• Journal of Ocean Engineering and Technology
• /
• v.29 no.5
• /
• pp.359-365
• /
• 2015

A reliability analysis of the gravity-based foundation of anoffshore wind turbine was performed by considering the uncertainties of the design variables, including environmental loads. The limit state functions of the gravity-based foundation were defined using the response limits of the support structures suggested in the DNV standard. The wind load couldbe obtained using the GH_bladed software, and the wave load was calculated using the Morison equation. Then, the extreme distributions of the wind and wave loads were estimated by applying the peak over threshold (POT) method to the wind and wave load data. The probability distribution characteristics of the soil properties were defined with reference to a southwest coast geotechnical survey report. The reliability index was evaluated for each failure mode using a first-order reliability method.

• Progress in Superconductivity and Cryogenics
• /
• v.24 no.1
• /
• pp.29-33
• /
• 2022

Recently, development of a cryogenic fluids storage tank for storing or transporting liquid hydrogen is actively in progress. In cryogenic fluids storage tanks, hydrogen evaporates due to the extreme temperature difference inside and outside the tank. As the mass of the cryogenic fluids changes with continuous vaporization, the fluids level also changes. Therefore, there is need for a method of accurately measuring the level change in the storage tank. In the case of general cryogenic fluids, it is difficult to accurately measure the level because the dielectric constant is very low. As a method of measuring cryogenic fluids level with low dielectric constant, it can be used an Millimeter wave (MM wave) FMCW radar sensor. However, the signal sensitivity is very weak and the level accuracy is poor. In this paper, the signal sensitivity is improved by designing the horn lens antenna of the existing 80 GHz FMCW radar sensor. Horn lens antenna is fabricated by FDM/SLA type 3D printer according to horn and lens characteristics. The horn is used to increase the signal gain and the lens improves the signal straightness. This makes it possible to measure the level of cryogenic fluids with a low dielectric constant.

• Journal of Korean Society of Water and Wastewater
• /
• v.37 no.6
• /
• pp.447-456
• /
• 2023

Risk assessment on Jeju Special Self-Governing Province(JSSGP)'s water supply facilities and establishment of adaptation measures for climate crisis factors were implemented. JSSGP's vulnerability to the climate crisis was high in the order of drought, heat wave, heavy rain and strong wind. As a drought adaptation measure, policies of water saving and revenue water ratio improvement were considered. As for the heat wave adaptation measure, the introduction of an advanced water treatment process was suggested in response to the increase of algae cell number which resulting in taste and odor problem. As for heavy rain adaptation measures, the installation and operation of automatic coagulant injection devices for water purification plants that take turbid surface water were proposed. As a measure to adapt to strong winds, stabilization of power supply such as installation of dual power line was proposed in preparation for power outages. It is expected that water facilities will be able to supply high-quality tap water to customers even under extreme climate conditions without interruption through risk assessment for climate crisis factors and active implementation of adaptation measures.

• Journal of the Korean Geographical Society
• /
• v.41 no.5 s.116
• /
• pp.527-544
• /
• 2006

This study provides a definition of heat waves, which indicate the conditions of strong sultriness in summer, appropriate to Korea and intends to clarify long term(1973-2006) averaged spatial and temporal patterns of annual frequency of heat waves with respect to their intensity. Based on examination of the Korean mortality rate changes due to increase of apparent temperature under hot and humid summer conditions, three consecutive days with at least $32.5^{\circ}C,\;35.5^{\circ}C,\;38.5^{\circ}C,\;and\;41.5^{\circ}C$ of daily maximum Heat Index are defined as the Hot Spell(HS), the Heat Wave(HW), the Strong Heat Wave(SHW), and the Extreme Heat Wave(EHW), respectively. The annual frequency of all categories of heat waves is relatively low in high-elevated regions or on islands adjacent to seas. In contrast, the maximum annual frequency of heat waves during the study period as well as annual average frequency are highest in interior, low-elevated regions along major rivers in South Korea, particularly during the Changma Break period(between late July and mid-August). There is no obvious increasing or decreasing trend in the annual total frequency of all categories of heat waves for the study period However, the maximum annual frequencies of HS days at each weather station were recorded mainly in the 1970s, while most of maximum frequency records of both the HW and the SHW at individual weather stations were observed in the 1990s. It is also revealed that when heat waves occur in South Korea high humidity as well as high temperature contributes to increasing the heat wave intensity by $4.3-9.5^{\circ}C$. These results provide a useful basis to help develop a heat wave warning system appropriate to Korea.

• Journal of Ocean Engineering and Technology
• /
• v.26 no.4
• /
• pp.77-85
• /
• 2012

A study was performed on the design of a mooring line to maintain the position of a floating WEC (wave energy conversion) system. The procedure to design a mooring line is set up and the safety of the designed mooring system is evaluated using commercial software, Orcaflex. The characteristics curve for one line is analyzed to determine the properties and pretension of a mooring line. While considering the ocean environmental condition and importance of a floating WEC system, a multi-line layout is determined. A 4-point mooring system with 4 lines shows the instability in the yaw motion of the floating WEC system under a designed ocean environmental condition. The redesigned 4-point mooring system with 8 lines is found to be safe on the condition of a harsh ocean environment. The floating WEC system with the redesigned mooring system also shows stable motion in surge and pitch under operating conditions. From a parametric study on the mooring line length, the extreme value of the mooring line tension is found to be very sensitive to the pretension and length of mooring line. The results of this study can contribute to the establishment of a design procedure for mooring lines.

• Atmosphere
• /
• v.29 no.4
• /
• pp.451-461
• /
• 2019

Medium-range forecast is highly dependent on ensemble forecast data. However, operational weather forecasters have not enough time to digest all of detailed features revealed in ensemble forecast data. To utilize the ensemble data effectively in medium-range forecasting, representative weather patterns in East Asia in this study are defined. The k-means clustering analysis is applied for the objectivity of weather patterns. Input data used daily Mean Sea Level Pressure (MSLP) anomaly of the ECMWF ReAnalysis-Interim (ERA-Interim) during 1981~2010 (30 years) provided by the European Centre for Medium-Range Weather Forecasts (ECMWF). Using the Explained Variance (EV), the optimal study area is defined by 20~60°N, 100~150°E. The number of clusters defined by Explained Cluster Variance (ECV) is thirty (k = 30). 30 representative weather patterns with their frequencies are summarized. Weather pattern #1 occurred all seasons, but it was about 56% in summer (June~September). The relatively rare occurrence of weather pattern (#30) occurred mainly in winter. Additionally, we investigate the relationship between weather patterns and extreme weather events such as heat wave, cold wave, and heavy rainfall as well as snowfall. The weather patterns associated with heavy rainfall exceeding 110 mm day^-1 were #1, #4, and #9 with days (%) of more than 10%. Heavy snowfall events exceeding 24 cm day^-1 mainly occurred in weather pattern #28 (4%) and #29 (6%). High and low temperature events (> 34℃ and < -14℃) were associated with weather pattern #1~4 (14~18%) and #28~29 (27~29%), respectively. These results suggest that the classification of various weather patterns will be used as a reference for grouping all ensemble forecast data, which will be useful for the scenario-based medium-range ensemble forecast in the future.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.26 no.1
• /
• pp.33-40
• /
• 2014

Reliability analysis of jacket type offshore wind turbine (OWT) support structure under extreme ocean environmental loads was performed. Limit state function (LSF) of OWF support structure is defined by using structural dynamic response at mud-line. Then, the dynamic response is expressed as the static response multiplied by dynamic response factor (DRF). Probabilistic distribution of DRF is found from response time history under design significant wave load. Band limited beta distribution is used for internal friction angle of ground soil. Wind load is obtained in the form of thrust force from commercial code called GH_Bladed and then, applied to tower hub as random load. In a numerical example, the response surface method (RSM) is used to express LSF of jacket type support structure for 5MW OWF. Reliability index is found using first order reliability method (FORM).

• International Journal of Naval Architecture and Ocean Engineering
• /
• v.12 no.1
• /
• pp.213-225
• /
• 2020

Floating Offshore Wind Turbines (FOWT) installed in the deep sea regions where stable and strong wind flows are abundant would have significantly improved energy production capacity. When designing FOWT, it is essential to understand the stability and motion performance of the floater. Water tank model tests are required to evaluate these aspects of performance. This paper describes a model test and numerical simulation for a 750-kW semi-submersible platform wind turbine model-II. In the previous model test, the 750-kW FOWT model-I suffered slamming phenomena from extreme wave conditions. Because of that, the platform freeboard of model-II was increased to mitigate the slamming load on the platform deck structure in extreme conditions. Also, the model-I pitch Response Amplitude Operators (RAO) of simulation had strong responses to the natural frequency region. Thus, the hub height of model-II was decreased to reduce the pitch resonance responses from the low-frequency response of the system. Like the model-I, 750-kW FOWT model-II was built with a 1/40 scale ratio. Furthermore, the experiments to evaluate the performance characteristics of the model-II wind turbine were executed at the same location and in the same environment conditions as were those of model-I. These tests included a free decay test, and tests of regular and irregular wave conditions. Both the experimental and simulation conditions considered the blade rotating effect due to the wind. The results of the model tests were compared with the numerical simulations of the FOWT using FAST (Fatigue, Aerodynamics, Structures, and Turbulence) code from the National Renewable Energy Laboratory (NREL).

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.30 no.6
• /
• pp.286-297
• /
• 2018

In the present study, wave measurements at KOGA-W01 were analyzed and then the numerical wind waves simulations have been conducted to investigate the characteristics of wind waves in the Yellow sea. According to the present analysis, even though the location of the wave stations are close to the coastal region, the deep water waves are prevailed due to the short fetch length. Chun and Ahn's (2017a, b) numerical model has been extended to the Yellow Sea in this study. The effects of tide and tidal currents should be included in the model to accommodate the distinctive effect of large tidal range and tidal current in the Yellow Sea. The wave hindcasting results were compared with the wave measurements collected KOGA-W01 and Kyeockpo. The comparison shows the reasonable agreements between wave hindcastings and measured data, however the model significantly underestimate the wave period of swell waves from the south due to the narrow computational domain. Despite the poorly prediction in the significant wave period of swell waves which usually have small wave heights, the estimation of the extreme wave height and corresponding wave period shows good agreement with the measurement data.

• Journal of the Korean Applied Science and Technology
• /
• v.32 no.3
• /
• pp.394-404
• /
• 2015

This study investigated the pharmacodynamics of betaine on the blood profile and short chain fatty acid levels in meat ducks exposed to heat wave. 400 heads of Cherry valley (Anasplatyrhynchos) meat ducks were completely randomized to 5 treatments (4 repetitions each), and were raised for 42 days. They were grouped into T1 (heat wave control group without betaine), T2 (betaine 400 ppm), T3 (betaine 800 ppm), T4 (betaine 1200 ppm), and T5 (normal control group without betaine). Compared to T1, the betaine addition groups showed higher body weight gain at shipment, with T3 showing the highest significant difference. For hematological indictors measured (red blood cells and platelets), the betaine addition groups showed significantly higher values than the heat wave control group. The pH of the former was lower but their electrolytes ($K^+$, $P^+$, and $Cl^-$) were significantly higher compared to the latter. For blood gas concentration, the former showed a significantly higher value than the latter. For the total short chain fatty acids, acetic acid, and propionic acid, the betaine addition groups and group fed broiler-high temperature diet showed higher values than the heat wave control group. On the other hand, the former showed significantly lower values in butyric acid, isobutyric acid, valeric acid, and isovaleric acid than the latter group. These results suggest that betaine has the pharmacodynamics that mediate heat stress, via the maintenance and control of the blood profile, osmotic pressure, gas concentration, and short chain fatty acid, of meat ducks under heat wave.