Damping Effect on the Wave Propagation in Carbon Steel Pipelines Under Fluid Hammer Conditions

2016 ◽  
Author(s):  
Dimitrios G. Pavlou ◽  
Muk Chen Ong
Keyword(s):  
High Speed ◽  
Integral Transforms ◽  
Fourier Integral ◽  
Pressure Shock ◽  
Pressure Oscillations ◽  
Algebraic Form ◽  
Flow Parameters ◽  
Damping Characteristics ◽  
Research Gap ◽  
Hoop Stresses

A sudden reduction of the fluid flow yields a pressure shock, which travels along the pipeline with a high speed. Due to this transient loading, dynamic hoop stresses are developed, that may cause catastrophic damages in pipeline integrity. The vibration of the pipe wall is affected by the flow parameters as well as by the elastic and damping characteristics of the material. Most of the studies on dynamic response of pipelines (a) neglect the effect of the material damping, and (b) are usually limited to harmonic pressure oscillations. The present work is an attempt to fill the above research gap. To achieve this target, an analytic solution of the governing motion equation of pipelines under moving pressure shock is derived. The proposed methodology takes into account both elastic and damping characteristics of the steel. With the aid of Laplace and Fourier integral transforms and generalized functions properties, the solution is based on the transformation of the dynamic partial differential equation into an algebraic form. Analytical inversion of the transformed dynamic radial deflection variable is achieved, yielding the final solution. The proposed methodology is implemented in an engineering example; and the results are shown and discussed.

Damping Effect on the Wave Propagation in Carbon Steel Pipelines Under Fluid Hammer Conditions

2017 ◽  
Vol 139 (4) ◽  
Author(s):  
Dimitrios G. Pavlou ◽  
Muk Chen Ong
Keyword(s):  
High Speed ◽  
Integral Transforms ◽  
Fourier Integral ◽  
Generalized Function ◽  
Pressure Shock ◽  
Algebraic Form ◽  
Flow Parameters ◽  
Damping Characteristics ◽  
Research Gap ◽  
Hoop Stresses

A sudden reduction of the fluid flow yields a pressure shock, which travels along the pipeline with a high-speed. Due to this transient loading, dynamic hoop stresses are developed that may cause catastrophic damages in pipeline integrity. The vibration of the pipe wall is affected by the flow parameters as well as by the elastic and damping characteristics of the material. Most of the studies on dynamic response of pipelines: (a) neglect the effect of the material damping and (b) are usually limited to harmonic pressure oscillations. The present work is an attempt to fill the above research gap. To achieve this target, an analytic solution of the governing motion equation of pipelines under moving pressure shock is derived. The proposed methodology takes into account both elastic and damping characteristics of the steel. With the aid of Laplace and Fourier integral transforms and generalized function properties, the solution is based on the transformation of the dynamic partial differential equation into an algebraic form. Analytical inversion of the transformed dynamic radial deflection variable is achieved, yielding the final solution. The proposed methodology is implemented in an engineering example; and the results are shown and discussed.

Rotordynamic Performance of a Rotor Supported on Bump Type Foil Gas Bearings: Experiments and Predictions

2006 ◽  
Vol 129 (3) ◽  
pp. 850-857 ◽  
Author(s):  
Luis San Andrés ◽  
Dario Rubio ◽  
Tae Ho Kim
Keyword(s):  
High Speed ◽  
Critical Speed ◽  
Load Capacity ◽  
Test System ◽  
Foil Bearings ◽  
Rotor Imbalance ◽  
Synchronous Motion ◽  
Damping Characteristics ◽  
Rotor Surface ◽  
Stiffness And Damping

Gas foil bearings (GFBs) satisfy the requirements for oil-free turbomachinery, i.e., simple construction and ensuring low drag friction and reliable high speed operation. However, GFBs have a limited load capacity and minimal damping, as well as frequency and amplitude dependent stiffness and damping characteristics. This paper provides experimental results of the rotordynamic performance of a small rotor supported on two bump-type GFBs of length and diameter equal to 38.10mm. Coast down rotor responses from 25krpm to rest are recorded for various imbalance conditions and increasing air feed pressures. The peak amplitudes of rotor synchronous motion at the system critical speed are not proportional to the imbalance introduced. Furthermore, for the largest imbalance, the test system shows subsynchronous motions from 20.5krpm to 15krpm with a whirl frequency at ∼50% of shaft speed. Rotor imbalance exacerbates the severity of subsynchronous motions, thus denoting a forced nonlinearity in the GFBs. The rotor dynamic analysis with calculated GFB force coefficients predicts a critical speed at 8.5krpm, as in the experiments; and importantly enough, unstable operation in the same speed range as the test results for the largest imbalance. Predicted imbalance responses do not agree with the rotor measurements while crossing the critical speed, except for the lowest imbalance case. Gas pressurization through the bearings’ side ameliorates rotor subsynchronous motions and reduces the peak amplitudes at the critical speed. Posttest inspection reveal wear spots on the top foils and rotor surface.

scholarly journals Analysis of Diesel Knock for High-Altitude Heavy-Duty Engines Using Optical Rapid Compression Machines

Energies ◽  
2020 ◽  
Vol 13 (12) ◽  
pp. 3080
Author(s):  
Xiangting Wang ◽  
Haiqiao Wei ◽  
Jiaying Pan ◽  
Zhen Hu ◽  
Zeyuan Zheng ◽  
...  
Keyword(s):  
High Altitude ◽  
High Speed ◽  
Ambient Pressure ◽  
Critical Conditions ◽  
Heavy Duty ◽  
Pressure Oscillations ◽  
Spray Impingement ◽  
Rapid Compression ◽  
The Given ◽  
Injection Pressures

In high altitude regions, affected by the low-pressure and low-temperature atmosphere, diesel knock is likely to be encountered in heavy-duty engines operating at low-speed and high-load conditions. Pressure oscillations during diesel knock are commonly captured by pressure transducers, while there is a lack of direct evidence and visualization images, such that its fundamental formation mechanism is still unclear. In this study, optical experiments on diesel knock with destructive pressure oscillations were investigated in an optical rapid compression machine. High-speed direct photography and simultaneous pressure acquisition were synchronically performed, and different injection pressures and ambient pressures were considered. The results show that for the given ambient temperature and pressure, diesel knock becomes prevalent at higher injection pressures where fuel spray impingement becomes enhanced. Higher ambient pressure can reduce the tendency to diesel knock under critical conditions. For the given injection pressure satisfying knocking combustion, knock intensity is decreased as ambient pressure is increased. Further analysis of visualization images shows diesel knock is closely associated with the prolonged ignition delay time due to diesel spray impingement. High-frequency pressure oscillation is caused by the propagation of supersonic reaction-front originating from the second-stage autoignition of mixture. In addition, the oscillation frequencies are obtained through the fast Fourier transform (FFT) analysis.

scholarly journals On the emergence of large clusters of acoustic power sources at the onset of thermoacoustic instability in a turbulent combustor

2019 ◽  
Vol 874 ◽  
pp. 455-482 ◽  
Author(s):  
Abin Krishnan ◽  
R. I. Sujith ◽  
Norbert Marwan ◽  
Jürgen Kurths
Keyword(s):  
High Speed ◽  
Power Production ◽  
Acoustic Power ◽  
Spatiotemporal Dynamics ◽  
Combustion Noise ◽  
Pressure Oscillations ◽  
Power Sources ◽  
Thermoacoustic Instability ◽  
Stable Combustion ◽  
Large Clusters

In turbulent combustors, the transition from stable combustion (i.e. combustion noise) to thermoacoustic instability occurs via intermittency. During stable combustion, the acoustic power production happens in a spatially incoherent manner. In contrast, during thermoacoustic instability, the acoustic power production happens in a spatially coherent manner. In the present study, we investigate the spatiotemporal dynamics of acoustic power sources during the intermittency route to thermoacoustic instability using complex network theory. To that end, we perform simultaneous acoustic pressure measurement, high-speed chemiluminescence imaging and particle image velocimetry in a backward-facing step combustor with a bluff body stabilized flame at different equivalence ratios. We examine the spatiotemporal dynamics of acoustic power sources by constructing time-varying spatial networks during the different dynamical states of combustor operation. We show that as the turbulent combustor transits from combustion noise to thermoacoustic instability via intermittency, small fragments of acoustic power sources, observed during combustion noise, nucleate, coalesce and grow in size to form large clusters at the onset of thermoacoustic instability. This nucleation, coalescence and growth of small clusters of acoustic power sources occurs during the growth of pressure oscillations during intermittency. In contrast, during the decay of pressure oscillations during intermittency, these large clusters of acoustic power sources disintegrate into small ones. We use network measures such as the link density, the number of components and the size of the largest component to quantify the spatiotemporal dynamics of acoustic power sources as the turbulent combustor transits from combustion noise to thermoacoustic instability via intermittency.

Dynamic Characteristics of Balanced Robotic Manipulators with Joint Flexibility

Robotica ◽  
1992 ◽  
Vol 10 (6) ◽  
pp. 485-495 ◽  
Author(s):  
S.B. Lee ◽  
H.S. Cho
Keyword(s):  
Dynamic Characteristics ◽  
High Speed ◽  
Dynamic Properties ◽  
Dynamic Performance ◽  
Robotic Manipulators ◽  
Open Loop ◽  
Joint Flexibility ◽  
Damping Characteristics ◽  
Large Joint ◽  
Joint Deformation

SUMMARYThe mass balancing of robotic manipulators has been shown to have favorable effects on the dynamic characteristics. In actual practice, however, since conventional manipulators have flexibility at their joints, the improved dynamic properties obtainable for rigid manipulators may be influenced by those joint flexibilities. This paper investigates the effects of the joint flexibility on the dynamic properties and the controlled performance of a balanced robotic manipulator. The natural frequency distribution and damping characteristics were investigated through frequency response analyses. To evaluate the dynamic performance a series of simulation studies of the open loop dynamics were made for various trajectories, operating velocities, and joint stiffnesses. These simulations were also carried out for the balanced manipulator with a PD controller built-in inside motor control loop. The results show that, at low speed, the joint flexibility nearly does not influence the performance of the balanced manipulator, but at high speed it tends to render the balanced manipulator susceptible to vibratory motion and yields large joint deformation error.

Prediction of the in-service performance of a railway hydraulic damper

2016 ◽  
Vol 231 (1) ◽  
pp. 19-32
Author(s):  
Wenlin Wang ◽  
Dingsong Yu ◽  
Rui Xu
Keyword(s):  
High Speed ◽  
Influential Factors ◽  
Service Performance ◽  
Relief Valve ◽  
High Speed Rail ◽  
Hydraulic Damper ◽  
Damping Characteristics ◽  
Model And Simulation ◽  
Wide Range ◽  
Entrained Air

In this study, an improved physical parametric model with key in-service parameters was established and experimentally validated for a high-speed railway hydraulic damper. A subtle variable oil property model was built and coupled into the full model to address the dynamic flow losses and the relief-valve system dynamics. Experiments were conducted to evaluate the accuracy and robustness of the full damper model and simulation, which determined the damping characteristics over an extremely wide range of excitation speeds. Further simulations with in-service conditions and excitations were performed using the validated model, and the results revealed that improper key in-service parameters, such as improper rubber attachment stiffness, entrained air ratios and small mounting clearances, can greatly degrade the damping capability of a hydraulic damper. The obtained physical model includes all the influential factors that have an impact on the damping characteristics, so it will serve as a useful basic theory in the prediction of in-service performance, optimal specification and product design optimization of hydraulic dampers for modern high-speed rail vehicles.

scholarly journals INVESTIGATION OF CRITICAL HEAT FLUX ON ABRADED INCONEL 625 TUBE

2020 ◽  
Vol 28 ◽  
pp. 15-22
Author(s):  
Ladislav Suk ◽  
Kamil Števanka ◽  
Taron Petrosyan ◽  
Daniel Vlček
Keyword(s):  
Surface Roughness ◽  
High Speed ◽  
Flow Boiling ◽  
Glass Tube ◽  
Annular Channel ◽  
Low Flow ◽  
Inconel 625 ◽  
Confocal Laser ◽  
Outer Diameter ◽  
Flow Parameters

Aim of this work was to study flow boiling in an annular channel at low pressure and low flow on a tube with modified surface roughness. The tube with the outer diameter of 9.14 mm and the heated length of 380 mm was made of Inconel 625 and was manually modified using 150 grit sandpaper. The tube was placed in a glass tube with an inner diameter of 14.8 mm. Outlet pressure was set to 120, 200 and 300 kPa with varying mass flow from 400 to 600 kg/(m2.s). A high speed camera was used to record several experiments to fully understand ongoing phenomena. Surface roughness was analysed using a confocal laser microscope and the effects of different mass flux and pressure on the CHF value were observed. Above all, the optimization of the flow parameters was done from the collected data and from the observed behaviour of the experimental loop.

scholarly journals Spatiotemporal dynamics during the transition to thermoacoustic instability: Effect of varying turbulence intensities

2018 ◽  
Vol 10 (4) ◽  
pp. 337-350 ◽  
Author(s):  
Nitin B George ◽  
Vishnu R Unni ◽  
Manikandan Raghunathan ◽  
RI Sujith
Keyword(s):  
High Speed ◽  
Equivalence Ratio ◽  
Pressure Fluctuations ◽  
Spatial Dynamics ◽  
Local Heat ◽  
Spatiotemporal Dynamics ◽  
Combustion Noise ◽  
Pressure Oscillations ◽  
Thermoacoustic Instability ◽  
Turbulence Generator

An experimental study on a turbulent, swirl-stabilized backward facing step combustor is conducted to understand the spatiotemporal dynamics during the transition from combustion noise to thermoacoustic instability. By using a turbulence generator, we investigate the change in the spatiotemporal dynamics during this transition for added turbulence intensities. High-speed CH* images of the flame (representative of the field of local heat release rate fluctuations ([Formula: see text]( x, y, t))) and simultaneous unsteady pressure fluctuations ([Formula: see text]( t)) are acquired for different equivalence ratios. In the study, without the turbulence generator, as the equivalence ratio is reduced from near stoichiometric values, we observe an emergence of coherence in the spatial dynamics during the occurrence of intermittency, enroute to thermoacoustic instability. As the turbulence intensity is increased using the turbulence generator, we find that there is an advanced onset of thermoacoustic instability. Spatial statistics and the instantaneous fields of [Formula: see text] show that during the transition from combustion noise to thermoacoustic instability, the emergence of coherent spatial structures in the instantaneous fields of [Formula: see text] for the experiments with higher turbulence intensities is advanced. However, as the equivalence ratio is reduced further, we notice that higher turbulence intensities result in the reduction of the strength of the pressure oscillations during the state of thermoacoustic instability. We find that, at these low equivalence ratios, there is a decrease in the coherence due to the dispersal of [Formula: see text], which explains the reduction in the strength of the pressure oscillations.

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