Lumped Model Research Articles

Operational transfer path analysis with regularized total least-squares method

Operational transfer path analysis (OTPA) uses only operational responses to characterize the paths, so it is efficient and widely used in various engineering fields. However, the operational responses are inevitably contaminated by errors, which seriously reduce the accuracy of OTPA. To reduce the influence of errors and improve the accuracy of OTPA, a Tikhonov regularized total least-squares method (RTLSM) which is based on the Tikhonov regularized least-squares method (RLSM) is used to estimate the transmissibility matrix, and then the individual contributions are calculated. The total least-squares method takes into account not only the influence of the errors in the target point responses but also the influence of the errors in the indicator point responses. Tikhonov regularization is introduced to regularize the total least-squares method to improve the ill-conditioning of the indicator point response matrix in the process of estimating the transmissibility matrix. An OTPA simulation on a lumped mass model and an OTPA experiment on an aluminum plate are studied to test the performance of the RLSM and RTLSM. Both simulation and experimental results show that the RTLSM is better than the RLSM in OTPA, and improved the accuracy of OTPA effectively.

Implementation of a solar aided refrigration unit for refrigerated trucks employing photovoltaic generators

Solar aided refrigeration system can represent a simple and feasible solution for improving the sustainability of refrigerated transport. The paper presents the design and the performance of an electric powered refrigeration unit integrated with photovoltaic generators installed on top of the refrigerated box of a light truck. The system prototype has been tested in stationary conditions, demonstrating the capacity of the solar system to impact significantly in the net energy balance of the refrigeration unit. The system performance during an urban multi-drop delivery scenario and hot climatic condition are then assessed using a dynamic lumped model simulation. Simulations are also used to discuss the sensitivity to the battery pack capacity size and the shading conditions caused by the urban canyon effects are investigated. Results demonstrate that, on a yearly base at Athens climatic conditions, the solar panels can provide from 65% to 112% of the energy consumed by the cooling unit, depending on the time spent by the truck under direct sunlight. Larger batteries are justified only when long periods of direct light are expected.

Coherence resonance in paleoclimatic modeling

Through a unified mathematical framework, the stochastic behavior of three celebrated low-order lumped models, previously proposed for paleoclimate simulations, is considered. Due to the coherence resonance mechanism, the feedbacks between noise and the dynamical system reproduce the hallmark of the Pleistocene climate, i.e. the 100 ky pulsation, in a range of the model parameters that is unexpectedly wide and far from the original modeling setting. In this way, the issue of arbitrary coefficient tuning of lumped approaches in paleoclimatology can be partially bypassed. A stability analysis of the considered dynamical systems allowed the parameter space to be exploited, in order to separate the deterministic-dominated region from the stochastic-dominated region. Noise intensity is varied and the closeness in the parameter space to Hopf bifurcations and/or bistable conditions is investigated in order to understand what conditions make the models prone to coherence resonance with a 100-ky pulsation, with or without the forcing induced by varying astronomical parameters.

Hybrid Battery Thermal Management System with NiTi SMA and Phase Change Material (PCM) for Li-ion Batteries

Poor heat dissipation and thermal runaway are most common in batteries subjected to fast charge or discharge and forced to work in hot or subzero ambient temperatures. For the safe operation of lithium-ion batteries throughout their lifecycle, a reliable battery thermal management system (BTMS) is required. A novel hybrid BTMS with a nickel-titanium (NiTi) shape memory alloy (SMA) actuated smart wire and phase change material (PCM) with expanded graphite (EG) is proposed in this study. A lumped electrochemical-thermal battery model is developed to analyze the efficiency of the proposed hybrid BTMS. The multiphysics BTMS is investigated by discharging at various electrical currents in both off-modes (inactivated SMA) and on-modes (activated SMA). Under on-mode BTMS operation, temperature elevation is reduced by 4.63 °C and 6.102 °C during 3 C and 5 C discharge, respectively. The proposed hybrid BTMS can be considered a competitive alternative for use in electrical vehicles due to its smart, compact, safe, and efficient performance in both cold and hot environments.

An extended LuGre-brush tyre model for large camber angles and turning speeds

ABSTRACT This paper presents a novel tyre model which combines the LuGre formulation with the exact brush theory recently developed by the authors, and which accounts for large camber angles and turning speeds. Closed-form solutions for the frictional state at the tyre-road interface are provided for the case of constant slip inputs, considering rectangular and elliptical contact patches. The steady-state tyre characteristics resulting from the proposed approach are compared to those obtained by employing the standard formulation of the LuGre-brush tyre models and the exact brush theory for large camber angles. Then, to cope with the general situation of time-varying slips and spins, two approximated lumped models are developed that describe the aggregate dynamics of the tyre forces and moment. In particular, it is found that the transient evolution of the tangential forces may be approximated by a system of two coupled ordinary differential equations (ODEs), whilst the dynamics of the self-aligning moment may be described by combining two systems of two coupled ODEs. Given its stability properties and ease of implementation, the lumped one may be effectively employed for vehicle state estimation and control purposes.

Analysis of reaction path and different lumped kinetic models for asphaltene hydrocracking

The product distribution of asphaltenes hydrocracking was studied in an autoclave with decalin as the liquid-phase system at different reaction temperatures and times to elucidate the relevant reaction mechanism. The results showed that the reaction products might be reversely condensed to generate secondary asphaltenes, resulting in a trend of first increasing and then decreasing the yields of some products at 420 °C. The significant yield increase of gas and gasoline at 420 °C might be due to the cracking of saturated and aromatic fractions to form light fractions. The conclusion was drawn the reaction behavior of asphaltenes hydrocracking under the research conditions followed the first-order reversible reaction kinetics by the reaction kinetic analysis, which further supported the inference that some products could recondense to form secondary asphaltenes. The four-lumped, five-lumped, and six-lumped models were constructed to study in depth the reaction behavior of asphaltene hydrocracking in the current system, and the results showed that the more similar the structure and composition of the reaction products to asphaltenes, the faster the reaction rate of their condensation to asphaltenes. Furthermore, the higher the temperature was more favorable to improve the selectivity and yield of transportation fuel diesel under the temperature of 380 °C-420 °C by the analysis of the ratio of rate constant. Although the applicability of lumped model was not positively correlated with the number of lumps, it is concluded that the six lumped model was the best model among the three models from the combined analysis of the applicability and the richness of the reaction information of the model.

A Novel Capacitive Microwave Power Sensor Based on Double MEMS Cantilever Beams

In order to improve the sensitivity characteristic and the fabrication reliability, a novel capacitive power sensor based on double MEMS cantilever beams is proposed in this work. It is designed and fabricated using GaAs MMIC process and MEMS technology. A lumped circuit model is built to study the microwave characteristic of this capacitive microwave power sensor. The influence of impedance value and electric length of the coplanar waveguide on the microwave performance of the double MEMS beams are studied. The microwave characteristic of both ports are measured. The return loss of port A is from −11.5dB to −14.6dB, and the return loss of port B is from −12.1dB to −14.3dB at 8-12GHz. The insertion loss of port A is from −3.6 dB to −2.8dB, and the insertion loss of port B is from −3.7 dB to −2.9dB at 8-12GHz. The measured results show that this capacitive power sensor has a good microwave characteristic. The measured sensitivity of this capacitive microwave power sensor is about 51.6 fF/W @10 GHz, and the theoretical sensitivity is 55.97 fF/W. The relative error is 7.8%. Compared with the capacitive microwave power detection system based on single cantilever beam, the sensitivity characteristics have been greatly improved. It is valuable to realize the multiple beams detection technology and enable further interesting possibilities in the field of microwave power detection.

Disturbance observer-Based control for microchannel cooling system

Disturbance observer-based systematic control is proposed for microchannel cooling systems experiencing unanticipated heat load. The objective is to apply an extended Kalman filter as the observer for a nonlinear system to estimate external disturbance and dynamic states and use active control to maintain the system parameters at desired values. Disturbance observer is designed based on one-dimensional lumped model. The robustness and performance of the observer are validated with experimental results, which show a maximum of 3% inaccuracy at steady states under various heat loads and mass flow rates. The estimated value of unanticipated evaporator heat load with the observer acts as the feedforward control signal for pump speed while the feedback control using the signal of evaporator wall temperature could further adjust the input values to achieve desired output. Results show that a system with a controller and disturbance observer can ensure the evaporator wall temperature and high heat performance under large variations of heat loads. System with disturbance observer-based control shows quick response, strong robustness, and stable operation.

“Thermal-dissolution based carbon enrichment” treatment of biomass: Modeling and kinetic study via combined lumped reaction model and machine learning algorithm

The homogenizing pyrolytic method denoted as the “Thermal-dissolution based carbon enrichment (TDCE)” was effective in converting different biomasses into value-added carbon products. However, the product yields from the TDCE process varied greatly despite the biomasses undergoing similar reactions. Consequently, a generalized kinetic study is essential in determining the different kinetic parameters of each biomass. In this study, the lumped reaction model was coupled with machine learning algorithm (ML-LRM) for the general acquisition of these kinetic parameters. 304 yield data of cellulose under different conditions were accurately predicted by the machine learning algorithm and were further utilized for subsequent kinetic modeling. In addition, the derived conversion pathways were quite reliable, as the one from predicted data was similar to that calculated from experimental data (R2 = 0.95) under experimental conditions, but with higher accuracy (R2 > 0.99). Moreover, a novel five-stage reaction mechanism was proposed to quantitatively and qualitatively describe the TDCE process based on the kinetic studies and the pre-proposed reaction mechanism. Consequently, the ML-LRM method was proven to be effective in elucidating the main reactions at any temperature throughout the TDCE treatment and can therefore provide guidance towards directed regulation and practical application of said products.

Design of Periodic End-Coupled Leaky-Wave Antenna With Asymmetrically Loading Unit

In this letter, a periodic end-coupled leaky-wave antenna is designed based on an asymmetrically loading unit. A simple balancing condition in the equivalent distributed circuit model is developed for the open stopband suppression by introducing a complex effective resonant frequency. The proposed balancing condition naturally satisfies both the frequency-balancing condition and Q-balancing condition in the lumped circuit model. Based on the derived formula, the physical parameters could be quantitatively determined. Subsequently, two typical periodic end-coupled leaky-wave antennas are designed, implemented, and verified experimentally. The measured reflection coefficient and the radiation results show that the open stopband at the broadside frequency is successfully suppressed.

Electromechanical Equivalent Circuit Model for Axisymmetric PMUTs With Elastic Boundary Conditions

Here we present an electromechanical lumped equivalent circuit model for the purpose of deriving the electrical input impedance and response of air-coupled axisymmetric polymer-based piezoelectric micromachined ultrasonic transducers (pMUT). In particular, this study presents the derivation and validation of polyvinylidene fluoride-co-trifluoroethylene P(VDF-TrFE) unimorph pMUT equivalent circuit models operating in the fundamental axisymmetric mode. Derivation of the equivalent circuit model is performed via the application of the Rayleigh-Ritz energy method towards determining effective pMUT radii due to an elastic boundary condition. The results of the model are shown to be in good agreement with finite element (FEM) simulations and experimental measurements of discrete pMUTs in air. In particular, the model is able to accurately predict the effective expansion in the pMUT radius due to the elastic boundary. The electromechanical model may also be used as a tool to characterize and/or evaluate the behavior of pMUT designs for ultrasound transducer applications.[2021–0156]

Global optimization of excitation directions for scavenging energy based on a cross-jointed L-shape multidirectional piezoelectric energy harvester

Energy harvesting technology can collect energy from environmental vibrations, but it is still challenging because the vibration from an environment is random and the directions vary. In this study, a novel cross-coupled L-shaped vibration piezoelectric energy harvester (CL-VPEH) was proposed to collect energy from different environmental vibration directions. This CL-VPEH consists of a vertical beam and a horizontal beam joint crosswise with two laminated piezoelectric layers. Finite element analysis was performed to study the voltage output and resonant frequency. A simplified lumped mass model of CL-VPEH under excitation from an arbitrary direction was built to describe its working principle and multi-directional energy-harvesting ability. The experimental results demonstrate that the CL-VPEH shows good agreement with the numerical and analytical solutions. The experimental results validate the CL-VPEH’s multidirectional energy harvesting ability. Using the lumped mass model, the performance of the CL-VPEH under every single-direction excitation is investigated. A weak power output area is found with a frequency range of 10 Hz − 25 Hz, which should be avoided in future applications of this kind of multiple-directional excitation energy harvesting.

Lumped spring model parameters of RC frame elements for seismic performance assessment

AbstractThis study presents lumped spring model parameters for nonlinear seismic analysis of reinforced concrete (RC) frame structures. The modified Ibarra‐Medina‐Krawinkler (M‐IMK) hysteresis model is used as a lumped spring to simulate the inelastic behaviour of a RC frame element. The influence of loading protocols on the calibration of model parameters is investigated and compared with other hysteresis models, such as the original IMK and Bouc‐Wen‐Baber‐Noori (BWBN) models. Less dependent on the loading protocol used for model identification, the parameters of the modified IMK hysteresis model are calibrated to model a database of 383 rectangular RC columns. To simplify the calibration process, the model parameters that define the monotonic response are determined based on code and empirical equations, while the parameters that control the hysteretic degradations are calibrated against the experimental results. The calibrated model parameters are used to develop regression equations for the model parameters based on physical variables, such as loading, dimensions, and material properties. It is found that the model parameters obtained from the experimental calibration and regression equations generate similar hysteresis curves. The performance of the lumped spring model to nonlinear time history analysis of RC structures subjected to earthquakes is also evaluated through a series of pseudo‐dynamic hybrid simulations.

A volume-averaged plasma model for heaterless C12A7 electride hollow cathodes

A volume-averaged hollow cathode plasma model is presented that serves as a preliminary design tool for orificed hollow cathodes. The plasma discharge volume is subdivided into two computational domains with separate sub-models that are used to determine the emitter and orifice region plasma parameters. The plasma model is coupled with a lumped node thermal model that uses power inputs from the plasma model to estimate the temperature distribution of the hollow cathode. The model has been implemented for conventional cylindrical emitter geometries and for novel disc-shaped emitters. A lanthanum hexaboride (LaB6) hollow cathode has been used to validate the cylindrical model results and shows good agreement with well-known trends of hollow cathodes and published model data, while a calcium aluminate electride (C12A7:e-) hollow cathode developed at Technische Universität Dresden (TUD) served as the basis for the disc configuration. The model results of the disc configuration are presented and discussed to identify trends and optimization potential for hollow cathodes using C12A7:e- emitters. The model results in combination with thermal measurements of the TUD hollow cathode indicate a work function of C12A7:e- in a hollow cathode plasma below 2 eV.

A lumped plasticity model for corrosion-damaged reinforced concrete columns

Chloride-induced corrosion is one of the most important causes of the strength degradation of reinforced concrete (RC) bridges. As the piers of RC bridges are important elements for sustaining lateral loads, corrosion of pier columns may lead to significant degradation of the structure. It is thus necessary to have an appropriate evaluation technique to assess the effect of corrosion on the behaviour of RC columns. Numerical modelling approaches based on a concentrated plastic hinge can predict structural behaviour rapidly and with acceptable accuracy, and are highly regarded by engineers. In this study, a numerical approach was conducted to develop an empirical lumped plasticity model (LPM) for corroded RC column elements. In this study, 13 440 RC column specimens, including corroded and uncorroded columns of both rectangular and circular cross-section, were analysed under monotonic and cyclic loading. The LPM was extracted based on regression of the results of cyclic and monotonic analyses. The calibrated model, valid for corroded and uncorroded columns, was assessed using experimental results and numerical models with data out of the range of those used in the parametric study and was found to have high accuracy. The newly developed plastic hinge model can be used to model and analyse corroded bridge columns rapidly. The results are appropriate for use in further assessments such as fragility or rehabilitation analyses.

Self-discharge estimation of supercapacitor modules at different ventilation levels

In most applications, a series connection of multiple supercapacitors is required to construct a module due to the low operating voltage of a single supercapacitor. Each supercapacitor in the module has a different temperature value because of inconsistent temperature distribution and different heat exchange rates. On the other hand, temperature affects the self-discharge process of a supercapacitor. Hence, the difference in the temperatures of supercapacitors leads to different self-discharge characteristics. In this study, the effect of temperature distribution on the self-discharge of a supercapacitor module consisting of eight electric double-layer capacitors (EDLC) is investigated. For this purpose, a lumped thermal model (LTM) is considered for the EDLC module. The parameters of the LTM are extracted from the experimental data. The measured (observed) core temperature of each EDLC cell from the LTM is substituted in the TAFEL equation and the self-discharge behavior of each cell is achieved according to its temperature. The total self-discharge of the EDLC module is obtained from the summation of all self-discharge voltage trajectories in the cells. In order to show the effectiveness of the proposed approach for analyzing the self-discharge phenomenon in the EDLC module, three different possible ventilation levels are considered.

Seismic Fragility and Risk Assessment of a Nuclear Power Plant Containment Building for Seismic Input Based on the Conditional Spectrum

A procedure for the seismic fragility assessment of nuclear power plants by applying ground motions compatible with the conditional probability distribution of a conditional spectrum (CS) is presented with a case study of a containment building. Three CSs were constructed using different control frequencies to investigate the influence of the control frequency. Horizontal component-to-component directional variability was introduced by randomly rotating the horizontal axes of the recorded ground motions. Nonlinear lumped mass stick models were constructed using variables distributed by Latin hypercube sampling to model the uncertainty. An incremental dynamic analysis was performed, and seismic fragility curves were calculated. In addition, a seismic input based on a uniform hazard response spectrum (UHRS) was applied to the seismic fragility assessment for comparison. By selecting a control frequency dominating the seismic response, the CS-based seismic input produces an enhanced ‘high confidence of low probability of failure’ capacity and lower seismic risk than the UHRS-based seismic input.

Hybrid modeling approach for the tether of an airborne wind energy system

The design of controllers for the automatic operation of airborne vehicles is challenging. Especially in the emerging research field of airborne wind energy, where tethered aircraft convert energy from wind at higher altitudes into electricity, the development of robust and safe control systems will be a critical success factor. Typically, these systems consist of one or more controlled aircraft, a ground station, and one or more tethers that transfer aerodynamic forces acting on the wings to the ground. To understand these systems and control them for real-time simulations, suitable tether models must extend the classical flight mechanical models. In this paper, a hybrid approach is presented, combining an elastic spring model with a catenary model of the tether. In particular, for real-time simulations in a model-in-the-loop environment where a static modeling approach is sufficient, this hybrid model is intended to provide an alternative to the commonly used spring models. Furthermore, such a static tether model neglects high-frequency dynamic oscillations that can occur with dynamic lumped mass models. As consequence, the focus is on primary influences such as stiffness and sag due to external loads. The developed hybrid model is analyzed and compared with the spring model for a simulated tethered flight. It can be concluded that this hybrid static model, although subject to strong assumptions such as symmetrical tether sag, represents the tether more accurately. For example, it allows a more precise design of the flight controller before conducting any flight tests. This model can be used as a reasonable alternative to the simple spring model whenever a static modeling approach of the tether is adequate.

Multiphysics modeling of proton exchange membrane water electrolysis: From steady to dynamic behavior

AbstractProton exchange membrane water electrolysis (PEMWE) is currently developed for the design of mature industrial‐scale manufactures with commercialization. It needs reducing hydrogen production cost by lowering material cost and increasing operating current density. In engineering perspectives, the study of electrolytic performance during dynamic operation is crucial for PEMWE system management and process control. However, there is few multiphysics models of PEMWE considering transient behavior. The one‐dimensional (1D) comprehensive dynamic multiphysics model allows to explore temporal transport phenomena in the PEMWE, and predict electrolytic performance. The 1D model is endorsed by the spatially lumped model from the literature. Changing values of structural and physical properties of porous transport layers (PTLs) and catalyst layers (CLs) allows the observation of their effects on the electrolytic performance and transport phenomena in two‐phase flow regime. It suggests that the appropriate PTL properties, and CL fabrication method can lower the cost and remain high electrolytic performance.

Field‐circuit coupled analysis of an electromagnetic launcher sliding contact

Under the extreme working conditions of high‐speed and high‐current sliding electrical contact, if an electromagnetic launcher's rails and armature are not in good contact, transition ablation may occur, which will reduce the life of the rails. Though the transition state can be evaluated based on the muzzle voltage waveform, the conventional lumped circuit model does not take into account the strong coupling relationship of the multi‐physical fields in the launching process—in particular, there is a lack of analysis of the melt wear of the armature. To overcome this challenge, a novel approach based on the field‐circuit coupled method is proposed in this study to analyze the performance of armature‐rail contact. First, the basic principle of the co‐simulation model was introduced. The circuit model, the electromagnetic field model, the temperature field model, and the armature‐rail contact force model were then built. Compared with the conventional circuit model, the field‐circuit coupled model presented in this paper can better analyze the transient changes of the contact performance and obtain more details of multi‐physical fields. Besides, the contact performance under different interference were compared through our proposed method. The method proposed in this study comprehensively considers the influence of the velocity skin effect, armature‐rail interference assembly, and the melt wear of the armature on the performance of armature‐rail contacts. The study can provide effective theoretical guidance for conducting performance analysis and designing the armature for an electromagnetic rail launcher. © 2022 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.