• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2002.04a
• /
• pp.10-13
• /
• 2002

Pogo is the instability resulting from the interaction between rocket structure and propulsion system of liquid propellant rocket. The coupling of structure and propulsion system can lead to severe problem in rocket. For the analysis of pogo, a time-invariant linearized mathematical model is developed for a selected flight time. Propulsion system is modeled using element representations for each components. The constitutive equation of propulsion system is a homogeneous second-order equation form in the Laplace domain. Rocket structure is modeled using FEM. From the results of modal analysis of structure, the behavior of structure can be represented. System equations for coupling structure and propulsion system are composed of all propulsion system equations and vehicle motion equations reacting on the vehicle by each component of propulsion system. The stability is obtained by the eigen solution of system matrix. The optimization of the design variables such as size, place of accumulator for suppressing pogo instability is carried out. This article of study can be used to determine the degree of stability, and guide the design of pogo suppression system.

• Journal of Astronomy and Space Sciences
• /
• v.20 no.4
• /
• pp.365-374
• /
• 2003

Satellite formation flying is currently an active area of research in the aerospace engineering. So it has been researched by various authors. In this study, a tracking controller using sliding mode techniques was designed to control a satellite for the satellite formation flying. In general, Hill's equations are used to describe the relative motion of the follower satellite with respect to the leader satellite. However the modified Hill's equations considering the $J_2$ perturbation were used for the design of sliding mode controller. The extended Kalman filter was applied to estimate the state vector based on the measurements of relative distance and velocity between two satellites. The simulation results show that the follower satellite tracks the desired trajectory well by thruster operations based on the sliding mode control law.

• Proceedings of the KSME Conference
• /
• 2000.04b
• /
• pp.580-585
• /
• 2000

Recently TEIS model, Two-zone model aid Stanitz equations are often used for off-design performance prediction of centrifugal compressor and pump. The prediction results often agree well with experimental data. However these models and equations have some important variables which have a great influence on overall performance prediction me. But no systematic study about these variables has been performed. So, in this paper, a systematic study about these variables influence on overall performance prediction owe is peformed. Finally the meaning of the variables and the research to be undertaken are discussed.

• Proceedings of the Korean Geotechical Society Conference
• /
• 2002.03a
• /
• pp.397-404
• /
• 2002

The bearing capacity of open-ended piles is affected by the degree of soil plugging, which is quantified by the IFR. There is not at present a design criterion for open-ended piles that explicitly considers the effect of IFR on pile load capacity In order to investigate this effect, model pile load tests using a calibration chamber were conducted on instrumented open-ended piles. The results of these tests show that the IFR increases with increasing relative density and increasing horizontal stress of soils. The unit base and shaft resistances decrease with increasing IFR. Based on the results of the model pile tests, new empirical relations for base load capacity and shaft load capacity of open-ended piles are proposed. In order to check the accuracy of predictions made with the proposed equations, the equations were applied to the full-scale pile load test preformed in this study, Based on the comparisons with the pile load test results, the proposed equations appear to produce satisfactory predictions.

• 제어로봇시스템학회:학술대회논문집
• /
• 1990.10a
• /
• pp.653-657
• /
• 1990

Since linearized equations of notion have much modelling errors, robust controller for disturbances and noises Is necessary for autopilot. In this paper, notion equations for underwater vehicle with six degree-of-freedom are derived and linearized. And robust autopilot for this system is designed by using LQG/LTR methodology.

• Journal of Biosystems Engineering
• /
• v.18 no.4
• /
• pp.344-350
• /
• 1993

The purpose of this study is to develop design equations to calculate optimum specifications and dimensions such as weight, engine horsepower, etc. of the tractor necessary to perform stable rotary tillage. The main results of this study are as follows. 1. A wheel-lug ought to receive a special resistance in downward direction which resists the lug's upward motion on wet sticky soil surface. The authors introduce a new academic name of the "lift resistance(上昇抵抗力, 상승저항력)" for such a force which resists retraction of a wheel lug from the soil in the upward trochoidal motion. This force is composed of the frictional force acting on the trailing and the leading lug side, and the "perpendicular adhesion(鉛直付着力, 연직부착력)" acting on the lug face and the undertread face on adhesive soil. 2. The "lift resistance ratio(上昇抵抗力係數, 상승저항력계수)" and the "perpendicular adhesion ratio(鉛直付着力係數, 연직부착력계수)" were defined, which are something similar to the definition of the motion resistance ratio, the traction coefficient, etc. 3. The design equation of the optimum weight of a rotary tiller mounted on the tractor derived by calaulating the forces acting on the rotary blades. 4. The design equations to calculate optimum specifications and dimensions such as weight, engine horsepower, etc. of the tractor necessary to perform stable rotary tillage were derived. It becomes clear that the optimum weight of a rotary tiller and a tractor can be estimated in planning design by means of putting about 21 design factors of the target into the equation. These equations are useful for planning design to estimate the optimum dimensions and specifications of a rotary tiller as well as a tractor by the use of known and/or unknown design parameters.

• Journal of the Korean Geotechnical Society
• /
• v.18 no.4
• /
• pp.199-206
• /
• 2002

The bearing capacity of open-ended piles is affected by the degree of soil plugging, which is quantified by the incremental filling ratio, IFR. However, most design criteria for open-ended piles do not consider the variation of pile bearing capacity with IFR. In this study, new design equations for calculating the pile base and shaft load capacities, based on IFR value of the pile, were proposed using the results of model pile tests. A full-scale pile load test was also conducted on fully instrumented open-ended pile driven into gravelly sand. The IFR for the pile was continuously measured during pile driving. In order to check the accuracy of predictions made with the proposed equations, the equations were applied to two examples, including the pile load test preformed in this study. Based on the comparisons with the pile load tests results, the proposed equations appear to produce satisfactory predictions.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.18 no.8
• /
• pp.895-903
• /
• 2007

Design equations of DC blocks terminated in arbitrary impedances are newly suggested and a microstrip DC block is tested for the perfect matching. The DC block is a two-port passive component and the power excited at a port is transmitted into another port. However, all the excited power at the input can not be delivered to the output and therefore most of the conventional DC blocks can not be perfectly matched with arbitrary termination impedances. To solve the matching problem, its one-port equivalent resonant circuit model, front which design equations can be derived, is newly suggested. Using the derived design equations, any DC block can be designed, perfectly matched without any restriction of coupling coefficients. To verify the derived design equations, measurements were carried out and the results are in good agreement with prediction, showing insertion and return losses at 4.1 GHz are 0.82dB and -31dB, respectively.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.13 no.5
• /
• pp.142-151
• /
• 2005

To predict the fatigue life of the Hub Bearing Unit(HBU), preload effect and initial axial clearance have to be considered. Various theory and equations for the HBU design used in the passenger car are well developed in many literatures. But most design hand book for bearings or bearing catalogues do not consider the initial axial clearance and preload effect. So there are limits and difficulties to use those data in actual bearing design. To consider the preload effect and initial axial clearance, complex elliptic integrals and nonlinear equations are involved. These equations are difficult to solve during the design process. In order to solve these problems effectively, a program is developed to solve these equations reliably and to help the designer in obtaining the performance data of the HBU such as load distribution, maximum contact stress and fatigue life. The preprocessor of the program helps users to prepare the input data through a dialog box and the post processor makes graphical presentation of the result. In this paper, theoretical and numerical background for the prediction of the fatigue life of the HBU is explained. A simple example is presented to show the usefulness of developed program.

• Journal of Korean Society of Steel Construction
• /
• v.25 no.2
• /
• pp.165-178
• /
• 2013

This paper presents a research work for the evaluation of the nominal flexural strength of composite girders in positive bending region. Current predicting equations for the nominal flexural strength of composite girders in the 2012 version of the Korea Bridge Design Codes based on Limit State Design Method are able to apply for the composite girders with conventional structural steels. For applying composite girders with high yield strength steels of HSB800 as well as HSB600, there is a need for improving the current predicting equations. In order to investigate the nominal flexural strength of composite girders, previous research works are carefully reviewed and parametric study using a moment-curvature analysis program is conducted to evaluate the ultimate moment capacity and the ductility of a wide range of composite girders. Based on the results of the parametric study, less conservative nominal flexural strength design equations are proposed for conventional composite girders. In addition, new design equations for predicting the nominal flexural strength of composite girders with HSB600 and HSB800 high-performance steels are provided.