• Journal of the Institute of Electronics and Information Engineers
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• v.51 no.6
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• pp.190-197
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• 2014

In this paper, we present a method for optical parameter-based material rendering with measuring the thickness of a material using ultrasonic waves. Thickness is an important element in determining the reflectance and transmittance of a material along with its optical characteristics and plays a crucial role in more realistic object rendering. In studies conducted thus far, thickness has been measured and used for rendering. The proposed method is a novel method attempted for the first time ever to render a material considering the thickness of a material whose thickness cannot be measured by visual assessment, using ultrasonic waves. It was implemented by measuring the sound velocity of the reference sample and applying the results to the thickness measurement of other objects that have the same characteristics. The characteristics of the objects measured are reflected in the quality of the final rendering, thus verifying the importance of thickness in rendering.

• The Journal of the Korea institute of electronic communication sciences
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• v.11 no.10
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• pp.955-962
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• 2016

In this paper, we propose a design method for speed controller, current control of a Brushless Direct Current(: BLDC) motor using disturbance rejection techniques. Disturbance assumes a back electromotive force occurring in the electrical system and the variation of the load acting on the rotary shaft from the outside of the motor. And it assumed to be constant during the time interval and the Luenberger's observer design. So that the error of the observer about the system status can converge to zero show how to set the appropriate gain. Further, to stabilize the whole system, and proposes a method for setting the appropriate PI gain control to improve the tracking performance. By applying the proposed controller to 120W BLDC motors were tested for the ability to follow the velocity and current reference. Since the simulation results of the steady state error is within 0.1%, we were able to show the usefulness of the tracking performance of the proposed controller.

• The Journal of the Acoustical Society of Korea
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• v.20 no.3
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• pp.76-82
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• 2001

Most fluid machines can be considered as periodic noise sources when operated under constant conditions, which allows for a frequency domain representation of the source and the associated acoustic field In the duct. In such a representation, the source is characterized by frequency-dependent values of both strength and impedance. Although knowledge of these values can be gained by either experimentation or by modeling, one-port acoustic characteristics of an in-duct source with high flow velocity, high temperature, and high sound level can be measured only by the multiload method using an overdetermined set of open pipes with different lengths as applied loads. However, the problem is that negative source resistances have been often measured. This paper reviews the possible causes of the problem, with reference to experimental and theoretical results, in an attempt to clarify the issue. A new interpretation is given for the violation of basic assumptions and the defect in the algorithm of multiload method. The major cause and mechanism of the problem is due to the violation of time invariance assumption of the source and the load impedance can seriously affect the final measured result of source impedance.

• Nuclear Engineering and Technology
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• v.52 no.2
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• pp.381-396
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• 2020

Investigations of the commercial aircraft impact effect on nuclear island infrastructures have been drawing extensive attention, and this paper aims to perform the safety assessment of Generation III nuclear power plant (NPP) buildings subjected to typical commercial aircrafts crash. At present Part I, finite element (FE) models establishment and validations for both the aircrafts and NPP buildings are performed. (i) Airbus A320 and A380 aircrafts are selected as the representative medium and large commercial aircrafts, and the corresponding fine FE models including the skin, beam, fuel and etc. are established. By comparing the numerically derived impact force time-histories with the existing published literatures, the rationality of aircrafts models is verified. (ii) Fine FE model of the Chinese Zhejiang Sanao NPP buildings is established, including the detailed structures and reinforcing arrangement of both the containment and auxiliary buildings. (iii) By numerically reproducing the existing 1/7.5 scaled aircraft model impact tests on steel plate reinforced concrete (SC) panels and assessing the impact process and velocity time-history of aircraft model, as well as the damage and the maximum deflection of SC panels, the applicability of the existing three concrete constitutive models (i.e., K&C, Winfrith and CSC) are evaluated and the superiority of Winfrith model for SC panels under deformable missile impact is verified. The present work can provide beneficial reference for the integral aircraft crash analyses and structural damage assessment in the following two parts of this paper.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.24 no.3
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• pp.180-188
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• 2014

Hyundai Motor Group(HMG) carried out experimental investigation of sunroof buffeting phenomena on a simplified car model called Hyundai simplified model(HSM). HMG invited participation from commercial CFD vendors to perform numerical investigation of sunroof buffeting for HSM model with a goal to determine whether CFD can predict sunroof buffeting behavior to sufficient accuracy. ANSYS Korea participated in this investigation and performed numerical simulations of sunroof buffeting for HSM using ANSYS fluent, the general purpose CFD code. First, a flow field validation is performed using closed sunroof HSM model for 60 km/h wind speed. The velocity profiles at three locations on the top surface of HSM model are predicted and compared with experimental measurement. Then, numerical simulations for buffeting are performed over range of wind speeds, using advanced scale resolving turbulence model in the form of detached eddy simulation (DES). Buffeting frequency and buffeting level are predicted in simulation and compared with experimental measurement. With reference to comparison between experimental measurements with CFD predictions of buffeting frequency and level, conclusion are drawn about predictive capabilities of CFD for real vehicle development.

• Korean Journal of Applied Biomechanics
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• v.27 no.4
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• pp.269-278
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• 2017

Objective: The purpose of this study was to develop a goal setting method for increasing the probability of a holed in a side inclined putting stroke. Method: Three-dimensional video data was recorded at a frequency of 120 hz per second after synchronizing 19 infrared motion capture systems (Qualisys, Gothenburg, Sweden). Putting green used a polycarbonate plate ($1.2{\times}2.4{\times}0.01meter$) with coefficient of friction (${\mu}=0.062$) and a real curve of the actual hole. Results: The velocity ratio between the club and the ball was 1:1.6 under various ball speed conditions in this study. The overall position of the break is 1 m to 1.4 m from the point where the ball leaves. If there is a slope, the ball follows the target line by the straightening force, and when it reaches 1 m position, the straightening force decreases by 30~50% and reaches to the deviation (break) point which is severely influenced by the slope. From here, the ball is aimed in a direction other than the target, and the size is affected by the slope. Conclusion: If there is a side slope, the ball moves away from the straight line, and the larger the slope, the closer the break point is to the starting point of the ball. Therefore, it is necessary to calculate the degree of departure according to the slope carefully, and it is preferable that the slower the speed is, the more the influence of the slope becomes. It is preferable to use the center of the hole as a reference when calculating the departure.

• Journal of the Korean Society of Safety
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• v.26 no.2
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• pp.13-19
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• 2011

The magnetic polishing is the useful method to finish using magnetic power of magnet. That method is one of precision polishing techniques and has an aim of the clean technology using for the pure of gas and inside of the clean pipe. The magnetic abrasive polishing method is not so common for machine that it is not spreaded widely. There are rarely researcher in this field because of non-effectiveness of magnetic abrasive. Therefore, in this paper deals with development of the magnetic abrasive using Sr-Ferrite. In this development, abrasive grain GC used to resin bond fabricated low temperature. And Sr-Ferrite of magnetic abrasive powder fabricated that Sr-Ferrite was crused into 200 mesh. The XRD analysis result show that only GC abrasive and Sr-Ferrite crystal peaks detected which explains resin bond was not any more chemical reaction. From SEM analysis it is found that GC abrasive and Sr-Ferrite were strong bonding with each other by bond. The magnetic polishing is performed by polishing the surface of pipe by attracting magnetic abrasives with magnetic fields. This can be widely applied for finishing machinery fabrications such as various pipes and for other safety processes. In this paper, we could have investigated in to the changes of the movement of magnetic abrasive grain. In reference to this result, we could have made the experiment which is set under the condition of the magnetic flux density, polishing velocity according to the form of magnetic brush.

• Structural Engineering and Mechanics
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• v.64 no.2
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• pp.243-257
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• 2017

Investigating the properties and durability of high-strength concrete exposed to sulfuric acid attack for the purpose of its application in structures exposed to this acid is of outmost importance. In this research, the resistance and durability of high-strength concrete containing macro-polymeric or steel fibers together with the pozzolans of silica fume or nano-silica against sulfuric acid attack are explored. To accomplish this goal, in total, 108 high-strength concrete specimens were made with 9 different mix designs containing macro-polymeric and steel fibers at the volume fractions of 0.5, 0.75, and 1.0%, as well as the pozzolans of silica fume and nano-silica with the replacement levels of 10 and 2%, respectively. After placing the specimens inside a 5% sulfuric acid solution in the periods of 7, 21, and 63 days of immersion, the effect of adding the fibers and pozzolans on the compressive properties, ultrasonic pulse velocity (UPV), and weight loss of high-strength concrete was investigated and the respective results were compared with those of the reference specimens. The obtained results suggest the dependency of the resistance and durability loss of high-strength concrete against sulfuric acid attack to the properties of fibers as well as their fraction in concrete volume. Moreover, compared with using nano-silica, using silica fume in the fibrous concrete mix leads to more durable specimens against sulfuric acid attack. Finally, an optimum solution for the design parameters where the crushing load of high-strength fibrous concrete is maximized was found using response surface method (RSM).

• Geomechanics and Engineering
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• v.22 no.4
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• pp.291-303
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• 2020

The deformation of the rock surrounding a tunnel manifests due to the stress redistribution within the surrounding rock. By observing the deformation of the surrounding rock, we can not only determine the stability of the surrounding rock and supporting structure but also predict the future state of the surrounding rock. In this paper, we used grey system theory to analyse the factors that affect the deformation of the rock surrounding a tunnel. The results show that the 5 main influencing factors are longitudinal wave velocity, tunnel burial depth, groundwater development, surrounding rock support type and construction management level. Furthermore, we used seismic prospecting data, preliminary survey data and excavated section monitoring data to establish a neural network learning model to predict the total amount of deformation of the surrounding rock during tunnel collapse. Subsequently, the probability of a change in deformation in each predicted section was obtained by using a Bayesian method for detecting change points. Finally, through an analysis of the distribution of the change probability and a comparison with the actual situation, we deduced the survey mark at which collapse would most likely occur. Surface collapse suddenly occurred when the tunnel was excavated to this predicted distance. This work further proved that the Bayesian method can accurately detect change points for risk evaluation, enhancing the accuracy of tunnel collapse forecasting. This research provides a reference and a guide for future research on the probability analysis of tunnel collapse.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.4
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• pp.501-509
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• 2010

A floating crane is a crane-mounted ship and is used to assemble or to transport heavy blocks in shipyards. In this paper, the static and dynamic response of a floating crane and a heavy block that are connected using elastic booms and wire ropes are described. The static and dynamic equations of surge, pitch, and heave for the system are derived on the basis of flexible multibody system dynamics. The equations of motion are fully coupled and highly nonlinear since they involve nonlinear mass matrices, elastic stiffness matrices, quadratic velocity vectors, and generalized external forces. A floating frame of reference and nodal coordinates are employed to model the boom as a flexible body. The nonlinear hydrostatic force, linear hydrodynamic force, wire-rope force, and mooring force are considered as the external forces. For numerical analysis, the Hilber-Hughes-Taylor method for implicit integration is used. The dynamic responses of the cargo are analyzed with respect to the results obtained by static and numerical analyses.