Nonlinear Resistance Research Articles

An experimental validation of a nonlinear acoustic resistance model for an acoustically compact area contraction with steady mean flow.

In a previously published paper, a model for the nonlinear acoustic response of an area contraction including bias flow was presented. The model's prediction for the zero-driving resistance grew progressively worse as the steady-flow Mach number increased. This trend suggests that the forward loss coefficients should depend on the steady Mach number. This letter provides an empirical fitting of this Mach number dependence, along with additional validation data for the model. These additional validation data corroborate the model's prediction that the nonlinear impedance is frequency independent. This letter additionally provides an experimental methodology for determining the characteristic length with sample results.

Data-Driven Reduced-Order Modeling of Convective Heat Transfer in Porous Media

This work presents a data-driven Reduced-Order Model (ROM) for parametric convective heat transfer problems in porous media. The intrusive Proper Orthogonal Decomposition aided Reduced-Basis (POD-RB) technique is employed to reduce the porous medium formulation of the incompressible Reynolds-Averaged Navier–Stokes (RANS) equations coupled with heat transfer. Instead of resolving the exact flow configuration with high fidelity, the porous medium formulation solves a homogenized flow in which the fluid-structure interactions are captured via volumetric flow resistances with nonlinear, semi-empirical friction correlations. A supremizer approach is implemented for the stabilization of the reduced fluid dynamics equations. The reduced nonlinear flow resistances are treated using the Discrete Empirical Interpolation Method (DEIM), while the turbulent eddy viscosity and diffusivity are approximated by adopting a Radial Basis Function (RBF) interpolation-based approach. The proposed method is tested using a 2D numerical model of the Molten Salt Fast Reactor (MSFR), which involves the simulation of both clean and porous medium regions in the same domain. For the steady-state example, five model parameters are considered to be uncertain: the magnitude of the pumping force, the external coolant temperature, the heat transfer coefficient, the thermal expansion coefficient, and the Prandtl number. For transient scenarios, on the other hand, the coastdown-time of the pump is the only uncertain parameter. The results indicate that the POD-RB-ROMs are suitable for the reduction of similar problems. The relative L2 errors are below 3.34% for every field of interest for all cases analyzed, while the speedup factors vary between 54 (transient) and 40,000 (steady-state).

Systematic investigation of the effect of layer thickness on the linear sensing characteristics of asymmetric structured CoFe/Rh/CoFe/Cu/CoFe fully epitaxial CIP-GMR based magnetic sensors

Giant magnetoresistance (GMR) devices known for their widespread application as magnetic field sensors face challenges owing to their nonlinear resistance response with the magnetic field. Here, we have developed CoFe(3 nm)/Rh(tRh nm)/CoFe(tmidCoFe nm)/bcc Cu(1.6 nm)/CoFe(ttopCoFe nm)/MgO(2 nm) based current in plane (CIP)-GMR devices and demonstrated linear MR curves with tunable characteristics. The MR ratio and saturating magnetic field were tunable between 3.9% and 23.5%, and 0.013 T and 1.5 T. The numerical simulation modeling confirmed biquadratic coupling between the bottom and middle CoFe layers through Rh and antiferromagnetic coupling between the middle and top CoFe layers through a Cu spacer, providing the linear MR. The fine-tuning of thicknesses of the middle and top CoFe layers provides supplementary routes for optimizing the sensitivity and operation field range of the CIP-GMR devices to specific magnetic sensor applications in the low and medium magnetic field range. The above results demonstrate that CIP-GMR devices with the asymmetric structure demonstrated in this study are promising for the next generation linear magnetic sensors.

A Unified View of Nonlinear Resistance Formulas for Seepage Flow in Coarse Granular Media

There are many studies on the nonlinear relationship between seepage velocity and hydraulic gradient in coarse granular materials, using different approaches and variables to define the resistance formula applicable to that type of granular media. On the basis of an analysis of the existing formulations developed in different studies, we propose an approach for comparing the results obtained by some of the most important studies on state-of-the-art seepage flow in coarse granular media.

Electrical resistance heating distribution on three dimensional Jeffrey radiating nanofluid flow past stretching surface

This study emphasis on the upshots of non-linear radiation and electrical resistance heating on a three dimensional Jeffrey dissipating nanoflow in view of convective surface conditions. The initial set of nonlinear dimensional boundary layer equation are transformed into a system of ordinary differential equations with suitable similarity variables and then This study emphasis on the upshots of non-linear radiation and electrical resistance heating on a three dimensional Jeffrey dissipating nanoflow in view of convective surface conditions. The initial set of nonlinear dimensional boundary layer equation are transformed into a system of ordinary differential equations with suitable similarity variables and then solved by shooting method using Mathematica software. For various representative quantities, the behavior of the momentum, energy and species diffusion along with engineering quantities near the surface are figured for different estimations of the fluid properties. The examination of present outcomes has been made with the existing work which is good agreed. This study helps in understanding the heat transfer rate is predominant in the non-linear radiation compared to linear radiation. Jeffrey fluid model has the capacity of describing the stress relaxation property, which usually viscous fluid lags and this is exhibited clearly in the study. Shear stress descends as the fluid pertinent parameter ascends.

Modeling the charging process of a coil by an HTS dynamo-type flux pump

The high-T c superconducting (HTS) dynamo exploits the nonlinear resistivity of an HTS tape to generate a DC voltage when subjected to a varying magnetic field. This leads to the so-called flux pumping phenomenon and enables the injection of DC current into a superconducting coil connected to the dynamo without current leads. In this work, the process of charging a coil by an HTS dynamo is examined in detail using two numerical models: the minimum electromagnetic entropy production and the segregated -formulation finite element model. The numerical results are compared with an analytical method for various airgaps and frequencies. Firstly, the I–V curves of the modeled HTS dynamo are calculated to obtain the open-circuit voltage, short-circuit current and internal resistance. Afterward, the process of charging a coil by the dynamo including the charging current curve and its dynamic behavior are investigated. The results obtained by the two models show excellent quantitative and qualitative agreement with each other and with the analytical method. Although the general charging process of the coil can be obtained from the I–V curve of the flux pump, the current ripples within a cycle of dynamo rotation, which can cause ripple AC loss in the HTS dynamo, can only be captured via the presented models.

Buckling Stability Analysis for Piles in the Slope Foundation Based on Cusp Catastrophe Theory

The aim of this paper is to analyze the buckling stability problem for piles in the slope foundation based on cusp catastrophe theory. Formulation of critical buckling load of piles in the slope foundation is obtained. The influential factors of slope angle, distribution of landslide thrust behind the pile, pile-embedded ratio, pile constraints, pile-side friction, pile-side soil resistance, and pile socketed ratio upon buckling stability characteristic for piles in the slope foundation are examined. The results reveal that when pile diameter remains unchanged, critical buckling load increases with the increase of pile length when pile-embedded ratio reaches 60%. When pile length remains unchanged, critical buckling load increases with the increase of pile diameter. Critical buckling load with the assumption of nonlinear horizontal elastic resistance of pile-side soil in the paper is more close to the value based on horizontal elastic resistance of pile-side soil suggested in the code. When slope angle increases, decreased extent of buckling critical load for piles 30–60 m in length is more obvious than the piles which are 10–30 m in length. Strengthening of pile constraints and increase of pile-embedded ratio and socketed ratio are helpful to pile critical buckling load increase. The influential factors of pile-side friction and landslide thrust behind the pile upon pile critical buckling load are tiny and can be neglected.

Nonlinear Variable Resistor-Based FCL for Fault Ride-Through Performance Enhancement of DFIG-Based Wind Turbines

Fault ride-through (FRT) requirement is a matter of great concern for doubly fed induction generator (DFIG-) based wind turbines (WTs). This study presents a nonlinear variable resistor- (NVR-) based bridge-type fault current limiter (BFCL) to augment the FRT performance of DFIG-based WTs. First, the BFCL operation and nonlinear control design consideration of the proposed NVR-based BFCL are presented. Then, the NVR-BFCL performance is validated through simulation in PSCAD/EMTDC software. In addition, the NVR-based BFCL performance is compared with the fixed resistor- (FR-) based BFCL for a three-phase symmetrical short circuit fault at the grid side. Simulation results reveal that the NVR-based BFCL provides a smooth and effective FRT scheme and outperforms the FR-based BFCL.

Single and triple insulator Metal-Insulator-Metal diodes for infrared rectennas

Tunnel-barrier rectifiers comprising single and triple insulator configurations have been fabricated by atomic layer deposition (ALD) to investigate the insulator (Al2O3, Ta2O5, Nb2O5) layer quality and rectification performance for inclusion in rectenna arrays for infrared energy harvesting. ALD has provided superior control of nanometer film thickness (1–3 nm) as well as insulator film quality as tunneling has been found to be the dominant conduction mechanism for all fabricated devices. The key rectifier properties, such as asymmetry, non-linearity, responsivity and dynamic resistance have been assessed from current-voltage (I-V) measurements. The Au/Al2O3/Ti diode exhibits zero bias responsivity of −0.6 A/W, showing that it can be used for energy harvesting applications without the aid of external bias. The effect of resonant tunneling on rectification performance of triple insulator non-cascaded (Ta2O5/Nb2O5/Al2O3) and cascaded (Nb2O5/Ta2O5/Al2O3) rectifiers has been observed from experimental I-V characteristics and substantiated by theoretical simulations. Superior low-voltage asymmetry (6 at 0.1 V) and responsivity (4.3 A/W at 0.35 V) for triple insulator MI3M rectifiers have been observed. The resonant tunneling does not provide enhanced rectification at low bias as previously reported, rather it has much smaller effect. The latter indicates that dissimilar metal electrodes rectifier configurations are more promising for inclusion in optical rectenna.

Analysis of the stressed-strained state of the foundation-shell at interaction with the elastic-plastic medium

On the basis of modern numerical implementations of the finite element method the article presents the justification of the adequacy of the method of solving the problems of structures straining in their contact interaction with the elastic-plastic nonlinear soil medium.
 Compatible calculations of structures and nonlinear bases, which are described by modern mechanical and soil models within one problem is a significant technical problem.
 The solution of the assigned tasks is possible only within the framework of numerical methods, the most common of which is the finite element method (FEM). The construction of the computational finite element model raises many complex questions that require additional detailed study. In addition, the compliance with the state building norms and regulations is an important factor for further practical use.
 The use of numerical methods in the calculation of machines and structures, taking into account their interaction with the elastic-plastic medium is largely determined by the complexity or even impossibility of analytical calculation due to the complexity of structural schemes, heterogeneity of material features, uneven soil layers, implementation of step-by-step work execution technologies and so on.
 The combination of the latest achievements in the field of structural mechanics and soil mechanics is a promising direction for the development of effective approaches to building discrete models of space systems “structure-nonlinear base” for solving applied problems.
 The use of the developed method allows to significantly specify the structures stress state interacting with the soil base, and to significantly specify the impact on the calculated level of the base bearing capacity. Only the simultaneous consideration of the nonlinear resistance of the soil base together with the plasticity and the structure destruction in the numerical simulation of the foundation-shell load provided good agreement with the natural experiment data as to the type of the boundary state and the bearing capacity level.

A modelling approach to describe the DC current-voltage behaviour of low-voltage zinc oxide varistors

Zinc oxide varistors are among the most important surge arresters. The current-voltage (I–V) behaviour of these devices can be approximated by a model of electrical networks of grain boundaries arranged in 3D space, where nonlinear resistors mimic the effective grain boundary behaviour of the varistor microstructure. A simplified version of the network model, namely parallel circuits of chains of serially connected resistors of different length (path model), is derived from a fully 3D model of the polycrystalline microstructure. A comparison of the path model with a complex resistor network based on the 3D model demonstrates that the network of highly nonlinear resistors has a very similar DC I–V characteristic as parallel paths of these resistors connected in series. The path model, whose parameters were adapted from microscopic I–V measurements, is able to reproduce the macroscopic I–V behaviour of real low-voltage zinc oxide varistors.

Experimental study and production model of multiscale stress sensitivity in tight oil reservoirs

ABSTRACT Stress sensitivity is an inevitable issue in the depletion exploitation of tight oil reservoirs, especially in the reformed multiscale region. Through a series of improved laboratory experiments, the stress sensitivity characteristics of multiscale media were thoroughly evaluated based on the primitive effective stress. Furthermore, based on the nonlinear seepage theory and equivalent seepage resistance method, a corresponding multiscale production prediction model of vertical wells in tight oil reservoirs with stress sensitivity established. The results showed that the decline in permeability of main fracture rock (12.86%) was more than twice that of the microfracture rock (5.25%), which was approximately four times that of the matrix rock (3.32%) in the selected pressure range. In addition, there was a fine power function relationship between permeability variation and effective stress in multiscale representative media. Compared with the actual daily production and cumulative production of the coring well, the production curve fitting of the proposed multiscale model was 91.25%, which was reliable to guide the development scheme design in the target block of tight oil reservoirs.

Resistivity of Cu, Ni and Sb in undercooled liquid state

With the help of non-contact measurement, electrical resistivity of Cu, Ni, Sb has been measured to study the influence of short range order on electrons scattering in the normal and undercooled liquid state. Till the maximum undercooling, linear resistivity-temperature dependence is obtained in Cu and Ni melts. Nonlinear resistivity behavior is obtained in undercooled liquid Sb till a maximum undercooling of about 60 degree. The increase in viscous flow activation energy reveals structure transition in Sb melts. A drop in resistivity of Cu melts is obtained accompanying the recalescence. The abrupt jump in resistivity of Sb reveals the rapid growth of Peierls distortion during rapid solidification process.

Modeling of Gapless MOSA at Low Current Region Considering Harmonic Content of Operating Voltage

A surge arrester is modeled as a simplified electrical circuit in power frequency applied voltage that consists of a capacitance branch in parallel with a nonlinear resistor. Under applied harmonic voltage, the obtained resistive current of the simplified model exhibits some deficiency, especially in its harmonic contents. This paper presents a harmonic model for metal-oxide surge arresters that can be utilized to simulate their performances under applied harmonic voltage. It has three parallel RC branches to simulate fundamental, third and fifth harmonics contents of total leakage current. Proposed and conventional models have been simulated under different applied harmonic voltages to show the capability of the proposed model. Also, real voltage and leakage current signals, which have been measured experimentally from a 20 kV metal-oxide surge arrester, have been compared with simulation results. Results show that the proposed model can simulate the performance of metal-oxide surge arresters more accurately than the conventional ones under applied harmonic voltages.

Electromagnetic and Thermal Analysis of a ZnO Element of Transmission‐Line Arrester for a Lightning Surge Current

The voltage generated across a zinc‐oxide (ZnO) element, in which a lightning impulse current flows, has been computed with the finite‐difference time‐domain (FDTD) method. Also, the distribution of temperature in the ZnO element has been computed on the basis of FDTD‐computed conduction current densities with a discretized heat equation. The ZnO element having a thickness of 37 mm and a diameter of 34 mm is represented with many 1 mm × 1 mm × 1 mm cubic cells, each of which has a nonlinear resistivity in each of the x, y, and z directions dependent on the electric field in each direction and the temperature in each cell. Waveforms of voltage appearing across the ZnO element and the temperature on the side surface of the ZnO element computed for a short lightning impulse current having a magnitude of 66 kA agree reasonably well with the corresponding measured ones. © 2021 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.

Superconducting Power Filter for Aircraft Electric DC Grids

A new device, referred to as Superconducting Power Filter (ScPF), is introduced to improve the stability of aircraft electric DC grids. This device is made of a non-inductive superconducting coil connected in series with a conventional RLC filter. The superconducting coil behaves as a nonlinear current-dependent resistance. By design, the superconductor does not undergo a full transition to the normal-resistive state and remains in the current-sharing regime. Thus, a quick response and recovery of the superconductor to transients can be achieved. In the present work, the thermo-electric model of the device incorporates a refined description of the transition from the superconducting state to the normal-resistive state of the superconductor. To check the feasibility of passive stabilization of embedded DC grids using ScPF, different widths and lengths of commercially available 2 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">nd</sup> generation High Temperature Superconducting (2G HTS) tapes were considered. We chose a case study simulating an equivalent circuit of a More Electric Aircraft (MEA) with an EPS-A3 architecture. For this particular case study, it is shown that the stability limit of the DC grid can be significantly increased, while preserving the reliability (no quench) and low cost (only a few meters of superconducting tape) of the ScPF.

Non-linear thermal resistance model for the simulation of high power GaN-based devices

We report on the modeling of self-heating in GaN-based devices. While a constant thermal resistance is able to account for the self-heating effects at low power, the decrease of the thermal conductance of semiconductors when the lattice temperature increases, makes necessary the use of temperature dependent thermal resistance models. Moreover, in order to correctly account for the steep increase of the thermal resistance of GaN devices at high temperature, where commonly used models fail, we propose a non-linear model which, included in an electro-thermal Monte Carlo simulator, is able to reproduce the strongly non-linear behavior of the thermal resistance observed in experiments at high DC power levels. The accuracy of the proposed non-linear thermal resistance model has been confirmed by means of the comparison with pulsed and DC measurements made in devices specifically fabricated on doped GaN, able to reach DC power levels above 150 W mm−1 at biases below 30 V.

Serum myokine levels after linear and flexible non-linear periodized resistance training in overweight sedentary women

ABSTRACT This study compared the capacity of linear-(LP) and non-linear periodized (NLP) resistance training to improve select myokines and metabolic parameters in overweight sedentary women. An additional purpose was to compare these variables between the overweight and lean women. Fitness- and age-matched overweight women between 28 and 43 years old were randomly allocated to LP (body fat [BF]% = 38.7 ± 2.6, n = 10), NLP (BF% = 39.3 ± 2.4, n = 9) and control (BF% = 39.8 ± 2.6, n = 9) groups. Lean women (BF% = 29.1 ± 2.3, n = 16) matched for age and fitness were also included for baseline comparison. Resistance training programmes (12 weeks, 3 d.wk−1, 9 exercises, 60–90% of 1-repetition maximum [1RM]) were performed with different periodization schemes. Glucose, insulin, interleukin (IL)−7, IL-15, and insulin-like growth factor (IGF)−1 levels were measured at baseline and after training. Overweight subjects had significantly lower IL-15, IGF-1 and higher insulin, glucose, and insulin resistance (homeostasis model assessment, HOMA-IR) than lean subjects at baseline (all, P < .05). IL-15 and VO2max increased significantly after NLP compared with CON, which was accompanied by a significant decrease in HOMA-IR (all, P < .03). Muscular endurance improved significantly in both models after training compared to CON (all, P < .01), but it increased more in NLP than in LP (P = .01). Both training protocols were equally effective at reducing BF% and increasing IGF-1, IL-7, muscle mass and bench press 1RM (P < .01). It appears that LP and NLP are both effective strategies for improving health markers in overweight women, but LP is not as effective as NLP to improve IL-15, HOMA-IR and aerobic capacity. Highlights Overweight women had a significantly lower IL-15 and IGF-1 compared to lean encounters, but no significant difference was noted for maximal strength, aerobic capacity, muscle mass, IL-7 and neutrophil/lymphocyte ratio. Twelve weeks of either linear or flexible non-linear periodized resistance training resulted in reduction in BF% and neutrophil/lymphocyte ratio, and increased IGF-1, IL-7, muscle mass and bench press 1RM, with no difference between the two training protocols. Linear protocol is not as effective as non-linear protocol to improve IL-15, HOMA-IR and aerobic capacity.

Study on vibration response of submerged floating tunnel considering vehicle eccentric load

The submerged floating tunnel (SFT) is a novel traffic structure for crossing long channels and deep waterways. The moving vehicles within the SFT have a remarkable influence on structural vibration response. To analyze the eccentric load effect of vehicles in the SFT, the structure is simplified as a spatial beam on elastic foundation, while the vehicle is simulated as a seven-DOF model with three dimensions. Using the Morison equation to express the effect of nonlinear fluid resistance, the vehicle-tunnel coupling vibration equations under the action of a motorcade running on one lane of the roadway are derived using the Hamilton Principle. Then, with the help of the mode superposition method and the fourth-order Runge–Kutta method, the solution for the equation is obtained. The accuracy of the proposed theoretical derivation and corresponding programming are verified by the finite element method. Based on the analysis, the SFT with a total span of 1000 m is selected as the research object to explore the spatial behavior of the SFT under vehicle-tunnel coupling vibration. The results show that the vertical displacement peak appears at the quarter-span of the tube, whereas the peaks of horizontal displacement and torsional angle appear at the mid-span under the eccentric load of a motorcade. The contribution of high order modes on the structural displacement should be considered. Moreover, the form of the motorcade affects the vertical displacement and torsional angle of the tube, and with the change of motorcade layout and vehicle speed, the resonance effect and vibration elimination effect will appear in the vehicle-tunnel coupling vibration system. Furthermore, the design parameters of the cable have a significant effect on the deformation resistance of the tube, therefore the selection and layout of the cable should take both the anchoring stiffness and material cost into account. For controlling the eccentric load effect, the inclined angle and installation angle of the cable are recommended to be 60° and 75°, respectively.

Analysis and Simulation of Ferroresonance Mechanism of Potential Transformer Based on Harmonic Balance Method

In power systems with voltage levels of 66kV and below, the bus potential transformer (PT) burnout accidents frequently occur. Based on the harmonic balance method, this paper analyzes the ferromagnetic resonance mechanism, and analyzes the fault waveform recorded by the fault recording system in the 66kV substation, and obtains the possible cause of the accident. The PSCAD/EMTDC software was used to build the electromagnetic transient model, and the PT burnout process was restored. It is concluded that the main cause of the accident is the ferromagnetic resonance overvoltage caused by the saturation of the PT iron core. Three solutions are also proposed, the PT primary side neutral point ground by nonlinear resistance, open triangle of PT short-time access a little resistance, and PT with better excitation characteristics are selected. The feasibility of the solutions is verified by simulation.