• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.3
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• pp.299-308
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• 2011

In this study, we develop a pressure observer to measure the cylinder length of a harbor-construction robot. For the robot control, sensors are required to measure the length of a hydraulic cylinder. The cylinder-position sensor is relatively expensive when the operating environment prohibits external approaches for the measurement of the cylinder position. LVDT or linear scales are usually mounted on the outside of the cylinder, which causes poor durability on a construction site. We use a pressure sensor to indirectly estimate the length of the cylinder. The pressure sensor is mounted inside a hydraulic valve box so that it is protected by the box and easy to waterproof for an underwater robot. By treating oil as a compressible fluid, we derive the nonlinear pressure dynamics as a function of the cylinder position, velocity, and pressure. The recursive least squares (RLS) algorithm is applied to identify the dynamic parameters, and the pressure observer estimates the cylinder position through the pressure acting on the head and the rod of the hydraulic cylinder. The position accuracy is relatively low, but it is acceptable for a construction robot that handles large armor stones.

• Transactions of the Korean Society of Automotive Engineers
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• v.22 no.1
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• pp.85-94
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• 2014

Tolerance accumulation has serious effect on the performance of an assembled body. This paper proposes the method which analyzes tolerance accumulation using Monte Carlo Simulation. This method can predict tolerance distribution of fully assembled body using the dimensional tolerance distribution of each part to be assembled. In this analysis, it is assumed that the tolerance of each part has the nominal distribution or uniform distribution. This analysis method is applied to ECV(External Control Valve), and the accumulated tolerance of the fully assembled ECV is obtained from the analysis. The results show that initial tolerance given to each part do not meet the design requirement of ECV. Hence, the tolerances of each part are modified and the additional analysis with the modified tolerances yields the results which satisfy the design requirements of ECV.

• Journal of the Korean Institute of Gas
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• v.18 no.2
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• pp.28-34
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• 2014

In the natural gas pressure regulation station, high pressure natural gas is decompressing using pressure regulation valves. Waste pressure occurred in the pressure regulation process can be recovered through adopting turbo expanders. However, in the waste pressure recovery process, Joule Thompson effect causes below $0^{\circ}C$ and this low temperature freezes outside land of pipeline or generates methane hydrate in the pipeline which can block the pipeline. Therefore, turbo expander systems are accompanying with a boiler for preheating natural gas. Molten carbonate fuel cell (MCFC), one of the high temperature fuel cell, can use natural gas as a direct fuel and is also exhausting low emission gas and generating electricity. In this paper, a thermodynamic analysis on the hybrid MCFC-turbo expander system is conducted. The fuel cell system is analyzed for the base load of the hybrid system.

• Journal of the Korean Electrochemical Society
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• v.26 no.4
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• pp.43-55
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• 2023

Mass transport through nanoporous structures such as nanopores or nanochannels has fundamental electrochemical implications and many potential applications as well. These structures can be particularly useful for water treatment, energy conversion, biosensing, and controlled delivery of substances. Earlier research focused on creating nanopores with diameters ranging from tens to hundreds of nanometers that can selectively transport cationic or anionic charged species. However, recent studies have shown that nanopores with diameters of a few nanometers or even less can achieve more complex and versatile transport control. For example, nanopores that mimic biological channels can be functionalized with specific receptors to detect viruses, small molecules, and even ions, or can be made hydrophobic and responsive to external stimuli, such as light and electric field, to act as efficient valves. This review summarizes the latest developments in nanopore-based systems that can control mass transport based on the size of the nanopores (e.g., length, diameter, and shape) and the physical/chemical properties of their inner surfaces. It also provides some examples of practical applications of these systems.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.2
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• pp.66-73
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• 2020

In the hydrogen compression cycle, which is currently being developed, hydrogen is compressed to a very high pressure using a compressor, and then stored and used in a high-pressure vessel. This shows that an increase in the temperature of hydrogen in the vessel due to a pressure rise during the filling process and the pressure fatigue due to the repeated cycle may cause problems in the reliability of the vessel. In this paper, for the entire processes in a 50 MPa hydrogen compression system, theoretical and numerical methods were conducted to analyze the following: the temperature increase of hydrogen in the vessel and the time required to reach thermal equilibrium with the surroundings, the change in temperature of hydrogen passing through the pressure reducing valve, and the required capacity of the heat exchanger for cooling the vessel. The results will be useful for the design and construction of hydrogen compression systems, such as hydrogen charging stations.