• The Transactions of the Korean Institute of Electrical Engineers B
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• v.52 no.5
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• pp.197-202
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• 2003

When a high-speed train reduces its operating velocity while decelerating from a maximum of 350 to 50 [km/h], the train applies eddy-current brakes, which results in a deceleration time of approximately 3minutes. Therefore, a high current is utilized in order to obtain a large braking force. Consequently, the temperature of the electromagnet and rail increases significantly. In this paper, The thermal characteristics on a single magnet pole with convection heat transfer coefficient are simulated by using 2D-FEM. To verify the analysis results, the computed temperatures are compared with the experimentally measured temperature at stationary state. Furthermore, transient-state thermal analysis is performed to predict the magnet temperatures as the train is decelerating.

• Journal of the Korean Society for Precision Engineering
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• v.24 no.5
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• pp.56-61
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• 2007

In the braking of railway rolling stock, the slip that is the relative velocity between train body and its wheel affects the adhesive force which is connected to the braking force. The coefficient of the adhesive force changes in accordance with the slip and the condition of a rail road. Namely, its value increases upon the maximum on a rail condition, and there it declines conversely while the magnitude of slip keeps rising on. First, this paper introduced a reference slip generator so that can utilize maximum adhesive forces with a disturbance observer for estimating unmeasurable current adhesive forces which is as an input of the generator. And, an adaptive sliding-mode control system has been synthesized for minimizing the error between reference and current slip. Finally the effectiveness of the proposed control system is evaluated by computer simulation.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.49 no.3
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• pp.131-137
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• 2000

2 phase 8 pole HB-type(flat-type) Linear Pulse Motor can be used as the high precision position actuator because of its many advantages (simple control circuit, high stiffness characteristics, etc). Also, using the microstep drive, its noise and vibration can be reduced considerably and positional resolution may be increased further. But, $20^{\circ}$tapered tooth shape to reduce the normal force have an much effect on the static thrust force characteristics. And, because of hybrid-type LPM, interaction between the permanent magnet and the excitation current have an effect on the various characteristics of LPM. Hence, in this paper, the effect of tooth shape on static thrust force characteristics was analyzed using the air gap permeance by finite element method. For analyzing the effect of unbalance between the m.m.f of permanent magnet and the m.m.f of excitation current, unbalanced m.m.f coefficient $\sigma$ were introduced with the permenace matrix and switching matrix.

• New & Renewable Energy
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• v.19 no.2
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• pp.23-30
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• 2023

Vortex-induced vibrations are a type of flow-induced vibrations caused by alternating lift forces. With increasing demand for renewable energy, the application of vortex-induced vibrations to renewable energy has been widely studied. Vortex-induced vibrations for aquatic clean energy (VIVACE) converter is a renewable energy device that generates electricity from rivers or oceans using vortex-induced vibrations. To increase the design life and power harnessing capacity of the VIVACE converter, the estimation of fluid forces due to vortex-induced vibrations is essential. Herein, vortex-induced vibrations were experimentally tested, and their amplitude and frequency response were measured. The amplitude results showed four different branches: initial branch, upper branch, lower branch, and desynchronization range. According to the fluid force coefficient results, the maximum lift coefficient occurred at the upper branch. Additionally, a mathematical model is proposed to estimate fluid forces due to vortex-induced vibrations without using measurement devices. This mathematical model enables the estimation of fluid force coefficients and phase lag using amplitude and frequency response of vortex-induced vibrations.

• Structural Engineering and Mechanics
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• v.27 no.2
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• pp.117-134
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• 2007

The force (load) reduction factor, R, which is one of the most important parameters in earthquake load calculation, is independent of the dimensions of the structure but is defined on the basis of the load bearing system of the structure as defined in earthquake codes. Significant damages and failures were experienced on prefabricated reinforced concrete structures during the last three major earthquakes in Turkey (Adana 1998, Kocaeli 1999, Duzce 1999) and the experts are still discussing the main reasons of those failures. Most of them agreed that they resulted mainly from the earthquake force reduction factor, R that is incorrectly selected during design processes, in addition to all other detailing errors. Thus this wide spread damages caused by the earthquake to prefabricated structures aroused suspicion about the correctness of the R coefficient recommended in the current Turkish Earthquake Codes (TEC - 98). In this study, an attempt was made for an approximate determination of R coefficient for widely utilized prefabricated structure types (single-floor single-span) with variable dimensions. According to the selecting variable dimensions, 140 sample frames were computed using pushover analysis. The force reduction factor R was calculated by load-displacement curves obtained pushover analysis for each frame. Then, formulated artificial neural network method was trained by using 107 of the 140 sample frames. For the training various algorithms were used. The method was applied and used for the prediction of the R rest 33 frames with about 92% accuracy. The paper also aims at proposing the authorities to change the R coefficient values predicted in TEC - 98 for prefabricated concrete structures.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.49 no.8
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• pp.514-521
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• 2000

This paper presents a direct thrust control scheme for permanent magnet linear synchronous motor(PMLSM) by using digital signal processor(DSP). And a simulation method for the direct thrust control of a permanent magnet linear synchronous motor using the equivalent circuit is presented. The detent force that was obtained by cubic spline method is considered in the simulation. Thrust correction coefficient is utilized to estimate actual thrust on the direct thrust control, which considers the longitudinal end effect due to the finite core length of the permanent magnet linear synchronous motor. The motor self inductance, the initial flux linkage by the permanent magnet is calculated in advance by the finite element analysis, and then the direct control simulation is carried out. As the results, thrust, current and speed are shwon.

• International Journal of Fluid Machinery and Systems
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• v.4 no.1
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• pp.150-160
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• 2011

This study focuses on the Achard turbine, a vertical axis, cross-flow, marine current turbine module. Similar modules can be superposed to form towers. A marine or river hydropower farm consists of a cluster of barges, each gathering several parallel rows of towers, running in stabilized current. Two-dimensional numerical modelling is performed in a horizontal cross-section of all towers, using FLUENT and COMSOL Multiphysics. Numerical models validation with experimental results is performed through the velocity distribution, depicted by Acoustic Doppler Velocimetry, in the wake of the middle turbine within a farm model. As long as the numerical flow in the wake fits the experiments, the numerical results for the power coefficient (turbine efficiency) are trustworthy. The overall farm efficiency, with respect to the spatial arrangement of the towers, was depicted by 2D modelling of the unsteady flow inside the farm, using COMSOL Multiphysics. Rows of overlapping parallel towers ensure the increase of global efficiency of the farm.

• Journal of Advanced Marine Engineering and Technology
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• v.39 no.2
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• pp.143-151
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• 2015

Recently, tidal current energy conversion is a promising way to harness the power of tides in order to meet the growing demands of energy utilization. A new concept of tidal current energy conversion device, named Vane Tidal Turbine (VTT), is introduced in this study. VTT has several special features that are potentially more advantageous than the conventional tidal turbines, such as propeller type tidal turbines. The purpose of this study on VTT is to analyze the possibility of extracting the hydrokinetic energy of tidal current and converting it into electricity, and evaluate the performance of turbines for various numbers of blades (six, eight and twelve) using Computational Fluid Dynamics (CFD). At various tip-speed ratios (TSR), the six-bladed turbine obtains the highest power and torque coefficients, power efficiency is up to 28% at TSR = 1.89. Otherwise, the twelve blade design captures the smallest portion of available tidal current energy at all TSRs. However, by adding more blades, torque extracted from the rotor shaft of twelve-bladed turbine is more uniform due to the less interrupted generation of force for a period of time (one revolution).

• Journal of Institute of Control, Robotics and Systems
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• v.4 no.4
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• pp.525-533
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• 1998

A conventional contact type brake system which uses a hydraulic system has mny Problems such as time delay response due to pressure build-up, brake pad wear due to contact movement, bulky size, and low braking performance in high speed region. As vehicle speed increases, a more powerful brake system is required to ensure vehicle safety and reliability. In this work, a contactless brake system of an eddy current type is proposed to overcome problems. Optimal torque control which minimizes a braking distance is investigated with a scaled-down model of an eddy current type brake. It is possible to realize optimal torque control when a maximum friction coefficient (or desired slip ratio) corresponding to road condition is maintained. Braking force analysis for a scaled-down model is done theoretically and experimentally compensated. To accomplish optimal torque control of an eddy current type brake system, a sliding mode control technique which is, one of the robust nonlinear control technique is developed. Robustness of the sliding mode controller is verified by investigating the braking performance when friction coefficient is varied. Simulation and experimental results will be presented to show that it has superior performance compared to the conventional method.

• KSTLE International Journal
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• v.6 no.2
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• pp.51-57
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• 2005

Surface texturing of tribological applications is an attractive technology of engineered surface. Therefore, reduction of friction is considered to be necessary for improved efficiency of machines. The current study investigated the potential of textured micro-scale grooves on bearing steel flat mated with pin-on-disk. We discuss reducing friction due to the influence of sliding direction at surface pattern. We can indicate lubrication mechanism as a Stribeck curve, which has a relationship between the friction coefficient and a dimensionless parameter for the lubrication condition. It was found that the friction coefficient was changed by the surface pattern and sliding direction, even when surface pattern was the same. It was thus verified that micro-scale grooves could affect the friction reduction considerably under mixed and hydrodynamic lubrication conditions. The lubrication regime influences the friction coefficient induced by the sliding direction of groove pattern. The friction coefficient depends on a combination of resistance force and hydrodynamic.