Radioisotope thermoelectric generators (RTGs) have been widely used as a promising power source for space mission, in which the Multi-Mission RTG (MMRTG) is the state of the art type. However, due to ...the scarcity of the 238Pu fuel and associated cost concerns, there exists an imperative need to increase the efficiency of RTGs. This requires intuitive, detailed and accurate system property predictions of the RTG system. In this work, a comprehensive finite element model of the MMRTG has been developed, by using a commercial software, COMSOL Multiphysics, including a full-size three-dimensional geometry model, temperature dependent materials and the thermoelectric and radiation heat transfer multiphysics fields involved. The calculation results agree well with reported experimental and simulated values. Through the obtained detailed temperature and voltage distribution, thermal and power properties of the MMRTG are characterized and the effects of non-uniform distributions of temperature and power generated in each TE couple are revealed. At last, the parametric analyses of operation conditions, thermal environment and key design factors are performed and several salient findings have been obtained. Through the analysis results, the design parameters and working mechanisms of the MMRTG are clarified, which can help the design and optimization of the future hundred-watt RTG.
•The comprehensive FEM method is first implemented in the MMRTG modeling and analysis.•The non-uniform distributions of temperature and power in TE modules are revealed.•Suitable load and sufficient thermal inventory ensure adequate power output.•The insensitivity of performance to ambient temperature expands MMRTG’s application.
The first stage of the structure life cycle, i.e. structural design, can be a source of eco-efficient outcomes. They can be achieved through optimisation of the amount of materials used, based of ...structural analyses. On the other hand the structure should be safe and reliably. The presented article conducts analyses aimed at assessing the accuracy, reliability, and safety of internal force values obtained with use of different subsoil models in reinforced concrete rectangular tank. The focus is on evaluating the performance of simplified subsoil models integrated into Finite Element Method (FEM) software: W1 (one-parameter Winkler model), W3 (three-parameter Winkler model) and DP (the tank modelled together with a solid subsoil simulated with the Drücker–Prager constitutive model). FEM was coupled with reliability analysis. The influence of the soil model on the values of internal forces in the tank walls (horizontal and vertical forces and bending moments) and in foundation slab (bending models) was assessed. The paper proves, by modelling the interaction of the structure with the soil, that the more simplified the FEM model, the values of internal forces differ from reality to higher extend. Therefore, the use of accurate models leads to structural optimization and ensures safety. In the analysed tank, in view of the watertightness demand, the reliability index of the structure was determined for the serviceability limit state of cracking. As the analyses have shown, the optimization of internal forces in the walls and foundation of the tank, through the use of an appropriate and reliable numerical model for analysis, results in a higher value of the reliability indices of individual sections for cracking and a lower probability of cracking.
•We present influence of the subsoil model on the safety of reinforced concrete structure of prismatic liquid tank.•We compare numerical analyses of exemplary sewage tank.•We evaluate relationship between reliability index and subsoil model.•We connect FEM analysis with reliability analysis.•We provide the necessary information about consequences of simplification in subsoil modelling.
Display omitted
•Method of coupling FEM model with “3D + 1D” model for large-scale PEMFC is proposed.•Non-uniform contact resistance distribution is investigated utilizing this method.•Performance ...reduces slightly when considering non-uniform contact resistance.•Current density gets more uneven when considering non-uniform contact resistance.•Deformed GDL under assembly affects both concentration loss and ohmic loss.
The assembly of proton exchange membrane (PEM) fuel cell has a significant influence on contact pressure of BP and GDL, which affects key parameters of GDL including contact resistance, porosity, and permeability. In this study, a large-scale finite element method (FEM) PEM fuel cell model is developed considering realistic assembly, which is assembled by 14 bolts. The contact pressure at the interface of GDL and BP is converted into non-uniform contact resistance incorporated into a self-developed “3D + 1D” full PEM fuel cell multi-phase model with the active area of 108 cm2. The “3D + 1D” model simplifies part of components along through-plane direction into 1D model to improve calculation efficiency and stability. The results show that the performance reduces slightly when considering non-uniform contact resistance compared with that considering uniform contact resistance. The uniformity of current density and temperature distributions reduces evidently when considering non-uniform contact resistance affecting the performance and durability, which demonstrates the necessity of treatment of non-uniform contact resistance. Furthermore, the effects of porosity and permeability of deformed GDL under different preloading torques on performance are investigated. It is found that the contact resistance reduces first and then flats as the preloading torques increase, which results in the same trend of electronic ohmic loss, while the concentration loss nearly linearly increases. The simulation shows that the PEM fuel cell shows the best performance when the preloading torque is 3 Nm. This study provides some meaningful guidance for PEM fuel cell stack assembly.
•The nanofluid flow in the blood vessel is simulated during the EPR effect on COMSOL Multiphysics.•Nanofluid flowing from the blood vessels to the tumor interstitium is simulated for ...concentration.•Physical properties of Fe3O4 MNPs immersed in Octane base fluid are computed using theoretical models.•Mesh dependent solution for the velocity of the blood vessel is investigated.•The temperature of the tumor is predicted quantitatively during heating by an external magnetic field
Nanotechnology has recently gained fame for its extensive use in biomedical applications particularly in magnetic fluid hyperthermia (MFH) of tumors. The magnetic nanoparticles (MNPs) are usually injected into the tumor either intravenously or through direct needle injection. Depending on the location of the tumor, the needle approach may not be appropriate and in the case, when the nanoflow rate is higher, it may produce cracks in the tumor. In this scenario, the intravenous approach following the enhanced permeation and retention effect (EPR) effect proves advantageous. In this paper, we have simulated the EPR effect of nanofluid flowing from blood vessels to the tumor through epithelial cells spacing and then its diffusion in the tumor interstitium using COMSOL Multiphysics. The velocity in the blood vessel and diffusion in the tumor have been simulated and analyzed using Finite Element Method (FEM) based models of Navier-Stokes equations and convection-diffusion equation. The simulation results show that the velocity and concentration are higher in the blood vessel and it decreases slowly while moving through epithelial spacing to the tumor interstitium. The heat transfer in the tumor interstitium is simulated and analyzed for temperature distribution quantitatively.
Deformation and fracture of a hydroxyl-terminated polybutadiene (HTPB)/ammonium perchlorate (AP)/aluminum solid propellant under quasi-static tensile loading are investigated by in situ synchrotron ...X-ray micro computed tomography (CT) and CT-image-based finite element method (FEM) modeling. Bulk stress–strain curve of the solid propellant, and the evolution of particle morphology, and mesoscale strain and particle displacement fields are obtained. Based on tracking and statistics, an automated analytical method is proposed to analyze the relationship between microcrack nucleation and initial structure. The AP particles undergo negligible deformation and orientation changes during tensile loading. Microcracks are mainly nucleated via tension-induced debonding at the maximum surface curvature of the AP particles, and propagate along the curvature gradient around AP particles. Larger AP particles are more prone to debond, and Al particles play a negligible role in deformation and fracture.
Display omitted
Fibre reinforced polymer composites have become an integral part of the bridge industry because of their versatility, high strength-to-weight ratio and enhanced durability. The novel idea of an ...all-composite structural system for road bridges has been proposed for the first time in Poland. The FRP bridge is a simply supported structure with 10.0 m long span and 7.66 m wide deck. The superstructure consists of four U-shaped girders bonded with sandwich deck slab, fabricated by means of a vacuum infusion. The bridge configuration, a finite element model developed for design and the proof test results are described in this paper. The test has shown that an all-composite bridge can meet the relevant strength and deflection design criteria. To develop an understanding of the long-term performance of the FRP bridge, a monitoring scheme utilizing distributed fibre-optic sensors was implemented to assess any changes in the bridge structural behaviour.
This study delves into the underlying causes of the atypical 'double rise' shape observed in hydrogen permeation rising transients on pure iron and low alloy steels. Electrochemical permeation ...experiments on pure iron reveal a fast initial rise, a short pseudo-plateau, and a slow second rise. Similar patterns emerge in the decaying transients. The micro-porosity present in material appears to act as reversible traps, affecting hydrogen diffusion. Surface damage, confirmed by SEM analysis, exacerbates the issue. Utilizing numerical simulations, an FEM model effectively replicates the 'double rise' behavior, attributed to limited recombination/dissociation kinetics at bulk-cavity interfaces. Overall, micro-porosity is identified as the primary factor behind this unique permeation curve shape.
•Hydrogen permeation on pure iron containing micro-porosities yielded abnormal curves.•The abnormal permeation behaviour is a bulk effect caused by micro-porosities.•H-charging inflicts damage to material: decreased permeability, blisters, cracks.•The double rise behaviour was simulated using non-equilibrium thermodynamic FEM model.
•Rate-dependent cohesive zone model for fracture simulation of polymeric coatings.•A data-driven approach for reverse identification of fracture parameters.•Identification strategy for minimizing the ...required amount of training samples.•High-fidelity finite element model for characterizing scratch-induced cracking behavior.•Good prediction of damage patterns and speed-dependent scratch characteristics.
As one of the key components of a vehicle, automotive coating systems are typical micro-size multilayer composites, which normally suffer from intricate scratch damage. Currently, it is a challenging task to reproduce the complex physical phenomena of automotive coatings with micron thickness using numerical simulations. The purpose of this work is to develop a computational framework for an accurate evaluation of such scratch damage. To achieve this end, a high-fidelity finite element (FE) model is proposed, where a rate-dependent cohesive zone model is developed to account for coating crack behaviors. A reverse identification approach based on the machine learning (ML) method is suggested to determine the rate-dependent cohesive parameters that are difficult to be measured via direct experiments. In the course of recognition, this work develops a two-step regional data augmentation strategy based on the existing single-shot recognition method. The developed strategy is capable of reducing the number of training data samples, while improving identification accuracy and robustness. With the identified cohesive parameters, the proposed finite element model is applied to simulate speed-dependent coating scratch behaviors. The good agreement between numerical and experimental results demonstrates the capacity of our developed computational framework for coating scratch problems.
•A model for PEM fuel cell with metallic bipolar plates coupling mechanics and multiphase non-isothermal electrochemical is proposed•Effect of various clamping pressures on transport properties of ...deformed gas diffusion layer is studied.•The concentration polarization occurs early and violently with the increases of clamping pressure.•The uniformity index of oxygen concentration and temperature is included to evaluate the PEM fuel cell performance comprehensively.•PEM fuel cell obtains 13.6% performance enhancement when the clamping pressure is 0.5MPa comparing to CPN.
The clamping pressure applied to proton exchange membrane fuel cell (PEMFC) stack alters the parameters related to mass transfer including porosity, permeability, conductivity and electrical contact resistance between metallic bipolar plates (BPs) and gas diffusion layers (GDLs). In this study, a model coupling mechanics and multiphase non-isothermal electrochemical is proposed, by considering the deformation of GDL, the impact of clamping pressure on a single straight channel of PEMFC is evaluated. The results show that oxygen concentration, oxygen reaction rate and current density are much lower under the rib, oxygen reaction rate gradually accumulates towards the region under the channel. With clamping pressure increasing, pressure drop increases remarkably, the average membrane water content slightly ascends, liquid water saturation near outlet of the channel increases while temperature under the rib descends. The power density enhances 13.6% from clamping pressure neglected (CPN) to 0.5MPa, and the parasitic power decreases 49.5% at the same time. However, the concentration loss occurs in advance and peak power density decreases when clamping pressure continues to increase. Although the uniformity indexes of oxygen concentration and temperature of 0.5 MPa are slightly higher than CPN, 0.5 MPa is still assumed to be the optimum clamping pressure.
