Dynamic Stability of a Water Brake Dynamometer

1998 ◽  
Vol 120 (1) ◽  
pp. 89-96 ◽  
Author(s):  
R. A. Van den Braembussche ◽  
H. Malys
Keyword(s):  
High Frequency ◽  
Low Frequency ◽  
Lumped Parameter Model ◽  
Stable Operation ◽  
Pressure Oscillations ◽  
Lumped Parameter ◽  
Flow Oscillations ◽  
Brake Dynamometer ◽  
Low Torque ◽  
Frequency Variations

A lumped parameter model to predict the high frequency pressure oscillations observed in a water brake dynamometer is presented. It explains how the measured low frequency variations of the torque are a consequence of the variation in amplitude of the high frequency flow oscillations. Based on this model, geometrical modifications were defined, aiming to suppress the oscillations while maintaining mechanical integrity of the device. An experimental verification demonstrated the validity of the model and showed a very stable operation of the modified dynamometer even at very low torque.

Surge in a Low-Speed Radial Compressor

1998 ◽  
Author(s):  
Corine Meuleman ◽  
Frank Willems ◽  
Rick de Lange ◽  
Bram de Jager
Keyword(s):  
Flow Rate ◽  
Pressure Rise ◽  
Flow Coefficient ◽  
Lumped Parameter Model ◽  
Pressure Oscillations ◽  
Vaned Diffuser ◽  
Flow Angle ◽  
Radial Compressor ◽  
Low Speed ◽  
Lumped Parameter

Surge is measured in a low-speed radial compressor with a vaned diffuser. For this system, the flow coefficient at surge is determined. This coefficient is a measure for the inducer inlet flow angle and is found to increase with increasing rotational speed. Moreover, the frequency and amplitude of the pressure oscillations during fully-developed surge are compared with results obtained with the Greitzer lumped parameter model. The measured surge frequency increases when the compressor mass flow is throttled to a smaller flow rate. Simulations show that the Greitzer model describes this relation reasonably well except for low rotational speeds. The predicted amplitude of the pressure rise oscillations is approximately two times too small when deep surge is met in the simulations. For classic surge, the agreement is worse. The amplitude is found to depend strongly on the shape of the compressor and throttle characteristic, which are not accurately known.

Nonlinear Oscillations of a Particle in the Plane Under Longitudinal End Excitation

2003 ◽  
Author(s):  
Rajesh K. Jha ◽  
Robert G. Parker
Keyword(s):  
Nonlinear Oscillations ◽  
Low Frequency ◽  
Period Doubling ◽  
Lumped Parameter Model ◽  
Lumped Parameter ◽  
Parametric Resonances ◽  
Jump Phenomena ◽  
Route To Chaos ◽  
Chaotic Nature ◽  
Two Degree Of Freedom

We study the forced vibrations of a two degree of freedom lumped parameter model of a belt span under longitudinal excitation. The belt inertia is modelled as a particle and the belt elasticity is modelled by two identical linear springs. Numerical integration is used to calculate free responses and perform frequency and amplitude sweeps. Frequency sweep results indicate parametric resonances, jump phenomena, sub- and super-harmonic responses, quasiperiodicity and chaos. Amplitude sweep at a low frequency shows bifurcations of limit cycles and the period doubling route to chaos. Poincare sections are computed to show the chaotic nature of the responses.

Pressure Oscillations Occurring in a Centrifugal Compressor System With and Without Passive and Active Surge Control

1994 ◽  
Author(s):  
Wiktor M. Jungowski ◽  
Marvin H. Weiss ◽  
Glenn R. Price
Keyword(s):  
Active Control ◽  
Centrifugal Compressor ◽  
Passive Control ◽  
Side Branch ◽  
Lumped Parameter Model ◽  
Stability Criteria ◽  
Pressure Oscillations ◽  
Short Side ◽  
Lumped Parameter ◽  
Surge Control

A study of pressure oscillations occurring in small centrifugal compressor systems without a plenum is presented. Active and passive surge control were investigated theoretically and experimentally for systems with various inlet and discharge piping configurations. The determination of static and dynamic stability criteria was based on Greitzer’s (1981) lumped parameter model modified to accommodate capacitance of the piping. Experimentally, passive control using globe valves closely coupled to the compressor prevented the occurrence of surge even with the flow reduced to zero. Active control with a sleeve valve located at the compressor was effective but involved a significant component of passive throttling which reduced the compressor efficiency. With an oscillator connected to a short side-branch at the compressor, effective active control was achieved without throttling. Both methods of active control reduced the flow rate at surge onset by about 30%. In general, the experiments qualitatively confirmed the derived stability criteria.

scholarly journals Mathematical Model of Suspension Seat-Person Exposed to Vertical Vibration for Off-Road Vehicles

2019 ◽  
Vol 16 (2) ◽  
pp. 6773-6782
Author(s):  
S. Aisyah Adam ◽  
N. A. A. Jalil ◽  
K. A. Md Razali ◽  
Y. G. Ng ◽  
M. F. Aladdin
Keyword(s):  
Human Body ◽  
Degrees Of Freedom ◽  
Low Frequency ◽  
Coupled System ◽  
Vertical Vibration ◽  
Lumped Parameter Model ◽  
Model Parameters ◽  
Road Vehicles ◽  
Lumped Parameter ◽  
Variable Function

Off-road drivers are exposed to a high magnitude of vibration at low frequency (0.5-25Hz), that can cause harm and possibly attribute to musculoskeletal disorder, particularly low-back pain. The suspension seat is commonly used on an off-road condition to isolate the vibration transmitted to the human body. Nevertheless, the suspension seat modelling that incorporates the human body is still scarce. The objective of this study is to develop a mathematical modelling to represent the suspension seat-person for off-road vehicles. This paper presents a three degrees-of-freedom lumped parameter model. A curve-fitting method is used for parameter identification, which includes the constraint variable function (fmincon()) from the optimisation toolbox of MATLAB(R2017a). The model parameters are optimised using experimentally measured of suspension seat transmissibility. It was found that the model provides a reasonable fit to the measured suspension seat transmissibility at the first peak of resonance frequency, around 2-3 Hz. The results of the study suggested that the human body forms a coupled system with the suspension seat and thus affects the overall performance of the suspension system.  As a conclusion, the influence of the human body should not be ignored in the modelling, and a three-degrees degree-of-freedom lumped parameter model provides a better prediction of suspension seat transmissibility. This proposed model is recommended to predict vibration transmissibility for off-road suspension seat.

scholarly journals Effect of Frequency Content of Earthquake on the Seismic Response of Interconnected Electrical Equipment

CivilEng ◽  
2020 ◽  
Vol 1 (3) ◽  
pp. 198-215
Author(s):  
Kashif Salman ◽  
Sung Gook Cho
Keyword(s):  
Seismic Response ◽  
Natural Frequency ◽  
Ground Motion ◽  
High Frequency ◽  
Seismic Analysis ◽  
Response Spectrum ◽  
Low Frequency ◽  
Stable Operation ◽  
Design Spectrum ◽  
Standard Design

To ensure the stable operation of safety-related nuclear power plant (NPP) equipment, they are tested by following the seismic qualification procedures. The in-cabinet response spectrum (ICRS) is used to test the mounted components. However, the ICRS varies significantly with the number of uncertainties that include (1) loaded and unloaded condition of the cabinets, (2) the number of connected cabinets (grouping effects), and (3) higher frequency contents in the seismic inputs. This study focuses on the ICRS generation and alteration induced due to the listed uncertainties. A prototype of an electrical cabinet was experimentally examined. Followed by the numerical modeling of the cabinet, the seismic analysis for the group of cabinets was performed using artificial ground motion compatible with the standard design spectrum and the real accelerograms of high and low frequency contents. The seismic response using finite element (FE) analysis manifests (1) natural frequency of loaded cabinets reduced due to the in-cabinet components while for the unloaded cabinets it increased significantly, (2) a consistent reduction in ICRS due to the grouping effect was recorded when excited by the lower-frequency motion, while it was amplified dramatically due to high-frequency pulses. Interconnected cabinets under the low-frequency input motions have a significant reduction of 50% in the ICRS that corresponds to the higher stiffness of the cabinets, while a 100% increase under the high frequency of ground motion was obtained. High frequency of ground motion, usually above 10 Hz, can cause the interconnected cabinets to resonate as the natural frequency of these equipment lies in this range.

scholarly journals Multilayer, Stacked Spiral Copper Inductors on Silicon with Micro-Henry Inductance Using Single-Level Lithography

2012 ◽  
Vol 2012 ◽  
pp. 1-8 ◽  
Author(s):  
Timothy Reissman ◽  
Joon-Sik Park ◽  
Ephrahim Garcia
Keyword(s):  
Metal Layer ◽  
Low Frequency ◽  
Power Converter ◽  
Fabrication Process ◽  
Lumped Parameter Model ◽  
Quality Factors ◽  
Single Level ◽  
Lumped Parameter ◽  
Strong Adhesion ◽  
Inner Diameter

We present copper structures composed of multilayer, stacked inductors (MLSIs) with tens of micro-Henry inductance for use in low frequency (sub 100 MHz), power converter technology. Unique to this work is the introduction of single-level lithography over the traditional two-level approach to create each inductor layer. The result is a simplified fabrication process which results in a reduction in the number of lithography steps per inductor (metal) layer and a reduction in the necessary alignment precision. Additionally, we show that this fabrication process yields strong adhesion amongst the layers, since even after a postprocess abrasion technique at the inner diameter of the inductors, no shearing occurs and connectivity is preserved. In total, three separate structures were fabricated using the single-level lithography approach, each with a three-layered, stacked inductor design but with varied geometries. Measured values for each of the structures were extracted, and the following results were obtained: inductance values of 24.74, 17.25, and 24.74 μH, self-resonances of 9.87, 5.72, and 10.58 MHz, and peak quality factors of 2.26, 2.05, and 4.6, respectively. These values are in good agreement with the lumped parameter model presented.

scholarly journals A New Lumped Approach for the Simulation of the Magnetron Injection Gun for MegaWatt-Class EU Gyrotrons

Energies ◽  
2021 ◽  
Vol 14 (8) ◽  
pp. 2068
Author(s):  
Nicolò Badodi ◽  
Antonio Cammi ◽  
Alberto Leggieri ◽  
Francisco Sanchez ◽  
Laura Savoldi
Keyword(s):  
High Frequency ◽  
Electron Cyclotron Resonance ◽  
Lumped Parameter Model ◽  
Electron Cyclotron Resonance Heating ◽  
Test Results ◽  
Radio Waves ◽  
Magnetron Injection Gun ◽  
Thermal Dynamics ◽  
Lumped Parameter ◽  
Current Emission

In the framework of the ITER (International Thermonuclear Experimental Reactor) project, one of the key components of the reactor is the ECRH (Electron Cyclotron Resonance Heating). This system has the duty to heat the plasma inside the tokamak, using high frequency and power radio waves, produced by sets of 1MW gyrotrons. One of the main issues related to the gyrotron operation is the output power drop that happens right after the beginning of a pulse. In this work, we study the underlying phenomena that cause the power drop, focusing on the gyrotron’s MIG (Magnetron Injection Gun) of the 1MW, 170 GHz European Gyrotron prototype for ITER. It is shown how the current emission and the temperature of the emitter are tightly bound, and how their interaction causes the power drop, observed experimentally. Furthermore, a simple yet effective lumped-parameter model to describe the MIG’s cathode thermal dynamics is developed, which is able to predict the power output of the gyrotron by simulating the propagation of the heat inside this component. The model is validated against test results, showing a good capability to reproduce the measured behavior of the system, while still being open to further improvements.

Pressure Oscillations Occurring in a Centrifugal Compressor System With and Without Passive and Active Surge Control

1996 ◽  
Vol 118 (1) ◽  
pp. 29-40 ◽  
Author(s):  
W. M. Jungowski ◽  
M. H. Weiss ◽  
G. R. Price
Keyword(s):  
Active Control ◽  
Centrifugal Compressor ◽  
Passive Control ◽  
Side Branch ◽  
Lumped Parameter Model ◽  
Stability Criteria ◽  
Pressure Oscillations ◽  
Short Side ◽  
Lumped Parameter ◽  
Surge Control

A study of pressure oscillations occurring in small centrifugal compressor systems without a plenum is presented. Active and passive surge control were investigated theoretically and experimentally for systems with various inlet and discharge piping configurations. The determination of static and dynamic stability criteria was based on Greitzer’s (1981) lumped parameter model modified to accommodate capacitance of the piping. Experimentally, passive control using globe valves closely coupled to the compressor prevented the occurrence of surge even with the flow reduced to zero. Active control with a sleeve valve located at the compressor was effective but involved a significant component of passive throttling which reduced the compressor efficiency. With an oscillator connected to a short side branch at the compressor, effective active control was achieved without throttling. Both methods of active control reduced the flow rate at surge onset by about 30 percent. In general, the experiments qualitatively confirmed the derived stability criteria.

Modeling and parametric study of a force-amplified compressive-mode piezoelectric energy harvester

2016 ◽  
Vol 28 (3) ◽  
pp. 357-366 ◽  
Author(s):  
Zhengbao Yang ◽  
Jean Zu ◽  
Jun Luo ◽  
Yan Peng
Keyword(s):  
Power Generation ◽  
Energy Harvester ◽  
Low Frequency ◽  
Lumped Parameter Model ◽  
Small Scale ◽  
Energy Harvesters ◽  
Piezoelectric Energy ◽  
Multi Stage ◽  
Lumped Parameter ◽  
Compressive Mode

Piezoelectric energy harvesters have great potential for achieving inexhaustible power supply for small-scale electronic devices. However, the insufficient power-generation capability and the narrow working bandwidth of traditional energy harvesters have significantly hindered their adoption. To address these issues, we propose a nonlinear compressive-mode piezoelectric energy harvester. We embedded a multi-stage force amplification mechanism into the energy harvester, which greatly improved its power-generation capability. In this article, we describe how we first established an analytical model to study the force amplification effect. A lumped-parameter model was then built to simulate the strong nonlinear responses of the proposed energy harvester. A prototype was fabricated which demonstrated a superior power output of 30 mW under an excitation of 0.3 g ([Formula: see text] m/s2). We discuss at the end the effect of geometric parameters that are influential to the performance. The proposed energy harvester is suitable to be used in low-frequency weak-excitation environments for powering wireless sensors.

Suppression of High Frequency Oscillations on Suspension System of Snow Groomer With Evolutionary Algorithms Optimization

2016 ◽  
Author(s):  
Pietro Marani ◽  
Cristian Ferrari
Keyword(s):  
Evolutionary Algorithms ◽  
High Frequency ◽  
Pareto Front ◽  
Suspension System ◽  
Design Parameters ◽  
Engineering Practice ◽  
Test Field ◽  
Pressure Oscillations ◽  
High Frequency Oscillations ◽  
Lumped Parameter

In current engineering practice for the design and dimensioning of hydropneumatic suspension systems, the effect of main parameters is considered; this approach can be used to implement approximate models basically suitable to describe low frequency and high amplitude oscillations of the machine. The target of this study is a Snow Groomer, a tracked vehicle driven by diesel engines and equipped in front with a shovel and behind with a cutter. When the machine drives over a snowfield, it pushes snow ahead of it and, at the same time, smooths out any surface unevenness. The suspension system is the key element to ensure the driver’s safety and comfort, the effectiveness of snow grooming and finally enhance the reliability of the machine components. The on-field testing had shown high frequency pressure oscillations transmitted from the sprocket to hydraulic system, propagated through the flexible hoses. Those Pressure Oscillations cause noise and can affect negatively the durability and reliability of the Machine. A lumped parameter non-linear dynamic model of the hydraulic circuit and of the machine interactions is built in Amesim environment, including Lax Wendroff wave propagation models, to make it able to catch the high frequency oscillations experienced in the test field. Most of the design parameters are fixed (such as vehicle weight and hydraulic lines length), other parameters can be varied to study the optimal solution, these parameters define the “factors” of the optimization problem. As a next step it is important to define the objectives of the optimization, in this case corresponding to various figures of merit describing the behavior of the system in different work conditions. The large number of factors included in the lumped parameter model generates an exponentially larger number of possible configurations. Moreover the relationship between factors and objective is not always possible to express with explicit mathematical models. Finally the presence of multiple and sometimes conflicting objectives forces more refined analysis methods to be adopted. For the above mentioned reasons a Multi-objective Optimization method is proposed taking advantage of Evolutionary Algorithms and Pareto Front optimization. Two different architectural solutions are analyzed and optimized using two different algorithms, Non Sorting Genetic Algorithm II (NSGAII) and Multiple Object Swarm Particle Optimization Algorithm (MOPSO). The results of the optimization belonging to the Pareto Front will be analyzed to assess the expected improvement of the suspension performance and will be chosen as candidates for a new setting of the Snow Groomer. Furthermore a comparison in terms of effectiveness and speed in finding solutions will be given for the current simulation environment.

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