• New & Renewable Energy
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• v.20 no.2
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• pp.26-34
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• 2024

Floating offshore wind turbines (FOWTs) have been developed to overcome large water depths and leverage the abundant wind resource in deep seas. However, wind-wave misalignment can occur depending on the weather conditions, and most megawatt (MW)-class turbines are horizontal-axis wind turbines subjected to yaw errors. Therefore, the power performance and dynamic response of super-large FOWTs exposed simultaneously to these external conditions must be analyzed. In this study, several scenarios combining wind-wave misalignment and yaw error were considered. The IEA 15 MW reference FOWT (v1.1.2) and OpenFAST (v3.4.1) were used to perform numerical simulations. The results show that the power performance was affected more significantly by the yaw error; therefore, the generator power reduction and variability increased significantly. However, the dynamic response was affected more significantly by the wind-wave misalignment increased; thus, the change in the platform 6-DOF and tower loads (top and base) increased significantly. These results can be facilitate improvements to the power performance and structural integrity of FOWTs during the design process.

• Nuclear Engineering and Technology
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• v.56 no.4
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• pp.1135-1144
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• 2024

With the increasing ratio of renewables in the grid, a low-carbon and stable base load source that also is capable of load tracking is in demand. Sodium cooled fast reactors (SFRs) coupled to thermal heat storage system (THS) is a strong candidate for the need. This research focuses on the designing and performance validation of a two-tank THS based on molten salt to integrate with a 280 MW_th sodium cooled fast reactor. Designing of the THS includes the vital component, sodium-to-salt heat exchanger which is a technology gap that needs to be filled, and designing and parameter selection of the tanks and related pumps. Modeling of the designed THS is conducted followed by the description of operation strategies and control logics of the THS. Finally, the dynamic simulation of the designed THS is conducted based on Fortran. Results show, the proposed power system meets the need of the design requirements to store heat for 18 h during a day and provide 500 MW_th for peak demand for the rest of the day.

• Journal of the Korean Society for Geothermal and Hydrothermal Energy
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• v.10 no.3
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• pp.8-16
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• 2014

Heating and hot water supply energy consumption of medium and multi boiler systems applied to military officer housing are compared with in-situ experiment and TRNSYS dynamic simulation program. In a multiple boiler system, small capacity boilers are connected in parallel to meet the required capacity. For handling partial loads, medium capacity boiler relies on on-off control, while multi boiler adopts PI control. Since multi boiler has higher efficiency and better control strategy, the results show that energy consumption can be reduced significantly with the multi boiler system.

• The Korean Journal of Ceramics
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• v.7 no.2
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• pp.63-69
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• 2001

We investigated strength degradations from cyclic contact fatigue in self-toughened glass-ceramics. Hertzian indentation was used to induce cyclic contact load. Dynamic fatigue was also performed with changing stress rates from 0.01 to 10000 MPa/sec. After that, strength data and fracture origins were analysed. As the number of contact cycles increased or stressing rate decreased, severe strength degradation occurred by as much as 50% because of radial cracks developed from microcrack coalescence.

• Proceedings of the Korean Radioactive Waste Society Conference
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• 2003.11a
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• pp.73-77
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• 2003

In order to predict the dynamic behaviors of uranium and cobalt in a fixed bed at various influent pH values of liquid waste, the adsorption system was regarded as multi-component adsorption between each ionic species in a solution. Langmuir isotherm parameters of each species were extracted by incorporating equilibrium data with the solution chemistry of uranium and cobalt using IAST. Prediction results were in good agreement with the experimental data, except for a high concentration and pH. Although there was some limitations in predicting the cobalt adsorption, this method may be useful in analyzing a complex adsorption system where various kinds of ionic species exist in a solution.

• ETRI Journal
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• v.40 no.5
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• pp.604-612
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• 2018

To solve the problem of unbalanced loads and the short network lifetime of heterogeneous wireless sensor networks, this paper proposes a node-selection algorithm based on energy balance and dynamic adjustment. The spacing and energy of the nodes are calculated according to the proximity to the network nodes and the characteristics of the link structure. The direction factor and the energy-adjustment factor are introduced to optimize the node-selection probability in order to realize the dynamic selection of network nodes. On this basis, the target path is selected by the relevance of the nodes, and nodes with insufficient energy values are excluded in real time by the establishment of the node-selection mechanism, which guarantees the normal operation of the network and a balanced energy consumption. Simulation results show that this algorithm can effectively extend the network lifetime, and it has better stability, higher accuracy, and an enhanced data-receiving rate in sufficient time.

• Journal of Information Processing Systems
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• v.7 no.1
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• pp.29-42
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• 2011

Wireless sensor networks are composed of a large number of sensor nodes with limited energy resources. One critical issue in wireless sensor networks is how to gather sensed information in an energy efficient way, since their energy is limited. The clustering algorithm is a technique used to reduce energy consumption. It can improve the scalability and lifetime of wireless sensor networks. In this paper, we introduce a clustering protocol with mode selection (CPMS) for wireless sensor networks. Our scheme improves the performance of BCDCP (Base Station Controlled Dynamic Clustering Protocol) and BIDRP (Base Station Initiated Dynamic Routing Protocol) routing protocol. In CPMS, the base station constructs clusters and makes the head node with the highest residual energy send data to the base station. Furthermore, we can save the energy of head nodes by using the modes selection method. The simulation results show that CPMS achieves longer lifetime and more data message transmissions than current important clustering protocols in wireless sensor networks.

• Steel and Composite Structures
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• v.5 no.5
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• pp.345-358
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• 2005

The response of single story buildings and other case studies are investigated to observe trends in response and to develop a better understanding of the impact of some design parameters on the seismic response of CBF. While it is recognized that many parameters have an influence on the behavior of braced frames, the focus of this study is mostly on quantifying energy dissipation in compression and its effectiveness on seismic performance. Based on dynamic analyses of single story braced frame and case studies, it is found that a bracing member designed with bigger R and larger KL/r results in lower normalized cumulative energy, i.e., cumulative compressive energy normalized by the corresponding tensile energy (${\sum}E_C/E_T$), in both cases.

• Structural Engineering and Mechanics
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• v.54 no.4
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• pp.809-827
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• 2015

In this paper, seismic energy response of inelastic steel structures under earthquake excitations is investigated. For this purpose, a numerical procedure based on nonlinear dynamic analysis is developed by considering material, geometric and connection nonlinearities. Material nonlinearity is modeled by the inversion of Ramberg-Osgood equation. Nonlinearity caused by the interaction between the axial force and bending moment is also defined considering stability functions, while the geometric nonlinearity caused by axial forces is described using geometric stiffness matrix. Cyclic behaviour of steel connections is taken into account by employing independent hardening model. Dynamic equation of motion is solved by Newmark's constant acceleration method in the time history domain. Energy response analysis of space frames is performed by using this proposed numerical method. Finally, for the first time, the distribution of the different energy types versus time at the duration of the earthquake ground motion is obtained where in addition error analysis for the numerical solutions is carried out and plotted depending on the relative error calculated as a function of energy balance versus time.

• Journal of Power System Engineering
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• v.21 no.6
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• pp.62-67
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• 2017

In order to achieve high efficiency of energy use and environment-friendly architectural design, various loads such as cooling, heating and hot water required by the building sector must be accurately predicted. Many studies used dynamic simulation tool to evaluate and analyze building energy performance. However, there are few studies on the comparative analysis of load results by each simulation and the evaluation of simulation characteristics and functions. In this study, the cooling, heating loads and energy demand of the buildings were evaluated using three dynamic simulations for the building with the same input conditions, and the characteristics of each simulation were compared and analyzed through the results. As a result of simulation comparative analysis, cooling, heating load and energy demand was lowest in square type and north-south direction conditions.