scholarly journals Optimization of Lumped Parameter Models to Mitigate Numerical Oscillations in the Transient Responses of Short Transmission Lines

Energies ◽  
2021 ◽  
Vol 14 (20) ◽  
pp. 6534
Author(s):  
Jaimis S. L. Colqui ◽  
Anderson R. J. de Araújo ◽  
Sérgio Kurokawa ◽  
José Pissolato Filho
Keyword(s):  
Power Systems ◽  
Transmission Lines ◽  
Lumped Parameter Model ◽  
Transient Responses ◽  
Lumped Parameter ◽  
Lumped Parameter Models ◽  
Spurious Oscillations ◽  
The Time Domain ◽  
Time Transformations ◽  
Good Agreement

The Lumped Parameter Model (LPM) is a known approach to represent overhead transmission lines (TLs), especially when these elements comprehend a few tens of kilometers. LPMs employ a large number of cascaded π-circuits to compute accurately the transient responses. These responses contain numerical spurious oscillations (NSO) characterized by erroneous peaks which distort the transient responses, mainly their peak values. Two modified LPM topologies composed of damping resistances inserted along the longitudinal or transversal branches of the cascaded π-circuits offer significant mitigations in the NSO. In this paper, in an effort to have the maximum mitigation of the NSO and low distortion in the transient responses, two modified topologies with optimized damping resistances are proposed to represent short TLs. Results demonstrate expressive attenuation in the peaks of NSO which reflect good agreement in comparison with the responses computed by the Bergeron’s line model. The mitigation of the NSO is carried out directly in the time domain and it does not require either analog or digital filters.Furthermore, no frequency-to-time transformations are necessary in this procedure. These alternative topologies can be incorporated into any electromagnetic transient program to study switching operations in power systems.

A Critical Examination of the Hysteresis in Wells Turbines Using CFD and Lumped Parameter Models

2019 ◽  
Author(s):  
T. Ghisu ◽  
F. Cambuli ◽  
P. Puddu ◽  
I. Virdis ◽  
M. Carta ◽  
...  
Keyword(s):  
Turbine Blades ◽  
Unsteady Aerodynamics ◽  
Lumped Parameter Model ◽  
Hysteretic Behavior ◽  
Critical Examination ◽  
Wells Turbine ◽  
Lumped Parameter ◽  
Lumped Parameter Models ◽  
Acceleration And Deceleration ◽  
The Common

Abstract The hysteretic behavior of OWC-installed Wells turbines has been known for decades. The common explanation invokes the presence of unsteady aerodynamics due to the continuously varying incidence of the flow on the turbine blades. This phenomenon is neither new nor unique to Wells turbines, as an aerodynamic hysteresis is present in rapidly oscillating airfoils and wings, as well as in different types of turbomachinery, such as wind turbines and helicopter rotors, which share significant similarities with a Wells turbine. An important difference is the non-dimensional frequency: the hysteresis appears in oscillating airfoils only at frequencies orders of magnitude larger than the ones Wells turbines operate at. This work contains a reexamination of the phenomenon, using both CFD and a lumped parameter model, and shows how the aerodynamic hysteresis in Wells turbines is negligible, and how the often measured differences in performance between acceleration and deceleration are caused by the capacitive behavior of the OWC system.

Characterization of pulmonary arterial input impedance with lumped parameter models

1987 ◽  
Vol 252 (3) ◽  
pp. H585-H593 ◽  
Author(s):  
B. J. Grant ◽  
L. J. Paradowski
Keyword(s):  
Input Impedance ◽  
Goodness Of Fit ◽  
Arterial Compliance ◽  
Characteristic Impedance ◽  
Lumped Parameter Model ◽  
Pulmonary Vasculature ◽  
Impedance Spectra ◽  
Lumped Parameter ◽  
Lumped Parameter Models ◽  
Pulmonary Arterial

The purpose of this study is to evaluate systematically the ability of lumped parameter models to approximate pulmonary arterial input impedance (Zin) and estimate characteristic impedance (Zc) and pulmonary arterial compliance (Cart). To assess goodness of fit, the parameters of each model were adjusted so that the model's impedance approximates the Zin measured in anesthetized cats. To assess the ability of the model to estimate Zc and Cart, the lumped parameter models were fitted to Zin calculated from a distributed parameter model of the feline pulmonary vasculature. In addition, we assessed the concordance between the lumped parameter model estimates of Zc and Cart. The results indicate that no one model was superior; any of four models would be a reasonable choice. A four-element model was used to compare Zin measured at different phases of the respiratory cycle. Small differences in the impedance spectra were found that have not been previously reported. We conclude that lumped parameter models can be used to provide close approximations to Zin, to estimate Zc and Cart, and to provide a useful approach for statistical comparisons of impedance spectra.

scholarly journals An Improved Lumped Parameter Model for a Piezoelectric Energy Harvester in Transverse Vibration

2014 ◽  
Vol 2014 ◽  
pp. 1-12 ◽  
Author(s):  
Guang-qing Wang ◽  
Yue-ming Lu
Keyword(s):  
Correction Factor ◽  
Transverse Vibration ◽  
Energy Harvester ◽  
Lumped Parameter Model ◽  
Distributed Parameter ◽  
Piezoelectric Energy ◽  
Distributed Parameter Model ◽  
Lumped Parameter ◽  
Lumped Parameter Models ◽  
Tip Mass

An improved lumped parameter model (ILPM) is proposed which predicts the output characteristics of a piezoelectric vibration energy harvester (PVEH). A correction factor is derived for improving the precisions of lumped parameter models for transverse vibration, by considering the dynamic mode shape and the strain distribution of the PVEH. For a tip mass, variations of the correction factor with PVEH length are presented with curve fitting from numerical solutions. The improved governing motion equations and exact analytical solution of the PVEH excited by persistent base motions are developed. Steady-state electrical and mechanical response expressions are derived for arbitrary frequency excitations. Effects of the structural parameters on the electromechanical outputs of the PVEH and important characteristics of the PVEH, such as short-circuit and open-circuit behaviors, are analyzed numerically in detail. Accuracy of the output performances of the ILPM is identified from the available lumped parameter models and the coupled distributed parameter model. Good agreement is found between the analytical results of the ILPM and the coupled distributed parameter model. The results demonstrate the feasibility of the ILPM as a simple and effective means for enhancing the predictions of the PVEH.

scholarly journals Modelling and Validation of Cavitating Orifice Flow in Hydraulic Systems

2021 ◽  
Vol 13 (13) ◽  
pp. 7239
Author(s):  
Paolo Casoli ◽  
Fabio Scolari ◽  
Massimo Rundo
Keyword(s):  
Lumped Parameter Model ◽  
Hydraulic Systems ◽  
Vena Contracta ◽  
Lumped Parameter ◽  
Lumped Parameter Models ◽  
Orifice Flow ◽  
Computational Fluid Dynamics Cfd ◽  
Set Up ◽  
Cfd Method ◽  
Hydraulic Valves

Cavitation can occur at the inlet of hydraulic pumps or in hydraulic valves; this phenomenon should be always avoided because it can generate abnormal wear and noise in fluid power components. Numerical modeling of the cavitation is widely used in research, and it allows the regions where it occurs more to be predicted. For this reason, two different approaches to the study of gas and vapor cavitation were presented in this paper. In particular, a model was developed using the computational fluid dynamics (CFD) method with particular attention to the dynamic modeling of both gaseous and vapor cavitation. A further lumped parameter model was made, where the fluid density varies as the pressure decreases due to the release of air and the formation of vapor. Furthermore, the lumped parameter model highlights the need to also know the speed of sound in the vena contracta, since it is essential for the correct calculation of the mass flow during vaporization. A test bench for the study of cavitation with an orifice was set up; cavitation was induced by increasing the speed of the fluid on the restricted section thanks to a pump located downstream of the orifice. The experimental data were compared with those predicted by CFD and lumped parameter models.

Lumped Parameter Modeling of Counterbalance Valves Considering the Effect of Flow Forces

2019 ◽  
Author(s):  
Annalisa Sciancalepore ◽  
Andrea Vacca ◽  
Oscar Pena ◽  
Steven T. Weber
Keyword(s):  
Controller Design ◽  
Complex Geometry ◽  
Control Volume ◽  
Analytical Description ◽  
Lumped Parameter Model ◽  
Hydraulic Control ◽  
Lumped Parameter ◽  
Proposed Model ◽  
Lumped Parameter Models ◽  
High Level

Abstract The lumped parameter approach based on equations describing of the physical behavior of the system still represents one of the most convenient way to simulate hydraulic control systems. The key advantages of this approach are given by its intrinsic simulation swiftness as well as the ease of deriving state space formulations for controller design purposes. However, the common limitation of lumped parameter models is the high level of simplification of for certain physical aspects. For the case of hydraulic control valves with complex geometry, the flow forces are usually one of the most difficult aspects to describe accurately. The present paper presents a lumped parameter model for counterbalance valves, which includes an accurate analytical approach to model the effect of the flow forces based acting on the valve poppet and piston. The model is based on a classic control volume scheme for the description of the flow through the valve, and it is coupled with a dynamic model for the descriptions of the motion of the moving parts inside the valve. The novelty of the proposed approach consists on the analytical description of the flow forces, which is based on fluid momentum considerations. After describing the modeling approach, the paper details the authors’ efforts for experimentally validate the model on the basis of tests performed on actual components. The comparison between simulation results and experimental data confirms the validity of the proposed model and also highlights the importance of accounting for flow forces while describing the operation of counterbalance valves, particularly for cases of high flow rates.

Lumped Parameter Model for Dynamic Performances of Plate-Fin Recuperator

2006 ◽  
Author(s):  
Ming Ding ◽  
Jie Wang ◽  
Xiaoyong Yang ◽  
Lei Shi ◽  
Qingshan Su
Keyword(s):  
Flow Rate ◽  
Lumped Parameter Model ◽  
Normal Operation ◽  
Electric Load ◽  
Transient Responses ◽  
The Core ◽  
Lumped Parameter ◽  
Influence Of Temperature On ◽  
Dynamic Performances ◽  
Full Power

A lumped parameter model was developed to study dynamic performances of plate-fin recuperator in high temperature gas-cooled reactor with direct helium turbine cycle (HTGR-GT). For the core heat capacitance of recuperator was far larger than heat capacitance and thermal flow rate of helium, it was reasonable to ignore the influence of heat capacitance of fluid on dynamic characteristics of recuperator and develop the lumped parameter model with infinite core heat capacitance. The model was solved by four-order Rounge-Kutta method, considering the influence of temperature on helium thermal properties. Based on the lump parameter model, transient response of outlet temperatures of recuperator was analyzed when step and ramp changes of inlet temperatures of recuperator took place in hot side, as well as mass flow rate of recuperator. Transient responses of the core temperature and outlet temperatures of helium were also analyzed while power was regulated in course of normal operation and total electric load was rejected from full power.

APPROXIMATING THE EFFECT OF VAN DER WAALS FORCE ON THE INSTABILITY OF ELECTROSTATIC NANO-CANTILEVERS

2011 ◽  
Vol 25 (29) ◽  
pp. 3965-3976 ◽  
Author(s):  
ALI KOOCHI ◽  
AMINREZA NOGHREHABADI ◽  
MOHAMADREZA ABADYAN
Keyword(s):  
Van Der Waals ◽  
Convergent Series ◽  
Lumped Parameter Model ◽  
Distributed Parameter ◽  
Analytical Results ◽  
Lumped Parameter ◽  
Fringing Field ◽  
Beam Type ◽  
Nano Electromechanical System ◽  
Good Agreement

Beam-type nano-electromechanical system (NEMS) is one of the most components in constructing nano-devices. Herein, a distributed parameter model is used to study the influence of van der Waals (vdW) attraction on the pull-in performance of the cantilever NEMS. Homotopy perturbation method (HPM) is applied to solve the nonlinear governing equation of the actuators in the form of convergent series. Moreover, analytical results are compared with those of numerical method as well as a lumped parameter model. The pull-in voltage and critical cantilever tip deflection of NEMS are determined. Results depict that vdW attraction decreases the pull-in deflection and voltage of the NEMS. On the other hand, the fringing field increases the pull-in deflection while decreases the pull-in voltage of the system. The analytical results have good agreement with numerical results and those available in the literature.

Segmental vibration transmissibility of seated occupant from lumped parameter models

2011 ◽  
Vol 18 (11) ◽  
pp. 1683-1689 ◽  
Author(s):  
Masilamany Santha Alphin ◽  
Krishnaswamy Sankaranarayanasamy ◽  
Suthangathan Paramashivan Sivapirakasam
Keyword(s):  
Degrees Of Freedom ◽  
Equations Of Motion ◽  
Biomechanical Model ◽  
Dynamic Parameter ◽  
Experimental Results ◽  
Lumped Parameter Model ◽  
Whole Body ◽  
Driving Frequency ◽  
Lumped Parameter ◽  
Lumped Parameter Models

One of the important parameters for the comfort of a seated occupant of a vehicle is the dynamic parameter. The effects of vibration depend on biomechanical characteristics, transmissibility (TR) and apparent mass. The range of input vibration at the seat and TR at the driving frequency will decide the magnitude of the displacement at any point of the human occupant. The most preferred form of biomechanical model for unidirectional whole body vibration is the lumped parameter model. Lumped parameter models are formulated by number of masses depending on the number of degrees-of-freedom (d.f.). The objective of this work is to study the vibration TR by developing the equations of motion (EOM) for different d.f. models for the seated occupant. Then the generated equations of motion for lumped parameter models are solved using the frequency domain technique. In this paper two, four, seven and 11 d.f. models are considered. The TR values are determined by solving the derived parameters using the MATLAB program. The maximum seats to head TR in the case of two, four, seven and 11 d.f. are obtained at the frequency of 2 Hz, 2.5 Hz, 3.15 Hz, and 4 Hz respectively. The TR obtained from models is compared with real time experimental results. The comparison shows a better fit for the TR obtained from the four and seven d.f. models. There is a wide deviation from the TR observed with two and 11 degrees of models when compared with experimental results of the past literature.

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