| 1. |
- Adiels, Emil, 1989, et al.
(författare)
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The geometry of the equilibrium of forces and moments in shells
- 2024
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Ingår i: Meccanica. - 1572-9648 .- 0025-6455. ; In Press
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate that the internal forces and moments in a shell structure can be described by 4 vectors in 3 dimensional space which could be used to express the equilibrium of a shell graphically. The internal forces and moments described by 2 of the 4 vectors actively carry imposed loads and imposed couples, while the other 2 describe ‘redundant’ internal forces and moments that are purely in equilibrium with themselves. Nevertheless redundant stresses and moments are important in controlling internal stresses and satisfying boundary conditions. We show that forces and moments ‘flow’ across a shell in exactly the same way that fluid flows, with a combination of irrotational flow and incompressible flow. The aim is that these ideas can help in the initial design of those shell structures which have to rely on bending moments in addition to membrane action in supporting loads, and also in the interpretation of results from an analysis using the finite element method. We demonstrate the use of the technique for the design of an umbrella structure like those built by Amancio Williams.
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| 2. |
- Andrikopoulos, Georgios, et al.
(författare)
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Design and Development of an Exoskeletal Wrist Prototype via Pneumatic Artificial Muscles
- 2015
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Ingår i: Meccanica (Milano. Print). - : Springer Science and Business Media LLC. - 0025-6455 .- 1572-9648. ; 50:11, s. 2709-2730
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Tidskriftsartikel (refereegranskat)abstract
- Full or partial loss of function in the shoulder, elbow or wrist is an increasingly common ailment caused by various medical conditions like stroke, occupational and sport injuries, as well as a number of neurological conditions, which increases the need for the development and improvement of upper limb rehabilitation devices. In this article, the design and implementation of the EXOskeletal WRIST (EXOWRIST) prototype is presented. This novel robotic appliance’s motion is achieved via pneumatic artificial muscles, a pneumatic form of actuation possessing crucial attributes for the development of an exoskeleton that is safe, reliable, portable and low-cost. Furthermore, the EXOWRIST’s properties are presented in detail and compared to the recent wrist exoskeleton technology, while its two degrees-of-freedom movement capabilities (extension-flexion, ulnar-radial deviation) are experimentally evaluated via a PID- based control algorithm. Experimental results involving initial testing of the proposed exoskeleton on a healthy human volunteer for the preliminary evaluation of the EXOWRIST’s attributes are also presented.
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| 3. |
- Andrikopoulos, George, et al.
(författare)
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HUmanoid Robotic Leg via pneumatic muscle actuators : implementation and control
- 2018
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Ingår i: Meccanica (Milano. Print). - : Springer. - 0025-6455 .- 1572-9648. ; 53:1-2, s. 465-480
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Tidskriftsartikel (refereegranskat)abstract
- In this article, a HUmanoid Robotic Leg (HURL) via the utilization of pneumatic muscle actuators (PMAs) is presented. PMAs are a pneumatic form of actuation possessing crucial attributes for the implementation of a design that mimics the motion characteristics of a human ankle. HURL acts as a feasibility study in the conceptual goal of developing a 10 degree-of-freedom (DoF) lower-limb humanoid for compliance and postural control, while serving as a knowledge basis for its future alternative use in prosthetic robotics. HURL’s design properties are described in detail, while its 2-DoF motion capabilities (dorsiflexion–plantar flexion, eversion–inversion) are experimentally evaluated via an advanced nonlinear PID-based control algorithm.
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| 4. |
- Atashipour, Seyed Rasoul, et al.
(författare)
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Elastic analysis of thick-walled pressurized spherical vessels coated with functionally graded materials
- 2014
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Ingår i: Meccanica. - : Springer Science and Business Media LLC. - 1572-9648 .- 0025-6455. ; 49:12, s. 2965-2978
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Tidskriftsartikel (refereegranskat)abstract
- In recent years, functionally graded material (FGM) has been widely explored in coating technology amongst both academic and industry communities. FGM coatings are suitable substitutes for many typical conventional coatings which are susceptible to cracking, debonding and eventual functional failure due to the mismatch of material properties at the coating/substrate interface. In this study, a thick spherical pressure vessel with an inner FGM coating subjected to internal and external hydrostatic pressure is analyzed within the context of three-dimensional elasticity theory. Young’s modulus of the coating is assumed to vary linearly or exponentially through the thickness, while Poisson’s ratio is considered as constant. A comparative numerical study of FGM versus homogeneous coating is conducted for the case of vessel under internal pressure, and the dependence of stress and displacement fields on the type of coating is examined and discussed.
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| 5. |
- Banerjee, Indradumna, et al.
(författare)
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Analogue tuning of particle focusing in elasto-inertial flow
- 2021
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Ingår i: Meccanica (Milano. Print). - : Springer Science and Business Media B.V.. - 0025-6455 .- 1572-9648. ; 56:7, s. 1739-1749
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Tidskriftsartikel (refereegranskat)abstract
- We report a unique tuneable analogue trend in particle focusing in the laminar and weak viscoelastic regime of elasto-inertial flows. We observe experimentally that particles in circular cross-section microchannels can be tuned to any focusing bandwidths that lie between the “Segre-Silberberg annulus” and the centre of a circular microcapillary. We use direct numerical simulations to investigate this phenomenon and to understand how minute amounts of elasticity affect the focussing of particles at increasing flow rates. An Immersed Boundary Method is used to account for the presence of the particles and a FENE-P model is used to simulate the presence of polymers in a Non-Newtonian fluid. The numerical simulations study the dynamics and stability of finite size particles and are further used to analyse the particle behaviour at Reynolds numbers higher than what is allowed by the experimental setup. In particular, we are able to report the entire migration trajectories of the particles as they reach their final focussing positions and extend our predictions to other geometries such as the square cross section. We believe complex effects originate due to a combination of inertia and elasticity in the weakly viscoelastic regime, where neither inertia nor elasticity are able to mask each other’s effect completely, leading to a number of intermediate focusing positions. The present study provides a fundamental new understanding of particle focusing in weakly elastic and strongly inertial flows, whose findings can be exploited for potentially multiple microfluidics-based biological sorting applications.
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| 6. |
- Bartel, T., et al.
(författare)
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A phenomenological model for the simulation of functional fatigue in shape memory alloy wires
- 2017
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Ingår i: Meccanica. - : Springer Science and Business Media LLC. - 0025-6455 .- 1572-9648. ; 52:4-5, s. 973-988
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Tidskriftsartikel (refereegranskat)abstract
- In this contribution, a modelling framework for functional fatigue in shape memory alloy wires is introduced. The approach is in particular designed to reproduce the effective response determined by experiments as published in, e.g., Eggeler et al. (Mat Sci Eng A 378:24–33, 2004). In this context, the decrease of transformation stresses, the increase of irreversible strains, and the occurrence of “characteristic points” with respect to the stress-strain relation is explicitly covered in the model formulation. The modelling approach for the phase transformations itself offers a large potential for further micromechanically well-motivated model extensions.
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| 7. |
- Bennitz, Anders, et al.
(författare)
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Thick-walled cylinder theory applied on a conical wedge anchorage
- 2011
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Ingår i: Meccanica (Milano. Print). - : Springer Science and Business Media LLC. - 0025-6455 .- 1572-9648. ; 46:5, s. 959-977
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we derive and examine an analytical model for the internal stresses and strains within the anchorage for a prescribed presetting distance. This model is derived from the theory of thick walled cylinders under the assumptions regarding plane stress and axial symmetry. We simplify the resulting system of ten nonlinear equations and derive a method for solving them numerically. A comparison of plotted results for three different angles on the wedge's outer surface and six different presetting distances follows. These results are also compared to both axi-symmetric and 3D FE (Finite Element) models. Analytical and FE axi-symmetric models show good correspondence, though compared to the 3D FE model, they show a clear difference in the predicted radial stress distribution on the FRP. Thus, the derived analytical model can be a useful and faster alternative to FE modeling of axi-symmetric anchorages. However, the model is of more restricted value and should be complemented by, for example, 3D FE models for other designs.
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| 8. |
- Berthelsen, Rolf, et al.
(författare)
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Finite element simulation of coating- induced heat transfer: application to thermal spraying processes
- 2016
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Ingår i: Meccanica. - : Springer Science and Business Media LLC. - 0025-6455 .- 1572-9648. ; 51:2, s. 291-307
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Tidskriftsartikel (refereegranskat)abstract
- Thermal spraying is a widely applied coating technique. The optimisation of the thermal spraying process with respect to temperature or temperature induced residual stress states requires a numerical framework for the simulation of the coating itself as well as of the quenching procedure after the application of additional material. This work presents a finite element framework for the simulation of mass deposition due to coating by means of thermal spraying combined with the simulation of nonlinear heat transfer of a rigid heat conductor. The approach of handling the dynamic problem size is highlighted with focus on the thermodynamical consistency of the derived model. With the framework implemented, numerical examples are employed and material parameters are fitted to experimental data of steel as well as of tungsten-carbide–cobalt-coating.
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| 9. |
- Chaparian, Emad, et al.
(författare)
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Yield-stress fluids in porous media : a comparison of viscoplastic and elastoviscoplastic flows
- 2020
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Ingår i: Meccanica (Milano. Print). - : SPRINGER. - 0025-6455 .- 1572-9648. ; 55:2, s. 331-342
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Tidskriftsartikel (refereegranskat)abstract
- A numerical and theoretical study of yield-stress fluid flows in two types of model porous media is presented. We focus on viscoplastic and elastoviscoplastic flows to reveal some differences and similarities between these two classes of flows. Small elastic effects increase the pressure drop and also the size of unyielded regions in the flow which is the consequence of different stress solutions compare to viscoplastic flows. Yet, the velocity fields in the viscoplastic and elastoviscoplastic flows are comparable for small elastic effects. By increasing the yield stress, the difference in the pressure drops between the two classes of flows becomes smaller and smaller for both considered geometries. When the elastic effects increase, the elastoviscoplastic flow becomes time-dependent and some oscillations in the flow can be observed. Focusing on the regime of very large yield stress effects in the viscoplastic flow, we address in detail the interesting limit of 'flow/no flow': yield-stress fluids can resist small imposed pressure gradients and remain quiescent. The critical pressure gradient which should be exceeded to guarantee a continuous flow in the porous media will be reported. Finally, we propose a theoretical framework for studying the 'yield limit' in the porous media.
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| 10. |
- Cirillo, E. N. M., et al.
(författare)
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Upscaling the interplay between diffusion and polynomial drifts through a composite thin strip with periodic microstructure
- 2020
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Ingår i: Meccanica (Milano. Print). - : Springer. - 0025-6455 .- 1572-9648. ; 55:11, s. 2159-2179
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Tidskriftsartikel (refereegranskat)abstract
- We study the upscaling of a system of many interacting particles through a heterogenous thin elongated obstacle as modeled via a two-dimensional diffusion problem with a one-directional nonlinear convective drift. Assuming that the obstacle can be described well by a thin composite strip with periodically placed microstructures, we aim at deriving the upscaled model equations as well as the effective transport coefficients for suitable scalings in terms of both the inherent thickness at the strip and the typical length scales of the microscopic heterogeneities. Aiming at computable scenarios, we consider that the heterogeneity of the strip is made of an array of periodically arranged impenetrable solid rectangles and identify two scaling regimes what concerns the small asymptotics parameter for the upscaling procedure: the characteristic size of the microstructure is either significantly smaller than the thickness of the thin obstacle or it is of the same order of magnitude. We scale up the diffusion-polynomial drift model and list computable formulas for the effective diffusion and drift tensorial coefficients for both scaling regimes. Our upscaling procedure combines ideas of two-scale asymptotics homogenization with dimension reduction arguments. Consequences of these results for the construction of more general transmission boundary conditions are discussed. We illustrate numerically the concentration profile of the chemical species passing through the upscaled strip in the finite thickness regime and point out that trapping of concentration inside the strip is likely to occur in at least two conceptually different transport situations: (i) full diffusion/dispersion matrix and nonlinear horizontal drift, and (ii) diagonal diffusion matrix and oblique nonlinear drift.
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