• Transactions of the Korean Society of Automotive Engineers
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• v.9 no.5
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• pp.157-164
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• 2001

This paper performs static and dynamic tests of a multi-leaf spring and a tapered leaf spring to investigate their hysteretic characteristics. In the static test, trapezoidal input load is applied with 0.1Hz excitation frequency and with zero initial loading conditions. In the dynamic test, sinusoidal input load is applied with five excitation amplitudes and three excitation frequencies. In these tests, static and dynamic hysteretic characteristics of the multi-leaf spring and the tapered leaf spring are compared, and, the effects of excitation amplitudes and frequencies on dynamic spring rate are also shown. In this paper, actual vehicle tests are performed to study the effects of hysteretic characteristics of the large-sized truck's handling performance. The multi-leaf spring or the tapered leaf spring is used in the front suspension. The actual vehicle test is performed in a double lane change track with three velocities. Lateral acceleration, yaw rate and roll angle are measured using a gyro-meter located at the mass center of the cab. The test results showed that a large-sized truck with a tapered leaf spring needs to have an additional apparatus such as roll stabilizer bar to increase the roll stabilizer due to hysteretic characteristics.

• Journal of the Society of Naval Architects of Korea
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• v.42 no.1 s.139
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• pp.10-17
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• 2005

Due to emission of vehicles during loading/unloading, ventilation system in Roll-on/Roll-off ship is inevitable; however it is very difficult to predict the ventilation performance before it is finally built in. Although the requirements for the ventilation system include air change rate and maximum allowable concentration of CO in the cargo holds, even prototype tests are hardly able to quantify the ventilation performance. In the present paper, a new method to assess the ventilation performance of Roll-on/Roll-off ship is proposed by using computational fluid dynamics. The air exchange is modeled by introducing multi-species transport of existing air In the holds and new air from the ventilation system. Conservation of multi-species as well as 3D Navier-Stokes equation are solved numerically in time dependent manner. Several cases of different configuration are considered. The results include predicted mass fraction of new air in the holds. It is also presented that CO concentration can be estimated based on the predicted air change performance. Due to the lack of experimental data, the computed results are not verified; however the proposed method can be applied as au assessment tool.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.18 no.4
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• pp.410-416
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• 2009

In recent years, the rollover accident of large class of vehicles has become important safety issue. Even though the rollover form a small percentage of all traffic accidents, they have a fatal effect upon the driver and passenger. Among the traffic accidents occurred in driving, the rollover is the major cause of traffic fatalities. Therefore, it is required to develop the analytical and experimental techniques for predicting rollover propensity of vehicles and also to improve the vehicle suspension design in the viewpoint of rollover resistance. In this study, the parameter sensitivities for the roll angle of SUV suspension are analyzed, and then the determined design parameters are optimized by using the regression model function of the response surface methods. The analysis results show that the roll angle of the optimized vehicle is decreased as compared with the initial vehicle and also the rollover possibility is decreased when the roll rate of the front suspension is larger than the roll rate of the rear suspension.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.8 no.2
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• pp.101-106
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• 2015

In this paper, to increase the throughput for wireless communication, FTN methods that is faster than Nyquist rate are used recently. To improve performance, turbo equalization algorithms that iteratively exchange probabilistic information between soft Viterbi equalizer and LDPC decoder to minimize ISI are applied in this paper. In FTN transmission, the performance depends on roll-off value and number of tabs of SRRC(Square Root Raised Cosine) filter. Therefore, Based on simulation, this paper present optimal number of filter coefficient and tab for various ISI factor of ${\tau}$.

• Journal of the Korea Institute of Military Science and Technology
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• v.21 no.6
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• pp.784-789
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• 2018

Accurate aerodynamic characterization of projectile is crucial for successful development of munition. The aerodynamic characterization of fin stabilized projectile is more difficult than characterization of traditional symmetric ballistic projectile. Instrumented free flight experiments were conducted to quantify rolling behavior of fin stabilized projectile. The instrumented projectiles were launched from a rifled tube and the onboard sensor data were acquired through a telemetry transmitter. Roll rate was measured for fin stabilized projectile by means of an angular rate sensor. And, roll damping coefficients were estimated from onboard sensor data acquired during gun firing and trajectory analysis of mathematical model.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.44 no.4 s.316
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• pp.70-77
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• 2007

Two kinds of QMF(Quadrature Mirror Filter) pairs are used in JPEG2000 standard, which don't have QMF distortions. However, the QMF pairs have the main disadvantages such that there are gentle roll-off rate, ripples in the passband and unequal band decomposition. In this paper, Maxflat(maximally flat) QMF pairs with a half-band gain are proposed for overcoming these problems. Maxflat QMF pairs are realized due to generalized closed-form formulas, and the filters have maximally flat response in the passband/stopband as well as sharp roll-off rate in the transition band. Comparing proposed filters and JPEG2000's filters in frequency domain, it is found that proposed filters have better performance JPEG2000's filters. Moreover, Maxflat QMF pairs show stopband-attenuation exceeding 200 dB almost everywhere.

• Korean Journal of Materials Research
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• v.17 no.10
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• pp.521-525
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• 2007

The microstructure and mechanical properties of an oxygen free copper processed by accumulative roll bonding(ARB) at low strain rate were studied. The copper sheets were highly strained up to an equivalent strain of ${\sim}6.4$ by ARB process at ambient temperature. The strain rate of the copper during the ARB was $2.6sec^{-1}$. The microstructure and mechanical properties of the ARB-processed copper were compared to those of the specimens processed by ARB at relatively high strain rate ($37sec^{-1}$). The microstructure and mechanical properties of the copper with ARB process was very similar to each other despite of some differences in recovery.

• International Journal of Aeronautical and Space Sciences
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• v.15 no.4
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• pp.412-418
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• 2014

This paper describes the development of variable stability system (VSS) control laws for the KFA-i to simulate the dynamics of KFA-m aircraft. The KFA-i is a single engine, Class IV aircraft and was selected as an in-flight simulator (IFS) aircraft, whereas the KFA-m is a simulated aircraft that is based on the F-16 aircraft. A 6-DoF math model of KFA-i aircraft was developed, linearized, and separated into longitudinal and lateral motion for VSS control law synthesis. The KFA-i aircraft has five primary control surfaces: two flaperons, two all movable horizontal tails, and one rudder. Flaperons are used for load control, the horizontal tails are used for pitch and roll rate control, and the rudder is used for yaw rate control. The developed VSS control law can simulate four parameters of the KFA-m aircraft simultaneously, such as pitch, roll, yaw rates, and load. The simulation results show that KFA-i follows the responses of KFA-m with high accuracy.

• Journal of the Korean Society for Precision Engineering
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• v.21 no.8
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• pp.112-119
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• 2004

This paper develops a computer model of a cabover type large truck for estimating the effects of the mounted method of frame on handling performance. The computer model considers two mounted methods of frame; flange mounted and web mounted. Frame is modeled by finite elements using MSC/NASTRAN in order to consider the flexibility of frame. The reliability of the developed computer model is verified by comparing the actual vehicle test results with the simulation results. The actual vehicle test is performed in a double lane change course, and lateral acceleration, yaw rate, and roll angle are measured. To estimate the effects of the mounted method of frame on handling performance, simulations are performed with the flange mounted and web mounted frame. Simulation results show that the web mounted frame＇s variations of roll angle, lateral acceleration, and yaw rate are larger than the flange mounted frame＇s variations, especially in the high test velocity and the second part of the double lane course. Also, simulation results show that the web mounted frame＇s tendencies of roll angle, lateral acceleration, and yaw rate advance the flange mounted frame＇s tendencies, especially in the high test velocity and the second part of the double lane course.

• Proceedings of the KSME Conference
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• 2007.05a
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• pp.1379-1382
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• 2007

In this paper, we present a simplified analytic approach for the prediction of roll force to be applicable to the grooveless rolling. The approach is based on the deformation shape deduced from physical considerations and employs the assumption that the deformation homogeneously occurs in three directions. Strain and strain rate are calculated by the geometric relationships between those components and the prescribed deformation functions. Then, stress components are obtained from the Levy-Mises' flow rule. By integrating the stress components along the rolling direction, roll force are finally obtained. The prediction accuracy of the proposed model is examined through comparison with results obtained from the finite element analysis.