• Magazine of the Korean Society of Agricultural Engineers
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• v.36 no.3
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• pp.113-121
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• 1994

Since it is difficult to expect the normal production of plants in greenhouses during hot summer season in Korea, certain provisions on the control of extreme environmental factors in summer should be considered for the year-round cultivation in greenhouses. This study was carried out to find a method to suppress the temperature rising of nutrient solution by cooling, which is able to contribute to the improvement of the plant growth environment in hydroponic greenhouse during hot summer season. A mechanical cooling system using the counter flow type with double pipe was developed for cooling the nutrient solution efficiently. Also the heat transfer characteristics of the system was analysed experimentally and theoretically, and compared with the existing cooling systems of nutrient solution. The cooling capacities of three different Systems, which used polyethylene tube in solution tank, stainless tube in solution tank, and the counter flow type with double pipe, were evaluated. The performance of each cooling system was about 41 %, 70% and 81 % of design cooling load in hydroponic greenhouse of 1 ,000m$^2$ on the conditions that the flow rate of ground water was 2m$^3$/hr and the temperature difference between two liquids was 10 ˚C According to the results analysed as above, the cooling system was found to have a satisfactory cooling capability for regions where ground water supply is available. Fer the other regions where ground water supply is restricted, more efficient cooling System should be developed.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.29 no.11
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• pp.53-58
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• 2015

Systemic heating and cooling air conditioning systems are popular in various industrial fields and even home. Recently, the rate of supply of this kind of multi-heat pump has been increased under ESCO financing supporting system. Generally the heat pumping system has a structural simplicity and easy installation benefits. and has good running efficiency under normal designed condition. But under extreme climate condition (over $+30^{\circ}C$, under $-10^{\circ}C$), this system exposes abnormal power consumption. It causes high progressive electric power rates and resultant peak power capacity of power plant. In this paper, a novel system concept of buffering refrigerant accumulator and constant pressure control system to relieve peak power load is proposed and this system's utility is verified with an prototype experimental system.

• International Journal of Ocean System Engineering
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• v.2 no.2
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• pp.82-91
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• 2012

Fillet welding is widely used in the assembly of ships and offshore structures. The T-joint configuration is frequently reported to experience fatigue damage when a marine structure meets extreme loads such as storm loads. Fatigue damage is affected by the magnitude of residual stresses on the weld. Recently, many shipping registers and design guides have required that the fatigue strength assessment procedure of seagoing structures under wave-induced random loading and storm loading be compensated based on the effect of residual stresses. We propose a computational procedure to analyze the residual stresses in a T-joint. Residual stresses are measured by the X-ray diffraction (XRD) method, and a 3-D finite element analysis (FEA) is performed to obtain the residual stress profile in the T-joint. The proposed finite element model is validated by comparing experiments with computational results, and the characteristics of the residual stresses in the T-joint are discussed.

• Journal of Korean Society on Water Environment
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• v.27 no.1
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• pp.88-97
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• 2011

To identify the inflow and outflow characteristics of allchthonous organic matters and examine the change of allochthonous organic matter load pattern due to the climate change, we investigated the temporal variations of DOC and POC concentrations within inflow water and dam discharge water and spatio-temporal distribution of POM within the lake water in Lake Soyang which is the largest dam reservoir in Korea in 2006. Most of allochthonous DOC flowed into the lake water during initial rain and was not affected by the amount of precipitation, whereas most of allochthonous POC flowed into during concentrated heavy rain and the concentration of POC was significantly associated with the amount of inflow water and precipitation. Calculated annual allochthonous organic matter loads in Lake Soyang from 2003 to 2006 using the regression equation between the amount of inflow water and the concentration of POC indicate allochthonous organic matter loads are mainly affected by total influx and extreme influx of inflow water. The spatio-temporal distribution of POM indicated allochthonous organic matter of inflow river during flood period in July transported from upper part to middle and lower part of the lake a month later respectively along the middle layer of water column in Lake Soyang.

• Wind and Structures
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• v.37 no.2
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• pp.95-104
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• 2023

The latest revision of AS/NZS 1170.2 incorporates some new research and knowledge on strong winds, climate change, and shape factors for new structures of interest such as solar panels. Unlike most other jurisdictions, Australia and New Zealand covers a vast area of land, a latitude range from 11° to 47°S climatic zones from tropical to cold temperate, and virtually every type of extreme wind event. The latter includes gales from synoptic-scale depressions, severe convectively-driven downdrafts from thunderstorms, tropical cyclones, downslope winds, and tornadoes. All except tornadoes are now covered within AS/NZS 1170.2. The paper describes the main features of the 2021 edition with emphasis on the new content, including the changes in the regional boundaries, regional wind speeds, terrain-height, topographic and direction multipliers. A new 'climate change multiplier' has been included, and the gust and turbulence profiles for over-water winds have been revised. Amongst the changes to the provisions for shape factors, values are provided for ground-mounted solar panels, and new data are provided for curved roofs. New methods have been given for dynamic response factors for poles and masts, and advice given for acceleration calculations for high-rise buildings and other dynamically wind-sensitive structures.

• Steel and Composite Structures
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• v.48 no.3
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• pp.251-262
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• 2023

There are many examples of steel structures subjected to severe environmental conditions with bolted connections directly exposed to extreme climatic agents such as freeze-thaw cycles or low temperatures. Some examples are: steel bridges, mining transfer towers, wind towers... These service conditions neither are included in Eurocode 3 or EN1090-2, nor there are references in other international standards. In this experimental research, 46 specimens of non-slip joints with HV M20 bolts and four different types of contact surfaces have been studied. Half of the specimens were subjected to fourteen twelve-hours freeze-thaw cycles, with periodic immersion in water and temperature oscillation. Subsequently, half of the connections were subjected to a slip test under monotonic load at temperature of -20 ± 0.5 ℃ and the other half at room temperature. The results were compared with others equal joints not subjected to freeze-thaw cycles and kept at room temperature for the same time. This finally resulted in 4 sets of joints by combining the freeze-thaw degradation or not with the low-temperature conditions or not in the slip testing. Therefore, a total of 16 different conditions were studied by also considering 4 different contact surfaces between the joined plates in each set. The results obtained show influence of environmental conditions on the slip resistant capacity of these joints.

• Wind and Structures
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• v.36 no.6
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• pp.355-366
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• 2023

Although machine learning (ML) techniques have been widely used in various fields of engineering practice, their applications in the field of wind engineering are still at the initial stage. In order to evaluate the feasibility of machine learning algorithms for prediction of wind loads on high-rise buildings, this study took the exposure category type, wind direction and the height of local wind force as the input features and adopted four different machine learning algorithms including k-nearest neighbor (KNN), support vector machine (SVM), gradient boosting regression tree (GBRT) and extreme gradient (XG) boosting to predict wind force coefficients of CAARC standard tall building model. All the hyper-parameters of four ML algorithms are optimized by tree-structured Parzen estimator (TPE). The result shows that mean drag force coefficients and RMS lift force coefficients can be well predicted by the GBRT algorithm model while the RMS drag force coefficients can be forecasted preferably by the XG boosting algorithm model. The proposed machine learning based algorithms for wind loads prediction can be an alternative of traditional wind tunnel tests and computational fluid dynamic simulations.

• The Research Journal of the Costume Culture
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• v.31 no.5
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• pp.692-704
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• 2023

This study analyzed 214 sports knee braces found on Chinese websites between October 2022 and November 2022 to assess product type (impact protection material, fastening method, and protection method), material composition, size, weight, and main characteristics. The product type was further categorized according to (1) use of hard guard and soft guard protection method; (2) cover type, strap type, and slip-on type fastening method; and (3) pressure type and support type protection method. It also noted the physical shock protection materials used, including foam (EVA or polyurethane) attached to joints as a buffer material and plastic (TPU or PP) that protects the user's knee from external impacts. The study found that the materials that primarily comprise sports knee braces are a combination of nylon, polyester, and neoprene. Additionally, it found that most sports knee braces available on the market are available in three sizes based on knee circumference: M (35-38cm), L (38-41cm), and XL (41-44cm), while some products are available in one size only. Furthermore, the majority of the 214 products studied weighed 200g, followed by 1,000g. Finally, in terms of product characteristics, many sports knee braces utilize ring-shaped silicone pads to distribute the load pressure on the knees or incorporate sturdy adhesive velcro to improve knee stability.

• Coupled systems mechanics
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• v.13 no.2
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• pp.95-113
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• 2024

In this paper, we will analyse the thermo-elastic behavior of the plate element of a structure arranged in a climatically aggressive environment (extreme temperature), we use a refined four-variable thick plate theory to take the shear effect into consideration, the proposed theory less computationally expensive and more accurate so that it incorporates the shear effect into the formulation. The plate is assumed to be simply supported on its four edges, so exact (closed-form) solutions are found according to the Navier expansion, and the governing stability equations and associated boundary conditions of the problem are obtained via the virtual works principle. The plate studied ismade of laminated composite materials, so a parametric study is needed to see the effect of different types of parameters and coupling on the critical temperature value causing thermo-elastic instability of the plate and also on the natural frequency of free vibration, as well as for other parameters such as anisotropy, slenderness and aspect ratio of the plate and finally the lamination angle. Numerical results are obtained for specially orthotropic and antisymmetrical plates and are compared with those obtained by othertheoriesin the literature to validate the analysis approach used.

• Structural Engineering and Mechanics
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• v.91 no.1
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• pp.103-121
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• 2024

The smoothed particle hydrodynamics (SPH) method is a numerical technique used in dynamic analysis to simulate the fluid-like behavior of materials under extreme conditions, such as those encountered in explosions or high velocity impacts. In SPH, fluid or solid materials are discretized into particles. These particles interact with each other based on certain smoothing kernels, allowing the simulation of fluid flows and predict the response of solid materials to shock waves, like deformation, cracking or failure. One of the main advantages of SPH is its ability to simulate these phenomena without a fixed grid, making it particularly suitable for analyzing complex geometries. In this study, the structural damage to a masonry arch bridge subjected to blast loading was investigated. A high-fidelity micro-model was created and the explosives were modeled using the SPH approach. The Johnson-Holmquist II damage model and the Mohr-Coulomb material model were considered to evaluate the masonry and backfill properties. Consistent with the principles of the JH-II model, the authors developed a VUMAT code. The explosive charges (50 kg, 168 kg, 425 kg and 1000 kg) were placed in close proximity to the deck and pier of a bridge. The results showed that the 50 kg charges, which could have been placed near the pier by a terrorist, had only a limited effect on the piers. Instead, this charge caused a vertical displacement of the deck due to the confinement effect. Conversely, a 1000 kg TNT charge placed 100 cm above the deck caused significant damage to the bridge.