• Journal of the Korean Solar Energy Society
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• v.29 no.5
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• pp.65-72
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• 2009

The new method is proposed to improve high speed detection of grid voltage phase and magnitude during a voltage dip due to a grid faults. Usually, A LPF(Low Pass Filter) is used in the feedback loop of PLL (Phase Locked Loop) system because the measured grid voltage contains harmonic distortions and sensor noises. so, a new design method of the loop gain of the PI -type controller in the PLL system is proposed with the consideration of the dynamics of the LPF. As a result, a better transient response can be obtained with the proposed design method. The LPF frequency and PI controller gain are designed in coordination according to the steady state and dynamic performance requirement. This paper shows the feasibility and the usefulness of the proposed methods through the computer simulation and the lab-scale experiments.

• Journal of Ocean Engineering and Technology
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• v.34 no.2
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• pp.110-119
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• 2020

Explosions and fires on offshore drilling units and process plants, which cause loss of life and environmental damage, have been studied extensively. However, research on drilling units increased only after the 2010 Deepwater Horizon accident in the Gulf of Mexico. A major reason for explosions and fires on a drilling unit is blowout, which is caused by a failure to control the high temperatures and pressures upstream of the offshore underwater well. The area susceptible to explosion and fire due to blowout is the drill floor, which supports the main drilling system. Structural instability and collapse of the drill floor can threaten the structural integrity of the entire unit. This study simulates the behavior of fire subsequent to blowout and assesses the thermal load. A heat transfer structure analysis of the drill floor was carried out using the assessed thermal load, and the risk was noted. In order to maintain the structural integrity of the drill floor, passive fire protection of certain areas was recommended.

• Earthquakes and Structures
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• v.11 no.6
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• pp.983-1000
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• 2016

To date the engineering community has seen facade systems as non-structural elements with high aesthetic value and a barrier between the outdoor and indoor environments. The role of facades in energy use in a building has also been recognized and the industry is also witnessing the emergence of many energy efficient facade systems. This paper will focus on using exterior skin of the double skin facade system as a dissipative movable element during earthquake excitation. The main aim of this study is to investigate the potential of the facade system to act as a damper system to reduce earthquake-induced vibration of the primary structure. Unlike traditional mass dampers, which are usually placed at the top level of structures, the movable/smart double skin facade systems are distributed throughout the entire height of building structures. The outer skin is moveable and can act as a multi tuned mass dampers (MTMDs) that move and dissipate energy during strong earthquake motions. In this paper, using a three dimensional 10-storey building structure as the example, it is shown that with optimal choice of materials for stiffness and damping of brackets connecting the two skins, a substantial portion of earthquake induced vibration energy can be dissipated which leads to avoiding expensive ductile seismic designs. It is shown that the engineering demand parameters (EDPs) for a low-rise building structures subjected to moderate to severe earthquakes can be substantially reduced by introduction of a smart designed double skin system.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 1999.10a
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• pp.411-416
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• 1999

The measurement of unsteady flow rate is of vital importance to clarify and improve the dynamic characteristics in pipeline, hydraulic components and system. There is also demand for a real time flow sensor of ability to measure unsteady flow rate with high accuracy and fast response to realize feedback control of flow rate in fluid power systems. In this paper, we propose an approach for estimating unsteady flow rate through a pipeline and components under high pressure condition. In the method, unsteady flow rate is estimated by using hydraulic pipeline dynamics and the measured pressure values at two distant points along the pipeline. The distributed parameter model of hydraulic pipeline is applied with consideration of frequency dependent viscosity friction and unsteady velocity distribution at a cross section of a pipeline. By using the self-checking functions of the method, the validity is investigated by comparison with the measured and estimated pressure waveforms at the halfway section on the pipeline. The results show good agreement between the estimated flow rate waveforms and theroetical those under unsteady laminar flow conditions. the method proposed here is useful in estimating unsteady flow rate through an arbitray cross section in hydraulic pipeline and components without installing an instantaneous flowmeter.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2000.04a
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• pp.629-634
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• 2000

Generally, the accuracy of motion control systems is strongly influenced by both the mechanical characteristics and servo characteristics of feed drive systems. In the fed drive systems of machine tools that consist of mechanical parts and electrical parts, a torsional vibration is often generated because of its elastic elements in torque transmission. Especially, a torsional vibration caused by the elasticity of mechanical elements might deteriorate the quick movement of system and lead to shorten the life time of the mechanical transmission elements. So it is necessary to analyze the electromechanical system mathematically to optimize the dynamic characteristics of the feed drive system. In this paper, based on the simplifies feed drive system model, radius errors due to position gain mismatch and servo response characteristic have been developed and an optimal criterion for tuning the gain of speed controller is discussed. The proportional and integral parameter gain of the feed drive controller are optimal design variables for the gain tuning of PI speed controller. Through the optimization problem formulation, both proportional and integral parameter are optimally tuned so as to compensate the radius errors by using the genetic algorithm. As a result, higher performance on circular profile tests has been achieved than the one with standard parameters.

• Journal of Power Electronics
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• v.18 no.3
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• pp.863-870
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• 2018

The traditional power control theories for the harmonic reduction methods in multilevel inverters are found to be unreliable under unbalanced load conditions. The unreliability in harmonic mitigation is caused by voltage fluctuations, non-linear loads, the use of power switches, etc. In general, the harmonics are reduced by filters. However, such devices are an expensive way to provide a smooth and fast response to secure power systems during dynamic conditions. Hence, the Decoupled Double Synchronous Reference Frame (DDSRF) theory combined with a State Delay Controller (SDC) is proposed to achieve a harmonic reduction in power systems. The DDSRF produces a sinusoidal harmonic that is the opposite of the load harmonic. Then, it injects this harmonic into power systems, which reduces the effect of harmonics. The SDC is used to reduce the delay between the compensation time for power injection and the generation of a reference signal. The proposed technique has been simulated using MATLAB and its reliability has been verified experimentally under unbalanced conditions.

• Journal of Power System Engineering
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• v.14 no.3
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• pp.77-82
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• 2010

In general, the control valves are essential components in hydraulic systems. Structural changes within the valves remain a challenge because many parameters of valve tend to interact in terms of static and dynamic performance. Therefore, the valve characteristics is applied directly to the stability of hydraulic system. Inner structure of the valve which is used mainly in the industries is made up poppet type and spool type. This paper made a description of the method for numerical analysis and modeling of the valve with a built-in moving part of four-type. Based on the physical parameters of the valves, a numerical model of objected valve is developed using the bond graph method. It is to verified the results that the moving part of four-type has an effect on pressure and flow characteristics. Also, It is analyzed the results which has an effect on response characteristic by angular of poppet valve face and inertia variation of the valve with a built-in moving part. In the results, it is confirmed that the rising and settling time vary with the shape of moving part in valve.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2011.04a
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• pp.171-176
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• 2011

The purposes of the research were to evaluate system performance and response of building structure under external load for full scale modal-testing-tower applied toggle bracing and lead rubber damper(LRD). The dynamic properties of the structure were measured before and after installing damper under harmonic excitation using the AMD and the results were compared. The harmonic excitation condition is to increase 0.01Hz sine sweep signal from 0.49Hz to 0.63Hz. As a result of measuring resonant frequency, before installing damper is 0.55Hz and after installing damper is 0.62Hz. The experimental results after installing damper were also distinguished from simulation results and the main cause of this results is temperature dependency property of rubber material.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2011.10a
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• pp.349-354
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• 2011

Tuned mass damper is widely used in many applications of industry. The main advantage of tuned mass damper is that it can increase the damping ratio of system and reduce the vibration amplitude. Meanwhile, the natural frequency of system will be divided by two peaks, and the peak speeds are closely related to the mass and the stiffness of auxiliary mass system added. In addition, the damping ratio will also affect the peak frequency of the dynamic response. In the present research, the nonlinear mechanical characteristics of rubber is investigated and put into use, since it is usually manufactured as the spring element of tuned mass damper. By the sense of the nonlinear stiffness as well as the damping ratio which can be changed by preload applied on, the shape memory alloy is proposed to control the auxiliary mass system by self-optimizing. Supported by the experiment data of rubber, the 1 DOF theoretical model and finite element model based on computer simulation are implemented to perform the feasibility of the proposed semi-active tuned mass damper working on the drive shaft.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.23 no.1
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• pp.25-33
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• 2013

The floating offshore wind turbines are usually exposed to the wave and wind excitations which are irregular and undirected. In this paper, the sloshing characteristics of annular cylindrical tank were experimentally investigated to reduce the structural dynamic motion of floating offshore wind turbine which is robust to the irregular change of excitation direction of wind and wave. The formula for the natural sloshing frequencies of this annular cylindrical tank was derived theoretically. In order to validate this formula, the shaking equipment was established and frequency response functions were measured. Two types of tank were considered. The first and second natural sloshing frequencies were investigated according to the depth of the water. It has been observed that between theoretical and experimental results shows a good agreement.