Magnetomechanical Simulation Research Articles

Composited silk fibroins ensured adhesion stability and magnetic controllability of Fe3O4-nanoparticle coating on implant for biofilm treatment.

Magnetic propulsion of nano-/micro-robots is an effective way to treat implant-associated infections by physically destroying biofilm structures to enhance antibiotic killing. However, it is hard to precisely control the propulsion in vivo. Magnetic-nanoparticle coating that can be magnetically pulled off does not need precise control, but the requirement of adhesion stability on an implant surface restricts its magnetic responsiveness. Moreover, whether the coating has been fully pulled-off or not is hard to ensure in real-time in vivo. Herein, composited silk fibroins (SFMA) are optimized to stabilize Fe3O4 nanoparticles on a titanium surface in a dry environment; while in an aqueous environment, the binding force of SFMA on titanium is significantly reduced due to hydrophilic interaction, making the coating magnetically controllable by an externally-used magnet but still stable in the absence of a magnet. The maximum working distance of the magnet can be calculated using magnetomechanical simulation in which the yielding magnetic traction force is strong enough to pull Fe3O4 nanoparticles off the surface. The pulling-off removes the biofilms that formed on the coating and enhances antibiotic killing both in vitro and in a rat sub-cutaneous implant model by up to 100 fold. This work contributes to the practical knowledge of magnetic propulsion for biofilm treatment.

DESIGNING PROGRAMMABLE FERROMAGNETIC SOFT METASTRUCTURES FOR MINIMALLY INVASIVE ENDOVASCULAR THERAPY.

Minimally invasive endovascular therapy (MIET) is an innovative technique that utilizes percutaneous access and transcatheter implantation of medical devices to treat vascular diseases. However, conventional devices often face limitations such as incomplete or suboptimal treatment, leading to issues like recanalization in brain aneurysms, endoleaks in aortic aneurysms, and paravalvular leaks in cardiac valves. In this study, we introduce a new metastructure design for MIET employing re-entrant honeycomb structures with negative Poisson's ratio (NPR), which are initially designed through topology optimization and subsequently mapped onto a cylindrical surface. Using ferromagnetic soft materials, we developed structures with adjustable mechanical properties called magnetically activated structures (MAS). These magnetically activated structures can change shape under noninvasive magnetic fields, letting them fit against blood vessel walls to fix leaks or movement issues. The soft ferromagnetic materials allow the stent design to be remotely controlled, changed, and rearranged using external magnetic fields. This offers accurate control over stent placement and positioning inside blood vessels. We performed magneto-mechanical simulations to evaluate the proposed design's performance. Experimental tests were conducted on prototype beams to assess their bending and torsional responses to external magnetic fields. The simulation results were compared with experimental data to determine the accuracy of the magneto-mechanical simulation model for ferromagnetic soft materials. After validating the model, it was used to analyze the deformation behavior of the plane matrix and cylindrical structure designs of the Negative Poisson's Ratio (NPR) metamaterial. The results indicate that the plane matrix NPR metamaterial design exhibits concurrent vertical and horizontal expansion when subjected to an external magnetic field. In contrast, the cylindrical structure demonstrates simultaneous axial and radial expansion under the same conditions. The preliminary findings demonstrate the considerable potential and practicality of the proposed methodology in the development of magnetically activated MIET devices, which offer biocompatibility, a diminished risk of adverse reactions, and enhanced therapeutic outcomes. Integrating ferromagnetic soft materials into mechanical metastructures unlocks promising opportunities for designing stents with adjustable mechanical properties, propelling the field towards more sophisticated minimally invasive vascular interventions.

Coupled magneto-mechanical finite element analysis of a power transformer in short circuit conditions

External short circuit is one of the most demanding load conditions a transformer can be subjected to. Short circuit withstand capability of power transformers is therefore quintessentially important in order to ensure the proper functioning of a power transformer during its lifetime. Accurate calculation of the forces and stresses a transformer is subjected to during a short circuit is a prerequisite for better, optimized design of the active part. Main focus of this paper is the investigation into dynamic electromagnetic and mechanical behaviour of a transformer winding subject to an external short circuit. For purposes of this simulation, a single-phase 100 MVA autotransformer active part was modelled using ANSYS and NACS software. Particular areas of the winding were modelled to a greater degree of detail in order to observe the effects of Lorentz forces during a short circuit on individual conductors. A transient coupled magneto-mechanical simulation of the transformer under short circuit conditions was carried out. When subject to dynamic short circuit forces, the winding discs exhibited a profoundly resonant behaviour indicating a strong relationship between the natural frequency of the winding and the resulting stresses and displacements incurred during a short circuit. It has been shown that the position of the yoke changes the orientation and the distribution of the magnetic field vectors at the top and the bottom of the winding, causing a non-uniform distribution of forces along the top discs of the winding. This non-uniform distribution of forces along the circular shape of the winding conductor caused high stresses at the positions within the winding which were previously considered to be under lower stress when calculated using 3D static FEM and analytical methods.

Finite Element Analysis of the Magneto-Mechanical Coupling Due to Punching Process in Electrical Steel Sheet

In this article, a finite element (FE) modeling of the punching effect on the magnetic properties of electrical steel sheet is carried out. For that, the modified anhysteretic Sablik model is applied together with the plastic strain distribution obtained from a punching process simulation performed using the software ABAQUS. First, a synchronous electrical machine is simulated including the effect of the punching process, and it shows the degradation of the magnetic flux density at the lamination edges and an increase of the iron losses. Then, results obtained from the magneto-mechanical simulation are investigated in terms of the method used to implement the plastic strain distribution in the FE computation. Two examples have been investigated: a square steel sheet and a tooth of an electrical machine.

Preferential excitation of a single nanomagnet using magnetoelastic coupling

We report preferential excitation and detection of the precessional spin dynamics of individual nanomagnets via magnetoelastic (MEL) resonance excitation. Surface acoustic waves (SAWs) are generated via the ultrafast optical excitation of a nonmagnetic grating (Al bars) with lithographically defined acoustic eigenmodes. We show that the precessional spin dynamics in two identical, elliptical nanomagnets with orthogonal orientations can be selectively excited by the SAWs via control of the applied magnetic field. Furthermore, we observe that both the amplitude and damping of the magnetoelastically induced precession depend on the relative orientation of the SAW with respect to the nanomagnets. Using magnetomechanical simulations, we show that the acoustic excitation is most efficient when the spatial distributions of the natural and SAW-driven magnetic resonances overlap. These findings reveal a direct connection between the geometry and MEL excitation efficiency and have implications for the rational design of nanoscale magnetomechanical devices.

Modeling the Magnetic Performance of a Fast Pneumatic Brake Actuator

A novel pneumatic valve was constructed to improve the response of air-actuated brakes for heavy vehicles to demand pressures generated during electronically controlled braking by an order of magnitude. Investigations were made into the interactions between the magnetic, mechanical, and electrical subsystems of the valve with a view toward informing design optimization. The valve was modeled using a magnetic circuit approach. The quasi-static model included the influences of the permanent magnet, field-line fringing, saturation, and the coil. Mechanical forces outputted by the model matched physical measurements with an error smaller than 10%, and magnetic fluxes throughout the circuit were generally within 20% of those found from experiments based on Faraday's law of induction, Gaussmeter measurements, and FEA simulations. A magneto-mechanical simulation of the valve switching states was created using mechanical and electrical equations, and curve-fits to the outputs of the magnetic circuit model. The simulation produced time histories of the valve's armature position that matched experimental measurements and adequately predicted working pressures. The final model required an approximation to the influence of the coil based on experimental results. Consequently, further research is recommended into the influence of solenoid coils on fringing in magnetic circuits.

SALOME as a Platform for Magneto-Mechanical Simulation

The design of superconducting magnets for accelerator and detector components dedicated to the future of high energy physics requires detailed analysis of their mechanical behavior, in particular under magnetic and/or thermal solicitations. Numerical simulation is more and more used to optimize these components and to improve their performances in constrained environments. In this context, the numerical modeling process may require to operate several computing codes, which involves the implementation of spatial discretization (meshes) that are not always compatible together. This situation raises the problem of data transfer and of possible dispersion of simulation parameters. Moreover, the numerical modeling process is not always formalized, and it can be difficult to iterate in the case of parametric studies. This paper describes the implementation of magneto-mechanical numerical processes into the SALOME open source platform. SALOME is a numerical framework which offers interoperability between Computer-Aided Design (CAD) modeling and Computer-Aided Engineering (CAE) simulation software. It makes the implementation of coupling between computing codes (computation schemes) accessible. This simulation platform also provides a generic and efficient user interface, and is as well fully scriptable in Python language. On the basis of the design of the SMC dipole magnet, the authors will describe the various modules of the platform (geometry, mesh, supervision and visualization), and present the status of the developments in progress. It will be pointed out what can be gained for magnet designers in terms of process formalization and transfer of know-how, and what is the level of complexity for the development of a dedicated software tool.

Magneto-mechanical simulations by a coupled fast multipole method–finite element method and multigrid solvers

The present paper addresses the analysis of large-scale three dimensional magneto-mechanical problems by means of a coupled boundary element–finite element procedure. Iterative techniques are used for the solution of the associated linear systems; their intrinsic ill-conditioning is cured by means of ad-hoc multigrid solvers and fast multipole techniques as accelerators. Some numerical examples are presented in order to test the performance of the proposed approach.

Self-aligned vertical mirror and V-grooves applied to an optical-switch: modeling and optimization of bi-stable operation by electromagnetic actuation

High performance silicon-based, micro-optical switches are being developed for application to optical networks. The mechanical part was fabricated in a one-level mask step by bulk micromachining of (1 0 0) monocrystalline silicon with KOH. The resulting structure was assembled with a 100 μm-thick Permalloy piece and then, it was associated to a small magnetic circuit for its electromagnetic actuation. In order to avoid power consumption while holding ON and OFF states, a bi-stable operation principle is proposed. The bi-stable behavior is obtained by using a stable mechanical position due to the cantilever stiffness and a second magnetic stable position due to a permanent magnet. Switching operation is provided by electrical currents in windings. The aim of this paper is to present a study on modeling and optimization of this system by means of Finite Element Modelling (FEM) simulations, using ANSYS software. Iterative magneto-mechanical simulations are performed. Optimization of dimensions and material properties is presented.

A rate-dependent magnetostrictive simulation method for silicon-iron sheets under harmonic excitation

We present a representation of non-single valued anisotropic magnetostrictive strain vs flux density based on a rate-dependency law. This model is used in a continuum magnetomechanical simulation method for the vibration of a thin silicon-iron sheet excited magnetically by a sinusoidally alternating flux.

Disruption problematics in segmented-blanket concepts

In tokamaks, the hostile operating environment originated by plasma disruption events requires that the first-wall/blanket/shield components sustain the large induced electromagnetic (EM) forces without significant structural deformation and within allowable material stresses. As a consequence, there is a need to improve the safety features of the segmented-blanket design concepts in order to satisfy the disruption problematics. The present paper describes recent investigations on internal blanket reinforcement systems needed in order to improve the first-wall/blanket/shield structural design for next-step and commercial fusion reactors. Particularly in the context of SEAFP and ITER activities, representative 3-D CAD models of the inboard and outboard blanket regions and the related magnetomechanical simulations are illustrated.