• 전자공학회논문지 IE
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• v.47 no.1
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• pp.22-33
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• 2010

The main purpose of this study was to develope a reflective journal and examine its effects on student's academic achievement and self-regulated learning strategies. For this study, 'a structured reflective journal' was designed through the steps of systems approach with the purpose of enhancing student's academic achievement and self-regulated learning strategies, especially meta-cognition and critical thinking. The reflective journal used in this study contained the constructive elements of (1) self-evaluation with 5 likert scale, (2) learning essay, (3) dialogue with peers, and (4) dialogue with professor. A total of 94 freshmen enrolled in one of two sections of the engineering courses(theory-based class and experiment and practice-based class) participated in the study for 8 weeks. A pre-test-post-test design was used to examine the effects of the application of reflective journal on student's achievement and self-regulated learning strategies. For the result, analysis of covariance was conducted to determine whether there were any academic achievement differences and self-regulated learning strategy differences. The results suggested that students were taking advantages of the reflective journal, and there were statistically significant differences in academic achievement in the experiment and practice-based class and self-regulated learning strategies in both classes.

• Journal of IKEEE
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• v.19 no.4
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• pp.566-572
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• 2015

In this paper, we calculate monostatic RCS(Radar Cross Section) and bistatic RCS for improving the Performance of the skin tracking of KSLV-II and the results were compared. EM(Electromagnetic) simulator was used for numerical analysis. For the two paths(L, S), after the vehicle was launched, RCS was calculated for region from 280 to 400 seconds. In the case of using the bistatic radar system, when the vehicle was launched to the L path, tracking performance was better when we receive RCS in Jeju than in Goheung. When the vehicle was launched to the S path, tracking performance was better when we receive RCS in Goheung than in Jeju. In the case of using the monostatic radar system, when the vehicle was launched to the L path, tracking performance was better when we receive RCS in Goheung than in Jeju. When the vehicle was launched to the S path, tracking performance was better when we receive RCS in Jeju than in Goheung.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.25 no.4
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• pp.355-362
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• 2012

Remaining useful life(RUL) prediction of a system is important in the prognostics field since it is directly linked with safety and maintenance scheduling. In the physics-based prognostics, accurately estimated model parameters can predict the remaining useful life exactly. It, however, is not a simple task to estimate the model parameters because most real system have multivariate model parameters, also they are correlated each other. This paper presents representative methods to estimate model parameters in the physics-based prognostics and discusses the difference between three methods; the particle filter method(PF), the overall Bayesian method(OBM), and the sequential Bayesian method(SBM). The three methods are based on the same theoretical background, the Bayesian estimation technique, but the methods are distinguished from each other in the sampling methods or uncertainty analysis process. Therefore, a simple physical model as an easy task and the Paris model for crack growth problem are used to discuss the difference between the three methods, and the performance of each method evaluated by using established prognostics metrics is compared.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.27 no.4
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• pp.239-245
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• 2014

Finite element modeling of composite structures may be cumbersome due to complex distributions of reinforcements. In this paper, an efficient scheme is proposed that can generate periodic meshes for the composite structures. Regular meshes with hexahedral finite elements are first prepared, and the elements are then trimmed to fit external surfaces of reinforcements in the composite structures. The trimmed hexahedral finite elements located at interfaces between the matrix and the reinforcements correspond to polyhedral finite elements, which allow an arbitrary number of nodes and faces in the elements. Because the trimming process is consistently conducted by means of consistent algorithms, the elements of the reinforcements are automatically compatible with those of the matrices. With the additional consideration of periodicity of reinforcements in a representative volume element(RVE), the proposed scheme provides periodic meshes in an efficient manner, which are compatible for each pair of periodic boundaries of the RVE. Therefore, periodic boundary conditions for the RVE are enforced straightforwardly. Numerical examples demonstrate the effectiveness of the proposed scheme for finite element modeling of complex composite structures.

• The Korean Journal of Air & Space Law and Policy
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• v.29 no.1
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• pp.97-126
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• 2014

October 4, 1957 the Soviet Sputnik 1 was launched into space the first time in the history of mankind. After launching, the realm of humankind was expanded to space. Today all countries of the world wage a fierce competition in order to utilize space for various purposes. World powers of space such as United States, Russia, China, and Japan, put reconnaissance satellites and ocean surveillance satellites into orbit, being able to easily see equipment and troops movement on earth. Each country makes efforts to occupy space assets through the militarization of space and expand national interests. Recently private companies or individuals involved in commercial space activities are becoming more prevalent. Thus, in addition to space activities for military purposes, commercial space activities become widespread. Individuals and private companies as well as nations are also involved in space activities. Outer space is not the monopoly of space powers such as the United States and Russia. The whole human race can benefit from free access to space, being the common heritage of mankind. In particular, outer space becomes an indispensable element of military activities and human life. Many countries are now entering space development, putting a lot of budget into new development programs. Republic of Korea also built the Narodo Space Center, starting its space development with budget and manpower. We have to find out ways to use space not only for military purposes but also for commercial space activities that can contribute to the national economy. In addition, through the joint efforts of the international community, we have to make efforts for preservation and peaceful use of space. Various issues relating to space activities and research should be studies in order to contribute to the progress of humanity. Those issues include the definition of outer space, space debris reduction and environmental conservation issues, non-bind measure cooperation - European International Code of Conduct, space law and national legislation related empowerment issues, arms control measures in space, and restrictions on the use of nuclear fuel. We also need to be involved in the discussion of those issues as one of responsible space countries. In addition, we try to find out regional cooperation schemes such as the ESA in the Europe actively. Currently in the Northeast Asia, cooperation bodies led by Japan and China respectively, are operated in the confrontational way. To avoid such confrontation, a new cooperative body needs to be established for cooperation on space exploration and information. The system to allow the exchange of satellite information for early warning of natural disasters needs to be built as well. In addition, efforts to enhance the effectiveness of the relevant international treaties on space, and fill in the blanks in international space laws should be made at the same time. To this end, we have to do a leading role in the establishment of standards such as non-binding measures (resolution) - Code of Conduct, being discussed in the UN and other organizations, and compliance with those standards. Courses in aerospace should be requires in law schools and educational institutes, and professional manpower need to be nurtured. In addition, the space-related technology and policy needs to be jointly studied among the private, public, and military groups, and the cross exchange among them should be encouraged.

• Particle and aerosol research
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• v.16 no.2
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• pp.31-47
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• 2020

Although interest in air quality has increased due to the frequent occurrence of high-concentration fine particulate matter recently, the official fine particulate matter measuring network has failed to provide spatial detailed air quality information. This is because current measurement equipment has a high cost of installation and maintenance, which limits the composition of the measuring network at high resolution. To compensate for the limitations of the current official measuring network, this study constructed a spatial high density measuring network using the fine particulate matter simple measuring device developed by Observer, W-Station. W-Station installed 48 units on Jeju Island and measured PM_2.5 for six months. The data collected in W-Station were corrected by applying the first regression equation for each section, and these measurements were compared and analyzed based on the official measurements installed in Jeju Island. As a result, the time series of PM_2.5 concentrations measured in W-Station showed concentration characteristics similar to those of the environmental pollution measuring network. In particular, the results of comparing the measurements of W-Station within a 2 km radius of the reference station and the reference station showed that the coefficient of determination (R²) was 0.79, 0.81, 0.67, respectively. In addition, for W-Station within a 1 km radius, the coefficient of determination was 0.85, 0.82, 0.68, respectively, showing slightly higher correlation. In addition, the local concentration deviation of some regions could be confirmed through 48 high density measuring networks. These results show that if a network of measurements is constructed with adequate spatial distribution using a number of simple meters with a certain degree of proven performance, the measurements are effective in monitoring local air quality and can be fully utilized to supplement or replace formal measurements.

• The Journal of the Acoustical Society of Korea
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• v.39 no.4
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• pp.351-363
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• 2020

Launch vehicles are subject to airborne acoustic loads during atmospheric flight and these effects become pronounced especially in transonic region. As the vibration due to the acoustic loads can cause malfunction of payloads, it is essential to predict and reduce the acoustic loads. In this study, a complete process has been developed for predicting airborne vibro-acoustic environment inside the payload pairing and subsequent noise reduction procedure employing acoustic blankets and Helmholtz resonators. Acoustic loads were predicted by Reynolds-Averaged Navier-Stokes (RANS) analysis and a semi-empirical model for pressure fluctuation inside turbulent boundary layer. Coupled vibro-acoustic analysis was performed using VA One SEA's Finite Element Statistical Energy Analysis (FE-SEA) hybrid module and ANSYS APDL. The process has been applied to a hammerhead launch vehicle to evaluate the effect of acoustic load reduction and accordingly to verify the effectiveness of the process. The presently developed process enables to obtain quick analysis result with reasonable accuracy and thus is expected to be useful in the initial design phase of a launch vehicle.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2004.03a
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• pp.48-54
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• 2004

The effects of injector spacing s and injector diameter d on mixing are numerically investigated in supersonic combustor with perpendicular injection behind a backward-facing step. Simulations are reported for airstream Mach number of 2.4. Parameters are changed on following 4 cases to investigate the effects of injector configuration on mixing efficiency $\eta_m$. In the case of varying d or s, dynamic pressure ratio $Rq(=(pu^2)_j/(pu^2)_a)$ is also varied to keep bulk equivalence ratio $\Phi({\oe})Rq.d^2/s)$ constant. (l) Injector spacing s is varied at constant $\Phi$=0.5, 1, 2 for injector diameter d=6mm. In the case of $\Phi$=1, $\eta_m$ has its maximum value at s=24mm. The reason is that increase of $\eta_m$. , by widening spacing at Rq=constant competes with decrease of $\eta_m$ by increasing Rq at s=constant. When spacing is narrow, the flow field of vicinity of injector becomes two-dimensional because adjacent jets interferes each other. By widening spacing, air is easily entrained by three-dimensional effect. This mechanism also appears in the case of $\Phi$=0.5, 2 for d=6mm, and $\eta_m$. reaches its maximum value at s=24mm for $\Phi$=0.5 and at s=42mm for $\Phi$=2. (2) In the case of injector diameter d varied at $\Phi$=1 for s=30mm, $\eta_m$. has its maximum value at d=3mm. The reason is that decrease of $\eta_m$ by increasing injector diameter competes with increase of $\eta_m$ by decreasing Rq at d=constant.(3) In the case of s varied at $\Phi$=0.5, 1,2 for d=3mm, the injector spacing at which mixing efficiency has its maximum value is s= 18mm for $\Phi$=0.5, s=24mm for $\Phi$=1, s=24mm for $\Phi$=2. Therefore it is found that d=3mm and s=24mm can be optimum configuration over a range of $\Phi$=0.5~2.(4) The effect of h on the optimum spacing is investigated. s is varied for d=6mm at step height h=4, 6, 8mm. The simulation results do not show significant change on the step height.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2017.05a
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• pp.248-250
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• 2017

The Mar-M-247 alloy is one of the most widely used materials for gas turbine components in aerospace filed and it shows excellent high temperature strength properties. Hot section parts, such as turbine nozzle and blade, are difficult to manufacture because of their complicated shape. So, the joining process usually applies to them. In this study, the high-temperature behavior of Mar-M-247 alloy at liquid diffusion bonding was investigated. Thus, we performed the diffusion bonding at $1,121^{\circ}C$ for 7 minutes, and observed changes in high temperature strength. As a result, the strength of the bonded specimens decreased by about 70% at $649^{\circ}C$, 60% at $825^{\circ}C$, and 45% at $1,000^{\circ}C$ compared to the base metal. As a result of observing the strength change with bonding time, the specimen bonded for 720 minutes showed a similar strength with the base metal at $649^{\circ}C$. Inferring this result, the joint is considered to be the one-body part.

• Korean Journal of Optics and Photonics
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• v.22 no.6
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• pp.262-268
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• 2011

MIRIS(Multi-purpose Infra-Red Imaging System) is the main payload of the STSAT-3(Korea Science and Technology Satellite. 3), which is being developed by KASI(Korea Astronomy & Space Institute). EOC(Earth Observation Camera), which is one of two infrared cameras in MIRIS, is the camera for observing infrared rays from the Earth in the range of $3{\sim}5{\mu}m$. The optical system of the EOC is a Cassegrain prescription with aspheric primary and secondary mirrors, and its aperture is 100mm. A ring type flexure supports the EOC primary mirror with pre-loading in order to withstand expected load due to the shock and vibration from the launcher. Here we attempt to use the same mechanism by which a retainer supports the lens. Through opto-mechanical analysis it was confirmed that the EOC primary mirror is effectively supported.