• Wind and Structures
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• v.26 no.5
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• pp.279-292
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• 2018

Inspired by the energy harvesting eel, a flexible flag behind a D-shape cylinder in a uniform viscous flow was simulated by using the immersed boundary method (IBM) along with low-speed wind tunnel experimentation. The flag in the wake of the cylinder was strongly influenced by the vortices shed from the upstream cylinder under the vortex-vortex and vortex-body interactions. Geometric and flow parameters were optimized for the flexible flag subjected to passive flapping. The influence of length and bending coefficient of the flexible flag, the diameters (D) of the cylinder and the streamwise spacing between the cylinder and the flag, on the energy generation was examined. Constructive and destructive vortex interaction modes, unidirectional and bidirectional bending and the different flapping frequency were found which explained the variations in the energy of the downstream flag. Voltage output and flapping behavior of the flag were also observed experimentally to find a more direct relationship between the bending of the flag and its power generation.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.10
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• pp.5156-5161
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• 2013

In distributed spatial data stream processing, processed tuples of downstream nodes are replicated to the upstream node in order to increase the utilization of distributed nodes and to recover the whole system for the case of system failure. However, while the data input rate increases and multiple downstream nodes share the operation result of the upstream node, the data which stores to output queues as a backup can be lost since the deletion operation delay may be occurred by the delay of the tuple processing of upstream node. In this paper, the adaptive upstream backup scheme based on operation throughput in distributed spatial data stream system is proposed. This method can cut down the average load rate of nodes by efficient spatial operation migration as it processes spatial temporal data stream, and it can minimize the data loss by fluid change of backup mode. The experiments show the proposed approach can prevent data loss and can decrease, on average, 20% of CPU utilization by node monitoring.

• Journal of the Korean Society of Propulsion Engineers
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• v.21 no.5
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• pp.54-60
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• 2017

In order to identify the characteristics of the flame transfer function gain, cold-flow transfer function was introduced, which is the part of the combustion instability research. Nitrogen and carbon dioxide was used to obtain the cold-flow transfer function and input/output variables was measured by hot wire anemometry. Density and fluid flow rate affect the cold-flow transfer function gain and peak frequency. In addition, acoustic resonance frequency affects the peak frequency of gain in the fuel feeding line.

• Advances in pediatric surgery
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• v.4 no.1
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• pp.16-26
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• 1998

Parenteral nutrition has been an essential part of postoperative care of neonates requiring major surgery who are unable to tolerate enteral feeding for long periods during the postoperative period. However, TPN via central venous catheters(central TPN), used in increasing trend, still presents significant morbidity. To find out whether TPN via peripheral veins(peripheral TPN) could be used as a viable alternative for postoperative parenteral nutrition in neonates, a clinical study was carried out by a retrospective analysis of 53 neonates subjected to peripheral TPN for more than 7 days after surgery. Operations consisted of procedures for esophageal atresia with tracheoesophageal fistula, gastroschisis and omphalocele. Surgery was performed at the Division of Pediatric Surgery, Department of Surgery, Hanyang University Hospitall, from 1983 to 1994. The mean total duration of TPN was 13.3 days (range; 7-58 days), the average daily total fluid intake was 117.6 ml/kg during TPN and 158.6 ml/kg during subsequent oral feeding. The average daily total calorie intake was 57.7 kcal/kg during full strength TPN and 101.3 kcal/kg during subsequent oral feeding. The mean urine output was maintained at 3.5 ml/kg/ hour during TPN and at 3.6 ml/kg/hour during subsequent oral feeding. The increment of body weight observed during TPN was 132 g in TEF, 53 g in gastroschisis and 3 g in omphalocele patients, while loss of body weight was not observed. The mortality rate was 5.7 %(3/53) and was related to the underlying congenital anomalies, not the TPN. The most common complication of peripheral TPN observed was laboratory findings suggestive of liver dysfunction in 23 cases(43.4 %) with no significant clinical symptom or signs in any case, transient pulmonary edema in one case, and generalized edema in one case. None of the major complications usually expected associated with central TPN were observed. The result of this study suggest that peripheral TPN can be used for adeguate postoperative nutritional support in neonates requiring 2 to 3 weeks of TPN.

• Childhood Kidney Diseases
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• v.24 no.1
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• pp.42-46
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• 2020

Disturbances in water and salt balances are relatively common in children after brain tumor surgery. However, the coexistence of different diseases of water and sodium homeostasis is challenging to diagnose and treat. The coexistence of combined central diabetes insipidus (CDI) and cerebral salt wasting syndrome (CSWS) is rare and may impede accurate diagnosis. Herein, we report the case of an 18-year-old girl who underwent surgery for a germinoma and who presented prolonged coexistence of CDI and CSWS. The patient was diagnosed with panhypopituitarism with CDI at presentation and was treated with hydrocortisone, levothyroxine, and desmopressin. Postoperatively, she developed polyuria of more than 3L/day, with a maximum daily urine output of 7.2 L/day. Her serum sodium level decreased from 148 to 131 mEq/L. Polyuria was treated with desmopressin at incremental doses, and hyponatremia was managed with fluid replacement. At 2 months after surgery, she presented with hyponatremia-induced seizure. Polyuria and hyponatremia combined with natriuresis indicated CSWS. Treatment with fludrocortisone were initiated; then, her electrolyte level gradually normalized. CSWS is self-limiting and generally resolves within 2 weeks. However, the patient in this study still required treatment with vasopressin and fludrocortisone at 16-months after surgery. Hyponatremia in a patient with CDI may be erroneously interpreted as inadequate CDI control or syndrome of inappropriate antidiuretic hormone secretion, leading to inappropriate treatment. The identification of the potential combination of CDI and CSWS is important for early diagnosis and treatment.

• Journal of the Korean Solar Energy Society
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• v.34 no.2
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• pp.73-81
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• 2014

Ocean thermal energy conversion(OTEC) is a power generation method that utilizes temperature difference between the warm surface seawater and cold deep sea water of ocean. As potential sources of clean-energy supply, Ocean thermal energy conversion(OTEC) power plants' viability has been investigated. Therefore, this paper evaluated the thermodynamic performance of solar-OTEC convergence system for the production with electric power and desalinated water. The comparison analysis of solar-OTEC convergence system performance was carried out as the fluid temperature, saturated temperature difference and pressure of flash evaporator under equivalent conditions. As a results, maximum system efficiency, electric power and fresh water output show at 40, 10, 2.5 kPa of the flash evaporator pressure, respectively. And their respective enhancement ratios were approximately 6.1, 18, 8.6 times higher than that of the base open OTEC system. Also, performance of solar-OTEC system is the highest in the flash evaporator pressure of 10 kPa.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.9
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• pp.923-932
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• 2011

Because of the instability of a flow pattern in the inlet transition square duct (hereinafter referred to as "transition duct") of a heat recovery steam generator (hereinafter referred to as "HRSG") in a combined cycle power plant, the Reynolds number in the first row of a tube bank is differs sharply from that in the sectional area of the transition duct. This causes differences in the heat flux in each tube in the tube bank. The computational fluid dynamics (CFD) predictions provide three-dimensional results for velocity, temperature, and other flow parameters over the entire domain of the duct and HRSG. A renormalization group theory (RNG) based k-${\epsilon}$�� turbulent model is used for obtaining the results cited in this study. A porous media option is used for modeling the tube banks and the number of transfer units method is used for determining the heat transfer characteristics. This study describes a comparison between the numerical simulation results and actual design output.

• Journal of Drive and Control
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• v.13 no.3
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• pp.24-31
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• 2016

The performance characteristics of a dynamic control system are evaluated according to the transient and steady-state responses. The transient performance is the controllability of the output for the tracking of the reference or the ability to reduce or reject the effects of unwanted disturbances; alternatively, the steady-state performance is represented by the magnitude of the control error at the steady state. As the effects of the two performances on each other are reciprocal, a controller design that shows a zero steady-state error for the ramp input is uncommon because of the challenge regarding the achievement of an acceptable transient response. This paper proposes a PI+double-integral controller for the elimination of the steady-state error for the ramp input while a sound transient performance is maintained. The control-gain design procedure is described by the second-order response for the step input and the response of the error dynamics for the ramp input. The PI+double-integral controller is designed for the first-order transfer function that is derived from a system identification with the open-loop experiment data of the dc-motor. The simple structure of the proposed controller enables the adoption of a low-end microcontroller for the implementation of a real-time control. The experiment results show that the control performance is as effective as that of the simulation analysis for the operating point of linear system; furthermore, the PI+double-integral controller can be conveniently applied to the control system, which is desirable for the improvement of the steady-state error.

• Journal of Drive and Control
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• v.14 no.2
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• pp.16-22
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• 2017

This paper presents the algorithm of an adaptive model-free-control-based steering control for multi-axle all-terrain cranes for which the recursive least squares with forgetting are applied. To optimally control the actual system in the real world, the linear or nonlinear mathematical model of the system should be given for the determination of the optimal control inputs; however, it is difficult to derive the mathematical model due to the actual system's complexity and nonlinearity. To address this problem, the proposed adaptive model-free controller is used to control the steering angle of a multi-axle crane. The proposed model-free control algorithm uses only the input and output signals of the system to determine the optimal inputs. The recursive least-squares algorithm identifies first-order systems. The uncertainty between the identified system and the actual system was estimated based on the disturbance observer. The proposed control algorithm was used for the steering control of a multi-axle crane, where only the steering input and the desired yaw rate were employed, to track the reference path. The controller and performance evaluations were constructed and conducted in the Matlab/Simulink environment. The evaluation results show that the proposed adaptive model-free-control-based steering-control algorithm produces a sound path-tracking performance.

• Journal of Drive and Control
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• v.14 no.2
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• pp.30-36
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• 2017

This paper presents a sliding mode observer-based fault detection algorithm for steering inputs of an all-terrain crane. All-terrain cranes with multi-axles have several steering modes for various working purposes. Since steering angles at the other axles except the first wheel are controlled by using the information of steering angle at the first wheel, a reliable signal of the first axle's steering angle should be secured for the driving safety of cranes. For the fault detection of steering input signal, a simplified crane model-based sliding mode observer has been used. Using a sliding mode observer with an equivalent output injection signal that represents an actual fault signal, a fault signal in steering input was reconstructed. The road steering mode of the crane's steering system was used to conduct performance evaluations of a proposed algorithm, and an arbitrary fault signal was applied to the steering angle at the first wheel. Since the road steering mode has different steering strategies according to different speed intervals, performance evaluations were conducted based on the curved path scenario with various speed conditions. The design of algorithms and performance evaluations were conducted on Matlab/Simulink environment, and evaluation results reveal that the proposed algorithm is capable of detecting and reconstructing a fault signal reasonably well.