• Journal of Wetlands Research
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• v.14 no.4
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• pp.457-469
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• 2012

Bedform data at 4 shallow zones in the Yellow Sea where waves as well as tidal range are high and bed material is relatively coarse were collected and analyzed here. Water depths in the study area where the bedform data were collected are 10 ~ 65 meters, and ripple lengths well developed are between 6 ~ 13 meters. Existing empirical formula for prediction of ripple length as for coexistence of waves and currents include Khelifa and Ouellet(2000) and Soulsby(2005), both of which have been based on laboratory measurements, or field measurements at different physical environment from the Yellow Sea with respect to tidal range, wave strength, and bed material. New scaling factors are proposed here for better prediction of the ripple length on coastal zone in the Yellow Sea.

• Journal of Fashion Business
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• v.11 no.4
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• pp.101-110
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• 2007

Since cotton fabrics with ripple finish treatment form wavy furrows on the surface or bumpy patterns, air circulation during wearing is good and the fabric is cool to the touch. The finishing principle is based on the mercerization, which utilizes the fact that cotton fibers contract in a concentrated NaOH solution. In this study, as fabric specimens, cotton fabrics with yarn counts of 40's, 60's and 80's were used. Concentrations of the NaOH solutions were 15%, 25%, and 35%. After dyeing fabrics using Rubia akane nakai, color and other properties were measured. As the concentration of the NaOH solution increased, the fabric became thicker and denser, and the number of occurrence of the prominence and depression per unit length became larger. The color of the region contracted by ripple finish became darker after dyeing, while the color of the untreated region became lighter, which enhanced the cubic effect of the ripple finish. As the count of the cotton yarn increased, the dyeability became better. As the concentration of the NaOH solution increased, the air permeability became lower.

• Transactions of the Korean Society of Automotive Engineers
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• v.6 no.4
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• pp.39-46
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• 1998

For permanent magnet brushless DC motors used for high speed fuel pumps, torque ripple is an important origin of vibration, acoustic noise and speed fluctuation. In this paper, the output torque profile of a PM motor with one phase energized is decomposed into the commutation torque, the reluctance torque and the armature reaction torque according to their source origins. It verifies that the output torque profile is qualitatively equivalent to the BEMF profile for low reluctance motors. This paper discusses the effect of magnet pole shaping and magnet arc length on the output torque and torque ripple. A magnet edge shaping is proposed to design a trapezoidal BEMF motor without torque ripple, with minimal sacrifice of the maximum output torque.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.16 no.6
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• pp.117-124
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• 2007

The pressure ripple in most hydraulic systems is the root cause of their noise and vibration. This paper reduced the pressure ripple using side branch hose for an axial piston pump applied to small excavator. First, in calculating open area, a new method using groove area of valve plate is proposed. Simulation model in AMESim environment is developed to verify proposed method, find effective length and diameter of branch hose. Finally, the comparisons with experiment results show that the proposed method is more effective than previous method in reducing the pressure ripple.

• Journal of Electrical Engineering and Technology
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• v.9 no.5
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• pp.1577-1581
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• 2014

This paper presents a method to minimize torque ripple of a V-type IPMSM using the PSO (Particle Swarm Optimization) method with FEM. The proposed algorithm includes one objective function and three design variables for a notch on the surface of a rotor. The simulation model of the V-type IPMSM has 3-phases, 8-poles and 48 slots with 2 notches on the one-pole rotor surface. The arc-angle, length and width of the notch are optimized to minimize the torque ripple of the motor. The cogging torque of the model is reduced by 55.6% and the torque ripple is decreased by 15.5 %. Also, the efficiency of the motor is increased by 15.5 %.

• Journal of KIISE:Computer Systems and Theory
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• v.33 no.1_2
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• pp.92-104
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• 2006

The proposed method for a force directed global placement algorithm exploits and extends techniques from two leading placers, Kraftwerk (& KraftwerkNC) and Mongrel. It combines the strengths of KraftwerkNC, force directed global placer, and Mongrel's ripple move technique which resolves cell overlaps effectively The proposed technique uses the force spreading technique used in Kraftwerk to optimize the ripple movement. While it is resolving the cell overlap and optimizing wire length physical net constraints are considered for timing. The experimental results obtained by the proposed approach shows significant improvement on wire length as well as on timing.

• Journal of the Korean Society for Precision Engineering
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• v.22 no.12 s.177
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• pp.51-60
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• 2005

This paper describes a robust control scheme for high-speed and long stroke scanning motion of high precision linear motor system consisting of linear motor, air bearing guide and position measurement system using heterodyne interferometer. Nowadays, semiconductor process and inspection of wafer or LCD need high speed and long travel length for their high throughput and extremely small velocity fluctuations or tracking errors. In order to satisfy these conditions, linear motor system are widely used because they have large thrust force and do not need motion conversion mechanisms such as ball screw, rack & pinion or capstan with which the system are burdened. However linear motors have a problem called force ripple. Force ripple deteriorates the tracking performances and makes periodic position errors. So, force ripple must be compensated. To maximize the tracking performance of linear motor system, we propose the control scheme which is composed of a robust control method, Time Delay Controller (TDC) and a feedforward control method, Zero Phase Error Tracking Control (ZPETC) for accurate tracking a given trajectory and an adaptive force ripple compensation (AFC) algorithm fur estimating and compensating force ripple. The adaptive ripple compensation is continuously refined on the basis of tracking error. Computer simulation results based on modeled parameters verify the effectiveness of the proposed control scheme for high-speed, long stroke and high precision scanning motion and show that the proposed control scheme can achieve a sup error tracking performance in comparison to conventional TDC control.

• Journal of Magnetics
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• v.19 no.4
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• pp.411-417
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• 2014

This paper presents the shape optimization of a permanent magnet synchronous motor to reduce the torque ripple and iron loss. Specifically, the harmonics of the electromotive force and cogging torque are decreased by adjusting the permanent magnet arrangement and non-uniform air gap length. In addition, an additional flux path along the q-axis is proposed with a unique rotor shape to increase the q-axis inductance and reluctance torque. The improvement in the performance of the proposed model is verified with simulated and experimental results.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.7 no.3
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• pp.22-28
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• 1998

This paper presents experimental investigations on the attenuation characteristics of pressure ripple in automotive power steering hydraulic hoses. Also, a mathematical model of hydraulic hoses is proposed to support design of the power steering hydraulic circuit and analyze the attenuation characteristics of pressure ripples. The experimental results show that the pulsation attenuation characteristics of hydraulic hoses is remarkably affected by the flexible metal tube inserted coaxially inside a hydraulic hose with a finite length as well as viscoelastic properties of hose wall. It is also shown that the predicted results by the model proposed here agree well with the measured results over a wied range of frequency.

• Journal of Magnetics
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• v.21 no.1
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• pp.72-77
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• 2016

Although the initial cost of permanent-magnet linear synchronous motors is high owing to the installation of armatures over the full length of the transportation lines, linear motors are useful for transportation systems because of their high speed, acceleration, and deceleration. For these reasons, research into reducing the cost of linear motors is necessary, and a stationary distributed-armature system has been suggested for installing armatures in sections where acceleration and deceleration of the mover are required. However, each armature has ends that significantly increase the cogging force, resulting in the increase in the thrust ripple of the mover. Therefore, in order to improve the thrust ripple of the system, the present study aims to provide auxiliary teeth on both ends of the armature to achieve an optimal design through an analysis of the contribution ratio with respect to factors regarding the design of the experiment and the objective function.