Linear Elements Research Articles

Effects of Nonlinear MPPT Control and PV Array on Stability Analysis for a Utility-Scale PV Energy System

Various studies have focused on the stability analysis of PV energy systems. However, the majority of these methods rely on a linearized model around an equilibrium point, which cannot exactly reveal the influence of the nonlinear power controller and PV array on the PV energy system at low frequencies. To conquer this gap, this article contributes to providing intuitive insight into stability analysis and establishing a complete system model including the PV panel, boost converter, DC line, central inverter and AC grid. The describing function (DF) of the nonlinear discontinuous element in PV and the transfer function of the linear elements in the system are derived to determine the system stability. To support the stability hypothesis based on the DF-based stability analysis method, a comparative study in contrast to existing stability analysis methods is provided. The impedance-based method may not be accurate when the division of the ‘source-load’ subsystem is different. The proposed DF method can offer further concluding remarks on MPPT control, the number of PV panels, DC/DC converter, etc. Based on a hardware-in-the-loop (HIL) operation, the proposed model is explicitly validated under different constraints, and the influence of control and circuit parameters on system stability are illustrated.

Post-selection in noisy Gaussian boson sampling: part is better than whole

Gaussian boson sampling (GBS) is originally proposed to show quantum advantage with quantum linear optical elements. Recently, several experimental breakthroughs based on GBS pointing to quantum computing supremacy have been presented. However, due to technical limitations, the outcomes of GBS devices are influenced severely by photon loss. Here, we present a practical method to reduce the negative effect caused by photon loss. We first show with explicit formulas that a GBS process can be mapped to another GBS processes. Based on this result, we propose a post-selection method which discards low-quality data according to our criterion to improve the performance of the final computational results, say part is better than whole. As an example, we show that the post-selection method can turn a GBS experiment that would otherwise fail in a ‘non-classicality test’ into one that can pass that test. Besides improving the robustness of computation results of current GBS devices, this post-selection method may also benefit the further development of GBS-based quantum algorithms.

Three-dimensional plasticity-based topology optimization with smoothed finite element analysis

AbstractThis paper presents a novel plasticity-based formulation for three-dimensional (3D) topology optimization of continuum structures. The proposed formulation addresses the optimization problem by combining mixed rigid-plastic analysis with density-based topology optimization, resulting in a volume minimization approach. Unlike conventional stress-constrained topology optimization methods that rely on linear elastic structural analysis, our developed formulation focuses on enhancing the loading capacity of the designed structures based on the plastic limit theory, leading to more cost-effective designs. To improve computational efficiency, we employ the smoothed finite element technique in our proposed method, enabling the utilization of linear tetrahedral elements for 3D mesh refinement. Moreover, the final formulation of our developed method can be efficiently solved using the advanced primal–dual interior point method, eliminating the need for a separate nonlinear finite element structural analysis. Numerical examples are presented to demonstrate the effectiveness of the proposed approach in offering enhanced design possibilities for continuum structures.

Phase-field modeling of brittle fracture in functionally graded materials using exponential finite elements

This study introduces a novel implementation of exponential finite element (EFE) shape functions within the phase field model for predicting fracture responses in functionally graded materials (FGMs). The proposed approach utilizes an effective fracture toughness concept to analyze load–displacement responses and crack paths in various examples of FGMs. To optimize computational efficiency, a mixed scheme combining both linear finite element (LFE) and EFE shape functions is employed. Specifically, only the critical elements are corrected using EFE shape functions. Comparative analysis of simulation results against converged outcomes demonstrates the superiority of the EFE scheme, even when employing coarser meshes. The EFE approach accurately predicts load–displacement responses and crack paths for the evaluated examples. The proposed implementation offers a reliable and efficient tool for studying fracture behavior in FGMs. Despite the higher integration schemes and orientation requirements associated with EFE shape functions, the additional computational effort is found to be negligible. Implementation aspects include a staggered iteration scheme, a hybrid tension–compression splitting scheme, and automatic orientation of EFE shape functions.

Potential of a linear woodland landscape element as ecological corridor for carabid beetles (Coleoptera: Carabidae): a case study from Poland

Fragmentation of landscapes and habitats has been identified as the main driver of biodiversity loss. Ecological corridors may support the conservation of biota in fragmented landscapes due to enhanced habitat connectivity. We conducted a study in order to assess the potential of a linear woodland landscape element along a railway line as ecological corridor using carabid beetles as indicators. The results showed that for some forest species the studied woodland strip has potential as an ecological corridor. Trophy and soil acidity were most often significantly correlated with parameters and species, but width of the woodland strip and distance from the forest site were of highest importance for the formation of the whole carabid assemblages. The results of our study provide with information regarding rules for the construction of woodland strips as ecological corridors. Management strategies should integrate such areas in concepts of sustainable regional development.

Large-scale parallel topology optimization of three-dimensional incompressible fluid flows in a level set, anisotropic mesh adaptation framework

This papers considers the topology optimization of duct flows governed by the three-dimensional steady state Navier–Stokes equations, using anisotropic mesh adaptation to achieve a high-fidelity description of all fluid–solid interfaces. The numerical framework combines an immersed volume method solving stabilized, linear equal-order finite element formulations cast in the Variational Multiscale (VMS) framework, and level set representations of the interface, used as a posteriori anisotropic error estimator to minimize the interpolation error under the constraint of a prescribed number of nodes in the mesh. Both the resolution and remeshing steps are performed in a massively parallel framework allowing for the optimization of large-scale systems. In particular, an original parallelization strategy is used for mesh adaptation, that combines local remeshing performed sequentially and independently on each subdomain with blocked interfaces, and constrained repartitioning to optimally move the interfaces between subdomains in an optimal way, both iterated until a satisfying mesh and partition are obtained. The proposed approach reduces the computational burden related to the call of the finite element solver, compared to classical optimization schemes working on uniform grids with similar mesh refinement. For a given number of nodes, it improves the accuracy in the geometric description of all layouts. Finally, it has the potential to alleviates the end user from most of the post-processing step aiming at extracting the final layout, due to ability of anisotropic adapted meshes to generate intrinsically smooth designs. Numerical results are provided for several three-dimensional problems of power dissipation minimization involving several dozen million state degrees of freedom, for which the optimal designs agree well with reference results from the literature, while providing superior accuracy over prior studies solved on isotropic meshes (in the sense that the flow is better resolved, especially in the near-wall regions, and the layouts are more smooth). The potential of the method for engineering problems of practical interest is eventually exposed by optimizing the distributor section conveying the cold fluid within the plates of a plate fin heat exchanger.

Processing GPR Surveys in Civil Engineering to Locate Buried Structures in Highly Conductive Subsoils

Many studies have illustrated the great benefit of ground-penetrating radar (GPR) in civil engineering. However, in some cases, this geophysical survey method does not produce the desired results due to the electromagnetic characteristics of the subsoil. This study presents the results obtained in two locations near Linares (southern Spain), evaluating the detection of structures buried in conductive host materials (0.02 S/m in site 1 and 0.015 S/m in site 2) characterized by strong signal attenuation. Accounting for the study depth, which was 1.5 m, a 500 MHz shielded GPR antenna was used at both sites. At the first site, a controlled experiment was planned, and it consisted of burying three linear elements. An iron pipe, a PVC pipe, and a series of precast blocks were buried at a depth of 0.5 m in a subsoil composed of highly conductive clayey facies. To eliminate additional multiples caused by other superficial structures and increasing the high-frequency content, the predictive deconvolution flow was applied. In the 3D processing, the cover surfaces technique was used. Once the acquired GPR signals was analyzed and the optimal processing flow established, a second site in which different infrastructures in a conductive host medium formed by marly facies was explored. The 2D flow and 3D processing applied in this work allows to detect and see the continuity of some structures not visible for the default processing.

Protective potential of different mouthguard thicknesses against perianaesthetic dental trauma: a patient specific-finite element study

Perianaesthetic dental trauma is a common anaesthesia-related complication. Theprevious studies have shown a lack of knowledge regarding mouthguard usage and controversial results related to perianaesthetic dental trauma prevention. This study aimed to conduct a finite element analysis of the compressive and tensile stresses on the tooth-periodontal ligament-bone complex using custom-made mouthguards of different thicknesses and glass fibre splints to prevent perianaesthetic dental trauma. Custom-fitted ethylene-vinyl acetate mouthguards of two different thicknesses (2 and 3 mm) and glass fibre splint were modelled. A linear static finite element analysis was performed by applying a rigid Macintosh laryngoscope to the palatal surface of the maxillary central incisors at 150 N. The model without a mouthguard and glass fibre splint showed the highest stress values at the palatinal root surfaces during the impact. Increasing the mouthguard thickness significantly decreased the stress-strain values regardless of the presence of the glass fibre splint. Maximum stresses in the group using the 3 mm mouthguard were the lowest compared with the other groups.

A Cartesian-octree adaptive front-tracking solver for immersed biological capsules in large complex domains

We present an open-source adaptive front-tracking solver for biological capsules in viscous flows. The membrane elastic and bending forces are solved on a Lagrangian triangulation using a linear Finite Element Method and a paraboloid fitting method. The fluid flow is solved on an octree adaptive grid using the open-source platform Basilisk. The Lagrangian and Eulerian grids communicate using an Immersed Boundary Method by means of Peskin-like regularized Dirac delta functions. We demonstrate the accuracy of our solver with extensive validations: in Stokes conditions against the Boundary Integral Method, and in the presence of inertia against similar (but not adaptive) front-tracking solvers. Excellent qualitative and quantitative agreements are shown. We then demonstrate the robustness of the present solver in challenging cases featuring extreme membrane deformations, very large computational domains and high volume fractions. Moreover, we illustrate the capability of the solver to simulate inertial capsule-laden flows in complex STL-defined geometries, opening the door for bioengineering applications featuring large three-dimensional channel structures. The source code and all the test cases presented in this paper are freely available.

Environmental and management factors drive biological communities and ecosystem services in agroecosystems along an urban-natural gradient

Biodiversity, ecosystem services and farming are inextricably linked. Peri-urban agricultural landscapes host wild species, provide essential services, and benefit citizens of nearby towns. We investigated the environmental and management factors that influence avian communities, pollinating insects and two key ecosystem services (pollination and nature-based recreation) along an urban-natural gradient dominated by agricultural areas (vineyards, apple orchards and grasslands) in northern Italy. Flower visiting-insects were mainly affected by management and environmental-climatic variables. The presence of flowers at the margins and within vineyard and apple orchard inter-rows best predicted the abundance of pollinators and flower-visiting insects in general. Different flower species exerted variable effects on different groups; a mix of flowering species should be recommended for supporting pollinators. Sward height and grassland cover promoted flower-visiting insect abundance, which was negatively affected by vineyards and apple orchards. Bird communities were mainly shaped by land-use/land-cover and management variables. Landscape heterogeneity and linear elements had a major positive effect on birds. Apple orchards negatively influenced species richness and the abundance of most avian species, while vineyards negatively impacted on overall bird abundance; hedgerows positively affected richness. Nature-based recreation was greater in areas with low or intermediate vineyard or urban cover. Apple orchards and intensively managed grasslands had negative, and waterways positive, effects on recreation. Peri-urban agricultural landscapes are important for biodiversity and ecosystem services, but apple orchards and large vineyards appear largely unsuitable. Maintaining heterogeneous landscapes and implementing biodiversity-friendly practices can further promote benefits for biodiversity and visitors and local populations. Synergic strategies that simultaneously promote the conservation of biodiversity and the supply of ecosystem services could be easily developed and implemented.

ОБОСНОВАНИЕ РАЦИОНАЛЬНОЙ КОНСТРУКЦИИ СКОЛЬЗУНОВ ТЕЛЕЖКИ ПАССАЖИРСКОГО ВАГОНА

At the first stage, a detailed dynamic solid-state model of a passenger car is developed which has a bolsterless truck. The dynamic model is a system of absolutely rigid bodies interconnected by elastically dissipative linear and nonlinear force elements, hinges and contact forces. The adequacy of the car dynamic model and the reliability of the results obtained are evaluated the results of running tests. Based on the developed solid-state dynamic model, a comprehensive study of the effect of the friction factor on the guide block support surfaces on the safety and dynamic performance of a passenger car under various modes of movement along the track, taking into account irregularities is carried out. As a result of modeling, a range of rational values of friction moments on the support guide blocks is obtained. The composition of the composite material for the support surfaces of the truck guide blocks is selected using neurocomputer modeling methods, the manufacture of the proposed composite material is tested, experimental studies of the characteristics of composite elements confirming their properties and safety were carried out.

Experimental modal analysis of a single-link flexible robotic manipulator with curved geometry using applied system identification methods

In this paper, the principal time-domain system identification methods are studied and used to carry out the experimental modal analysis of a single-link flexible manipulator with curved geometry in a comparative fashion. The identification process carried out in this study is aimed at deriving first-order state-space dynamical models and second-order configuration-space dynamical models of the single-link flexible manipulator by using an array of fundamental system identification procedures, which includes the ARX (AutoRegressive eXogenous method), SSEST (State-Space ESTimation method), N4SID (Numerical Algorithm for Subspace State-Space System Identification), ERA/OKID (Eigensystem Realization Algorithm combined with the Observer/Kalman Filter Identification method), and TFEST (Transfer Function ESTimation method) methods. The main goal of this paper is, therefore, to perform a comparative study between the most fundamental system identification procedures applied to the numerical and experimental analysis of the structural vibrations of a flexible manipulator having a curved geometric shape. First, this paper poses the theoretical foundations for the development of the numerical study and the experimental testing to be performed for the case study. Subsequently, the flexible manipulator analyzed in this work is modeled with various levels of complexity, which range from a simple lumped parameter model to a linear finite element model developed by integrating the interconnections between the SOLIDWORKS and ANSYS software. By doing so, the computational procedures applied to the time-domain experimental measurements of the dynamic behavior of the flexible manipulator allow for reconstructing first-order and second-order mechanical models of the structural system of interest in the MATLAB simulation environment. The numerical results and the experimental tests reported in this investigation demonstrate the effectiveness of all the time-domain system identification approaches considered in the paper.

Auto Mesh generation algorithm for the convex domain with the triangular elements

Mesh creation is one of the primary tasks in implementing the Finite Element Method (FEM) to solve two- and three-dimensional boundary value problems. However, the whole procedure becomes tedious and problematic when higher-order finite elements are employed to construct mesh and prepare corresponding element data. In this study, we strive to develop a versatile algorithm for discretizing the two-dimensional domain using linear, quadratic, and cubic triangular finite elements. The algorithm is developed based on n vertices (actual or more in number) that constitute the boundary of the domain, along with a computed (n+1)-th point such as the centroid. The algorithm, using this input, generates an initial mesh consisting of n triangular elements. Then, in every subsequent step, the algorithm increases the number of triangles in the mesh fourfold compared to the previous step. The algorithm we present here can employ (a) straight-sided (linear, quadratic, and cubic) triangular elements to generate the mesh for domains with polygonal boundaries and (b) both straight-sided and curved (quadratic and cubic) triangular elements with two straight sides and one curved side to generate meshes for domains with curved boundaries. Thus, the algorithm generates the desired meshes if the vertices are specified once at the initial step. Additionally, the inclusion of the mathematical expression of the curved boundary enables the algorithm to generate the fine mesh for the curved domain utilizing higher-order curved and straight-sided triangular elements. We also present a computer code in MATLAB incorporating the algorithm to create the mesh, prepare the element's data, and determine the element's connectivity.
 GANIT J. Bangladesh Math. Soc. 43.1 (2023) 017- 035

Numerical Stability and Dispersion Analysis of the 2-D FDTD Method Including Lumped Elements

The numerical stability and dispersion analysis of the extended two-dimensional finite-difference time-domain (2D-FDTD) method are systematically studied. Particularly, three different passive linear lumped elements including the resistor, inductor, and capacitor are analyzed, respectively. Moreover, three different formulations of the explicit, semi-implicit, and implicit schemes are discussed, respectively. Furthermore, by combining the von Neumann technique and Jury criterion, the numerical stability of the extended 2D-FDTD method is analyzed, which has not been reported thus far. Theoretical results show that: 1) For the resistor, the stability condition is same as the FDTD method unloaded case. 2) For the inductor, in the explicit and implicit schemes, the stability is connected with the value of the inductance; for the semi-implicit scheme, the stability is independent of the value of the inductance. 3) For the capacitor, the stability relationship is related to both the mesh size and the value of the capacitance. On the other hand, based on the Norton equivalent circuit, the analysis of the numerical dispersion of the extended 2D-FDTD is presented; and some interesting theoretical results are deduced. Finally, the microstrip circuits including the three lumped elements are simulated to demonstrate the validity of the theoretical results.

Modeling of Linear-Nonlinear Behavior in Electrical Contacts With Interaction Interference

The reliability of electrical contacts is important to the quality of signal transmission. In this letter, an equivalent circuit model is proposed to illustrate the linear-nonlinear interaction effect in coaxial connectors. The linear region is simplified to a cascade system composed of impedance matching and impedance mismatch networks, while the nonlinear region is equivalent to a contact impedance network coupling a module defined by nonlinear I-V relation. By tuning values of each component in the presented circuit, the effect of linear and nonlinear elements on scattering characteristics and passive intermodulation (PIM) are observed. The S-parameters are sensitive to linear network with equivalent inductance and capacitance, but the PIM behavior is affected by both nonlinear resistance and linear resistance which are temperature and frequency dependent. Connectors with designed contact resistance are tested separately in different frequency band and environmental temperature, verifying the proposed model in predicting scattering performance and PIM behavior.

Hybrid Quantum Systems for Higher Temperature Quantum Information Processing

The ability to operate superconducting quantum computers at higher temperatures would greatly expand their utility and range of applications. This could be achieved by increasing resonance frequencies and/or utilizing collective modes that are less noisy and more robust against decoherence. We discuss several nonlinear resonator concepts in which the roles of linear and nonlinear elements are reversed vs. the transmon. The simplest version is a nonlinear <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LC</i> resonator with a linear superconducting inductor and a nonlinear capacitor employing a nonlinear dielectric material. Due to progress in tunable dielectrics for 6G, some ferroelectric composites may enable operation of a nonlinear dielectric – superconductor qubit at hundreds of gigahertz. Other nonlinear dielectric materials include quantum paraelectrics and charge density wave materials. These are of interest due to robust collective modes resulting from macroscopically occupied states. Other proposed nonlinear resonators employing nonlinear dielectrics include quarter- and half-wavelength resonators. Voltage tunability is a potential feature of the proposed concepts.

Designing the working surfaces of rotary planetary mechanisms

Purpose. To design a method for smoothing the working surfaces of stator and rotor with the use of computer simulation to eliminate the impact of the rotor on the stator when they interact. Methodology. Special and general methods of research have been used: interpolation of the point series – to determine the contour nodes of the rotor and the stator of the rotary-planetary machine; formation of B-splines – to construct a point series whose coordinates are structurally determined; technology of automated formation of curves in CAD-system SolidWorks – for modelling of functional surfaces of a planetary-rotary compressor. Findings. Algorithms for formation of the contours representing curves defined analytically or constructively with a given accuracy have been developed. The obtained contours are used in the CAD system as linear elements of the surface model. The developed method has been tested in the simulation of functional surfaces of a planetary-rotary compressor. Optimization of the body shape and rotor profiles in order to increase the productivity of the rotary-planetary machine has been carried out. Originality. The developed algorithms make it possible to determine the original point series belonging to any curve and provide a given interpolation accuracy when forming a B-spline contour or second-order curve arcs. Computer models of the body surfaces of the rotor are formed on the basis of the gear ratio of the planetary-rotary mechanism and the rotor dimensions. In order to increase the performance of the compressor, the working surfaces of the rotor have been optimized. The maximum volume of the working chamber was increased by increasing the radius of the moving gear of the planetary-rotary mechanism. In order to prevent the rotor from jamming during compressor operation, the rotor contour was changed. Practical value. The method for modelling the surfaces of complex shape in CAD-system has been developed on the basis of creating contours which with given accuracy represent lines from the surface determinant. This method makes it possible to form computer models of complex surfaces on the basis of a framework consisting of curves absent in CAD libraries.

Experimental Study on the Influence of Model Parameters on the Dimensional Deviation of Printed Parts

Not being affected by the structural complexity of the print model is one of the outstanding features of 3D printing, but model parameters have an important influence on the dimensional accuracy of the printed parts. In order to explore the influence of model parameters on dimensional deviation, on the basis of designing experimental models and carrying out printing experiments, we have studied the effect of three model parameters (placement method, two-dimensional contour components, and model inclination) on printing accuracy through the dimensional deviation rate. It has been found that the inclination angle of the model mainly affects the dimensional error in the height direction; different models can change the filling method of the cross-section contour from a curve to a straight line by changing the placement method, which can reduce the dimensional error of the two-dimensional contour of the model; the contour composed of linear elements has a lower deviation rate than the contour composed of curved elements.

Thermal Postbuckling of Heated Uniform Columns Considering Green Nonlinearity: A Novel Liner Finite Element Formulation

Thermal postbuckling behavior of uniform, heated columns is presented, by using a novel linear Finite Element (FE) formulation. In this investigation, the general Green axial nonlinear strain- displacement relation is used, instead of the popularly used simpler von-Karman nonlinearity, which is a subset of Green nonlinearity. In the earlier complex nonlinear FE formulations, time consuming iterative or step-by-step methods are used to obtain the solution for thermal postbuckling. In the novel FE formulation, normally used FES , for performing linear buckling analysis, is proposed to obtain thermal postbuckling loads. The nodal degrees of freedom are deflection and its first derivative with respect to the axial coordinate. The geometric nonlinearity is incorporated through the tensile loads induced, with axially restrained ends of the column, due to large deflections. The effectiveness of the novel FE formulation is demonstrated, from the numerical results obtained, in terms of the ratio of thermal postbuckling to buckling loads, for specified reference deflection and slenderness ratios, of the columns with different boundary conditions. The numerical results reveal some interesting phenomena of thermal postbuckling behavior of columns.

Refined Fredkin gate assisted by cross-Kerr nonlinearity

Resource-efficient quantum information processing is equal to the minimal cost of the quantum resources required by quantum logic gates to a certain extent. In this paper, we propose a refined scheme for setting up a polarized Fredkin gate assisted by weak cross-Kerr nonlinearity, X-homodyne detectors, and some linear optical elements. The realization of the Fredkin gate is definite and has a highly successful probability of being close to the unit, which is feasible with the current technology. Moreover, in contrast to the Fredkin gates that have been proposed, the scheme has the advantages of requiring less quantum resource without auxiliary photons, comparatively simplified circuits, lower requirements on the interaction strength, and robustness against photon loss, thus it can be used for scalable quantum computation.