• Korean Journal of Materials Research
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• v.25 no.10
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• pp.523-530
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• 2015

Electricity generation through fossil fuels has caused environmental pollution. To solve this problem, research on new renewable energy (solar, wind, geothermal heat, etc.) to replace fossil fuels is in progress. These devices are able to consistently generate power. However, they have many drawbacks, such as high installation costs and limitations in possible set-up environments. Thus, piezoelectric harvesting technology, which is able to overcome the limitations of existing energy technologies, is actively being studied. Piezoelectric harvesting technology uses the piezoelectric effect which occurs in crystals that generate voltage when stress is applied. Therefore, it has advantages such as a wider installation base and lower technological cost. In this study, a piezoelectric energy harvesting device based on constant wave motion was investigated. This device can regenerate electricity in a constant turbulent flow in the middle of the sea. The components of the device are circuitry, a steel bar, an bimorph piezoelectric element and buoyancy elements. In addition, a multiphysical analysis coupled with the structure and piezoelectric elements was conducted to estimate the performance of the device. With this piezoelectric energy harvesting device, the displacement and electric power were analyzed.

• Journal of the Society of Disaster Information
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• v.14 no.3
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• pp.343-351
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• 2018

Purpose: Recently, As the size of the structure increased, the necessity of reducing its weight was raised. To reduce weight In concrete structures, a hollow slab is proposed as an alternative for weight reduction effect. Method: It is difficult to construct the hollow body due to buoyancy, and the shear performance is insufficient due to the decreased cross section. Slabs were fabricated using unidirectional hollow bodies such as PVC pipes, and experiments were conducted about construction performance and structural performance. Results: The buoyancy preventive device has been improved the construction performance by preventing floating hollow body, it has been confirmed that it has adequate performance to be used as a hollow slab system because it has enough expected shear performance. Coclusion: Hollow ratio has a little connection with bending performance, but after the yielding load, it is necessary to consider the secondary stiffness of structure, and is is supposed that the decrease of shear performance with the increase of hollow core ratio can be complemented with shear reinforcement.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.32 no.2
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• pp.158-165
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• 2008

The carbon dioxide properties change sharply near the critical or pseudo-critical point in the heat transfer processes. The reduction in turbulent, convective heat transfer parameters observed in some supercritical data and in experiments with common gases can be due to property variation, acceleration, buoyancy or combinations of these phenomena, depending on the conditions of the applications. In this study, the measurement for the secondary flow driven by buoyancy was carried out on the supercritical carbon dioxide turbulent flows in the different boundary condition with the constant mass flow rate. The available measuring techniques were used to clarify the behaviour of any supercritical fluid. Laser Doppler Velocimeter (LDV) and a special device was used to measure the secondary velocity and turbulent characteristics of the supercritical flows.

• Journal of Drive and Control
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• v.12 no.2
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• pp.7-13
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• 2015

In this study, we suggested the wave power generator using horizontal motions of the wave for use in the coastal sea. The length of the horizontal movement of the wave in the vicinity of the sea surface is larger than the length of the vertical reciprocating movement of the wave, hence the proposed device has a wave power transmission plate. In addition, because the motion of the wave is maximum to the sea surface, by arranging the buoyancy tanks at the top of the wave power transmission plate, it is always capable of vertical movement in accordance with the sea surface. To confirm the usefulness of the proposed wave power generator, we constructed a mathematical model of the wave power generator and carried out simulation using bondgraph. Furthermore, the efficiency was verified by measuring the degree of electrical energy production through a preliminary experiment.

• Transactions of the Korean hydrogen and new energy society
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• v.13 no.2
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• pp.127-134
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• 2002

A Study on the application of ultrasonic with high frequency is carried out as a plan to rise the efficiency of the hydrogen fuel production in an electrolysis of water. KOH is selected as an electrolyte and concentrations are 0 %, 10 %, 20 %, and 30%. The solvent is city water. A measurable device of buoyancy by an electronic balance and a measurable device of voltage with a sensor of pressure are planned newly as a measuring device to measure the quantity of hydrogen production. An ultrasonic transducer with high frequency of 2 MHz is selected to give them the ultrasonic forcing. In results, it is clarified that ultrasonic influences the decrease of overpotential in the electrolytic solution. And basic data according to the pole interval and the temperature are obtained.

• Progress in Superconductivity and Cryogenics
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• v.23 no.3
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• pp.26-31
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• 2021

Advanced classification of Cs contaminated soil by using a magnetic force-assisted selection pipe was investigated. A selection pipe is a device that sort particles depending on their particle size, based on the relationship between buoyancy, drag, and gravity force acting on the particles. Radioactive cesium is concentrated in small-particle size soil components with a large specific surface area. Hence, the volume of the Cs contaminated soil can be reduced by recycling the large-particle size soil components with low radioactive concentration. One of the problems of the selection pipe was that the radioactive concentration of the stayed soil in the selection pipe exceeds 8000 Bq/kg, which is the standard value of recycling of Cs contaminated soil, due to low classification accuracy. In this study, magnetic fields were applied to the lab-scale selection pipe from upper side to improve the classification accuracy and to reduce the radioactive concentration of the stayed soil.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.14 no.4
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• pp.73-84
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• 2015

Electricity generation using fossil fuels has caused environmental pollution. To solve this problem, research on new renewable energy sources (solar, wind power, geothermal heat, etc.) to replace fossil fuels is ongoing. These devices are able to generate power consistently. However, they have many weaknesses, such as high installation costs and limits to possible setup environments. Therefore, an active study on piezoelectric harvesting technology that is able to surmount the limitations of existing energy technologies is underway. Piezoelectric harvesting technology uses the piezoelectric effect, which occurs in crystals that generate voltage when stress is applied. Therefore, it has advantages, such as a wider installation base and lower technological costs. In this study, a piezoelectric harvesting device imitating seaweed, which has a consistent motion caused by fluid, is used. Thus, it can regenerate electricity at sea or on a bridge pillar, which has a constant turbulent flow. The components of the device include circuitry, springs, an electric generator, and balancing and buoyancy elements. Additionally, multiphysics analysis coupled with fluid, structure, and piezoelectric elements is conducted using COMSOL Multiphysics to evaluate performance. Through this program, displacement and electric power were analyzed, and the actual performance was confirmed by the experiment.

• Journal of Drive and Control
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• v.14 no.2
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• pp.45-51
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• 2017

Semi-submersible drilling rigs are offshore plants that perform functions such as ocean exploration for oil and gas acquisition, drilling and production, and storage and unloading of crude oil and gas. Semi-submersible drilling rigs use watertight dampers as emergency buoyancy holders. Since the watertight damper is an emergency shutoff device, it is mainly driven by a pneumatic driving system that can operate without a power supply. The pneumatic driving system has highly non-linear characteristics due to compressibility of air and external disturbance such as static and Coulomb friction. In this paper, a new control algorithm is proposed for a watertight damper driving system based on the sliding mode control with a disturbance observer. To evaluate control performance and robust stability of the designed controller, the control results were compared with the results obtained using the state feedback controller. As a result, it was confirmed that the pneumatic driving system for driving the watertight damper using the sliding mode controller with a disturbance observer can obtain excellent control performance against the parameter changes and the disturbance input.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.7 no.1
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• pp.1-8
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• 2011

Advanced SITs of the evolutionary PWRs have the advantage that they can passively control the ECC water discharge flow rate. Thus, the LPSI pumps can be eliminated from the safety injection system owing to the benefit of the advanced SITs. In the present study, a passive sealing plate was designed in order to overcome the shortcoming of the advanced SITs, i.e., the early nitrogen discharge through the stand pipe. The operating principle of the sealing plate depends only on the natural phenomena of buoyancy and gravity. The performance of the sealing plate was evaluated using the VAPER test facility, equipped with a full-scale SIT. It was verified that the passive sealing plate effectively prevented the air discharge during the entire duration of the ECC water discharge. Also, the major performance parameters of the advanced SIT were not changed with the installation of the sealing plate.

• Korean Journal of Computational Design and Engineering
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• v.18 no.6
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• pp.399-406
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• 2013

This paper describes a new simulation technique for advection-diffusion phenomena over the sea surface using the lattice Boltzmann method (LBM), capable of predicting oil dispersion from tankers. The LBM is used to solve the pollutant transport problem within the framework of the ocean environment. The sea space is represented by the lattices, where each lattice has the information on oil transportation. Since dispersed oils (i.e., oil droplets) at sea are transported by convection due to waves, buoyancy, and turbulent diffusion, the conservation of mass and many physical oil transport rules were used in the prediction model. Since the LBM is modeled using the uniform lattices and simple rules, it can be easily accelerated by the parallel mechanism, for example, GPU-accelerated method. The proposed model using the LBM is used to simulate a simple pollution event with the oil pollutants of 10,000 kL. The simulation results indicate that the LBM method accelerated with the GPU is 6 times faster than that without the GPU.