• Journal of Positioning, Navigation, and Timing
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• v.8 no.3
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• pp.107-117
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• 2019

When a vehicle moves with a high rotation rate, it is not easy to measure the angular velocity using an off-the-shelf gyroscope. If the angular velocity is estimated using the extended Kalman filter in the gyro-free inertial navigation system, the effect of the accelerometer error and initial angular velocity error can be reduced. In this paper, in order to improve the navigation performance of the gyro-free inertial navigation system, an angular velocity estimation method is proposed based on an extended Kalman filter with an accelerometer random bias error model. In order to show the validity of the proposed estimation method, angular velocities and navigation outputs of a vehicle with 3 rev/s rotation rate are estimated. The results are compared with estimates by other methods such as the integration and an extended Kalman filter without an accelerometer random bias error model. The proposed method gives better estimation results than other methods.

• Advanced Composite Materials
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• v.18 no.4
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• pp.381-394
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• 2009

The kinetics of centrifugal infiltration of fibrous tubular preform is built theoretically, and simulations are conducted to study the effects of various casting conditions on infiltration kinetics and macrosegregation by combining with the energy, mass and kinetic equations. A similarity way is used to simplify the one-dimensional model and the parameter is ascertained by an iterative method. The results indicate that the increase of superheat, initial preform temperature, porosity tends to enlarge the remelting region and decrease copper solute concentration at the infiltration front. Higher angular velocity leads to smaller remelting region and solute concentration at the tip. The pressure in the infiltrated region increase significantly when the angular velocity is much higher, which requires a stronger preform. It is observed that the pressure distribution is mainly determined by the angular velocity, and the macrosegregation in the centrifugal casting is greatly dependent on the superheat of inlet metal matrix, initial temperature and porosity of the preform, and the angular velocity.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1996.11a
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• pp.1017-1022
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• 1996

This paper presents results of dynamic analysis of the missile initial motion arising from the missile detent force. Using ADAMS (Automatic Dynamic Analysis of Mechanical System) software, a non-linear 46-DOF (Degree of Freedom) model is developed for the launcher system including missile and launch tube contact problem. From the dynamic analysis, it is found that initial angular velocity of the missile increases when the missile detent force increases (more than 18 g) and also rocket exhaust plume is taken into account. To achieve the missile launching s ability, it needs to reduce the missile initial detent force and exhaust plume area of the launcher. Results of the dynamic analysis on the system natural frequency agree well with those obtained from experimental modal tests. The overall results suggest that the proposed method is a useful tool for prediction of initial missile stability as well as d :sign of the missile launcher system.

• Journal of the Korean Society for Precision Engineering
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• v.4 no.4
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• pp.56-71
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• 1987

Determination of navigation variables (latitude, longitude, and altitude) near the earth's surface is termed 'Terrestrial Navigation'. The quantities that are measured inertially are the total acceleration (or the integral fo this acceleration over a fixed time interval) and the total angular rate (or the integral of this angular rate over the same time interval). These measurements when suitably compensated can be manipulated to yield the navigation variables. Hence, it is essential that the initial values of position, orientation and velocity are accurately set up during the initial alignment process. Initial alignment of gimballed inertial navigation system ( GINS) is accomplished by gyrocompassing techniques. These cannot be used, in the case of strapdown inertial navigation system(SDINS), where the inertial instruments are directly strapped down to a vehicle frame. The basic objective of this paper is the development of digital method for the determination of the initial axes erection of a SDINS from vibration and sway currupted data on the launch pad.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.4 no.3
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• pp.245-253
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• 2006

A test of the 1/3 scale model was conducted to verify the tip-over analysis of a dry. concrete storage cask under a hypothetical accident condition. The tip-over analysis was executed using the velocity at each point as the initial conditions of the model just before the impact. The initial velocity was determined from the initial angular velocity, which would make the equivalent kinetic energy to the potential energy. To confirm the structural integrity of the canister, the visual testing and the non-detective testings such as Liquid Penetrant testing and Ultrasonic Testing were conducted. The lid of a storage cask was plastically deformed near the impact point. The structural integrity of storage cask was maintained. To verify the tip-over analysis the strains and the accelerations acquired by the tip-over test were compared with those by the analyses. The results of the analysis were larger than the test results about two times.

• The Bulletin of The Korean Astronomical Society
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• v.36 no.1
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• pp.54.2-54.2
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• 2011

It is the conventional wisdom that the Poynting-Robertson effect is essentially the outcome of the interplay between absorption and reemission processes. For a better understanding of the motion of charged particles around a compact star with strong radiation, we reached an alternative interpretation for the Poynting-Robertson effect based on the covariant formalism and found that it is attributed to the combination of the aberration and the Lorentz transformation of the radiation stress-energy tensor. As a general relativistic application of the Poynting-Robertson effect, we studied the dynamics of test particles around the spinning relativistic star with strong radiation. We discovered that the combination of the angular momentum and the finite size of the star generates "radiation counter drag" which exerts on the test particle to enhance its specific angular momentum, contrary to the radiation drag. The balance of the radiation drag and the radiation counter drag renders the particle to hover around the spinning luminous star at the "suspension orbit". The radial position and the angular velocity of the particle on the "suspension orbit" are determined by the angular momentum, the luminosity, and the size of the central star only, and they are independent of the initial position and velocity of the particle.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.21 no.4
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• pp.688-697
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• 2017

It is very difficult to solve mathematically the optimal control problem for non - linear mobile robots to move to target points with minimum energy related to velocity, acceleration and angular velocity in minimum time. This paper proposes a method to obtain optimal control gains with which mobile robots move with minimum energy related to velocity, acceleration and angular velocity in minimum time using genetic algorithms. Mobile robots are non - linear systems so that their optimal control gains depend on initial positions. Hence initial positions are divided into some partition points and optimal control gains are obtained at each partition point with genetical algorithms. These optimal control gains are used to train neural networks that generate proper control gains at arbitrary initial position. Finally computer simulation studies have been conducted to verify the effectiveness of the method proposed in this paper.

• Korean Journal of Applied Biomechanics
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• v.24 no.1
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• pp.67-74
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• 2014

This study researched into the left-right inclination of the rear foot at the lower limb joints, knee joint angle, angular velocity of the knee joint, angular acceleration and the max. Based on the analysis of kinematics according to the changes in the height of step box (6, 8, 10 inches) during step aerobics of female college students majoring in physical education. The findings of this study are as follows: Then angle of the knee joint decreased as the height of the step box increased the min. Angle was measured right before the right foot was on the step box, and the angle tended to decrease as the step box get heightened. The left-right inclination of the rearfoot angle according to the height of step box increased as the height increased. In the 'pull-up' stage during which the weight was loaded on the right foot the angle increased, while in the right foot stepping stage during which the right foot was on the ground, the left-right inclination of the rearfoot angle increased as the height of the step box increased. The angular velocity of the knee joint according to the height of step box started increasing when the right foot initially stepped on the step box and during the initial stepping section, the angular velocity decreased as the height of step box increased. The changes in angular acceleration of the knee joint according to the height of step box increased as the height of step box increased.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.8 no.3
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• pp.413-422
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• 1996

Freezing of water in von-$K{\acute{a}}rm{\acute{a}}n$ swirling flow is considered. The transient behavior of the temperature distribution in both solid and liquid phases and freezing rate are determined. The fluid flow induced by the rotation of solid strongly inhibits the freezing process. The thickness of frozen layer is inversely proportional to the square root of the angular velocity of solid. As the angular velocity or initial liquid temperature becomes larger, the freezing process is more strongly inhibited by the fluid flow. When phase change is present, the transient heat transfer rate is greater than the case with no phase change.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.4
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• pp.525-540
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• 1997

The effect of mold rotation on the transport process and resultant macrosegregation pattern during solidification of an Al-Cu alloy contained in a vertical axisymmetric annular mold cooled from the inner wall is numerically investigated. The mold initially at rest starts to rotate at a prescribed angular velocity simultaneously with the beginning of cooling. Computed results for a representative case show that the mold rotation essentially suppresses the development of both thermal and solutal convections in the melt, creating distinct characteristics such as the liquidus front, flow pattern and temperature distribution from those for the stationary mold. Thermal convection which develops at the early stages of cooling is soon extinguished by the rotating flow induced during spin-up, and thus does not effectively remove the initial superheat from the melt. On the other hand, solutal convection, though it weakens considerably and is confined within the mushy zone, still predominates over the solute redistribution process. With increasing the angular velocity, the solute transport in the axial direction is enhanced, whereas that in the radial direction is reduced. The final macrosegregation formed in the mold rotating at moderate angular velocities appears to be favorable in comparison with the stationary casting, in that not only relatively homogenized composition is achieved, but also a severely positive-segregated channel is restrained.