• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.44 no.6
• /
• pp.492-501
• /
• 2016

Three-Loop autopilot is generally used for the acceleration control of guided missiles. Because the acceleration command to the three-loop autopilot is given as values at the center of gravity, feedback information of IMU should be obtained at the same position. However, the position of IMU might not be located at the center of gravity due to the sub-system assignment. This paper presents the stability analysis of three-loop autopilot with respect to the arbitrary position of IMU and variation rate of center of gravity. Gain and phase margins are calculated for several trim points for general anti-tank missiles.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.35 no.1
• /
• pp.29-34
• /
• 2022

In this paper, the floor acceleration for the seismic design of non-structural elements was evaluated using the core shape as a planar variable. Linear time history analysis using 20 models with 5 different planes and 4 different floors on each plane depending on the change in the shape (position and specific gravity) of the core in the square biaxially symmetric plane was performed. The analysis confirmed that the torsional amplification of the floor acceleration was up to 1.7 times in the plane subjected to eccentricity depending on the position of the core, and the effect of torsion was the greatest in the middle floor of the structure. In a plane where only the specific gravity of the core was changed without eccentricity, when the period was less than 0.4694 s, the maximum floor acceleration decreased in the lower floors and increased in the upper floors as the period increased. Conversely, when the period was 0.4694 s or more, it was confirmed that the floor acceleration increased in the lower part and decreased in the upper part as the period increased.

• Journal of The Korean Astronomical Society
• /
• v.46 no.1
• /
• pp.41-47
• /
• 2013

I present a simple scheme for the treatment of gravitational interactions on galactic scales. In anal- ogy with known mechanisms of quantum field theory, I assume ad hoc that gravitation is mediated by virtual exchange particles-gravitons-with very small but non-zero masses. The resulting den- sity and mass profiles are proportional to the mass of the gravitating body. The mass profile scales with the centripetal acceleration experienced by a test particle orbiting the central mass, but this comes at the cost of postulating a universal characteristic acceleration $a_0{\approx}4.3{\times}10^{-12}msec^{-2}$ (or $8{\pi}a_0{\approx}1.1{\times}10^{-10}msec^{-2}$). The scheme predicts the asymptotic flattening of galactic rotation curves, the Tully-Fisher/Faber-Jackson relations, the mass discrepancy-acceleration relation of galaxies, the surface brightness-acceleration relation of galaxies, the kinematics of galaxy clusters, and "Renzo's rule" correctly; additional (dark) mass components are not required. Given that it is based on various ad-hoc assumptions and given further limitations, the scheme I present is not yet a consistent theory of gravitation; rather, it is a "toy model" providing a convenient scaling law that simplifies the description of gravity on galactic scales.

• Journal of the Korea Society of Computer and Information
• /
• v.19 no.5
• /
• pp.43-52
• /
• 2014

In this paper, we propose Gravity Removal and Vector Rotation algorithm for counting steps of wearable device, and we evaluated the proposed GRVR algorithm with Micro-Electro-Mechanical (MEMS) 3-axis accelerometer equipped in low-power wearable device while the device is mounted on various positions of a walking or running person. By applying low-pass filter, the gravity elements are canceled from acceleration on each axis of yaw, pitch and roll. In addition to DC-bias removal and the low-pass filtering, the proposed GRVR calculates acceleration only on the yaw-axis while a person is walking or running thus we count the step even if the wearable device's axis are rotated during walking or running. The experimental result shows 99.4% accuracies for the cases where the wearable device is mounted in the middle and on the right of the belt, and 91.1% accuracy which is more accurate than 83% of commercial 3-axis pedometer when worn on wrist for the case of axis-rotation.

• Proceedings of the IEEK Conference
• /
• 2003.07c
• /
• pp.2725-2728
• /
• 2003

The manipulability of robot provides useful Information for the design and path planning of robots. This paper shows an influence of joint velocities to acceleration of robot end-effector using a dynamic manipulability polytope. The main idea of this paper is that the dynamic manipulability polytope of robot can be divided to three intermediate polytope, the torque-dependant polytope, velocity-dependent polytope, and gravity-dependant polytope. The velocity-dependant polytope is made from the limits of robot joint velocities while the torque-dependant polytope is made from the limits of the joint torques. Combining of these two intermediate polytopes and considering the gravity-dependant polytope, the overall dynamic manipulability polytope of robot is obtained. This investigation will be useful on the field of space robot and high-speed application.

• Proceedings of the Earthquake Engineering Society of Korea Conference
• /
• 2002.09a
• /
• pp.75-82
• /
• 2002

The Mononobe-Okabe method is generally used to evaluate the dynamic earth force for the seismic design of retaining walls. However, the Mononobe-Okabe method does not consider the effects of the dynamic interactions between the backfill soil and the wall. In fact, a phase difference exists between the inertia force and the seismic earth pressure. In this study, shaking table tests were peformed on gravity walls retaining dry backfill sand to analyze the influence of several parameters (the unit weight of the wall, the input acceleration and base friction) on the development of the seismic earth pressure. The experiments revealed that the magnitude of the inertia force mobilized during seismic loading affected the seismic earth pressure. The difference in the phase angles between the inertia force and the seismic earth pressure was retained at 180 degrees before the wall failed but its magnitude changed significantly as the wall began to fail.

• Economic and Environmental Geology
• /
• v.32 no.6
• /
• pp.653-660
• /
• 1999

Any mechanical system has a natural oscillation which can be excited, and the earth is no exception. The earth can oscillate in an indefinite number of normal modes of oscillation, rather like a giant bell. The various free modes are generally sparated into two categoridal modes and toroidal modes. Clearly the toroidal modes will produce no perturvation of the gravity field and no vertical acceleration on the surface of the earth. Hence only spheroidal modes can be detected with a gravimeter. EarthTide gravimeter was installed at AIMST in order to observe free modes of the earth. Eight major earthquakes including chinese earthquake (magnitude 7.3) with free oscillations of the earth are observed during one year (1998. 8. 1∼1999.7.31). And then the earth tides components were eilminated from earthquake records using a numerical Butterworth highpass filter. Spectral analysis of gravity readings repersent that 48 observations of shheroidal modes. The relationships between instrumental observations and theoretical predictions based on the Gutenberg earth model agree well those resulting from free oscillation in Korea.

• Journal of the Korean Society for Precision Engineering
• /
• v.33 no.10
• /
• pp.789-796
• /
• 2016

The weight of an antenna system pointing satellite on the mobile platform is restricted by the weight limit of the mobile platform. The maximum power of the actuator driving the antenna system is thus limited because a high power actuator needs a heavier weight. Thus, a drive system is designed to have a low torque requirement by reducing the gravitational torque depending on gravity or acceleration of the mobile platform, including vibration, shock, and accelerated motion. To reduce the gravitational torque, the mathematical model of the gravitational torque is preferentially obtained. However, the method to directly estimate the mathematical model in an antenna system has not previously been reported. In this paper, a method is proposed to estimate the gravitational torque as a mathematical model in the antenna system. Additionally, a method is also proposed to calculate the optimal weight of the balancing weight to compensate for the gravitational torque.

• Proceedings of the Korean Society of Coastal and Ocean Engineers Conference
• /
• 2003.08a
• /
• pp.10-17
• /
• 2003

Acoustic and pressure type seabed installed wave sensors have advantage in observing long period infra-gravity wave and tsunami, while buoy type wave gauges which measure acceleration of the moored buoy motion are not able to detect long period waves. That's why most of the Japanese coastal wave observation sensors are seabed installed typed ones. Nationwide Japanese coastal wave observation systems with seabed installed sensors are gradually clarifying long-period tsunami profiles and infra-gravity wave characteristics (Nagai.et.al., 1996, 1997,2000,2002a,2002b). (omitted)

• Journal of Drive and Control
• /
• v.13 no.1
• /
• pp.49-53
• /
• 2016

The accurate calculation of bucket tip position has a large influence on showing the motion of an excavator on the display device of the excavator and controlling the excavator automatically. It is generally known that Inertial Measurement Unit (IMU) sensors are more accurate than accelerometer-based sensors while the boom, arm or bucket moves because additional forces beyond gravity add additional acceleration to the sensors. To prove the accuracy difference between the two types of sensors, a position recognition system using an accelerometer-based sensor and an IMU sensor is implemented on the excavator. The experimental results show that the system using the IMU sensor significantly reduces the position recognition error while bucket moves and additional force beyond gravity exists.