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The paper discusses the theory of critical strain energy levels for structures with lumped parameters. The theoretical assumptions and profs for common case are presented. The idea of external actions and strain energy field separation leads to the minimum strain energy principle. It has the self-stress of the structure physical sense. In the general case, a structure's extremal values of parameters are determined from an eigenvalue problem. The critical levels criterion means the self-stress state change. The strain energy consists of two parts: strain energy, which equilibrates the action work, and residual strain energy, which does not allow a deformable body to collapse. This allows for the total and residual strain energy to be calculated. The traditional problem formulation does not give us that option. The proposed theory is illustrated on a rod system, which explains the change in the selfstress state of the structure in a simple manner. The static matrix and stiffness matrix are obtained for the three-bar structure. The eigenvalue problem allows us to obtain the principal values of the nodal reactions and displacements of the structure. New formulations of structural design and structural analysis tasks are given. The results are compared with classical methods of solution. The formulations of weak link problems and progressive limit state problems are given. A structure's residual load capacity is evaluated by the residual strain energy. [ABSTRACT FROM AUTHOR]

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Variable stiffness link (VSL) manipulators are robotic arms that can adjust their link stiffness in real time to improve their adaptability and precision. They are particularly useful in industrial environments where safe collaboration with human workers is required. However, modeling and controlling these non-linear systems is a major challenge due to their complexity. This research paper presents a mathematical model for a 3DOF VSL manipulator, which is the first step towards optimizing performance, improving safety, and reducing costs. The accuracy and reliability of the model are demonstrated through verification experiments that strengthen confidence in its validity for engineering and scientific research. This study contributes to the understanding of the dynamics of VSL manipulators and provides insights for future advances in the use of such robots. By using the proposed model, the efficiency and precision of VSL manipulators can be improved while ensuring safe human–robot interaction in various industrial applications. [ABSTRACT FROM AUTHOR]

The purpose of this study is to evaluate both the temperature and the initial moisture content of the material in mathematical models of drying. For this, empirical lumped parameter models were fitted based on experimental data of moisture over time. Furthermore, a new semi‐empirical drying kinetics model was applied. This model was developed using the generalization of arbitrary order of the Lewis equation obtained through the Laplace transform. After performing the fit, the fractional order model for drying wheat seeds as a temperature function was generalized. Distributed parameter models were also fitted to evaluate the influence of initial moisture content on drying kinetics and to estimate the moisture profile along the position inside the seed. It was verified that the fractional order model presented statistical results similar to models with a higher number of constants, being used to generalize the kinetic drying model for the three wheat cultivars. Generalized models showed better fits for the 3 cultivars with first‐degree function, and the maximum global deviation was 10%, 15%, and 20% for the cultivars BRS–Atobá, BRS–Jacana, and BRS–Sanhaço, respectively. In addition, the distribution of moisture content inside the seed was verified by the distributed parameter model, which predicted the experimental data with an overall deviation of around 10%. [ABSTRACT FROM AUTHOR]

The main objective of the present work was to assess the temperature and the initial moisture content using models of lumped and distributed parameters, in the description of the drying kinetics in the thin layer of the new Brazilian black soybean cultivar. Lumped models (Page, Newton, Approximation of Diffusion, Hii, Law and Cloke, and Midilli) were fitted based on experimental moisture content data for drying experiments carried out in different temperatures. Fractional order model was also performed and it was generalized as a function of temperature. Distributed parameter models were also fitted to evaluate the influence of initial moisture content on drying kinetics, in addition to estimating the moisture profile along the position inside the black soybean seed. Results indicated that the best kinetic fitting of drying by the lumped parameter technique was obtained for models with a greater number of parameters. Practical applications: Results indicated that the best kinetic fitting of drying by the lumped parameter technique was obtained for models with a greater number of parameters. The generalized model showed with first degree function, and the maximum global deviation was 15%, and distributed parameters were predicted with a maximum overall deviation of 10%. This result portrays that the fractional order model can be applied to describe the continuous drying process. [ABSTRACT FROM AUTHOR]

Asymmetric thermal zones or even non-rectangular structures are common in residential buildings. These types of structures are not easy to model with specialized programs, and it is difficult to know the heat flows and the relationships between the different variables. This paper presents a methodology for modeling structures with multiple thermal zones using the graph theory arrangement. The methodology allows for generating a mathematical model using all the walls of each thermal zone. The modeling method uses the lumped parameter technique with a structure of two resistors and two capacitors for each thermal zone. The walls and internal surfaces of each zone define the thermal resistances, and the elements for the network structure are created by reducing resistances. The structure selected as a case study is similar to a residential apartment, which demonstrates the possibility of modeling complex and non-traditional structures. The accuracy of the generated mathematical model is verified by comparison with experimental data recorded in a scaled-down model. The reduced model is constructed using a 1:10 ratio with a real apartment. The proposed methodology is used to generate a graph arrangement adjusted to the case study, using the surfaces to build the mathematical model. The experimental data allowed to adjust the simulation results with errors in the range of 1.88% to 6.63% for different thermal zones. This methodology can be used to model different apartments, offices, or non-asymmetric structures and to analyze individual levels in buildings. [ABSTRACT FROM AUTHOR]

The generation of mathematical models for the analysis of buildings with multiple thermal zones is a large and complex task. Furthermore, the order and complexity of the dynamical model are increased by the number of included thermal zones. To overcome this problem, this paper presents an algorithm to define the mathematical model automatically, using the geometric and physics parameters as inputs. Additionally, the spatial position of each thermal zone must be recorded in an arrangement called a contact matrix. The algorithm for modeling systems with multiple thermal zones is the main contribution of this work. This algorithm is presented in pseudocode format and as an annex, an implementation in MATLAB software. One of the advantages of this methodology is that it allows us to work with parallelepipeds and not necessarily cubic thermal zones. The algorithm allows us to generate mathematical models with symbolic variables, starting from the knowledge of how many thermal zones compose the system and its geometric organization. This information must be organized in a matrix arrangement called a contact matrix. Different arrays of thermal zones were constructed with wooden boxes to verify the functionality of the models generated with the algorithm. Each case provided information that allowed us to adjust the mathematical models and their simulations, obtaining a range of errors between experimental and simulated temperatures from 2.08 to 5.6 , depending on the number of thermal zones studied. [ABSTRACT FROM AUTHOR]

Copyright of Przegląd Elektrotechniczny is the property of Przeglad Elektrotechniczny and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In this paper, we propose a transmission line model to represent three-phase untransposed transmission lines with vertical symmetry. Here, we decouple a transmission line into its propagation modes using Concordia's matrix, which is the proper orthogonal form of Clarke's matrix that has its columns normalised. Due to the usage of Concordia's matrix, the transmission line is decoupled into two coupled modes and one uncoupled mode. We represent the uncoupled mode by a single-phase transmission line, and the coupled modes by a two-phase transmission line without vertical symmetry. We compute voltages and currents for the single-phase transmission line using the classic Lumped Parameter Model. Voltages and currents in the two-phase transmission line are calculated using a cascade of coupled L circuits pairs. Modal voltages and currents are then transformed back to the phase domain. We compare the results obtained with the proposed model to those obtained with two well-known time domain models, the classic modal lumped parameter model and the lumped parameter model available in the Alternate Transients Program ATP. Results show that the proposed model agrees with time-domain models and has the advantage that is developed in the time domain without needing any inverse transformations. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this paper is to propose a new simplified numerical model, based on a very compact semi-empirical formulation, able to simulate the fluid dynamics behaviors of an electrohydraulic servovalve taking into account several effects due to valve geometry (e.g. flow leakage between spool and sleeve) and operating conditions (e.g. variable supply pressure or water hammer). Design/methodology/approach: The proposed model simulates the valve performance through a simplified representation, deriving from the linearized approach based on pressure and flow gains, but able to evaluate the mutual interaction between boundary conditions, pressure saturation and leak assessment. Its performance was evaluated comparing with other fluid dynamics numerical models (a detailed physics-based high-fidelity one and other simplified models available in the literature). Findings: Although still showing some limitations attributable to its simplified formulation, the proposed model overcomes several deficiencies typical of the most common fluid dynamic models available in the literature, describing the water hammer and the nonlinear dependence of the delivery differential pressure with the spool displacement. Originality/value: Although still based on a simplified formulation with reduced computational costs, the proposed model introduces a new nonlinear approach that, approximating with suitable precision the pressure-flow fluid dynamic characteristic of a servovalve, overcomes the shortcomings typical of such models. [ABSTRACT FROM AUTHOR]

The present work describes a lumped parameter approach for the filling analysis of engine lubrication systems. Filling analyses are typically carried out by means of multi-phase 3-D CFD models but, despite allowing detailed and reliable results, they require very demanding computational capabilities. Based on these premises, the authors present a modelling procedure to address the topic by means of a lumped parameter approach. By introducing a detailed modelling technique, the proposed method offers the possibility to reproduce not only the common and simple elements such as pipes and bends, but also permits the discretization of complex three-dimensional fluid domains. The proposed approach has been applied to the lubrication system of a heavy-duty V6 engine: since long stop intervals are planned during the engine lifetime, the filling time of the system plays a fundamental role. The analysis has been run with the obtained 0-D model, simulating at different lubricant temperature. The predictive capabilities of the numerical model are presented in terms of flow pattern and filling time of the circuit branches. The simulation has also been performed by means of a 3-D CFD model, providing the possibility of a result comparison: since this methodology is nowadays considered the state of the art for this kind of analyses, the results are taken as reference to evaluate the capabilities of the proposed 0-D approach. The comparative analysis concerns both the overall distribution of the lubricant over time, and the local phenomena. The differences in terms of computational effort are considered as well, to assess the approximation of the lumped parameter approach with respect to the complex but more accurate three-dimensional models. The results highlight the accuracy of the methodology on the estimation of the filling time. Moreover, the proposed procedure reveals great advantages in terms of computational effort. [ABSTRACT FROM AUTHOR]

The steady-state approaches traditionally used to assess the capacity of overhead transmission power lines are being progressively replaced by procedures that consider the real and extremely variable weather conditions that are present along the path of the line under analysis (Dynamic Thermal Rating). Dynamic Thermal Rating (DTR) does not just estimate the temperature of the conductor in the different spans of the line, but also some mechanical quantities like their tension and sag, in order to appreciate the limitations imposed by the constraint of the minimum ground clearance. Modern DTR procedures need, therefore, proper mechanical models of the lines, in order to assess what happens both in normal and fault conditions. This paper proposes a comparison between a Finite Element Method (FEM) and a novel lumped-parameter model implemented through the Modelica language. Different realistic scenarios have been considered, like gusts of wind and the presence of ice. The outcomes of the two dynamic models have been compared to identify a trade-off between the accuracy of results and the computational time, as well as the dependency on the number of lumped masses used to model the line. [ABSTRACT FROM AUTHOR]

Critical inlet pressure (CIP) is a key parameter for ensuring the long life and steady operation of aircraft piston pumps. In the past, this parameter was determined through experimental methods that had drawbacks such as a long duration and narrow application range. To identify an alternate approach that can be substituted for the traditional approach, a numerical model for determining the CIP that considers the dynamic effects of the transient period is proposed in this paper. First, a dynamic model of the pressure-controlled piston pump was established in the form of differential equations based on the lumped parameter method. Next, the fluid model for vapor cavitation and air aeration was derived using homogeneous mixture theory with consideration of the effects of compressibility of both liquid and gaseous phases. Simulation investigation highlighted how the shaft speed, inlet pressure, and transient time influence the fluid properties inside the piston chamber, and a method for determining the CIP both for steady and transient conditions is presented. Finally, tests were conducted on an aircraft piston pump in open-circuit applications for verifying the applicability of the proposed numerical model. [ABSTRACT FROM AUTHOR]

Short-time thermal transient identification method was successfully adopted to evaluate the winding thermal parameters of induction motors for industry applications. In this work, the modeling approach and the identification methodology are extended to the more sophisticated case of multiple three-phase machines. The generalized model takes into consideration the mutual heat exchange between the windings as well as the possible causes of temperature mismatch. A complete procedure to evaluate the parameters of the modified model is provided, supported by experimental validation on a 7.5 kW machine with two three-phase windings in contact at slot level. The method covers any type of multiple three-phase machines, whatever the thermal promiscuity of the winding sets: From deep coupling as the ones presented, to the case where only the end-turns are in contact, to the completely decoupled case. The proposed technique can be useful for the machine design and for real-time temperature monitoring during operation. [ABSTRACT FROM AUTHOR]

Copyright of Electronic Components & Materials is the property of Electronic Components & Materials and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Some specific application fields of electric motors, such as food and beverage applications, require highly demanding hygiene procedures that involve a highly aggressive environment for the motor, including frequent high pressure and high temperature washing with water or more aggressive detergents. Specific materials and protection features are used in motors to better withstand such environment; however, these have an impact on performance and lead to oversized machines. This paper describes some solutions and their impact on performance, with specific focus on the thermal properties of the analyzed machine. [ABSTRACT FROM AUTHOR]

An active air thrust bearing controlled by an Arduino board and digital valves is described. A numerical model for the complete system is developed to design the control and perform a sensitivity analysis based on geometric parameters such as the conductance of the valves. Model validation is based on experimental open-loop and closed-loop tests. The purpose of the model is to determine the range of force and air gap height in which the pad can be controlled. [ABSTRACT FROM AUTHOR]

This paper presents the validation of a first-order winding thermal model in machine operative conditions. The proposed model can be used in motor control strategies for the winding temperature prediction during transient overload, or vice versa, for the prediction of the maximum time duration of the overload maintaining the winding temperature within the limit imposed by the class of insulation. The thermal model has been validated using two different electrical machines. The first one is a 10-kW automotive starter-generator prototype for mini-hybrid powertrain equipped with distributed bar windings, while the second one is a 2.2 kW total enclosed fan cooled industrial induction motor equipped with conventional stranded wire windings. Depending on the application for both machines, a short-duty transient operation in overload conditions could be required. In particular, the automotive starter-generator must accomplish engine cranking and torque assistance during the vehicle acceleration and braking, while the industrial induction machine could operate in intermittent service in overload conditions when used in machine tool applications. As a consequence, an accurate stator winding temperature prediction is mandatory to fully exploit the machine performance. For both motors, the thermal model parameters have been evaluated by fast experimental approach, and, subsequently, the model has been validated during operative overload conditions. [ABSTRACT FROM AUTHOR]

This work addresses the problem of finding expressions for the radiation impedance of a circular plate with cuts (holes + slits) and mounted in an infinite baffle. Due to the nontrivial nature of the structural geometry and the boundary conditions, analytical solution of the required Rayleigh integral is difficult for this case. The analysis in this case is carried out numerically using COMSOL Multiphysics. The air on top in contact with the vibrating plate, loads the plate with additional mass and also dissipates away energy depending on the frequency of vibration. The numerical solution obtained using FEA needs to be converted into suitable frequency based expressions. We use curve fitting to relate these radiation impedance values to an already reported equivalent circuit (for modeling the radiation impedance) in the literature. The detailed method of lumped parameter extraction, as well as the method of reduction of the circuit to its high and low frequency counterparts, is reported in this paper. The method described here is a generic one and can be used for any kind of geometry. [ABSTRACT FROM AUTHOR]

This paper presents mathematical modeling and numerical simulation results for a miniature, planar, spiral transformer (MPST) fabricated in micro-electromechanical MEMS technology. When the MPST is magnetic nanofluid cored, magnetization body forces occur, entraining it into a complex flow. This particular MPST design is then compared with other competing solutions concerning the lumped (circuit) parameters. Finally, the heat transfer problem is solved for different electromagnetic working conditions to assess the thermal loads inside the MPST. [ABSTRACT FROM AUTHOR]

This paper presents an analytical model of a common-mode choke suitable for accurate calculation of the choke impedance over a wide frequency range. The model consists of lumped parameters (resistances, inductances, and capacitances) related to individual turns of the coils wound on the core. It takes into account the mutual interactions between the turns and the core with respect to their inductive and capacitive links. The variation of the core permeability and losses with frequency up to 100 MHz is also included. The open-mode impedance characteristic calculated analytically for a VAC 6123x425 single-phase common-mode choke shows very good agreement with the 3-D finite-element model and the measured characteristic from 150 kHz up to 30 MHz, thus confirming the accuracy of the model over a wide frequency range. [ABSTRACT FROM AUTHOR]

This article proposes a frequency-dependent transmission line model based on state-space techniques. To include the frequency effect associated with distributed parameters in the state matrices, the line frequency-dependent longitudinal parameters are fitted by a rational function and then introduced in lumped elements representation by an equivalent RL circuit; this procedure is known as vector fitting. Subsequently, the system of ordinary differential equations that represents the transients of currents and voltages on a three-phase transmission line is represented in state space. After the state equations are solved by numerical and analytic methods, the results are compared to a frequency-dependent lumped model implemented by the commercial software MICROTRAN (an electromagnetic transient program; Microtran Power Systems Analysis Corporation, Vancouver, Canada). Following this, the results obtained from the proposed lumped model are compared to results from a distributed-parameters model based on Fourier transform. Some of the principal advantages for using the proposed state-space model instead of a distributed-parameters modeling are the easy modeling of several electromagnetic phenomena over transmission lines directly in the time domain without the use of inverse transforms and that a detailed description of the voltages and currents along the line can be described with good approximation. These attributes are not observed for models based on distributed parameters. All simulations are performed considering the switching operation of a 440-kV three-phase line, and by this procedure, it is possible to analyze the accuracy of the proposed line modeling. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the effect of vacuum sealing the backside cavity of a Capacitive Micromachined Ultrasonic Transducer (CMUT). The presence or absence of air inside the cavity has a marked effect upon the system parameters, such as the natural frequency, damping, and the pull-in voltage. The presence of vacuum inside the cavity of the device causes a reduction in the effective gap height which leads to a reduction in the pull-in voltage. We carry out ANSYS simulations to quantify this reduction. The presence of vacuum inside the cavity of the device causes stress stiffening of the membrane, which changes the natural frequency of the device. A prestressed modal analysis is carried out to determine the change in natural frequency due to stress stiffening. The equivalent circuit method is used to evaluate the performance of the device in the receiver mode. The lumped parameters of the device are obtained and an equivalent circuit model of the device is constructed to determine the open circuit receiving sensitivity of the device. The effect of air in the cavity is included by incorporating an equivalent compliance and an equivalent resistance in the equivalent circuit. [ABSTRACT FROM AUTHOR]

In this paper, a three-phase transformer model is developed to be suitable for slow transient and power-quality studies. The proposed model takes into account the eddy currents, the magnetic core topology, and the nonlinear characteristics of the core material. In order to model the eddy currents effects in the magnetic core, Bertotti's work for the eddy currents is used and nonlinear resistors dependent on the magnetic core topology are proposed. A systematic procedure is developed for the determination of the incremental self and mutual inductances of the windings. The nonlinear characteristics of the core material are represented either by a magnetization curve or by a hysteresis loop. The hysteresis loop is introduced either by the mathematical model proposed by Tellinen or by the macroscopic model presented by Jiles-Atherton. Simulations results are compared to published measurements in order to verify the proposed model. [ABSTRACT FROM AUTHOR]

Hemodynamic instability, mostly due to vertical lifting of the heart, is usually observed during beating-heart surgical procedures. However, some hemodynamic parameters, such as coronary blood flow, are not routinely measured. A digital computer model of the circulation able to simulate and analyze the effects of heart lifting and the Trendelenburg maneuver, and thus supply detailed hemodynamic information to the clinicians would provide a useful analytical tool. A lumped parameters model of the circulation was applied to both β-blocked and not β-blocked pigs. The results confirmed a drop of cardiac output and coronary flow during heart lifting and a rise of both variables after the Trendelenburg maneuver for β-blocked animals. In not β-blocked pigs, the analysis was more complex but the model reproduced experimental data and permitted coronary flow to be estimated. These results showed the feasibility of numerical simulation for specific circulatory conditions encountered during beating-heart surgery. [ABSTRACT FROM AUTHOR]

Mathematical model-building and analysis techniques are presented for the hydraulic percussion systems. Some models are proposed for the use in calculating specific designs of percussive facilities. The similarity criteria are determined to compare systems with different sets of elements. [ABSTRACT FROM AUTHOR]

Based on the new concept that intrathoracic and abdominal pressure variations cause blood flow in most of the cardiopulmonary resuscitation (CPR) techniques, two mathematical models were developed to explore related mechanisms of blood flow. The models were based on a representation of the cardiovascular system by resistive, capacitive and inductive elements, and the existence of venous and cardiac unidirectional valves. Cyclic intrathoracic and abdominal pressure variations were simulated by modulating the pressure within the corresponding vessels. It was found that blood flow during CPR is highly dependent on venous valving and aortic valve competence. The systemic blood flow was calculated to be between 10 and 20 per cent of its normal value. The maximum flow under a cyclic pressure of 50 mmHg was 663 m/min, which was achieved with a pulse rate of 115 cycles per min and a duty cycle (ratio of artificial systole to cycle duration) of 58 per cent. The coronary blood flow was found to occur only during artificial diastole and was actually reversed during the compression phase. The systemic blood flow increased when pressure variations were delivered to the chest alone or when some phase lag was introduced between the thoracic and abdominal pressure waves. The mathematical model presented provided a tool to study the effect of thoracic and abdominal pressure waves on the circulation in CPR. The information derived from the model can be used to design better methods for CPR. [ABSTRACT FROM AUTHOR]

Non-conventional thermal zones are low-cost and ecology friendly alternatives to the housing needs of populations in various situations, such as surviving natural disasters or addressing homelessness. However, it is necessary to guarantee thermal comfort for occupants, while aiming to minimize energy consumption and wastage in refrigeration systems. To reduce the cooling requirements in non-conventional thermal zones it is necessary to model the structure and analyze the principal factors contributing to internal temperature. In this paper, a geodesic dome is modellingusing the lumped parameter technique. This structure is composed of a wooden skeleton and wooden floor, with a canvas surface as its exterior. The mathematical model was tuned using experimental data, and its parameters were classified using Monte Carlo sensitivity analysis. The mathematical model was used to evaluate the impact on internal temperature and occupants' comfort when two strategies are considered. The results obtained indicatee internal temperature reductions down to a range of 7% to 11%; this result is reflected directly in the energy used to refrigerate the thermal zone, contributing to the objective of providing houses with lower energy consumption. [ABSTRACT FROM AUTHOR]