Contact Detection Research Articles

On Minkowski difference-based contact detection in discrete/discontinuous modelling of convex polygons/polyhedra

PurposeContact detection for convex polygons/polyhedra has been a critical issue in discrete/discontinuous modelling, such as the discrete element method (DEM) and the discontinuous deformation analysis (DDA). The recently developed 3D contact theory for polyhedra in DDA depends on the so-called entrance block of two polyhedra and reduces the contact to evaluate the distance between the reference point to the corresponding entrance block, but effective implementation is still lacking.Design/methodology/approachIn this paper, the equivalence of the entrance block and the Minkowski difference of two polyhedra is emphasised and two well-known Minkowski difference-based contact detection and overlap computation algorithms, GJK and expanding polytope algorithm (EPA), are chosen as the possible numerical approaches to the 3D contact theory for DDA, and also as alternatives for computing polyhedral contact features in DEM. The key algorithmic issues are outlined and their important features are highlighted.FindingsNumerical examples indicate that the average number of updates required in GJK for polyhedral contact is around 6, and only 1 or 2 iterations are needed in EPA to find the overlap and all the relevant contact features when the overlap between polyhedra is small.Originality/valueThe equivalence of the entrance block in DDA and the Minkowski difference of two polyhedra is emphasised; GJK- and EPA-based contact algorithms are applied to convex polyhedra in DEM; energy conservation is guaranteed for the contact theory used; and numerical results demonstrate the effectiveness of the proposed methodologies.

Assembly dynamics of a large space modular satellite antenna

The autonomous assembly technology can be used to construct large space structures such as space telescopes, satellite antennas and space stations. A novel computation methodology to study the assembly dynamics of a large space modular satellite antenna is proposed. The system rigid body and flexible body are respectively described by the natural coordinate formulation (NCF) and the absolute nodal coordinate formulation (ANCF). A parameterized inverse kinematics resolution method is used to evaluate the arm joint rotation angles of a rigid assembly manipulator with 7 degree-of-freedom (DOF). To minimize the disturbance of the floating satellite base attitude, an efficient particle swarm optimization (PSO) algorithm with Latin hypercube sampling skill (LHS-PSO) is used to find the optimized arm joint trajectories of the assembly manipulator arms. In the optimization process the oriented bounding box (OBB) contact detection method is also embedded to eliminate the trajectories which may lead to the arm-satellite or arm-arm impact problems. Finally, two numerical examples are provided to validate the proposed computation methodology. The results show that the satellite base attitude almost return back to its initial state after completing the assembly process by using the optimized joint trajectories.

High‐Order Shift Current Induced Terahertz Emission from Inorganic Cesium Bromine Lead Perovskite Engendered by Two‐Photon Absorption

AbstractHigh‐order nonlinear optical phenomena are interesting from a fundamental point of view as they reveal intrinsic symmetries of the materials. Potentially they can also be used for practical optoelectronic applications. High‐order shift current is one of these phenomena, and yet it has never been detected in experiments, primarily due to the difficulty in conventional contact detection. In this work, the shift current due to the two‐photon absorption (TPA) from all‐inorganic perovskite CsPbBr3 is first observed by a contactless and nondestructive terahertz (THz) emission method. The results reveal that the THz emission is dominated by a high‐order shift current (fourth‐order nonlinear optical effect) with the below‐bandgap photon energy of femtosecond laser excitation. The high‐order shift current origins from the broken inversion symmetry induced by the dynamic stereochemical activity of the Pb2+ lone pair. A microscopic TPA‐assisted nonlinear optical model is presented to describe the photophysical process of the THz emission. The model matches well with the quadratic pump fluence and angular dependence of the THz emission. This work can not only open a new venue for the all‐inorganic perovskite‐based nonlinear optoelectronics and THz devices, but also afford a THz technology for the high‐order nonlinear effect analysis.

Elastomer Encapsulated Pressure Sensor With Engineered Air Cavity for Force Sensing

Ground contact and force detection sensors are of critical technical importance in the realization of articulated robots capable of navigating unknown or challenging terrains. Current force sensors for robotic ground contact have limitations, including being too heavy, vulnerability to inertial noise, and lacking robustness and redundancy against failure. In this paper, we present the design, laboratory testing, and flight testing of a novel force sensor which addresses the aforementioned difficulties. The force sensor presented here is based on a custom elastomer dome with an engineered air cavity adhered to a barometric pressure sensor. Uniquely, we may tailor the sensitivity and range of the sensor by engineering the elastomer shape and the air cavity within it. Further, the large deformations incurred by the sensor are exploited to design a sensor enclosure which transfers large loads to structural members rather than onto the force sensor itself. An experimentally validated finite element model is developed to numerically predict the response of the sensor under an applied load. The model is used to perform trade studies on the geometry and material properties of the elastomer dome with a focus on developing design rules for this new type of sensor. With these simple design rules and finite element model, we design, manufacture, and test these new sensors as individuals and within arrays specifically for use on a rotorcraft robotic landing gear.

A collision model for DNS with ellipsoidal particles in viscous fluid

The article proposes an algorithm to model the collision between arbitrary ellipsoids in viscous fluid. It is composed of several steps, each improving upon the standard procedure employed in the current literature. First, an efficient contact detection algorithm is presented. Then, the semi-implicit Immersed Boundary Method of Tschisgale et al. (2018) is enhanced by the collision forces using the hard-sphere approach, so that the resulting model accounts for fluid forces throughout the entire collision process. Additionally, a new lubrication model is proposed that applies a constant lubrication force in the region where hydrodynamic forces are not resolved by the spatial grid. The new collision model is validated against benchmark test cases of particle wall collisions with excellent agreement. Furthermore, the collision of an ellipsoidal particle with a wall is investigated. The normal restitution coefficient in the case of ellipsoidal particles does not solely depend upon the Stokes number as in the case of spherical particles but is also a function of its shape, and the orientation before the collision. Using the new model, the effect of these parameters on the rebound trajectory is studied. It is found that the maximum normal restitution coefficient decreases significantly as the flatness of the particle increases. Also, the coefficient of restitution depends on the particle orientation, a tendency increasing with particle flatness.

Triboelectric proximity and contact detection using soft planar spiral electrodes

In this study, planar spiral electrodes for triboelectric contact and proximity detection are investigated. The spiral electrodes are created using liquid metal in a soft elastomer in order to make the sensor flexible and stretchable. When the metallic object to be detected comes in contact with the silicon elastomer surrounding the electrodes, charge transfer occurs, and this can be utilized for contact and noncontact sensing of the metallic object in flat or curved geometries. An equivalent electrical circuit model for the noncontact system is proposed and found to be in good agreement with the experimental data. A comparison between triboelectric proximity detection and eddy current resonance frequency proximity detection, using the same electrode geometry, shows that the two methods have comparable sensitivity. An added advantage of the triboelectric system is that it transforms mechanical into electrical energy and thereby allows one to monitor the triboelectrical signal upon impact of a metal object, and the experimental data show that the generated current scales with the impact force.

NURBS-based DEM for non-spherical particles

The discrete element method (DEM) is used to analyze complex practical granular systems; however, the representation of real shapes is an important consideration because behavior of non-spherical particles is unlike that of spherical particles both individually and collectively. In this study, we use non-uniform rational basis-splines (NURBS) to describe the shapes of non-spherical particles and introduce a contact detection scheme based on quadratic convergence, to simulate the behaviors of elliptical particles. The simulation results are compared with those based on polygons, in terms of the shape description and contact treatment, to demonstrate the high accuracy and efficiency of NURBS-based DEM.

Contact detection between convex polyhedra and superquadrics in discrete element codes

Particle shape substantially influences the bulk behaviour of granular systems. Hence, much scientific interest has been devoted to the adoption of non-spherical fundamental particles in discrete element method simulations. Two examples of such particles are polyhedra, which are highly angular, and superquadrics, which are best suited to simulate rounded particles. It is desirable to use both types of particle together in a simulation to capture the broadest possible range of particle shapes. In this paper, a novel contact detection algorithm is presented for a convex polyhedron and superquadric. This algorithm was implemented in a C++ code which was used to verify the correctness of the algorithm and evaluate its efficiency using the Monte Carlo method. The proposed contact detection algorithm is particularly efficient for many-faceted polyhedra as the effect of increasing the number of faces on the evaluation time is small.

A poly‐superellipsoid‐based approach on particle morphology for DEM modeling of granular media

SummaryParticle morphology plays a key role in affecting physical and mechanical behaviors of granular media. While various mathematical approaches and shape descriptors have been proposed to describe the morphological properties of granular particles, it remains a challenge to effectively incorporate them for efficient discrete modeling of granular materials. This study presents a new poly‐superellipsoid‐based approach for three‐dimensional discrete element method (DEM) modeling of non‐spherical convex particles. A uniform mathematical description of 3D poly‐superellipsoidal surface is employed to represent a realistic granular particle, which is shown to be versatile and effective in reproducing a wide range of shape features (including elongation, flatness, angularity, and asymmetry) for real particles in nature. A novel optimization approach based on hybrid Levenberg‐Marquardt (LM) and Gilbert‐Johnson‐Keerthi (GJK) algorithms is further developed for efficient and robust contact detection in DEM simulation of poly‐superellipsoidal assemblies. Simulations of granular packing and triaxial compression tests show that the proposed approach is generally robust and efficient for both dynamic and quasistatic modeling of granular media.

First-person Video Analysis for Evaluating Skill Level in the Humanitude Tender-Care Technique

In this paper, we describe a wearable first-person video (FPV) analysis system for evaluating the skill levels of caregivers. This is a part of our project that aims to quantize and analyze the tender-care technique known as Humanitude by using wearable sensing and AI technology devices. Using our system, caregivers can evaluate and elevate their care levels by themselves. From the FPVs of care sessions taken by wearable cameras worn by caregivers, we obtained the 3D facial distance, pose and eye-contact states between caregivers and receivers by using facial landmark detection and deep neural network (DNN)-based eye contact detection. We applied statistical analysis to these features and developed algorithms that provide scores for tender-care skill. In experiments, we first evaluated the performance of our DNN-based eye contact detection by using eye contact datasets prepared from YouTube videos and FPVs that assume conversational scenes. We then performed skill evaluations by using Humanitude training scenes involving three novice caregivers, two Humanitude experts and seven middle-level students. The results showed that our eye contact detection outperformed existing methods and that our skill evaluations can estimate the care skill levels.

Application of the Teagar-Kaiser energy operator and wavelet transform for detection of finger tapping contact and release times using accelerometery.

The Teager-Kaiser energy operator (TKEO), when applied to a signal gives an estimation of the instantaneous energy of that signal. It, therefore, accentuates both frequency and amplitude changes in a signal. To date, it has been primarily used in communications systems and most popularly in electromyographic signal analysis to detect bursts of muscle activity, however, it has the potential to be used in a number of applications including accelerometer and movement data.A new algorithm was developed which used the TKEO to detect contact times during a finger tapping task from accelerometer data recorded from the index finger. The accuracy of the algorithm was assessed in 7 healthy control subjects during continuous finger tapping across a range of frequencies from 0.5Hz to 2.5Hz. The algorithm proved to be sensitive, correctly identifying at least 99% of all contacts in each of the finger tapping conditions that were tested. The mean absolute error of the contact detection is 14.7 ± 6 ms, while the mean absolute error of the release detection is 36.5 ± 36.3 ms. The proposed algorithm provides a method for the automatic detection of the temporal occurrences of the events of the finger tapping task using only a tri-axial accelerometer. The approach presented provides a means for objective assessment of finger tapping tasks for evaluation of the fine dexterity of the upper limb.

Classical contact detection algorithms for 3D DEM simulations: Drawbacks and solutions

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.

Discrete element simulation of cylindrical particles using super-ellipsoids

A discrete element model based on super-ellipsoids was used to simulate cylindrical particle flow. The model can describe a cylindrical particle accurately provided the shape indices of the super-ellipsoids are set to appropriate values. To achieve more rapid calculations, we implemented an “oriented bounding box algorithm” (OBBA) for the initial contact detection of cylindrical particles. Several types of simulations were performed to validate the super-ellipsoid model and the contact-detection algorithm. First, the effect of shape index of the super-ellipsoids on model accuracy was investigated through three simulations: impact of a cylindrical particle on a flat wall, flow of cylindrical particles in a rotating tumbler, and segregation of cylindrical particles of different length flowing down a bounded heap. The simulation results show that the super-ellipsoids describe cylindrical particles accurately when the shape index that specifies the sharpness of the cylinder edges is sufficiently large. The efficiency of the OBBA is measured by simulations in which a box is filled with cylindrical particles and a tumbler that contains cylindrical particles is rotated. The simulation results show that the OBBA can accelerate the calculations significantly. The effect of particle shape (such as aspect ratio and shape index) on the calculation speed was obtained. The simulation of rod-like particles tended to take more calculation time than that of disk-like particles, and the simulation time increased with an increasing particle-shape index.

Collocated and Simultaneous Measurements of RF Current and Voltage on a Trace in a Noncontact Manner

With the trend of miniature, high-integrated assembly modules are common in modern industry. The measurement of the flowing current and voltage on a trace is basic for diagnosis and monitoring of these modules. The traditional contact detection method is not practical especially in conditions of high power and small space. In this paper, we demonstrate a novel method for collocated and simultaneous measurements of radio frequency current and voltage on a trace in a noncontact and movable manner. The measurements are achieved by using a compact probe with both voltage and current detectors, as well as an algorithm based on the transfer functions quantifying the capacitive and inductive couplings between the detectors and the tested trace. The proposed method is verified and applied for continuous power measurements, collocated and simultaneous measurements of transient voltage and current pulses and the dynamic voltage and current of a switching device.

Responding to the Ebola virus disease outbreak in DR Congo: when will we learn from Sierra Leone?

Responding to the Ebola virus disease outbreak in DR Congo: when will we learn from Sierra Leone?

Classification of individuals and the potential to detect sexual contact using the microbiome of the pubic region

In the absence of traditional DNA evidence, detection of sexual contact during intercourse is an important need for forensic analysis that might be addressed by studies of the pubic microbiome. Since 16S sequencing of various other body parts has shown that the microbiome may be individualizing, we reasoned that transfer of the assailant’s microbiome to a victim might be detectable. Microbiome profiles were generated from pubic hairs and swabs taken from the pubic mound region of 12 couples and 19 singles, and evaluated for similarity over an average of four collection times with varying degrees of self-reported sexual activity. A model constructed using a Random Forest classifier was able to predict samples belonging to the same individual collected up to 6 months apart, demonstrating the stability of the pubic mound microbiome over this time frame. Couples were found to be significantly more similar to one another than to unrelated members of the opposite sex, in proportion to shared sexual activity. Further analyses using the Deblur method to assign operational taxonomic units (OTUs) establish that at least 10% of the victim’s pubic microbiome must be derived from the attacker in order to detect transfer, but that single transfer events will not generally be discovered. Nevertheless, Bayesian SourceTracker software is shown to have potential to establish that sexual contact occurred when the assailant is known, or to exonerate suspects as contributors to a mixed microbiome. Our results establish limited potential of the pubic hair/pubic area microbiome as a tool for forensic associations.

Development of a GPGPU‐parallelized hybrid finite‐discrete element method for modeling rock fracture

SummaryThe hybrid finite‐discrete element method (FDEM) is widely used for engineering applications, which, however, is computationally expensive and needs further development, especially when rock fracture process is modeled. This study aims to further develop a sequential hybrid FDEM code formerly proposed by the authors and parallelize it using compute unified device architecture (CUDA) C/C++ on the basis of a general‐purpose graphics processing unit (GPGPU) for rock engineering applications. Because the contact detection algorithm in the sequential code is not suitable for GPGPU parallelization, a different contact detection algorithm is implemented in the GPGPU‐parallelized hybrid FDEM. Moreover, a number of new features are implemented in the hybrid FDEM code, including the local damping technique for efficient geostatic stress analysis, contact damping, contact friction, and the absorbing boundary. Then, a number of simulations with both quasi‐static and dynamic loading conditions are conducted using the GPGPU‐parallelized hybrid FDEM, and the obtained results are compared both quantitatively and qualitatively with those from either theoretical analysis or the literature to calibrate the implementations. Finally, the speed‐up performance of the hybrid FDEM is discussed in terms of its performance on various GPGPU accelerators and a comparison with the sequential code, which reveals that the GPGPU‐parallelized hybrid FDEM can run more than 128 times faster than the sequential code if it is run on appropriate GPGPU accelerators, such as the Quadro GP100. It is concluded that the GPGPU‐parallelized hybrid FDEM developed in this study is a valuable and powerful numerical tool for rock engineering applications.

Feasible numerical method for analysis of offshore pipeline in installation

Feasible numerical method for a structural analysis of a pipeline configuration during the installation process is presented. The method considers the whole pipeline, which is partially suspended and partially laid-on a seabed, as a single continuous segment, and is valid for a complete range of laying angles between 0°–90°, i.e., valid for both S-lay and J-lay configurations. The method accounts for a pipeline–seabed interaction and the pipeline is modeled by means of nonlinear large deformation beam theory. The numerical solution is carried out in an incremental-iterative manner by following the actual pipeline installation process, and thus allowing efficient treatment of pipeline-seabed interaction circumventing the further complexities with contact detection. At each increment, the length of the pipeline is increased and new sequential equilibrium configuration is assessed by direct minimization of a total potential energy approximated as a Riemann sum, which yields algebraic system of nonlinear finite difference equations that is further solved by iterations with Newton-Raphson technique. The simplicity, flexibility and robustness of the proposed method allow to enhance the efficiency of engineering calculations and design. Accounting for a bending stiffness in a suspended part allows analyzing variations in laying angle and lay tension independently. The method convergence is validated and compared with Abaqus. The results are in an excellent agreement. Moreover, the comparison with Abaqus shows that for the selected parameters the assumption that the pipeline is inextensible and unshearable is very reasonable. Representative parametric study is conducted to demonstrate the feasibility of the method. Parametric study considers the effects of laying angle (0°–90°), lay tension, laying water depth (up to 3000 m) and seabed stiffness.

A contact algorithm for voxel-based meshes using an implicit boundary representation

Numerical methods operating on structured grids have become popular since they offer good run time performance and are able to process directly voxel-based digital data from image recordings. Hence, the general framework of these fast solvers presupposes an unfitted boundary approximation avoiding complicated meshing of bodies. This allows an efficient handling with geometrical issues. Nevertheless, contacts between deformable solids are hard to deal with in the presence of this boundary representation. For this difficulty we suggest the usage of an implicit boundary representation combined with a modified saddle point formulation, resembling Nitsche’s approach. Both ideas give an elegant approach for discretizing the contact terms and enable a simple contact detection. Moreover, we suggest an intermediate surface as new reference contact area which fits well into our proposed method. In the end we present numerical results and analyze the accuracy and convergence rate. Furthermore, we demonstrate the current application range of our approach for problems with multiple contacts. In this paper we focus only on frictionless contact with small deformations.

Automatic contact detection between rope fibers

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.