Implementation in VIBIC of an Improved Time-Domain Simulation Model for Fluidelastic Instability in Tube Arrays

2014 ◽  
Author(s):  
Teguewinde Sawadogo ◽  
Yingke Han ◽  
Njuki Mureithi
Keyword(s):  
Time Domain ◽  
Continuous Extension ◽  
Computer Code ◽  
Force Model ◽  
Time Domain Simulation ◽  
Runge Kutta Method ◽  
Tube Arrays ◽  
Fluidelastic Instability ◽  
Excitation Mechanisms ◽  
Delay Differential

VIBIC (Vibration of Beams with Intermittent Contacts) is a non-linear dynamics computer code developed and maintained by Atomic Energy of Canada Limited over the past 40 years in collaboration with universities. Its main application is the assessment of possible vibration damage to steam-generator and heat exchanger tubes. This assessment is done by performing simulations of the vibration response of beam-like structures to various flow-induced excitation mechanisms, such as turbulence buffeting, vortex shedding, and fluidelastic excitation. Fluidelastic excitation is potentially the most damaging flow-induced excitation mechanism. The fluidelastic effect has, until now, been incorporated in VIBIC using the frequency-based Connors model. To properly perform a time-domain simulation of fluidelastic-induced vibration, a time-domain fluidelastic force model is needed. In the present work, a time-domain formulation of the fluidelastic forces based on the quasi-steady model is implemented in VIBIC. The time delay inherent to the quasi-steady model is taken into account by using a delayed displacement in the expression of the fluidelastic forces. The resulting modal equations are delay differential equations that are solved using a continuous extension of the Runge-Kutta method. Both linear and nonlinear fluid force models are incorporated. The fluidelastic instability results predicted by the models are compared to known theoretical and experimental results for validation. The predictions of the models are in good agreement with those results. The results given by the nonlinear quasi-steady fluidelastic forces are found to be more realistic than those of the linear quasi-steady fluidelastic forces. A realistic simulation of the post-instability behaviour is made possible through the use of the nonlinear fluidelastic forces.

scholarly journals Convolution-based time-domain simulation for fluidelastic instability in tube arrays

2021 ◽  
Author(s):  
Mingjie Zhang ◽  
Ole Øiseth
Keyword(s):  
Impulse Response ◽  
Response Function ◽  
Time Domain ◽  
Impulse Response Function ◽  
Time Domain Simulation ◽  
Unit Step ◽  
Tube Arrays ◽  
Unit Impulse ◽  
The Time Domain ◽  
Unit Impulse Response

AbstractA convolution-based numerical algorithm is presented for the time-domain analysis of fluidelastic instability in tube arrays, emphasizing in detail some key numerical issues involved in the time-domain simulation. The unit-step and unit-impulse response functions, as two elementary building blocks for the time-domain analysis, are interpreted systematically. An amplitude-dependent unit-step or unit-impulse response function is introduced to capture the main features of the nonlinear fluidelastic (FE) forces. Connections of these elementary functions with conventional frequency-domain unsteady FE force coefficients are discussed to facilitate the identification of model parameters. Due to the lack of a reliable method to directly identify the unit-step or unit-impulse response function, the response function is indirectly identified based on the unsteady FE force coefficients. However, the transient feature captured by the indirectly identified response function may not be consistent with the physical fluid-memory effects. A recursive function is derived for FE force simulation to reduce the computational cost of the convolution operation. Numerical examples of two tube arrays, containing both a single flexible tube and multiple flexible tubes, are provided to validate the fidelity of the time-domain simulation. It is proven that the present time-domain simulation can achieve the same level of accuracy as the frequency-domain simulation based on the unsteady FE force coefficients. The convolution-based time-domain simulation can be used to more accurately evaluate the integrity of tube arrays by considering various nonlinear effects and non-uniform flow conditions. However, the indirectly identified unit-step or unit-impulse response function may fail to capture the underlying discontinuity in the stability curve due to the prespecified expression for fluid-memory effects.

The Effect of Flat Bar Supports on Streamwise Fluidelastic Instability in Heat Exchanger Tube Arrays

2015 ◽  
Vol 137 (6) ◽  
Author(s):  
Marwan Hassan ◽  
David S. Weaver
Keyword(s):  
Sliding Friction ◽  
Chemical Plants ◽  
Streamwise Direction ◽  
Flow Induced Vibration ◽  
Direction Parallel ◽  
Short Period ◽  
Tube Arrays ◽  
Fluidelastic Instability ◽  
Excitation Mechanisms ◽  
Ambient Turbulence

Flow-induced vibration is an important criterion for the design of heat exchangers in nuclear, fossil, and chemical plants. Of the several known vibration excitation mechanisms, fluidelastic instability (FEI) is the most serious because it can cause tube failures in a relatively short period of time. Traditionally, FEI has been observed to occur in the direction transverse to the flow and antivibration bars have been used to stiffen the tubes against this motion. More recently, interest has increased in the possibility of FEI occurring in the streamwise direction, parallel to the flow. This is the subject of the present paper. Numerical simulations have been carried out to study the effects of tube-to-support clearance, tube sliding friction, tube-to-support preload, and ambient turbulence levels on the FEI threshold in the streamwise direction. As one would expect, increasing friction and tube preload against the support both tend to stabilize the tube against streamwise FEI. Importantly, the results also show that decreasing tube-support clearances destabilizes streamwise FEI while having little effect on transverse FEI. Increasing ambient turbulence levels also has the effect of destabilizing streamwise FEI.

The Effect of Flat Bar Supports on Streamwise Fluidelastic Instability in Heat Exchanger Tube Arrays

2014 ◽  
Author(s):  
Marwan Hassan ◽  
David S. Weaver
Keyword(s):  
Sliding Friction ◽  
Streamwise Direction ◽  
Flow Induced Vibration ◽  
Direction Parallel ◽  
Short Period ◽  
Tube Arrays ◽  
Fluidelastic Instability ◽  
Excitation Mechanisms ◽  
The Subject ◽  
Ambient Turbulence

Flow-induced vibration is an important criterion for the design of heat exchangers in nuclear, fossil and chemical plant. Of the several known vibration excitation mechanisms, fluidelastic instability (FEI) is the most serious because it can cause tube failures in a relatively short period of time. Traditionally, FEI has been observed to occur in the direction transverse to the flow and anti-vibration bars (AVB) have been used to stiffen the tubes against this motion. More recently, interest has increased in the possibility of FEI occurring in the streamwise direction, parallel to the flow. This is the subject of the present paper. Numerical simulations have been carried out to study the effects of tube-to-support clearance, tube sliding friction, tube-to-support preload, and ambient turbulence levels on the FEI threshold in the streamwise direction. As one would expect, increasing friction and tube preload against the support both tend to stabilize the tube against streamwise FEI. Importantly, the results also show that decreasing tube-support clearances destabilizes streamwise FEI while having little effect on transverse FEI. Increasing ambient turbulence levels also has the effect of destabilizing streamwise FEI.

Fluidelastic Instability of a Single Flexible Tube in a Rigid Tube Array

2010 ◽  
Author(s):  
Ahmed Khalifa ◽  
David Weaver ◽  
Samir Ziada
Keyword(s):  
Nuclear Power ◽  
Power Plants ◽  
Precise Control ◽  
Flexible Tube ◽  
Tube Arrays ◽  
Fluidelastic Instability ◽  
Excitation Mechanisms ◽  
The Stability ◽  
Square Array ◽  
Special Case

Tube and shell heat exchangers are commonly used in both fossil and nuclear power plants. The unexpected failure for such components is expensive and potentially dangerous. Of the various excitation mechanisms which can cause excessive tube vibration, fluidelastic instability is the most dangerous and therefore has received the most attention. The present study reviews the experimental work published in the open literature which involves the use of a single flexible tube in a rigid array to study fluidelastic instability. The data are categorized based on the array geometry into four main groups, parallel triangular, normal triangular, rotated square, and square array patterns. It is concluded from this review that the simplification of using a single flexible tube in a rigid array to study fluidelastic instability should be done with great care, and precise control of some parameters is essential to obtain reliable and repeatable results. Fluidelastic instability of a single flexible tube in a rigid array may occur in some cases, and may be used to improve our understanding of the phenomenon. However, it must be noted that this behavior is a special case and not generally useful for determining the stability of tube arrays.

Simulation of Fluidelastic Vibrations of Heat Exchanger Tubes With Loose Supports

2006 ◽  
Author(s):  
Marwan Hassan
Keyword(s):  
Fluid Flow ◽  
Heat Exchanger ◽  
Flow Velocity ◽  
Nonlinear Dynamic Analysis ◽  
Fretting Wear ◽  
Radial Clearance ◽  
Force Model ◽  
Forcing Function ◽  
Tube Arrays ◽  
Fluidelastic Instability

Fluidelastic instability is regarded as the most complex and destructive flow excitation mechanism in heat exchanger tube arrays subjected to cross fluid flow. Several attempts have been made for modelling fluidelastic instability in tube arrays in order to predict the stability threshold. However, fretting wear prediction requires a nonlinear computation of the tube dynamics in which proper modelling of the fluid forcing function is essential. In this paper, a time domain simulation of fluidelastic instability is presented for a single flexible tube in an otherwise rigid array subjected to cross fluid flow. The model is based on the unsteady flow theory proposed by Lever and Weaver [1] and Yetisir and Weaver [2]. The developed model has been implemented in INDAP (Incremental Nonlinear Dynamic Analysis Program), an in-house finite element code. Numerical investigations were performed for two linear tube-array geometries and compared with published experimental data. A reasonable agreement between the numerical simulation and the experimental results was obtained. The fluidelastic force model was also coupled with a tube/support interaction model. The developed numerical model was utilized to study a loosely-supported cantilever tube subjected to air flow. Tube-to-support clearance, random excitation level, and flow velocity were then varied. The results indicated that the loose support has a stabilizing effect on the tube response. Both rms impact force and normal work rate increased as a result of increasing the flow velocity or the support radial clearance. Contact ratio exhibited a sharp increase at a flow velocity higher than the instability threshold of the first unsupported mode. In addition, an interesting behaviour has been observed, namely the change of tube’s equilibrium position due to fluid forces. This causes a single-sided impact. At a higher turbulence level, double-sided impact conditions were dominant. The influence of these dynamic regimes on the tube/support parameters was also addressed.

Time Domain Simulation of Vortex-Induced Vibrations Based on Phase-Coupled Oscillator Synchronization

2015 ◽  
Author(s):  
Mats J. Thorsen ◽  
Svein Sævik ◽  
Carl M. Larsen
Keyword(s):  
Vortex Shedding ◽  
Time Domain ◽  
Hydrodynamic Force ◽  
Circular Cross Section ◽  
Cross Flow ◽  
Force Model ◽  
Time Domain Simulation ◽  
Local Flow ◽  
Hydrodynamic Damping ◽  
Vortex Induced Vibrations

Since 2012, there has been ongoing development of a simplified hydrodynamic force model at the Norwegian University of Science and Technology which enables time domain simulation of vortex-induced vibrations (VIV). Time domain simulation has a number of advantages compared to frequency domain. More specifically, having a time domain formulation of the hydrodynamic force which is efficient and reliable, will allow designers to include any relevant non-linear effects in their simulations, thereby increasing the level of realism and confidence in the results. The present model computes the dynamic cross-flow and in-line fluid force on a circular cross-section based on the incoming local flow velocity and the motion of the cylinder section. The most important difference between this and other existing models is the way synchronization between the vortex shedding and cylinder motion is taken into account. In contrast to the traditional VIV prediction tools, the vortex shedding frequency is in this model free to vary within a specified range, and changes according to the instantaneous phase difference between the cylinder velocity and the vortex shedding process itself. Hence, the oscillating lift and drag forces continuously update their frequencies, trying to lock on to the frequency of vibration. Combined with a simple hydrodynamic damping model and a constant added mass, it has previously been shown that highly realistic results can be obtained. In this paper, the theoretical background is reviewed, and the capabilities of the model are tested against new cases. These are: i) High mode VIV of tension-dominated riser in sheared flow, and ii) Low mode VIV of a pipeline with high bending stiffness. Both cross-flow and in-line vibrations are considered, and comparison with experimental observations is given. Based on the results, strengths and weaknesses of the model is discussed, and an outline of future developments is given.

Study of HVDC System and Subsynchronous Oscillation

2015 ◽  
Vol 1092-1093 ◽  
pp. 356-361
Author(s):  
Peng Fei Zhang ◽  
Lian Guang Liu
Keyword(s):  
Power Plant ◽  
Time Domain ◽  
Simulation Method ◽  
Time Domain Simulation ◽  
Stable Convergence ◽  
Turbine Generator ◽  
Plant Model ◽  
Subsynchronous Oscillation ◽  
Hvdc System ◽  
Simulation Results

With the application and development of Power Electronics, HVDC is applied more widely China. However, HVDC system has the possibilities to cause subsynchronous torsional vibration interaction with turbine generator shaft mechanical system. This paper simply introduces the mechanism, analytical methods and suppression measures of subsynchronous oscillation. Then it establishes a power plant model in islanding model using PSCAD, and analyzes the effects of the number and output of generators to SSO, and verifies the effect of SEDC and SSDC using time-domain simulation method. Simulation results show that the more number and output of generators is detrimental to the stable convergence of subsynchronous oscillation, and SEDC、SSDC can restrain unstable SSO, avoid divergence of SSO, ensure the generators and system operate safely and stably

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