• Journal of the Korean Society of Propulsion Engineers
• /
• v.18 no.5
• /
• pp.1-11
• /
• 2014

Sympathetic detonation (SD) of high explosives occurs when a detonating donor initiates neighboring acceptors. The present study focuses on the hydrodynamic simulation of one-on-one sympathetic detonation of 155 mm charge filled with PBXN-109. Both unbuffered and buffered SD configurations are performed while changing the distance between each charge, in order to investigate the detonation sensitivity to a donor initiation. The cause of a SD is by a shock impact for the unbuffered case at a close range, while at a distant range, blast fragment penetration is the primary cause. The buffers can reduce the incident sensitivity to a SD by reducing the strengths of shock wave and impinging fragments.

• Wind and Structures
• /
• v.14 no.6
• /
• pp.517-536
• /
• 2011

The assessment of wind-induced motion plays an important role in the development and design of the majority of today's structures that push the limits of engineering knowledge. A vital part of the design is the prediction of wind-induced tall building motion and the assessment of its effects on occupant comfort. Little of the research that has led to the development of the various international standards for occupant comfort criteria have considered the effects of the low-frequency motion on task performance and interference with building occupants' daily activities. It has only recently become more widely recognized that it is no longer reasonable to assume that the level of motion that a tall building undergoes in a windstorm will fall below an occupants' level of perception and little is known about how this motion perception could also impact on task performance. Experimental research was conducted to evaluate the performance of individuals engaged in a manual tracking task while subjected to low level vibration in the frequency range of 0.125 Hz-0.50 Hz. The investigations were carried out under narrow-band random vibration with accelerations ranging from 2 milli-g to 30 milli-g (where 1 milli-g = 0.0098 $m/s^2$) and included a control condition. The frequencies and accelerations simulated are representative of the level of motion expected to occur in a tall building (heights in the range of 100 m -350 m) once every few months to once every few years. Performance of the test subjects with and without vibration was determined for 15 separate test conditions and evaluated in terms of time taken to complete a task and accuracy per trial. Overall, the performance under the vibration conditions did not vary significantly from that of the control condition, nor was there a statistically significant degradation or improvement trend in performance ability as a function of increasing frequency or acceleration.

• International Journal of Naval Architecture and Ocean Engineering
• /
• v.7 no.3
• /
• pp.580-594
• /
• 2015

Liquid sloshing in two-dimensional (2-D) and three-dimensional (3-D) rectangular tanks is simulated by using a level set method based on the finite volume method. In order to examine the effect of natural frequency modes on liquid sloshing, we considered a wide range of frequency ratios ($0.5{\leq}fr{\leq}3.2$). The frequency ratio is defined by the ratio of the excitation frequency to the natural frequency of the fluid, and covers natural frequency modes from 1 to 5. When fr = 1, which corresponds to the first mode of the natural frequency, strong liquid sloshing reveals roof impact, and significant forces are generated by the liquid in the tank. The liquid flows are mainly unidirectional. Thus, the strong bulk motion of the fluid contributes to a higher elevation of the free surface. However, at fr = 2, the sloshing is considerably suppressed, resulting in a calm wave with relatively lower elevation of the free surface, since the waves undergo destructive interference. At fr = 2, the lower peak of the free surface elevation occurs. At higher modes of $fr_3$, $fr_4$, and $fr_5$, the free surface reveals irregular deformation with nonlinear waves in every case. However, the deformation of the free surface becomes weaker at higher natural frequency modes. Finally, 3-D simulations confirm our 2-D results.

• Atmosphere
• /
• v.31 no.4
• /
• pp.377-394
• /
• 2021

The recent largest forest fire in the Yeongdong region, Goseung/Okgae fires of 2019 occurred during YangGang wind event. The wind can be locally gusty and extremely dry, particularly in the complex terrain of Yeongdong. These winds can cause and/or rapidly spread wildfires, the threat of which is serious during the dry spring season. This study examines the spatial variability of the surface wind and its coupling with the upper atmospheric wind using the data during the IOP of the Gangwon Yeongdong Wind Experiments (G-WEX) conducted in 2020 and the data during YangGang wind event on 4~5 April 2019. In the case of IOPs, strong wind at the surface with a constant wind direction appears in the mountain area, and weak wind with large variability in wind direction appears from foothill to the coast in the vicinity of Gangneung region. However, in the 2019 event, strong wind at the surface with a constant wind direction appears in the entire region from the mountain to the coast, even with the stronger wind in the coast than in some part of the mountain area. The characteristics of the upper atmospheric wind related with the spatial distribution of surface wind show that during IOPs of G-WEX, a strong downdraft exists near the mountaintop in the level of about 1 to 4 km. However, in the 2019 event a strong downdraft is reinforced, when its location moves toward the coast and descends close to the ground. These downdrafts are generated by the breaking of mountain waves.

• The Journal of the Korea Contents Association
• /
• v.19 no.2
• /
• pp.638-649
• /
• 2019

The development of career knowledge and career attitude in adolescence is significant to achieve a successful transition to adulthood. The aim of this study was to assess effects of family income and career guidance and counseling experience on changes in career maturity during the transition from high school to college. The study used data from Youth Panel 2007 collected by Korea Employment Information Service. The data included 456 adolescents who were high school students in the first and third waves of survey and college students in the fifth wave of survey. The results suggested that family income was a significant factor affecting the career maturity of adolescents. The experience of career guidance and counseling while in high school had a sustained and positive impact on the career maturity of adolescents even after entering college. Therefore, career education in the secondary educational system should expand continuously.

• ALGAE
• /
• v.34 no.2
• /
• pp.141-151
• /
• 2019

The 1982-83, 1986-87, 1991-92, and 1997-98 El $Ni{\tilde{n}}o$-Southern Oscillations (ENSOs) were compared with regards to their strength and timing in the tropical Pacific Ocean, changes in ocean temperature and wave intensity, and their impacts to giant kelp populations in the Northeast Pacific. The Multivariate ENSO Index, oceanographic data, and kelp abundance data all show that the 1982-83 and 1997-98 ENSOs were stronger and resulted in greater losses of giant kelp than the 1986-87 and 1991-92 ENSOs, but that the 1982-83 and 1997-98 ENSOs differed with regard to the arrival of destructive waves relative to when the ocean waters warmed and cooled. The 1982-83 ENSO was more destructive to the giant kelp populations in central California, USA than the 1997-98 ENSO, but the 1997-98 ENSO was more destructive to the giant kelp in southern California. These events appeared similarly destructive to the populations in Baja California, Mexico. Recovery of the kelp populations also varied among the two strong ENSOs due to the ocean conditions following each ENSO. In southern and Baja California, recovery was slow following the 1982-83 ENSO, while recovery was more rapid following the 1997-98 ENSO. Unfortunately, the monitoring programs used to evaluate the kelp populations stopped shortly after the 1997-98 ENSO, resulting in a lack of data for comparisons with the more recent weak ENSOs that occurred between 2002 and 2010, or with the strong ENSO that occurred in 2014-2016. This supports the need for continued long-term monitoring programs to better understand how climate anomalies impact coastal ecosystems.

• Membrane and Water Treatment
• /
• v.12 no.1
• /
• pp.43-49
• /
• 2021

The Commercial polymeric membranes like Polysulfone (PSF), Polyvinylidene difluoride (PVDF) and Polyacrylonitrile (PAN) which are an integral part of water purification investigation were chosen for the shockwave (SW) exposure experiment. These membranes were prepared by blending polymer (wt. %) / DMF (solvent) followed by phase-inversion casting technique. Shockwaves are generated by using Reddy Tube lab module (Table-top Shocktube) with range of pressure (1.5, 2.5 and 5 bar). Understanding the changes in membrane before and after shock wave treatment by parameters, i.e., pure water flux (PWF), rejection (%), porosity, surface roughness (AFM), morphology (SEM) and contact angle which can significantly affect the membrane's performance. Flux values PSf membranes shows increase, 465 (pristine) to 524 (1.5wt%) LMH at 50 Psi pressure and similar enhancement was observed at 100Psi (625 to 696 LMH). Porosity also shows improvement from 73.6% to 76.84% for 15wt% PSf membranes. It was observed that membranes made of polymers such as PAN and PSF (of high w/w %) exhibits some resistance against shockwaves impact and are stable compared to other membranes. Shockwave pressure of up to 1.5 bar was sufficient enough to change properties which are crucial for performance. Membranes exposed to a maximum pressure of 5 bar completely scratched the surface and with minimum pressure of 1.5bar is optimum enough to improve the water flux and other parameters. Initial results proved that SW may be suitable alternative route to minimize/control membrane fouling and improve efficiency.

• Journal of the Korea Society of Computer and Information
• /
• v.26 no.8
• /
• pp.173-180
• /
• 2021

The purpose of the present study was to investigate the relationship between perceived parenting style and life satisfaction among adolescents transitioning from middle to high schools and to ascertain whether self-esteem functions as a mediating variable between the two aforementioned variables. Based on the results of literature review, a research model, in which there were perceived parenting style, self-esteem, and life satisfaction as latent variables, was designed. The current study analyzed the 6th and 7th wave data of the 4th grade panel of elementary school from the Korea Children and Youth Panel Survey (KCYPS). Major results were as follows. First, perceived democratic parenting style had a significant positive effect on life satisfaction whereas controlling parenting style did not have a significant impact on life satisfaction. Second, self-esteem partially mediated the effect of perceived democratic parenting style on life satisfaction. Third, self-esteem fully mediated the effect of perceived controlling parenting style on life satisfaction. Finally, implications and recommendations were provided to improve parenting style and to enhance self-esteem of adolescents experiencing school transitions.

• Journal of Digital Convergence
• /
• v.20 no.4
• /
• pp.301-308
• /
• 2022

The current paper not only investigates the intermediating process of the association between servant leadership and safety behavior, but also tries to find a factor which enhances the positive influence of servant leadership. To do that, this study tried to identify the mediating effect of employee's psychological safety between servant leadership and safety behavior, as well as the moderating influence of perspective taking ability in the servant leadership-psychological safety link. By utilizing 3 wave survey data from 235 employees in Korean companies with conducting structural equation modeling(SEM), this paper found that servant leadership had a positive influence on safety behavior through mediating effect of employee's psychological safety. In addition, the perspective taking ability positively moderated the positive impact of servant leadership on psychological safety.

• The Journal of the Korea Contents Association
• /
• v.22 no.4
• /
• pp.301-313
• /
• 2022

This study aims to investigate the causal relationship between variables of UTAUT2 model and the acceptance intention by Netflix and Wavve intention to adopt and acceptance intent by plan package. The results indicate that (1)First, the intention of Netflix adoption was influenced by performance expectancy, effort expectancy, hedonic motivation, price value, and habit; (2) the intention of wave adoption was influenced by performance expectancy, social influence, price value, and habit. (3)in the acceptance intention of Netflix's acceptance intent by plan package, price value and habit, performance expectancy and habit influenced on the acceptance intent of premium plan, and did not affect the standard plan; (4) in the acceptance intention of the basic plan by the Wavve plan, the price value had a negative effect on the acceptance intention of the basic plan, and the habit had a positive effect.The social impact on the acceptance intention of the standard rate plan, the price value and habit of the acceptance intention of the premium rate plan were affected.