Port based modeling of spatial visco-elastic contacts

In this paper, the geometrical description of viscoelastic contacts is described using physical modeling concepts based on energy conservation and network theory. The proposed model is on one side simple enough to be used in real time applications and on the other captures the geometrical features and coupling of a complete spatial geometric unisotropical contact

Port-Hamiltonian modeling for soft-finger manipulation

In this paper, we present a port-Hamiltonian model of a multi-fingered robotic hand, with soft-pads, while grasping and manipulating an object. The algebraic constraints of the interconnected systems are represented by a geometric object, called Dirac structure. This provides a powerful way to describe the non-contact to contact transition and contact viscoelasticity, by using the concepts of energy flows and power preserving interconnections. Using the port based model, an Intrinsically Passive Controller (IPC) is used to control the internal forces. Simulation results validate the model and demonstrate the effectiveness of the port-based approach

Mathematical modelling and numerical simulation of the morphological development of neurons

BACKGROUND: The morphological development of neurons is a very complex process involving both genetic and environmental components. Mathematical modelling and numerical simulation are valuable tools in helping us unravel particular aspects of how individual neurons grow their characteristic morphologies and eventually form appropriate networks with each other. METHODS: A variety of mathematical models that consider (1) neurite initiation (2) neurite elongation (3) axon pathfinding, and (4) neurite branching and dendritic shape formation are reviewed. The different mathematical techniques employed are also described. RESULTS: Some comparison of modelling results with experimental data is made. A critique of different modelling techniques is given, leading to a proposal for a unified modelling environment for models of neuronal development. CONCLUSION: A unified mathematical and numerical simulation framework should lead to an expansion of work on models of neuronal development, as has occurred with compartmental models of neuronal electrical activity

Generation of segmental chips in metal cutting modeled with the PFEM

The Particle Finite Element Method, a lagrangian finite element method based on a continuous Delaunay re-triangulation of the domain, is used to study machining of Ti6Al4V. In this work the method is revised and applied to study the influence of the cutting speed on the cutting force and the chip formation process. A parametric methodology for the detection and treatment of the rigid tool contact is presented. The adaptive insertion and removal of particles are developed and employed in order to sidestep the difficulties associated with mesh distortion, shear localization as well as for resolving the fine-scale features of the solution. The performance of PFEM is studied with a set of different two-dimensional orthogonal cutting tests. It is shown that, despite its Lagrangian nature, the proposed combined finite element-particle method is well suited for large deformation metal cutting problems with continuous chip and serrated chip formation

3D DISCRETE ELEMENT SIMULATIONS OF ACOUSTIC DISPERSION IN SEDIMENTS

Sound speed dispersion and frequency dependence of attenuation in marine sediments are important for any undersea activities using acoustics, such as remote sensing and target detection. Current established models use grain shearing and fluid viscosity as the source of loss in sediments, both of which may not be significant given the relatively small strains imposed by most acoustics' signals. In this paper, we analyze a source of attenuation due to compressional losses in grains, modeled with a dashpot term. Discrete element modelling (DEM) using Large Scale Atomic Molecular Massively Parallel Simulator (LAMMPS) was used to model motions of distinct particles in the system. A small amplitude pressure wave was introduced into the channel via an oscillating boundary wall and its effect on each discrete particle was measured to obtain the sound speed and attenuation coefficient. The measurements with sets of varying frequencies for system size of up to 50000 particles exhibit similar relationships with experimental data used for comparison in this paper. In particular, we were able to recover the observed frequency dependence of attenuation, following a power law of frequency squared at low frequencies and the square root of frequency at high frequencies for all system sizes used in our analysis. The small number of parameters used in our theory present a much more tractable and parsimonious problem for geo-acoustic inversion than the more complicated established models.Major, Republic of Singapore NavyApproved for public release. Distribution is unlimited