• Title/Summary/Keyword: 모멘트방정식

Search Result 170, Processing Time 0.025 seconds

A Study of Computation Methods for Dynamic Damping Coefficients of an Airship (비행선의 동적 감쇠계수 계산 방법에 관한 연구)

  • Park, Su Hyeong;Jang, Byeong Hui;Kim, Yu Jin;Gwon, Jang Hyeok
    • Journal of the Korean Society for Aeronautical & Space Sciences
    • /
    • v.31 no.5
    • /
    • pp.10-17
    • /
    • 2003
  • Dynamic stability is critically required to stabilize an airship which is statically unstable. Numerical computations were performed in order to support and confirm the foced oscillation wind tunnel tests. To analyze the low-speed flow filed around the airship, a low-Mach number preconditioned method was applied. Using two computation methods, variations of the dynamic damping coefficients were examined. Numerical results show that it is dynamically stable for three directional moments, but unstable for normal or side force. It is revealed that the damping coefficients are more sensitive to the direction of the angular rate than the angle of attack or the magnitude og angular rate.

Design of Cam Contour for Constant Hangers (등하중지지대의 캠 윤곽 설계)

  • Lee, Gun-Myung;Park, Mun-Soo
    • Transactions of the Korean Society of Mechanical Engineers A
    • /
    • v.35 no.6
    • /
    • pp.669-675
    • /
    • 2011
  • A constant hanger is a device for supporting pipes in plants. It supplies a constant force to a supporting pipe even if the pipe moves because of thermal expansion. In this paper, we propose a method for designing the contour of a cam for a constant hanger. It has been shown that the contour of a cam must satisfy the geometrical relation of the cam, the force balance equation for the load tube, the relation between the side spring compression and the cam rotation angle, and the moment balance equation for the cam. A calculation procedure to solve these equations simultaneously is proposed, and a constant hanger is designed successfully.

Numerical Investigation of Mother Plane Interference Effect on the Supersonic Air-launched Rocket (초음속 공중발사 로켓의 모선 간섭현상 수치적 연구)

  • Kim, Young-Shin;Lee, Jae-Woo;Byun, Yung-Hwan;Park, Jun-Sang
    • Journal of the Korean Society for Aeronautical & Space Sciences
    • /
    • v.33 no.4
    • /
    • pp.17-26
    • /
    • 2005
  • Numerical investigation has been made on the aerodynamic characteristics of supersonic air-launching rocket, as a new concept launching mechanism. Parametric study on the variations of launching velocity, incident angle and mounting location of the rocket has been performed using three dimensional Euler equations. Influential factors at separating stage of the rocket were extracted through comprehensive analyses, and, the response surface models were constructed for those factors. From the study, the aerodynamic behavior of the air-launching rocket at supersonic speed and useful guidelines for the optimal mounting location of the rocket have been obtained.

Development of a Ship Calculation Program Based On the Geometric Model (형상모델 기반 선박계산 전산프로그램 개발)

  • Sang-Su Park;Kyu-Yeul Lee
    • Journal of the Society of Naval Architects of Korea
    • /
    • v.36 no.2
    • /
    • pp.121-134
    • /
    • 1999
  • In this paper, a ship calculation program is developed, which prof[nuts hydrostatics and volume calculation intact and damage stability and hull variation. Hull form and compartment geometry are expressed with NURBS curve wire-frame model. Hydrostatics and volume calculation are performed directly with the intersection method between section geometry and 3D planar surface. Equilibrium ship position is calculated with hydrostatic equilibrium equation which is linearized by 1st order Taylor series expansion sequentially. The developed program shows more accurate results and easy uses than the latter.

  • PDF

The Characteristic of Electric Field Penetration into Infinite Conducting Plane with an Aperture Due to HEMP Incidence (HEMP 파원에 의한 무한 도체 평판 개구의 침투 전계 특성)

  • Lim, Byoung-Jin;Jung, Sung-Woo;Cho, Byung-Doo;Kim, Ki-Chai
    • The Journal of Korean Institute of Electromagnetic Engineering and Science
    • /
    • v.21 no.12
    • /
    • pp.1454-1459
    • /
    • 2010
  • This paper presents the comparison of electric field penetration in Bell laboratories and IEC 61000-2-9 standard when HEMP source penetrates through an aperture in a planar conducting plane of infinite extent. HEMP electric field distributions assume in order to interpret this problem. Integral equation is derived and solved by Galerkin's method of moments for calculating the penetrating electric field. It is shown that penetrated electric field of IEC 61000-2-9 standard is greater than the Bell Laboratories waveform in resonance of lower frequency band, but those waveforms are similar in shape to frequency domain.

Limit Velocity for Lateral Stable Bed in Natural Curved Channels (자연하천 만곡부의 횡방향 안정하상을 위한 한계속도)

  • Choe, Jong-In
    • Journal of Korea Water Resources Association
    • /
    • v.35 no.2
    • /
    • pp.195-201
    • /
    • 2002
  • In this study, an equation is proposed to estimate the limit velocity for lateral stable bed in a curved channel stream. The stable bed on lateral direction is satisfied when there is no more deformation occurs on the transverse bed slope and non-scouring condition in a bend. A theoretical equation for limit velocity is derived using a transverse bed slope model. So, the limit velocity has its theoretical background in the equilibrium of two forces, lateral shear force at the bed due to longitudinal flow and the corresponding lateral bed shear force. To verify the equation, data from four natural river channels were used. There is good agreement between the calculated values using this equation and the measured values. The corrections in equation was found to be correlated with the averaged particle Froude number.

Chaos Control of the Pitch Motion of the Gravity-gradient Satellites in an Elliptical Orbit (타원궤도상의 중력구배 인공위성의 Pitch운동의 혼돈계 제어)

  • Lee, Mok-In
    • Journal of the Korean Society for Aeronautical & Space Sciences
    • /
    • v.39 no.2
    • /
    • pp.137-143
    • /
    • 2011
  • The pitch motion of a gravity-gradient satellite can be chaotic, depending on the ratio of mass moments of inertia and the eccentricity of the satellite orbit. For a precise prediction of motion, chaotic pitch motion has to be changed to non-chaotic motion. Feedback control can be used to obtain nonchaotic pitch motion. For chaos control and stabilization of the pitch motion of a gravity-gradient satellite, a feedback control system is designed, based on the linear nonautonomous system obtained by linearizing the nonlinear pitch motion. The control law obtained has two parameters and is applied to chaotic nonlinear pitch motion. The nonlinear control system satisfies the proposed control objectives in the range of the nonchaotic parameter space.

Dynamic Response and Control of Airship with Gust (외란이 작용하는 비행선의 동적 반응 및 제어)

  • Woo, G.A.;Park, I.H.;Oh, S.J.;Cho, K.R.
    • Journal of the Korean Society for Aeronautical & Space Sciences
    • /
    • v.30 no.6
    • /
    • pp.69-77
    • /
    • 2002
  • To acquire the dynamic response and design the controller of the airship, the longitudinal motion of the airship with respect to the vertical gust, which is the nonlinear system, was studied. The effects of the apparent mass and moment of the airship delay the dynamic response and the settling time, which are slower than those of conventional airplanes. The current object of the airship is designed to cruise at 500~1000m altitude. At that height, the atmospheric conditions are generally unstable by wind gust. In this paper, it has been studied for the case of vertical gust, since the apparent mass effects are dominant in has been studied for the case of vertical gust, since the apparent mass effects are dominant in that plane. In addition to the study of the dynamic responses of the airship, the controller was designed using the PID-controller. When the gust was applied, airship responses were recovered of equilibrium states. However, it takes too ling time for recovery and the speed of airship is reduced. So, the aim in this paper was to fasten the recovery speed and to get back the cruising velocity. The control parameters were determined from the stability mode analysis, and the control inputs were the thrust and the elevator deflection angle.

Reliability Analysis of Plane Stress Element According to Limit State Equations (한계상태방정식에 따른 평면응력요소의 신뢰성해석)

  • Park, Seok Jae;Choi, Wae Ho;Kim, Yo Suk;Shin, Yeong-Soo
    • Journal of Korean Society of Steel Construction
    • /
    • v.13 no.5
    • /
    • pp.567-575
    • /
    • 2001
  • In order to consider statistical properties of probability variables used in the structural analysis the conventional approach using the safety factor based on past experience usually estimated the safety of a structure Also the real structures could only be analyzed with the error in estimation of loads material characters and the dimensions of the members. But the errors should be considered systematically in the structural analysis Safety of structure could not precisely be appraised by the traditional structural design concept Recently new aproach based on the probability concept has been applied to the assessment of structural safety using the reliability concept Thus the computer program by the Probabilitstic FEM is developed by incorporating the probabilistic concept into the conventional FEM method. This paper estimated for the reliability of a plane stress structure by Advanced First-Order Second Moment method using von Mises, Tresca and Mohr-Coulomb failure criterions. Verification of the reliability index and failure probability of attained by the Monte Carlo Simulation method with the von Mises criterion were same as PFEM, but the Monte Carlo Simulation were very time-consuming. The variance of member thickness and load could influence the reliability and failure probability most sensitively among the design variables from the results of the parameter analysis. The proper failure criterion according to characteristic of materials must be used for safe design.

  • PDF

Equivalent Suspension Bridge Model for Tower Design of Multi-span Suspension Bridges (다경간 현수교 주탑 설계를 위한 등가 현수교 모델)

  • Choi, Dong-Ho;Na, Ho-Sung;Yi, Ji-Yop;Gwon, Sun-Gil
    • Journal of Korean Society of Steel Construction
    • /
    • v.23 no.6
    • /
    • pp.669-677
    • /
    • 2011
  • The multi-span suspension bridge generally has more than three towers and two main spans. To economically and effectively design a multi-span suspension bridge, the proper stiffness ratio of the center tower to the side tower must be determined. This study was conducted to propose a method of figuring out briefly the structural behavior of the towers in a multi-span suspension bridge. In the equivalent suspension bridge model, the main cable of the multi-span suspension bridge is idealized as an equivalent cable spring, and the external loads of horizontal and vertical forces that were calculated using the tensile forces of the main cable were applied on top of the towers. The equilibrium equations of the equivalent multi-span suspension bridge model were derived and the equations were solved via nonlinear analysis. To verify the proposed method, a sample four-span suspension bridge with a main span length of 3,000 m was analyzed using thefinite element method. The displacements and moment reactions of each tower in the proposed method were compared with the FEM analysis results. Consequently, the results of the analysis of the equivalent suspension bridge model tended to be consistent with the results of the FEM analysis.