• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.38 no.1
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• pp.1-11
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• 2010

The definition of the speed of sound is reexamined since it is crucial in the numerical analysis of compressible real gas flows. The thermodynamic speed of sound (TSS), $a_{th}$, and the characteristic speed of sound (CSS), $a_{ch}$, are derived using generalized equation of state (EOS). It is found that the real gas EOS, for which pressure is not linearly dependent on density and temperature, results in slightly different TSS and CSS. in this formalism, Roe's approximate Riemann solver was derived again with corrections for real gases. The results show a little difference when the speeds of sound are applied to the Roe's scheme and Advection Upstream Splitting Method (AUSM) scheme, but a numerical instability is observed for a special case using AUSM scheme. It is considered reasonable to use of CSS for the mathematical consistency of the numerical schemes. The approach is applicable to multi-dimensional problems consistently.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.39 no.3
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• pp.218-224
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• 2011

A modal method is presented for the investigation of the effects of measurement errors in damage detection for dynamic structural systems. The structural modifications to the baseline system result in the response changes of the perturbed structure, which are measured to determine a unique system in the inverse problem of damage detection. If the numerical modal data are exact, mathematical programming techniques can be applied to obtain the accurate structural changes. In practice, however, the associated measurement errors are unavoidable, to some extent, and cause significant deviations from the correct perturbed system because of the intrinsic instability of eigenvalue problem. Hence, a self-equilibrating inverse system is allowed to drift in the close neighborhood of the measured data. A numerical example shows that iterative procedures can be used to search for the damaged structural elements. A small set of selected degrees of freedom is employed for practical applicability and computational efficiency.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.39 no.5
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• pp.623-630
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• 2019

As the Asian region becomes strategically important in the international construction market, competition among construction firms has been more intense. While existing literature on the Asian construction market have mainly focused on qualitative approaches to market entry strategies and risk assessment, quantitative research to explain the dynamic competitive structure of the market has been rarely conducted. To address this issue, this study analyzes the structure of contract performance in the Asian region based on the data from 3,996 projects awarded to Korean construction firms from 2009 to 2017. In addition, this study applies a mathematical model using both static (market concentration) and dynamic (market mobility and instability) analyses. Consequently, the static analysis indicates that market concentration led by top-four firms tends to be increased, and on the dynamic aspect, the market position of Korean construction firms is recently weakened and fluctuated in most of the Asian regions and the construction sectors. The methodology and result of this paper would be meaningful not only to understand the underlying structure of industry-level performance but also to provide a useful reference for establishing competitive strategies towards the Asian market.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.5
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• pp.621-626
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• 2019

The driver's steering wheel maneuver is a typical disturbance that causes excessive body motion and traveling instability of a vehicle. Abrupt and extreme operation can cause rollover depending on the geometric and dynamic characteristics, e.g., SUV vehicles. In this study, to cope with the performance limitation of conventional cars, fundamental research on the structurization of a control system was performed as follows. Mathematical modeling of the lateral behavior induced by driver input was carried out. A controller was designed to reduce the body motion based on this model. An algorithm was applied to secure robust control performance against modeling errors due to parameter uncertainty, $H_{\infty}$. Using the decoupled 1/4 car, a dynamic load simulating model considering the body moment was suggested. The simulation result showed the validity of the load-simulating model. The framework for a lateral behavior control system is proposed, including an experimental 1/4 vehicle unit, load simulating module, suspension control module, and hardware-in-the-loop simulation technology.

• Korean Chemical Engineering Research
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• v.52 no.5
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• pp.574-580
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• 2014

Storage tanks of Carbon dioxide ($CO_2$) carriers utilized for the purpose of carbon capture and storage (CCS) into subsea strata have to undergo a pre-cooling session before beginning to load cryogenic liquid cargos in order to prevent physical and thermal deterioration of tanks which may result from cryogenic $CO_2$ contacting tank walls directly. In this study we propose dynamic model to calculate the tank inflow of $CO_2$ gas injected for precooling process and its dynamic simulation results under proportional-integral control algorithm. We selected two cases in which each of them had one controlled variable (CV) as either the tank pressure or the tank temperature and discussed the results of that decision-making on the pre-cooling process. As a result we demonstrated that the controlling instability arising from nonlinearity and singularity of the mathematical model could be avoided by choosing tank pressure as CV instead of tank temperature.

• KSBB Journal
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• v.14 no.2
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• pp.230-234
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• 1999

To improve the crossflow untrafiltration flux, we applied periodic oscillations in transmembrane pressure gradient in order to promote fluid turbulence by inducing repeated compression and relaxation of the cake/gel layer. The oscillatory forms used were square-, sine-, triangle-wave, and pumping interruption. The permeate flux profiles were mathematically simulated and compared with the experimental data. The result showed the periodic pumping interruption most effectively improved the overall flux by up to about 32%. Enough pumping off-time, at least on the order of tens of seconds, was needed to allow the solutes in the layer to diffuse back to the bulk phase. It was better to start the oscillations earlier before the layer was fully established. The square-wave oscillation yielded about 11% increase, which was particularly pronounced in the later part of the filtration. Either the amplitude or the period of the oscillations resulted little influence on flux.actate ester, and lactate ester produced in esterification reaction was distilled simultaneously with hydrolysis reaction into lactic acid. When the yields of lactic acid recovered by batch reactive distillations with various alcohols were compared, the yield of lactic acid was increased as the volatility of lactate ester was increased. In this batch reactive distillation, because the mixtures condensed in partial condensor were flown to reboiler through distillation column, the recovery yield of lactic acid was affected by operation temperature of partial condensor. Hydrolysis reaction into lactic acid in distillation column rarelyoccurred because of short retention time of lactate ester and water. Lactate ester was reacted into lactic acid in reboiler.

• Journal of the Korean School Mathematics Society
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• v.12 no.4
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• pp.545-562
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• 2009

Calculus is used in various parts of human life and the basis of social science such as economics and public administration. Yet that is still considered important in the field of science and technology only, and there have been a lot of disputes on that phenomenon. Fortunately, calculus is going to be taught as part of the academic high school second-year mathematics curriculum in and after 2010. Students who face calculus for the first time should be helped not to lose interest in differentiation learning, not to be apprehensive of it nor to avoid it. The purpose of this study was to examine the types of errors made by students in the course of solving differentiation problems in an effort to lay the foundation for differentiation education. A pilot test was conducted after generalized differentiation problems to which students were usually exposed were selected, and experts were asked to review the pilot test. And then a finalized test was implemented to make an error analysis according to an error type analysis framework to serve the purpose.

• Proceedings of the Korean Society for the Gifted Conference
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• 1994.08a
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• pp.1.2-37
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• 1994

Currently Korea encourages gifted high schoolers and junior high schoolers to participate in international achievement contests such as International Olympiads. Participants for these contests are selected nationwide among gifted students in areas of mathematics, physics, chemistry, and others. They go through a series of screening tests and programs. One of the screening processes IS Korean Olympiad School, which provides study programs each summer for student-candidates prior to following year's International Olympiads. Approximately 40 students of high schools and junior high schools, in each subject of study, gather at Korean Olympiad Summer School, and they go through intensive study programs during a short period of time. Out of 40 candidates,' less than 10 students are finally selected to participate in International Olympiads. In this study, a psycho-educational program called "Situation Coping Training Program" was developed to enhance ahievement motivation for these student-candidates. This study was to see if this training program actually improved their cognitive, emotive motivation factors, and to see how this training program affected their achievement level. Training was administered for five days. This training program was found effective for participants to increase self-efficacy, internal locus of control, and anxiety copmg. These cognitive and emotive motivation factors, other than intelligence, were found to have positive relationship with achievement level, of which self-efficacy and attribution style of students were found as two best predictors of achievement. This training program was perceived as necessary. by participants, and helpful for recovering self-confidence and self-control as well as coping pressure. Suggestions were made that this kind of training program be administered as a regular curriculum in preparative study programs such as Korean Olympiads, since cognitive, emotive motivation factors are related with achievement, and furthermore, be utilized in all gifted education programs in Korea. in Korea.

• Information Systems Review
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• v.16 no.2
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• pp.61-76
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• 2014

Recently, students have raised negative awareness of the test because of school records and irrational difficulty level of the College Scholastic Ability Test. They go so far as to commit suicide because of failure in entering school. It becomes a social problem and it is rising more and more interested in entering school. The educational game was created based on considering this social environment. Namely, students can enter university as playing online or mobile game through Enter Literacy Assessment game service. The Enter Literacy Assessment game service provides various tests which are math, english, science or essay that real university wants through online or mobile game. For this, general concept about Enter Literacy Assessment game service and characteristic establishment and limitation of existing research should be understood. The research refers to relationship between Self-Determination Theory which is the representative theory related with psychological desire of human intrinsic and Enter Literacy Assessment game service. Therefore, development of Enter Literacy assessment Serious Game is a new opportunity factor to take two dominants which are secure of university competitive power and excellent personnel and challenge for development of serious game.

• Journal of Korean Medicine Rehabilitation
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• v.30 no.4
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• pp.179-186
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• 2020

The aim of this study was to report the effect of Korean medicine treatments and vestibular rehabilitation practice on an stroke patient with dizziness. The patient received Korean medicine treatments, such as acupuncture and herbal medication, and vestibular rehabilitation practice. The effects of treatments were assessed with the Korean dizziness handicap inventory, Korean activities-specific balance confidence scale, Korean vestibular disorders activities of daily living scale. Researchers conducted gait analysis for evaluation patient's gait disturbance's improvement during treatments. The intensity of dizziness were significantly reduced after the complete treatment. After treatment with traditional Korean medicine and vestibular rehabilitation practice, the patient showed significant improvements in symptoms and gait parameters. This case proved that combined therapy of Korean medicine treatment and vestibular rehabilitation practice can be useful for stroke patients who suffered from dizziness. however, studies of larger populations are required in the future.