• Journal of the Korean Society of Propulsion Engineers
• /
• v.21 no.6
• /
• pp.64-72
• /
• 2017

The longitudinal dynamic instability which can occur in the fueling process of a space launch vehicle is called pogo. It is caused by coupling between the fuselage and propulsion system and they would be formed as a closed-loop system. so that the amplitude of the response may increase or decrease. In this paper, a mathematical model which is applicable to the systematic pogo analysis of a general launch vehicle is developed for an example of space shuttle. The formulations are composed of the linearized second-order differential equation for the propulsion system, and of the pressure, weight displacement, and generalized displacement. Those are important parameters for pogo analysis, are derived through eigenvalue analysis. By the formulation suggested in this paper, it is expected that mathematical modeling method of the pogo system can be obtained and systematic pogo stability analysis for any launch vehicle will be enabled.

• Journal of the Korean Society of Propulsion Engineers
• /
• v.2 no.3
• /
• pp.99-106
• /
• 1998

The performance of the turbofan engine, a medium scale civil aircraft which has been developing in Rep. of Korea, was analyzed and the control scheme for optimization the performance was studied. The dynamic and real-time linear simulation was performed in the previous study The result was that the fuel scedule of the step increase overshoot the limit temperature(3105 $^{\cire}R$) of the high pressure turbine and got small surge margine of the high pressure compressor. Therefore a control scheme such as the LQR(Linear Quadratic Regulator) was applied to optimizing the performance in this studies. The linear model was expected for designing controller and the real time linear model was developed to be closed to nonlinear simulation results. The system matrices were derived from sampling operating points in the scheduled range and then the least square method was applied to the interpolation between these sampling points, where each element of matrices was a function of the rotor speed. The control variables were the fuel flow and the low pressure compressor bleed air. The controlled linear model eliminated the inlet temperature overshoot of the high pressure turbine and obtained maximum surge margins within 0.55. The SFC was stabilized in the range of 0.355 to 0.43.

• Journal of the Korea Society of Computer and Information
• /
• v.16 no.7
• /
• pp.105-115
• /
• 2011

In Vision-based Intelligent Transportation System(ITS) the segmentation of road region is a very basic functionality. Accordingly, in this paper, we propose a region segmentation method using adaptive pattern extraction technique to segment road regions and sky regions from original images. The proposed method consists of three steps; firstly we perform the initial segmentation using Mean Shift algorithm, the second step is the candidate region selection based on a static-pattern matching technique and the third is the region growing step based on a dynamic-pattern matching technique. The proposed method is able to get more reliable results than the classic region segmentation methods which are based on existing split and merge strategy. The reason for the better results is because we use adaptive patterns extracted from neighboring regions of the current segmented regions to measure the region homogeneity. To evaluate advantages of the proposed method, we compared our method with the classical pattern matching method using static-patterns. In the experiments, the proposed method was proved that the better performance of 8.12% was achieved when we used adaptive patterns instead of static-patterns. We expect that the proposed method can segment road and sky areas in the various road condition in stable, and take an important role in the vision-based ITS applications.

• Journal of the Korea Convergence Society
• /
• v.8 no.9
• /
• pp.365-372
• /
• 2017

Squat exercise is one of the important free weight exercises that can safely and effectively expect the athletic performance by establishing the rationale. Therefore, it is necessary to study the side effects caused by incorrect exercise, scientific countermeasures and to develop a exercise estimation model. It is effective and accurate to use a variety of assistive devices to calibrate athletic posture. The issues of the structural analysis for designing a foot plate for squat exercise is to model the behavior by the dynamic behavior. It should be consider that the center of gravity of each segmented body is different when the maximum load is applied. It is applied to complete system design through simulation method with kinematic dynamic, ground reaction force and load analysis for the free weight exercise equipment, VR device, and safety foot plate. In this paper, the authors propose the design method for the vertical load distribution applied in the design of the foot plate used for the squat exercise mechanism, and based on these results, design make the more safe and reliable free weight exercise equipment system.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.16 no.5
• /
• pp.3548-3556
• /
• 2015

In order to fulfill the needs of reliable and economically feasible foundation, engineers should consider not only the working load that can endure extreme conditions but also apprehending precise behavior of continuous dynamic load while designing the foundation of offshore wind power generators. To actualize the foundation, a model pile was made in miniature. Also, calibration chamber was made and a 500mm height of sand-bed was made to perform "static lateral load experiment" and "repetitive loading experiment", total of two Lateral load tests. As a result, in Static Lateral load test, the bigger length/diameter of model pile led an increase in load displacement. However, when performing "Cyclic Lateral load test", the increase in number of under loading led the decrease in horizontal displacement from each repeated lateral load. While performing Static Lateral load test and repeated loading experiment, we could observe the decreasing in the rate of ultimate lateral load capacity increase of the pile. Also, it turned out that the higher relative density of the ground, the lower ultimate lateral load capacity by repeated horizontal loading.

• International Journal of Highway Engineering
• /
• v.4 no.4 s.14
• /
• pp.41-52
• /
• 2002

This study dealt with analysis of size effect of testing apparatus for Kim test which measures rut resistance characteristics of asphalt mixture under static loading. Two columns in different diameter with each column having different radios of round cut (Curvature) at the bottom were used for testing asphalt mixture. Deformation load ($P_{max}$) and deformation strength ($K_D$) were found to have relatively high correlation with rut depth and dynamic stability of asphalt concrete. Diameter of specimen was not a significant factor in this test. From the statistical correlation analysis with rutting properties, the radius of curvature and diameter of loading column were found to be important factor affecting the results of the test. Among the radios (r) of curvatures, r=0.5cm and 1.0cm showed much higher correlation than the column without curvature, and r=1.0cm being better between the two. The column with diameter of 4cm showed better correlation than diameter of 3cm. Therefore, the column of 4cm diameter with r=1.0cm was found to be the best among various apparatus sizes. Prediction models for rut depth and dynamic stability were developed for each aggregate mixture based on Kim test variables using SAS STEPWISE procedure. Therefore, if this test method is validated through further study, Kim test can be used for selecting asphalt mixture with the highest resistance against permanent deformation.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.17 no.9
• /
• pp.1-11
• /
• 2016

The effect of the migration of nanoparticles near the wall of a channel on the convective heat transfer in a laminar flow of $SiO_2$ nanoparticle suspensions (nanofluids) under constant wall heat flux boundary conditions was numerically and experimentally investigated in this study. The dynamic thermal conductivity of the aqueous $SiO_2$ nanofluids was measured using T-type thermocouples attached to the outer surface of a stainless steel circular tube (with a length of 1 m and diameter of 1.75 mm). The nanofluids used in this study were synthesized by dispersing $SiO_2$ spherical nanoparticles with a diameter of 24 nm in de-ionized water (DIW). The enhancement of the thermal conductivity of the nanofluids (e.g., an increase of up to 7.9 %) was demonstrated by comparing the temperature profiles in the flow of the nanofluids with that in the flow of the basefluids (i.e., DIW). However, this trend was not demonstrated in the computational analysis, because the numerical models were based on continuum assumptions and flow features involving nanoparticles in a stable colloidal solution. Thus, to explore the non-continuum effects, such as the modification of the morphology caused by nanoparticle-wall interactions on the heat exchanging surfaces (e.g., the isolated and dispersed precipitation of the nanoparticles), additional experiments were performed using DIW right after the measurements using the nanofluids.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.17 no.10
• /
• pp.300-309
• /
• 2016

Curved beams are increasingly used in buildings, vehicles, ships, and aircraft, which has resulted in considerable effort towards developing an accurate method for analyzing the dynamic behavior of such structures. The stability behavior of elastic curved beams has been the subject of many investigations. Solutions to the relevant differential equations have traditionally been obtained by the standard finite difference or finite element methods. However, these techniques require a great deal of computer time for a large number of discrete nodes with conditions of complex geometry and loading. One efficient procedure for the solution of partial differential equations is the differential quadrature method (DQM). This method has been applied to many cases to overcome the difficulties of complex algorithms and high storage requirements for complex geometry and loading conditions. Out-of-plane buckling of curved beams with rotatory inertia were analyzed using DQM under uniformly distributed radial loads. Critical loads were calculated for the member with various parameter ratios, boundary conditions, and opening angles. The results were compared with exact results from other methods for available cases. The DQM used only a limited number of grid points and shows very good agreement with the exact results (less than 0.3% error). New results according to diverse variation are also suggested, which show important roles in the buckling behavior of curved beams and can be used for comparisons with other numerical solutions or experimental test data.

• Applied Chemistry for Engineering
• /
• v.30 no.4
• /
• pp.435-444
• /
• 2019

In this study, two types of nonionic saccharide biosurfactants, GP-6 and GP-7, were prepared from coconut oil and the structure of resulting products was investigated by FT-IR, $^1H-NMR$ and $^{13}C-NMR$ spectrophotometer. The interfacial properties of GP-6 and GP-7 were found to be excellent from interfacial property measurements such as critical micelle concentration, static and dynamic surface tensions, interfacial tension, emulsification power, wetting property and foam stability. Detergency test evaluated by using a Terg-o-tometer showed moderately good detergency compared to that of conventional surfactants used in detergent formulations. Biodegradability, acute oral toxicity, acute dermal irritation and acute eye irritation tests revealed that both surfactants possess excellent mildness and superior environmental compatibility indicating the potential applicability to detergent products formulations. In particular, GP-6 can be considered as a strong candidate in detergent formulations since it is more surface active, mild and readily biodegradable than GP-7.

• Journal of Korea Water Resources Association
• /
• v.51 no.spc
• /
• pp.1135-1148
• /
• 2018

Previous studies on reservoir operation have been assumed that the climate in the future would be similar to that in the past. However, in the presence of climate non-stationarity, Robust Optimization (RO) which finds the feasible solutions under broader uncertainty is necessary. RO improves the existing optimization method by adding a robust term to the objective function that controls the uncertainty inherent due to input data instability. This study proposed Robust-SDP that combines Stochastic Dynamic Programming (SDP) and RO to estimate dam operation rules while coping with climate non-stationarity. The future inflow series that reflect climate non-stationarity were synthetically generated. We then evaluated the capacity of the dam operation rules obtained from the past inflow series based on six evaluation indicators and two decision support schemes. Although Robust-SDP was successful in reducing the incidence of extreme water scarcity events under climate non-stationarity, there was a trade-off between the number of extreme water scarcity events and the water scarcity ratio. Thus, it is proposed that decision-makers choose their optimal rules in reference to the evaluation results and decision support illustrations.