• Journal of the Korean Society of Propulsion Engineers
• /
• v.22 no.1
• /
• pp.80-88
• /
• 2018

The function of a vehicle holding device (VHD) is to securely hold a launch vehicle on the launch pad and release the launch vehicle at maximum thrust after engine ignition to allow lift-off of the launch vehicle. During the release of the launch vehicle, to prevent the Ka doing a doing a doing mode, which is the vertical oscillation of the entire liquid propellant, the release of the launch vehicle should be gradual. In this study, for the gradual release of a launch vehicle, a hydraulic system comprising an accumulator and pyro valve to operate a hydraulic cylinder and control the speed of the cylinder with an orifice is introduced. Through a test, the influence of design variables on the cylinder speed is analyzed. Based on this, the design values of the hydraulic cylinder are determined. Through this study, the engineering basis for developing a VHD releasing a launch vehicle at maximum thrust is provided.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.44 no.12
• /
• pp.1087-1094
• /
• 2016

The responsibility of the vehicle holding device (VHD) is to hold the launch vehicle while it is stayed on launch pad and release the holding mechanism to allow a lift-off of launch vehicle at a moment of lift-off. During a release of the holding mechanism, in order to prevent the Ka doing a doing a doing mode which is vertical oscillation of entire liquid propellant and very severe for vehicle structure, gradual release of holding force is required. Also, a release operation of all 4 VHD should be synchronized very precisely. In this study, to comply the "gradual release and synchronized operation requirement", concept of VHD hydraulic system using an accumulator, pyro valve and orifice to control speed of hydraulic cylinder is proposed instead of using complicated hydraulic components. Then through multi-body dynamic analysis and computational hydraulic analysis, a size of orifice to meet a target speed of hydraulic cylinder is calculated. Through this study, simple and reliable VHD hydraulic system complying requirements is designed.

• Journal of Drive and Control
• /
• v.9 no.1
• /
• pp.10-17
• /
• 2012

Nowadays, the demand of energy saving is increasing more and more while the natural resources have been exhausted. Besides, the emission gas caused by vehicles has been being a serious environment problem. Therefore, many studies have been carried out, especially focusing on braking energy regeneration, in order to save energy as well as reduce emission of mobile vehicles. In this paper, we propose a closed-loop hydrostatic transmission for braking energy regeneration with two configurations to reduce the energy consumption by recovering the braking energy. The effectiveness of the proposed system was verified by simulation. The simulation results indicated that the pressure coupling configuration gave better performance in comparison to flow coupling configuration about 40.8%, 61.7% and 53.8% reduction of fuel consumption in 10 mode, 10 mode modified profile and highway schedules, respectively.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.8 no.4
• /
• pp.703-707
• /
• 2007

The line pressure control system for an automotive transmission in which a bleed type variable force solenoid(VFS) is applied, has been constructed and experimentally investigated. The hydraulic circuit of the system includes a line pressure control valve, a reducing valve, an accumulator, various orifices and a VFS. Static and dynamic responses of the throttle and line pressure have been monitored and discussed for various test conditions.

• Transactions of the Korean hydrogen and new energy society
• /
• v.22 no.4
• /
• pp.552-558
• /
• 2011

A 50 kW class rotating body type wave energy converter consisted of two floating bodies and a PTO (Power Takeoff) unit is studied. As an wave energy extractor, the body is designed to have a VLCO (Variable Liquid-Column Oscillator) having a liquid filled U-tube with air chambers. Owing to the oscillation of the liquid in the U-tube caused by the air spring effect of the air chambers, the amplitude of response of the VLCO becomes significantly amplified for a target wave period. The PTO converts the rotational moment introduced from the relative motion of the hinged bodies to an hydraulic power by means of a cylinder. A high pressure accumulator, hydraulic motor and a generator are equipped in the PTO to convert the hydraulic power to electric power. A control law for adjusting the oscillation period of the VLCO is proposed for the efficient operation of the VLCO with various wave conditions. It is found that the effect of the air spring has an important role to play in making the oscillation of the VLCO match with the ocean wave. In this way, the wave energy converter equipped with the VLCO provides the most effective mode for extracting energy from the ocean wave.

• Journal of Drive and Control
• /
• v.13 no.3
• /
• pp.32-38
• /
• 2016

For this paper, the position-control performances of dual EHA(electro-hydrostatic actuator) systems were investigated according to two cases wherein the double-rod- and single-rod-type hydraulic cylinders were combined. Since the control performance is significantly dependent on the load conditions including external forces such as the inertia load, it is proposed here that the two sub-EHAs are driven by separate position and force controllers, instead of two identical position controllers. According to the simulation results, the best performance was achieved by the position-controlled single-rod-type EHA that was combined with a force-controlled double-rod-type EHA. As the force-controlled double-rod-type EHA compensated for the external loads on the position-controlled single-rod-type EHA, the position-control performance was not influenced by external forces including the inertia load. In addition, the position-controlled single-rod-type EHA contributed to the enhancement of the damping ratio by absorbing the pressure peaks through its internal accumulator. Due to the symmetrical piston areas, the double-rod-type EHA is more suitable for force control than the single-rod- type EHA.

• Nuclear Engineering and Technology
• /
• v.42 no.6
• /
• pp.690-703
• /
• 2010

Sampling based uncertainty analysis was carried out to quantify uncertainty in predictions of best estimate code RELAP5/MOD3.2 for a thermal hydraulic test (10% hot leg break LOCA) performed in the Large Scale Test Facility (LSTF) as a part of an IAEA coordinated research project. The nodalisation of the test facility was qualified for both steady state and transient level by systematically applying the procedures led by uncertainty methodology based on accuracy extrapolation (UMAE); uncertainty analysis was carried out using the Latin hypercube sampling (LHS) method to evaluate uncertainty for ten input parameters. Sixteen output parameters were selected for uncertainty evaluation and uncertainty band between $5^{th}$ and $95^{th}$ percentile of the output parameters were evaluated. It was observed that the uncertainty band for the primary pressure during two phase blowdown is larger than that of the remaining period. Similarly, a larger uncertainty band is observed relating to accumulator injection flow during reflood phase. Importance analysis was also carried out and standard rank regression coefficients were computed to quantify the effect of each individual input parameter on output parameters. It was observed that the break discharge coefficient is the most important uncertain parameter relating to the prediction of all the primary side parameters and that the steam generator (SG) relief pressure setting is the most important parameter in predicting the SG secondary pressure.

• Nuclear Engineering and Technology
• /
• v.26 no.1
• /
• pp.126-139
• /
• 1994

Best-estimate thermal-hydraulic codes, CATHARE2 V1.2 and RELAP5/MOD3, hate been assessed against the BETHSY 6.2 tc six-inch cold leg break loss-of-coolant accident (LOCA) test. Main objective is to analyze the overall capabilities of the two codes on physical phenomena of concern during the small break LOCA i.e. two-phase critical flow, depressurization, core water level de-pression, loop seal clearing, liquid holdup, etc. The calculation results show that the too codes predict well both in the occurrences and trends of major two-phase flow phenomena observed. Especially, the CATHARE2 calculations show better agreements with the experimental data. However, the two codes, in common, show some deviations in the predictions of loop seal clearing, collapsed core water level after the loop seal clearing, and accumulator injection behaviors. The discrepancies found from the comprision with the experimental data are larger in the RELAP5 results than in the CATHARE2. To analyze the deviations of the two code predictions in detail, several sensitivity calculations have been performed. In addition to the change of two-phase discharge coefficients for the break junction, fine nodalization and some corrections of the interphase drag term are made. For CATHARE2, the change of interphase drag force improves the mass distribution in the primary side. And the prediction of SG pressure is improved by the modification of boundary conditions. For RELAP5, any single input change doesn't improve the whole result and it is found that the interphase drag model has still large uncertainties.

• Nuclear Engineering and Technology
• /
• v.50 no.3
• /
• pp.356-367
• /
• 2018

A series of tests dedicated to station blackout (SBO) accident scenarios have been recently performed at the $Prim{\ddot{a}}rkreislauf-Versuchsanlage$ (primary coolant loop test facility; PKL) facility in the framework of the OECD/NEA PKL-3 project. These investigations address current safety issues related to beyond design basis accident transients with significant core heat up. This work presents a detailed analysis using the best estimate thermal-hydraulic code TRACE (v5.0 Patch4) of different SBO scenarios conducted at the PKL facility; failures of high- and low-pressure safety injection systems together with steam generator (SG) feedwater supply are considered, thus calling for adequate accident management actions and timely implementation of alternative emergency cooling procedures to prevent core meltdown. The presented analysis evaluates the capability of the applied TRACE model of the PKL facility to correctly capture the sequences of events in the different SBO scenarios, namely the SBO tests H2.1, H2.2 run 1 and H2.2 run 2, including symmetric or asymmetric secondary side depressurization, primary side depressurization, accumulator (ACC) injection in the cold legs and secondary side feeding with mobile pump and/or primary side emergency core coolant injection from the fuel pool cooling pump. This study is focused specifically on the prediction of the core exit temperature, which drives the execution of the most relevant accident management actions. This work presents, in particular, the key improvements made to the TRACE model that helped to improve the code predictions, including the modeling of dynamical heat losses, the nodalization of SGs' heat exchanger tubes and the ACCs. Another relevant aspect of this work is to evaluate how well the model simulations of the three different scenarios qualitatively and quantitatively capture the trends and results exhibited by the actual experiments. For instance, how the number of SGs considered for secondary side depressurization affects the heat transfer from primary side; how the discharge capacity of the pressurizer relief valve affects the dynamics of the transient; how ACC initial pressure and nitrogen release affect the grace time between ACC injection and subsequent core heat up; and how well the alternative feeding modes of the secondary and/or primary side with mobile injection pumps affect core quenching and ensure stable long-term core cooling under controlled boiling conditions.