Hand Side Research Articles

Temperature Distribution Analysis of PEM Electrolyzer in High Current Density Operation By Numerical Simulation

Introduction High current density operation of water electrolysis enables mass production of hydrogen in a small system. With respect to high current density operation, alkaline water electrolysis, which are currently widely used for hydrogen production, has material-related limitations like ohmic resistance. However, polymer electrolyte membrane water electrolysis (PEMWE) has less limitations for higher current density operation, so that high current density operation of PEMWE is an advantageous feature compared with other water electrolysis technologies. High current density operation also leads to lower capital cost by reducing electrode area. A large amount of heat is however generated in high current density operation1, which could lead to nonuniform temperature distribution in the cell and therefore understanding the internal cell temperature distribution is important. Some researchers studied internal cell temperature distribution by numerical simulation2 , 3, but, to the best of our knowledge, no study has been done so far in a current density range of up to 10 A cm-2. The aim of this study is, by numerical analysis, to clarify internal cell temperature distribution around 10 A cm-2 which is the operating range of future PEM water electrolysis.4 Experimental A two-dimensional computational fluid dynamics (CFD) model for a 1 cm×1 cm PEM electrolysis cell consisting of MEA, GDL and flow channel was developed for numerical analysis of I-V characteristics and cell temperature distribution. CFD software COMSOL Multiphysics ver. 6.0 was used for the simulation. The cell temperature was fixed at 80 oC and the flow rate of water was set to be 5 to 15 ml min-1. Water was supplied from left hand side to the anode, and from right hand side to the cathode, as shown in Fig 1(b). The thickness of electrolyte membrane was set to be 51, 127, and 183 μm simulating Nafion 212, 115, and 117. I-V characteristics were analyzed by simulating the potential scan from 1.3 V to 2.5 V. The cell temperature distribution was analyzed in a steady state. The essential material property parameters for the calculations were procured from literature survey. Mass transport resistance, not yet understood sufficiently,5 was not considered in this calculation. The relation between current density and internal cell temperature distribution was investigated. Results and discussion Figure 1 shows I-V characteristics of a PEMWE cell simulated by following operating conditions: electrolyte membrane thickness of 51 μm; the flow rate of the supply water of 5 ml min-1, and the cell voltage of 2.5 V (current density of 11.8 A cm-2) in a steady state. Figure 1(a) shows linear I-V characteristics consisting predominantly ohmic overpotential in high current density region due to ignored mass transport resistance in this calculation. The cell temperature distribution in Fig. 1(b) shows that the cell temperature increased towards the outlet of water supply on the anode side and that temperature difference of approximately 20 K was generated between the inlet and outlet of water supply on the anode side. Temperature difference was suppressed by increasing the flow rate of water supplied. This result suggests the importance of appropriate rate of water supply for uniform cell temperature distribution especially in high current density operation. References M. Suermann, T. J. Schmidt, and F. N. Büchi, Electrochim. Acta, 211, 989–997 (2016).S. Toghyani, E. Afshari, E. Baniasadi, S. A. Atyabi, and G. F. Naterer, Energy, 152, 237–246 (2018).M. Upadhyay, A. Kim, S. S. Paramanantham, H. Kim, D. Lim, S. Lee, S. Moon, and H. Lim, Appl. Energy, 306, 118016 (2022).A. Villagra and P. Millet, Int. J. Hydrogen Energy, 44, 9708–9717 (2019).M. Suermann, T. J. Schmidt, and F. N. Buchi, ECS Trans., 69, 1141–1148 (2015). Figure 1

Introduction to Ansys NVH solutions focusing on the Vibro Acoustics

Product validation focusing on NVH heavily relies on physical testing which put NVH focused validation on right hand side of the Product Validation Process. Due to this, lot many times design changes are not possible or expensive or time consuming which reduces overall product quality. Industries like Automotives and ground transportation, Aero and Defense, High Tech, Industrial products making huge investments on NVH validation to win over customer perception battle. Ansys geared up in providing industry leading NVH Solution with Mechanical, LS-Dyna, Motion, Sound along with other products like Maxwell, Fluent, Optislang. NVH workflows driven by highly correlated simulation models, Integration of our key industry leading technologies and Guided, Automated, DOE friendly, Cloud native NVH Solutions are our TOP 3 goals. To introduce Ansys NVH Solutions focusing on the Vibro-Acoustics to Acoustical Society of America communities, we will cover key capabilities from different products briefly and demonstrate NVH Workflows in detail. Electric Motor NVH Simulation—Excitation generated due to Electro Magnetic forces Powertrain/Driveline/Gearbox NVH Simulation—Excitation generated due to multi body dynamics simulationFan NVH Simulation—Excitation generated due to structural vibration of fan driven by flow simulation.

Changes in medial elbow joint space with differences in contraction strength of flexor-pronator muscle under elbow valgus stress.

The relationship between contraction strength of the flexor-pronator muscles (FPMs) and elbow valgus braking function has not been clarified. The purpose of this study was to investigate changes in medial elbow joint space when there is a difference in contraction strength of FPMs under elbow valgus stress. Subjects were 20 healthy male university students, and the elbow joint on the nondominant hand side was used for measurements. The body position for limb measurement was sitting in a chair, with the shoulder abducted 60° and in 90° of external rotation, with 90° of elbow flexion. At first, maximum voluntary contraction (MVC) of the FPMs by grip motion was measured using a hand grip dynamometer under 60-N valgus stress. Contraction strengths of 10% MVC, 30% MVC, and 50% MVC were used. Ultrasonographic images of the medial elbow joint space (JS) were taken in the starting limb position. Using the Telos device system, load was then gradually increased by +10N/s, and at the time of 60-N valgus stress, an image of the JS was taken. Furthermore, the subject adjusted to the set contraction strength (for about 5sec) with 60-N valgus stress applied, and an image of the JS was taken while maintaining the set contraction strength. Each MVC condition (10% MVC, 30% MVC, and 50% MVC) was performed randomly. Three ultrasonographic images were taken within 10seconds, and the average value of the three images was adopted as the JS. Compared with the JS under 60-N valgus stress, the JS was significantly reduced under 60-N valgus stress + 50% MVC. No significant difference was observed between the starting limb position and 60-N valgus stress + 50% MVC. FPMs may require muscle activity ≥50% MVC to brake 60-N elbow valgus stress.

Attractors of 2D Navier–Stokes system of equations in a locally periodic porous medium

This article deals with two-dimensional Navier–Stokes system of equations with rapidly oscillating term in the equations and boundary conditions. Studying the problem in a perforated domain, the authors set homogeneous Dirichlet condition on the outer boundary and the Fourier (Robin) condition on the boundary of the cavities. Under such assumptions it is proved that the trajectory attractors of this system converge in some weak topology to trajectory attractors of the homogenized Navier–Stokes system of equations with an additional potential and nontrivial right hand side in the domain without pores. For this aim, the approaches from the works of A.V. Babin, V.V. Chepyzhov, J.-L. Lions, R. Temam, M.I. Vishik concerning trajectory attractors of evolution equations and homogenization methods appeared at the end of the XX-th century are used. First, we apply the asymptotic methods for formal construction of asymptotics, then, we verify the leading terms of asymptotic series by means of the methods of functional analysis and integral estimates. Defining the appropriate axillary functional spaces with weak topology, we derive the limit (homogenized) system of equations and prove the existence of trajectory attractors for this system. Lastly, we formulate the main theorem and prove it through axillary lemmas.

Genetic algorithmic based approach for multiple-objective probabilistic fractional programming problem involving discrete random variables.

This manuscript presents a technique for solving a multiple-objective probabilistic fractional programming problem with discrete random variables. A multiple-objective probabilistic mathematical model is constructed with fractional objectives. In the model, some parameters of coefficients and right hand side parameters of restrictions are assumed as random variables having Pascal and Hyper geometric distributions. The feasibility of probabilistic constraints is checked by means of stochastic simulation. Genetic algorithm approach method is used to obtain the Pareto optimal solution of the proposed model without finding the deterministic model. Genetic algorithm parameters are fixed in all generation. The proposed method is coded by C++ programming language. To illustrate the method, a numerical example and practical example on the case of supply chain management are presented. The result shows that the values of the objective functions are conflicting each other.

Lyapunov characterizations on input-to-state stability of nonlinear systems with infinite delays

This paper addresses Lyapunov characterizations on input-to-state stability (ISS) of time-varying nonlinear systems with infinite delays. With novel ISS definitions in the case of nonlinear systems with infinite delays, we present several results on their ISS Lyapunov characterizations in the form of both ISS Lyapunov theorems and converse ISS Lyapunov theorems. It is shown that an infinite-delayed system is (locally) ISS if it has a (local) ISS Lyapunov functional, and conversely, there exists a (local) ISS Lyapunov functional if it is (locally) ISS. To prove the converse ISS Lyapunov theorems, we establish a key technical lemma bridging ISS/LISS and robust asymptotic stability of systems with infinite delays and two converse Lyapunov theorems concerning robust asymptotic stability of systems with infinite delays. Two distinctive advantages of this work are that a large class of infinite dimensional spaces are allowed and the results are established based on a more general Lipschitz condition, i.e., the right hand side Lipschitz (RS-L) condition. An example is provided for illustration of the obtained results.

Computational Theology

This paper analyses an amazingly close analogy between models of generalised trinitarin logics on the one hand side and class hierarchies in the field of object-oriented programming on the other, thus linking philosophy of religion and computer science. In order to bring out this analogy as clear and precise as possible, we utilise a metaobject protocol for the actual implementation of the theological models. These formal implementations lead to the insight that the analogy can be pushed even further, and we lay bare and analyse the close relation between the theological notion of subordination of divine persons and precedence in structures of multiple inheritance. The implementation of theoretical godheads finally leads to new metaobject programming techniques, thus underlining the cross-fertilisation between theology and computer science.

Characterisation of Singular Domains in Threshold-Dependent Biological Networks

Threshold-dependent networks behave like piecewise smooth system which belongs to a class of systems with discontinuous right hand side. It can be studied with piecewise linear differential equations. At threshold values and their intersections, known as switching boundaries and surfaces, the state of such networks is not defined because of singularity at such points. These states are termed singular states or domains of the network. This study is to characterise, in terms of number, singular domains of any order in a network and the total number of such domains. It shall also propose new definitions for walls which are switching domains of order one. The new definition, which derives from Fillipov’s First Order Theory on characterisation of (sliding) wall, shall be shown to prove better than existing ones as it can reveal intrinsic behaviours in such networks.

Some New Oscillation Results for Higher-Order Nonlinear Differential Equations with a Nonlinear Neutral Term

The authors study the oscillatory behaviors of solutions of higher-order nonlinear differential equations with a nonlinear neutral term. The right hand side of their equation contains both an advanced and a delay term, and either (or both) of them can be sublinear or superlinear. The influence of these terms on the oscillatory and asymptotic behaviors of solutions is investigated by using a comparison to first-order advanced and delay differential equations. New oscillation criteria are presented that improve and extend many known oscillation criteria in the literature. An example is provided to illustrate the results.

Regularization of Inverse Initial Problem for Conformable Pseudo-Parabolic Equation with Inhomogeneous Term

The main goal of the paper is to approximate two types of inverse problems for conformable heat equation (or called parabolic equation with conformable operator); as follows, we considered two cases: the right hand side of equation such that F x , t and F x , t = φ t f x . Up to now, there are very few surveys working on the results of regularization in L p spaces. Our paper is the first work to investigate the inverse problem for conformable parabolic equations in such spaces. For the inverse source problem and the backward problem, use the Fourier truncation method to approximate the problem. The error between the regularized solution and the exact solution is obtained in L p under some suitable assumptions on the Cauchy data.

A simple Chimera grid method with an implicit Dirichlet/Neumann coupling scheme for flows with moving boundaries

A simple Chimera grid method is developed for complex flows with moving boundaries. Based on the interpolation condition, a coupling strategy is proposed where algebraic equations are reconstructed to couple different domains. With respect to other methods, the coupling of different domains can be accomplished with the employment of any discretization scheme and the iterative process or the iterative solver are avoided. The process of reconstruction is simple to be implemented by the node-by-node replacement, which makes little change on the original code. In addition, the reconstructed system matrix keeps symmetric and positive definite, hence the old solver is appliable. The developed method has a clear physical meaning, namely the transmission condition of Dirichlet/Neumann type. The interpolation condition makes the variable continuous across the interior boundaries, which is the Dirichlet condition, while the Neumann condition is imposed by the reconstruction of the system matrix and the right hand side. For the flows with moving boundaries, this method cannot be applied directly as the interpolation condition varies. The corresponding change on reconstruction of the right hand side is conducted to resolve moving boundaries. Finally, the reliability and the accuracy of the present method are validated by several benchmark problems. The simulation results show that the accuracy of the discretization scheme is not affected by the present coupling strategies.

Interior estimates for the Monge–Ampère type fourth order equations

In this paper, we give several new approaches to study interior estimates for a class of fourth order equations of Monge-Amp\`ere type. First, we prove interior estimates for the homogeneous equation in dimension two by using the partial Legendre transform. As an application, we obtain a new proof of the Bernstein theorem without using Caffarelli-Guti\'errez's estimate, including the Chern conjecture on affine maximal surfaces. For the inhomogeneous equation, we also obtain a new proof in dimension two by an integral method relying on the Monge-Amp\`ere Sobolev inequality. This proof works even when the right hand side is singular. In higher dimensions, we obtain the interior regularity in terms of integral bounds on the second derivatives and the inverse of the determinant.

Rectifiability of divergence-free fields along invariant 2-tori

We find conditions under which the restriction of a divergence-free vector field B to an invariant toroidal surface S is rectifiable; namely constant in a suitable global coordinate system. The main results are similar in conclusion to Arnold’s Structure Theorems but require weaker assumptions than the commutation [B,nabla times B] = 0. Relaxing the need for a first integral of B (also known as a flux function), we assume the existence of a solution u: S rightarrow {mathbb {R}} to the cohomological equation Bvert _S(u) = partial _n B on a toroidal surface S mutually invariant to B and nabla times B. The right hand side partial _n B is a normal surface derivative available to vector fields tangent to S. In this situation, we show that the field B on S is either identically zero or nowhere zero with Bvert _S/Vert BVert ^2 vert _S being rectifiable. We are calling the latter the semi-rectifiability of B (with proportionality Vert BVert ^2 vert _S). The nowhere zero property relies on Bers’ results in pseudo-analytic function theory about a generalised Laplace-Beltrami equation arising from Witten cohomology deformation. With the use of de Rham cohomology, we also point out a Diophantine integral condition where one can conclude that Bvert _S itself is rectifiable. The rectifiability and semi-rectifiability of Bvert _S is fundamental to the so-called magnetic coordinates, which are central to the theory of magnetically confined plasmas.

Interior and up to the boundary regularity for the fractional [formula omitted]-Laplacian: The convex case

We establish interior and up to the boundary Hölder regularity estimates for weak solutions of the Dirichlet problem for the fractional g−Laplacian with bounded right hand side and g convex. These are the first regularity results available in the literature for integro-differential equations in the context of fractional Orlicz–Sobolev spaces.

Alternating step size method for solving ill-posed linear operator equations in energetic space

An alternating step size method for solving ill-posed linear operator equations is introduced in energetic space, a subspace of the Hilbert space. Focus is on the case of a positive bounded self-conjugated operator under the assumption that the error for the right hand side of the equation is available. The advantage of the energetic norm is that does not require smoothness of the exact solution x. Convergence of the new method is discussed and shown to be faster for similar error estimates. Furthermore, the conditions for convergence in the energetic norm are derived which also imply convergence in the original Hilbert space norm. The new method is demonstrated on several numerical examples of the integral equation in L20,1 space, taken from the class of inverse problems in potential theory, and convergence speed compared with that of the fixed step size method. Finally, a novel real-word application of the integral equation is proposed: deblurring averages of trial-to-trial jittered EEG responses. When applying the Kosambi–Hilbert Torsion (KTH) to align these responses, the jitter is more effectively reduced and alignment improves with the deblurred average as a reference than with the original average.

A numerical implementation for the high-order 2D virtual element method in MATLAB

We present a numerical implementation for the Virtual Element Method that incorporates high order spaces. We include all the required computations in order to assemble the stiffness and mass matrices, and right hand side. Convergence of the method is verified for different polygonal partitions. An specific mesh-free application that allows to approximate harmonic functions is discussed, which is based on high-order projections onto polynomial spaces of degree k; this approach only requires to solve a k(k − 1)/2 linear system, reducing significantly the number of operations compared to usual finite or virtual element methods, and can be modified for different virtual spaces and elliptic partial differential equations.

Finding the dimension of a non-empty orthogonal array polytope

By using representation theory, we reduce the size of the set of possible values for the dimension of the convex hull of all feasible points of an orthogonal array (OA) defining integer linear description (ILD). Our results address the conjecture that if this polytope is non-empty, then it is full-dimensional within the affine space where all the feasible points of the ILD’s linear description (LD) relaxation lie, raised by Appa et al. (2006). In particular, our theoretical results provide a sufficient condition for this polytope to be full-dimensional within the LD relaxation affine space when it is non-empty. This sufficient condition implies all the known non-trivial values of the dimension of the (k,s) assignment polytope. However, our results suggest that the conjecture mentioned above may not be true. More generally, we provide previously unknown restrictions on the feasible values of the dimension of the convex hull of all feasible points of our OA defining ILD. We also determine all possible corresponding sets of equality constraints up to equivalence that can potentially be implied by the integrality constraints of this ILD. Moreover, we find additional restrictions on the dimension of the convex hull of all feasible points, and larger sets of corresponding equality constraints for the n=2 and even s cases. Each of these cases possesses symmetries that do not necessarily exist in the 3≤n or odd s cases. Finally, we discuss how to decrease the number of possible values for the dimension of the convex hull of all feasible points of an arbitrary ILD as well as generate sets of corresponding equality constraints with the zero right hand side. These are the only sets of zero right hand side equality constraints up to equivalence that can potentially be implied by the integrality constraints of the ILD.

Data-oriented description of texture-dependent anisotropic material behavior

In metallurgical processes, as for example cold rolling or deep drawing of sheet metal, it is frequently observed that the crystallographic texture, and with it the anisotropic mechanical properties of a material, evolve dynamically. Hence, to describe such processes, it is necessary to model the functional dependence of anisotropic material parameters on the texture, which itself can vary locally with the different plastic strain histories. In this work, we present a new data-oriented approach to parametrize the anisotropic yield function Barlat Yld2004-18p from micromechanical simulations for different textures. This is accomplished by applying supervised machine learning (ML) methods to express the relationship between different crystallographic textures and the material parameters of the yield function. The crystallographic textures are chosen to vary continuously between a random texture on the one hand side, and a unimodal Goss or Copper texture the other. These crystallographic textures are rather common in sheet metal forming. In this way, furthermore, the transition from isotropic plasticity to a rather severe case of anisotropy can be modeled, which is thought to mimic the dynamical evolution of the texture in a metallurgical process. It is found that a regularization strategy is necessary to circumvent the known non-uniqueness between Yld2004-18p parameters and the resulting plastic yield behavior. After this regularization, a unique relationship between the material parameters and the yield onset is established, making it possible to train different ML models with excellent accuracy and generalization properties to anisotropic plastic material behavior. The trained ML models are able to reliably predict the coefficients of unknown textures even with a small amount of training data and, thus, to correctly represent the yield behavior resulting from the various textures. The proposed method represents an efficient extension of the description of anisotropic plastic yielding as it establishes a data-oriented way to explicitly consider microstructural parameters in the material description, which opens new pathways to formulate material models that include the process history.

NUMERICAL METHOD FOR SOLVING THE DIRICHLET BOUNDARY VALUE PROBLEM FOR NONLINEAR TRIHARMONIC EQUATION

In this work, we consider the Dirichlet boundary value problem for nonlinear triharmonic equation. Due to the reduction of the problem to operator equation for the pair of the right hand side function and the unknown second normal derivative of the function to be sought, we design an iterative method at both continuous and discrete levels for numerical solution of the problem. Some examples demonstrate that the numerical method is of fourth order convergence. When the right hand side function does not depend on the unknown function and its derivatives, the numerical method gives more accurate results in comparison with the results obtained by the interior method of Gudi and Neilan.

Determining the Significant Kinematic Features for Characterizing Stress during Surgical Tasks Using Spatial Attention.

It has been shown that intraoperative stress can have a negative effect on surgeon surgical skills during laparoscopic procedures. For novice surgeons, stressful conditions can lead to significantly higher velocity, acceleration, and jerk of the surgical instrument tips, resulting in faster but less smooth movements. However, it is still not clear which of these kinematic features (velocity, acceleration, or jerk) is the best marker for identifying the normal and stressed conditions. Therefore, in order to find the most significant kinematic feature that is affected by intraoperative stress, we implemented a spatial attention-based Long-Short-Term-Memory (LSTM) classifier. In a prior IRB approved experiment, we collected data from medical students performing an extended peg transfer task who were randomized into a control group and a group performing the task under external psychological stresses. In our prior work, we obtained "representative" normal or stressed movements from this dataset using kinematic data as the input. In this study, a spatial attention mechanism is used to describe the contribution of each kinematic feature to the classification of normal/stressed movements. We tested our classifier under Leave-One-User-Out (LOUO) cross-validation, and the classifier reached an overall accuracy of 77.11% for classifying "representative" normal and stressed movements using kinematic features as the input. More importantly, we also studied the spatial attention extracted from the proposed classifier. Velocity and acceleration on both sides had significantly higher attention for classifying a normal movement (p <= 0.0001); Velocity (p <= 0.015) and jerk (p <= 0.001) on non-dominant hand had significant higher attention for classifying a stressed movement, and it is worthy noting that the attention of jerk on non-dominant hand side had the largest increment when moving from describing normal movements to stressed movements (p = 0.0000). In general, we found that the jerk on non-dominant hand side can be used for characterizing the stressed movements for novice surgeons more effectively.