scholarly journals Extremely large-amplitude oscillation of soft pipes conveying fluid under gravity

2020 ◽  
Vol 41 (9) ◽  
pp. 1381-1400
Author(s):  
Wei Chen ◽  
Ziyang Hu ◽  
Huliang Dai ◽  
Lin Wang
Keyword(s):  
Flow Velocity ◽  
Inclination Angle ◽  
Large Amplitude ◽  
Nonlinear Dynamic Analysis ◽  
Low Flow ◽  
Pipe Length ◽  
Inclination Angles ◽  
Internal Fluid Flow ◽  
The Stability ◽  
Conveying Fluid

Abstract In this work, the nonlinear behaviors of soft cantilevered pipes containing internal fluid flow are studied based on a geometrically exact model, with particular focus on the mechanism of large-amplitude oscillations of the pipe under gravity. Four key parameters, including the flow velocity, the mass ratio, the gravity parameter, and the inclination angle between the pipe length and the gravity direction, are considered to affect the static and dynamic behaviors of the soft pipe. The stability analyses show that, provided that the inclination angle is not equal to π, the soft pipe is stable at a low flow velocity and becomes unstable via flutter once the flow velocity is beyond a critical value. As the inclination angle is equal to π, the pipe experiences, in turn, buckling instability, regaining stability, and flutter instability with the increase in the flow velocity. Interestingly, the stability of the pipe can be either enhanced or weakened by varying the gravity parameter, mainly dependent on the value of the inclination angle. In the nonlinear dynamic analysis, it is demonstrated that the post-flutter amplitude of the soft pipe can be extremely large in the form of limit-cycle oscillations. Besides, the oscillating shapes for various inclination angles are provided to display interesting dynamical behaviors of the inclined soft pipe conveying fluid.

Parametric Resonances of a Cantilevered Pipe Conveying Fluid: A Nonlinear Analysis

1995 ◽  
Author(s):  
C. Semler ◽  
M. P. Païdoussis
Keyword(s):  
Flow Velocity ◽  
Standard Form ◽  
Harmonic Component ◽  
Harmonic Balance Method ◽  
Pipe Conveying Fluid ◽  
Mean Flow ◽  
Incremental Harmonic Balance Method ◽  
Inertial Terms ◽  
The Stability ◽  
Conveying Fluid

Abstract This paper deals with the nonlinear dynamics and the stability of cantilevered pipes conveying fluid, where the fluid has a harmonic component of flow velocity, assumed to be small, superposed on a constant mean value. The mean flow velocity is near the critical value for which the pipe becomes unstable by flutter through a Hopf bifurcation. The partial differential equation is transformed into a set of ordinary differential equations (ODEs) using the Galerkin method. The equations of motion contain nonlinear inertial terms, and hence cannot be put into standard form for numerical integration. Various approaches are adopted to tackle the problem: (a) a perturbation method via which the nonlinear inertial terms are removed by finding an equivalent term using the linear equation; the system is then put into first-order form and integrated using a Runge-Kutta scheme; (b) a finite difference method based on Houbolt’s scheme, which leads to a set of nonlinear algebraic equations that is solved with a Newton-Raphson approach; (c) the stability boundaries are obtained using an incremental harmonic balance method as proposed by S.L. Lau. Using the three methods, the dynamics of the pipe conveying fluid is investigated in detail. For example, the effects of (i) the forcing frequency, (ii) the perturbation amplitude, and (iii) the flow velocity are considered. Particular attention is paid to the effects of the nonlinear terms. These results are compared with experiments undertaken in our laboratory, utilizing elastomer pipes conveying water. The pulsating component of the flow is generated by a plunger pump, and the motions are monitored by a noncontacting optical follower system. It is shown, both numerically and experimentally, that periodic and quasiperiodic oscillations can exist, depending on the parameters.

scholarly journals Influence of Dry Friction on the Dynamics of Cantilevered Pipes Conveying Fluid

2022 ◽  
Vol 12 (2) ◽  
pp. 724
Author(s):  
Zilong Guo ◽  
Qiao Ni ◽  
Lin Wang ◽  
Kun Zhou ◽  
Xiangkai Meng
Keyword(s):  
Flow Velocity ◽  
Friction Force ◽  
Dry Friction ◽  
Critical Flow Velocity ◽  
Pipe System ◽  
Pipes Conveying Fluid ◽  
Cantilevered Pipe ◽  
The Stability ◽  
Friction Parameters ◽  
Conveying Fluid

A cantilevered pipe conveying fluid can lose stability via flutter when the flow velocity becomes sufficiently high. In this paper, a dry friction restraint is introduced for the first time, to evaluate the possibility of improving the stability of cantilevered pipes conveying fluid. First, a dynamical model of the cantilevered pipe system with dry friction is established based on the generalized Hamilton’s principle. Then the Galerkin method is utilized to discretize the model of the pipe and to obtain the nonlinear dynamic responses of the pipe. Finally, by changing the values of the friction force and the installation position of the dry friction restraint, the effect of dry friction parameters on the flutter instability of the pipe is evaluated. The results show that the critical flow velocity of the pipe increases with the increment of the friction force. Installing a dry friction restraint near the middle of the pipe can significantly improve the stability of the pipe system. The vibration of the pipe can also be suppressed to some extent by setting reasonable dry friction parameters.

Stability and Dynamic Evolution of Sliding Fluid-Transporting Pipes in Three-Dimensional Sense

2020 ◽  
Vol 20 (03) ◽  
pp. 2050036
Author(s):  
Xiping Sun ◽  
Hao Yan ◽  
Huliang Dai
Keyword(s):  
Flow Velocity ◽  
Three Dimensional ◽  
Flow Speed ◽  
Low Flow ◽  
Single Type ◽  
Dynamic Evolution ◽  
Transient Vibration ◽  
Aerial Refueling ◽  
Dynamic Behaviors ◽  
Conveying Fluid

This paper deals with the stability and dynamic evolution of a sliding pipe conveying fluid in the three-dimensional sense. The pipe is assumed to slide out from a fixed channel so that its free end is moving at the same time, a problem often associated with instabilities in applications of aerial refueling operation. To tackle this problem, the nonlinear governing equations of motion are derived by using the Hamilton’s principle and then reduced to a set of ordinary differential equations by the Galerkin’s method. A parametric study is performed to explore the transient vibration responses of the pipe for different values of flow velocity and sliding rate. Various dynamic behaviors are detected for the pipe in sliding and conveying fluid. The results show that 3-D oscillations of the pipe occur when the flow velocity exceeds a certain value, which can be affected by the sliding rate. For various flow velocities, the evolution of the dynamic characteristics of the sliding pipe can be classified into three typical types of motion. When at low flow velocity, the pipe is mainly subjected to a single type of 3-D motion. When the flow speed increases to high values, multi-type of 3-D motion consisting of three typical types occurs on the pipe. In addition, the pipe can display planar motions, transferring from one plane to the other. The result presented herein is helpful to understand the stabilities and dynamic behaviors of sliding-pipe systems used in aerial refueling applications.

scholarly journals Stability of a Melt Pool during 3D-Printing of an Unsupported Steel Component and Its Influence on Roughness

Materials ◽  
2020 ◽  
Vol 13 (3) ◽  
pp. 808
Author(s):  
Mateusz Skalon ◽  
Benjamin Meier ◽  
Andreas Gruberbauer ◽  
Sergio de Traglia Amancio-Filho ◽  
Christof Sommitsch
Keyword(s):  
Inclination Angle ◽  
Cross Sections ◽  
Energy Input ◽  
Contact Angles ◽  
Steel Component ◽  
Powder Bed ◽  
Melt Pool ◽  
Inclination Angles ◽  
3D Printed ◽  
The Stability

The following work presents the results of an investigation of the cause–effect relationship between the stability of a melt pool and the roughness of an inclined, unsupported steel surface that was 3D-printed using the laser powder bed fusion (PBF-L/M) process. In order to observe the balling effect and decrease in surface quality, the samples were printed with no supporting structures placed on the downskin. The stability of the melt pool was investigated as a function of both the inclination angle and along the length of the melt pool. Single-track cross-sections were described by shape parameters and were compared and used to calculate the forces acting on the melt pool as the downskin was printed. The single-melt track tests were printed to produce a series of samples with increasing inclination angles with respect to the baseplate. The increasing angles enabled us to physically simulate specific solidification conditions during the sample printing process. As the inclination angle of the unsupported surface increased, the melt-pool altered in terms of its size, geometry, contact angles, and maximum length of stability. The balling phenomenon was observed, quantified, and compared using roughness tests; it was influenced by the melt track stability according to its geometry. The research results show that a higher linear energy input may decrease the roughness of unsupported surfaces with low inclination angles, while a lower linear energy input may be more effective with higher inclination angles.

scholarly journals Design of Low Flow Undershot Type Water Turbine

2019 ◽  
Vol 2 (2) ◽  
pp. 50 ◽  
Author(s):  
E. Y. Setyawan ◽  
S. Djiwo ◽  
D. H. Praswanto ◽  
P Suwandono ◽  
P. Siagian
Keyword(s):  
Energy Source ◽  
Flow Velocity ◽  
Power Efficiency ◽  
River Flow ◽  
Low Flow ◽  
Simple Design ◽  
Computational Power ◽  
Water Turbine ◽  
Type Water ◽  
The Stability

Many water sources around us which have kinetic energy to run waterwheels are not optimally utilized. This energy can be converted into an energy source that can produce electricity. Therefore this study produced a design of a waterwheel that could be used in low-flow rivers to produce electricity by adding generators. Waterwheel modeling using Ansys is calculated based on flow assumptions. Modeling using this system provides advantages in the form of computational power efficiency, the stability of numerical calculations and the accuracy of the resulting solutions. Numerical analysis of the waterwheel is assumed that the waterwheel is half floating on the surface of the water. As stated in the limitation of the problem that the incoming water flowing at a speed of 5 m/s from the flow moves the wheel. The flow rate of water that hit the blade on the waterwheel causes the waterwheel to rotate which is pressured by the flow of water with a number of 12 blades. With a relatively simple design, the waterwheel produces a wheel rotation I of 91 Rpm and II of 78 Rpm, with a torque of 39.2 N by using some analysis of this design can be applied to river flow with low flow velocity. The relatively simple design makes it easy to be produced and maintenance. River flow used is in the Malang District with a flow velocity of 1 m/s gets a power of 1128 W on waterwheel I while on waterwheel II gets a power of 967 W.

scholarly journals W1FINITE ELEMENT ANALYSIS OF PIPES CONVEYING FLUID MOUNTED ON VISCOELASTIC FOUNDATIONS

2019 ◽  
Vol 19 (3) ◽  
pp. 14 ◽  
Author(s):  
Nawras Mostafa
Keyword(s):  
Flow Velocity ◽  
Natural Frequency ◽  
Damping Ratio ◽  
Fluid Velocity ◽  
Critical Flow ◽  
Fluid Density ◽  
Element Analysis ◽  
Pipe Length ◽  
Critical Flow Velocity ◽  
Conveying Fluid

AbstractIn this study, the stability of a simply supported pipeline conveying fluid with different velocities and resting on viscoelastic foundation is investigated by using finite element analysis, and the critical fluid velocity with different parameters such as stiffness and viscous coefficients of foundation are obtained. This structural system could be found in pipes conveying petrol, water, and sewage. The foundation is simulated using the modified Winkler's model to introduce the effect of time dependent viscosity term. Some known results are confirmed and some new ones obtained. Two components of foundation, stiffness and viscosity, seemed to act on the critical flow velocity of the pipe in contrary trend. Where, increasing the foundation stiffness tended to increase the critical flow velocity in the pipe. While, increasing foundation viscosity attempted to decrease it. At some ranges of pipe length, the foundation viscosity effect seems to be more extreme. Increasing the fluid velocity leads to monotonic reduction in the system damping ratio. Two parameters, pipe length and fluid density which relate to the natural frequency of pipeline conveying fluid are studied in detail and the results indicate that the effect of Coriolis force on natural frequency is become more effective by increasing pipe length and fluid density besides increasing fluid flow velocity.

scholarly journals Near-occlusion is difficult to diagnose with common carotid ultrasound methods

2021 ◽  
Vol 63 (5) ◽  
pp. 721-730
Author(s):  
Elias Johansson ◽  
Davide Vanoli ◽  
Isa Bråten-Johansson ◽  
Lucy Law ◽  
Richard I Aviv ◽  
...  
Keyword(s):  
Flow Velocity ◽  
Sensitivity And Specificity ◽  
Low Flow ◽  
Reference Standard ◽  
Carotid Ultrasound ◽  
Ultrasound Method ◽  
Velocity Parameter ◽  
Near Occlusion

Abstract Purpose To assess the sensitivity and specificity of common carotid ultrasound method for carotid near-occlusion diagnosis. Methods Five hundred forty-eight patients examined with both ultrasound and CTA within 30 days of each other were analyzed. CTA graded by near-occlusion experts was used as reference standard. Low flow velocity, unusual findings, and commonly used flow velocity parameters were analyzed. Results One hundred three near-occlusions, 272 conventional ≥50% stenosis, 162 <50% stenosis, and 11 occlusions were included. Carotid ultrasound was 22% (95%CI 14–30%; 23/103) sensitive and 99% (95%CI 99–100%; 442/445) specific for near-occlusion diagnosis. Near-occlusions overlooked on ultrasound were found misdiagnosed as occlusions (n = 13, 13%), conventional ≥50% stenosis (n = 65, 63%) and < 50% stenosis (n = 2, 2%). No velocity parameter or combination of parameters could identify the 65 near-occlusions mistaken for conventional ≥50% stenoses with >75% sensitivity and specificity. Conclusion Near-occlusion is difficult to diagnose with commonly used carotid ultrasound methods. Improved carotid ultrasound methods are needed if ultrasound is to retain its position as sole preoperative modality.

scholarly journals Acoustic Emission Characteristics and Joint Nonlinear Mechanical Response of Rock Masses under Uniaxial Compression

Energies ◽  
2021 ◽  
Vol 14 (1) ◽  
pp. 200
Author(s):  
Zhongliang Feng ◽  
Xin Chen ◽  
Yu Fu ◽  
Shaoshuai Qing ◽  
Tongguan Xie
Keyword(s):  
Acoustic Emission ◽  
Uniaxial Compression ◽  
Inclination Angle ◽  
Failure Modes ◽  
Strain Curve ◽  
Particle Flow Code ◽  
Rock Masses ◽  
Physical Experiments ◽  
Inclination Angles ◽  
Joint Inclination

The joint arrangement in rock masses is the critical factor controlling the stability of rock structures in underground geotechnical engineering. In this study, the influence of the joint inclination angle on the mechanical behavior of jointed rock masses under uniaxial compression was investigated. Physical model laboratory experiments were conducted on jointed specimens with a single pre-existing flaw inclined at 0°, 30°, 45°, 60°, and 90° and on intact specimens. The acoustic emission (AE) signals were monitored during the loading process, which revealed that there is a correlation between the AE characteristics and the failure modes of the jointed specimens with different inclination angles. In addition, particle flow code (PFC) modeling was carried out to reproduce the phenomena observed in the physical experiments. According to the numerical results, the AE phenomenon was basically the same as that observed in the physical experiments. The response of the pre-existing joint mainly involved three stages: (I) the closing of the joint; (II) the strength mobilization of the joint; and (III) the reopening of the joint. Moreover, the response of the pre-existing joint was closely related to the joint’s inclination. As the joint inclination angle increased, the strength mobilization stage of the joint gradually shifted from the pre-peak stage of the stress–strain curve to the post-peak stage. In addition, the instantaneous drop in the average joint system aperture (aave) in the specimens with medium and high inclination angles corresponded to a rapid increase in the form of the pulse of the AE activity during the strength mobilization stage.

Corrosion Rate Measurement by Hydrogen Effusion In Dynamic Aqueous Systems At Elevated Temperature and Pressure

CORROSION ◽  
1959 ◽  
Vol 15 (4) ◽  
pp. 29-32
Author(s):  
M. KRULFELD ◽  
M. C. BLOOM ◽  
R. E. SEEBOLD
Keyword(s):  
Elevated Temperature ◽  
Corrosion Rate ◽  
Flow Velocity ◽  
High Flow ◽  
Low Flow ◽  
Aqueous Systems ◽  
Effusion Rates ◽  
Temperature And Pressure ◽  
Effusion Method ◽  
Hydrogen Effusion

Abstract A method of applying the hydrogen effusion method to the measurement of corrosion rates in dynamic aqueous systems at elevated temperature and pressure is described. Data obtained in low carbon steel systems are presented, including (1) reproducibility obtained in measured hydrogen effusion rates at a flow velocity of 1 foot per second at a temperature of 600 F and 2000 psi, and (2) a quantitative comparison between the hydrogen effusion rates in static and in low flow velocity dynamic systems at this temperature and pressure. Some observations are included on corrosion rate measurements in a high flow velocity (30 feet per second) loop by the hydrogen effusion method. Implications of these measurements with regard to the comparison between high flow velocity corrosion and low flow velocity corrosion are mentioned and some data indicating high local sensitivity of the hydrogen effusion method are noted. Some possible difficulties involved in the method are pointed out. 2.3.4

Nonlinear Analysis of L-shaped Pipe Conveying Fluid with the Aid of Absolute Nodal Coordinate Formulation

2021 ◽  
Author(s):  
K. Zhou ◽  
H.R. Yi ◽  
Huliang Dai ◽  
H Yan ◽  
Z.L. Guo ◽  
...  
Keyword(s):  
Theoretical Model ◽  
Flow Velocity ◽  
Absolute Nodal Coordinate Formulation ◽  
Strong Relationship ◽  
Excitation Amplitude ◽  
Pipe Conveying Fluid ◽  
Base Excitation ◽  
Absolute Nodal Coordinate ◽  
Nonlinear Behaviors ◽  
Conveying Fluid

Abstract By adopting the absolute nodal coordinate formulation, a novel and general nonlinear theoretical model, which can be applied to solve the dynamics of combined straight-curved fluid-conveying pipes with arbitrary initially configurations and any boundary conditions, is developed in the current study. Based on this established model, the nonlinear behaviors of the cantilevered L-shaped pipe conveying fluid with and without base excitations are systematically investigated. Before starting the research, the developed theoretical model is verified by performing three validation examples. Then, with the aid of this model, the static deformations, linear stability, and nonlinear self-excited vibrations of the L-shaped pipe without the base excitation are determined. It is found that the cantilevered L-shaped pipe suffers from the static deformations when the flow velocity is subcritical, and will undergo the limit-cycle motions as the flow velocity exceeds the critical value. Subsequently, the nonlinear forced vibrations of the pipe with a base excitation are explored. It is indicated that the period-n, quasi-periodic and chaotic responses can be detected for the L-shaped pipe, which has a strong relationship with the flow velocity, excitation amplitude and frequency.

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