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This work reviews the main techniques to model dynamical systems with contact-impact events. Regularized and non-smooth formulations are considered, wherein the fundamental features associated with each approach are analyzed. A brief description of contact dynamics is presented, and an overview of the state-of-the-art of the main aspects related to the contact dynamics discipline is provided. This paper ends by identifying gaps in the current techniques and prospects for future research in the field of contact mechanics in multibody dynamics., This work has been supported by The Portuguese Foundation of Science and Technology under the national support to R&D units grant, with the reference project UIDB/04436/2020 and UIDP/04436/2020. The author would like to express his sincere and deepest gratitude to Professor Jorge Ambrosio (University of Lisbon), Professor Hamid M. Lankarani (Wichita State University), Professor Parviz Nikravesh (The University of Arizona), Professor Christoph Glocker (ETH Zurich), Professor Remco Leine (University of Stuttgart), Professor Friedrich Pfeiffer (Technical University of Munich), and Professor Andres Kecskemethy (University of Duisburg-Essen) for sharing their knowledge on contact dynamics. Their incredible passion and profound enthusiasm on contact problems in dynamical systems have been a permanent source of inspiration and motivation for many and many generations of researchers.

This paper presents a geometrical modelling principle for the modelling of yarns at the fibre level. The woven and the knitted textile structures are built of yarns, which on the other side, are fibrous assemblies. In many yarn and fabric modelling works, yarns are considered as a single line element; however, most yarns are composed of a number of staple or filament fibres. It is then very important to understand the yarn at the micro level for a better understanding, production and application of the above structures. The current paper aims to present the modelling and implementation of yarn structures at the fibre level using the algorithmic geometrical modelling principle. The research work uses basic assumptions for the building of the models and various implementation issues, connected with the proper representation of the single multi-filament yarns, plied yarns and finally the staple fibre yarns. Except for visualization, the generated yarn models are prepared as a basis for mechanical, thermal, fluid flow and other simulations of textile structures using FEM, CFD and other numerical tools.

A novel approach is presented for simulating non-spherical particles in the discrete element method (DEM). A particle's shape is described through a hierarchy of representations using spherical harmonic expansions. The expansion is computed at nodes, obtained by discretising the particle's surface. A low-degree expansion, i.e., one containing few terms, is sufficient to approximate a particle's overall shape without any surface texture. Expansions are computed to high degrees only at interparticle contacts, rather than for the entire particle, which reduces the computational cost. The advantages of this approach include the ability to simulate a wide range of particle shapes and adaptive resolution depending on spatial and temporal considerations. An additional unique benefit is that changes of particle shape due to chipping can be captured in DEM for the first time. This is accomplished by progressively omitting more of the highest-degree terms from the expansion to give an increasingly smooth surface.

In the preceding Part I, a combined experimental-numerical study to characterize fine spray-dried powder used in the ceramic tile pressing process was presented. In the present Part II, the algorithm proposed by (Mazhar, 2011) to solve the numerical simulation of powder dynamics through the Discrete Element Method (DEM) was extended. In this paper, the original algorithm was adapted for efficient use on multi-core CPUs and a single GPU. In both cases, history-dependent contact models were considered. The efficiency of the algorithms was compared among them and with LIGGGHTS, a reference software package for particle simulation using DEM. The results demonstrated a higher performance of the codes developed compared to LIGGGHTS, particularly in demanding scenarios with a large number of particles (more than 1 million) of small size (median diameter in volume less than 1 mm). In particular, the CPU-based algorithm was suitable for simulating the mould filling in ceramic tiles industry.

X-ray computed tomography (XCT) is regularly employed in geomechanics to non-destructively measure the solid and pore fractions of soil and rock from reconstructed 3D images. With the increasing availability of high-resolution XCT imaging systems, researchers now seek to measure microfabric parameters such as the number and area of interparticle contacts, which can then be used to inform soil behaviour modelling techniques. However, recent research has evidenced that conventional image processing methods consistently overestimate the number and area of interparticle contacts, mainly due to acquisition-driven image artefacts. The present study seeks to address this issue by systematically assessing the role of XCT acquisition parameters in the accurate detection of interparticle contacts. To this end, synchrotron XCT has been applied to a hexagonal close-packed arrangement of glass pellets with and without a prescribed separation between lattice layers. Different values for the number of projections, exposure time, and rotation range have been evaluated. Conventional global grey value thresholding and novel U-Net segmentation methods have been assessed, followed by local refinements at the presumptive contacts, as per recently proposed contact detection routines. The effect of the different acquisition set-ups and segmentation techniques on contact detection performance is presented and discussed, and optimised workflows are proposed.

Fictional contacts occur in many mechanical systems, and often affect their dynamic response, since the collisions cause a significant change the systems’ characteristics, namely in terms of velocities. This work describes and compared different formulations to handle frictional contacts in multi-rigid-body dynamics. For that, regularized and non-smooth techniques are revisited. In a simple manner, the regularized methods describe the contact forces as a continuous function of the indentation, while the non-smooth formulations use unilateral constraints to model the contact problems, which prevent the indentation from occurring. The main motivation for the performing this study came from the permanent interest in developing computational models for the dynamic modeling of contactimpact events under the framework of multibody systems methodologies. The problem of modeling and simulating contacts with friction in multibody systems includes several steps, the definition of the contact geometry; the determination of the contact points; the resolution of the contact itself; and the evaluation of the transitions between different contact regimens. The last two aspects are investigated in this work within the context of contact dynamics. In the sequel of this process, an application example is utilized to show the effectiveness of the modelling process of contact problems in multibody systems. Finally, future developments and new perspectives for further developments related to contact-impact problems are presented and discussed in this study., This work has been supported by FCT, under the national support to R&D units grant, with the reference project UIDB/04436/2020 and UIDP/04436/2020.

International audience; Understanding and modeling contact behavior of rope-like structures imposed by pure torsion represents a very difficult topic among the non-smooth mechanical problems. Apart from the high non-linearities on the boundary conditions, the location of real contact areas between inter fibers becomes a prerequisite difficulty. In this paper, a new three-stages contact searching algorithm based on bounding volume hierarchies and orthogonal projections is developed for fiber contact problems involving large deformation. In particular, an improved axis aligned bounding boxes hierarchy based on the specific geometry component is proposed, which can directly result in vertex-element pairs. The frictional contact forces are solved in a reduced system within the bi-potential framework. The algorithms are implemented into the in-house finite element software FER/Impact and some numerical examples are carried out to illustrate the proposed methods.

Accurate and fast contact detection between a robot manipulator and objects is crucial for safe robot–object and human–robot interactions. Traditional collision detection techniques relied on force–torque sensors and Columb friction cone estimation. However, the strain gauges used in the conventional force sensors require low-noise and high-precision electronics to deliver the signal to the final user. The Signal-to-Noise Ratio (SNR) in these devices is still an issue in light contact detection. On the other hand, the Eccentric Rotating Mass (ERM) motors are very sensitive to subtle touch as their vibrating resonant state loses immediately. The vibration, in this case, plays a core role in triggering the tactile event. This project’s primary goal is to use generated and received vibrations to establish the scope of object properties that can be obtained through low-frequency generation on one end and Fourier analysis of the accelerometer data on the other end. The main idea behind the system is the phenomenon of change in vibration propagation patterns depending on the grip properties. Moreover, the project’s original aim is to gather enough information on vibration feedback on objects of various properties and compare them. These data sets are further analyzed in terms of frequency and applied grip force correlations in order to prepare the ground for pattern extraction and recognition based on the physical properties of an object.

A study to investigate contact detection and recognition of the cutting state by means of the acoustic emission (AE) technique in ultra-precision turning is presented. Detection of accurate cutting-edge position was achieved through investigation of the contact limit between the cutting edge and workpiece through use of the AE technique. Moreover, to recognize the cutting state, changes in AE signals instigated by corresponding changes in the cutting condition were monitored. In the contact-detection experiment, contact between the cutting edge and workpiece was detected with a cut depth of 10 nm. Likewise, in the cutting state recognition experiment, AE signal waveforms were observed to demonstrate changes corresponding to changes in the cutting state. These results confirm the feasibility of using the AE technique in cutting state monitoring experiments.

A novel granular discrete element method (DEM) is introduced to simulate mixtures of particles of any convex shape. To quickly identify pairs of particles in contact, the method first uses a broad-phase and a narrow-phase contact detection strategy. After this, a contact resolution phase finds the contact normal and penetration depth. A new algorithm is introduced to effectively locate the contact point in the geometric center of flat faces in partial contact. This is important for a correct evaluation of the torque on each particle, leading to a much higher stability of stacks of particles than with previous algorithms. The granular DEM is used to generate random packings in a cylindrical vessel. The simulated shapes include non-spherical particles with different aspect ratio cuboids, cylinders and ellipsoids. More complex polyhedral shapes representing sand and woodchip particles are also used. The latter particles all have a unique shape and size, resembling real granular particle packings. All packings are analyzed extensively by investigating positional and orientational ordering.

This work presents a general formulation to identify the contact points for the interaction between wheels and rails in the context of railway dynamics simulations. This formulation treats the wheel and rail as parametric surfaces and searches the contact between each wheel strip and the rail independently to avoid the numerical difficulties due to the wheel concave zone. This methodology assumes the rail as locally straight and takes advantage that its potential contacting surface is always convex. For the evaluation of contact forces, two Hertzian-based models are employed for normal and creep forces. A trailer vehicle running on a curved track is used to demonstrate the effectiveness of this methodology., The first authorissupported by the Portuguese Foundation for Science and Technology (FCT) under grant PD/BD/114154/2016.This work is also supported by FCT with the reference project UIDB/04436/2020

This article belongs to the Topic Dynamical Systems: Theory and Applications. In the present work, different algorithms for contact detection in multibody systems based on smooth contact modelling approaches are presented. Beginning with the simplest ones, some difficult interactions are subsequently introduced. In addition, a brief overview on the different kinds of contact/impact modelling is provided and an underlining of the advantages and the drawbacks of each of them is determined. Finally, some practical examples of each interaction are presented and analyzed and an outline of the issues arisen during the design process and how they have been solved in order to obtain stable and accurate results is given. The main goal of this paper is to provide a resource for the early-stage researchers in the field that serves as an introduction to the modelling of simple contact/impact events in the context of multibody system dynamics. The authors would like to acknowledge the Spanish Government through the MCYT Project "RETOS2015: sistema de monitorización integral de conjuntos mecánicos críticos para la mejora del mantenimiento en el transporte-maqstatus". The authors would also like to acknowledge the financial support received by the Community of Madrid through its multi-year agreement with University Carlos III focused on its policy "Excelencia para el Profesorado Universitario".

PURPOSE: Commercially available microtechnology devices containing accelerometers, gyroscopes, magnetometers, and global positioning technology have been widely used to quantify the demands of rugby union. This study investigated whether data derived from wearable microsensors can be used to develop an algorithm that automatically detects scrum events in rugby union training and match play. METHODS: Data were collected from 30 elite rugby players wearing a Catapult OptimEye S5 (Catapult Sports, Melbourne, Australia) microtechnology device during a series of competitive matches (n = 46) and training sessions (n = 51). A total of 97 files were required to 'train' an algorithm to automatically detect scrum events using random forest machine learning. A further 310 files from training (n = 167) and match-play (n = 143) sessions were used to validate the algorithm's performance. RESULTS: Across all positions (front row, second row, and back row), the algorithm demonstrated good sensitivity (91%) and specificity (91%) for training and match-play events when the confidence level of the random forest was set to 50%. Generally, the algorithm had better accuracy for match-play events (93.6%) than for training events (87.6%). CONCLUSIONS: The scrum algorithm was able to accurately detect scrum events for front-row, second-row, and back-row positions. However, for optimal results, practitioners are advised to use the recommended confidence level for each position to limit false positives. Scrum algorithm detection was better with scrums involving >/=5 players and is therefore unlikely to be suitable for scrums involving 3 players (eg, rugby sevens). Additional contact- and collision-detection algorithms are required to fully quantify rugby union demands.

Internal clearance is a functional key characteristic of bearings. The bearing clearance can be evaluated using rigid body movements of the inner ring. Due to the deviations of dimension and roundness the contact areas between the bearing components cannot be predicted. Hence contact detection is necessary. For this purpose the herein presented concept is based on a raytrace algorithm. The concept can be used for the simulation of the bearing clearance for deviated bearing components. This enables the evaluation of the influence of dimensional and form deviations on the bearing clearance.

© 2017 Elsevier Ltd A fast direct search (FDS) algorithm is presented to increase the efficiency of contact detection for convex polygonal and polyhedral particles. All contact types are detected using only a small subset of these contact types: vertex-to-edge for polygons while vertex-to-face and edge-to-edge for polyhedra. First, an initial contact list is generated. Then in subsequent steps the contact list is updated by checking only local boundaries of the blocks and their separation. An exclusion algorithm is applied to avoid unnecessary examination for particles that are near but not-in-contact. The benchmark tests show that the FDS produces significant speed-up in various cases.

In this paper, classified theoretical models, consisting of contact with and placement of microsphere and picking operations, are simplified and established to depict the interactive behaviors of external and internal forces in pushing manipulations, respectively. Sliding and/or rolling cases, resulting in the acceleration of micromanipulations, are discussed in detail. Effective contact detection is achieved by combining alterations of light-shadow and relative movement displacement between the tip-sphere. Picking operations are investigated by typical interactive positions and different end tilt angles. Placements are realized by adjusting the proper end tilt angles. These were separately conducted to explore the interactive operations of nonconductive glass microspheres in a scanning electron microscope. The experimental results demonstrate that the proposed contact detection method can efficiently protect the end-tip from damage, regardless of operator skills in initial positioning operations. E-beam irradiation onto different interactive positions with end tilt angles can be utilized to pick up microspheres without bending the end-tip. In addition, the results of releasing deviations away from the pre-setting point were utilized to verify the effectiveness of the placement tilt angles.

The present paper sheds new light on ongoing drawbacks of three classical algorithms dedicated to initial contact detection between overlapping convex polyhedra, (i) Cundall’s common plane, (ii) Nezami’s fast common plane and (iii) Gilbert-Johnson-Keerthi’s algorithm (GJK). Solutions to these drawbacks are suggested and implemented into revised versions of those three algorithms, which are further benchmarked for accuracy and speed using nine overlapping contact situations. The benchmarking results show that the revised version of GJK, called GJK - TD , and Nezami (revised) return values of the contact normal components and overlap depth which are identical to machine precision, whereas Cundall (revised) results differ beyond the ninth decimal place. Furthermore, for a given contact situation, GJK-TD returns those values within a few tens of microseconds on average, whereas Nezami (revised) and Cundall (revised) are respectively 6 and 65 times more computationally intense. It is believed that the robustness and efficiency of GJK-TD will boost its use into DEM simulations, all the more that this versatile algorithm may easily be customized to detect contact between convex polyhedra and spheroid particles.

A tactile image sensor employing a camera is capable of obtaining rich tactile information through image sequences with high spatial resolution. There have been many studies on the tactile image sensors from more than 30 years ago, and, recently, they have been applied in the field of robotics. Tactile image sensors can be classified into three typical categories according to the method of conversion from physical contact to light signals: Light conductive plate-based, marker displacement- based, and reflective membrane-based sensors. Other important elements of the sensor, such as the optical system, image sensor, and post-image analysis algorithm, have been developed. In this work, the literature is surveyed, and an overview of tactile image sensors employing a camera is provided with a focus on the sensing principle, typical design, and variation in the sensor configuration.

This article presents a novel approach to collision detection based on distance fields. A novel interpolation ensures stability of the distances in the vicinity of complex geometries. An assumed gradient formulation is introduced leading to a C1-continuous distance function. The gap function is re-expressed allowing penalty and Lagrange multiplier formulations. The article introduces a node-to-element integration for first order elements, but also discusses signed distances, partial updates, intermediate surfaces, mortar methods and higher order elements. The algorithm is fast, simple and robust for complex geometries and self contact. The computed tractions conserve linear and angular momentum even in infeasible contact. Numerical examples illustrate the new algorithm in three dimensions.

In this paper, a fast automatic precision approaching system is developed for electrochemical nanofabrication using visual and force-displacement sensing. Before the substrate is fabricated, the template should approach the substrate accurately to establish the initial gap between the template and substrate. During the approaching process, the template is first quickly moved towards the substrate by the stepping motor until a specified gap is detected by the visual feedback. Then, the successive approach using the switch of macro-micro motion with a force-displacement sensing module is triggered to make the template contact with the substrate to nanometre accuracy. The contact force is measured by the force-displacement sensing module which employs the high-resolution capacitive displacement sensor and flexure compliant mechanism. The high sensitivity of this capacitive displacement sensor ensures high accuracy of the template-substrate contact. The experimental results show that the template can reach the substrate accurately and smoothly, which verifies the effectiveness of the proposed approaching system with the visual and the force-displacement sensing modules.

Highlights • Presents asynchronous variational integrators in the context of finite elements with continuous strain fields. • Illustrates an enhanced interpretation of the current space–time front. • Provides a strategy for estimating the critical time step size using CAG elements, nodal integration or SFEM., This article presents a novel approach to collision detection based on distance fields. A novel interpolation ensures stability of the distances in the vicinity of complex geometries. An assumed gradient formulation is introduced leading to a C1-continuous distance function. The gap function is re-expressed allowing penalty and Lagrange multiplier formulations. The article introduces a node-to-element integration for first order elements, but also discusses signed distances, partial updates, intermediate surfaces, mortar methods and higher order elements. The algorithm is fast, simple and robust for complex geometries and self contact. The computed tractions conserve linear and angular momentum even in infeasible contact. Numerical examples illustrate the new algorithm in three dimensions.

The Discrete Element Method (DEM) recently presents numerical tool widely used in simulation of heterogeneous solids. The method captures dynamic behaviour of solid by considering motion and interaction of material particles. The most computationally expensive procedure of the DEM is search of contacts for particles, therewith each pair of colliding particles has to be identified. To investigate and accelerate computational performance of the DEM, computational performance study of two popular cell and sorting contact search algorithms was done in the present work. Both algorithms are implemented into DEMMAT code. Series of numerical tests was conducted for the above purposes by considering distributed filling of hopper. Mono-sized and poly-dispersed assemblies of elastic spherical particles were examined and computational performance during particle flow is illustrated.

Wire bonder is important equipment in semiconductor end-package. The benefits of using force sensor are precisely force control and earlier contact detection. In this paper, we introduced an application of a force sensor in the wire bonding process. We proposed the control strategy of the whole bonding process with the force sensor. In the bonding process, it's very important to make sure the safety before switching between the force control and position control. A contact detection method in force mode was introduced to get a smooth switch from position control to force control. Before switching from the force control to position control, a two-steps method was proposed to prevent vibrations. The experiments results show that a good bonding performance was achieved by applying with the force sensor.

A novel methodology consisting of three hierarchical levels is proposed for the detection phase of contact mechanics simulations. The top level of the hierarchy uses kinematic information from the objects involved in the simulation to determine approximate collision times. These instants then determine when the engine resumes operation for further detection. By using bounding volume hierarchies, the second level of detection precludes contact by computing simple exclusion tests on bounding volumes of increasing tightness. When contact cannot be ruled out by using simple tests, the final level of detection comes into effect by using thorough checks on finite element primitives. To that purpose, a robust optimization-based formulation that does not rely on orthogonal projections is outlined. The detection framework can be used to predict the exact collision time among finite element discretizations. The performance of the proposed methodology is investigated with a set of examples.