Contact Force Model Research Articles

Optimization research on dynamic behavior for mechanism with clearance joint and wear

This paper proposes a new optimization method by immune algorithm to reduce the impact of clearance joint and wear on the dynamics of mechanisms. Firstly, the dynamic model of crank-slider mechanism is built by Lagrange principle, and the wear phenomenon of clearance joint is characterized by Archard model. Then, the motion function reliability model of mechanism is presented by Stress-Strength interference (SSI) theory. Secondly, the optimization model of mechanism is derived and the surrogate model of the maximum contact force of clearance joint is indicated by response surface method (RSM), the immune algorithm is used to find the optimal solution of the surrogate model. Finally, the impact of wear and optimization on dynamic behavior, nonlinear dynamics, and motion function reliability of mechanism is investigated. The results show that wear clearance joint seriously affects the performance of mechanism. After optimization, the dynamic behavior and nonlinear dynamics of mechanism are improved, and the motion function reliability of mechanism is increased. This paper raises foundation for predicting the performance of mechanisms considering wear clearance joint, and provides theoretical guidance for optimization design and fault diagnosis of mechanisms.

Multibody dynamic modeling of the behavior of flexible instruments used in cervical cancer brachytherapy.

The steep radiation dose gradients in cervical cancer brachytherapy (BT) necessitate a thorough understanding of the behavior of afterloader source cables or needles in the curved channels of (patient-tailored) applicators. The purpose of this study is to develop and validate computer models to simulate: (1) BT source positions, and (2) insertion forces of needles in curved applicator channels. The methodology presented can be used to improve the knowledge of instrument behavior in current applicators and aid the development of novel (3D-printed) BT applicators. For the computer models, BT instruments were discretized in finite elements. Simulations were performed in SPACAR by formulating nodal contact force and motion input models and specifying the instruments' kinematic and dynamic properties. To evaluate the source cable model, simulated source paths in ring applicators were compared with manufacturer-measured source paths. The impact of discrepancies on the dosimetry was estimated for standard plans. To validate needle models, simulated needle insertion forces in curved channels with varying curvature, torsion, and clearance, were compared with force measurements in dedicated 3D-printed templates. Comparison of simulated with manufacturer-measured source positions showed 0.5-1.2mm median and<2.0mm maximum differences, in all but one applicator geometry. The resulting maximum relative dose differences at the lateral surface and at 5mm depth were 5.5% and 4.7%, respectively. Simulated insertion forces for BT needles in curved channels accurately resembled the forces experimentally obtained by including experimental uncertainties in the simulation. The models developed can accurately predict source positions and insertion forces in BT applicators. Insights from these models can aid novel applicator design with improved motion and force transmission of BT instruments, and contribute to the estimation of overall treatment precision. The methodology presented can be extended to study other applicator geometries, flexible instruments, and afterloading systems.

Approximate contact force model for viscoelastic materials based on generalized Maxwell model

This paper proposes a novel approximate model for estimating the normal contact force between a rigid sphere and a viscoelastic half-space based on the generalized Maxwell model. The relaxation function derived from the generalized Maxwell model is applied to the solution to the elastic contact problem based on the elastic–viscoelastic correspondence to obtain an integral expression of pressure for viscoelastic contact. Using the approximate method on the basis of Taylor series, the integral expression is translated into an explicit function of displacement, velocity, time and material properties. A normal contact force model is established by integrating the pressure over contact area. A relaxation test of Nafion® XL is conducted to capture the viscoelastic parameters, and these parameters are employed to simulate the contact behaviors using the finite element method (FEM) to determine the scale factor in the contact force model. In order to verify the validity of the approximate model, the outcomes obtained from the model are compared with those generated by the FEM. A parametric study is conducted to analyze the effects of variations in parameters on normal contact behaviors. The results indicate that the established model is able to predict the contact responses of the viscoelastic materials with complex mechanical characteristics.

Research of influencing factors on tripping speed of double plungers turbine overspeed protector

The over-speed protection mechanism is very important for the safe operation of the steam turbine, but in actual production, the tripping speed often fluctuates and deviates from the set value, resulting in a decrease in the reliability of the unit operation. In this paper, the factors that affect the tripping speed of double plungers turbine overspeed protection mechanism are analysed, the mechanism of mechanical vibration and friction that cause the tripping speed to fluctuate is explored through theoretical calculation and simulation analysis, and the change of spring dynamic stiffness by using the dynamic stiffness matrix method and finite element simulation is analysed. The change of friction force under different contact modes is calculated by using the L-N contact force model and the modified Coulomb friction model, and the change of tripping speed under non-ideal friction conditions is explored through dynamic simulation.

An Improved Contact Force Model of Polyhedral Elements for the Discrete Element Method

The discrete element method (DEM) serves as a robust tool for simulating the mechanical behavior of granular materials. The accuracy of the DEM simulation is determined by the calculation of contact forces between elements. Compared to spherical elements, the contact modes of polyhedral elements are more complex. In this work, the contact force between polyhedral elements under different contact modes was investigated by experiment. Based on the experimental results, the normal stiffness coefficient in the Cundall’s contact model was modified. The improved contact force model was then applied in the DEM simulation and validated by means of comparison with the results of packing experiments. The research results demonstrate that the improved contact force model can be effectively applied to the simulation of different contact modes between polyhedral elements. The results of the packing experiment highly coincide with the results of the DEM simulation, which confirms the accuracy and reliability of the improved contact force model.

An Enhanced Circumferential Winkler Contact Force Model for Cylindrical Clearance Joints

In deployable space structures, the clearance size of joints is small, and the contact between the journal and bearing should sometimes be treated as a conformal contact, resulting in the imprecision of the contact force models in evaluating contact forces. This study proposes an enhanced hybrid theoretical and numerical contact force model to calculate the clearance joints’ contact force. Firstly, a basic formula of a dimensionless contact force is proposed, and an optimized surrogate function of the shape correction coefficient is obtained using finite element method (FEM) and response surface method (RSM). Then, the proposed model is validated by comparing it with various contact force models. Finally, this paper discussed the applicability of the proposed model in detail. These results indicate that the dimensionless expression of the proposed model is reasonable and can reasonably describe the relationship between contact force and penetration depth. The proposed model has been proven to have an excellent correlation with FEM and a minor relative error. The application scope of the proposed model is unlimited to the clearance size and the joint size. The proposed model provides a foundation for accurate impact models and is vital for the structural dynamic problems of high-precision space structures.

Rigid flexible coupling contact mechanism for oral and maxillofacial skin and soft tissues

Background and Objectives:The existing medical clinical treatment institutions mostly use rigid structures to come into contact with flexible skin. The rigid flexible coupled contact biomechanical model for the skin is the first step that urgently needs to be considered in the process of medical clinical operations. However, there has been currently no effective biomechanical contact model available. Methods:Based on the principle of elastic interface deformation, the basic biomechanical characteristics of oral and maxillofacial skin and soft tissues were analyzed to address the unknown mechanism of rigid body and maxillofacial contact in oral imaging operations. A nonlinear characterization method for the mechanical properties of oral and maxillofacial skin soft tissues was proposed by deriving a general contact force model that takes into account energy dissipation. However, the problem of the inability to obtain analytical solutions for the parameters of the dynamic model exists. It is necessary to perform particle swarm parameter identification on different nonlinear contact models and verify the accuracy of the algorithm through numerical simulation. A maxillofacial contact experiment was conducted to verify the operation process of an oral imaging robot. Results:After experimental analysis, it was found that the comprehensive average error between the model and the actual contact force was 0.13325 N. The absolute error of the maximum deformation displacement was below 0.18 N, which verified the effectiveness and safety of the contact model in the contact process of the oral imaging robot system. Conclusions:The results indicate that the output force of the model has been in good agreement with the actual contact force.

Enhanced modelling of planar radial-loaded deep groove ball bearings with smooth-contact formulation

AbstractBearings are mechanical components designed to restrict the relative rotary motion between moving parts and transmit loads with low friction. Their performance directly impacts the durability, efficiency and reliability of various machinery. Therefore, bearing failures can lead to economic costs, repair/stoppage times, accidents and regulatory compliance issues. In the context of Industry 4.0, the development of detailed and reliable computational models for simulating bearings’ dynamics plays a crucial role in establishing digital twins and implementing advanced predictive maintenance strategies.This work focuses on modelling radial-loaded deep groove ball bearings under the multibody systems dynamics framework and the components of the bearing (inner and outer rings, rolling elements, and cage) are treated as separate bodies. A smooth contact approach is utilised to characterise the contact/impact phenomena, providing flexibility and efficiency in monitoring the whole contact event. In this sense, suitable normal and friction contact force models are used to describe those interactions between the contacting bodies. The main contribution of this work relies on the modelling strategies to represent the cage/rolling element interaction.Having that in mind, several multibody models of radial-loaded deep groove ball bearings are developed considering different modelling assumptions, resulting in dynamic analyses with various levels of complexity. The underlying simplifications are described, and their main advantages and shortcomings are discussed. The simulation results demonstrated the significant impact of accurately selecting the modelling parameters. The promising results of this study pave the way for future investigations, extending to other geometries of rolling contact bearings and working conditions.

Development of a contact force model with a fluid damping factor for immersed collision events

Impact behavior in a fluidic environment is an inevitable phenomenon in multibody systems. This investigation studies the motion of a contact body in an unbounded and incompressible Newtonian viscous fluid. In allusion to the physical impact in immersed fluid, a dissipated coefficient is introduced to describe the dissipated energy caused by the hydrodynamic forces, including the drag force, added mass force, and history force. To attain the fluid damping factor during impact, the kinetic energy corresponding to the physical impact has four discrepant destinations at the end of the compression phase. According to this principle, a new fluid damping factor is derived based on the energy conservation during impact for simultaneously depicting the coupling between liquid and solid and the coupling between solid and solid. More importantly, to determine the coefficient of restitution (CoR) corresponding to the actual physical impact, a new CoR is proposed according to the definitions of dry and wet CoRs. Subsequently, since both compression and recovery phases happen in the presence of hydrodynamic forces, fluid damping force should be imposed on the Hertz contact model. Consequently, a new contact force model with a fluid damping factor tailored for immersed collision events is proposed. Although the viscosity of the fluid is not explicitly exhibited in the hysteresis damping loop from the new contact force model, the effect of fluid on the immersed collision cannot be neglected, especially for the initial distance of contact bodies. Finally, the rationality and correctness of the proposed model are validated by the reference solution obtained from the solitary wave propagation of a horizontal one-dimension granular chain.

A continuous contact-force model for the impact analysis of viscoelastic materials with elastic aftereffect

A continuous contact-force model for the impact analysis of viscoelastic materials with elastic aftereffect

Influence of two kinds of clearance joints on the dynamics of planar mechanical system based on a modified contact force model

This study takes the slider-crank mechanism with revolute joint and translational joint as the research object and studies the contact force model of the clearance joint and the influence of the hybrid clearance joints on the nonlinear dynamic behavior of the mechanism. A modified contact force model is established based on the simplified elastic oscillator model, which can be used as a normal force in clearance joint. In the new contact force model, the component n of the indentation depth can be arbitrarily selected and it can support the calculation of contact force for both fully elastic recovery, non-elastic recovery and fully inelastic recovery. Based on the LuGre friction model, the tangential friction model of the clearance joint is given. Thus, the normal force and tangential force during the dynamic contact of the clearance joint are formed. Combining Lagrange’s equations of the first kind with the modified normal force and tangential friction force, the dynamic equations of the multi-body system with clearance joints are established. The Baumgarte stabilization method is used to improve the numerical stability. The correctness of the dynamic prediction model in the mechanism with clearance joint is verified by experiment. The dynamic analysis of the slider-crank mechanism with mixed clearance joints shows that the revolute clearance joint has a greater influence on the mechanism than the translational clearance, and the revolute clearance joint plays a leading role in the dynamic response.

Frictionless line-to-line contact: Comparison of mortar and unbiased formulation in combination with Lagrange-multiplier and penalty method

Recent developments in the beam-to-beam contact mechanics have prompted us to investigate further into the relations between different formulations and contact-force models. Specifically we address in this paper the recently developed mortar method for beams and develop its variant based on the penalty method. This allows an in-depth comparison between the two formulations. Furthermore, we design an unbiased approach and introduce a new discretisation technique developed specifically for this method. The unbiased line-to-line method is also combined both with the Lagrange-multiplier and the penalty method. All developed elements have been tested using the same examples to provide an objective comparison between formulations in terms of robustness and computational cost.

The role of physical lost circulation materials type on the evolution of strong force chains of plugging zone in deep fractured tight reservoir

The selection of physical lost circulation materials (LCMs) type plays a crucial role in formulating effective plugging slurry. The structural stability of the plugging zone, formed by LCMs, is a decisive factor in determining their effectiveness in deep fractured reservoirs. In this study, combined with the Hertz contact model and calibration of contact forces of photoelastic particles, the color gradient mean square method was employed to quantitatively characterize the strong force chains evolution of the three typical types of plugging zones. Results showed that the incorporation of flexible particles into the LCMs enhanced the average shear strength, increased the proportion, and promoted the development of circular structures within the strong force chains, thereby facilitating stronger shear stability. This research provides new insight to understand the role of physical LCMs type on the mesoscale failure mechanism of plugging zone in deep fractured tight reservoir.

Dynamic Investigations on the Wear Behavior of a 3D Revolute Joint Considering Time-Varying Contact Stiffness: Simulation and Experiment

The existence of the relative radial and axial movements of a revolute joint’s journal and bearing is widely known. The three-dimensional (3D) revolute joint model considers relative radial and axial clearances; therefore, the freedoms of motion and contact scenarios are more realistic than those of the two-dimensional model. This paper proposes a wear model that integrates the modeling of a 3D revolute clearance joint and the contact force and wear depth calculations. Time-varying contact stiffness is first considered in the contact force model. Also, a cycle-update wear depth calculation strategy is presented. A digital image correlation (DIC) non-contact measurement and a cylindricity test are conducted. The measurement results are compared with the numerical simulation, and the proposed model’s correctness and the wear depth calculation strategy are verified. The results show that the wear amount distribution on the bearing’s inner surface is uneven in the axial and radial directions due to the journal’s stochastic oscillations. The maximum wear depth locates where at the bearing’s edges the motion direction of the follower shifts. These findings help to seek the revolute joints’ wear-prone parts and enhance their durability and reliability through improved design.

Data-driven modeling for complex contacting phenomena via improved neural networks considering link switches

Recent years saw tremendous developments of data-driven modeling in various engineering fields. As for the contact modeling between complex surfaces, the utilization of neural networks successfully eliminates the limitations encountered by the traditional physics-based contact modeling strategy. However, contrary to its increasingly extensive applications, very little attention has been paid to the role of network hyper-parameters in reducing the model redundancy and improving its training efficiency. In this work, a novel neural network considering link switches has been presented for the data-driven modeling of complex contact phenomena. In order to further boost its prediction performance, genetic algorithm (GA) is employed for the optimal settings of relevant hyper-parameters. An indoor experimental setup is utilized to demonstrate the effectiveness of the presented methodology. Comprehensive comparisons with the base models indicate the superiorities of the established locally-connected-neural-network-based contact force model for complex geometries.

Dynamic modeling and analysis of vehicle scissor door mechanism with mixed clearance based on a hybrid contact force model

Dynamic modeling and analysis of vehicle scissor door mechanism with mixed clearance based on a hybrid contact force model

Numerical simulations for largely deformed beams and rings adopting a nontensile smoothed particle hydrodynamics algorithm

Three typical elastic problems, including beam bending, truss extension and compression, and two-rings collision are simulated with smoothed particle hydrodynamics (SPH) using Lagrangian and Eulerian algorithms. A contact-force model for elastic collisions and equation of state for pressure arising in colliding elastic bodies are also analytically derived. Numerical validations, on using the corresponding theoretical models, are carried out for the beam bending, truss extension and compression simulations. Numerical instabilities caused by largely deformed particle configurations in finite/large elastic deformations are analysed. The numerical experiments show that the algorithms handle small deformations well, but only the Lagrangian algorithm can handle large elastic deformations. The numerical results obtained from the Lagrangian algorithm also show a good agreement with the theoretical values. doi: 10.1017/S1446181123000160

Analysis of process parameter sensitivities of jet-based direct mixing gas phase hetero-agglomeration by DEM/CFD-modelling

A new approach to the formation of hetero-agglomerates, originating from mixtures of particles of different materials, has been proposed and analysed. The aim is to develop a process capable of producing hetero-agglomerates with a high relative number of contacts between particles of different materials. The proposed process is a jet based mixing gas phase hetero-agglomeration approach where the particle systems are dispersed into the gas phase and brought together by two particle laden jets. The process is analysed using Discrete Element Method (DEM) one-way coupled with Computational Fluid Dynamics (CFD), including models for adhesive contact forces, turbulence-induced fluctuating fluid forces and Coulomb forces for charged materials. Particle mass flow, particle surface energy, jets relative alignment, gas inflow velocity, particle size and electrical charge are varied to understand their effect on the hetero-agglomerate formation. This allows conclusions to be drawn about process intensification that can be used in subsequent experimental investigations.

Characterization of joint contact model considering friction of variable stator vane mechanism and application to principle-level mechanism

For the characterization of joint contact model of the variable stator vane (VSV) mechanism, the dry friction properties of joint materials must be taken into account. In this paper, the important parameters characterizing the joint contact model are experimentally tested, and then the characterized contact model containing the parameters is utilized for the dynamic analysis of a principle-level VSV mechanism test rig, including the dry friction rotary pair. Firstly, the friction tests and the vibration tests induced by the friction process are carried out. Then an ideal comprehensive dynamic model of the scaled system of VSV mechanism’s single kinematic chain is established through the Lagrange multiplier method. The friction coefficient values obtained from the test are embedded into the contact force model considering friction factors and compared with other macro models. The accuracy of the hybrid contact model is verified through a one-shot contact-impact simulation and the corresponding displacement is measured for evaluation with accuracy of established ideal dynamic model. Finally, the influence of different driving methods on the dynamic characteristics of the system is analyzed.

AL-ProMP: Force-relevant skills learning and generalization method for robotic polishing

Skill learning in robot polishing is gaining attention and becoming a hot issue. Current studies on skill learning in robot polishing are mainly about trajectory skills, and force-relevant skills learning models are less studied. A skill learning method with good generalization and robustness is one of the elements worth investigating. In this study, a force-relevant skills learning method called arc-length probabilistic movement primitives (AL-ProMP) is proposed to improve the efficiency of robot polishing force planning. AL-ProMP learns the mapping between the contact force and polishing trajectory, and the temporal scaling factor and force scaling factor in AL-ProMP enable better robustness of force planning in speed scaling tasks and polishing tasks in different scenarios. Speed scaling is an important property for adaptation of the polishing policy. For the generalization of polishing skills to different polishing tools in robotics disc polishing tasks of unknown geometric model workpieces, a novel force scaling factor for different polishing discs is proposed according to the contact force model. In addition, polishing contact position learning provides the basis for polishing trajectory generalization. Finally, it is experimentally verified that the proposed method is effective in learning and generalizing the demonstrated skills and improving the polishing surface quality of the workpiece with unknown geometric model.