• Energy Research

Abstract The dynamic responses of a Li-ion battery pack deployed on hybrid electric vehicles are studied with a high fidelity finite element model and a parametric reduced-order model. The effects of microstructure transformation in the electrode materials caused by lithium-ion intercalation/deintercalation on the evolution of dynamic responses are investigated including the effects of the state of charge, aging, and cell-to-cell variations. The dynamic responses obtained from a finite element analysis show two interesting phenomena. First, the high modal density is controllable with the design modification of a pack component. Second, dynamic responses, especially the evolution of the natural frequencies of the fixed-boundary modes, of a Li-ion battery pack provide useful information to estimate the dynamic states or health states of the battery. A probabilistic analysis is also carried out considering stochastic operational conditions of hybrid electric vehicles with a parametric reduced-order model. The probabilistic analysis not only suggests appropriate modes and locations for monitoring its dynamic responses, but also determines the maximum response level of every cell in the battery pack. The proposed modeling approach can improve the safety and reliability of the structural design of battery cells and packs. Furthermore, it can be useful for the identification of the battery states during the operation.

This study presents a concise yet effective approach for vertically extrapolating Weibull parameters, using the power law approximation of the wind velocity profile, which describes the exponential increase in mean wind speed with height, as specified in IEC 61400-1. A robust method is necessary to extrapolate wind data collected at lower mast heights to higher locations. Current extrapolation methods are typically constrained in their applicable height range, requiring the development of a new model to accommodate the trend toward larger wind turbines. The proposed formulation is based on extrapolating the Weibull shape and scale parameters from a reference height and assuming a power law velocity profile controlled by the wind shear exponent. The extrapolation function was derived by stretching the Weibull distribution to align with a power law relating average wind speed to height, followed by normalization of the result. Also, a revised empirical formula for the vertical extrapolation of Weibull parameters to heights exceeding 100 m is proposed and validated for accuracy. The Weibull parameter extrapolation method introduced in this study is particularly useful for wind farm development and estimating conditions relevant to the flight testing of unmanned aerial vehicles.

Abstract Wind resource assessments with onsite wind data are indispensable when estimating the economic feasibility of developing a large-scale commercial offshore wind farm. However, several factors of the data measured from a meteorological mast, including short observation period and instrument errors, may result in uncertainty concerning wind resource assessments. To mitigate the uncertainty of wind resource assessments at the candidate site for a large-scale commercial offshore wind farm, HeMOSU-1, the first offshore meteorological mast in Asia, has been in operation for more than 6 years since it was installed at the western coast of the Korean Peninsula in 2010. A vertical wind lidar was also installed for quantitative evaluations and calibrations of the measured data from HeMOSU-1. This study analyzed several parameters associated with the long-term wind characteristics through cross-validation between HeMOSU-1 and the wind lidar. The parameters affecting the prediction results include the shading effect from the mast, year-to-year variation, the long-term correction methods, and the period of onsite measurements. Based on this analysis, long-term wind potentials are estimated with reliable parameters.

Abstract We have conducted a feasibility study on the development of offshore wind farms around the Korean Peninsula as part of the national plan. This study deals with the selection of the optimal site for an offshore wind farm. We set rating indices in order to select an optimal site of the candidate coasts, which include the expected B/C (benefit to cost) ratio, the possible installation capacity of the wind farm, the convenience of grid connection, and so on, for each candidate site. The expected B/C ratio is described as the benefit from the annual energy production compared to the costs that correspond to the construction of the turbine foundation, and the grid connection between the offshore wind farm and the substation on land. It can be found from the evaluation that the construction costs associated with the substructure and grid connection are crucial in determining the location of the first offshore wind farm in Korea. Consequently, we could select a top site among the candidate sites to be implemented as the first national project of offshore wind farm development.

Abstract This paper reviews foundations for offshore wind energy convertors considering the significant growth of offshore wind energy since the early 2000s. The characteristics of various foundation types (i.e., gravity, pile, suction caisson, and float type) and the current status of field application are discussed. Moreover, the mechanical characteristics of soil are described in the sense that these characteristics including modulus, strength, damping, and modulus degradation of soil play critical roles for the design of offshore foundations. By using these mechanical properties of soil, theoretical studies to consider structure-soil interaction are classified (into equivalent spring models, distributed spring models, and continuous element models) and explained. Field and laboratory experiments on the response of structure embedded in soil to static and dynamic loads are discussed. Based on the review of previous studies, directions for future research and study on offshore wind turbine are suggested.

Abstract In recent years, many countries have been endeavoring to exploit the offshore wind energy in terms of overcoming the limitations of on-land wind energy. Considering that mountains cover 70 percent of the Korean Peninsula and arable plains for wind energy are negligibly small, Korean government aggressively drives the offshore wind development of the Korean Peninsula. In this context, KEPCO-RI (Korea Electric Power Corporation-Research Institute) has been performing a feasibility study for construction of the first offshore wind farm in Korea, including wind resource assessments around the Korean Peninsula. This paper provides a summary of the offshore wind resources of the Korean Peninsula, by analyzing marine buoy datasets measured at 5 positions over the period of 12 years, the QuikSCAT satellite data measured over 9 years, and a numerical wind map based on meteorological data measured for 4 years. Based on these datasets, wind resources are assessed, and economical efficiency is evaluated by means of the expected capacity factor. The analyzing results will be utilized to decide location of the first offshore wind farm in Korea.

Although design of offshore wind turbines has many similarities to that of onshore turbines, a lot of considerations should be made for the additional substructure imposed on hydrodynamic loads. The additional substructure prolongs the total tower length, increasing the tower bending moment and lowering the natural bending frequencies of the tower. Accordingly, system dynamic analyses associated with hydrodynamic load should be performed in the frequency domain in order to avoid bending modes of tower from the operation frequency ranges. In this paper, a method to generate hydrodynamic load for a finite element analysis is introduced, considering the characteristics of sea conditions for a candidate site of demonstration offshore wind farm in the west sea of Korea. In addition, a wind energy conversion system with a monopile foundation is fully modeled using the finite element method to simulate the various conditions based on IEC standard. Based on the FEM analyses of tower bending modes, optimal dimensions of the monopile for the candidate site are proposed.

Previous evaluations of the safety of the Ulchin Nuclear Power Plant in the event of a tsunami have the shortcoming of uncertainty of the tsunami sources. To address this uncertainty, maximum and minimum wave heights at the intake of Ulchin NPP have been estimated through a parametric study, and then assessment of the safety margin for the intake has been carried out. From the simulation results for the Ulchin NPP site, it can be seen that the coefficient of eddy viscosity considerably affects wave height at the inside of the breakwater. In addition, assessment of the safety margin shows that almost all of the intake water pumps have a safety margin over 2 m, and Ulchin NPP site seems to be safe in the event of a tsunami according to this parametric study, although parts of the CWPs rarely have a margin for the minimum wave height.