• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.48 no.9
• /
• pp.691-701
• /
• 2020

An actuator mixer design using convex optimization technique situation where the propulsion system of an electric VTOL UAV during vertical take-off and landing maneuvers is proposed. The attainable control set to analyze the impact from failure of each motor and propeller can be calculated and illustrated using the properties of the convex function. The control allocation can be defined as a convex function optimization problem to obtain an optimal solution in real time. The mixer is implemented using a convex optimization solver, and the performance of the control allocation methods is compared to the attainable control set. Finally, the proposed mixer is compared with other techniques with nonlinear sux degree-of-freedom simulation.

• Proceedings of the KSR Conference
• /
• 2007.11a
• /
• pp.1610-1615
• /
• 2007

This paper presents a characteristics of linear induction motor considering airgap variation for railway transit in order to achieve high performance of the vehicle. The operating principle of a LIM(Linear induction motor) is identical to a rotary induction motor. Space-time variant magnetic fields are generated by the primary part across the airgap and induce the electro-motive force(EMF) in the secondary part, a conducting sheet. This EMF generates the eddy currents, which interact with the airgap flux and so produce the thrust force known as Loren's force. Even though the operating principal is exactly same as a rotary motor, the linear motor has a finite length of the primary or secondary parts and it causes static and dynamic end-effect which is the discontinuous airgap flux phenomenon. This end-effect causes the deterioration of the system performance, especially in high-speed operation. Another problem is that construction tolerance restricts the minimum airgap in order to prevent a collision between the primary part and the secondary reaction plate. More over, as the airgap length is getting smaller, the attraction force between the primary part and secondary parts is getting larger dramatically and the attraction force would be another friction against propulsion. Therefore, it is necessary to figure out the characteristics of linear induction motor considering airgap variation in order to achieve high performance of the vehicle. The dynamic model of LIM taking into account end-effects is derived. Then the modified mechanical load equation considering the effect of the attraction and thrust force according to the airgap variation is analyzed. The simulation results are presented to show the effect of the LIM according to the airgap variation.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.46 no.5
• /
• pp.393-401
• /
• 2018

Reliability prediction of an electronic arm fire device(EAFD) was studied which is applied to prevent accidental ignition in a solid rocket motor. For predicting the reliability, the main components of the EAFD were first defined(Control unit, LEEFI, TBI) and the operating principle of each component was analyzed. Performance modeling of each part is established using selected input variables through system analysis. When complex analysis is required, we approximated it with polynomial equation using response surface method. Monte-Carlo simulation is applied to performance modeling to estimate the design reliability.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.42 no.9
• /
• pp.745-751
• /
• 2014

For the multi-nozzle propulsion, the rupture pressure of nozzle closure has an effect on the initial strain rate of ignition. Moreover, the deviation of rupture pressure for each nozzle closure leads to side forces which can disturb the attitude control of rocket. When designed, it should be considered whether nozzle closures are ruptured equally and exactly in the intented pressure. In this paper, the rupture behavior is analyzed by analytical and experimental methods for plate and "+" notched nozzle closures. The rupture pressure and deviation for operating temperature, whether notched or not and notched directions are analyzed. This paper provides a comparison between rupture pressure prediction of finite elements method which tool is Abaqus/Explicit and results of the rupture test. Jonson-Cook shear failure model which corresponds to the damage initiation criterion were used in this simulation.

• Proceedings of the KSR Conference
• /
• 2008.06a
• /
• pp.1903-1908
• /
• 2008

This paper presents a characteristics of linear induction motor considering airgap variation for railway transit in order to achieve high performance of the vehicle. The operating principle of a LIM(Linear induction motor) is identical to a rotary induction motor. Space-time variant magnetic fields are generated by the primary part across the airgap and induce the electro-motive force(EMF) in the secondary part, a conducting sheet. This EMF generates the eddy currents, which interact with the airgap flux and so produce the thrust force known as Loren's force. Even though the operating principal is exactly same as a rotary motor, the linear motor has a finite length of the primary or secondary parts and it causes static and dynamic end-effect which is the discontinuous airgap flux phenomenon. This end-effect causes the deterioration of the system performance, especially in high-speed operation. Another problem is that construction tolerance restricts the minimum airgap in order to prevent a collision between the primary part and the secondary reaction plate. More over, as the airgap length is getting smaller, the attraction force between the primary part and secondary parts is getting larger dramatically and the attraction force would be another friction against propulsion. Therefore, it is necessary to figure out the characteristics of linear induction motor considering airgap variation in order to achieve high performance of the vehicle. The dynamic model of LIM taking into account end-effects is derived. Then the modified mechanical load equation considering the effect of the attraction and thrust force according to the airgap variation is analyzed. The simulation results are presented to show the effect of the LIM according to the airgap variation.

• Journal of the Korean Institute of Intelligent Systems
• /
• v.18 no.4
• /
• pp.482-487
• /
• 2008

In case of flooding, the underwater flight vehicle (UFV) executes the blowing by blowing ballast tanks off using high pressure air (HPA), while it also uses control planes and a propulsion unit to reduce the overshoot depth caused by a flooding and blowing sequence. However, the conventional whole HPA blow-off method lets the body on the surface after blowing despite slight flooding. This results in the unnecessary mission failure or body exposure. Therefore, it is necessary to keep the body at the near surface by the blowing control while reducing the overshoot depth. To solve this problem, an adaptive blowing control algorithm, which is based on the decomposition method expanding the expert knowledge in depth control and the adaptive method using fuzzy basis function expansion (FBFE), is proposed. To verify the performance of the proposed algorithm, the blowing control of UFV is performed. Simulation results show that the proposed algorithm effectively solves the problems in the UFV blowing control system online.

• Korean Journal of Remote Sensing
• /
• v.38 no.4
• /
• pp.343-353
• /
• 2022

An attempt to derive the surface temperature from the Korea Multi-purpose Satellite (KOMPSAT)-3A mid-wave infrared (MWIR) data acquired over the southern California on Nov. 14, 2015 has been made using the MODerate resolution atmospheric TRANsmission (MODTRAN) radiative transfer model. Since after the successful launch on March 25, 2015, the KOMPSAT-3A spacecraft and its two payload instruments - the high-resolution multispectral optical sensor and the scanner infrared imaging system (SIIS) - continue to operate properly. SIIS uses the MWIR spectral band of 3.3-5.2 ㎛ for data acquisition. As input data for the realistic simulation of the KOMPSAT-3A SIIS imaging conditions in the MODTRAN model, we used the National Centers for Environmental Prediction (NCEP) atmospheric profiles, the KOMPSAT-3Asensor response function, the solar and line-of-sight geometry, and the University of Wisconsin emissivity database. The land cover type of the study area includes water,sand, and agricultural (vegetated) land located in the southern California. Results of surface temperature showed the reasonable geographical pattern over water, sand, and agricultural land. It is however worthwhile to note that the surface temperature pattern does not resemble the top-of-atmosphere (TOA) radiance counterpart. This is because MWIR TOA radiances consist of both shortwave (0.2-5 ㎛) and longwave (5-50 ㎛) components and the surface temperature depends solely upon the surface emitted radiance of longwave components. We found in our case that the shortwave surface reflection primarily causes the difference of geographical pattern between surface temperature and TOA radiance. Validation of the surface temperature for this study is practically difficult to perform due to the lack of ground truth data. We therefore made simple comparisons with two datasets over Salton Sea: National Aeronautics and Space Administration (NASA) Jet Propulsion Laboratory (JPL) field data and Salton Sea data. The current estimate differs with these datasets by 2.2 K and 1.4 K, respectively, though it seems not possible to quantify factors causing such differences.

• Journal of Advanced Navigation Technology
• /
• v.28 no.4
• /
• pp.386-392
• /
• 2024

This paper constructs a precise dynamics model using flightlab, a specialized program for rotor modeling and performance analysis, to simulate urban air mobility (UAM). flightlab is well-suited for detailed modeling of UAM, particularly requiring detailed aerodynamic characteristics under high-altitude and urban wind conditions. The study focuses on implementing and analyzing a lift-cruise UAM model with distributed propulsion using flightlab. The lift-cruise model integrates motors for vertical take-off and fixed-wing flight. Given the limited specific examples of such UAM models in flightlab and challenges in evaluating with conventional fixed-wing or drone models, this research implements and verifies the lift-cruise model using matlab, comparing its performance against flightlab results to validate the modeling approach. This research aims to explore the potential of flightlab for detailed UAM modeling and contribute to technological advancements in future urban transportation.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.22 no.4
• /
• pp.611-620
• /
• 2021

The maintenance industry is mainly progressing based on condition-based maintenance after corrective maintenance and preventive maintenance. In condition-based maintenance, maintenance is performed at the optimum time based on the condition of equipment. In order to find the optimal maintenance point, it is important to accurately understand the condition of the equipment, especially the remaining useful life. Thus, using simulation data (C-MAPSS), a prediction model is proposed to predict the remaining useful life of a turbofan engine. For the modeling process, a C-MAPSS dataset was preprocessed, transformed, and predicted. Data pre-processing was performed through piecewise RUL, moving average filters, and standardization. The remaining useful life was predicted using principal component analysis and the k-NN method. In order to derive the optimal performance, the number of principal components and the number of neighbor data for the k-NN method were determined through 5-fold cross validation. The validity of the prediction results was analyzed through a scoring function while considering the usefulness of prior prediction and the incompatibility of post prediction. In addition, the usefulness of the RUL prediction model was proven through comparison with the prediction performance of other neural network-based algorithms.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.17 no.10
• /
• pp.600-608
• /
• 2016

This paper proposes a new high-efficient interleaved phase-shift full-bridge (PSFB) converter for low-voltage and high-current power systems. The proposed converter is composed of three switch-bridges and two transformers in the primary side and two rectifiers in the secondary side. Each transformer handles half of the total power with an interleaved operation, so that the proposed converter has high system reliability, as much as the conventional interleaved PSFB converter. The soft-switching characteristics of the proposed converter are better than those of the conventional converter due to the modulated primary side configuration. The proposed converter represents a single lagging-leg bridge, which has a poor soft switching condition in its operation, while the conventional converter has two lagging-leg bridges in its operation. Therefore, the number of switches having hard-switching conditions is reduced by half in the proposed converter. In addition, the reduced switch counts in the primary side of the proposed converter helps decrease the complexity of the proposed converter compared to that of the conventional converter. The operational principle and analysis are presented in this paper and the characteristics are verified using a PSIM simulation with 3kW server power specification.