• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.15 no.3
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• pp.153-159
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• 2005

The purpose of this study was to assess the ergonomic risks of lifting tasks in a marine diesel engine manufacturing industry using the National Institute for Occupational Safety and Health(NIOSH) Revised Lifting Equation(NLE). Average Lifting Index(LI=Weight of Load/Recommended Weight Limit) of a total number of 45 lifting tasks was $1.6{\pm}0.7$. The LIs were above 1 at 34 tasks(75.6%), and above 2 at 11 tasks(24.4%). Parts management showed the highest average LI value (LI=2.3) in all departments, which resulted from high frequency and heave load of lifting. The common and significant ergonomic risk factors in the processes were the heavy weight of diesel engine parts and the long horizontal distance. In addition, some lifting tasks had such potential risk factors as the long vertical distance, the high frequency of lifts or the long work duration.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.22 no.1
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• pp.132-141
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• 1998

A parallel version of sheet forming analysis program was developed. This version is compatible with any parallel computers which support MPI that is one of the most recent and popular message passing libraries. For this purpose, SERI-SFA, a vector version which runs on Cray Y-MP C90, a sequential vector computer, was used as a source code. For the sake of the effectiveness of the work, the parallelization was focused on the selected part after checking the rank of CPU consumed from the exemplary calculation on Cray Y-MP C90. The subroutines associated with contact algorithm was selected as targe parts. For this work, MPI was used as a message passing library. For the performance verification, an oil pan and an S-rail forming simulation were carried out. The performance check was carried out by the kernel and total CPU time along with theoretical performance using Amdahl's Law. The results showed some performance improvement within the limit of the selective paralellization.

• Journal of Korean Institute of Industrial Engineers
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• v.25 no.2
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• pp.266-273
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• 1999

The maximum work capacity at various shoulder angles was estimated in terms of joint moment through maximum voluntary contraction (MVC) measurement, and the result was compared to workload computed from 3-D static lifting model (3DSSPP) based upon national institute of safety and health (NIOSH) lifting guideline (1991). The electromyography (EMG) of anterior/posterior deltoid and trapezius muscle was also recorded to study the function of individual muscle during asymmetric shoulder lifting. Psychophysical workload was measured to observe the difference from MVC or biomechanical estimation. An apparatus was constructed for the study and twenty five trials including five flexion angles and five add/abduction angles were performed isometrically. Results indicated that MVC at 30 degree of flexion was the strongest whereas MVC at 120 degree was the weakest. In case of add/abduction, MVC decreased to 77 to 89 % during add/abduction compared to the MVC at neutral position. Regarding the normalized EMG value, a substantial increase was observed at 30 and 60 degree abduction. More importantly, the shoulder moment computed from maximum permissible limit (MPL) was greater than the moment at MVC condition during 30 degree adduction. Current result can be used as a reference information for a safe workplace design to prevent the shoulder from an excessive work load in industry.

• Proceedings of the Korean Nuclear Society Conference
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• 1996.05a
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• pp.471-476
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• 1996

In this study, the method to use the phase shift keying (PSK) communication technique in smart transmitter is presented. In nuclear applications. smart transmitters for various parameters are expected to improve the accuracy of measurement and to reduce the load of calibration work. The capability of communication in field level is the most important merit of the smart transmitter. The most popular method is using of digital and analog techniques simultaneously - transmitting measurements from the field at 4∼20mA while modulating the current to carry digital information in both directions over the same twisted pairs. Conventional smart transmitters use the frequency shift keying (FSK) method for digital communication. Generally, however, the FSK method has the speed limit at 1200 bps. Amount of information to transmit becomes increasing as the processing technique is improved. The PSK method is noticeable alternative for high speed digital communication, but it has non-zero DC component. In order to use the PSK method in the field transmission with smart transmitter, the method to remove the DC component is studied in this work.

• Structural Engineering and Mechanics
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• v.71 no.4
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• pp.351-361
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• 2019

Present article deals with the static stability analysis of compositionally graded nanocomposite beams reinforced with graphene oxide powder (GOP) is undertaken once the beam is subjected to an induced force caused by nonuniform magnetic field. The homogenized material properties of the constituent material are approximated through Halpin-Tsai micromechanical scheme. Three distribution types of GOPs are considered, namely uniform, X and O. Also, a higher-order refined beam model is incorporated with the dynamic form of the virtual work's principle to derive the partial differential motion equations of the problem. The governing equations are solved via Galerkin's method. The introduced mathematical model is numerically validated presenting a comparison between the results of present work with responses obtained from previous articles. New results for the buckling load of GOP reinforced nanocomposites are presented regarding for different values of magnetic field intensity. Besides, other investigations are performed to show the impacts of other variants, such as slenderness ratio, boundary condition, distribution type and so on, on the critical stability limit of beams made from nanocomposites.

• Smart Structures and Systems
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• v.24 no.4
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• pp.435-446
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• 2019

The existing piezoelectric spherical transducers with fixed prescribed dynamic characteristics limit their application in scenarios with multi-frequency or frequency variation requirement. To address this issue, this work proposes an improved design of piezoelectric spherical transducers using the resistance tuning method. Two piezoceramic shells are the functional elements with one for actuation and the other for tuning through the variation of load resistance. The theoretical model of the proposed design is given based on our previous work. The effects of the resistance, the middle surface radius and the thickness of the epoxy adhesive layer on the dynamic characteristics of the transducer are explored by numerical analysis. The numerical results show that the multi-frequency characteristics of the transducer can be obtained by tuning the resistance, and its electromechanical coupling coefficient can be optimized by a matching resistance. The proposed design and derived theoretical solution are validated by comparing with the literature given special examples as well as an experimental study. The present study demonstrates the feasibility of using the proposed design to realize the multi-frequency characteristics, which is helpful to improve the performance of piezoelectric spherical transducers used in underwater acoustic detection, hydrophones, and the spherical smart aggregate (SSA) used in civil structural health monitoring, enhancing their operation at the multiple working frequencies to meet different application requirements.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2021.10a
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• pp.249-251
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• 2021

PBFT (Practical Byzantine Fault Tolerant) is a consensus algorithm that guarantees higher processing speed compared to PoW (Proof of Work) and absolute finality that records are not overturned due to the superiority of computing power. However, due to the complexity of the message, there is a limit that the network load increases exponentially as the number of participating nodes increases. PBFT is an important factor in determining the performance of a blockchain network, but studies on evaluation metrics and evaluation technologies are lacking. In this paper, we propose a PBFT evaluation framework that is convenient to change the consensus algorithm to easily evaluate quantitative indicators and improved methods for evaluating PBFT.

• Journal of Mechanical Science and Technology
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• v.14 no.1
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• pp.30-38
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• 2000

This paper presents a framework how to estimate crack driving forces in terms of crack-tip opening displacement and J-integral for mismatched dissimilar joints with interface cracks. The mismatch in elastic, thermal, and plastic hardening properties is not considered, but the mismatch in plastic yield strengths is emphasized here. The main outcome of the present work is that the existing methods to estimate crack driving forces for homogeneous materials can be used with slight modification. Such modification includes (i) mismatch- corrected limit load solutions, and (ii) evaluating the contribution of each material in dissimilar joints to the total crack driving force, which depends on the strength mismatch of the dissimilar joints.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2004.05a
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• pp.27-32
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• 2004

Recently, the expansion of social infrastructures and urban redevelopment, the construction works have been a rapidly increase. The subway's noise and vibration are on a continuously increasing status in its importance as by the industrial and cultural development process. Nevertheless, in our country, adequate alternative idea for the construction noise and vibration are not yet established. In this point, the purpose of this study is to know the vibration effect to the structure. This study was used to determine the standard of vibration and the way of losing vibration. The case of construction site is a good example. The data of this study was obtained by a construction company in Korea. Vibration effect could cause structural problems and affect human mental state. The results of this study are as follows; check the vibrating point, determine the suitable limit of vibration, make a good plan and construction.

• Journal of the Korean Society of Tobacco Science
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• v.23 no.1
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• pp.90-93
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• 2001

In order to save hanging labor hours and reduce work intensity for bulk curing of the flue-cured tobacco, and electric hoist was developed. It consists of a pair of square steel frames with side plates and rolling casters to move back and forth on the second tire of bulk barn, and wire rope type lift was attached to the beneath of its top center. The lift driven by DC motor could be controlled by operating switch with one limit switch and control box, and a scissors shaped gripper was deviced to grip tobacco rack to the end of wire rope. As the results of experiments with electric hoist, labor hours for hanging could be saved by 30 to 40% as compared with those in conventional method. With simple and light structure, it was possible for even woman to load the harvested tobacco, and it could be recommended for farmers to use this device with reasonable price.