• Tribology and Lubricants
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• v.34 no.1
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• pp.1-8
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• 2018

This paper presents the analysis of friction master curves for a sliding elastomer on rough granite. The hysteresis friction is calculated using an analytical model that considers the energy spent during the local deformation of the rubber due to surface asperities. The adhesion friction is also considered for dry friction prediction. The viscoelastic modulus of the rubber compound and the large-strain effective modulus are obtained from dynamic mechanical analysis (DMA). We accurately demonstrate the large strain of rubber that contacts with road substrate using the GW theory. We found that the rubber block deforms approximately to 40% strain. In addition, the viscoelastic master curve considering nonlinearity (at 40% strain) is derived based on the above finding. As viscoelasticity strongly depends on temperature, it can be assumed that the influence of velocity on friction is connected to the viscoelastic shift factors gained from DMA using the time-temperature superposition. In this study, we apply these shift factors to measure friction on dry granite over a velocity range for various temperatures. The measurements are compared to simulated hysteresis and adhesion friction using the Kluppel friction theory. Although friction results in the low-speed band match well with the simulation results, there are differences in the predicted and experimental results as the velocity increases. Thus, additional research is required for a more precise explanation of the viscoelastic material properties for better prediction of rubber friction characteristics.

• Journal of The Korean Society of Agricultural Engineers
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• v.56 no.6
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• pp.75-84
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• 2014

This study aims to develop the program for design of a reinforced earth retaining wall. For this purpose, the external stability such as overturning, sliding and bearing capacity and the internal stability such as pull-out failure and tensile rupture of the reinforced earth retaining wall with the reinforcement spacing and the backfill inclination were examined. In addition, the calculated results from the developed program were verified by comparing with the simulated results based on the three-dimensional finite element analysis. It is expected that this program contributes to effective design of the reinforced earth retaining wall.

• International Journal of Fluid Machinery and Systems
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• v.4 no.1
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• pp.199-208
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• 2011

This work presents numerical results, using OpenFOAM, of the flow in the swirl flow generator test rig developed at Politehnica University of Timisoara, Romania. The work shows results computed by solving the unsteady Reynolds Averaged Navier Stokes equations. The unsteady method couples the rotating and stationary parts using a sliding grid interface based on a GGI formulation. Turbulence is modeled using the standard k-${\varepsilon}$ model, and block structured wall function ICEM-Hexa meshes are used. The numerical results are validated against experimental LDV results, and against design velocity profiles. The investigation shows that OpenFOAM gives results that are comparable to the experimental and design profiles. The unsteady pressure fluctuations at four different positions in the draft tube is recorded. A Fourier analysis of the numerical results is compared whit that of the experimental values. The amplitude and frequency predicted by the numerical simulation are comparable to those given by the experimental results, though slightly over estimated.

• Journal of Korean Association for Spatial Structures
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• v.13 no.2
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• pp.57-66
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• 2013

There are a number of construction methods to build spatial structures such as erection method, Element method, Block method, Sliding method, Lift-up method and Push-up method. These methods are uneconomical and low accuracy, and require long construction duration because of a need of a scaffold or a tower crane to build spatial roof frame. In this study, the construction method to erect a truss structure was proposed as an economical and easy installation method. The proposed method has end hinges of keel truss and winches with horizontal cable. This method makes safe and accurate production and reduces construction duration because trusses are built on the floor or supporter. The goal of this study is to verify the validity of construction method by building scale model using the proposed method.

• Korean Institute of Interior Design Journal
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• v.15 no.1 s.54
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• pp.139-146
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• 2006

This study shows the floor plan types and the space composition of multi-used toilets in public-toilets of Choongchung-Do. The areas of multi-used toilets are various from 4.8m2 to 10.5m2 And there Is usually one multi-used toilet in one public-toilet, but some public-toilets have two multi-used toilets. Multi-used toilets have several equipments such as toilet stool, urinal, washstand, change diaper, chair for baby-care, toilet stool for child, urinal for child, so on. All the multi-used toilets have toilet stool and washstand, but urinal and change diaper were used restrictively, and chair for baby-care, toilet stool for child, urinal for child were used in few cases. There are six types how the multi-used toilets are located in public-toilets, five types of multi-used toilet forms, and five types how the equipments are installed in multi-used toilets. The dotted blocks are installed partially in line type, and partially in spot type. But some cases, there was no installation of dotted block. Auto-sliding door were usually applicated, and some other types of door system were used restrictively. This study offers not only the present conditions, but also the appropriate planning directions of the multi-used toilets.

• Tribology and Lubricants
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• v.27 no.6
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• pp.293-301
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• 2011

Understanding of the tribological characteristics of polytetrafluoroethylen (PTFE) and ultra-high-molecular-weight polyethylene (UHMWPE) is crucial for their applications such as bearing and total joint replacement. In this work, the effect of the surface roughness of carbon steel on the tribological behaviors of PTFE and UHMWPE was experimentally investigated by using block-on-ring tribotester with friction force monitoring capability. It was found that that the amount of material transfer layers of PTFE formed on the carbon steel was significantly larger than those of UHMWPE, which was responsible the lower friction coefficient of PTFE. It was also concluded that the effect of surface roughness of carbon steel on the friction coefficient of UHMWPE was more significant than that of PTFE. For UHMWPE, it was found that the effect of surface roughness of counterface was varied with respect to applied normal force and sliding as well. Based on Archard's wear law, the wear coefficient of PTFE and UHMWPE was calculated to be $3{\times}10^{-5}$ ~ $8{\times}10^{-5}$ and $7{\times}10^{-6}$ ~ $2{\times}10^{-5}$, respectively.

• Tribology and Lubricants
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• v.30 no.6
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• pp.378-383
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• 2014

This study predicts the of the hysteretic friction of a rubber block sliding on an SMA asphalt road. The friction of filled rubber on a rough surface is primarily determined by two elements:the viscoelasticity of the rubber and the multi-scale perspective asperities of the road. The surface asperities of the substrate exert osillating forces on the rubber surface leading to energy dissipation via the internal friction of the rubber when rubber slides on a hard and rough substrate. This study defines the power spectra at different length scales by using a high-resolution surface profilometer, and uses rubber and road surface samples to conduct friction tests. I consider in detail the case when the substrate surface has a self affine fractal structure. The theory developed by Persson is applied to describe these tests through comparison with the hysteretic friction coefficient relevant to the energy dissipation of the viscoelastic rubber attributable to cyclic deformation. The results showed differences in the absolute values of predicted and measured friction, but with high correlation between these values. Hence, the friction prediction model is an appropriate tool for separating the effects of each factor. Therefore, this model will contribute to clearer understanding of the fundamental principles of rubber friction.

• Journal of Drive and Control
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• v.18 no.4
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• pp.28-34
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• 2021

Among the currently available types of fuel, LNG emits a relatively small amount of nitrogen oxide and carbon dioxide when it burns in the engine. However, since LNG is a flammable material, leakage during bunkering can lead to accidents, such as fires. Therefore, it is necessary to install a remote operation emergency shut-down (ESD) valve to block the flow and leakage of LNG in an emergency situation that occurs during bunkering. The ESD valve uses a hydraulic driving device consisting of a hydraulic control valve and a hydraulic motor to control globe valve disc displacement, which regulates the flow path for LNG transfer. At this time, there are various nonlinearities in hydraulic driving devices; hence, it is necessary to design a controller with robust control performance against these uncertainties. In this study, modeling of the ESD valve was carried out, and a sliding mode controller to control the displacement of the globe valve disc was designed. As a result, it was confirmed that the designed control performance could be achieved by overcoming nonlinearity characteristics using the designed controller.

• Journal of the Korean Geotechnical Society
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• v.26 no.3
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• pp.47-57
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• 2010

Yield seismic coefficient plays an important role in the estimation of permanent displacement of a soil slope subjected to earthquake using Newmark's sliding block theory. However, yield seismic coefficients currently used in practices are not mechanically rigorous since most of them are estimated using limit equilibrium methods considering equilibrium condition only. Therefore, estimation of permanent displacement of a soil slope based on existing yield seismic coefficient may cause problems. Limit analysis estimating the range of mechanically rigorous solution is thought to be effective in evaluating the validity of existing yield seismic coefficient. In this study, a simple stability chart for yield seismic coefficient useful in practices is proposed by considering various slope conditions including stability number, slope inclination, strength parameters, etc.

• Tunnel and Underground Space
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• v.14 no.3
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• pp.167-174
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• 2004

This paper is to introduce an article published in Rock Mechanics and Rock Engineering, 2003. In this research, a fracture mechanics model is developed to illustrate the importance of time-dependence far brittle fractured rock. In particular a model is developed fer the time-dependent degradation of rock joint cohesion. Degradation of joint cohesion is modeled as the time-dependent breaking of intact patches or rock bridges along the joint surface. A fracture mechanics model is developed utilizing subcritical crack growth, which results in a closed-form solution for joint cohesion as a function of time. As an example, a rock block containing rock bridges subjected to plane sliding is analyzed. The cohesion is found to continually decrease, at first slowly and then more rapidly. At a particular value of time the cohesion reduces to value that results in slope instability. A second example is given where variations in some of the material parameters are assumed. A probabilistic slope analysis is conducted, and the probability of failure as a function of time is predicted. The probability of failure is found to increase with time, from an initial value of 5% to a value at 100 years of over 40%. These examples show the importance of being able to predict the time-dependent behavior of a rock mass containing discontinuities, even for relatively short-term rock structures.