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.

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.

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.

Generalized Mellin Convolutions and their Asymptotic Expansions

1984 ◽  
Vol 36 (5) ◽  
pp. 924-960 ◽  
Author(s):  
R. Wong ◽  
J. P. Mcclure
Keyword(s):  
Asymptotic Expansions ◽  
Fractional Integral ◽  
Integral Transform ◽  
Integral Transforms ◽  
Generalized Function ◽  
Positive Parameter ◽  
Ordinary Sense ◽  
Integrable Functions ◽  
Classical Integral ◽  
Image Position

A large number of important integral transforms, such as Laplace, Fourier sine and cosine, Hankel, Stieltjes, and Riemann- Liouville fractional integral transforms, can be put in the form1.1where f(t) and the kernel, h(t), are locally integrable functions on (0,∞), and x is a positive parameter. Recently, two important techniques have been developed to give asymptotic expansions of I(x) as x → + ∞ or x → 0+. One method relies heavily on the theory of Mellin transforms [8] and the other is based on the use of distributions [24]. Here, of course, the integral I(x) is assumed to exist in some ordinary sense.If the above integral does not exist in any ordinary sense, then it may be regarded as an integral transform of a distribution (generalized function). There are mainly two approaches to extend the classical integral transforms to distributions.

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 Development of a Digital Model of a Beta Function Based on Mellin’s Integral Transforms

2021 ◽  
Vol 2096 (1) ◽  
pp. 012108
Author(s):  
A M Makarov ◽  
A S Ermakov ◽  
E A Pisarenko ◽  
V A Ryndiuk
Keyword(s):  
Signal Processing ◽  
High Speed ◽  
Beta Function ◽  
Integral Transforms ◽  
Digital Model ◽  
Computer Algorithms ◽  
Unknown Phase ◽  
Phase Sequence ◽  
Logarithmic Functions ◽  
Special Case

Abstract The implementation of a digital model of the beta function for use in computer algorithms is a time-consuming task. This is due to the complexity of the high-precision representation of its integrand functions, which require a large number of intermediate operations, which entails a large load on the computational power. Purpose: Development of the basic theoretical provisions of the integral Mellin transform in relation to the theory of signal processing against the background of noise and research of their discrete representation. Results: It is shown in the paper that the beta function can be considered as a special case of Mellin’s integral transforms. Based on this statement, a mathematical model of the beta function was developed. Using the properties of parametrically periodic oscillations belonging to the class of trigonometric-logarithmic functions, it was possible to create a digital model for representing the beta function. Practical relevance: Based on the established digital model can be realized a high-speed algorithm for calculating the beta function with a given accuracy. Such algorithms can serve as a basis for creating signal processing programs in order to detect wideband phase-shift keyed signals against a background of noise with an unknown phase sequence. An example of using such algorithms is the search for Wi-Fi bugs.

Using Change Point Analysis for Image Processing of Developing Adiabatic Two-Phase Flow After Expansion Valve

2007 ◽  
Author(s):  
Chad D. Bowers ◽  
Predrag S. Hrnjak
Keyword(s):  
Change Point ◽  
High Speed ◽  
Separation Distance ◽  
Change Point Analysis ◽  
Working Fluid ◽  
High Speed Camera ◽  
Two Phase ◽  
Flow Parameters ◽  
Point Analysis ◽  
Expansion Valve

This paper presents a method of analyzing images obtained from a high speed camera in a study of developing two-phase refrigerant flow after an expansion valve, using a technique known as Change Point Analysis. Specifically, a method for automating the determination of separation distance and the location of the liquid/vapor interface in stratified type flows is outlined. The experiments were conducted in transparent PVC tubes, with inner diameters of 8.7mm and 15.3mm. A working fluid of oil free R134a was used. Dynamic flow parameters of inlet quality and mass flux were varied from 5–35% and 15–40g/s, respectively. Flow visualization was achieved through the use of a high speed camera.

Sign in / Sign up

Export Citation Format

Share Document