CONTACT FORCE MODEL FOR A BEAM WITH DISCRETELY SPACED GAP SUPPORTS AND ITS APPROXIMATED SOLUTION

Park, Nam-Gyu,Suh, Jung-Min,Jeon, Kyeong-Lak Korean Nuclear Society 2011 Nuclear Engineering and Technology Vol.43 No.5

This paper proposes an approximated contact force model to identify the nonlinear behavior of a fuel rod with gap supports; also, the numerical prediction of interfacial forces in the mechanical contact of fuel rods with gap supports is studied. The Newmark integration method requires the current status of the contact force, but the contact force is not given a priori. Taylor's expansion can be used to predict the unknown contact force; therefore, it should be guaranteed that the first derivative of the contact force is continuous. This work proposes a continuous and differentiable contact force model with the ability to estimate the current state of the contact force. An approximated convex and differentiable potential function for the contact force is described, and a variational formulation is also provided. A numerical example that considers the particularly stiff supports has been studied, and a fuel rod with hardening supports was also examined for a realistic simulation. An approximated proper solution can be obtained using the results, and abrupt changes from the contacting state to non-contacting state, or vice versa, can be relieved. It can also be seen that not only the external force but also the developed contact force affects the response.

CONTACT FORCE MODEL FOR A BEAM WITH DISCRETELY SPACED GAP SUPPORTS AND ITS APPROXIMATED SOLUTION

박남규,서정민,전경락 한국원자력학회 2011 Nuclear Engineering and Technology Vol.43 No.5

This paper proposes an approximated contact force model to identify the nonlinear behavior of a fuel rod with gap supports;also, the numerical prediction of interfacial forces in the mechanical contact of fuel rods with gap supports is studied. The Newmark integration method requires the current status of the contact force, but the contact force is not given a priori. Taylor’s expansion can be used to predict the unknown contact force; therefore, it should be guaranteed that the first derivative of the contact force is continuous. This work proposes a continuous and differentiable contact force model with the ability to estimate the current state of the contact force. An approximated convex and differentiable potential function for the contact force is described, and a variational formulation is also provided. A numerical example that considers the particularly stiff supports has been studied, and a fuel rod with hardening supports was also examined for a realistic simulation. An approximated proper solution can be obtained using the results, and abrupt changes from the contacting state to non-contacting state, or vice versa, can be relieved. It can also be seen that not only the external force but also the developed contact force affects the response.

Contact forces generated by fallen debris

Sun, Jing,Lam, Nelson,Zhang, Lihai,Gad, Emad,Ruan, Dong Techno-Press 2014 Structural Engineering and Mechanics, An Int'l Jou Vol.50 No.5

Expressions for determining the value of the impact force as reported in the literature and incorporated into code provisions are essentially quasi-static forces for emulating deflection. Quasi-static forces are not to be confused with contact force which is generated in the vicinity of the point of contact between the impactor and target, and contact force is responsible for damage featuring perforation and denting. The distinction between the two types of forces in the context of impact actions is not widely understood and few guidelines have been developed for their estimation. The value of the contact force can be many times higher than that of the quasi-static force and lasts for a matter of a few milli-seconds whereas the deflection of the target can evolve over a much longer time span. The stiffer the impactor the shorter the period of time to deliver the impulsive action onto the target and consequently the higher the peak value of the contact force. This phenomenon is not taken into account by any contemporary codified method of modelling impact actions which are mostly based on the considerations of momentum and energy principles. Computer software such as LS-DYNA has the capability of predicting contact force but the dynamic stiffness parameters of the impactor material which is required for input into the program has not been documented for debris materials. The alternative, direct, approach for an accurate evaluation of the damage potential of an impact scenario is by physical experimentation. However, it can be difficult to extrapolate observations from laboratory testings to behaviour in real scenarios when the underlying principles have not been established. Contact force is also difficult to measure. Thus, the amount of useful information that can be retrieved from isolated impact experiments to guide design and to quantify risk is very limited. In this paper, practical methods for estimating the amount of contact force that can be generated by the impact of a fallen debris object are introduced along with the governing principles. An experimental-calibration procedure forming part of the assessment procedure has also been verified.

Stick-slip algorithm in a tangential contact force model for multi-body system dynamics

차호영,Juhwan Choi,류한식,최진환 대한기계학회 2011 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.25 No.7

Contact force of Multi-body dynamics (MBD) system can be classified two parts. First is a normal force and the other is a tangential force called friction force. And the friction force can be represented by two states such as stick and slip. The stick-slip phenomenon is simply described as a simple contact model which is a rigid body contacted on a sloped surface. If the calculated friction coefficient between the body and sloped surface is less than the static friction coefficient, the body should be stuck. If the calculated friction coefficient is greater than the static friction coefficient, the body will be sliding along the surface. The phenomenon is called as stick and slip state of friction, respectively. Usually many researchers and commercial MBD software used a coulomb friction force model which is defined with an only function of relative velocity. This kind of friction force model will be called a conventional friction force model in this paper. A big problem of the conventional model can not describe a stick state of friction phenomenon. In the case of conventional friction force model, the body will be sliding even though friction state is stick. Because, the relative velocity must have a non-zero value in order to generate the friction force. To solve this kind of problem, we propose a stick-slip friction force model including a spring like force. In the case of stick-slip friction force model, the body can be stuck on the sloped surface because the friction force will be a non-zero value,even though the relative velocity approaches zero. We defined a relative displacement variable called stiction deformation. In this paper,the stick-slip friction model is proposed and applied in the contact algorithm of MBD system. And then two friction models are compared with numerical examples. With the proposed stick-slip friction model, more realistic results are achieved.

Contact forces generated by fallen debris

Jing Sun,Nelson Lam,Lihai Zhang,Emad Gad,Dong Ruan 국제구조공학회 2014 Structural Engineering and Mechanics, An Int'l Jou Vol.50 No.5

Expressions for determining the value of the impact force as reported in the literature and incorporated into code provisions are essentially quasi-static forces for emulating deflection. Quasi-static forces are not to be confused with contact force which is generated in the vicinity of the point of contact between the impactor and target, and contact force is responsible for damage featuring perforation and denting. The distinction between the two types of forces in the context of impact actions is not widely understood and few guidelines have been developed for their estimation. The value of the contact force can be many times higher than that of the quasi-static force and lasts for a matter of a few milli-seconds whereas the deflection of the target can evolve over a much longer time span. The stiffer the impactor the shorter the period of time to deliver the impulsive action onto the target and consequently the higher the peak value of the contact force. This phenomenon is not taken into account by any contemporary codified method of modelling impact actions which are mostly based on the considerations of momentum and energy principles. Computer software such as LS-DYNA has the capability of predicting contact force but the dynamic stiffness parameters of the impactor material which is required for input into the program has not been documented for debris materials. The alternative, direct, approach for an accurate evaluation of the damagepotential of an impact scenario is by physical experimentation. However, it can be difficult to extrapolate observations from laboratory testings to behaviour in real scenarios when the underlying principles have not been established. Contact force is also difficult to measure. Thus, the amount of useful information that can be retrieved from isolated impact experiments to guide design and to quantify risk is very limited. In this paper, practical methods for estimating the amount of contact force that can be generated by the impact of a fallen debris object are introduced along with the governing principles. An experimental-calibration procedure forming part of the assessment procedure has also been verified.

유도전동기 회전자 제작시 압입작업 평가

박상철(Sang-Chul Park) 한국산학기술학회 2016 한국산학기술학회논문지 Vol.17 No.10

산업체에서 널리 사용되고 있는 유도전동기의 회전자를 제작하기 위하여 rotor core slot에 Cu bar를 열박음(shrinkage fit)작업으로 고정한 후 bar 표면을 punch로 원주방향으로 순차적으로 1.5~3mm 압입(swaging)작업시 rotor core slot과 bar 접촉면에 작용하는 contact tangential force의 크기와 분포를 단순화된 2차원 plane strain 해석모델을 사용하여 각각의 압입조건에 대하여 평가하였으며 또한 생산성 향상을 고려한 rotor core slot 설계시 slot 형상에 따른 접촉력 분포를 평가하여 rotor core slot 설계시 필요한 정보를 제공하고자 수치해석적인 방법을 사용하여 parametric study를 수행하였다. 이러한 탄소성 수치해석 결과 1) rotor core 압입작업시 bar 접촉면에 작용하는 contact force는 소성변형이 먼저 발생하는 bar 상부에 크게 작용하며 2) 순차적인 rotor core 압입작업시 bar 접촉면에 작용하는 total contact force는 바로 인접한 bar에 대한 압입작업에 의해서만 영향을 받으며 그 영향으로 약 55% 정도 total contact force가 증가하며 3) 생산성을 고려하여 rotor core를 설계하는 경우에 contact force를 증가시키기 위해서는 core slot의 폭보다 길이를 길게 하는 것이 바람직하다는 사실을 알 수 있었다. This study evaluates the magnitudes and distributions of contact tangential forces with the swaging depth of punch acting at the contact surfaces between a rotor core slot and a Cu bar during a sequential rotor core swaging process. The effects of the core slot shape on the magnitudes and distributions of the total contact forces were investigated to improve the productivity of the rotor core swaging process. Parametric elastic-plastic numerical analyses were performed using simplified two-dimensional cyclic symmetric plane strain models to evaluate the contact force distributions at the contact surfaces. The numerical analysis results show that the total contact tangential forces increased by about 55% with the adjacent Cu bar swaging process. The length of the core slot is a dominant factor in the core slot design as result of the increased total contact tangential forces during the swaging process of the rotor core.

Molecular dynamics study of the nanosized droplet spreading: The effect of the contact line forces on the kinetic energy dissipation

Yoon, Hong Min,Kondaraju, Sasidhar,Lee, Jung Shin,Suh, Youngho,Lee, Joonho H.,Lee, Joon Sang Elsevier 2017 APPLIED SURFACE SCIENCE - Vol.409 No.-

<P><B>Abstract</B></P> <P>Recent studies have revealed that contact line forces play an important role in the droplet spreading process. Despite their significance, the physics related to them has been studied only indirectly and the effect of contact line forces is still being disputed. We performed a molecular dynamics simulation and mimicked the droplet spreading process at the nanoscale. Based on the results of the simulation, the contact line forces were directly calculated. We found that the forces acting on the bulk and the contact line region showed different trends. Distinct positive and negative forces, contact line spreading, and friction forces were observed near the contact line. We also observed a strong dependency of the atomic kinetics in the contact line region on the variations in the contact line forces. The atoms of the liquid in the contact line region lost their kinetic energy due to the contact line friction force and became partially immobile on the solid surface. The results of the current study will be useful for understanding the role of the contact line forces on the kinetic energy dissipation in the contact line region.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Contact line forces, including friction and spreading forces are directly calculated. </LI> <LI> Overall trends of variations in contact line forces during droplet spreading process show characteristics of contact line forces. </LI> <LI> Detail relations of contact line forces and atomic kinetics in the contact line provide a clear evidence of the possible energy dissipation mechanism in droplet spreading process. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

보행 모의 실험을 위한 발목 없는 하지 외골격 로봇의 지면 접촉 모델 최적화

최기명,김상형,조창현 한국로봇학회 2023 로봇학회 논문지 Vol.18 No.4

The purpose of this study is to optimize parameters of a contact model to obtain similar ground contact force of human walking. Dynamic walking simulation considering ground contact is performed to determine load specifications when developing walking assist robots. Large contact forces that are not observed in actual experimental data occur during the simulation at the initial contact (e.g., heel contact). The large contact force generates unrealistic large joint torques. A lower exoskeleton robot with no ankles is developed with the Matlab simscape and the nonlinear hyper volumetric contact model is applied. Parameters of the nonlinear hyper volumetric model were optimized using actual walking contact force data. As a result of optimization, it was possible to obtain a contact force pattern similar to actual walking by removing the large contact force generated during initial contact.

Concave Wall Surface Tracking for Aerial Manipulator Using Contact Force Estimation Algorithm

Seon-il Lee,Hyeongseok Kim,Uikyum Kim,Hyeonbeom Lee 제어로봇시스템학회 2020 제어로봇시스템학회 국제학술대회 논문집 Vol.2020 No.10

This paper presents a control algorithm of a contact-based inspection for an Unmanned Aerial Vehicle (UAV) manipulator without using a force sensor. The conventional contact-based operation methods for a ground-based manipulator require a force sensor, but the force measurement is noisy on uneven surfaces. The noisy measurement can cause an unstable flight of the UAV when using direct force measurement as an input. To resolve this issue, we design a contact-force estimation algorithm of a UAV and desired trajectory generation algorithm. Contact-force is estimated by using the dynamics of a UAV and IMU sensor. In addition, to track the concave wall safely, we propose a heading-angle alignment algorithm. Through the Gazebo simulation, we show that the proposed method is effective compared to the force-sensor-based existing method.

확장된 칼만필터를 이용한 2축 로봇 매니퓰레이터의 접촉힘 추정

이중욱,허건수 한국공작기계학회 2001 한국생산제조학회지 Vol.10 No.4

Recent requirements for the fast and accurate motion in industrial robot manipulators need more advanced control tech-niques. To satisfy the requirements, importance of force control is being continuously increased and the expensive force sensor is usually installed to obtain the contact force information in practice. This information is indispensable for the force control of maintaining the desired contact force. However, the sensor cost is too high to be used in industrial applications. In this paper, it is proposed to estimate the contact force occurring between the end-effector of 2 DOF robots and environment. The contact force estimation system is developed based on the static and dynamic models of 2 DOF robot manipula-tors, where the contact force is described with respect to the link torque. The Extended Kalman Filter is designed and its performance is verified in simulations.