• Tribology and Lubricants
• /
• v.13 no.3
• /
• pp.63-72
• /
• 1997

The stability of a rotor-bearing system supported by swirl-controlled hybrid journal bearing with pair-type angled injection orifices is investigated for improvement of the whirl frequency ratio by allowing effective control of the tangential flow inside the bearing clearance, i.e., by achieving more freedom in controlling strength and direction of the supply tangential flow inside the bearing clearance. It is suggested that the system instability can be improved through the change of bearing dynamic characteristic parameters with the swirl control. The orifice diameter $d_0$ and recess injection angle $\alpha$ along with combinations of swirl/anti-swirl supply pressures and directions (3.0~3.0 MPa, 4.0~2.0 MPa, 2.0~4.0 MPa) are selected for design parameters for swirl-controlled effective factors dependent on journal speeds (3000, 9000, 15000, 21000 rpm). It has been found that the orifice diameter $d_0$ shows strong effects on effective maneuverability of direct-stiffness and direct damping values, while recess injection angle $\alpha$ results in substantial effects on the magnitude and direction of cross-stiffness. Specifically, recess injection parameters which are functions of angle of orifice feeding flow and recess dimensions showed very feasible effect on the stability control of swirl-controlled rotor-bearing system.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.23 no.3
• /
• pp.254-262
• /
• 2015

This paper presents 3D collision deformation modelling methodologies using photogrammetry for reconstruction of vehicle accidents. A vehicle's deformation shape in collision provides important information on how the vehicle collided. So effective measurement(scanning) and construction of a corresponding appropriate model are essential in the analysis of collision deformation shape for obtaining much information related to collision accident. Two measurement methods were used in this study: Indirect-photogrammetry which requires relatively small amount of photos or videos, and direct-photogrammetry which requires large amount of photos directly taken for the purpose of 3D modelling. When the indirect-photogrammetry method, which was mainly used in this study, lacked enough photographic information, already secured 2D numerical deformation data was used as a compensation. This made 3D collision deformation modelling for accident reconstruction analysis possible.

• Steel and Composite Structures
• /
• v.13 no.1
• /
• pp.15-33
• /
• 2012

For an axially loaded box-shaped member, the width-to-thickness ratio of the plate elements preferably should not be greater than 40 for Q235 steel grades in accordance with the Chinese code GB50017-2003. However, in practical engineering the plate width-to-thickness ratio is up to 120, much more than the limiting value. In this paper, a 3D nonlinear finite element model is developed that accounts for both geometrical imperfections and residual stresses and the ultimate capacity of welded built-up box columns, with larger width-to-thickness ratios of 60, 70, 80, and 100, is simulated. At the same time, the interaction buckling strength of these members is determined using the effective width method recommended in the Chinese code GB50018-2002, Eurocode 3 EN1993-1 and American standard ANSI/AISC 360-10 and the direct strength method developed in recent years. The studies show that the finite element model proposed can simulate the behavior of nonlinear buckling of axially loaded box-shaped members very well. The width-to-thickness ratio of the plate elements in welded box section columns can be enlarged up to 100 for Q235 steel grades. Good agreements are observed between the results obtained from the FEM and direct strength method. The modified direct strength method provides a better estimation of the column strength compared to the direct strength method over the full range of plate width-to-thickness ratio. The Chinese code and Eurocode 3 are overly conservative prediction of column capacity while the American standard provides a better prediction and is slightly conservative for b/t = 60. Therefore, it is suggested that the modified direct strength method should be adopted when revising the Chinese code.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• v.11 no.3
• /
• pp.1373-1392
• /
• 2017

WiFi Direct (WD) is a state of the art technology for a Device-to-Device (D2D) communication in 802.11 networks. The performance of the WD system can be significantly affected by some key factors such as the type of application, specifications of MAC and PHY layer parameters, and surrounding environment etc. It is, therefore, important to develop a system model that takes these factors into account. In this paper, we focus on investigating the design parameters of the PHY layer that could maximize the efficiency of the WD 802.11 system. For this purpose, a basic theoretical model is formulated for a WD network under a 2x2 Multiple In Multiple Out (MIMO) TGn channel B model. The design level parameters such as input symbol rate and antenna spacing, as well as the effects of the environment, are thoroughly examined in terms of path gain, spectral density, outage probability and Packet Error Rate (PER). Thereafter, a novel adaptive algorithm is proposed to choose optimal parameters in accordance with the Quality of Experience (QoE) for a targeted application. The simulation results show that the proposed method outperforms the standard method thereby achieving an optimal performance in an adaptive manner.

• The Transactions of the Korean Institute of Power Electronics
• /
• v.8 no.3
• /
• pp.211-220
• /
• 2003

This paper presents an implementation of direct torque control (DTC) of Reluctance Synchronous Motor (RSM) with an efficiency optimization. The equipment circuit in Reluctance Synchronous Motor which consider with iron losses is theoretically analyzed and the optimal current ration between torque current and exiting current analytically derived to drive RSM at maximum efficiency. For RSM, torque dynamics can be maintained even with controlling the flux level because a torque is directly proportional to the stator current unlike induction motor. The experimental results are presented to validate the applicability of the proposed method. The developed control system show high efficiency features with 1.0 Kw RSM having 2.57 ratio of d/q reluctance.

• Journal of Magnetics
• /
• v.10 no.2
• /
• pp.41-43
• /
• 2005

We have investigated an optical waveguide isolator with a multimode interference section by wafer direct bonding, operating at a wavelength $1.55\;{\mu}m$. In order to fabricate the device for monolithic integration, the wafer direct bonding between a magnetic garnet material as a cladding layer and a semiconductor guiding layer has been achieved. We found that wafer direct bonding between InP and GGG $(Gd_3Ga_5O_{12})$ is effective for the integration of a waveguide optical isolator. The isolation ratio was obtained to be 2.9 dB in the device.

• Journal of computational fluids engineering
• /
• v.12 no.3
• /
• pp.41-46
• /
• 2007

Dynamic behavior of immiscible gas bubble attached to the wall in channel flow plays very important role in many engineering applications. Special attention has been paid to micro direct methanol fuel cell(${\mu}$DMFC) where surface tension becomes dominant factor with minor gravitational effect due to its reduced size. Therefore, displacement of $CO_2$ bubble generating on a cathode side in ${\mu}$DMFC can be very difficult and efficient removal of $CO_2$ bubbles will affect the overall machine performance considerably. We have focused our efforts on studying the dynamic behavior of immiscible bubble attached to the one side of the wall on 2D rectangular channel subject to external shear flow. We used Level Contour Reconstruction Method(LCRM) which is the simplified version of front tracking method to track the bubble interface motion. Effects of Reynolds number, Weber number, advancing/receding contact angle and property ratio on bubble detachment characteristic has been numerically identified.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
• /
• v.12 no.3
• /
• pp.59-66
• /
• 1998

In this paper, the thrust control of PWM Inverter-Fed SLIM(Single-sided Linear Induction Motor) is achieved with Space Vector control and PI control. The trembling of air gap length which is occurred between the primary winding core and the secondary structure of the SLIM must be minimized in order to get quick response characteristics. First, the equivalent circuits and voltage equations of SLIM are shown on th suitable d-q axis which analyze characteristics of the thrust and the normal force. Also, modeling and analysis of the equivalent circuits transferred d-q axis are able to make robust transient torque from the current regulation in the equivalent circuit. These results exemplified the direct drive of SLIM with the reference speed and torque were verified by experiments.

• International Journal of Automotive Technology
• /
• v.5 no.3
• /
• pp.165-172
• /
• 2004

Phenomenological models for direct injection diesel engine emissions including NO, soot, and HC were implemented into a full engine cycle simulation and validated with experimental data obtained from representative heavy-duty DI diesel engines. The cycle simulation developed earlier by Jung and Assanis (2001) features a quasi-dimensional, multi-zone, spray combustion model to account for transient spray evolution, fuel-air mixing, ignition and combustion. In this study, additional models for HC emissions were newly implemented and the models for NO, soot, and HC emissions were validated against experimental data. It is shown that the models can predict the emissions with reasonable accuracy. However, additional effort may be required to enhance the fidelity of models across a wide range of operating conditions and engine types.

• The Transactions of the Korean Institute of Electrical Engineers D
• /
• v.54 no.3
• /
• pp.180-185
• /
• 2005

Microstrip antennas generally have a lot of advantages that are thin profile, lightweight, low cost, and conformability to a shaped surface application with integrated circuitry. In addition to military applications, they have become attractive candidates in a variety of commercial applications such as mobile satellite communications, the direct broadcast system (DBS), global positioning system (GPS), and remote sensing. Recently, many of the researches have been achieved for improving the impedance bandwidth of microstrip antennas. The basic form of the microstrip antenna, consisting of a conducting patch printed on a grounded substrate, has an impedance bandwidth of $1\~2\%$. For improvement of narrow bandwidth of microstrip patch, we were designed U-slot microstrip patch antenna in this paper. This antenna had wide bandwidth for all personal communication services (PCS) and IMT-2000. For the design of U-slot microstrip patch antenna using a finite difference time domain(FDTD) method. This numerical method could get the frequency property of U-slot patch antenna and the electromagnetic fields of slots.