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.

Towards Direct Numerical Simulation of Compressible Orifice Flow

2013 ◽  
Author(s):  
Bernhard Manhartsgruber
Keyword(s):  
Numerical Simulation ◽  
Stationary Flow ◽  
Parameter Tuning ◽  
Good Choice ◽  
Fluid Power ◽  
Model Complexity ◽  
Hydraulic Systems ◽  
Vast Number ◽  
Lumped Parameter ◽  
Orifice Flow

Simulation methods from simple lumped parameter approaches to complex computational fluid dynamics codes have become a widely used tool in the fluid power community. Certain tasks like the predicition of flow forces on the control spools in valves or the design of port plates in axial piston pumps are usually treated by the aid of numerical simulation. Like in many other cases, the underlying principle is the control of flow by orifices. The importance of orifice flow for hydraulic systems is reflected by the vast number of publications on various aspects of orifice flow in the fluid power literature. In lumped parameter simulations, the orifice equation giving the flow rate as a square root of the pressure drop is widely used even in transient cases where it is not clear whether the flow develops fast enough to justify the assumption of stationary flow. On the other end of the model complexity spectrum computational fluid dynamcis codes are used in the fluid power community. These very complex models require a high number of parameters for the tuning of turbulence models, wall models, and the like. The quality of the results heavily dependes on a good choice for these parameters. Additionally, the vast majority of turbulent flow simulations is done with the assumption of an incompressible fluid. Very often, the results from simulations deviate heavily from measurement results and only after parameter tuning a good match between model and simulation is achieved. This paper suggests the use of direct numerical simulations for simple and prototypical geometries in order to gain a better understanding for transient orifice flows lacking the fully developed flow assumed in traditional models.

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.

Soft Switching in Switched Inertance Hydraulic Circuits

2016 ◽  
Author(s):  
Alexander C. Yudell ◽  
James D. Van de Ven
Keyword(s):  
High Speed ◽  
Soft Switching ◽  
Power Delivery ◽  
Lumped Parameter Model ◽  
Energy Losses ◽  
Hydraulic Systems ◽  
Zero Voltage Switching ◽  
Lumped Parameter ◽  
Capacitive Element ◽  
Zero Voltage

Switched Inertance Hydraulic Systems (SIHS) use inductive, capacitive, and switching elements to boost or buck a pressure from a source to a load in an ideally lossless manner. Real SIHS circuits suffer a variety of energy losses, with throttling of flow during transitions of the high-speed valve resulting in 44% of overall losses. These throttling energy losses can be mitigated by applying the analog of zero-voltage-switching, a soft switching strategy, adopted from power electronics. In the soft switching circuit, the flow that would otherwise be throttled across the transitioning valve is stored in a capacitive element and bypassed through check valves in parallel with the switching valves. To evaluate the effectiveness of soft switching in a boost converter SIHS, a lumped parameter model was constructed. The model demonstrates that soft switching can improve the efficiency of the circuit up to 42% and extend the power delivery capabilities of the circuit by 76%.

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.

Investigations on Wave Propagation of the Pressure Pulsation in a Helmholtz-Type Hydraulic Silencer With a Hemispherical Vessel

2016 ◽  
Vol 139 (1) ◽  
Author(s):  
Takayoshi Ichiyanagi ◽  
Tetsuya Kuribayashi ◽  
Takao Nishiumi
Keyword(s):  
Wave Propagation ◽  
Resonance Frequency ◽  
Pressure Pulsation ◽  
Lumped Parameter Model ◽  
Design Stage ◽  
Hydraulic Systems ◽  
Lumped Parameter ◽  
Reasonable Cost ◽  
Attenuation Characteristics ◽  
Step Section

The Helmholtz-type hydraulic silencer is one of the most practical silencers for attenuating pressure pulsations in hydraulic systems owing to its simple structure and reasonable cost. Maximum attenuation performance can be attained at the resonance frequency in accordance with the principle of Helmholtz resonance. Therefore, it is extremely important to precisely determine the resonance frequency at the design stage. It was clarified in our previous study that the shape of the volume vessel affects the resonance frequency of the silencer because of the wave propagation of pressure pulsation inside the volume vessel. In this study, the attenuation characteristics and wave propagation in a silencer with a hemispherical vessel are investigated. A mathematical model that takes into account the propagation of a one-dimensional wave in the radial direction of the hemispherical vessel is proposed and compared with the step section approximation model and the classic lumped parameter model. Furthermore, the effectiveness of the theoretical analysis is verified by experiments wherein the dimensional specifications of the vessel and neck are adjusted.

A Study of Shaft Vibration Based on Transfer Matrix

2013 ◽  
Vol 365-366 ◽  
pp. 339-343
Author(s):  
Chang Tan ◽  
Zhi Ling Guo ◽  
Rui Kun Zhou
Keyword(s):  
Numerical Simulation ◽  
Transfer Matrix ◽  
Critical Speed ◽  
Lumped Parameter Model ◽  
Lumped Parameter ◽  
The Common ◽  
Shaft Vibration ◽  
Set Up

This paper first analyze the method of transfer matrix, set up the lumped parameter model. then figure out the common transfer matrix of shaft. Take some shaft as an example, using matlab calculate the critical speed and analyze the result. The analysis can provide basis and method for shaft vibration numerical simulation.

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 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.

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.

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