• 제목/요약/키워드: Direct Problem

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Direct Numerical Simulation of Channel Flow with Wall Injection

  • Na, Yang
    • Journal of Mechanical Science and Technology
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    • 제17권10호
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    • pp.1543-1551
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    • 2003
  • The present study investigates turbulent flows subject to strong wall injection in a channel through a Direct Numerical Simulation technique. These flows are pertinent to internal flows inside the hybrid rocket motors. A simplified model problem where a regression process at the wall is idealized by the wall blowing has been studied to gain a better understanding of how the near-wall turbulent structures are modified. As the strength of wall blowing increases, the turbulence intensities and Reynolds shear stress increase rapidly and this is thought to result from the shear instability induced by the injected flows at the wall. Also, turbulent viscosity grows rapidly as the flow moves downstream. Thus, the effect of wall-blowing modifies the state of turbulence significantly and more sophisticated turbulence modeling would be required to predict this type of flows accurately.

다중채널 직접구동 엑츄에이터의 구동전류 동일화 루프 설계 (Current Equation Loop Design of Muti-channel Direct Drive Valve Actuation)

  • 남윤수
    • 한국정밀공학회지
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    • 제17권10호
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    • pp.162-169
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    • 2000
  • A Direct Drive Valve(DDV) hydraulic actuation system which is commonly used as an aircraft's control surface driving actuator has multi-loop control structure to ensure its safety operation. However, because of not perfect matching of one self channel characteristics with the others, the servo valve driving current of each channel can be widely different. Therefore, the long-time use of DDV actuator without any correction of these channel current offsets will cause the problem of performance or life expectancy degradation due to unwanted heats in the linear motor. A current equalization loop structure which can minimizes current offsets between channels is introduced and designed. The performance of the current equalization loop is investigated and verified through the analytic and experimental ways.

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경관보전직접지불제 작물의 생산비 실증분석 (An Empirical Analysis on the Production Cost of Landscape Crops in the Direct Payment Program for Rural Landscape Conservation)

  • 김광남;김미영;이형순
    • 농촌계획
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    • 제16권3호
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    • pp.19-26
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    • 2010
  • The purpose of this paper is to evaluate optimum rate of payment and to [md the new advanced direction for the program for rural landscape conservation. We used direct evaluation method for income and production costs. According to the survey, we had done from 41 complexes(farmers) joined this program, the average production cost of landscape crops of type1 is calculated at 178,582 won per 10a and 111,517 won as type2. If the classification of crop type is adjusted, the problem formulated is improved to make possible support at the current payment rate.

Direct Numerical Simulation of Turbulent Scalar Transport in a Channel with Wall Injection

  • Na, Yang
    • Journal of Mechanical Science and Technology
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    • 제18권4호
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    • pp.597-605
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    • 2004
  • Turbulent temperature field in a channel subject to strong wall injection has been investigated via direct numerical simulation technique. These flows are pertinent to internal flows inside hybrid rocket motors. A simplified model problem where a regression process at the propellant surface is idealized by wall injection has been investigated to understand how the temperature field is modified. The effect of strong wall injection displaces thermal boundary layer away from the wall and this causes a sharp drop of friction temperature. Turbulent diffusivity and dissipation time scale for temperature field are found to show large variations in the streamwise direction under application of wall blowing. It is, thus, expected that more sophisticated turbulence models would be required to predict the disturbed temperature field accurately.

구동력 계산법 및 H$\infty$제어를 병용한 직접구동방식 머니퓰레이터의 퀘적제어 (Robust Trajectory Control of Direct Drive Manipulator based on combining H$\infty$ Controller and Computed Torque Method)

  • Kim, C.K.;Kang, B.S.;Kwak, Y.K.
    • 한국정밀공학회지
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    • 제13권10호
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    • pp.123-129
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    • 1996
  • Computed torque method has been used for precise trajectory control of the robotic system that involves nonlinear dynamics. It is hard to know exact values of robot system parameters, and the robot arm receives umpredictable interference from the working environment. These disturbances, especially in a direct drive robot, are directly transmitted to actuating motor without reduction. Modelling error and distrubance can cause significant errors in a trajectory tracking problem. In this paper, we propose a new controller that $H_{\infty}$controller is conbined to robot system linearized by computed torque. Simula- tions are made for comparing the performance of the proposed controller with that of a nonlinear $H_{\infty}$ controller proposed by Chen and also computed torque method.hod.

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DDS를 이용한 BCPFSK모뎀 설계 및 성능 평가에 관한 연구 (A Study on Design and Performance Evaluation of the BCPFSK Modem Using the DDS)

  • 김경복;최정수;조형래
    • 한국정보통신학회:학술대회논문집
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    • 한국해양정보통신학회 2000년도 추계종합학술대회
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    • pp.166-171
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    • 2000
  • 현대 무선 통신에서는 제한된 주파수 자원을 효율적으로 사용하기 위해 스펙트럼 효율성이 매우 중요한 문제로 여겨지고 있다. 또한 시스템구조 측면에서는 저 가격, 저 전력 및 초경량에 목표를 두고 제작되고 있다. 본 논문에서는 직접 디지털 주파수합성기(DDS ; Direct Digital Synthesize.)를 이용하여 스펙트럼 효율이 우수한 BCPFSK(Binary Continuous Phase Frequency Shift Keying)를 직접 변조하였으며, 시스템 구조로는 직접 변환(Direct Conversion) 구조를 적용하여, 433 MHz대의 BCPFSK 출력을 갖는 송 ·수신기를 설계하고 성능을 평가하였다.

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로봇의 궤적추종제어를 위한 직접학습 제어법칙의 구현 (Implementation of a Direct Learning Control Law for the Trajectory Tracking Control of a Robot)

  • 김진형;안현식;김도현
    • 대한전기학회:학술대회논문집
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    • 대한전기학회 2000년도 추계학술대회 논문집 학회본부 D
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    • pp.694-696
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    • 2000
  • In this paper, the Direct Learning Control is applied to robot's trajectory tracking control to solve the problem that lies in the existing Iterative Learning Control(ILC) and the tracking Performance is analyzed and the better approach is searched using computer simulation and experiments. It is assumed that the Direct Learning Control(DLC) is saved onto memory basically after obtaining control input Profiles for several Periodic output trajectories using the ILC. In case the new output trajectory has special relations with the previous output trajectories, there is an advantage that the desired control input profile can be obtained without iterative executions only using the DLC. The robot's tracking control system is comprised of DSP chip. A/D converter, D/A converter and high-speed pulse counter included in the control board and the performance is examined by carrying out the tracking control for the given output trajectory.

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Design of Continuous Variable Structure Tracking Controller With Prescribed Performance for Brushless Direct Drive Drive Servo Motor

  • Lee, Jung-Hoon
    • Journal of Electrical Engineering and information Science
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    • 제3권1호
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    • pp.58-66
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    • 1998
  • A continuous, accurate, and robust variable structure tracking controller(CVSTC) is designed for brushless direct drive servo motors(BLDDSM). Although conventional variable structure controls can give the desired tracking performances, there exists an inevitable chattering problems in control input which is undesirable for direct drive systems. With the presented algorithm, not only the chattering problems are removed by using the efficient compensation of the disturbance observer, but also the prescribed tracking trajectory can be obtained using the sliding dynamics when an initial of the desired trajcetory is different from that of a BLDDSM. The design of the sliding mode tracking controller for the prescribed, accurate, and robust tracking performance without the chattering problem is given based on the results of the detailed stability analysis. The usefulness of the suggested algorithm is demonstrated through the computer simulation for a BLDDSM under load variations.

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Speech Enhancement Using Blind Signal Separation Combined With Null Beamforming

  • Nam Seung-Hyon;Jr. Rodrigo C. Munoz
    • The Journal of the Acoustical Society of Korea
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    • 제25권4E호
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    • pp.142-147
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    • 2006
  • Blind signal separation is known as a powerful tool for enhancing noisy speech in many real world environments. In this paper, it is demonstrated that the performance of blind signal separation can be further improved by combining with a null beamformer (NBF). Cascading the blind source separation with null beamforming is equivalent to the decomposition of the received signals into the direct parts and reverberant parts. Investigation of beam patterns of the null beamformer and blind signal separation reveals that directional null of NBF reduces mainly direct parts of the unwanted signals whereas blind signal separation reduces reverberant parts. Further, it is shown that the decomposition of received signals can be exploited to solve the local stability problem. Therefore, faster and improved separation can be obtained by removing the direct parts first by null beamforming. Simulation results using real office recordings confirm the expectation.

DIRECT INVERSE ROBOT CALIBRATION USING CMLAN (CEREBELLAR MODEL LINEAR ASSOCIATOR NET)

  • Choi, D.Y.;Hwang, H.
    • 제어로봇시스템학회:학술대회논문집
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    • 제어로봇시스템학회 1990년도 한국자동제어학술회의논문집(국제학술편); KOEX, Seoul; 26-27 Oct. 1990
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    • pp.1173-1177
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    • 1990
  • Cerebellar Model Linear Associator Net(CMLAN), a kind of neuro-net based adaptive control function generator, was applied to the problem of direct inverse calibration of three and six d.o.f. POMA 560 robot. Since CMLAN autonomously maps and generalizes a desired system function via learning on the sampled input/output pair nodes, CMLAN allows no knowledge in system modeling and other error sources. The CMLAN based direct inverse calibration avoids the complex procedure of identifying various system parameters such as geometric(kinematic) or nongeometric(dynamic) ones and generates the corresponding desired compensated joint commands directly to each joint for given target commands in the world coordinate. The generated net outputs automatically handles the effect of unknown system parameters and dynamic error sources. On-line sequential learning on the prespecified sampled nodes requires only the measurement of the corresponding tool tip locations for three d.o.f. manipulator but location and orientation for six d.o.f. manipulator. The proposed calibration procedure can be applied to any robot.

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