• Journal of the Society of Naval Architects of Korea
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• v.59 no.1
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• pp.9-17
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• 2022

In this paper, wind load on a semi-submersible rig was investigated using Computational Fluid Dynamics (CFD). A maritime atmospheric boundary layer model for wind profile was implemented such that the wind profile shapes were retained throughout the computational domain. Wind load on the semi-submersible rig was calculated under the maritime atmospheric boundary layer and matched well with the results from wind tunnel test within a ±20% error. Overturning moments with variation of draft were investigated by decomposing into drag and lift components. It was observed that the contribution from lift to the overturning moments increased as the draft got higher. The majority of the lift components originated from deckbox which served as a lifting body due to the accelerated streamlines between waterline and the bottom of the deckbox.

• Smart Structures and Systems
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• v.34 no.2
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• pp.87-96
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• 2024

Smart materials, such as magnetorheological (MR) fluid, have received considerable research attention in recent years due to their unique capabilities. MR fluid, which possesses a magnetic field controllable viscosity, has been extensively studied for vehicular applications with the aim of synthesizing optimal MR fluids, designing optimal MR dampers, and developing control strategies. However, a comprehensive study that primarily focuses on developing a cost-effective semi-active suspension system for a commercial vehicle in a developing nation is still lacking. This study addresses this gap by synthesizing an in-house MR fluid and studying its rheological properties. Subsequently, a novel single-sensor-based controller is developed and closed-loop simulations are conducted on a quarter-car semi-active model. Finally, the overall semi-active quarter-car suspension system is experimentally tested using a suspension test rig. The performance of the proposed system in terms of ride comfort and road holding is evaluated and is compared with simple control strategies. The dynamic range of the developed semi-active MR damper is found to be around 2.3, indicating a significant MR effect. The results suggest an intermediate response using the proposed acceleration-driven controller (ADV) at lower frequencies and similar performance to that of the skyhook controller at higher frequencies. The cost-effective methodology proposed in this study is effective and can be adapted for other semi-active engineering applications.

• Journal of the Korean Society for Precision Engineering
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• v.34 no.3
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• pp.205-210
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• 2017

Critical speed analysis was conducted for a active steering bogie prototype, developed to improve the curving performance of railway vehicles. The critical speed for the design concept was about 169.2k m/h. To validate the analysis result, we performed a critical speed test for the prototype bogie using a roller-rig tester. The test results showed that the critical speed for the prototype bogie was about 165 km/h. From the analysis and test results, The critical speed for the prototype bogie was determined to be 165 km/h. Considering the maximum operating speed of the test vehicle is 100 km/h, the prototype bogie is considered stable.

• Tribology and Lubricants
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• v.11 no.2
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• pp.44-55
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• 1995

Frictional characteristics with the change of dynamic parameters, such as stiffness, inertia and damping, in the friction measurement at dry sliding surfaces were experimentally and theoretically investigated throughout the study. Dynamic frictional force and the variation in the normal load were mainly measured at the various conditions of system dynamic parameters with which stiffness in the normal direction, loading mechanisms and test materials were varied. For the normal load, mechanisms using both a dead weight and a pneumatic cylinder were applied, which resulted in change of the inertia and damping of the test rig. Test materials were steel, rosin and PTFE, which have different types of intrinsic frictional characteristics. Test results showed that frictional characteristics under different dynamic parameters could be different even though the operating variables were the same and also they could result in the variation in the normal load, which could consequently affect the wear mechanism.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.21 no.12
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• pp.2187-2195
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• 1997

A semi-active suspension test system was designed and built for the experimental study. Vehicle parameters were estimated through tests and a quarter-car model was validated by comparing computer simulation results and laboratory test results. Alternative semi-active suspension control laws have been tested using the test system. Modulable damper used in this study is a "reverse" damper with 42 states which is controlled by a stepper motor. Experimental results have shown that semi-active suspensions have potential to improve ride quality of automobiles.tomobiles.

• Journal of the Korean Society of Industry Convergence
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• v.2 no.2
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• pp.155-163
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• 1999

In this study, single cylinder engines with different tumble ratio were made to find out in-cylinder fluid motion and flame propagation. Tumble ratio derived from the steady state flow rig test. Flame propagation speed was obtained using cylinder head gasket ionization probe and the piston ionization probe. And the combustion pressure in cylinder was measured to analyze the combustion characteristics. In case of high tumble engine, BSFC and BSHC were decreased and BSNOx was increased at part load test. Also BMEP and combustion peak pressure was increased at full load test. Tumble flow motion had an great effects on initial burning period rather than main burning period in part load test.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2001.11a
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• pp.59-62
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• 2001

Flow induced vibration in steam generators has caused dynamic interactions between tubes and contacting materials resulting in fretting wear . Series of experiments have been performed to examine the wear properties of Inconel 690 steam generator tubes in various environmental conditions. For the present study, the test rig was designed to examine the fretting wear and rolling wear properties in high temperature(room temperature - 290。C) water. The test was performed at constant applied load and sliding distance to investigate the effect of test temperature on wear properties of the steam generator tube materials. To investigate the wear mechanism of material, the worn was observed using scanning electron microscopy. The weight loss increase at higher test temperature was caused by the decrease of water viscosity and the mechanical property change of tube material. The mechanical property changes of steam generator tube material, such as decrease of hardness or yield stress in the high temperature tests. From the SEM observation of worn surfaces, the severe wear scars were observed in specimens tested at the higher temperature.

• Nuclear Engineering and Technology
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• v.55 no.4
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• pp.1555-1562
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• 2023

Natural circulation phenomena have been nowadays largely revisited aiming to investigate the performances of passive safety systems in carrying-out heat removal under accidental conditions. For this purpose, assessment studies using CFD (Computational Fluid Dynamics) and also 3D thermal-hydraulic system codes are considered at different levels of the design and safety demonstration issues. However, these tools have not being extensively validated for specific natural circulation flow regimes involving flow mixing, temperature stratification, flow recirculation and instabilities. In the present study, an experimental test case based on a small-scale pool test rig experiment performed by Korea Atomic Energy Research Institute, is considered for code-to-code and code-to-experimental data comparison. The test simulation is carried out using the FLUENT and the 3D thermal-hydraulic system CATHARE-2 codes. The objective is to evaluate and compare their prediction capabilities with respect to the test conditions of the experiment. It was observed that, notwithstanding their numerical and modelling differences, similar agreement results are obtained. Nevertheless, additional investigations efforts are still needed for a better representation of the considered phenomena.

• Tribology and Lubricants
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• v.16 no.1
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• pp.27-32
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• 2000

This paper describes that the leaf spring damper (LSD) developed by authors can be controled by side clearance between side covers and leaf springs. The test rig and two prototype dampers with different side clearance were manufactured. Experiments were performed to investigate the effects of side clearance on the damping of the leaf spring damper. The stiffness and damping coefficients are obtained from the displacements and the reaction forces generated by rotating the eccentric shaft. All dynamic coefficients are plotted with the excitation frequency which is adjusted by rotating speed of the shaft.

• Tribology and Lubricants
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• v.24 no.4
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• pp.170-178
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• 2008

In this paper, it is described how the problems appeared at the previous proto type sensor are improved. As changing the pressure and temperature of engine oil in a test rig, the modified sensor is tested. Then, the measured results of capacitance and the corresponding dielectric constants under various temperatures and pressures are shown. It turns out that the electrical signal gotten from the electrodes of newly developed sensor can be more stable under the various operating conditions.