• Proceedings of the Korea Water Resources Association Conference
• /
• 2021.06a
• /
• pp.256-256
• /
• 2021

Saint-Venant 방정식은 수평규모가 수심규모보다 큰 천수흐름을 기술하는 수리동역학 모형으로 지난 수십년간 공학적 분야에서 널리 이용되어 왔다. 최근에도 기후변화에 따른 도시 홍수의 위기 증대로 홍수위기관리의 관심이 높아짐에 따라 홍수파(flood wave), 도시침수(urban inundation), 돌발홍수(flash flood) 등의 신속한 예측을 위한 Saint-Venant 방정식의 연구가 활발히 진행되고 있다. 그러나 도시와 같은 인공구조물이 즐비한 상황에서 천수흐름을 해석하는 고전적인 수치해법들은 다양한 불연속 지형들의 존재로 인하여 불안정하며 지배방정식의 정해로 수치해가 잘 수렴하지 않는 문제가 있다. 지난 수년간 이를 해결하기 위해 불연속한 지형을 안정적으로 해결할 수 있는 수치기법의 연구가 진행되어 왔으나, 정해로의 수렴성, 정확성에 관하여 연구가 부족한 실정이다. 본 연구는 수치해법의 주요 구조를 구성하는 Saint-Venant 방정식의 불연속한 지형조건에 대한 리만 문제의 정해를 연구하였다. 쌍곡선형 시스템의 특징을 고려하여 요소파들(elementary waves)의 공식을 유도하였는데, 질량과 에너지의 보존법칙에 위배되지 않으며 운동량이송부의 비선형성과 지형의 불연속에 의한 비엄격성을 고려할 수 있는 조건을 제시하였다. 또한, 유도된 요소파들을 바탕으로 L-M & R-M 커브이론(Han et al. 2014)을 사용할 수 있는 조건과 당위성을 증명하였고, 이를 바탕으로 Saint-Venant 방정식의 정해법을 구성하였다. 리만문제의 다양한 초기조건들을 바탕으로 모든 경우의 정해 구조를 조사하였고, 이를 통해 불연속 지형에 대한 Saint-Venant 지배방정식의 정해가 다수해를 갖을 수 있음을 보였으며, 이를 근사할 수 있는 수치기법의 전략을 소개하였다.

• Journal of Internet Computing and Services
• /
• v.15 no.1
• /
• pp.171-178
• /
• 2014

This paper presents dynamic modelling of a virtual object in augmented reality environments when external forces are applied to the object in real-time fashion. In order to simulate a natural behavior of the object we employ the theory of Newtonian physics to construct motion equation of the object according to the varying external forces applied to the AR object. In dynamic modelling process, the physical interaction is taken placed between the augmented object and the physical object such as a haptic input device and the external forces are transferred to the object. The intrinsic properties of the augmented object are either rigid or elastically deformable (non-rigid) model. In case of the rigid object, the dynamic motion of the object is simulated when the augmented object is collided with by the haptic stick by considering linear momentum or angular momentum. In the case of the non-rigid object, the physics-based simulation approach is adopted since the elastically deformable models respond in a natural way to the external or internal forces and constraints. Depending on the characteristics of force caused by a user through a haptic interface and model's intrinsic properties, the virtual elastic object in AR is deformed naturally. In the simulation, we exploit standard mass-spring damper differential equation so called Newton's second law of motion to model deformable objects. From the experiments, we can successfully visualize the behavior of a virtual objects in AR based on the theorem of physics when the haptic device interact with the rigid or non-rigid virtual object.

• Journal of the Korean Chemical Society
• /
• v.51 no.6
• /
• pp.569-576
• /
• 2007

In this study, the effect of grouping by communication apprehension level in paired think-aloud problem solving was examined. Three classes of 9th graders (N=99) were randomly assigned to a control group, homogeneous group or heterogeneous group based on the test scores of their communication apprehension. After the instructions concerning ‘writing balanced chemical equation', ‘the law of conservation of mass', and ‘the law of definite proportions' for 7 class hours, students' chemistry problem solving ability and the perception to the paired think-aloud problem solving were examined. Two-way ANOVA results revealed that there was an interactive effect in the score of chemistry problem solving ability test. In simple effect test for the students of low communication apprehension, the scores of the heterogeneous group were found to be significantly higher than those of the control group. However, the students in homogeneous group had relatively positive perceptions to the paired think-aloud problem solving.

• Journal of Korea Water Resources Association
• /
• v.45 no.1
• /
• pp.39-52
• /
• 2012

Surface-subsurface interactions are an intrinsic component of the hydrologic response within a watershed. In general, these interactions are considered to be one of the most difficult areas of the discipline, particularly for the modeler who intends simulate the dynamic relations between these two major domains of the hydrological cycle. In essence, one major complexity is the spatial and temporal variations in the dynamically interacting system behavior. The proper simulation of these variations requires the need for providing an appropriate coupling mechanism between the surface and subsurface components of the system. In this study, an approach for modelling surface-subsurface flow and transport in a fully intergrated way is presented. The model uses the 2-dimensional diffusion wave equation for sheet surface water flow, and the Boussinesq equation with the Darcy's law and Dupuit-Forchheimer's assumption for variably saturated subsurface water flow. The coupled system of equations governing surface and subsurface flows is discretized using the finite volume method with central differencing in space and the Crank-Nicolson method in time. The interactions between surface and subsurface flows are considered mass balance based on the continuity conditions of pressure head and exchange flux. The major module consists of four sub-module (SUBFA, SFA, IA and NS module) is developed.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.20 no.1
• /
• pp.409-418
• /
• 2019

Debris flows occur in mountainous areas due to heavy rains resulting from climate change and result in disasters in the downstream area. The purpose of this study is to estimate the impact force of a debris flow when a check dam according is installed in various locations in the channel of a highly mountainous area. A Finite Differential Element Method (FDM) model was used to simulate the erosion and deposition based on the equation for the mass conservation and momentum conservation while considering the continuity of the fluid. The peak impact force from the debris flow occurred at 0 to 5 sec and 15 to 20 sec. When the supplied water discharge was increased, greater peak impact force was generated at 16 to 19 sec. This means that when increasing the water supply, the velocity of the debris flow became faster, which results in increased energy of the consolidation between the particles of the water and the sediment made. If a number of check dams were to be set up, it would be necessary to investigate the impact force at each location of the check dam. The results of this study could provide useful information in predicting the impact force of the debris flow and in installing the check dams in appropriate locations.

• Journal of Korean Society of Environmental Engineers
• /
• v.36 no.9
• /
• pp.597-603
• /
• 2014

The aim of the present study is to compare sound performance depending on thickness, materials, and structure of polymer soundproof panels consisting of PC, PMMA, HDPE, and PP, respectively. As a result of comparing sound transmission loss (STL) of single layer panel made of four types of polymer, the better sound transmission loss was obtained in order of PC, PMMA, HDPE, and PP, which was obviously followed mass law. 8 mm of single panel showed 5~6 dB(A) greater STL than that of 4 mm panels and lower frequency for coincidence effect so that STL of 8 mm panels decreased around 4,000~5,000 Hz, indicating less STL of 4 mm panels than those of 8 mm. When it comes to structure, 4 mm panels with air layer appeared similar value of STL with 8 mm single panels under 300 Hz. In range of high frequency above 2,000 Hz, 4 mm panels with air layer performed better than 8 mm of single layer panel while resonance effects were observed at 500~630 Hz. It was found that these results could be practically utilized as fundamental data for noise barriers design considering the change to each condition.

• Fire Science and Engineering
• /
• v.33 no.5
• /
• pp.37-47
• /
• 2019

In the present study, the influences of the fire curtain and natural vent in a theater fire were investigated through the numerical simulation of a reduced-scale model of a theater fire using the Fire Dynamics Simulator (FDS). Based on a previous experimental study using the reduced-scale model, the 1/14 reduced-scale model and its conditions were constructed according to the law of similarity with a real-scale theater. Through a series of numerical simulations, the smoke movements were visualized, and the temperatures in the stage and auditorium, mass flow rate of the outflow through natural vent, and time at which smoke started moving toward the auditorium were measured and analyzed. The general trends on the effects of the fire curtain and natural vent during the theater fire predicted by the present numerical simulation were similar to the previous experimental results. For quantitative comparison of the present numerical simulation and previous experimental results, the mean percentage errors of temperatures in the stage and auditorium, and the mass flow rate of outflow through the natural vent were calculated. The present numerical simulation results showed good agreement with previous experimental results with reasonable accuracy.

• Journal of Korean Society of Environmental Engineers
• /
• v.32 no.8
• /
• pp.787-794
• /
• 2010

Recently, with sudden increase of supplying rate of cars and quantity of goods transported, traffic noisy becomes one of important factors obstruct environment of exhibition and view facilities have purpose in calmness and unsatisfaction about this is high now. Therefore, in case of exhibition and view facilities, it has to be grasped that satisfaction degree about the noisy in and out of the exhibition room by performing effect valuation on traffic noisy from design step. However the level of internal noise cannot be measured at the design phrase of the structure due to the noise of traffic. Up until now a walls transmission loss, based on the law of mass, is predicted using this method. However measuring the internal sound level after actual construction reveals that there is a large difference from measurements made at the design stage, and it is very difficult to find a solution after the opening of the structure. From research looking from this perspective the internal sound level was predicted- calculating the internal sound absorption ability, using acoustic simulation and loss prevention of an insulated wall- based on data collected to evaluate the internal sound of an exhibition room at a Folk Museum adjacent to a freeway. The results of this research are considered to provide important data for the prediction of internal sound level at the time of construction of exhibition facilities similar to this.

• Fire Science and Engineering
• /
• v.32 no.3
• /
• pp.51-59
• /
• 2018

Although a fire curtain plays an important role in preventing smoke from spreading to the auditorium in a theater fire, there has been insufficient research on fire curtains. In this study, to check the accuracy of numerical simulation, for previous experiments using a reduced scale model, a numerical simulation was carried out, and the results were compared with previous experimental data. The fire curtain effect was then predicted numerically. A Fire Dynamics Simulator (FDS) was used, and the natural exhaust vent sizes were set to ~10%, ~5%, and ~1% of the stage floor area. The smoke movement was visualized, and the mass flow rates and temperatures were measured and analyzed. In addition, the law of similarity was used to examine the influence of a fire curtain in a real scale theater fire. Without the fire curtain, the present numerical simulation results were in agreement with the previous experimental data within reasonable accuracy. Meanwhile, the fire curtain affects the mass flow rates through the natural exhaust vent and proscenium opening, as well as the start time of soot outflow to the auditorium. Overall, the present results can be used to develop a fire curtain system.

• Journal of the Korean Society of Propulsion Engineers
• /
• v.3 no.2
• /
• pp.1-9
• /
• 1999

Applicability of the pressure gradient method which is formulated based on pressure gradient is verified against turbulent flow analysis. In the pressure gradient method, pressure gradient instead of pressure itself is obtained using continuity constraint. Since correct pressure gradient is found only when mass conservation is satisfied, pressure gradient method can reflect physics of flow field properly The pressure gradient method is formulated with semi-staggered grid system which locates each primitive variables on the same grid point but evaluates pressure gradient in-between. This grid system ensures easy programming and reflection of correct physics in analysis. For verifying applicability of this method, the pressure gradient method is applied to turbulent flow analysis with low Reynolds number $\kappa$-$\varepsilon$ model. Turbulent flows include fully developed channel flow, backward-facing step flow, and conical diffuser flow. Prediction results show that the pressure gradient method can be applied to turbulent flow analysis. However, the pressure gradient method requires somewhat long computation time. Proper way to find optimum under-relaxation factor, $\gamma$, is also need to be developed.