• Journal of Drive and Control
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• v.18 no.4
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• pp.59-64
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• 2021

In this paper, a mathematical pressure dynamics model for a variable thrust solid propulsion system with an electric actuator was derived from the mass conservation of gas. To solve the problem induced by modeling uncertainties in the propellant model and the dead zone of the actuator, a nonlinear pressure controller combined with a nonlinear disturbance observer was designed using a mathematical model of the system. The simulation results showed that the proposed pressure controller could reduce tracking errors compared to another conventional nonlinear controller even in situations where input disturbances were present.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.11a
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• pp.116-121
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• 2011

Performance of Secondary Injection Thrust Vector Control system is investigated under various secondary injection operating conditions. 3-dimensional converging-diverging nozzle having 8 secondary injection nozzles is used in this numerical study. Total pressure of flow inside the nozzle is about 70bars, and total temperature set to 300K for cold flow simulation. Effect of secondary injection flow rate and injection nozzle configuration is considered in this research. Simulation is conducted with commercial CFD code Ansys Fluent v13. Spalart-Allmaras(1-equation)model is used for turbulence modeling with AUSM+ scheme. Various performance factors as Axial thrust, side force, system specific impulse ratio are considered and explained for system performance evaluation.

• Journal of the Korean Society for Aviation and Aeronautics
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• v.30 no.4
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• pp.57-64
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• 2022

A study on propllers for unmaned aerial vehicles is conducted using the open softwares. Since the shape of the propeller is closely related to the thurst characteristics of the propulsion system, adopting an appropriate propeller will significantly reflect stable aerodynamic performances. In this study, propellers for unmanned aerial vehicles were modeled by using OpenVSP and Propel for comparison, the thrust characteristics according to the number of blades and the diameter of the propeller were analyzed. In addition, the tendency of thrust characteristics according to various propeller pitch angles was confirmed. Based on the analysis results of this study, the applicability of the propeller shape to the design of the unmanned aerial vehicle was confirmed. It is shownthat the analysis results of this study can be utilized when modeling the propeller shape in research such as a conceptual design of unmanned aerial vehicle. In this case, it should be noted that OpenVSP does not involve the viscous effect of air.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.13 no.6
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• pp.480-489
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• 1988

Although CDP stacking of common depth gathering is used to get the zero-offset-section, the exploding reflector concept is examined for the modeling of zero source to receiver offset sections in this paper. The acoustic wave equation is compared with a one way wave equation which represents the upgoing wave field only. The one way wave equation used is not derived through an expansion and, therefore, can represent dips up do 90b degrees and may not lost the signals by the dipping angles. There is apparently no simple counterpart of this equation is the space domain and it can be conveniently implemented only by a Fourier method. This paper compares their modeling technique with ray tracing and wave method for over thrust structure which is one of the geological structures are dificult to process and interpret. As a result of modeling much clean and accurate signals, especially, diffractions form the corner and dipping angles can be gathered.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.20 no.4
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• pp.355-360
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• 2010

In this study, a modeling process of a 3-axis planar alignment stage is suggested. Vibration tests using a laser vibro-meter is performed to find the modeling parameters of the stage. By analyzing the result of the test, the stiffness of prismatic joints and revolute joints, as well as the contact conditions of the thrust bearings, can be calculated. The modeling of the stage was validated by comparing six normal mode shapes, which are acquired from experiments and simulations.

• Journal of Korean Association for Spatial Structures
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• v.20 no.2
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• pp.95-104
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• 2020

Phaya-Thon-Zu temple has a unique architectural style connected by the three temples, and cultural values are highly as murals remain on some of the walls. However, various damages in internal walls and vaults have occurred due to earthquake and environmental influences. In order to analyze these damages, accurate structural analysis is required, but structural modeling is difficult, because Phaya-Thon-Zu temple is the complex masonry structure which is stacked with small bricks. Therefore, this study intends to analyze the causes of damages by examining collapse mechanism for cross section and longitudinal section of vaults in the entrance hall and shrine by using thrust line analysis, which is a geometric method, and to compare it with the actual damage situation.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.29 no.3
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• pp.127-133
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• 2017

Performance analysis has been carried out on a high side scroll compressor that had a fixed scroll equipped with a circular oil groove on its thrust surface. Oil was supplied to the oil groove through an intermittent opening from a high pressure oil reservoir formed inside the orbiting scroll hub. Oil in the groove was then delivered to both suction and back pressure chambers by pressure differentials and viscous pumping action of the orbiting scroll base plate. Mathematical modeling of this oil groove system was incorporated into a main compressor performance simulation program for an optimum oil groove design. The study findings were as follows. Pressure in the oil groove can be controlled by changing its configuration and the oil passage area. With an enlarged oil passage, the pressure in the oil groove heightens due to an increased flow rate, but the pressure elevation in the back pressure chamber is small, resulting in reduced friction loss at the thrust surface between the two scrolls. On the other hand, by increasing the oil passage area, the oil content in the refrigerant flow increases. Considering all these factors, the energy efficiency ratio could be improved by about 3.6% under the ARI condition by an optimal oil groove design.

• Proceedings of the KIEE Conference
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• 2009.04b
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• pp.41-43
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• 2009

This paper deals with determination of parameters of permanent magnet linear synchronous machine(PMLSM) for high thrust and improvement of speed performance. To satisfy these characteristics, PMLSM with double-sided PM mover and slotless ring-winding stator is presented. And using multilaver method, this paper analyzes the electromagnetic field phenomena and estimates parameters such as back-EMF and thrust constant. These parameters are used to derive DC link voltage of voltage source inverter with space vector pulse width modulation(SVPWM) using a digital signal processor and encoder pulse signal. The DC link voltage is one of the most important factor for accurate design. It enables to determinate dynamic operating range of system. Hence, performance evaluation is performed through dynamic modeling. Finally, in this paper, dynamic characteristics according to DC link voltage are presented as experiment result.

• Geomechanics and Engineering
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• v.37 no.3
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• pp.197-211
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• 2024

This research studies the effect of geotechnical factors on EPB-TBM performance parameters. The modeling was performed using simple and multivariate linear regression methods, artificial neural networks (ANNs), and Sugeno fuzzy logic (SFL) algorithm. In ANN, 80% of the data were randomly allocated to training and 20% to network testing. Meanwhile, in the SFL algorithm, 75% of the data were used for training and 25% for testing. The coefficient of determination (R²) obtained between the observed and estimated values in this model for the thrust force and cutterhead torque was 0.19 and 0.52, respectively. The results showed that the SFL outperformed the other models in predicting the target parameters. In this method, the R² obtained between observed and predicted values for thrust force and cutterhead torque is 0.73 and 0.63, respectively. The sensitivity analysis results show that the internal friction angle (φ) and standard penetration number (SPT) have the greatest impact on thrust force. Also, earth pressure and overburden thickness have the highest effect on cutterhead torque.

• Proceedings of the KIEE Conference
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• 2009.07a
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• pp.724_725
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• 2009

This paper deals with control parameters deduction and dynamic analysis of hybrid thrust magnetic bearing(HTMB). The flux density at air-gap is obtained from system modeling which considers permanent magnet and electro magnet. The vertical force is derived from flux density using maxwell's stress tensor. An accurate linear model is obtained by using linear approximations of the attraction force around the nominal equilibrium point. The dynamic simulation of the HTMB using the PD controller is conducted and control parameters are deducted.