• The korean journal of orthodontics
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• v.47 no.6
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• pp.353-364
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• 2017

Objective: The objective of this study was to investigate the effects of miniscrew-assisted rapid palatal expansion (MARPE) on changes in airflow in the upper airway (UA) of an adult patient with obstructive sleep apnea syndrome (OSAS) using computational fluid-structure interaction analysis. Methods: Three-dimensional UA models fabricated from cone beam computed tomography images obtained before (T0) and after (T1) MARPE in an adult patient with OSAS were used for computational fluid dynamics with fluid-structure interaction analysis. Seven and nine cross-sectional planes (interplane distance of 10 mm) in the nasal cavity (NC) and pharynx, respectively, were set along UA. Changes in the cross-sectional area and changes in airflow velocity and pressure, node displacement, and total resistance at maximum inspiration (MI), rest, and maximum expiration (ME) were investigated at each plane after MARPE. Results: The cross-sectional areas at most planes in NC and the upper half of the pharynx were significantly increased at T1. Moreover, airflow velocity decreased in the anterior NC at MI and ME and in the nasopharynx and oropharynx at MI. The decrease in velocity was greater in NC than in the pharynx. The airflow pressure in the anterior NC and entire pharynx exhibited a decrease at T1. The amount of node displacement in NC and the pharynx was insignificant at both T0 and T1. Absolute values for the total resistance at MI, rest, and ME were lower at T1 than at T0. Conclusions: MARPE improves airflow and decreases resistance in UA; therefore, it may be an effective treatment modality for adult patients with moderate OSAS.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.213-213
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• 2013

Even weak van der Waals (vdW) adhesion between two-dimensional solids may perturbtheir various materials properties owing to their low dimensionality. Although the electronic structure of graphene has been predicted to be modified by the vdW interaction with other materials, its optical characterization has not been successful. In this report, we demonstrate that Raman spectroscopy can be utilized to detect a few % decrease in the Fermi velocity ($v_F$) of graphene caused by the vdW interaction with underlying hexagonal boron nitride (hBN). Our study also establishes Raman spectroscopic analysis which enables separation of the effects by the vdW interaction from those by mechanical strain or extra charge carriers. The analysis reveals that spectral features of graphene on hBN are mainly affected by change in vF and mechanical strain, but not by charge doping unlike graphene supported on $SiO_2$ substrates. Graphene on hBN was also found to be less susceptible to thermally induced hole doping.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.12
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• pp.1559-1565
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• 2013

This study aims to investigate the dynamic interaction characteristics between Maglev vehicles and an elevated guideway. A more detailed model for the dynamic interaction of the vehicle/guideway is proposed. The proposed model incorporates a 3D full vehicle model based on prototyping, flexible guideway by a modal superposition method, and levitation electromagnets including the feedback controller into an integrated model. The proposed model was applied to an urban transit Maglev developed for a commercial application to analyze the dynamic response of the vehicle and guideway, and the effect of the surface roughness of the rail, mid-span guideway deflections, and air gap variations are then investigated from the numerical simulation.

• Journal of the Korean Geotechnical Society
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• v.32 no.1
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• pp.19-33
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• 2016

Stability analysis based on the limit equilibrium method combined with the result of infiltration analysis is commonly used to evaluate the effect of rainfall infiltration on the slope stability. Soil is a three-phase mixture composed of solid particle, water and air. Therefore, a fully coupled mixture theories of stress-deformation behavior and the flow of water and air should be used to accurately analyze the process of rainfall infiltration through soil slope. The purpose of this study is to study the effect of interaction of air and water flow on the mechanical stability of slope. In this study, stability analyses based on the coupled hydro-mechanical model of three-phases were conducted for slope of weathered granite soil widespread in Korea. During the process of hydro-mechanical analysis strength reduction technique was applied to evaluate the effect of rainfall infiltration on the slope stability. The results showed an increase of air pressure during infiltration because rain water continuously displaced the air in the unsaturated zone. Such water-air interaction in the pore space of soil affects the stress-deformation behavior of slope. Therefore, the results from the three-phase model showed different behavior from the solid-water model that ignores the transport effect of air in the pores.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.41 no.6
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• pp.429-434
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• 2017

A molecular-continuum hybrid method was developed to simulate microscale and nanoscale fluids where continuum fluidics cannot be used to predict Couette flow. Molecular dynamics simulation is used near the solid surface where the flow cannot be predicted by continuum fluidics, and Navier-Stokes equations are used in the other regions. Numerical simulation of Couette flow was performed using the hybrid method to investigate the effect of solid-liquid interaction and surface roughness in a nanochannel. It was found that the solid-liquid interaction and surface roughness influence the boundary condition. When the surface energy is low, slippage occurs near the solid surface, and the magnitude of slippage decreases with increase in surface energy. When the surface energy is high, a locking boundary condition is formed. The roughness disturbs slippage near the solid surface and promotes the locking boundary condition.

• The Journal of Korean Physical Therapy
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• v.25 no.5
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• pp.288-296
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• 2013

Purpose: This study was conducted in order to determine whether mechanical horseback-riding training depending on velocity can improve vestibular function and static postural balance on standing in healthy adults. Methods: For evaluation of vestibular function, electrooculography (EOG) of vertical and horizontal was performed for identification of the motion of eyes. For evaluation of static postural balance, COP distance, time spent on the sharpened Romberg test with neck extension (SRNE) were measured. Measurements were performed three times before training, three weeks after training, and six weeks after training. Participants were randomly assigned to three groups: fast velocity-mechanical horse -riding training (FV-MHRT, n=12), moderate velocity-mechanical horse-riding training (MV-MHRT, n=12), and slow velocity-mechanical horse-riding training (SV-MHRT, n=12). Results: According to the result for vertical, horizontal EOG, there was significant interaction in each group in accordance with the experiment time (p<0.05). The FV-MHRT group showed a significant decrease compared with the MV- MHRT, SV-MHRT groups (p<0.05). According to the result for static postural balance, the time spent, COP distance in SRNE showed significant interaction in each group in accordance with the experiment time (p<0.05). The time spent on the SRNE showed a significant increas in FV-MHRT, SV-MHRT (p<0.05). The COP distance of SRNE showed a significant increase in MV-MHRT (p<0.05). Conclusion: The MHRT velocity activated mechanism of vestibular spinal reflex (VSR), vestibular ocular reflex (VOR), also helped to strengthen vestibular function and static postural balance. In addition, it should be applied to different velocity of MHRT according to the specific purpose.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.7
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• pp.709-715
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• 2011

In order to observe the wake interaction between tip vortices generated by a two-bladed rotor with slightly different pitch angles, the velocity components of the tip vortices were measured by using a two-dimensional LDV system. It was observed that the swirl velocity components of the ensuing blade deviated from the Vatistas' n = 2 vortex model and the axial velocity components of the preceding blade deviated from the Gaussian profile. It was also found that in the wake-age range of $200^{\circ}$ to $240^{\circ}$, the filament of the ensuing blade tip vortex was stretched as result of the closing in of two vortices. The results from these observations suggest the possibility that a similar wake interaction is generated in actual rotor blades, especially, in the ones with articulated hubs.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.39 no.5
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• pp.461-466
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• 2015

Atomic force microscopy (AFM) is powerful tool for determining properties of samples based on interactions between the sample surface and an approaching probe tip. In this study, we modeled the interactions between the sample and the tip of the AFM microcantilever as a single nonlinear spring with an equivalent stiffness element and simulated the dynamic behaviors of the AFM microcantilevers using the finite element method (FEM) and ANSYS software. With the simulation results, we analyzed the complex dynamic responses of the AFM cantilever using proper orthogonal decomposition (POD). In addition, we compared the simulation and experimental results using the same method. Consequently, we suggest an effective method to express the interaction between the tip and sample, and we confirm that the influence of the higher order model due to the interaction between the tip and sample is increased.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.41 no.7
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• pp.481-487
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• 2017

The interaction between a shock wave and a boundary layer causes boundary layer separation, shock train, and in some cases, strong unsteadiness in the flow field. Such a situation is also observed in a shock tube, where the reflected shock wave interacts with the unsteady boundary layer. However, only a few studies have been conducted to investigate the shock train phenomenon in a shock tube. In the present study, numerical studies were conducted using the two-dimensional axisymmetric domain of a shock tube, and compressible Navier-Stokes equations were solved to clarify the flow characteristics of shock train phenomenon inside a shock tube. A detailed wave diagram was developed based on the present computational results, which were validated with existing experimental data.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.8
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• pp.1091-1096
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• 2010

This study was conducted to provide reference data for designing an alarm system that can help prevent the overturning of a container crane under wind load. Two methods, namely, fluid-structure interaction (FSI) analysis and windtunnel test, were adopted in this investigation. To evaluate the effect of wind load on the stability of the crane, a 50-ton-class container crane that is widely used in container terminals was adopted as the analysis model and 19 values were considered as design parameters for wind direction. First, the wind-tunnel test for the reduced-scale container crane model was performed according to the wind direction by using an Eiffel type atmospheric boundary-layer wind tunnel. Next, the FSI analysis for the real-scale container crane was conducted using ANSYS and CFX. Then, the uplift force determined from the FSI analysis was compared with that determined from the wind-tunnel test. Finally, a formula to compensate for the difference between the results of the FSI analysis and the wind-tunnel test was proposed.