• The Journal of Korea Robotics Society
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• v.13 no.3
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• pp.174-181
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• 2018

For a mobile robot that travels along a terrain consisting of various geology, information on tire force and friction coefficient between ground and wheel is an important factor. In order to estimate the lateral force between ground and wheel, a lot of information about the model and the surrounding environment of the vehicle is required in conventional method. Therefore, in this paper, we are going to estimate lateral force through simple model (Minimal Argument Lateral Slip Curve, MALSC) using only minimum data with high estimation accuracy and to improve estimation reliability of the friction coefficient by using the estimated lateral force data. Simulation is carried out to analyze the correlation between the longitudinal and transverse friction coefficients and slip angles to design the simplified lateral force estimation model by analysing simulation data and to apply it to the actual field environment. In order to verify the validity of the equation, estimation results are compared with the conventional method through simulation. Also, the results of the lateral force and friction coefficient estimation are compared from both the conventional method and the proposed model through the actual robot running experiments.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.21 no.3
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• pp.140-148
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• 2009

Capillary tubes are widely used as expansion device in small refrigeration systems. The refrigerant flowing in the capillary tube experiences frictional and accelerational head losses and flashing simultaneously. In this paper flow characteristics of adiabatic capillary tubes were simulated with various friction factor models, two-phase viscosity models, and two-phase frictional multiplier models. The predicted pressure distribution and mass flow rate are compared with experimental data reported in literature. It is confirmed that the predicting accuracy with homogeneous model can be improved by employing suitable correlations of friction factor, two-phase viscosity and two-phase frictional multiplier.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.29 no.7 s.238
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• pp.938-946
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• 2005

Friction is a dominant nonlinear factor in servomechanisms, which seriously deteriorates system accuracy. A friction compensator is indispensable to fabricate high-performance servomechanisms. In order to compensate for the friction in the servomechanism, identification of the friction elements is required. To estimate the friction of the servomechanism, an accurate linear element model of the system is required first. Tn this paper, a nonlinear friction model, in which static, coulomb and viscous frictions as well as Stribeck effect are included, is identified through the describing function approximation of the nonlinear element. A nonlinear element composed of two relays is intentionally devised to induce various limit cycle conditions in the velocity control loop of the servomechanism. The friction coefficients are estimated from the intersection points of the linear and nonlinear elements in the complex plane. A Butterworth filter is added to the velocity control loop not only to meet the assumption of the harmonic balance method but also to improve the accuracy of the friction identification process. Validity of the proposed method is confirmed through numerical simulations and experiments. In addition, a model-based friction compensator is applied as a feedforward controller to compensate fur the nonlinear characteristics of the servomechanism and to verify the effectiveness of the proposed identification method.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2009.05a
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• pp.445-449
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• 2009

With the recent increase in the demand for the net-shape forming, numerical simulations are being commonly adopted to increase the efficiency and effectiveness of design of bulk metal forming processes. Proper consideration of tribological problems at the contact interface between the tool and workpiece is crucial in such simulations. In other words, lubrication and friction play important roles in metal forming by influencing the metal flow, forming load and die wear. In order to quantitatively estimate such friction condition or lubricant characteristic, the constant shear friction model is widely used for bulk deformation analyses. For this, new friction testing method based on the forward or backward extrusion process is proposed to predict the shear friction factor in this work. In this method, the tube-shaped punch pressurizes the workpiece so that the heights at the center and outer of punch (or mandrel) become different according to the friction condition. That is, the height at the center of punch is higher than that at the outer of the punch when the friction condition at the contact interface is severe. From this founding, the proposed friction testing method can be applied to effectively evaluate the friction condition in bulk metal forming processes.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.13 no.7
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• pp.588-594
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• 2001

The purpose of this study is to investigate the thermal and hydrodynamic characteristics of the channel in corrugated plate type heat exchangers numerically. Numerical work has been conducted using the Reynolds Stress Model(RSM) by utilizing the commercial finite-volume code, FLUENT. Based on this model, the dependence of heat transfer and friction factor on geometrical parameters have been investigated. It is found that larger corrugation angle give higher values of heat transfer coefficients and friction factors. As the reynolds number increases, the heat transfer coefficient also increases. It is also observed that the heat transfer coefficient reaches maximum while the friction factor stays relatively low at same corrugation angle. Through the analysis, it is found that the optimum corrugation angle for the heat exchanger performance exists. It is noted that the flow repulsions at the contact point of the two fluid streams make the low mixing more active for larger corrugation angle and high reynolds number.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.12 no.7
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• pp.2913-2918
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• 2011

This paper proposed the friction model using Preisach algorithm with neural network based on experimental results. In order to apply the neural network algorithm, the back propagation update rule was used and the updated weighting factor of neural network was applied to distribute function of Preisach model. In order to implement the proposed algorithm, the LabView software was used to apply to the precision control of mechanical system. The evaluation of the proposed friction model was executed through experiments.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.14 no.12
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• pp.1004-1013
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• 2002

Turbulent carbon dioxide flows and cooling heat transfers under supercritical state in a straight duct with a square cross-section are numerically analyzed employing low Reynolds number $\kappa-\varepsilon$ model and algebraic stress model. The flow is assumed to be (quasi-incompressible. Predicted Nusselt number and friction factor are compared with the experimental data, Blasius correlation for friction factor and Dittus-Boelter correlation for Nusselt number. Computational results for the Fanning's friction factor agree well with the all Rohsenow and Choi's correlation, Liou and Hwang's experimental data and Blasius correlation. The results obtained by algebraic stress model agree more with the Liou and Hwang's experimental data, while the results obtained by low Reynolds number $\kappa-\varepsilon$ model agree more with Blasius correlation. In the computation of Nusselt number, Dittus-Boelter correlation can not exactly fit the computational results. Therefore we propose the new correlation$Nu=0.053Re^{0.73}Pr^{0.4}$for the turbulent cooling heat transfer of carbon dioxide under supercritical state.

• Tribology and Lubricants
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• v.24 no.6
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• pp.378-385
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• 2008

In foil bearings, the friction between bumps and their mating surfaces is the major factor which exerts great influence on the bearing performance. From this point of view, many efforts have been made to improve the understanding of the influence of the friction on the foil bearing performance by developing a number of analytical models. However, most of them did not consider the hysteretic behavior of the foil structure resulting from the friction. The present work developed the static structural model in which hysteretic behavior of the friction was considered. The foil structure was modeled using finite element method and the algorithm which determines the conditions of the contact nodes and the directions of the friction forces was used to take into account the friction. The developed model was integrated into the foil bearing prediction code to investigate the effects of the friction on the static performance of the bearing. The results of analysis show that multiple static equilibrium positions are presented for the one static load under the influence of the friction, inferring its great effects on the dynamic performance. However, the effect of friction on the minimum film thickness which determines load capacity of the bearing is negligible.

• Proceedings of the KSME Conference
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• 2000.04b
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• pp.25-30
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• 2000

Plate and shell heat exchanger(P&SHE) has been applied to the refrigeration and air conditioning systems as evaporators or condensers fur their high efficiency and compactness. The purpose of this study is to analyze the characteristics of pressure drop in plate and shell heat exchanger. An experiment for single phase (low pressure drop in plate and shell heat exchanger was performed. Also numerical work was conducted using the FLUENT code for $ {\kappa}-{\varepsilon}$ model. The dependence of friction factor on geometrical Parameters was numerically investigated. The study examines the internal flow and the pressure distribution in the channel of plate and shell heat exchanger. The results of CFD analysis compared with experimental data, and the difference of frictor factor in plate side and shell side are 10% and 12%, respectively. Therefore, the CFD analysis model is effectively predict the performance of plate and shell heat exchanger.

• International Journal of Concrete Structures and Materials
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• v.11 no.2
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• pp.285-300
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• 2017

This study investigates the seismic performance of a staggered wall structure designed with conventional strength based design, and compares it with the performance of the structure designed by capacity design procedure which ensures strong column-weak beam concept. Then the seismic reinforcement schemes such as addition of interior columns or insertion of rotational friction dampers at the ends of connecting beams are validated by comparing their seismic performances with those of the standard model structure. Fragility analysis shows that the probability to reach the dynamic instability is highest in the strength designed structure and is lowest in the structure with friction dampers. It is also observed that, at least for the specific model structures considered in this study, R factor of 5.0 can be used in the seismic design of staggered wall structures with proposed retrofit schemes, while R factor of 3.0 may be reasonable for standard staggered wall structures.