• Transactions of the Korean Society of Mechanical Engineers A
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• v.32 no.3
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• pp.280-289
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• 2008

This paper presents design of the quantitative feedback control system of the three axes hydraulic road simulator with respect to the dummy wheel for uncertain multiple input-output(MIMO) feedback systems. This simulator has the uncertain parameters such as fluid compressibility, fluid leakage, electrical servo components and nonlinear mechanical connections. This works have reproduced the random input signal to implement the real road vibration's data in the lab. The replaced $m^2$ MISO equivalent control systems satisfied the design specifications of the original $m^*m$ MIMO control system and developed the mathematical method using quantitative feedback theory based on schauder's fixed point theorem. This control system illustrates a tracking performance of the closed-loop controller with low order transfer function G(s) and pre-filter F(s) having the minimum bandwidth for parameters of uncertain plant. The efficacy of the designed controller is verified through the dynamic simulation with combined hydraulic model and Adams simulator model. The Matlab simulation results to connect with Adams simulator model show that the proposed control technique works well under uncertain hydraulic plant system. The designed control system has satisfied robust performance with stability bounds, tracking bounds and disturbance. The Hydraulic road simulator consists of the specimen, hydraulic pump, servo valve, hydraulic actuator and its control equipments

• Advances in Energy Research
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• v.4 no.1
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• pp.87-106
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• 2016

In this research, optimum design of the combined solar collector, geothermal heat pump and thermal seasonal storage system for heating and cooling a sample greenhouse is studied. In order to optimize the system from technical point of view some new control strategies and functions resulting from important TRNSYS output diagrams are presented. Temperatures of ground, rock bed storage, outlet ground heat exchanger fluid and entering fluid to the evaporator specify our strategies. Optimal heat storage is done with maximum efficiency and minimum loss. Mean seasonal heating and cooling COPs of 4.92 and 7.14 are achieved in series mode as there is no need to start the heat pump sometimes. Furthermore, optimal parallel operation of the storage and the heat pump is studied by applying the same control strategies. Although the aforementioned system has higher mean seasonal heating and cooling COPs (4.96 and 7.18 respectively) and lower initial cost, it requires higher amounts of auxiliary energy either. Soil temperature around ground heat exchanger will also increase up to $1.5^{\circ}C$ after 2 years of operation as a result of seasonal storage. At the end, the optimum combined system is chosen by trade-off between technical and economic issues.

• The KSFM Journal of Fluid Machinery
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• v.9 no.6 s.39
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• pp.54-62
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• 2006

An experiment about performance characteristics is conducted on a double chamber vane-type rotor. Three different rotors, which have 6, 8 and 9 vanes, are applied to the driver and various lift holes at the rear plate are used to increase the effective vane height. The inner diameter of a double chamber cylinder is ${\phi}27mm$, and the length of the cylinder is 65 mm. The maximum offset length between the rotor outer surface and the cylinder inner surface is 4.5 mm. In this study, specific output torques and powers are measured, and also noise and vibration are measured at the real operating situation. The operating torque on the double chamber is increased to 17% compared to the operating torque obtained at the single chamber which has the same size. The experimental results of noise and vibration show that the operating sound and vibration are directly related to the operating power generated by the double chamber rotor.

• The KSFM Journal of Fluid Machinery
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• v.12 no.5
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• pp.39-46
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• 2009

This paper outlines how the on-line performance monitoring system can be used to improve the efficiency and maintenance of the equipments. And a method of the heat rate allocation to each equipment was suggested to monitor the performance of combined cycle power plants. This calculates the expected heat rate of current conditions and compares it with actual values. Loss allocation in heat rate is reconciled by calculating the magnitude of the deficiency contributed by major components, such as the gas turbine, heat recovery steam generator, steam turbine and condenser. Expected power output is determined by a detailed model and correction curves of the plant. This simulation models are found to reproduce high accuracy in behavior of the cycle for various operating conditions, both in design and in off-design condition. Errors are lower than 2% in most cases.

• The KSFM Journal of Fluid Machinery
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• v.19 no.5
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• pp.61-67
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• 2016

Turbine blade cooling is one of the major technologies to enhance the performance of gas turbine and combined cycle power plants. In this study, two cases of coolant pre-cooling schemes were applied in combined cycle power plant: decrease of coolant mass flow needed to cool turbine blade and increase of turbine inlet temperature (TIT). Both schemes are benefited by the decrease of coolant temperature through coolant pre-cooling. Under the same degree of pre-cooling, increasing TIT exhibits larger plant power boost and higher plant efficiency than reducing coolant flow. As a result, the former produces the same gas turbine power with a much smaller degree of pre-cooling than the latter. Another advantage of increasing TIT is a higher plant efficiency. Even with an assumption of partial achievement of the theoretically predicted TIT, the method of increasing TIT can provide considerably larger power output.

• The KSFM Journal of Fluid Machinery
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• v.10 no.4
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• pp.29-38
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• 2007

In this study, flow structure in a two-stage centrifugal compressor for a turbo-chiller with the refrigerant, R134a, was numerically investigated at the design point of the compressor using a commercial code. Flow characteristics in the passages of impeller, diffuser and return channel were analyzed in detail including velocity vector, secondary flow, Mach number and pressure contours in blade spanwise and meridional plane for each stage. The estimation on the one-dimensional output from the preliminary design and three-dimensional shape of the impeller blade and the meridional shape of the return channel were performed through the flow analysis, while some numerical schemes and techniques including Multiple Frames of Reference technique, real gas property data and inlet boundary condition changes, which were used in CFD, were compared with their features. The results will be used as reference data for a new design of 3-D impeller shape to improve R134a compressor performance.

• The KSFM Journal of Fluid Machinery
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• v.14 no.5
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• pp.24-30
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• 2011

500W class MTG(Micro turbine generator) operating at 400,000 rpm is under development. From the cycle analysis, it is decided that the self-sustaining speed of MTG is 200,000rpm and the generating speed is 400,000 rpm. Therefore, motor should be designed so that it is able to rotate the rotor up to 200,000rpm and generator should designed so that it is able to generate 500W output at 400,000rpm. First step to design motor/generator is to determine the power and efficiency requirement. Not only the power into the compressor and from the turbine at the operating speed but also the mechanical and electrical losses should be considered in determining the power and efficiency requirement. This study presents the procedure and the results of determining the power and efficiency requirement considering the mechanical and electrical losses depending on the rotating speed which is measured from the experiment.

• International Journal of Naval Architecture and Ocean Engineering
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• v.8 no.5
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• pp.456-465
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• 2016

In order to optimize the performance of a Wells turbine with fixed guide vanes, the designs of an end plate and a ring on the tip of the turbine rotor are proposed as penetrating blade tip treatments. In this study, numerical investigations are made using computational fluid dynamics (CFD)-based ANSYS Fluent software, and validated by corresponding experimental data. The flow fields are analyzed and non-dimensional coefficients $C_A$, $C_T$ and ${\eta}$ are calculated under steady-state conditions. Numerical results show that the stalling phenomenon on a ring-type Wells turbine occurs at a flow coefficient of ${\phi}=0.36$, and its peak efficiency can reach 0.54, which is 16% higher than that of an unmodified turbine and 9% higher than in the case of an endplate-type turbine. In addition, quasi-steady analysis is used to calculate the mean efficiency and output work of a wave cycle under sinusoidal flow conditions. As a result, it has been found that the ring-type turbine is superior to other types of Wells turbines.

• The KSFM Journal of Fluid Machinery
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• v.8 no.4 s.31
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• pp.20-26
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• 2005

When the pumps are started or stopped for the operation or tripped due to the power failure, the hydraulic transients occur as a result of the sudden change in velocity. The field tests on the waterhammer were carried out for Pangyo booster pumping station in which had six booster pumps and two in-line pumps with the motor of output 1,700 kW, respectively. The booster pumping station was equipped with the pump control valve as the main surge suppression device, and the surge relief valve as auxiliary one. But the pump control valve had not early controlled in the planned closing mode, the slamming occurred to the valve of which abruptly closed during the large reverse flow. Because the positive pressure wave caused by the pump failure was superposed on the slam surge, the upsurge increased so extremely that the pump control valve was damaged. After the air chambers were additionally installed in the booster pumping station, it was preyed that the water supply system acquire the safety and reliability on the pressure surge.

• The KSFM Journal of Fluid Machinery
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• v.15 no.6
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• pp.18-24
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• 2012

This study simulated the operation of a steam injected gas turbine combined heat and power (CHP) system. A full off-design analysis was carried out to examine the change in the turbine blade temperature caused by steam injection. The prediction of turbine blade temperature was performed for the operating modes suggested in the previous study where the limitation of compressor surge margin reduction was analyzed in the steam injected gas turbine. It was found that both the fully injected and partially injected operations suggested in the previous study would cause the blade temperature to exceed that of the pure CHP operation and the under-firing operation would provide too low blade temperature. An optimal operation was proposed where both the turbine inlet temperature and the injection amount were modulated to keep both the reference turbine blade temperature and the minimum compressor surge margin. The modulation was intended to maintain a stable compressor operation and turbine life. It was shown that the optimal operation would provide a larger power output than the under-firing operation and a higher efficiency than the original partially injected operation.