• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 1999.03b
• /
• pp.103-107
• /
• 1999

In this paper, a computer simulation technique for the forging process having a floating die is presented. The penalty rigid-plastic finite element method is employed together with an iteratively force-balancing method, in which the convergence is achieved when the floating die part is in force equilibrium within the user-specified tolerance. The force balance is controled by adjusting the velocity of the floating die in an automatic manner. An application example of a three-stage cold forging process is given.

• International Journal of Precision Engineering and Manufacturing
• /
• v.8 no.2
• /
• pp.85-89
• /
• 2007

Linear ball guideways have been used recently in precision or ultra-precision positioning devices. However, when the inner balls begin to roll or the moving direction reverses, these guideways are subject to rolling friction or nonlinear spring behavior. An ultra-precision device with a linear motor, referred to as a 'tunnel actuator' (TA), has been constructed to measure these phenomena. The application of a TA is beneficial for two reasons: it mostly cancels the attractive magnetic force between the stator and mover (armature), and its magnetic flux leakage is very low. The influence of the nonlinear spring behavior in ball guideways was investigated in this study using the pure driving force from a TA. The equilibrium between the driving force from the TA and the nonlinear spring force provided great accuracy for a positioning stage using a linear ball guideway.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.29 no.7 s.238
• /
• pp.983-989
• /
• 2005

The effects of mechanical parameters on the characteristics of chemical mechanical polishing(CMP) can be directly evaluated by friction force. The piezoelectric quartz sensor for friction force measurement was installed, and friction force could be detected during CMP process. Furthermore, friction energy can be calculated by multiplying relative velocity by integration of the friction force throughout the polishing time. $SiO_2$ slurry for interlayer dielectric(ILD) CMP was used in this experiment to consider the relation of frictional characteristics and polishing results. From this experiment, it is proven that the friction energy is an essential factor of removal rate. Also, the friction force is related to removal amount per unit length(dH/ds) and friction energy has corelation to the removal rate(dH/dt) and process temporature. Moreover, within wafer non-unifornity(WIWNU) is related to coefficient of friction because of the mechanical moment equilibrium. Therefore, the prediction of polishing result would be possible by measuring friction force.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.22 no.3
• /
• pp.130-135
• /
• 2014

In this paper, a new estimation method is proposed to calculate steering rack axial force using a 3 dimensional tire mesh model when a car is standing on the road. This model is established by considering changes of camber angle and contact patch between the tires and the ground according to steering angle. The steering rack bar axial force is estimated based on the static equilibrium equations of forces and moments. A tire friction force is supposed to act on the center point of the contact patch, and the proportional coefficient of friction depending on contact patch is suggested. Using the proposed estimation method, rack axial force sensitivity analysis is evaluated according to changes of suspension geometry. Then optimal motor power of Motor Driven Power Steering(MDPS) is evaluated using suggested rack forces.

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 1997.10a
• /
• pp.93-97
• /
• 1997

Since the modified membrane element has the same external appearance as the ordinary membrane element, it is not able to apply the thickness variation of sheet metal in the blank holder to the contact treatment and the equally distributed blank holding force should be inevitably imposed on sheet metal along the periphery regardless of the contact status. But sheet metal does not contact with the blank holder at the periphery, nor the blank holding force is distributed uniformly along the boundary. To impose the blank holding force properly, the scheme is improved so that the blank holding force at each node imposed on sheet metal is dependent on the calculated thickness derivation and a state of equilibrium with the total blank holding force. The validity of the improved scheme is demonstrated with the simulation of cylindrical and rectangular cup deep drawing.

• Korean Journal of Computational Design and Engineering
• /
• v.21 no.1
• /
• pp.90-98
• /
• 2016

When ships and offshore plants are flooded or the floating crane is equipped with a heavy object, these floating structures are excessively inclined. In this case, immersion, heel, and trim affecting the hydrostatic restoration performance are very large and are coupled each other. In this paper, in order to calculate a static equilibrium position of floating structures with excessive inclination, the nonlinear governing equations were constructed by sequential linearization. In the governing equation, the immersion, heel, and trim are fully coupled, and the equations are represented using a plane area, a primary moment, and a moment of inertia of the water plane area. Therefore, it is possible to calculate the additional factor related the water plane area for estimating stability. Position and orientation of the floating structure are obtained by iterative calculation. The calculated results are compared with the previous studies in the aspect to the performance and the accuracy.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 2005.06a
• /
• pp.1954-1957
• /
• 2005

A quantitative evaluation of postural balance training using a virtual reality bicycle system was performed. In the experiment, the effectiveness of virtual reality bicycle system on postural balance training was analyzed with four male subjects in their twenties. The parameters measured during cycling were cycling time, average velocity, number of times subject deviated from path, and weight shift. Those parameters were evaluated for the quantification of the extent of control. We also measured the parameters on postural control capability after 5th trial and 10th trial in a balance testing system with a force plate to find out the effectiveness of the training. In the balance test with force plate, it was found out that the weight shift was almost zero and the deviation from the target trace reduced significantly after the training with the virtual cycle. The result showed that the virtual bicycle system was an effective system as a rehabilitation training device.

• Journal of Korean Society of Steel Construction
• /
• v.17 no.6 s.79
• /
• pp.727-736
• /
• 2005

This study presents a method of determining the optimum cable tension forces for the proper initial equilibrium state of a cable-stayed bridge using the least square method. The proposed method minimizes the errors, i.e., the differences, such as the deflection and the moments of the girder and the tower, between the target values from a continuous beam by considering the cable anchor point as supports of the girder and the responses obtained from the analysis of the entire cable-stayed bridge system. Especially, the proposed method can selectively control the adjustment of the tower moment, the girder moment, and the deflections by introducing the weighing matrix. Through numerical analysis and comparisons with existing studies, the usefulness and validity of the proposed method was verified.

• Geomechanics and Engineering
• /
• v.22 no.6
• /
• pp.553-564
• /
• 2020

In this study, a simple numerical approach for a circular tunnel opening in strain-softening surrounding rock is proposed considering out-of-plane stress and seepage force based on Biot's effective stress principle. The plastic region of strain-softening surrounding rock was divided into a finite number of concentric rings, of which the thickness was determined by the internal equilibrium equation. The increments of stress and strain for each ring, starting from the elastic-plastic interface, were obtained by successively incorporating the effect of out-of-plane stress and Biot's effective stress principle. The initial value of the outmost ring was determined using equilibrium and compatibility equations. Based on the Mohr-Coulomb (M-C) and generalized Hoek-Brown (H-B) failure criteria, the stress-increment approach for solving stress, displacement, and plastic radius was improved by considering the effects of Biot's effective stress principle and the nonlinear degradation of strength and deformation parameters in plastic zone incorporating out-of-plane stress. The correctness of the proposed approach is validated by numerical simulation.

• Journal of Advanced Research in Ocean Engineering
• /
• v.2 no.3
• /
• pp.112-128
• /
• 2016

Capsize and sinking of a coastal car ferry has occurred in a Korean offshore area and has caused hundreds of human casualties. The rapid turn and improper cargo loading are inferred as the main reasons of the accident. It has motivated to develop a new system of cargo securing with improved safety of Korean coastal ferries. This paper provides a new approach regarding cargo securing safety assessment which is purely based on force equilibrium conditions, because IMO CSS is suitable for the ocean-going vessels. The mathematical formulations are presented for the new approach. This paper also introduces a newly developed safety assessment system based on the new approach. Most outstanding features are that it can utilize acceleration data produced from hydrodynamic motion analyses or assumed maximum extents of ship motion components and that securing safety assessment is simultaneously possible for unlimited number of cargoes with finite number of lashings.