• 대한기계학회논문집A
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• 제28권8호
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• pp.1152-1158
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• 2004

In this study a MRAC(model reference adaptive control) for fluid power elevator model system was designed. The MRAC was compared with PI control in case of applying to the elevator model system with constant external load and changing external load. In this case external load was produced by a single fluid power cylinder combined with pressure control valve. In conclusion the MRAC control performance was better than PI control performance because overshoot and steady state error of the elevator model system controlled by the MRAC were not appeared for constant and changing external load.

• 항공우주기술
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• 제2권2호
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• pp.115-123
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• 2003

본 논문에서는, KSR-III 김발엔진 구동장치 시스템의 원활한 작동을 보장하기 위한 방안으로 릴리프밸브의 적용을 고려하였다. 비행 중의 김발엔진 지지구조물에서의 진동 및 급격한 외란 등에 의해 구동기에 과도한 토크가 작용하는 경우, 구동기의 작동불능 및 로켓의 성능저하가 발생 가능함을 보였으며, 릴리프밸브의 적용을 통해 그러한 불안정성을 해소시킬 수 있음 을 보였다. 6자유도 시뮬레이션 분석을 통해, 릴리프밸브의 작동압이 낮을수록, LOHM 파라미터가 작을수록 시스템의 성능 면에서 유리하다는 결과를 제시하였으며, 릴리프밸브를 채용함에 따라 로켓에 작용하는 TWD 등의 외란을 감소시키는 효과도 발생함을 보일 수 있었다.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1995년도 추계학술대회 논문집
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• pp.569-572
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• 1995

In this study, a hydraulic modulator of solenoid-flow type ABS, the master sylinder, and the wheel cylinder are modeled and simulated for increasing pressure characteristics of the brake. Response can be predicted by external force of the the master sylinder and pulses to the solenoid valve as input. For a demonstration of simulation result, experiment is done under the same condition as simulation condition after experimental apparatus of 1/4 car model is constructed. When factors of flow control valve are changed, the effect of each factor to response, how to improve response, and the most critical factors are considered from simulated result of time constant.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2001년도 추계학술대회논문집 I
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• pp.517-521
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• 2001

Measurement techniques for the in-duct source characteristics of fluid machines can be classified into direct method and load method, according to whether the technique employs an external acoustic source or not. It has been known that the two methods yield different results and the load method used to come up with a negative source resistance, in spite of the fact that a very accurate prediction of radiated noise can be obtained by using any result. This paper is focused to the effect of time-varying nature of fluid machines on the output result. For this purpose, a simplified fluid machine consisting of a reservoir, a valve and a pipe is considered as representing a typical linear, periodic, time-varying system and the measurement techniques are simulated by utilizing the Hill equation and its steady-state forced response. In the load method, the source impedance turns out being dependent on the valve impedance at the calculation frequency and the valve and load impedances at other frequencies as well.

• 대한기계학회논문집A
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• 제26권8호
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• pp.1565-1576
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• 2002

By way of driving a 2-way on/off solenoid hydraulic valve with a pulse width modulation (PWM) signal, control of the pressure in a certain volume is frequently used in various applications. However, the pressure built-up according to the duty ratio and carrier frequency of the PWM signal is not so well understood. In order to clarify the characteristics of 2-way valve hydraulic pressure control systems, in this paper two formula fur the mean and ripple of the load pressure were derived through theoretical analysis. And the accuracy of the derived formula were verified by comparison with the experimental test result. Generally 2-way valve systems are constructed as a bleed-off circuit, while 3-way valves are used as a control element in a meter-in circuit pressure control system. In a bleed-off circuit, the system supply pressure from a hydraulic power pack does not remain constant, but changes according to their external load. In turn, the relief valve in the hydraulic power pack reacts accordingly showing complicated dynamic behavior, which makes an analytical study difficult. In order to resolve the problem, simple but accurate empirical dynamic models fer a bleed-off system were used in the course of formula derivation. As the result, selection criteria for two major control parameters of the driving signal is established and the basic strategy to suppress the unnecessary pressure fluctuation can be provided for a hydraulic pressure control system using a 2-way on/off solenoid valve.

• 한국유체기계학회 논문집
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• 제10권5호
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• pp.20-26
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• 2007

Some gate valves are susceptible to pressure locking and thermal binding which prevent the safety function. The safety related gate valves susceptible to pressure locking and thermal binding shall be identified and taken preventive actions to ensure the safety function. The identification of the gate valves susceptible to pressure locking and thermal binding needs the evaluation of system design, valve and piping arrangement, test requirements, and operating conditions. Application of preventive methods should consider the system safety function, applicability, effectiveness, interface with system design, and cost. The selection procedure of valves susceptible to pressure locking and thermal binding can be effectively used in industry including nuclear power plants. In order to prevent the pressure locking, the hole can be drilled through the one disc of upstream side or down stream and the external equalizing line can be installed from bonnet to downstream or upstream. The double disc parallel seat valve type can be used instead of flexible wedge gate valve to prevent the thermal binding. The identification of gate valves susceptible to pressure locking and thermal binding, and preventive actions will meet the regulatory requirements and enhance the availability and safety of plants.

• 에너지공학
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• 제27권4호
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• pp.13-19
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• 2018

본 연구에서는 위상최적화에 기초한 발전설비용 버터플라이 밸브 디스크 부품의 경량설계가 수행되었다. 이때 상용 유한요소해석 소프트웨어가 사용되었으며 기존 상용 밸브 디스크의 외형을 유지시키면서 내부의 불필요 공간을 제거하여 경량구조를 갖도록 하였다. 먼저 밸브 디스크의 원판과 브라켓을 분리하여 각각 최적설계 하였다. 최적의 형상이 선정되면 이들을 조립하여 3차원 경량 밸브 디스크 모델을 완성하였다. 이후 이 모델에 설계 압력을 적용하여 유한요소해석 후 구조적 안전성을 확인하였다.

• 한국산학기술학회논문지
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• 제18권12호
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• pp.57-64
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• 2017

오늘날 EU환경규제로 포장용 완충재로 사용되는 EPS(스티로폼) 대체용 공기 충진 완충재는 출시 이후 점진적으로 시장이 확대되는 포장업계 블루칩이다. 공기충진형 완충재는 뛰어난 완충능력과 친환경성으로 EPS를 대체하여 빠르게 시장을 확장하고 있다. 기존 공기 충진 완충재에 대비하여 원료절감과 공정향상, 직관적 미관 향상을 모두 충족하는 새로운 선택 충진형 공기 충진재 제조기술이다. 본 연구는 다단 에어셀 충진 밸브성형기술은 선택충전 기술을 바탕으로, 밸브형성 구조기술을 적용하여 선택적으로 다양한 형태로 충진이 가능한 기술이다. 다단 에어셀 충진 밸브성형기술의 구조도는 밸브단이 구분된 제1주입필름, 밸브필름, 제2주입필름 등 3겹의 필름을 적층하여 복수의 주입구를 형성한 기술이다. 기존의 기술은 연결된 다수의 공기주머니에 공기를 주입하기 위한 별도의 외부 공기주입로가 필수적으로 구성되어야 하나, 본 연구는 공기 주머니의 내부에 외부 공기주입로가 형성되어 공기를 주입하기 위한 외부 공기주입로가 외견상 없어짐으로써 그에 따른 원재료 및 공정이 감소하고, 공기가 주입되어 원형 튜브로 팽창하는 과정에서 단면의 길이가 63~66%로 축소되는 공기주머니와 다르게 공기주입 후 내부 공기가 배출되고 단면이 원래의 길이를 유지하여 불필요하게 접힌 채 붙어 있는 외부 공기주입로를 내부에 일체화 하여 완충재의 미관이 향상되는 기술적 특징과 다수의 연속된 공기주머니에 선택적으로 공기를 충전할 수 있는 선택충전에 관한 것으로 기존 기술대비 뛰어난 차별성을 갖는 스마트한 공기충전형 완충재 제조 기술이다.

• ALGAE
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• 제37권1호
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• pp.33-47
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• 2022

Two new species of Pseudostaurosiropsis are described based on material collected from rivers in southern United States of America, P. californicus sp. nov. and P. elaboratus sp. nov. Both species have specific characters that set them apart from taxa currently ascribed to the genus. Pseudostaurosiropsis californicus sp. nov. has lanceolate valves with subrostrate, broadly rounded apices, an axial area at the same level as the virgae in internal and external views and both are at the same level as striae in external view, the spine tips are dentate and their growth is produced by filamentous extensions, and it has equal-sized apical pore fields on both valve extremes. On the other hand, P. elaboratus sp. nov. has heavily silicified valves, the virgae are slender than the striae in outer view and wider in inner view, it only has a single, externally occluded apical pore field on one valve extreme, and the spines have a solid core. All species within Pseudostaurosiropsis are contrasted with one another and unique features are described for each based on literature and newly collected image data from type material. The genus is reconsidered and two distinguishing features are recognized: rotae externally occluding the areolae and areolae that are funnel-shaped. These features are contrasted with those in other genera and additional published species that should be included in Pseudostaurosiropsis are discussed.

• 한국기계가공학회지
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• 제2권4호
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• pp.46-52
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• 2003

For position control of electro-hydraulic servo system, single rod cylinders and double rod cylinders are used. Single rod cylinders have simple structure for manufacturing but different volume ratio of two sides induce to non-linearity in process of then mathematical modeling. So only with conventional PID control method it is difficult to control single rod cylinders precisely. For mole precise position control of single rod cylinders, a controller which is inserted a velocity feedback PID controller and MRAC controller are proposed. With experiment control performances of three control methods are compared. In case of experiment, for external varying load to the system, a hydraulic cylinder and a pressure control valve are used. In conclusion a MRAC is considered a suitable control method for external varying load.