• Title/Summary/Keyword: Dynamic Grid

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Numerical Study on Taylor Bubble Rising in Pipes

  • Shin, Seung Chul;Lee, Gang Nam;Jung, Kwang Hyo;Park, Hyun Jung;Park, Il Ryong;Suh, Sung-bu
    • Journal of Ocean Engineering and Technology
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    • v.35 no.1
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    • pp.38-49
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    • 2021
  • Slug flow is the most common multi-phase flow encountered in oil and gas industry. In this study, the hydrodynamic features of flow in pipes investigated numerically using computational fluid dynamic (CFD) simulations for the effect of slug flow on the vertical and bent pipeline. The compressible Reynold averaged Navier-Stokes (RANS) equation was used as the governing equation, with the volume of fluid (VOF) method to capture the outline of the bubble in a pipeline. The simulations were tested for the grid and time step convergence, and validated with the experimental and theoretical results for the main hydrodynamic characteristics of the Taylor bubble, i.e., bubble shape, terminal velocity of bubble, and the liquid film velocity. The slug flow was simulated with various air and water injection velocities in the pipeline. The simulations revealed the effect of slug flow as the pressure occurring in the wall of the pipeline. The peak pressure and pressure oscillations were observed, and those magnitudes and trends were compared with the change in air and water injection velocities. The mechanism of the peak pressures was studied in relation with the change in bubble length, and the maximum peak pressures were investigated for the different positions and velocities of the air and water in the pipeline. The pressure oscillations were investigated in comparison with the bubble length in the pipe and the oscillation was provided with the application of damping. The pressures were compared with the case of a bent pipe, and a 1.5 times higher pressures was observed due to the compression of the bubbles at the corner of the bent. These findings can be used as a basic data for further studies and designs on pipeline systems with multi-phase flow.

A Study on Characteristic of Hybrid PCS for Solar Power Generation Considering on a Residential Lithium Battery ESS. (가정용 리튬배터리 ESS를 고려한 태양광 발전 하이브리드 PCS 특성에 관한 연구)

  • Hwang, Lark-Hoon;Na, Seung-kwon;Choi, Byung-Sang
    • Journal of Advanced Navigation Technology
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    • v.26 no.1
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    • pp.35-45
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    • 2022
  • In this paper, we modeled the devices used easily in PV system circuits. In addition, for full operation of the photovoltaic system, a complete operation system for the DC-DC buck-boost converter and the MPPT control system was modeled and simulated to confirm good operation. we were constructed an actual system with the same conditions in the simulation and experimented. The purpose is to confirm the stable power supply through the load leveling by presenting the PCS considering ESS of photovoltaic power generation. we will do study to apply hybrid capacitors that have high energy density to the same size compared to the EDLC to DVR. As a result, we proposed a single-phase 3 kW grid-connected solar power converter.

Prediction of Rolling Moment for a Hand-Launched UAV Considering the Interference Effect of Propeller Wake (프로펠러 후류 간섭 효과를 고려한 투척식 무인기 롤 모멘트 예측)

  • Sang-Mann, Woo;Dong-Hyun, Kim;Ji-Min, Park
    • Journal of Aerospace System Engineering
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    • v.16 no.6
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    • pp.114-122
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    • 2022
  • This paper explores three-dimensional unsteady computational fluid dynamic (CFD) analyses with an overset grid technique to analyse the wake effect created by a rotating propeller on a hand-launched unmanned aerial vehicle (UAV). Additionally, the influence of actual aileron deflection on the equilibrium condition of the rolling moment is examined in various hand-launched take-off conditions. The results of this study demonstrate the importance of initial aileron deflection in increasing the initial rolling stability during the hand-launched take-off process. Furthermore, an aerodynamic database is constructed to rapidly predict the aileron set values required for different take-off speeds and angle-of-attacks.

Horizon Run Spin-off Simulations for Studying the Formation and Expansion history of Early Universe

  • Kim, Yonghwi;Park, Jaehong;Park, Changbom;Kim, Juhan;Singh, Ankit;Lee, Jaehyun;Shin, Jihye
    • The Bulletin of The Korean Astronomical Society
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    • v.46 no.2
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    • pp.45.1-45.1
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    • 2021
  • Horizon Run 5 (HR5) is a cosmological hydrodynamical simulation which captures the properties of the Universe on aGpc scale while achieving a resolution of 1kpc. This enormous dynamic range allows us to simultaneously capture the physics of the cosmic web on very large scales and account for the formation and evolution of dwarf galaxies on much smaller scales. On the back of a remarkable achievement of this, we have finished to run follow-up simulations which have 2 times larger volume than before and are expected to complementary to some limitations of previous HR simulations both for the study on the large scale features and the expansion history in a distant Universe. For these simulations, we consider the sub-grid physics of radiative heating/cooling, reionization, star formation, SN/AGN feedbacks, chemical evolution and the growth of super-massive blackholes. In order to do this project, we implemented a hybrid MPI-OpenMP version of the RAMSES code, 'RAMSES-OMP', which is specifically designed for modern many-core many thread parallel systems. These simulation successfully reproduce various observation result and provide a large amount of statistical samples of Lyman-alpha emitters and protoclusters which are important to understand the formation and expansion history of early universe. These are invaluable assets for the interpretation of current ΛCDM cosmology and current/upcoming deep surveys of the Universe, such as the world largest narrow band imaging survey, ODIN (One-hundred-square-degree Dark energy camera Imaging in Narrow band).

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Performance Evaluation of Machine Learning Model for Seismic Response Prediction of Nuclear Power Plant Structures considering Aging deterioration (원전 구조물의 경년열화를 고려한 지진응답예측 기계학습 모델의 성능평가)

  • Kim, Hyun-Su;Kim, Yukyung;Lee, So Yeon;Jang, Jun Su
    • Journal of Korean Association for Spatial Structures
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    • v.24 no.3
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    • pp.43-51
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    • 2024
  • Dynamic responses of nuclear power plant structure subjected to earthquake loads should be carefully investigated for safety. Because nuclear power plant structure are usually constructed by material of reinforced concrete, the aging deterioration of R.C. have no small effect on structural behavior of nuclear power plant structure. Therefore, aging deterioration of R.C. nuclear power plant structure should be considered for exact prediction of seismic responses of the structure. In this study, a machine learning model for seismic response prediction of nuclear power plant structure was developed by considering aging deterioration. The OPR-1000 was selected as an example structure for numerical simulation. The OPR-1000 was originally designated as the Korean Standard Nuclear Power Plant (KSNP), and was re-designated as the OPR-1000 in 2005 for foreign sales. 500 artificial ground motions were generated based on site characteristics of Korea. Elastic modulus, damping ratio, poisson's ratio and density were selected to consider material property variation due to aging deterioration. Six machine learning algorithms such as, Decision Tree (DT), Random Forest (RF), Support Vector Machine (SVM), K-Nearest Neighbor (KNN), Artificial Neural Networks (ANN), eXtreme Gradient Boosting (XGBoost), were used t o construct seispic response prediction model. 13 intensity measures and 4 material properties were used input parameters of the training database. Performance evaluation was performed using metrics like root mean square error, mean square error, mean absolute error, and coefficient of determination. The optimization of hyperparameters was achieved through k-fold cross-validation and grid search techniques. The analysis results show that neural networks present good prediction performance considering aging deterioration.

A Study on a Real-Time Aerial Image-Based UAV-USV Cooperative Guidance and Control Algorithm (실시간 항공영상 기반 UAV-USV 간 협응 유도·제어 알고리즘 개발)

  • Do-Kyun Kim;Jeong-Hyeon Kim;Hui-Hun Son;Si-Woong Choi;Dong-Han Kim;Chan Young Yeo;Jong-Yong Park
    • Journal of the Society of Naval Architects of Korea
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    • v.61 no.5
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    • pp.324-333
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    • 2024
  • This paper focuses on the cooperation between Unmanned Aerial Vehicle (UAV) and Unmanned Surface Vessel (USV). It aims to develop efficient guidance and control algorithms for USV based on obstacle identification and path planning from aerial images captured by UAV. Various obstacle scenarios were implemented using the Robot Operating System (ROS) and the Gazebo simulation environment. The aerial images transmitted in real-time from UAV to USV are processed using the computer vision-based deep learning model, You Only Look Once (YOLO), to classify and recognize elements such as the water surface, obstacles, and ships. The recognized data is used to create a two-dimensional grid map. Algorithms such as A* and Rapidly-exploring Random Tree star (RRT*) were used for path planning. This process enhances the guidance and control strategies within the UAV-USV collaborative system, especially improving the navigational capabilities of the USV in complex and dynamic environments. This research offers significant insights into obstacle avoidance and path planning in maritime environments and proposes new directions for the integrated operation of UAV and USV.

A Study on Task Allocation of Parallel Spatial Joins using Fixed Grids (고정 그리드를 이용한 병렬 공간 조인의 태스크 할당에 관한 연구)

  • Kim, Jin-Deok;Seo, Yeong-Deok;Hong, Bong-Hui
    • The KIPS Transactions:PartD
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    • v.8D no.4
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    • pp.347-360
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    • 2001
  • The most expensive spatial operation in spatial databases is a spatial join which computes a combined table of which tuple consists of two tuples of the two tables satisfying a spatial predicate. Although the execution time of sequential processing of a spatial join has been so far considerably improved, the response time is not tolerable because of not meeting the requirements of interactive users. It is usually appropriate to use parallel processing to improve the performance of spatial join processing. However, as the number of processors increases, the efficiency of each processor decreases rapidly because of the disk bottleneck and the overhead of message passing. This paper proposes the method of task allocation to soften the disk bottleneck caused by accessing the shared disk at the same time, and to minimize message passing among processors. In order to evaluate the performance of the proposed method in terms of the number of disk accesses and message passing, we conduct experiments on the two kinds of parallel spatial join algorithms. The experimental tests on the MIMD parallel machine with shared disks show that the proposed semi-dynamic task allocation method outperforms the static and dynamic task allocation methods.

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Performance Evaluation of FDS for Predicting the Unsteady Fire Characteristics in a Semi-Closed ISO 9705 Room (반밀폐된 ISO 9705 화재실에서 비정상 화재특성 예측을 위한 FDS의 성능평가)

  • Mun, Sun-Yeo;Hwang, Cheol-Hong
    • Fire Science and Engineering
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    • v.26 no.3
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    • pp.21-28
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    • 2012
  • The objective of this study is to evaluate the prediction accuracy of FDS(Fire Dynamic Simulator) for the thermal and chemical characteristics of under-ventilated fire with unsteady fire growth in a semi-closed compartment. To this end, a standard doorway width of the full-scale ISO 9705 room was modified to 0.1 m and the flow rate of heptane fuel was increased linearly with time (until maximum 2.0 MW based on ideal heat release rate) using a spray nozzle located at the center of enclosure. To verify the capability of FDS, the predicted results were compared with a previous experimental data under the identical fire conditions. It was observed that with an appropriate grid system, the numerically predicted temperature and heat flux inside the compartment showed reasonable agreement with the experimental data. On the other hand, there were considerable limitations to predict accurately the unsteady behaviors of CO and CO2CO2 concentration under the condition of continuous fire growth. These results leaded to a discrepancy between the present evaluation of FDS and the previous evaluation conducted for steady-state under-ventilated fires. It was important to note that the prediction of transient CO production characteristics using FDS was approached carefully for the under-ventilated fire in a semi-closed compartment.

Modeling Three-dimensional Free Surface Flow around Thin Wall Incorporation Hydrodynamic Pressure on δ-coordinate (δ-좌표계에서 동수압 계산 수중벽체 인근흐름 수치모형실험)

  • Kim, Hyo-Seob;Yoo, Ho-Jun;Jin, Jae-Yul;Jang, Chang-Hwan;Lee, Jung-Su;Baek, Seung-Won
    • Journal of Wetlands Research
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    • v.16 no.3
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    • pp.327-336
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    • 2014
  • Submerged thin walls are extreme case of submerged rectangular blocks, and could be used for many purposes in rivers or coastal zones, e.g. to tsunami. To understand flow characteristics including flow and pressure fields around a specific submerged thin wall a numerical model was applied which includes computation of hydrodynamic pressure on σσ-coordinate. σσ-coordinate has strong merits for simulation of subcritical flow over mild-sloped beds. On the other hand σσ-coordinate is quite poor to treat sharp structures on the bed. There have been a few trials to incorporate dynamic pressure in σσ-coordinate by some researchers. One of the previous approaches includes process of sloving the Poisson equation. However, the above method includes many high-order terms, and requires long cpu for simulation. Another method SOLA was developed by Hirt et al. for computation of dynamic pressure, but it was valid for straight grid system only. Previous SOLA was modified for σσ-coordinate for the present purpose and was adopted in a model system, CST3D. Computed flow field shows reasonable behaviour including vorticity is much stronger than the upstream and downstream of the structure. The model was verified to laboratory experiments at a 2DV flume. Time-average flow vectors were measured by using one-dimensional electro-magnetic velocimeter. Computed flow field agrees well with the measured flow field within 10 % error from the speed point of view at 5 profiles. It is thought that the modified SOLA scheme is useful for σσ-coordinate system.

Active VM Consolidation for Cloud Data Centers under Energy Saving Approach

  • Saxena, Shailesh;Khan, Mohammad Zubair;Singh, Ravendra;Noorwali, Abdulfattah
    • International Journal of Computer Science & Network Security
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    • v.21 no.11
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    • pp.345-353
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    • 2021
  • Cloud computing represent a new era of computing that's forms through the combination of service-oriented architecture (SOA), Internet and grid computing with virtualization technology. Virtualization is a concept through which every cloud is enable to provide on-demand services to the users. Most IT service provider adopt cloud based services for their users to meet the high demand of computation, as it is most flexible, reliable and scalable technology. Energy based performance tradeoff become the main challenge in cloud computing, as its acceptance and popularity increases day by day. Cloud data centers required a huge amount of power supply to the virtualization of servers for maintain on- demand high computing. High power demand increase the energy cost of service providers as well as it also harm the environment through the emission of CO2. An optimization of cloud computing based on energy-performance tradeoff is required to obtain the balance between energy saving and QoS (quality of services) policies of cloud. A study about power usage of resources in cloud data centers based on workload assign to them, says that an idle server consume near about 50% of its peak utilization power [1]. Therefore, more number of underutilized servers in any cloud data center is responsible to reduce the energy performance tradeoff. To handle this issue, a lots of research proposed as energy efficient algorithms for minimize the consumption of energy and also maintain the SLA (service level agreement) at a satisfactory level. VM (virtual machine) consolidation is one such technique that ensured about the balance of energy based SLA. In the scope of this paper, we explore reinforcement with fuzzy logic (RFL) for VM consolidation to achieve energy based SLA. In this proposed RFL based active VM consolidation, the primary objective is to manage physical server (PS) nodes in order to avoid over-utilized and under-utilized, and to optimize the placement of VMs. A dynamic threshold (based on RFL) is proposed for over-utilized PS detection. For over-utilized PS, a VM selection policy based on fuzzy logic is proposed, which selects VM for migration to maintain the balance of SLA. Additionally, it incorporate VM placement policy through categorization of non-overutilized servers as- balanced, under-utilized and critical. CloudSim toolkit is used to simulate the proposed work on real-world work load traces of CoMon Project define by PlanetLab. Simulation results shows that the proposed policies is most energy efficient compared to others in terms of reduction in both electricity usage and SLA violation.