• Ocean Systems Engineering
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• 제6권4호
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• pp.377-400
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• 2016

Dropped objects are among the top ten causes of fatalities and serious injuries in the oil and gas industry (DORIS, 2016). Objects may accidentally fall down from platforms or vessels during lifting or any other offshore operation. Proper planning of lifting operations requires the knowledge of the risk-free zone on the sea bed to protect underwater structures and equipment. To this end a three-dimensional (3D) theory of dynamic motion of dropped cylindrical object is expanded to also consider ocean currents. The expanded theory is integrated into the authors' Dropped Objects Simulator (DROBS). DROBS is utilized to simulate the trajectories of dropped cylinders falling through uniform currents originating from different directions (incoming angle at $0^{\circ}$, $90^{\circ}$, $180^{\circ}$, and $270^{\circ}$). It is found that trajectories and landing points of dropped cylinders are greatly influenced by the direction of current. The initial conditions after the cylinders have fallen into the water are treated as random variables. It is assumed that the corresponding parameters orientation angle, translational velocity, and rotational velocity follow normal distributions. The paper presents results of DROBS simulations for the case of a dropped cylinder with initial drop angle at $60^{\circ}$ through air-water columns without current. Then the Monte Carlo simulations are used for predicting the landing point distributions of dropped cylinders with varying drop angles under current. The resulting landing point distribution plots may be used to identify risk free zones for offshore lifting operations.

• Journal of the Korean Society for Railway
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• 제16권6호
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• pp.447-453
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• 2013

Since PSDs(Platform Screen Doors) are set up at many subway stations, their design related to safety has become gradually important. In particular, the interference check with a running railway vehicle is the most important of performance indices because the collision between PSDs and vehicles can be dangerous for passengers in the car and on platforms. When the train comes into a station with a curvature, the passenger car has a large translational and rotational motion and the displacement is enough for coming in contact with PSD. The performance is affected by many design parameters such as rail design parameters and vehicle velocity. This study proposes dynamic analysis models for railway vehicles and rails. Some parameters were also considered in the models to determine their influence on the performance.

• Korean Membrane Journal
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• 제5권1호
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• pp.43-53
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• 2003

The selectivity of a gas in the carbon molecular sieve membrane (CMSM) can be expressed as the ratio of the product of the diffusivity and the solubility of two different gases. The diffusivity is also expressed as the product of the entropy and the total energy (kinetic and potential energy) in the nano-sized pore of the membrane. The present study calculates the entropic-energy and selectivity of penetrant gases such as H$_2$, O$_2$, N$_2$, and CO$_2$ from the gas-in-a box theory to physically analyze the diffusivity of penetrant gas in slit-shaped pore of CMSM focusing on the restriction of gas motion based on the size difference between penetrant gas pairs. The contribution of each energy term is converted to entropic term separately. By the conjugated calculation for each entropic-energy, the entropic effects on diffusivity-selectivity for gas pairs such as H$_2$/N$_2$, CO$_2$/N$_2$, and O$_2$/N$_2$ were analyzed within active pore of CMSM. In the activated diffusion domain, the calculated value of entropic-selectivity lies between 9.25 and 111.6 for H$_2$/N$_2$, between 3.36 and 6.0 for CO$_2$/N$_2$, and between 1.25 and 16.94 for O$_2$/N$_2$, respectively. The size decrement of active pore in CMSM had the direct effect on the reduction of translational entropic-energy and the contribution of vibrational entropic-energy for N$_2$, O$_2$, and H$_2$ was almost negligible. However, the vibrational entropic term of CO$_2$ might extravagantly affect on the entropic-selectivity.

• Structural Engineering and Mechanics
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• 제21권6호
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• pp.713-735
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• 2005

Due to the complexity of mathematical expressions, the literature concerning the free vibration analysis of plates carrying multiple three-degree-of-freedom (dof) spring-mass systems is rare. In this paper, the three degrees of freedom (dof's) for a spring-mass system refer to the translational motion of its lumped mass in the vertical ($\bar{z}$) direction and the two pitching motions of its lumped mass about the two horizontal ($\bar{x}$ and $\bar{y}$) axes. The basic concept of this paper is to replace each three-dof spring-mass system by a set of equivalent springs, so that the free vibration characteristics of a rectangular plate carrying any number of three-dof spring-mass systems can be obtained from those of the same plate supported by the same number of sets of equivalent springs. Since the three dof's of the lumped mass for each three-dof spring-mass system are eliminated to yield a set of equivalent springs, the total dof of the entire vibrating system is not affected by the total number of the spring-mass systems attached to the rectangular plate. However, this is not true in the conventional finite element method (FEM), where the total dof of the entire vibrating system increases three if one more three-dof spring-mass system is attached to the rectangular plate. Hence, the computer storage memory required by using the presented equivalent spring method (ESM) is less than that required by the conventional FEM, and the more the total number of the three-dof spring-mass systems attached to the plate, the more the advantage of the ESM. In addition, since manufacturing a spring with the specified stiffness is much easier than making a three-dof spring-mass system with the specified spring constants and mass magnitude, the presented theory of replacing a three-dof spring-mass system by a set of equivalent springs will be also significant from this viewpoint.

• Tribology and Lubricants
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• 제37권6호
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• pp.253-260
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• 2021

Metal pipes are used in a wide range of applications, from plumbing systems of large construction sites to small devices such as medical tools. When a liquid is enforced to flow through a metal pipe, a higher flow rate is beneficial for higher efficiency. Using high pressures can enhance the flow rate yet can be harmful for medical applications. Thus, we consider an optimal geometrical design to increase the flow rate in medical devices. In this study, we focus on cannulas, which are widely used small metal pipes for surgical procedures, such as liposuction. We characterize the internal flow rate driven by a negative pressure and explore its dependence on the key design parameters. We quantitatively analyze the suction characteristics for each design variable by conducting computational fluid dynamics simulations. In addition, we build a suction performance measurement system which enables the translational motion of cannulas with pre-programmed velocity for experimental validation. The inner diameter, section geometry, and hole configuration are the design factors to be evaluated. The effect of the inner diameter dominates over that of section geometry and hole configuration. In addition, the circular tube shape provides the maximum flow rate among the elliptical geometries. Once the flow rate exceeds a critical value, the rate becomes independent of the number and width of the suction holes. Finally, we introduce a slippery liquid-infused nanoporous surface (SLIPS) coating using nanoparticles and hydrophobic lubricants that effectively improves the flow rate and antifouling property of cannulas without altering the geometrical design parameter.

• Transactions of the Korean Society of Mechanical Engineers A
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• 제39권1호
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• pp.79-87
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• 2015

This paper proposes a floating-type wave energy conversion system that consists of a mechanical part (yo-yo vibrating system, motion rectifying system, and power transmission system) and electrical part (power generation system). The yo-yo vibrating system, which converts translational input to rotational motion, is modeled as a single degree-of-freedom system. It can amplify the wave input via the resonance phenomenon and enhance the energy conversion efficiency. The electromechanical model is established from impedance matching of the mechanical part to the electrical system. The performance was analyzed at various wave frequencies and damping ratios for a wave input acceleration of 0.14 g. The maximum output occurred at the resonance frequency and optimal load resistance, where the power conversion efficiency and electrical output power reached 48% and 290 W, respectively. Utilizing the resonance phenomenon was found to greatly enhance the performance of the wave energy converter, and there exists a maximum power point at the optimum load resistance.

• Journal of Korean Society of Steel Construction
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• 제26권3호
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• pp.177-189
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• 2014

When floor vibration problems occur in existing buildings, TMD (tuned mass damper) can be a viable alternative to resolving the problem. Only when TMD has been exactly tuned to the natural frequency of the floor, it can control the vibration as intended in design. However, TMD gets inefficient in the situation where the natural frequency changes as a result of the uncontrollable variation of the floor mass weight. This physical phenomenon is often called as TMD-off-tuning. This study proposes asymmetric TMD for enhancing the robustness of floor vibration control against uncertain natural frequencies. The proposed TMD features two asymmetric linear springs such that the floor vibrational energy can be dissipated through both the translational and rotational motion. An easy-to-use graphical optimization method was developed in this study. The asymmetric TMD proposed outperformed in vibration control by 28% compared to that of conventional TMD. The robustness of asymmetric TMD of this study was two times higher than that of conventional TMD.

• The Journal of Korean Society for Radiation Therapy
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• 제27권1호
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• pp.79-86
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• 2015

Purpose : The purpose of this study was to determine the proper treatment time of stereotactic body radiation therapy for spine metastasis cancer by using the image guidance system of CyberKnife(Accuray Incorporated, USA) which is able to correct movements of patients during the treatment. Materials and Methods : Fifty seven spine metastasis cancer patients who have stereotactic body radiation therapy of CyberKnife participate, 8 of them with cervical spine cancer, 26 of them with thoracic spine cancer, and 23 of them with lumbar spine cancer. X-ray images acquired during the treatment were classified by treatment site. From the starting point of treatment, motion tendency of patients is analyzed in each section which is divided into every 5 minutes. Results : In case of cervical spine, there is sudden increase of variation in 15 minutes after the treatment starts in rotational direction. In case of thoracic spine, there is no significantly variable section. However, variation increases gradually with the passage of time so that it is assumed that noticeable value comes up in approximately 40 minutes. In case of lumbar spine, sharp increase of variation is seen in 20 minutes in translational and rotational direction. Conclusion : Without having corrections during the treatment, proper treatment time is considered as less than 15 minutes for cervical spine, 40 minutes for thoracic spine, and 20 minutes for lumbar spine. If treatment time is longer than these duration, additional patient alignments are required or PTV margin should be enlarged.

• 한국해양학회지
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• 제30권3호
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• pp.170-183
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• 1995

Eddies and surface current field in the southwestern part of the East Sea were investigated using satellite-tracked drifters, CTD, and ADCP from November 1992 to September 1993. Trajectories of surface drifters provided information for the first time on the meandering motion of the East Korean Warm Current in the Ullung Basin (referred as UB) and clearly indicated the existence of cyclonic and anticyclonic eddies of various scales. Anticyclonic eddies persisting for a relatively long period were observed in UB and the southwestern corner of the Northern (Japan) Basin (SNB), while a cyclonic eddy was found in the coastal area between Sokcho and Donghae during the summer. Analysis shows that the eddy in UB behaved as a stationary eddy at least during the observation period and the cyclonic eddy was closely related to the existence of a cold water mass. The anticyclonic eddy in SNB was larger than that in UB, but much elongated in shape. The eddy in UB is characteristic of major and minor axes of about 120 and 70 km, revolution period of 13.6 days, mean swirl velocity of about 24 cm/s, and mean eddy kinetic energy of 392 cm$\^$2//s$\^$2/. The eddy in SNB is described as follows; major and minor axes of 168 and 86 km, period of 14.9 days, mean swirl velocity of 29 cm/s and mean eddy kinetic energy of 629 cm$\^$2//s$\^$2/. The mean translational speed is about 3 cm/s for both eddies. The agreement of the surface current pattern in UB observed by ADCP with the geostrophic flow pattern may suggest that the eddy in UB was nearly in geostrophic balance. The eddy was found to be strongly bottom-controlled.

• The Journal of Korean Academy of Prosthodontics
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• 제61권4호
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• pp.257-267
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• 2023

Purpose. The purpose of the study was to fabricate a prototype robotic simulator for dental education, to test whether it could simulate mandibular movements, and to assess the possibility of the stimulator responding to stimuli during dental practice. Materials and methods. A virtual simulator model was developed based on segmentation of the hard tissues using cone-beam computed tomography (CBCT) data. The simulator frame was 3D printed using polylactic acid (PLA) material, and dentiforms and silicone face skin were also inserted. Servo actuators were used to control the movements of the simulator, and the simulator's response to dental stimuli was created by pressure and water level sensors. A water level test was performed to determine the specific threshold of the water level sensor. The mandibular movements and mandibular range of motion of the simulator were tested through computer simulation and the actual model. Results. The prototype robotic simulator consisted of an operational unit, an upper body with an electric device, a head with a temporomandibular joint (TMJ) and dentiforms. The TMJ of the simulator was capable of driving two degrees of freedom, implementing rotational and translational movements. In the water level test, the specific threshold of the water level sensor was 10.35 ml. The mandibular range of motion of the simulator was 50 mm in both computer simulation and the actual model. Conclusion. Although further advancements are still required to improve its efficiency and stability, the upper-body prototype simulator has the potential to be useful in dental practice education.