• Journal of Energy Engineering
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• v.26 no.1
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• pp.23-27
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• 2017

An expander of an organic Rankine cycle is an essential component that significantly influences its entire performance and cycle efficiency. The inlet pressure and temperature of the expander used for the organic Rankine cycle are limited by the expander's mechanical properties and the characteristics of the working fluid. The organic Rankine cycle's output, heat absorption, and efficiency are altered by the inlet pressure and temperature of the expander. In this study, a theoretical comparative analysis was conducted on an organic Rankine cycle's performance changes, which are dependent on the inlet condition of the expander. The working fluid is an R134a refrigerant, and the expander is a positive-displacement type.

• Journal of the Korean Institute of Intelligent Systems
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• v.17 no.5
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• pp.701-706
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• 2007

Recently, a number of researches about linear magnetorheological(MR) damper using valve-mode characteristics of MR fluid have sufficiently undertaken, but researches about rotary MR damper using shear-mode characteristics of MR fluid are not enough. In this paper, we performed vibration control of shear-mode MR damper for unlimited rotating actuator of mobile robot. Also fuzzy logic based vibration control for shear-mode MR damper is suggested. The parameters, like scaling factor of input/output and center of the triangular membership functions associated with the different linguistic variables, are tuned by genetic algorithm. Simulation results demonstrate the effectiveness of the fuzzy-skyhook controller for vibration control of shear-mode MR damper under impact force.

• Journal of Ocean Engineering and Technology
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• v.35 no.6
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• pp.403-413
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• 2021

As the size of ships increases, the size and output power of their thrusters also increase. When a large ship berths or unberths, the jet flow produced from its thruster has an adverse effect on the stability of quay walls. In this study, we conducted a numerical analysis to examine the impact of the thruster jet flow of a 30,000 TEU container ship, which is expected to be built in the near future, on the stability of a quay wall. In the numerical simulation, we used the fluid-structure interaction analysis technique of LS-DYNA, which is calculated by the overlapping capability using an arbitrary Lagrangian Eulerian formulation and Euler-Lagrange coupling algorithm with an explicit finite element method. As the ship approached the quay wall and the vertical position of the thruster approached the mound of the quay wall, the jet flow directly affected the foot-protection blocks and armor stones. The movement and separation of the foot-protection blocks and armor stones were confirmed in the area affected directly by the thruster jet flow of the container ship. Therefore, the thruster jet flows of ultra-large ships must be considered when planning and designing ports. In addition, the stability of existing port structures must be evaluated.

• New & Renewable Energy
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• v.20 no.1
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• pp.116-125
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• 2024

Ultra-low-head is an unexplored classification among the sites in which hydroelectric power can be produced. This is typically owing to the low power output and the economic value of the turbines available in this segment. A turbine capable of operating in an ultra-low-head condition without the need of a dam to produce electricity is developed in this study. A gate structure installed at a shallow water channel acting as a weir generates artificial head for the turbine mounted on the gate to produce power. The turbine and generator are designed to be compact and submersible for an efficient and silent operation. The gate angle is adjustable to operate the turbine at varying flow rates. The turbine is designed and tested using computational fluid dynamics tools prior to manufacturing and experimental studies. A parametric study of the runner blade parameters is conducted to obtain the most efficient blade design with minimal hydraulic losses. These parameters include the runner stagger and runner leading edge flow angles. The selected runner design showed improved hydraulic characteristics of the turbine to operate in an ultra-low-head site with minimal losses.

• Journal of the Earthquake Engineering Society of Korea
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• v.6 no.2
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• pp.63-71
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• 2002

This paper examines the ASCE first generation benchmark problem for a seismically excited cable-stayed bridge, and proposes a new semi-active control strategy focusing on inclusion of effects of control-structure interaction. This benchmark problem focuses on a cable-stayed bridge in Cope Girardeau, Missouri, USA, for which construction is expected to be completed in 2003. Seismic considerations were strongly considered in the design of this bridge due to the location of the bridge in the New Madrid seismic zone and its critical role as a principal crossing of the Mississippi River. In this paper, magnetorheological(MR) fluid dampers are proposed as the supplemental damping devices, and a clipped-optimal control algorithm is employed. Several types of dynamic models for MR fluid dampers, such as a Bingham model, a Bouc-Wen model, and a modified Bouc-Wen model, are considered, which are obtained from data based on experimental results for full-scale dampers. Because the MR fluid damper is a controllable energy-dissipation device that cannot add mechanical energy to the structural system, the proposed control strategy is fail-safe in that bounded-input, bounded-output stability of the controlled structure is guaranteed. Numerical simulation results show that the performance of the proposed semi-active control strategy using MR fluid dampers is quite effective.

• Nutritional Sciences
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• v.9 no.2
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• pp.124-130
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• 2006

To examine the effects of alcohol consumption on body fluid restoration and fat mobilization following exercise induced dehydration, nine healthy collegiate men ($24{\pm}2yrs,\;177{\pm}5cm,\;72{\pm}8kg,\;10.5{\pm}2.3%$ body fat) underwent three experiments. In each experiment, subjects ran on a treadmill to reduce individual body mass to $2.2{\pm}0.1%$ and consumed one of three beverages containing 0, 4, or 8% alcohol over 60 min followed by 4 hr of resting recovery. They consumed approximately 150% of weight loss $(2053{\pm}204,\;2091{\pm}149,\;and\;1943{\pm}295mL)$ and content of alcohol was $9.9{\pm}1.0(0%),\;71.9{\pm}5.1(4%)$, and $132.2{\pm}20.1g$ (8% trial). Body weight, urine volume and samples, blood samples, and thirst sensation were measured five times; at baseline, immediately after exercise, and 0, 1st, and 4th hr of recovery. Blood alcohol concentration after ingestion was $0.0{\pm}0.0(0%),\;0.1{\pm}0.02(4%)$, and $0.2{\pm}0.03%$ (8% trial). No differences in blood sodium and potassium concentrations, and urine specific gravity were noticed over time periods and trials. Thirst sensation tended to be elevated in all trials immediately after exercises and urine output was elevated during the recovery. The magnitude of changes in these variables was proportional to the alcohol concentrations, but not statistically significant. While serum osmolality was not different among trials and time periods in 0 and 4% trials, it was higher during recovery than the baseline in the 8% trial (P<0.01). Triglycerides did not change throughout the time period and among trials. Free fatty acids were elevated after exercise in all trials and 4th hr of recovery in 0% (P<0.05). Subjects' net body fluid balance at 4th hr of recovery was negatively maintained and proportional to alcohol concentrations. Only 8% trials showed a significant reduction at 1st and 4th hr of recovery compared to 0 hr. The results suggested that diuretic effect of alcohol after moderate level of dehydration appeared dose dependent, but beverage containing alcohol up to 4% did not induce impaired rehydration than alcohol free drinks. Alcohol effects on fat mobilization during recovery appeared to be minimal and the mechanism is unclear.

• Transactions of the Korean hydrogen and new energy society
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• v.33 no.1
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• pp.95-104
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• 2022

Micro hydropower is a readily available renewable energy source that can be harvested utilizing hydrokinetic turbines from shallow water canals, irrigation and industrial channel flows, and run-off river stream flows. These sources generally have low head (<1 m) and low velocity which makes it difficult to harvest energy using conventional turbines. A horizontal-axis screw turbine was designed and numerically tested to extract power from such low-head water sources. The 3-bladed screw-type turbine is placed horizontally perpendicular to the incoming flow, partially submerged in a narrow water channel at no-head condition. The turbine hydraulic performances were studied using Computational Fluid Dynamics models. Turbine design parameters such as the shroud diameter, the hub-to-shroud ratios, and the submerged depths were obtained through a steady-state parametric study. The resulting turbine configuration was then tested by solving the unsteady multiphase free-surface equations mimicking an actual open channel flow scenario. The turbine performance in the shallow channel were studied for various Tip Speed Ratios (TSR). The highest power coefficient was obtained at a TSR of 0.3. The turbine was then scaled-up to test its performance on a real site condition at a head of 0.3 m. The highest power coefficient obtained was 0.18. Several losses were observed in the 3-bladed turbine design and to minimize losses, the number of blades were increased to five. The power coefficient improved by 236% for a 5-bladed screw turbine. The fluid losses were minimized by increasing the blade surface area submerged in water. The turbine performance was increased by 74.4% after dipping the turbine to a bottom wall clearance of 30 cm from 60 cm. The final output of the novel horizontal-axis screw turbine showed a 2.83 kW power output at a power coefficient of 0.63. The turbine is expected to produce 18,744 kWh/year of electricity. The design feasibility test of the turbine showed promising results to harvest energy from small hydropower sources.

• Proceedings of the KSR Conference
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• 2011.05a
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• pp.585-593
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• 2011

Actual fire test under a laboratory and fire simulation by using computer are considered into main methodology in order to estimate and predict fire size of railway train. Even if practical fire size could be obtained from the full-model railway car test such as a large scale cone-calorimeter test, it is not always possible and realistic due to that expensive cost and attendant dangers could in no way be negligible. In this point of view, fire simulation analysis method based on the computational fluid dynamics could be proposed as an alternative and it seems to be also efficient and reasonable. However, simulation results have to be verified and validated in accordance with the proper procedure including comparing analysis with the actual fire test. In this paper, fire load and growth aspect was investigated through the room corner test (ISO 9705) for the mock-up model of the actual railway car. Then, it was compared with the output data derived from the simulation by using Pyrolysis Model of the FDS (Fire Dynamics Simulator, by NIST) for the exact same domain and condition corresponding with pre-performed room-corner test. This preliminary verified and validated fire modeling method could enhance the reliability of output data derived from the fire simulation under the similar domain and condition.

• Journal of Advanced Marine Engineering and Technology
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• v.36 no.5
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• pp.595-602
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• 2012

In this study, for the purpose of reduction of $CO_2$ gas emission and to increase recovery of waste heat from ships, the ORC (Organic Rankine Cycle) is investigated and offered for the conversion of temperature heat to electricity from waste heat energy from ships. Simulation was performed with waste heat from the exhaust gasse which is relatively high temperature and cooling sea water which is relatively low temperature from ships. Various fluid is used for simulation of the ORC system with variable temperature and flow condition and efficiency of system and output power is compared. Finally, 2,400kW output power is obtained by system optimization of the preheater and reheater utilizing waste heat form sea water cooling system.

• Journal of Advanced Marine Engineering and Technology
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• v.35 no.8
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• pp.1063-1069
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• 2011

This paper presents aerodynamic power outputs of wind turbine of 6 MW wind farm composed of 3 sets of 2 MW wind turbine according to the separation distance by using CFD. Layout design including offshore wind farm and onshore wind farm is key factor for the initial investment cost, annual energy production and maintenance cost. For each wind turbine rotor, not actuator disc model with momentum source but full 3-dimensional model is used for CFD and it has a great technical meaning. The results of this study can be applied to the offshore wind farm layout design effectively.