Methodology of Teaching Methods of FEM Analysis Using Software ANSYS

This paper presents the authors' experience of teaching the finite element method (FEM) at university. With the development of computational tools in the second half of the twentieth century, there was also the development of computational methods focused on the algorithmization of engineering tasks based on FEM. From the solution of individual problems of the state of stress and deformation from the influence of the external environment, a complex solution of the mutual interaction of the system of deformable bodies (elements) has been performed while improving the physical and geometric characteristics of modern materials and structures. Many processes in the automatic design system take place as if in a "black box" and the process of verifying the achieved results becomes the most important stage in the design activity. Without knowledge of the theoretical basis of FEM, physical and mathematical modeling, verification procedures and methods, the design of a structure cannot be safe and reliable. In this paper we present one of the possibilities how the student can get acquainted with the theoretical foundations of FEM and with computational procedures using ANSYS software.

One Soft Step: Bio-Inspired Artificial Muscle Mechanisms for Space Applications

Soft robots, devices with deformable bodies and powered by soft actuators, may fill a hitherto unexplored niche in outer space. All space-bound payloads are heavily limited in terms of mass and volume, due to the cost of launch and the size of spacecraft. Being constructed from stretchable materials allows many possibilities for compacting soft robots for launch and later deploying into a much larger volume, through folding, rolling, and inflation. This morphability can also be beneficial for adapting to operation in different environments, providing versatility, and robustness. To be truly soft, a robot must be powered by soft actuators. Dielectric elastomer transducers (DETs) offer many advantages as artificial muscles. They are lightweight, have a high work density, and are capable of artificial proprioception. Taking inspiration from nature, in particular the starfish podia, we present here bio-inspired inflatable DET actuators powering low-mass robots capable of performing complex motion that can be compacted to a fraction of their operating size.

Topology Optimization of Deformable Bodies with Linear Dynamic Impact and Frictionless Contact Condition

There has been an increasing demand for the design of an optimum topological layout in several engineering fields for a simple part, along with a system that considers the relative behaviors between adjacent parts. This paper presents a method of designing an optimum topological layout to achieve a linear dynamic impact and frictionless contact conditions in which relative behaviors can be observed between adjacent deformable parts. The solid isotropic method with penalization (SIMP) method is used with an appropriate filtering scheme to obtain an optimum topological layout. The condensed mortar method is used to handle the non-matching interface, which inevitably occurs in the impact and contact regions, since it can easily apply the existing well-known topology optimization approach even in the presence of a non-matching interface. The validity of the proposed method is verified through a numerical example. In the future, the proposed optimization approach will be applied to more general and highly nonlinear non-matching interface problems, such as friction contact and multi-physics problems.

Attractive forces slow contact formation between deformable bodies underwater

Thermodynamics tells us to expect underwater contact between two hydrophobic surfaces to result in stronger adhesion compared to two hydrophilic surfaces. However, the presence of water changes not only energetics but also the dynamic process of reaching a final state, which couples solid deformation and liquid evacuation. These dynamics can create challenges for achieving strong underwater adhesion/friction, which affects diverse fields including soft robotics, biolocomotion, and tire traction. Closer investigation, requiring sufficiently precise resolution of film evacuation while simultaneously controlling surface wettability, has been lacking. We perform high-resolution in situ frustrated total internal reflection imaging to track underwater contact evolution between soft-elastic hemispheres of varying stiffness and smooth–hard surfaces of varying wettability. Surprisingly, we find the exponential rate of water evacuation from hydrophobic–hydrophobic (adhesive) contact is three orders of magnitude lower than that from hydrophobic–hydrophilic (nonadhesive) contact. The trend of decreasing rate with decreasing wettability of glass sharply changes about a point where thermodynamic adhesion crosses zero, suggesting a transition in mode of evacuation, which is illuminated by three-dimensional spatiotemporal height maps. Adhesive contact is characterized by the early localization of sealed puddles, whereas nonadhesive contact remains smooth, with film-wise evacuation from one central puddle. Measurements with a human thumb and alternatively hydrophobic/hydrophilic glass surface demonstrate practical consequences of the same dynamics: adhesive interactions cause instability in valleys and lead to a state of more trapped water and less intimate solid–solid contact. These findings offer interpretation of patterned texture seen in underwater biolocomotive adaptations as well as insight toward technological implementation.

Formulation and existence of weak solutions for a problem of adhesive contact with elastoplasticity and hardening

This paper presents the weak formulation of a quasi-static evolution model for two deformable bodies with uni-directional adhesive unilateral contact on which external loads act. Small deformations and linearized elastoplasticity with hardening are assumed. The adhesion component is rate-dependent or rate-independent according to the choice of the viscosity coefficient of the glue; elastoplasticity is considered rate-independent. The weak formulation is expressed as a doubly non-linear problem with unbounded multivalued operators, as a function of internal and boundary displacements, plastic and symmetric strain tensors, and the bonding field and its gradient. This paper differs from other formulations by coupling the equations defined inside and on the boundary of the solids in functional form. In addition to this novelty, we verify the existence of solutions by a path other than that displayed in similar articles. The existence of solutions is demonstrated after considering a succession of doubly non-linear problems with an unbounded operator, and verifying that the solution of one of the problems is also a solution to the objective problem. The proof is supported by previous results from non-linear Partial differential equations theory with monotone operators.

Free and Forced Vibration Modes of the Human Fingertip

Computational analysis of free and forced vibration responses provides crucial information on the dynamic characteristics of deformable bodies. Although such numerical techniques are prevalently used in many disciplines, they have been underutilized in the quest to understand the form and function of human fingers. We addressed this opportunity by building DigiTip, a detailed three-dimensional finite element model of a representative human fingertip that is based on prior anatomical and biomechanical studies. Using the developed model, we first performed modal analyses to determine the free vibration modes with associated frequencies up to about 250 Hz, the frequency at which humans are most sensitive to vibratory stimuli on the fingertip. The modal analysis results reveal that this typical human fingertip exhibits seven characteristic vibration patterns in the considered frequency range. Subsequently, we applied distributed harmonic forces at the fingerprint centroid in three principal directions to predict forced vibration responses through frequency-response analyses; these simulations demonstrate that certain vibration modes are excited significantly more efficiently than the others under the investigated conditions. The results illuminate the dynamic behavior of the human fingertip in haptic interactions involving oscillating stimuli, such as textures and vibratory alerts, and they show how the modal information can predict the forced vibration responses of the soft tissue.

Drift of individual marine floating debris and clusters of debris, incl. waste materials incl. plastics: translational and rotational dynamics of rigid and deformable bodies at the sea surface

<p>The first version of the Litter -TEP (Thematic Exploitation Platform), which was developed by ARGANS Ltd on a grant of the Copernicus Marine Environment monitoring service (CMEMS), aimed at forecasting litter introduction by rivers and marine drift on the European North-Western Shelf (NWS) so as to help local coastal communities schedule beach cleansing and assess the potential origin of materials collected. It relies on the classic approximation that the pieces or patches of litter are passively transported like Lagrangian floats by currents, whether largescale, mesoscale, sub-mesoscale, Eckman, tides, Stokes drift, the elusive Langmuir circulation…</p><p>Yet, windage, i.e. the effect of wind on items with a freeboard, is often more critical than transport by currents. To stay in the ‘Lagrangian Particle Tracking’ framework, but correct the discrepancy between ground-truth and drift speed’s and direction’s forecast, windage has been grossly modelled in the Litter TEP as if we had an enhanced ocean surface layer drift which affects similarly all floating litter. Yet, neither ocean transport nor this modelling allows to reproduce the formation of litter rows. Hence the current study: coming back to the basics of classical mechanics (Newton-Euler equations for translations & rotations of rigid bodies) we have performed simulation of marine debris’ dynamics at the interface between i. the turbulent atmospheric surface layer (ASL) which is at the bottom of the atmospheric boundary layer (ABL), and ii. the wave breaking layer (WBL) which tops the wave-affected-surface-layer (WASL) within the turbulent ocean boundary layer (OBL), in maturing wave fields (wave age <1) in the open ocean, that are characterized by wind gusts, wave crest breaking and spray. The classic framework for the drift of flotsam, by which wind-induced drag force exerted on objects floating on the sea surface causes motion relative to ocean currents (i.e. leeway drift), and vice-versa, is obviously right; but that it reaches an equilibrium stationary state between the wind-induced drag force and current-induced one on the floating objects in a relatively short timescale proves wrong. In various situations a litter piece will constantly change its attitude and settings in the water, yet reaching a +/- time-invariant time state (but not time-independent) though chaotic. In short: if litter pieces “sail”, it is without Control & Command. The litter drift, i.e. motion from source to sink, might therefore be drastically different from usual views, temporarily by orders of magnitude, and on the long run by factors 2 to 3.</p><p>For a proper assessment of the behavior of litter pieces, one needs precise modelling of wind profiles above the waves in a non-equilibrium boundary layer (wind gusts above the wave crests and counter wind in the troughs), of wave breaking that creates shock dynamics (surf, immersion and/or flight), of sea spray that batters the litter pieces, and .</p><p>Our modelling applies to rigid bodies lighters, cans, wood…, and shall be extended to deformable bodies for algae, plastic bags…, as well as entangled debris that are +/- linked together. We look for partners to perform scaled physical experiments in tanks.</p>