Calculation Of Contact Forces Research Articles

Improved friction force calculation with an augmented open-close iteration formulation in discontinuous deformation analysis

In applying discrete numerical methods to model large-displacement problems, such as rockslides, accurate contact force calculation requires correct representation of the evolving contact status. In the discontinuous deformation analysis (DDA), open-close iteration (OCI) serves the crucial role of ascertaining that contact status is properly updated throughout an assembly of discrete blocky elements. OCI is a simple, straightforward and intuitive procedure but has shortcomings that affect analysis accuracy. Alternatives are generally computationally involved and have other issues, and OCI with its large installed base can still be one of the most desirable ways to track contact state with proper improvements. This is exactly this study aims to achieve. This study proposes an augmented open-close iteration (AOCI) algorithm that amends the shortcomings of OCI through: (1) it enhances the modeling of transition between contact states; (2) it provides the control mechanism for improving shear forces and shear movement direction also during OCI iteration. The AOCI is easy to add to the existing structure of OCI. The improved performance of AOCI over the traditional approach is demonstrated using both static and dynamic test cases.

Amending Research on the Expression of the Contact Force of the Spindle Barrel Finishing Based on EDEM Simulation

The spindle barrel finishing is commonly used to improve the surface integrity of the important parts of the high-end equipment while it is difficult to provide enough test artifacts for the traditional trial and error experiment to obtain the desirable processing technology. The EDEM simulation of the spindle barrel finishing can provide effective help for the process design, however, the difference between the simulation and experiment is closely related to the selection of the contact model during simulation. In this paper, simulations and experiments are conducted based on the identical apparatus and conditions to facilitate the comparison and validation between each other. Based on the Hertz contact theory, the effect of the material properties of contact objects and the relative position of the workpiece on the contact force is qualified. The expression of the correlation coefficient of the contact model is deduced. Then the formula for calculating the contact force between the barrel finishing abrasive and the workpiece that includes influence coefficient of the material properties and the relative positions is established. Finally, the contact force calculation formula is verified by changing the rotating speed. The result shows that the material correction coefficient ranges from 1.41 to 2.38, which is inversely related to the equivalent modulus E. The position correction coefficient ranges from 2.0 to 2.3. The relative error value between the calculation result and the experimental test result is from 0.58% to 14.07%. This research lay a theoretical foundation for the correction theory of the core elements of the spindle barrel finishing process.

Research of Contact Response of an Elastic Sphere Impacting a Rigid Plate Based on the Mass-Spring-Damped Oscillator Model and Dimensionless Parameter \omega_\Omega

The contact theory, such as the Hertz theory and Hunt-Crossley model can just solve the contact response when the sphere goes to the maximum compression but can't solve the contact process. In traditional research the impact process is considered as a single degree of freedom dynamical spring-damping system, however, the calculated contact force is much greater than the actual one. Based on the shortage of the conducted studies, a new dimensionless parameter Omega is proposed in this paper, the mass-spring-damped oscillator model (MSDOM) and the new contact theory with the consideration of the sphere mass and Omega are established. The correctness of the theoretical model is verified by 3D simulation, and the optimal contact force model is obtained. Furthermore, influence rules of material properties and contact parameters on contact response were studied. The results show that the contact deformation, velocity, piecewise nonlinear contact force and acceleration based on MSDOM and Omega are effective to calculate the contact response. The contact stiffness, damping, material properties of sphere and elastic modulus of the plate have different influence on the contact response while the Poisson's ratio nu_2 has little effect on it.

Kinetic analysis of polyhedral block system using an improved potential-based penalty function approach for explicit discontinuous deformation analysis

The complexity of polyhedral block systems (e.g., small blocks, flat blocks with small angles, edges, or faces) poses challenges in the kinetic analysis of rock block systems. This paper proposed an improved potential-based penalty function approach within an explicit three-dimensional (3D) discontinuous deformation analysis (DDA) framework for efficient and robust kinetic analysis of rock block systems. An explicit formulation of 3D DDA based on velocity verlet algorithm is first derived. A novel definition of potential function is then proposed with details of the key algorithms for overlap judgment of convex polyhedron, construction of intersection polyhedron and numerical integral for computation of contact force. The improved potential-based penalty function method is robust and efficient for complex convex polyhedral shapes. Several benchmark and application examples verify the feasibility, accuracy and robustness of the proposed methods in solving contact of polyhedral block systems.

Real-time Rigid Body Simulation Using Fully Penalty-based Method

This paper proposes a real-time rigid body simulator whose objects consist of the contact points. This simulator calculates the contact force using the penalty method. In this simulator, the calculation of contact force can be simplified by considering the point side and surface side separately. The simulator determines whether one contact point has penetrated the floor or the surface of an object, and calculates the contact force according to the amount of penetration. The contact force applied to the object can be easily obtained by repeating this calculation at all contact points.

Research on the relationship between the rail corrugation and the vibration response of the wheel-rail system

Rail corrugation is a very common phenomenon in high-speed railways. Rail corrugation can cause increased vibration of trains and tracks, and may even affect the safety of train operation. Therefore, this paper will analyze the vibration of the wheel-rail system caused by the rail corrugation. The actual transient rolling contact model is established by using explicit and implicit finite element methods. Through the calculation of the wheel-rail contact force and the wheel-rail mode, the vibration relationship between the rail corrugation and the wheel-rail system is obtained. It can provide some references for further analysis of the cause of rail corrugation.

An accurate geometric contact force model for super-quadric particles

Inter-particle contact force calculation between non-spherical particles is a fundamental problem in discrete element method (DEM) with yet no conclusive solutions. This paper presents a general geometric force model (GFM) to calculate contact forces and contact areas between particles with smooth surfaces. Special attention is paid to accurate calculation of the original geometric parameters defined in Hertz theory instead of using the simplified models currently adopted. In particular, a recently proposed mathematical technique is implemented to reliably calculate the principal curvatures and principal directions. The new model is applied to super-quadric particles. In particular, the prediction of the model is compared to those by the simplified models and the accurate contact force database in a comprehensive way based on orientation discretization. The accurate contact force database is obtained by the sub-particle scale finite element method (FEM), and a script is developed to automate the set-up of the FEM model for different contact scenarios. The comparisons show that the new model is obviously more accurate than the simplified models, and the analysis depicts that the errors of the simplified models result from the simplified geometric parameters. Such errors also affect the prediction of the contact area, which is important to the transport properties of particle assemblies. The new force model can be used in DEM to improve the accuracy of the simulation, and can also be useful to the contact mechanics of non-spherical elements.

Modeling and Simulation of Transient Impact Behavior of Elastic-Plastic Beam

The transverse spherical impact on an elastic-plastic beam is formulated and investigated herein. Both semi-analytical procedure and finite element (FEM) solution are elaborated. The semi analytical solution combines a finite difference method with the Hertz contact theory. The transient response of impact beams is computed by considering the loaded and unloaded phases. The contact force calculation is based on the model proposed by Stronge. To validate our semi-analytical model, a 3D finite element model has been developed. The comparison between the predictions from the presented semi-analytical and those from the 3D finite element models shows that the semi analytical model achieves very accurate predictions at a marginal computational time.

An efficient 3D DEM-FEM contact detection algorithm for tire-sand interaction

The combined discrete-finite element method is often used for dynamic interaction simulations, in which contact detection is the most time-consuming but critical constituent. Therefore, it is significant to develop an accurate and efficient contact detection algorithm. In this study, an efficient contact detection algorithm termed TSC (tire-sand contact) is developed for dealing with the interactions between spherical discrete elements and hexahedral finite elements. The global search of TSC is suitable for the contact detection of tire-sand interaction. In the global search phase, according to the contact characteristics of tire movement on granular terrain, the potential contact pairs are quickly determined by using the method of dynamically changing the slave nodes and master segments within a moving contact region. The local search is based on the principle of inside-outside algorithm, and the contact region is divided into three types, i.e. surface contact region, edge contact region and node contact region. In the local search phase, the invalid contact pairs and repeated contact pairs can be quickly excluded from the multiple potential contact pairs of one particle according to the relevant judgment conditions. And the Hertz-Mindlin contact model is used in corresponding contact force calculation. As a result, the quick contact search and accurate evaluation of contact force are accomplished. Finally, several numerical examples are presented to validate the accuracy and efficiency of the TSC algorithm in 3D contact analysis, which also demonstrates the advantages of the proposed algorithm in tire-sand interaction simulations.

Performance analysis of flexible intelligent hand prosthesis

The study of flexible intelligent hand prosthesis has important practical significance for handicapped people. Aiming at the grasping force control of flexible hand prosthesis, this paper draws lessons from the anatomical structure design of human hand, and proposes a fingertip grasping force control method based on linear tension feedback. The control strategy can realize the stable control of fingertip grasping force. The static mechanical model of finger is established, and the mathematical relationship of fingertip contact force calculation in static state is obtained. Then a friction compensation method is proposed. The experimental results show that the fitting value of the friction moment of the lasso matches well with the test value, and the error after friction compensation is obviously reduced.

On the sensitivity of Finite Element results in the calculation of the lateral thrust for all-steel buckling-restrained braces

The paper discusses the numerical analysis of all-steel buckling-restrained braces. These devices are designed to work in an inherently unstable regime, and their behavior is acutely sensitive both to any configuration detail in reality, and to any adopted parameter in their analysis. Their dissipative axial behavior can be reasonably well predicted by any suitable FEM model, if a good constitutive law is available. Nevertheless, it is shown here that an apparently accurate FEM calculation of the lateral contact forces, generated by the buckled core when it contacts the external containment profiles, produces results so sensitive to modelling details that they are practically devoid of an acceptable degree of accuracy. These observations might raise some doubts about the advisability of employing this type of bracing in normal engineering practice. In our viewpoint, a similar conclusion could be reached for any structural element designed to work in an unstable regime, unless the imperfections – of any type, including possible modelling details – could be explicitly taken into account, either parametrically or in a statistical way.

Analysis of contact-impact dynamics of soft finger tapping system by using hybrid computational model

• An efficient hybrid computational model to analyze frictional impact responses during tapping of soft finger is developed. • A lumped-parameter model taking the tangential compliance into account is presented to calculate contact forces. • Event driven scheme and computational strategy are given to solve non-smooth differential equation. • Numerical results are compared with three-dimensional LS-DYNA solutions. • A ‘reserve slip’ phenomenon caused by large tangential contact compliance is captured. The aim of this paper is to develop an efficient hybrid computational model to analyze the frictional impact dynamic responses of soft finger during the tapping event. The large deformation field and inertial field of soft structure are discretized by absolute nodal coordinate formulation. Lagrange multiplier method is adopted to account for the constraints between neighbor phalanges. Considering tangential contact compliance, a lumped-parameter model at the local contact zone is presented to calculate contact forces. The governing equations of soft finger tapping system expressed by generalized coordinates are derived. An event driven scheme is given to analyze and evaluate the stick–slip transitions. The governing equation is integrated by generalized- α method. The applications of the hybrid computational model are demonstrated using various soft finger tapping systems acted by different driven moments. The feasibility of the proposed model is validated by comparing with the LS-DYNA solution. The error of the solution calculated by the proposed model for the peak value of contact force is less than 8%. Furthermore, numerical results show that the large structural compliance and driven moments have significant effect on the frictional impact responses. The normal relative motion between the fingertip and the rough target surface will experience 1∼4 compression-restitution transitions when Young's Modulus is from 0.01 GPa to 1 GPa or the slenderness ratio of phalanx is from 10.7 to 32. When the posture of soft finger is convex at impact instance, the tangential relative motion will experience 3 slip–stick transitions during the contact process. In addition, it also can be found that the tangential contact compliance can reverse the direction of slip (i.e. ‘reverse slip’ phenomenon).

Constitutive properties of irregularly shaped lunar soil simulant particles

With the development of ISRU Technology, lunar soil has become an important kind of building material for lunar base. Although the particle shape of lunar soil is extremely irregular, the non-linear mechanical property of lunar soil particles is rarely researched. In this paper, the relationship between the displacement and the contact force of lunar soil particles were researched. First, a series of experiments on normal mechanical properties of lunar soil particles based on the high-precision micro-operation test bed were carried out. Second, a contact model for irregular lunar soil particles was established. The irregular particles are equivalent to spherical particles, and an equivalent algorithm based on piecewise function fitting was proposed. Finally, a series of simulation were carried out to verify the equivalent algorithm in the discrete element method software EDEM. The results provided a solid theoretical basis for the calculation of contact forces between irregularly shaped lunar soil particles.

Design and Analysis of Novel Actuation Mechanism with Controllable Stiffness

Actuators intended for human–machine interaction systems are usually designed to be mechanically compliant. Conventional actuators are not suitable for this purpose due to typically high stiffness. Advanced powered prosthetic and orthotic devices can vary their stiffness during a motion cycle and are power-efficient. This paper proposes a novel actuator design that modulates stiffness by means of a flexible beam. A motorized drive system varies the active length of the cantilever beam, thus achieving stiffness modulation. New large deflection formulation for cantilever beams with rolling contact constraints is used to determine the moment produced by the actuator. To validate the proposed solution method, an experiment was performed to measure large static deformations of a cantilever beam with the same boundary conditions as in the actuator design. The experiments indicate excellent agreement between measured and calculated contact forces between beam and roller, from which the actuator moment is determined.

Nonlinear viscoelastic-plastic material modelling for the behaviour of ice in ice-structure interactions

In this paper, a three-dimensional constitutive ice model with nonlinear viscoelastic and plastic components acting in series is proposed for the dynamic simulation of ice-structure interactions. The former component corresponds to a nonlinear Burgers model, in which the deviatoric behaviour is viscoelastic and the volumetric behaviour is elastic. The Burgers model is combined with the well accepted Glen's law and Ashby and Duval’ law to describe the time-dependent behaviour and distribution in relaxation time. A hydrostatic pressure- and octahedral shear stress-dependent Tsai-Wu-type yield criterion is adopted to invoke the plastic state. The proposed ice model is assumed to be isotropic and is implemented in the commercial software LS-DYNA as a user-defined material. Verification of this model is implemented via simulations of creep and indentation experiments and via the simulation of a scenario of ice-rigid steel plate collision. The simulation of creep experiments shows that this material model can reflect the viscoelastic properties of ice quite well. The calculated contact force and pressure-area curves agree well with the results of indentation experiments. And the ice-rigid steel plate collision example yields reasonable results, indicating that the proposed model has a good capacity for describing the brittle behaviour of ice. The numerical verification proves that the proposed ice material model has a wide range of potential applications.

A fast volumetric contact force computation of rigid bodies by decomposition and iteration

A fast volumetric contact force computation of rigid bodies by decomposition and iteration

A novel absolute nodal coordinate formulation thin plate tire model with fractional derivative viscosity and surface integral-based contact algorithm

A new absolute nodal coordinate formulation thin plate tire model, which includes the damping property of the rubber and an efficient tire–road contact algorithm is given. The fractional derivative viscosity constitutive model is proposed in this paper based on the complete form of the absolute nodal coordinate formulation thin plate element, which is created to describe the stress-free initially curved configuration of the tire. A new contact algorithm based on the integration of the contact pressure within the contact patch is developed. By solving the simultaneous equations of the tire geometry and road profile, the dimensionless coordinates for the boundary points of contact patch could be obtained directly. A self-adaptable Gauss integration strategy is introduced to perform the integration of the contact pressure within the varying region, so the integration could reach high precision by few integration points. The calculation of contact force is determined based on penalty method and smoothed Coulomb friction model. The application of fractional derivative viscosity on the absolute nodal coordinate formulation thin plate element is demonstrated by numerical results. A pressurized Golf tire model is given to show the feasibility of the proposed tire–ground contact algorithm.

Application of SPH-FE method for fluid-structure interaction using immersed boundary method

PurposeThis paper aims to propose a new smoothed particle hydrodynamics (SPH)-finite element (FE) algorithm to study fluid–structure interaction (FSI) problems.Design/methodology/approachThe fluid domain is discretized based on the theory of SPH), and solid part is solved through FE method, similar to other SPH-FE methods in the previous studies. Instead of master-slave technique, the interpolating (kernel) functions of immersed boundary method are implemented to couple fluid and solid domains. The procedure of modeling completely follows the classic IB framework where forces and velocities are transferred between interacting parts. Three benchmark FSI problems are simulated and the results are compared with those of similar numerical and experimental works.FindingsThe proposed SPH-FE algorithm with promising and acceptable results can be utilized as a reliable method to simulate FSI problems.Originality/valueContrary to most SPH-FE algorithms, the calculation of contact force is not required at interacting boundaries and no iterative process is proposed to calculate forces, velocities and positions at new time step.

A stable node-based smoothed finite element method for metal forming analysis

In this paper, a stable node-based smoothed finite element method (SNS-FEM) is presented for analyzing metal forming problems using linear triangular or tetrahedral elements. In present method, the numerical integration domains are approximately circular or spherical regions of the node-based smoothing domains generated by the node-based smoothed finite element method (NS-FEM). Four or six supplementary integration points, which are symmetrically located at the crossover points of the region and the coordinate axis, are employed for each node to form the stabilization items associated with the variance of smoothed shape function gradient. Through this operation without the introducing of any uncertain parameter, the SNS-FEM not only significantly cures the temporal instability of NS-FEM but also performs better in effectiveness and efficiency than FEM, which is well validated by several numerical examples containing benchmark cases. Additionally, a simple but effective contact algorithm including contact searching and contact force computation is presented.

Subjects with medial and lateral tibiofemoral articular cartilage defects do not alter compartmental loading during walking

BackgroundHealthy cartilage is essential for optimal joint function. Although, articular cartilage defects are highly prevalent in the active population and hamper joint function, the effect of articular cartilage defects on knee loading is not yet documented. Therefore, the present study compared knee contact forces and pressures between patients with tibiofemoral cartilage defects and healthy controls. Potentially this provides additional insights in movement adaptations and the role of altered loading in the progression from defect towards OA. MethodsExperimental gait data collected in 15 patients with isolated cartilage defects (8 medial involvement, 7 lateral-involvement) and 19 healthy asymptomatic controls was processed using a musculoskeletal model to calculate contact forces and pressures. Differences between two patient groups and controls were evaluated using Kruskal-Wallis tests and individually compared using Mann-Whitney-U tests (alpha <0.05). FindingsThe patients with lateral involvement walked significantly slower compared to the healthy controls. No movement adaptations to decrease the loading on the injured condyle were observed. Additionally, the location of loading was not significantly affected. InterpretationThe current results suggest that isolated cartilage defects do not induce significant changes in the knee joint loading distribution. Consequently, the involved condyle will capture a physiological loading magnitude that should however be distributed over the cartilage surrounding the defect. This may cause local degenerative changes in the cartilage and in combination with inflammatory responses, might play a key role in the progression from articular cartilage defect to a more severe OA phenotype.