• Proceedings of the Korean Geotechical Society Conference
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• 2010.09a
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• pp.825-839
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• 2010

The global and domestic market for offshore wind farm is expected to grow fast, and the design and installation of substructure and foundation is getting more important. As for the offshore wind farms located in the shallow(depth < 20m) water, the construction and installation of the substructure and foundation makes up about 1/4 ~1/3 of the offshore wind farm construction cost, and the portion is expected to increase because the turbine capacity is increasing from 2 ~ 3MW to 5MW or larger and the water depth of wind farms is also increasing over 30m. As a foundation for offshore wind turbine, the suction caisson foundation is being considered to be a highly competitive alternative to the conventional monopile or gravity based structure, because it has features suitable for the offshore construction such as quick installation, no heavy equipment for penetration and no hammering noise for driving. In order to study the installation behaviour of the suction caisson, laboratory tests were performed with sand. The pore water pressure and displacement were measured to analyze the suction pressure during penetration, the penetration speed and the amount of heaving.

• Journal of Navigation and Port Research
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• v.29 no.10 s.106
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• pp.847-852
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• 2005

In order to evaluate the safety of navigation at sea and the safety of mooring on berthing, it is necessary that the wave and wind induced ship dynamic motion should be measured in real time domain for the validity of theoretical evaluation method such as sea-keeping performance and safety of mooring. In this paper, the basic design of sensors is discussed and some system configurations were shown. The developed system mainly consists of 4 kinds of sensors such as three-dimensional accelerator, two-dimensional tilt sensor, azimuth sensor and two displacement sensors. Using this measuring system, it can be obtained the 6 degrees of freedom of ship dynamic motions at sea and on berthing such as rolling, pitching, yawing, swaying, heaving, surging under the certain external forces.

• Journal of Ocean Engineering and Technology
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• v.20 no.5 s.72
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• pp.42-48
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• 2006

This paper shows theresults of centrifuge model experiments to investigate the behavior of a replacement method in dredged and reclaimed ground. For this experimental work, centrifuge model tests were carried out to investigate the behavior of a replacement method in soft clay ground. Basic soil property tests were performed to find the mechanical properties of clay soil sampled from the southern coast of Korea, which was used for the ground material in the centrifuge model tests. The reconstituted clay ground of the model was prepared by applying reconsolidntion pressure in a 1 g condition with a specially built model container. Centrifuge model tests were carried out under the artificially accelerated gravitational level of 50 g. Replacement material of lead with a certain degree of angularity was used and placed until the settlement of the replacement material embankment reached a state of equilibrium. Vertical displacement of the replacement material was monitored during tests. The depth and shape of the replacement, especially the slope of the penetrated material and the water content of the clay ground were measured after finishing tests. Model tests for investigating the stability of an embankment after backfilling were also performed to simulate the behavior of a dike treated with replacement and backfilled with sandy material. As a result of the centrifuge model test, the behavior of the replacement, the mechanism of the replacement material being penetrated into clay ground, and the depth of the replacement were evaluated.

• Journal of Multimedia Information System
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• v.7 no.2
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• pp.189-196
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• 2020

We have developed a device for recording biological data by inserting three electrodes and a needle with an angular velocity sensor into the moth for the purpose of measuring the electromyogram of the flapping and the corresponding lift force. With this measurement, it is possible to evaluate the moth-physiological function of moths, and the amount of pesticides that insects are exposed to (currently LD50-based standards), especially the amount of chronic low-concentration exposure, can be reduced the dose. We measured and recorded 2-channel electromyography (EMG) and angular velocity corresponding to pitch angle (pitch-like angle) associated with wing flapping for 100 sweet potato hawkmoths (50 females and 50 males) with the animals suspended and constrained in air. Overall, the angular velocity and amplitude of EMG signals demonstrated high correlation, with a correlation coefficient of R = 0.792. In contrast, the results of analysis performed on the peak-to-peak (PP) EMG intervals, which correspond to the RR intervals of ECG signals, indicated a correlation between ΔF fluctuation and angular velocity of R = 0.379. Thus, the accuracy of the regression curve was relatively poor. Using a DC amplification circuit without capacitive coupling as the EMG amplification circuit, we confirmed that the baseline changes at the gear change point of wing flapping. The following formula gives the lift provided by the wing: angular velocity × thoracic weight - air resistance - (eddy resistance due to turbulence). In future studies, we plan to attach a micro radio transmitter to the moths to gather data on potential energy, kinetic energy, and displacement during free flight for analysis. Such physiological functional evaluations of moths may alleviate damage to insect health due to repeated exposure to multiple agrochemicals and may lead to significant changes in the toxicity standards, which are currently based on LD50 values.

• Journal of the Korean Society of Safety
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• v.27 no.4
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• pp.7-12
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• 2012

In this study, the solidification characteristics inside the AC7A casting material was analyzed using the numerical analysis method and was verified using the experimental method by the pre-heated temperature conditions of metal casting device. For the numerical analysis, "COMSOL Multiphysics", the commercial code based on the finite element analysis(FEA), was used in order to predict the thermal deformation of the AC7A casting material including temperature, displacement and stress distribution. Also, in order to verify the results calculated by the numerical analysis, the experiment for temperature measurement inside the AC7A casting material was performed using the K-type thermocouple under the same condition of numerical analysis method. In the numerical results, thermal deformation inside AC7A casting material was well-suited for manufacturing products when the pre-heated temperatures of the metal casting device was $250^{\circ}C$. When the results of the temperature distribution were experimentally measured and were compared with those of the numerical result, it appeared that there was some temperature difference because of the latent heat by phase change heat transfer. However, the result of cooling temperature and patterns were almost similar except for the latent heat interval. The solidification characteristics was closely related to the temperature difference between the surface and inside of the casting.

• Progress in Medical Physics
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• v.28 no.4
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• pp.164-170
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• 2017

One of the methods to consider the effect of respiratory motion of a tumor target in radiotherapy is to establish a treatment plan with the internal target volume (ITV) created based on an accurate analysis of the target motion displacement. When this method is applied to intensity modulated radiotherapy (IMRT), it is expected to yield a different treatment dose distribution under the motion condition according to the IMRT method. In this study, we prepared ITV-based IMRT plans with conventional IMRT using fixed gantry angle beams, RapidArc using volumetric modulated arc therapy, and tomotherapy using helical therapy. Then, the variation in dose distribution caused by the target motion was analyzed by the dose measurement in the actual motion condition. A delivery quality assurance plan was prepared for the established IMRT plan and the dose distribution in the actual motion condition was measured and analyzed using a two-dimensional diode detector placed on a moving phantom capable of simulating breathing movements. The dose measurement was performed considering only a uniform target shape and motion in the superior-inferior (SI) direction. In this condition, it was confirmed that the error of the dose distribution due to the target motion is minimum in tomotherapy. This is thought to be due to the characteristic of tomotherapy that treats the target sequentially by dividing it into several slices. When the target shape is uniform and the main target motion direction is SI, it is considered that tomotherapy for the ITV-based IMRT method has a characteristic which can reduce the dose difference compared with the plan dose under the target motion condition.

• 한국신재생에너지학회:학술대회논문집
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• 2007.06a
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• pp.101-104
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• 2007

Mechanical behavior in metal bipolar plate of a fuel cell stack was studied using finite element analysis. The fuel stack is essentially composed of a metal bipolar plate (metal BP), a gasket, an end plate, a membrane electrolyte assembly (MEA), and a gas diffusion layer (GDL). It is important to maintain a suitable fastening force of Metal BP, because it influences the power efficiency of the fuel cell stack. After a gasket and a GDL are placed on the metal BP, the reaction force with the displacement is measured. The channel of metal bipolar plate is replaced by a simple geometrical plate. The results of FEM are similar to those of experiment. Therefore mechanical behavior in metal BP of a fuel cell stack can be estimated by using FEM.

• Journal of the Korean Society for Nondestructive Testing
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• v.31 no.5
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• pp.522-528
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• 2011

Artificial basilar membranes made of PVDF(polyvinylidene fluoride) are manufactured using microfabrication processes. The mechanical behavior of PVDF artificial basilar membrane was measured to evaluate its performance as a mechanical frequency analyzer using scanning LDV(laser Doppler vibrometer). The experimental setup consists of the microfabricated artificial basilar membrane, a loud speaker connected to an amplifier for generating acoustic pressure of specific spectral pattern, and a scanning LDV with controlling unit for measuring the displacement of the membrane on the incoming acoustic stimulation. The microfabricated artificial basilar membrane was attached tightly upon a package containing a chamber which can be filled with silicone oil before placed on the experimental setup stage. The experiment results showed that the microfabricated artificial basilar membrane has a property as a mechanical frequency analyzer.

• Tribology and Lubricants
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• v.14 no.4
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• pp.15-22
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• 1998

Recently, the importance of variable displacement piston pump is increasing in industrial world. Especially, most consumers require various range of pressures and flow rates. Pressure compensator is a system controlling flow rate in piston pump at low cost and, therefore, satisfies the need of consumers. However, the system has serious problems, such as response and leakage. The response and leakage are affected by clearance between actuator piston and cylinder, roughness of surface, and spool overlap. In this paper, these effects are investigated experimentally, and optimal clearance and chamfer is obtained. While diameter of cylinder is fixed and diameter of actuator piston is changed in this experiment, response and leakage are measured. Also parameters such as roughness and processing accuracy are changed for piston of fixed clearance. Experimental setup modelled into several parts of actuator piston, cylinder, spool, and swash plate. Input pressure is changed by function generator and proportional valve. The result of this experiment shows that leakage increases very much in proportion to the increase of clearance, and especially leakage occurs enormously when clearance is more than 0.002. The response is not good because as clearance increases leakage increases and as clearance decreases viscous damping effect increases. Accordingly, it is found out that optimal clearance range exists for tile response, within about 0.0012∼0.0014, at this time. Futhermore, the better roughness and geometrical accuracy of actuator piston are, the smaller are leakage and friction. The paper informs that response and leakage are influenced by and geometrical accuracy of actuator piston, roughness of surface, and the clearance between actuator piston and cylinder, and that optimal design of actuator piston in the pressure compensator is possible.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.28 no.9
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• pp.1408-1414
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• 2004

The use of flip-chip technology has many advantages over other approaches for high-density electronic packaging. ACF (anisotropic conductive film) is one of the major flip-chip technologies, which has short chip-to-chip interconnection length, high productivity, and miniaturization of package. In this study, thermal fatigue lift of ACF bonding flip-chip package has been predicted. Elastic and thermal properties of ACF were measured by using DMA and TMA. Temperature dependent nonlinear hi-thermal analysis was conducted and the result was compared with Moire interferometer experiment. Calculated displacement field was well matched with experimental result. Thermal fatigue analysis was also conducted. The maximum shear strain occurs at the outmost located bump. Shear stress-strain curve was obtained to calculate fatigue life. Fatigue model for electronic adhesives was used to predict thermal fatigue life of ACF bonding flip-chip packaging. DOE (Design of Experiment) technique was used to find important design factors. The results show that PCB CTE (Coefficient of Thermal Expansion) and elastic modulus of ACF material are important material parameters. And as important design parameters, chip width, bump pitch and bump width were chose. 2$^{nd}$ DOE was conducted to obtain RSM equation far the choose 3 design parameter. The coefficient of determination ($R^2$) for the calculated RSM equation is 0.99934. Optimum design is conducted using the RSM equation. MMFD (Modified Method for feasible Direction) algorithm is used to optimum design. The optimum value for chip width, bump pitch and bump width were 7.87mm, 430$\mu$m, and 78$\mu$m, respectively. Approximately, 1400 cycles have been expected under optimum conditions. Reliability analysis was conducted to find out guideline for control range of design parameter. Sigma value was calculated with changing standard deviation of design variable. To acquire 6 sigma level thermal fatigue reliability, the Std. Deviation of design parameter should be controlled within 3% of average value.