Multi-physics Solver Research Articles

Analysis and Simulation of Forcing the Limits of Thermal Sensing for Microbolometers in CMOS-MEMS Technology.

Room-temperature highly sensitive microbolometers are becoming very attractive in infrared (IR) sensing with the increase in demand for the internet of things (IOT), night vision, and medical imaging. Different techniques, such as building extremely small-scale devices (nanotubes, etc.) or using 2D materials, showed promising results in terms of high sensitivity with the cost of challenges in fabrication and low-noise readout circuit. Here, we propose a new and simple technique on the application of joule heating on a clamped–clamped beam without adding any complexity. It provides much better uniformity in temperature distribution in comparison to conventional joule heating, and this results in higher thermal stresses on fixed ends. This consequently brings around 60.5× improvement in the overall temperature sensitivity according to both theory and COMSOL (multiphysics solver). The sensitivity increased with the increase in the stiffness constant, and it was calculated as 134 N/m for a device with a 60.5× improvement. A considerable amount of decrease in the operation temperature (36× below 383 K and 47× below 428 K) was achieved via a new technique. That’s why the proposed solution can be used either to build highly reliable long-term devices or to increase the thermal sensitivity.

The effect of crystal anisotropy and plastic response on the dynamic fracture of energetic materials

The thermomechanical behavior of solids includes dissipative processes such as plastic deformation and fracture. The relative importance of these processes on the response of energetic materials has been a subject of study for many decades due to their significance on ignition and reaction. However, a constitutive model to simulate the anisotropy of the crack patterns and the effect of plastic deformation due to slip in energetic materials is not yet available. Finite strain thermomechanical constitutive equations that couple crystal plasticity, an equation of state, and an anisotropic phase field damage model are presented. The model is implemented in a multiphysics finite element solver and used to simulate recent experiments on β-HMX (octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine) by Zaug et al. The simulations reproduce qualitatively the crack pattern and the crystal orientation dependence of the observed damage. Specifically, more damage is observed when the crystal is impacted in the (010) direction, while more plastic deformation is observed when the load is applied in the (110) direction. The present model represents a step forward to understand the interplay between plasticity and fracture in shocked β-HMX single crystals. It can be used to gain insights into temperature increase and hot-spot formation under shock.

Manufacturing of unidirectional glass-fiber-reinforced composites via frontal polymerization: A numerical study

Frontal polymerization (FP) is explored as a faster and energy-efficient manufacturing method for dicyclopentadiene (DCPD) matrix, E-glass-fiber-reinforced composites through a series of numerical simulations based on a homogenized reaction-diffusion model. The simulations are carried out over a range of values of fiber volume fraction using (i) a transient, nonlinear, multi-physics finite element solver, and (ii) a semi-analytic steady-state solver. We observe that the front velocity and temperature decrease with an increase in the fiber volume fraction until a critical point is reached, beyond which FP is no longer observed as the front is quenched. To highlight the effect of the material properties of the reinforcing phase, the dependencies of the front velocity, width and maximum temperature on the fiber volume fraction obtained for glass/DCPD composites are compared to those associated with carbon/DCPD composites.

A deep learning-based hybrid approach for the solution of multiphysics problems in electrosurgery

Multiphysics modeling of evolving topology in the electrosurgical dissection of soft hydrated tissues is a challenging problem, requiring heavy computational resources. In this paper, we propose a hybrid approach that leverages the regressive capabilities of deep convolutional neural networks (CNN) with the precision of conventional solvers to accelerate multiphysics computations. The electro-thermal problem is solved using a finite element method (FEM) with a Krylov subspace-based iterative solver and a deflation-based block preconditioner. The mechanical deformation induced by evaporation of intra- and extracellular water is obtained using a CNN model. The CNN is trained using a supervised learning framework that maps the nonlinear relationship between the micropore pressure and deformation field for a given tissue topology. The simulation results show that the hybrid approach is significantly more computationally efficient than a FEM-based solution approach using a block-preconditioned Krylov subspace solver and a parametric solution approach using a proper generalized decomposition (PGD) based reduced order model. The accuracy of the hybrid approach is comparable to the ground truth obtained using a standard multiphysics solver. The hybrid approach overcomes the limitations of end-to-end learning including the need for massive datasets for training the network.

Investigating T-finned Barrels for Machine Guns: Enhancement in Heat Dissipation and Flexural Rigidity Along with Weight Reduction

This design innovation work is related to design and comparison of thermo-structural characteristics of a light-weight machine gun barrel. Compared to traditionally used thicker profile counter parts of machine gun barrels, these barrels were concluded to have lighter weight, better heat dissipation capability and better flexural rigidity. These barrels do not have rigidity problems like finned pencil barrels; neither have they extra weight addition, as in case of thicker profile barrels (H-Bars). To conduct the analysis, two same-length models of barrels bored for 5.56 × 45 mm, were modelled using Solidworks 15 software. The subsequent analysis using ANSYS 14.5 multi-physics solver simulated the condition of cook-off, which is an almost steady state reached after sustaining firing of 600 rounds (for 5.56 × 45 mm ammunition). It is a usual technical requirement expected from every durable machine gun, before the barrel is changed. The results showing maximum heat flux were transported to structural analysis workbench to measure the longitudinal deformation in both barrels under the gravity. The results concluded that T-finned barrels even after having less material, thus less weight, portrayed better heat dissipation characteristics and significantly less longitudinal deformation, thus better flexural rigidity and at the same time better accuracy retention than the conventional unfinned H-Bars.

Disturbance of a natural hydrogeochemical system caused by the construction of a high-level radioactive waste facility: The case study of the central storage facility at Villar de Cañas, Spain

ABSTRACT This paper analyzes the natural hydrogeochemical conditions of the future Central Storage Facility site at Villar de Canas and evaluates the evolution of the system associated with its construction. The characterization of the hydrogeochemical structure of the system is based on a comprehensive field and laboratory survey, which allowed us to define both the distribution of materials and their hydro-chemo-mechanical properties under isothermal conditions. The resulting observations were used to develop a numerical model in a multiphysics environment solver, which was calibrated from the monitoring of the hydraulic head distribution and from detailed geochemical analysis of water samples. The numerical model indicated that the behavior of the system is governed by a very slow underground flow regime and by equilibrium with gypsum and the dissolution of other sulfated phases; these results also suggest that the construction of facilities will not significantly disturb these processes, showing a very small effect of chemistry on the mechanical evolution (vertical displacements).

Development of an SP3 neutron transport solver for the analysis of the Molten Salt Fast Reactor

The aim of this paper is the extension of a multiphysics OpenFOAM solver for the analysis of the Molten Salt Fast Reactor (MSFR), developed in previous works (Cervi et al., 2017, 2018). In particular, the neutronics sub-solver is improved by implementing a new module based on the SP3 approximation of the neutron transport equation. The new module is successfully tested against a Monte Carlo model of the MSFR, in order to assess its correct implementation. Then, a neutronics analysis of the MSFR is carried out on a simplified axial-symmetric model of the reactor. Particular focus is devoted to the analysis of the MSFR helium bubbling system and its effect on reactivity. The presence of bubbles inside the reactor is handled with a two-fluid thermal-hydraulics module, previously implemented into the solver. The void reactivity coefficient is evaluated on the basis of the bubble spatial distribution calculated by the multiphysics solver. Then, the results are compared to simulations carried out with uniform bubble distributions, highlighting significant differences between the two approaches. The outcomes of this work constitute a step forward in the multiphysics analysis of the Molten Salt Fast Reactor and represent a useful starting point for the optimization of the MSFR helium bubbling system, as well as for the development of appropriate control strategies.

Development of a multiphysics numerical solver for modeling the behavior of clay-based engineered barriers

Abstract This work describes the development of a numerical module with a multiphysics structure to simulate the thermo-hydro-chemo-mechanical behavior of compacted bentonites. First, the conceptual model, based on the state-of-the-art formulation for clay-based engineered barriers in deep geological repositories, is described. Second, the advantages of multiphysics-based modules are highlighted. Then, the guidelines to develop a code using such tools are outlined, presenting an example of implementation. Finally, the simulation of three tests that illustrate the behavior of compacted bentonites assesses the scope of the developed code. The satisfactory results obtained, and the relative simplicity of implementation, show the opportunity of the modeling strategy proposed.

Towards an Ultra-Sensitive Temperature Sensor for Uncooled Infrared Sensing in CMOS⁻MEMS Technology.

Microbolometers and photon detectors are two main technologies to address the needs in Infrared Sensing applications. While the microbolometers in both complementary metal-oxide semiconductor (CMOS) and Micro-Electro-Mechanical Systems (MEMS) technology offer many advantages over photon detectors, they still suffer from nonlinearity and relatively low temperature sensitivity. This paper not only offers a reliable solution to solve the nonlinearity problem but also demonstrate a noticeable potential to build ultra-sensitive CMOS–MEMS temperature sensor for infrared (IR) sensing applications. The possibility of a 31× improvement in the total absolute frequency shift with respect to ambient temperature change is verified via both COMSOL (multiphysics solver) and theory. Nonlinearity problem is resolved by an operating temperature sensor around the beam bending point. The effect of both pull-in force and dimensional change is analyzed in depth, and a drastic increase in performance is achieved when the applied pull-in force between adjacent beams is kept as small as possible. The optimum structure is derived with a length of 57 µm and a thickness of 1 µm while avoiding critical temperature and, consequently, device failure. Moreover, a good match between theory and COMSOL is demonstrated, and this can be used as a guidance to build state-of-the-art designs.

Performance investigations of cross flow hydro turbine with the variation of blade and nozzle entry arc angle

Mistreatment of small hydropower sources requires the use of small turbines that combine efficiency and economy which can suitably provide the power requirements of rural and small societies. In this context, the cross flow hydro turbines are extensively used due to their simpler in design, ease of maintenance, low initial cost. Although the cross flow hydro turbine has moderated efficiency, but it has operated at low head and discharge. Hence, the objective of the present investigation is to increase the efficiency of a cross flow hydro turbine with the geometric modification. In the present study, the numerical investigation of cross flow hydro turbine has been carried out using multi-physics finite volume solver in ANSYS FLUENT. The three dimensional unsteady simulations have been conducted using shear stress transport k-omega turbulence model. The performance of cross flow hydro turbine has been investigated by changing the inlet blade angle from 5° to 40° and nozzle entry arc angle from 65° to 85° with the number of blades being 20. The rotational speed of the turbine has been varied from 200 rpm to 800 rpm. The total pressure and velocity field have been examined to evaluate the performance coefficients. From the unsteady results, the maximum efficiency has been found at the inlet blade angle, 5° and nozzle entry arc angle, 65° with the runner rotational speed of 600 rpm. However, with the consideration of the manufacturing feasibility inlet blade angle and nozzle entry arc angle have been considered as 10° and 65° respectively to be the most promising design configuration. The effect of temperature of the flowing water on performance of the turbine also has been studied. The maximum efficiency at inlet blade angle, 10° has been found to be 93.8% at 600 rpm. By incorporating the nozzle entry arc angle, maximum efficiency has been found to be 97.8% at nozzle entry arc angle, 65° with rotational speed 600 rpm and inlet blade angle, 10°. The efficiency of the current design configuration has been found 20% higher compare to the existing model.

Application of multiphysics model order reduction to doppler/neutronic feedback

In this paper, a proper orthogonal decomposition based reduced-order model is presented for parametrized multiphysics computations. Our application physics is Doppler feedback in a simplified model of the molten salt fast reactor concept. The reduced model is created using the method of snapshots where the offline training set is obtained by exercising a full-order model created with the OpenFOAM based multiphysics solver, GeN-Foam. The steady state models solve the multi-group diffusion k-eigenvalue equations with moving precursors together with the energy equation. A fixed velocity field is assumed throughout the computations, hence the momentum and continuity equations are not solved. The discrete empirical interpolation method is used for the efficient coupling of the ROM solvers, while the input parameter space is surveyed using the improved distributed latin hypercube sampling algorithm.

Modeling non-equilibrium discharge and validating transient plasma characteristics at above-atmospheric pressure

Non-equilibrium plasma generated from positive-pulsed nanosecond electrical discharges into desiccated air is simulated in this paper using a multi-dimensional, multi-physics plasma solver. A pin-to-pin electrode configuration is used with a fixed 5.2 mm gap spacing. Peak pulse voltages range between 10.2 and 22.5 kV. Care is taken to match the exact electrode profile from the experiments, and adjust the electron collision frequency so that breakdown limits closely match those from corresponding experimental results. The optimized numerical simulations predict qualitative streamer structure that is in close agreement with experimental observations. Quantitative measurements of atomic oxygen at the anode tip and qualitative estimates of streamer gas heating are closely matched by simulations. The model results are used to provide insight into the spatial and temporal development of the transient plasma. The work performed in this paper delivers a numerical tool that can be extremely useful to link the post-discharge plasma properties to low-temperature plasma ignition mechanisms that are of great interest for the automotive industry.

Surrogate-Based Optimization Using an Open-Source Framework: The Bulbous Bow Shape Optimization Case

Shape optimization is a very time-consuming and expensive task, especially if experimental tests need to be performed. To overcome the challenges of geometry optimization, the industry is increasingly relying on numerical simulations. These kinds of problems typically involve the interaction of three main applications: a solid modeler, a multi-physics solver, and an optimizer. In this manuscript, we present a shape optimization work-flow entirely based on open-source tools; it is fault tolerant and software agnostic, allows for asynchronous simulations, and has a high degree of automation. To demonstrate the usability and flexibility of the proposed methodology, we tested it in a practical case related to the naval industry, where we aimed at optimizing the shape of a bulbous bow in order to minimize the hydrodynamic resistance. As design variables, we considered the protrusion and immersion of the bulbous bow, and we used surrogate-based optimization. From the results presented, a non-negligible resistance reduction is obtainable using the proposed work-flow and optimization strategy.

An insight into the drag and lift characteristics of modified Bach and Benesh profiles of Savonius rotor

This investigation is focused on studying the flow physics around a modified Bach and Benesh profiles of Savonius rotor. A considerable amount of research has been done on improving the efficiency of Savonius rotors by optimizing the various design parameters. But most of these studies concentrate on power and torque coefficients. Deeper investigation of drag and lift characteristics could result in refining the efficiency. In view of this, 2D unsteady simulations are conducted using multi-physics CFD solver to find the instantaneous forces (drag and lift) acting on the rotors. The shear stress transport (SST) k-ω turbulence model is used for solving 2D unsteady Reynolds Averaged Navier-Stokes (RANS) equations. The total pressure, velocity magnitude and turbulence intensity contours are created at various angle of rotor rotation. The investigation shows that the drag coefficient (CD) for the modified Bach profile is higher than the Benesh profile. The results obtained are compared with those of semicircular-profile at the identical conditions.

An open source DNS solver for the simulation of Active Magnetocaloric Regenerative cycles

This paper describes the development of a new versatile multiphysics solver, whose final objective is to characterize Active Magnetocaloric Regenerative (AMR) cycles. The description is followed by a thorough validation divided in two parts. First, the separate simulations of the constituent physics are validated (porous geometry generation, fluid flow, Conjugated Heat Transfer and magnetic field). Then, the whole AMR code is compared to a measured prototype. The results are in all cases close to published numerical or experimental data. Also, two coupling mechanisms are studied, the temperature dependency of the viscosity of the Heat Transfer Fluid (HTF), and the influence of the magnetic permeability on the internal magnetic field of Gadolinium metal. Both effects prove to be negligible to compute the temperature field of a Magnetic Regenerator (MR). Moreover, by neglecting these effects the magnetic and flow fields of the MR can be computed beforehand, which reduces substantially the computational load at run time. Finally, the speed-up of the parallel multiphysics solver is evaluated.

Design and Electro-Thermo-Mechanical Behavior Analysis of Au/Si₃N₄ Bimorph Microcantilevers for Static Mode Sensing.

This paper presents a design optimization method based on theoretical analysis and numerical calculations, using a commercial multi-physics solver (e.g., ANSYS and ESI CFD-ACE+), for a 3D continuous model, to analyze the bending characteristics of an electrically heated bimorph microcantilever. The results from the theoretical calculation and numerical analysis are compared with those measured using a CCD camera and magnification lenses for a chip level microcantilever array fabricated in this study. The bimorph microcantilevers are thermally actuated by joule heating generated by a 0.4 μm thin-film Au heater deposited on 0.6 μm Si3N4 microcantilevers. The initial deflections caused by residual stress resulting from the thermal bonding of two metallic layers with different coefficients of thermal expansion (CTEs) are additionally considered, to find the exact deflected position. The numerically calculated total deflections caused by electrical actuation show differences of 10%, on average, with experimental measurements in the operating current region (i.e., ~25 mA) to prevent deterioration by overheating. Bimorph microcantilevers are promising components for use in various MEMS (Micro-Electro-Mechanical System) sensing applications, and their deflection characteristics in static mode sensing are essential for detecting changes in thermal stress on the surface of microcantilevers.

Numerical simulation of natural convection in open-cells metal foams

The aim of this work is to present results obtained through a multi-physics solver used to numerically determine the thermal behaviour of an open-cells metal foam in the case of natural convection. Particular attention is addressed to the right geometry definition in order to capture the intrinsic foam characteristics, thus, the elementary cell used for describing the unitary metal foam one is the tetrakaidecahedron. In addition, in order to improve its isotropy, a random deformation on the basic structure has been introduced. This feature allows to locally deviate flow paths with obvious benefits in terms of heat exchange, with reducing preferential paths arising while packing the elementary cell over the volume. This mesh generation approach is coupled with a hybrid solver based on the lattice Boltzmann framework for the fluid-dynamics field reconstruction and on finite volume method for solving the energy equation so to retrieve temperature evolution. For the first time, high order differencing scheme are used in temperature discretization with obvious benefits in computational accuracy. Numerical results are compared with a set of experimental data available for a range of Rayleigh numbers and for different foam geometries. The agreement between numerical and experimental data is satisfactory with positive outcomes for future model developments.

A CFD framework for offshore and onshore wind farm simulation

We present a wind simulation framework for offshore and onshore wind farms. The simulation framework involves an automatic hybrid high-quality mesh generation process, a pre-processing to impose initial and boundary conditions, and a solver for the Reynolds Averaged Navier-Stokes (RANS) equations with two different turbulence models, a modified standard k-ϵ model and a realizable k-ϵ model in which we included the Coriolis effects. Wind turbines are modeled as actuator discs. The wind farm simulation framework has been implemented in Alya, an in-house High Performance Computing (HPC) multi-physics finite element parallel solver. An application example is shown for an onshore wind farm composed of 165 turbines.

Modelling of compacted bentonite swelling accounting for salinity effects

This paper presents a formulation to incorporate the influence of water salinity on the swelling behaviour of a MX-80 bentonite into previously developed hydro-mechanical models that can reproduce swelling under dilute conditions. The effects of salinity on macro- and microstructural water chemical potentials were introduced. In addition, a description of solute transport was included to characterise the evolution of the system's salinity. A simplified geochemical model was adopted to idealise the geochemical complexity of bentonite. In addition, the modelling of the destructuration process that occurs during swelling was modified to account for the effect of salinity. The formulation was implemented in a multiphysics partial differential equation finite element solver, and the numerical model was used to simulate several vertical free swelling tests with feed water of different salt contents (deionised, 10, 35 and 70g/L). The results demonstrate that even though the model can be developed further, it represents a significant improvement over models that do not account for the effects of salinity.

RF-MEMS-Based DPDT Switch on Silicon Substrate for Ku-Band Space-Borne Applications

A RF-MEMS (radio-frequency microelectromechanical-system) based DPDT (double pole double throw) switch for the Ku band has been designed and analyzed for this article. The switch topology is based on the FG-CPW (finite ground-coplanar waveguide) configuration of a microstrip-transmission line. An FEM-based multiphysics solver is used for the evaluation of the spring constant, stress distribution, and pull-in voltage regarding the requirements of the switch-beam unit. The electromagnetic performance of the switch is investigated for a <TEX>$675{\mu}m$</TEX> thick silicon substrate. For the operational frequency of 14.5 GHz, an insertion loss better than -0.3 dB, a return loss better than -40 dB, and input/output- and output-port isolations better than -35 dB are achieved for the switching unit.