Frictional Collision Research Articles

On the discontinuous dynamics of a class of 2-DOF frictional vibration systems with asymmetric elastic constraints

<abstract><p>In this paper, the discontinuous dynamic behavior of a two-degree-of-freedom frictional collision system including intermediate elastic collision and unilateral elastic constraints subjected to periodic excitation is studied by using flow switching theory. In this system, given that the motion of each object might have a velocity that is either greater than or less than zero and each object experiences a periodic excitation force that has negative feedback, because the kinetic and static friction coefficients differ, the flow barrier manifests when the object's speed is zero. Based on the discontinuity or nonsmoothness of the oscillator's motion generated by elastic collision and friction, the motion states of the oscillator in the system are divided into 16 cases and the absolute and relative coordinates are used to define various boundaries and domains in the oscillator motion's phase space. On the basis of this, the G-function and system vector fields are used to propose the oscillator motion's switching rules at the displacement and velocity boundaries. Finally, some dynamic behaviors for the 2-DOF oscillator are demonstrated via numerical simulation of the oscillator's stick, grazing, sliding and periodic motions and the scene of sliding bifurcation. The mechanical system's optimization designs with friction and elastic collision will benefit from this investigation's findings.</p></abstract>

Elastoplastic frictional collisions with Collisional-SPH

Elastoplastic frictional collisions are encountered in a wide range of applications. For modelling these, inclusion of both the elastoplastic material response and history-dependent collisional forces is essential. The Collisional-SPH method, originally developed for elastic collisions, incorporates frictional collision forces into SPH and accounts for their history-dependence. In this paper, CSPH is extended to model elastoplastic collisions by incorporating an elastoplastic material model. A thorough validation of this elastoplastic CSPH method is presented. CSPH is then used to analyse the influence of deformation on history-dependent collision forces. It is found that the elastoplastic deformation and the resulting shape change of the substrate alter the contact-zone mechanics by influencing the local tangential force distribution. These effects become more pronounced with increasing deformation.

Design and experimental research on buffer protection of high-g penetrator for deep space exploration

Deep space exploration technology is an important development direction for scientific exploration. The penetrator method has been proposed as an inexpensive method of studying planetary bodies. The basic principle of this method is that the detection equipment carried by the high-speed penetrator hits a planetary body at a high speed and is buried up to several meters below the surface to carry out detection work. During the frictional collision process with the planets crust, the instantaneous acceleration peaks of the scientific payload (electronic instrumentation) are large. Shock protection of these payloads is necessary to improve their survival and mission success. In this paper, with the goal of improving the survival rate of scientific loads inside a penetrator, a penetrator with a multilayer energy-absorbing structure is developed, in which cushioning protection measures, such as an aluminum foam-filled corrugated tube(AFFT) structure, polyurethane rubber, and epoxy resin potting, are applied to the penetrator. Since the analysis of this process is a highly nonlinear problem, a numerical modeling method is the main approach in this paper. The LS-DYNA software platform was used to simulate the penetrators penetration process on a moon soil medium. The results obtained using empirical formulas and theoretical derivations were compared with the results of numerical analysis to ensure the accuracy of the penetration simulation model. The finite element model of the penetrator was then verified and modified by conducting shock response spectral experiments and shock simulations. The results showed that the spacer scheme had a positive effect on the impact isolation and energy absorption. In addition, this scheme provides an important reference for the design of the penetrator prototype to guarantee the success of subsequent ground rocket sled experiments.

Frictional collision acceleration and damage of potato peel: an experimental study

ABSTRACT To obtain the acceleration characteristics of frictional collision between potato and rod, and reveal the mechanism of potato peel damage, a frictional collision test rig was designed to conduct single factor test and peel damage threshold test. Results showed that the maximum frictional collision acceleration (MFCA) decreased linearly with the increase of potato mass and increased linearly with the increase of initial height. The MFCA of potato colliding with the horizontal rod was smaller than that with the vertical rod, and the MFCA with the rolling rod was smaller than that with the fixed rod. The MFCA decreased in turn when potato was collided with 65Mn-rubber, 65Mn-plastic and 65Mn. The acceleration threshold of peel damage for 250 g potato was the smallest when it collided with 65Mn rod fixed in the horizontal direction from 50 mm height, which was 15.56 m/s2. The acceleration threshold was the largest for the collision with 65Mn-rubber rod fixed in the vertical direction, which was 113.6 m/s2. The research methods and conclusions of this article provided a basis for the analysis of potato peel damage mechanism, and also provided a reference method for researches on the peel damage of solid–like agricultural materials and food.

Optimization of a dust concentration measuring device based on the Coanda effect

The accuracy of the existing dust measurement device comprising a straight pipe is not sufficiently high for low particle speeds. In this paper, a measuring pipe based on the Coanda effect is designed, an experimental model is established using Gambit 2.4, and a numerical simulation is performed using Fluent 6.3. In this way, speed nephograms at the middle section of the device pipe were obtained for different dust particle sizes. By comparing the velocity data of a devices comprising a straight tube, a venturi tube, or a Coanda tube, it was found that the velocity of the particles passing through the Coanda tube was higher than that for the other tubes. Therefore, the probability of frictional collision within the Coanda tube increases, thereby increasing the inductive charge of the particles. By calculating the electrostatic induction of the particles using MATLAB, it was found that the charge carried by the particles in the improved device significantly increased (25% on average). It is concluded that these findings are of significance for designing the structure of novel dust concentration measurement devices.

A regularized approach for frictional impact dynamics of flexible multi-link manipulator arms considering the dynamic stiffening effect

The present study offers a regularized approach for multi-link flexible manipulator arms with frictional impacts. The complex risks of global dynamics simulation, which involve nonlinear frictional impact, stick–slip, and foreshortening deformation, as well as multi-scale numerical problems, were implemented. The system is described as an assembly of $n$ flexible links connected by $n$ rotary joints. The stretching, bending, and the torsional deformations of the flexible links were considered in addition to the flexibility and mass of the joint. The introduction of a contact force potential energy approach transformed the non-differentiable functions of the normal and tangential frictions into differentiable ones, thereby generating Lagrange equations for the general recursive formulation of the systems. A numerical simulation for the double pendulum and spatial manipulator arms collision with targets was generated, thereby allowing the calculation of the frequent switching between the stick/sliding and forward/backward sliding. Several normal contact and friction models were adopted, and their corresponding results were analyzed. The generated ordinary differential equations of the proposed smoothed algorithm were solved using explicit solvers to verify any improvements in the global computational efficiency of the frictional collision dynamics for the flexible manipulator arms.

Disentangling the multiple effects of a novel high pressure jet device upon bacterial cell disruption

High-pressure jet devices (HPJDs) support high throughput and are cost-effective in reducing excess activated sludge. We aimed to identify the dominant mechanism among frictional shear, collision, and cavitation on bacterial cell disruption and intercellular substances eluted by an HPJD. An HPJD was modified to disassociate these three mechanisms so that they could be analyzed separately. Gram-negative and Gram-positive bacteria (Escherichia coli and Bacillus subtilis, respectively) were subjected to treatment by the modified HPJD device. Frictional shear, collision, and cavitation were found to damage 11.12±1.12%, 11.97±1.12%, and 23.70±2.35% of E. coli cell and 5.2±1.57%, 7.81±1.09%, and 28.54±3.45% of B. subtilis cell, respectively. The application of atomic force microscopy (AFM) displayed different morphological changes of E. coli and B. subtilis cells induced by frictional shear, collision, and cavitation. Frictional shear and collision deformed E. coli cells but not severely B. subtilis cells, merely increasing the cell surface roughness. In contrast, cavitation directly contributed to implosion of B. subtilis cells, resulting in higher concentrations of released intracellular DNA, polysaccharide and protein than those by frictional shear and collision. Despite the distinct cell disruption mechanisms, cavitation commonly provided the most intense effect on cell disintegration and the release of intracellular components for both E. coli and B. subtilis.

Numerical simulations of the frictional collisions of solid balls on a rough surface

Three-dimensional simulations of the frictional collision between solid balls moving on a rough surface are analyzed in this paper. The analysis is performed in the context of pool and snooker, two popular games in the pocket billiards family. Accurate simulations of ball motion in billiard games are useful for television broadcasts, training systems and any robotic game playing systems. Studying solid ball collisions in a three-dimensional space requires careful consideration of the different phenomena involved in ball motion such as rolling, sliding and ball spin about a general axis. A set of differential equations are derived describing ball dynamics during collisions. In the absence of explicit analytical solutions to the differential equations, a numerical procedure is performed to determine post-collision ball velocities and spins after collision. In addition, the paper also presents a methodology to analyze the curved, slip trajectories of balls immediately after impact. The results presented here, when compared with some experimental shots, show that the percentile errors in post-collision velocities are reduced by the proposed method. The prediction accuracies for ball travel direction are increased twofold by the proposed impact simulation algorithm.

Soft hollow particle damping identification in honeycomb structures

The aim of this study is to provide a structural damping solution for space applications to enhance mission performance of honeycomb structures. Classical particle dampers are enclosures partially filled with small metallic or glass spheres, attached to a vibrating structure. The induced damping mechanism is mainly due to frictional losses and collision effects. This paper deals with replacing classical hard particles with soft hollow ones. This study is oriented toward experimental investigations and theoretical validation in order to distinguish dissipation phenomena. The experimental approach first relies on identifying the damping in small honeycomb samples filled with particles. Instead of dissipation by friction and impact, the elliptical shape of the measured hysteresis loops highlights that visco-elastic behavior is dominant with these specific soft particle dampers. Then, experimental and numerical validations are performed on aluminum honeycomb cantilever beams filled with particles. To take into account the effect of the particles, equivalent oscillators, based on the previous experimental damping identification, are added to a finite element model. These kinds of particle dampers are highly nonlinear as a function of excitation frequency and amplitude. It is shown that good damping efficiency is achieved across a large frequency range with low impact on structure stiffness. This paper suggests a convenient method to model the structural damping induced by soft hollow particles.

Kinetic solutions for electrons in multi-cusp ion source

Some analytical kinetic solutions are obtained for the primary and plasma electrons in multi-cusp ion source. The characteristics based on these solutions are discussed, such as frictional coefficient, collision frequency, electron current, electron diffusion, electron density, and electrical conductivity. A code based on one of these solutions is developed to discuss the plasma electrons diffusion; the simulation results are qualitatively consistent with our current experiences.

Molecular dynamics of atomic rearrangements at perturbed surfaces

This work describes the results of numerical simulations regarding the formation and evolution of local excitations at the surface of Ni crystals. Excitations were induced by carrying out a fracture process or a frictional collision between two rough surfaces. In the former case, excited atoms appear at the surfaces formed by fracture as a consequence of the sudden change in their coordination number. In the latter case, local excitations are instead connected with the stress fields originated from the contact between surface asperities. Surfaces are in both cases characterized by an inhomogeneous distribution of energy and temperature, which gives rise to a certain number of excited regions of different size. The properties of the different groups of excited atoms were monitored as a function of time to estimate their lifetime and excitation degree. The possible effect of local excitations on the kinetics of solid-gas reactions is also qualitatively inferred.

Insight into the role of hydration on protein dynamics

The potential energy surface of a protein is rough. This intrinsic energetic roughness affects diffusion, and hence the kinetics. The dynamics of a system undergoing Brownian motion on this surface in an implicit continuum solvent simulation can be tuned via the frictional drag or collision frequency to be comparable to that of experiments or explicit solvent simulations. We show that the kinetic rate constant for a local rotational isomerization in stochastic simulations with continuum solvent and a collision frequency of 2 ps(-1) is about 10(4) times faster than that in explicit water and experiments. A further increase in the collision frequency to 60 ps(-1) slows down the dynamics, but does not fully compensate for the lack of explicit water. We also show that the addition of explicit water does not only slow down the dynamics by increasing the frictional drag, but also increases the local energetic roughness of the energy landscape by as much as 1.0 kcal/mol.

Computer Simulation of Rapid Granular Flow Through an Orifice

Rapid granular flow through an orifice (nozzle-shaped flow restrictor) located at the bottom of a vertical tube has been studied using three-dimensional direct computer simulation with the purpose of investigating (1) characteristics of rapid granular flows through the flow restrictor, (2) the choking condition of rapid flow at the orifice and thus conditions at which the maximum discharge rate takes place for the given orifice, and (3) a functional relationship between the discharge rate and flow quantities such as granular temperature and solid fraction. In the present simulation, where the frictional hard-sphere collision operator was employed, it was possible to obtain both rapid and slow (choked) flows through the orifice by controlling the number of particles in the system. The results show that the profile of granular temperature in the vicinity of the orifice plays an important role in determining the choking condition at the orifice. Flow appears to be choked when an adverse granular conduction occurs locally at the orifice in the direction opposite to the mean flow. On the other hand, flow is not choked when the fluctuation energy is conducted in the mean flow direction near the orifice. When flow is not choked, the discharge rate through the orifice increases with increasing solid fraction or normal stress. Once the flow becomes choked, however, the discharge rate decreases as the solid fraction or normal stress increases. Also for inelastic, rough particles, the discharge rate is found to be proportional to the granular temperature to the power of 1.5 and inversely proportional to the gravitational acceleration and the tube length.

Long dynamics simulations of proteins using atomistic force fields and a continuum representation of solvent effects: calculation of structural and dynamic properties.

Long dynamics simulations were carried out on the B1 immunoglobulin-binding domain of streptococcal protein G (ProtG) and bovine pancreatic trypsin inhibitor (BPTI) using atomistic descriptions of the proteins and a continuum representation of solvent effects. To mimic frictional and random collision effects, Langevin dynamics (LD) were used. The main goal of the calculations was to explore the stability of tens-of-nanosecond trajectories as generated by this molecular mechanics approximation and to analyze in detail structural and dynamical properties. Conformational fluctuations, order parameters, cross correlation matrices, residue solvent accessibilities, pKa values of titratable groups, and hydrogen-bonding (HB) patterns were calculated from all of the trajectories and compared with available experimental data. The simulations comprised over 40 ns per trajectory for ProtG and over 30 ns per trajectory for BPTI. For comparison, explicit water molecular dynamics simulations (EW/MD) of 3 ns and 4 ns, respectively, were also carried out. Two continuum simulations were performed on each protein using the CHARMM program, one with the all-atom PAR22 representation of the protein force field (here referred to as PAR22/LD simulations) and the other with the modifications introduced by the recently developed CMAP potential (CMAP/LD simulations). The explicit solvent simulations were performed with PAR22 only. Solvent effects are described by a continuum model based on screened Coulomb potentials (SCP) reported earlier, i.e., the SCP-based implicit solvent model (SCP-ISM). For ProtG, both the PAR22/LD and the CMAP/LD 40-ns trajectories were stable, yielding C(alpha) root mean square deviations (RMSD) of about 1.0 and 0.8 A respectively along the entire simulation time, compared to 0.8 A for the EW/MD simulation. For BPTI, only the CMAP/LD trajectory was stable for the entire 30-ns simulation, with a C(alpha) RMSD of approximately 1.4 A, while the PAR22/LD trajectory became unstable early in the simulation, reaching a C(alpha) RMSD of about 2.7 A and remaining at this value until the end of the simulation; the C(alpha) RMSD of the EW/MD simulation was about 1.5 A. The source of the instabilities of the BPTI trajectories in the PAR22/LD simulations was explored by an analysis of the backbone torsion angles. To further validate the findings from this analysis of BPTI, a 35-ns SCP-ISM simulation of Ubiquitin (Ubq) was carried out. For this protein, the CMAP/LD simulation was stable for the entire simulation time (C(alpha) RMSD of approximately 1.0 A), while the PAR22/LD trajectory showed a trend similar to that in BPTI, reaching a C(alpha) RMSD of approximately 1.5 A at 7 ns. All the calculated properties were found to be in agreement with the corresponding experimental values, although local deviations were also observed. HB patterns were also well reproduced by all the continuum solvent simulations with the exception of solvent-exposed side chain-side chain (sc-sc) HB in ProtG, where several of the HB interactions observed in the crystal structure and in the EW/MD simulation were lost. The overall analysis reported in this work suggests that the combination of an atomistic representation of a protein with a CMAP/CHARMM force field and a continuum representation of solvent effects such as the SCP-ISM provides a good description of structural and dynamic properties obtained from long computer simulations. Although the SCP-ISM simulations (CMAP/LD) reported here were shown to be stable and the properties well reproduced, further refinement is needed to attain a level of accuracy suitable for more challenging biological applications, particularly the study of protein-protein interactions.

On a proper electron collision frequency for a Fokker–Planck collision model with Jicamarca applications

Recently, Sulzer and Gonzalez (J. Geophys. Res. 104 (22) (1999) 22, 535) showed that the previously neglected effect of electron–electron and electron–ion Coulomb collisions has a significant impact on determining the incoherent scatter autocorrelation functions (IS-ACFs) observed at Jicamarca. Considering the physically and mathematically complicated nature of Coulomb collisions, they evaluated these effects with lengthy numerical computations which actually simulated the random electron trajectories for different possible electron velocities and for different state parameters of the medium, in a Monte Carlo-like simulation. Their conclusions have been readily accepted by the IS community for Jicamarca pointing angles very close to perpendicular to the magnetic field, but a controversy arose when the application of their results to angles around 3 ∘ off perpendicular to the magnetic field implied electron effective collision frequencies larger than the accepted values published in existing literature. Here we have taken a more analytical approach by using a simplified Fokker–Planck collision model with a velocity-independent collision frequency. We can reproduce the results of Sulzer and Gonzalez with this simplified analytical model, provided that an effective, velocity-independent collision frequency is used whose value depends upon the angle between the radar beam direction and the magnetic field. The physical reason for this seemingly strange result is that, for incoherent scatter, the relative importance of the Fokker–Planck friction and velocity diffusion terms changes with this angle. Furthermore, we estimated values for the electron frictional collision coefficient based on the more precise velocity-dependent one and found that, indeed, the large values are justified, supporting the previously controversial results of Sulzer and Gonzalez (1999).

Kinetic theory for identical, frictional, nearly elastic spheres

We derive a simple kinetic theory for collisional flows of identical, slightly frictional, nearly elastic spheres that is based on a physically realistic model for a frictional collision between two spheres. When the coefficient of friction is small, the equations of balance for rotational momentum and energy can be solved in approximation. This permits the rotational temperature to be related to the translation temperature and the introduction of an effective coefficient of restitution in the rate of dissipation of translation fluctuation energy. With this incorporation of the additional loss of translational energy to friction and the rotational degrees of freedom, the structure of the resulting theory is the same as for frictionless spheres.

Fluidization in dry landslides

This paper aims at determining the physical properties affecting the distance travelled by landslides with dry particles, and elucidating the mechanism of the properties affecting landslide fluidization. The procedure is as follows: laboratory landslide experiments were conducted to verify the simulation model which was proposed to represent the movement of landslides. Further, sensitivity analysis for some physical properties affecting the travel distance were conducted using this model. The simulation model could identify the coordinates, velocity and angular velocity for every particle in three-dimensional space, and the kinetic energy of particles consumed by inelastic and frictional collision with each other in the model. The travel distances of landslides simulated by the model were verified by laboratory experiments statistically where the physical properties for the particles and slope angle were changed. Then, sensitivity analysis for the physical properties were conducted using the model to clarify the effect of the properties on the travel distance. It was proven that there were no significant differences between the travel distances represented by the simulation model and those found experimentally using statistical analysis (i.e. the simulation model could represent virtual real landslides). From the sensitivity analysis using the simulation model, the travel distances were positively correlated to volume, or number of particles, and negative correlated to the slope angle, kinetic friction and rolling friction of particles when the initial potential energies were the same. The mass of particles of equal size did not affect the distance travelled. As the number of particles increased, the simulated travel distances tended to be longer compared with theoretical travel distances calculated using the friction between particles and the slope. Consequently, we could determine the distance of the lumped mass model as being critical between fluidized and non-fluidized landslides.

An exact solution for the first stage of frictional collision of a die and an elastic half-space

The first stage of frictional collision of a die and an isotropic linear elastic half-space is studied. The die is a blunt convex rigid body having an arbitrary shape with two orthogonal planes of symmetry, which are both orthogonal to the boundary of the half-space. The problem is investigated using the technique of integral characteristics of solutions to boundary-initial value problems introduced by Borodich. We consider non-frictionless boundary-initial contact problems, for example, adhesive or frictional. Expressions are obtained for the relations between time, depth of indentation, and velocity of the body. In particular cases, when the body is an elliptic paraboloid, a blunt four-sided pyramid or an elliptic cone, some expressions have simple algebraic forms. A proof is given that the expressions are independent of the boundary conditions in the contact region.

Effects of frictional and anisotropic collision on the constitutive relations for a simple shear flow of spheres

An extension of a previous analysis for shearing flow of disks is presented. Constitutive relations are derived for a simple shear flow of spheres. Binary collision is assumed to be the dominant stress generating mechanism. The frictional forces between colliding spheres are modeled in detail. The anisotropy of collision on the surface of a sphere is quantified. This anisotropy is caused by the mean shearing motion, which favors collision on the upstream face of the flowing spheres. The singularity which existed in previous calculations of the stress state is removed. The singularity is removed as a result of the correct modeling of frictional collision. The magnitude of stresses is also increased due to the consideration of anisotropy.

Frictional forces and collision frequencies between moving ion and neutral gases

Two different terms are used in literature for the frictional force between moving ion and neutral gases. It is shown how the corresponding collision frequencies have to be defined in order to keep both terms valid. An expression is derived for the momentum transfer collision frequency ν in between ions and neutral particles as a function of temperature and the relative flow velocity ¦ν i − ν n¦ . The result indicates that for most practical applications v in may be considered as independent of ¦ν i − ν n¦ . However, for very high velocities, e.g. a convection flow from the magnetosphere into the ionosphere, this dependence may be significant. Numerical values for ν in are presented. In the case of collisions between ions and their parent neutral gases, laboratory values are used for the resonant charge exchange cross section obtained for high energies, but a correction is made for the much smaller thermal energies in the temperature range typical for ionospheric conditions in order to take into account the effect of curved particle trajectories due to attractive electrostatic forces.