• Transactions of the Korean Society of Mechanical Engineers A
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• v.27 no.6
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• pp.871-878
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• 2003

With the development of micro -technology, the demand for micro actual ing device is increasing. But, it is difficult to achieve high resolution and wide bandwidth with the conventional contact systems. So, the contact-free systems which are suspended or levitated by magnetic force or air bearing were proposed. These systems can be applied to high precision stages and alignment apparatuses. This paper describes a magnetically suspended system with four degrees of freedom which are composed of three rotations (roll, pitch, yaw), and one translation ( z). The operating principle and the structure of the system are similar to variable reluctance type electric machines. In this study, the force analysis is executed using magnetic circuit and virtual work principle, and the equations that describe the dynamics of the system are presented. The multivariable PID controller is adapted to the system and the experiment is executed.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.33 no.3
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• pp.218-223
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• 2009

The micro pattern machining on the surface of wide mold is not easy to be simulated by conventional software. In this paper, a software is developed for micro pattern cutting simulation. The 3d geometry of v-groove, rectangular groove, pyramid and pillar patterns are visualized by C++ and OpenGL library. The micro cutting force is also simulated for each pattern.

• Transactions of The Korea Fluid Power Systems Society
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• v.5 no.4
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• pp.10-16
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• 2008

In this paper, the authors benchmark a servo valve model for the fuel supply system of Auxiliary Power Unit (APU) in the KHP helicopter. This valve is directly driven with a torque motor, and the size of small gap controlled by a flapper can make change of flow rate under given pressure drop between inlet and outlet. CFD analyses using a commercial code, ANSYS-CFX 10 are performed for the series of three-dimensional models at various openness conditions. The computational results on simplified models show that CFD can play a fine roll in the design of flow path as well as in the estimation of flow force due to its precision and good repeatability. Consequently, the CFD analysis helps valve designers to understand its flow characteristics from the basis of physical fundamentals.

• Journal of Auto-vehicle Safety Association
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• v.5 no.1
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• pp.50-55
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• 2013

When it comes to commercial vehicles, their unique characteristics - center of gravity, size, weight distribution - make them particularly vulnerable to rollover. On top of that, conventional heavy vehicle brake exhibits longer actuation delays caused in part by long air lines from brake pedal to tires. This paper describes rollover prevention algorithm that copes with the characteristics of commercial vehicles. In regard of compensating for high actuating delay, predicted rollover index with short preview time has been designed. Moreover, predicted rollover index with longer preview time has been calculated by using road curvature information based on environment information. When rollover index becomes larger than specific threshold value, desired braking force is calculated in order to decrease the index. At the same time, braking force is distributed to each tire to make yaw rate track desired value.

• Composites Research
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• v.29 no.6
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• pp.353-357
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• 2016

An appropriate way to fabricate a hybrid composite containing evenly dispersed carbon nano tubes(CNTs) is to stacking B-stage resin films that contain evenly dispersed CNTs and various reinforcing fiber layers alternatively. In the present study, B-stage resin films are manufactured via shear mixing and three-roll milling. CNT dispersion in resin via these two processes are evaluated by SEM on their fracture surfaces. For more efficient process, the dispersivities are evaluated according to the number of calendering passes. Samples are made for different number of passes during calendering, and their dispersions are evaluated via SEM fractographs as well as by measuring their electrical conductivities. Additionally, the optimal process conditions are obtained by measuring the electrical conductivity and evaluating their dispersivity of the samples prepared by gap mode and force mode.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.21 no.10
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• pp.897-904
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• 2011

When whole-body is exposed to vertical vibration, asymmetry shape of human body affects the response on the translational(fore-aft, lateral, vertical) and rotational(roll, pitch, yaw) motion. While the translational motion has been studied with various titles, it has been rare to study the rotational motion of human body exposed to vertical excitation because of lack of experimental equipment. This study was performed by using a 6-axis force plate installing strain gage type sensors for the rotational response. Sixteen male subjects were exposed to vertical vibration on rigid seat in order to investigate apparent mass of three translational motion and apparent eccentric mass of three rotational motion. Random signal was generated to make excitation vibration which was on an effective frequency range of 3~40 Hz, and magnitude of 0.224 m/$s^2$ r.m.s. The frequency range and magnitude used was selected for the vibration of passenger vehicle on idling condition. As the result, cross-axis apparent masses of fore-and-aft and lateral direction were not significant showing 20 % and 3 % of vertical apparent mass relatively. And apparent eccentric mass of pitch motion was dominant when compared to that of roll and yaw motion, which is reasoned by asymmetry direction of human body sitting on a seat.

• Journal of Ocean Engineering and Technology
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• v.30 no.6
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• pp.451-457
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• 2016

For a carferry with a displacement of 1,633 tonf, a seakeeping analysis-based direct load approach (DLA) was used in Part I of these series, where the final deliverable was the long-term probabilistic acceleration components. In Part II of these series, the tangential acceleration components are explained based on two approaches: a standard called the IMO CSS code and simple formulas with the probable maximum roll and pitch rotations. The subsequent tangential acceleration-induced external force components are also introduced for these two approaches. The lashing strength components were selected from the IMO CSS code. It was assumed that two different vehicles (a car and a truck) were stowed at the most distant locations on the main deck to assume the largest tangential acceleration components and were secured with four steel wires with longitudinal and transverse lashing angles of $45^{\circ}$. Four cases were considered, with different methods for predicting the acceleration components and different tools for the external loads and lashing strengths involved: cases Rule-LS (rule-based maximum probable roll and pitch angles for predicting the acceleration components in conjunction with LashingSafety), DLA-LS (seakeeping-based long-term acceleration components with LashingSafety), CSS-LC (IMO CSS code-based acceleration components using LashCon), and CSS-LS (IMO CSS code-based acceleration components using LashingSafety). In terms of the acceleration and external force components, the CSS-LC and CSS-LS results are more than two times the results of Rule-LS. Thus, when the external forces and lashing strengths are evaluated using CSS-LC and CSS-LS, the truck needs more lashing wires, while Rule-LS and DLA-LS predict that the present lashing configuration is on the safe side.

• Journal of the Korean Society for Precision Engineering
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• v.21 no.12
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• pp.127-132
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• 2004

It is very important to find out causes of strip pinching for the high quality of products and fer the stable operation of rolling system. We have examined the strip pinching from three points of view to find out the causes of strip pinching in rolling system: strip shape, rolling operation conditions, and behavior of strip. Wedge, off center, and difference of rolling force through CMD(Cross machine direction) are found to possibly provide major initial causes of strip pinching. Generally strip pinching occurred in the tail of strip. Thus, computer simulations by using a FEM code were also carried out to find out the initial mechanism of strip pinching depending upon the force and geometric boundary conditions at the time of strip tail rolling. The strong compression force effect due to the sudden release of strip tail from the work roll and non-uniform strip tail shape (ex. Fish tail) across the CMD were found to provide possible major causes of strip pinching.

• Journal of Institute of Control, Robotics and Systems
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• v.16 no.6
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• pp.532-538
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• 2010

SD (Smart Door) is a human friendly power-assisted door system initially targeted for passenger car doors. The Smart Door offers comfort and safety to passengers or/and drivers by supplying additional power. Amount of power supplied by the Smart Door system is depend on the environment where the automotive is situated. It realizes comfort, for example, when the force applied by the passenger to the door is expected to be abnormal, the SD system tries to compensate passenger's effort by supplying additional force. In this study, to enhance the ease of opening and closing the doors of the passenger vehicle, a Smart Door with a power assist mechanism consisting of a motor was developed and analysed. A power assist mechanism mounted within the vehicle's door is designed and modeled for simulation purpose. The required force necessary to control the designed mechanism during the vehicle's roll, pitch and the opening angle of the door has been considered. To this end, we propose a power-assisting control strategy called "gravity cancellation". The system is analysed by numerical simulation with the gravity cancellation control algorithm.

• The KSFM Journal of Fluid Machinery
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• v.18 no.5
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• pp.49-53
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• 2015

Thrust vector control is the method which generates the side force and roll moment by controlling exhausted gas directly in a rocket nozzle. TVC is classified by mechanical and fluid dynamic methods. Mechanical methods can change the flow direction by several objects installed in a rocket nozzle exhaust such as tapered ramp tabs and jet vane. Fluid dynamic methods control the flight direction with the injection of secondary gaseous flows into the rocket nozzle. The tapered ramp tabs of mechanical methods are used in this paper. They installed at the rear in the rocket nozzle could be freely moved along axial and radial direction on the mounting ring to provide the mass flow rate which is injected from the rocket nozzle. TVC of the tapered ramp tabs has the potential to produce both large axial thrust and high lateral force. We have conducted the experimental research and flow analysis of ramp tabs to show the performance and the structural integrity of the TVC. The experiments are carried out with the supersonic cold flow system and the schlieren graph. This paper provides to analyze the location of normal shock wave and distribution of surface pressure on the region enclosed by the tapered ramp tabs.