformability of steel framed buildings subjected to wind loads. However, when this technique is inadequate to keep floor accelerations within acceptable levels of human comfort, dampers placed in series with the steel braces can be adopted. To check the effectiveness of braces equipped with viscoelastic (VEDs) or friction dampers (FRDs), a numerical investigation is carried out focusing attention on a three-bay fifteen-storey steel framed building with K-braces. More precisely, three alternative structural solutions are examined for the purpose of controlling wind-induced vibrations: the insertion of additional diagonal braces; the insertion of additional diagonal braces equipped with dampers; the insertion of both additional diagonal braces and dampers supported by the existing K-braces. Additional braces and dampers are designed according to a simplified procedure based on a proportional stiffness criterion. A dynamic analysis is carried out in the time domain using a step-by-step initial-stress-like iterative procedure. Along-wind loads are considered at each storey assuming the time histories of the wind velocity, for a return period $T_r=5$ years, according to an equivalent wind spectrum technique. The behaviour of the structural members, except dampers, is assumed linear elastic. A VED and an FRD are idealized by a six-element generalized model and a bilinear (rigid-plastic) model, respectively. The results show that the structure with damped additional braces can be considered, among those examined, the most effective to control vibrations due to wind, particularly the floor accelerations. Moreover, once the stiffness of the additional braces is selected, the VEDs are slightly more efficient than the FRDs, because they, unlike the FRDs, dissipate energy also for small amplitude vibrations.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 1999.10a
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• pp.15-15
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• 1999

In chip plating, several parameters must be taken into consideration. Current density, solution concentration, pH, solution temperature, components volume, chip and media ratio, barrel geometrical shape were most likely found to have an effect to the process yields. The 3 types of barrels utilized in chip plating industry are the conventional rotating barrel. vibrational barrel (vibarrel), and the centrifugal type. Conventional rotating barrel is a close type and is commonly used. The components inside the barrel are circulated by the barrel's rotation at a horizontal axis. Process yield has known to have higher thickness deviation. The vibrational barrel is an open type which offers a wide exposure to electrolyte resulting to a stable thickness deviation. It rotates in a vertical axis coupled with multi-vibration action to facilitate mixed up and easy transportation of components, The centrifugal barrel has its plated work centrifugally compacted against the cathode ring for superior electrical contact with simultaneous rotary motion. This experiment has determined the effect of barrel vibration intensity to the plating thickness distribution. The procedures carried out in the experiment involved the overall plating process., cleaning, rinse, Nickel plating, Tin-Lead plating. Plating time was adjusted to meet the required specification. All other parameters were maintained constant. Two trials were performed to confirm the consistency of the result. The thickness data of the experiment conducted showed that the average mean value obtained from higher vibrational intensity is nearer to the standard mean. The distribution curve shown has a narrower specification limits and it has a reduced variation around the target value, Generally, intensity control in vi-barrel facilitates mixed up and easy transportation of components, However, it is desirable to maintain an optimum vibration intensity to prevent solution intrusion into the chips' internal electrode. A cathodic reaction can occur in the interface of the external and internal electrode. $2HD{\;}+{\;}e{\;}{\rightarrow}20H{\;}+{\;}H_2$ Hydrogen can penetrate into the body and create pressure which can cause cracks. At high intensity, the chip's motion becomes stronger, its contact between each other is delayed and so plating action is being controlled. However, the strong impact created by its collision can damage the external electrode's structure thereby resulting to bad plating condition. 1 lot of chip was divided into two equal partion. Each portion was loaded to the same barrel one after the other. Nickel plating and tin-lead plating was performed in the same station. Portion A maintained the normal barrel vibration intensity and portion B vibration intensity was increased two steps higher. All other parameters, current, solution condition were maintained constant. Generally, plating method find procedures were carried out in a best way to maintained the best plating condition. After plating, samples were taken out from each portion. molded and polished. Plating thickness was investigated for both. To check consistency of results. 2nd trial was done now using different lot of another characteristics.

• The Transactions of the Korean Institute of Power Electronics
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• v.18 no.4
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• pp.367-375
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• 2013

The mechanical vibration of a PM synchronous motor at low speeds due to the back emf harmonics may be serious problems in some application such as MDPS(Motor driven power steering), electric vehicles. In this paper, torque ripple reduction for an interior PM synchronous motor including back emf harmonics is proposed. The dq flux linkage harmonics of the permanent magnet are estimated on real time by using the dq currents of the real system and the model of the MRAS observer. Based on the estimated flux linkage harmonics, the dq harmonic currents for reducing the torque ripples are compensated on the dq reference currents. The estimation of the flux linkage harmonics by the MRAS observer and the torque ripple reduction of the proposed algorithm was verified by the simulation and experiment.

• Journal of Institute of Control, Robotics and Systems
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• v.2 no.2
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• pp.96-101
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• 1996

In this paper, a simulator is designed along with S/W package for crane controllers. Due to trolley's acceleration or deceleration, cranes inherently cause swing motion of the objects in transporting heavy objects. This swing not only deteriorates the crane handling safety but also increases the processing time. To overcome these drawbacks, the fuzzy rule-based simulator is developed with inhibitory swing at final action. The computer simulation shows that the swing at initial and final positions is removed fast with small position error. The proposed simulator can be used for handling object stabley and the study of effectiveness in unmanned operation of cranes.