Time Domain Models for Damping-Controlled Fluidelastic Instability Forces in Tubes With Loose Supports

2010 ◽  
Vol 132 (4) ◽  
Author(s):  
Marwan Hassan ◽  
Achraf Hossen
Keyword(s):  
Time Domain ◽  
Cross Flow ◽  
Work Rate ◽  
Interaction Parameters ◽  
Similar Response ◽  
Fluid Force ◽  
Support Interaction ◽  
Fluidelastic Instability ◽  
The Impact ◽  
Normal Work

This paper presents simulations of a loosely supported cantilever tube subjected to turbulence and fluidelastic instability forces. Several time domain fluid force models are presented to simulate the damping-controlled fluidelastic instability mechanism in tube arrays. These models include a negative damping model based on the Connors equation, fluid force coefficient-based models (Chen, 1983, “Instability Mechanisms and Stability Criteria of a Group of Cylinders Subjected to Cross-Flow. Part 1: Theory,” Trans. ASME, J. Vib., Acoust., Stress, Reliab. Des., 105, pp. 51–58; Tanaka and Takahara, 1981, “Fluid Elastic Vibration of Tube Array in Cross Flow,” J. Sound Vib., 77, pp. 19–37), and two semi-analytical models (Price and Païdoussis, 1984, “An Improved Mathematical Model for the Stability of Cylinder Rows Subjected to Cross-Flow,” J. Sound Vib., 97(4), pp. 615–640; Lever and Weaver, 1982, “A Theoretical Model for the Fluidelastic Instability in Heat Exchanger Tube Bundles,” ASME J. Pressure Vessel Technol., 104, pp. 104–147). Time domain modeling and implementation challenges for each of these theories were discussed. For each model, the flow velocity and the support clearance were varied. Special attention was paid to the tube/support interaction parameters that affect wear, such as impact forces and normal work rate. As the prediction of the linear threshold varies depending on the model utilized, the nonlinear response also differs. The investigated models exhibit similar response characteristics for the lift response. The greatest differences were seen in the prediction of the drag response, the impact force level, and the normal work rate. Simulation results show that the Connors-based model consistently underestimates the response and the tube/support interaction parameters for the loose support case.

Time Domain Models for Damping-Controlled Fluidelastic Instability Forces in Tubes With Loose Supports

2009 ◽  
Author(s):  
Marwan Hassan ◽  
Achraf Hossen
Keyword(s):  
Time Domain ◽  
Work Rate ◽  
Analytical Models ◽  
Interaction Parameters ◽  
Similar Response ◽  
Force Coefficient ◽  
Fluid Force ◽  
Support Interaction ◽  
Fluidelastic Instability ◽  
Normal Work

This paper presents simulations of a loosely supported cantilever tube subjected to turbulence and fluidelastic instability forces. Several time-domain fluid force models simulating the damping controlled fluidelastic instability mechanism in tube arrays have been presented. These models include the negative damping model based on the Connors equation, fluid force coefficient-based models (Chen and Tanaka and Takahara), and two semi-analytical models (Price and Pai¨doussis; and Lever and Weaver). Time domain modelling and implementation challenges for each of these theories were discussed. For each model the flow velocity and the support clearance were varied. Special attention was paid to the tube/support interaction parameters that affect wear, such as impact forces and normal work rate. As the prediction of the linear threshold varies depending on the model utilized, the nonlinear response also differs. The investigated models exhibit similar response characteristics for the lift response. The greatest differences were seen in the prediction of the drag response, impact force level and normal work rate. Simulation results show that the Connors-based model consistently underestimates the response and the tube/support interaction parameters for the loose support case.

Time Domain Models for Damping-Controlled Fluidelastic Instability Forces in Multi-Span Tubes With Loose Supports

2010 ◽  
Author(s):  
Marwan Hassan ◽  
Robert Rogers ◽  
Andrew Gerber
Keyword(s):  
Flow Velocity ◽  
Time Domain ◽  
Work Rate ◽  
Interaction Parameters ◽  
Similar Response ◽  
Critical Flow Velocity ◽  
Fluid Force ◽  
Support Interaction ◽  
Fluidelastic Instability ◽  
The Impact

This paper presents simulations of a loosely supported multi-span tube subjected to turbulence and fluidelastic instability forces. Several time-domain fluid force models simulating the damping controlled fluidelastic instability mechanism in tube arrays are presented. These models include the negative damping model based on the Connors equation, fluid force coefficient-based models (Chen; Tanaka and Takahara), and two semi-analytical models (Price and Pai¨doussis; and Lever and Weaver). Time domain modelling challenges for each of these theories are discussed. The implemented models are validated against available experimental data. The linear simulations show that the Connors-equation based model exhibits the most conservative prediction of the critical flow velocity when the recommended design values for the Connors equation are used. The models are then utilized to simulate the nonlinear response of a three-span cantilever tube in a lattice bar support subjected to air crossflow. The tube is subjected to a single-phase flow passing over one of the tubes spans and the flow velocity and the support clearance are varied. Special attention is paid to the tube/support interaction parameters that affect wear, such as impact forces, contact ratio, and normal work rate. As was seen for the linear cases, the reduced flow velocity at the instability threshold differs for the fluid force models considered. The investigated models do, however, exhibit similar response characteristics for the impact force, tip lift response, and work rate, except for the Connors-based model that overestimates the response and the tube/support interaction parameters for the loose support case, especially at large clearances.

Vibration and Work-Rate Measurements of Steam-Generator U-Tubes in Air-Water Cross-Flow

2002 ◽  
Author(s):  
Victor P. Janzen ◽  
Erik G. Hagberg ◽  
James N. F. Patrick ◽  
Michel J. Pettigrew ◽  
Colette E. Taylor ◽  
...  
Keyword(s):  
Cross Flow ◽  
Work Rate ◽  
Vibration Response ◽  
Fretting Wear ◽  
Steam Generators ◽  
Two Phase ◽  
Void Fractions ◽  
Vibration Properties ◽  
Wide Range ◽  
Fluidelastic Instability

In nuclear power plant steam generators, the vibration response of tubes in two-phase cross-flow is a general concern that in some cases has become a very real long-term wear problem. This paper summarizes the results of the most recent U-bend vibration-response tests in a program designed to address this issue. The tests involved a simplified U-tube bundle with a set of flat-bar supports at the apex, subjected to two-phase air-water cross-flow over the mid-span region of the U-bend. Tube vibration properties and tube-to-support interaction in the form of work-rates were measured over a wide range of flow velocities for homogeneous void fractions from zero to 90%, with three different tube-to-support clearances. The measured vibration properties and work-rates could be characterized by the relative influence of the two most important flow-induced excitation mechanisms at work, fluidelastic instability and random-turbulence excitation. As in previous similar tests, strong effects of fluidelastic instability were observed at zero and 25% void fraction for pitch velocities greater than approximately 0.5 m/s, whereas random turbulence dominated the tube vibration and work-rate response at higher void fractions. In both cases, a link between vibration properties and the effect of the flat-bar supports could be established by comparing the vibration crossing frequency, extracted from time-domain vibration signals, to the participation of the lowest few vibration modes and to the measured work-rate. This approach may be useful when fluidelastic instability, random turbulence and loose supports all combine to result in high work-rates. Such a combination of factors is thought to be responsible for excessive U-tube fretting-wear in certain types of operating steam generators.

Streamwise Fluidelastic Instability of Tube Arrays in Two-Phase Cross Flow

2014 ◽  
Author(s):  
Stephen Olala ◽  
Njuki W. Mureithi
Keyword(s):  
Nuclear Power ◽  
Single Phase ◽  
Cross Flow ◽  
Force Measurements ◽  
Two Phase Flows ◽  
Two Phase ◽  
Fluid Force ◽  
Void Fractions ◽  
Tube Arrays ◽  
Fluidelastic Instability

In-plane instability of tube arrays has not been a major concern to steam generator designers until recently following observations of streamwise tube failure in a nuclear power plant in U.S.A. However, modeling of fluidelastic instability in two-phase flows still remains a challenge. In the present work, detailed steady fluid force measurements for a kernel of an array of tubes in a rotated triangular tube array of P/D=1.5 subjected to air-water two-phase flows for a series of void fractions and a Reynolds number (based on the pitch velocity), Re = 7.2 × 104 has been conducted. The measured steady fluid force coefficients and their derivatives, with respect to streamwise static displacements of the central tube, are employed in the quasi-steady model [1, 2], originally developed for single phase flows, to analyze in-plane fluidelastic instability of multiple flexible arrays in two-phase flows. The results are consistent with dynamic stability tests [3].

Numerical Characterization of the Area Perturbation and Timelag for a Vibrating Tube Subjected to Cross-Flow

2014 ◽  
Author(s):  
Salim El Bouzidi ◽  
Marwan Hassan ◽  
Lais L. Fernandes ◽  
Atef Mohany
Keyword(s):  
Tube Bundle ◽  
Cross Flow ◽  
Theoretical Models ◽  
Design Guidelines ◽  
Navier Stokes ◽  
Arbitrary Lagrangian Eulerian ◽  
Dynamic Simulations ◽  
Numerical Characterization ◽  
Fluidelastic Instability ◽  
The Impact

Fluidelastic instability can have disastrous effects on the integrity of steam generators. Over the last five decades there has been a great deal of research done in an attempt to understand this phenomenon. These efforts have resulted in several theoretical models and design guidelines. The semi-analytical model of fluidelastic instability initially developed by Lever and Weaver is based on a single tube in a channel flow. The mechanism responsible for instability was found to be one of flow redistribution. While previous studies have been able to characterize the pressure and velocity within a tube bundle, the behaviour of the area of the channel has not yet been fully investigated. The current study aims to characterize the area of the channel surrounding the tube. Reynolds Averaged Navier Stokes (RANS) equations are cast in an Arbitrary Lagrangian Eulerian (ALE) form and are used to compute the flow conditions in a rigid tube bundle due to a single flexible tube vibrating in the transverse direction. The properties of the velocity field are used to determine the channel boundaries. Properties of the channel area such as area perturbation, mean area, and area phase are investigated for various reduced flow velocities. Dynamic simulations are conducted to determine the impact on the stability threshold for transverse fluid force cases using a mass damping parameter range of 10–200.

Modeling of Fluidelastic Instability Forces in Fully Flexible Tube Arrays

2007 ◽  
Author(s):  
Faisal Mahmood ◽  
Marwan Hassan
Keyword(s):  
Flow Field ◽  
Time Domain ◽  
Tube Bundle ◽  
Cross Flow ◽  
High Mass ◽  
System Response ◽  
Domain Modeling ◽  
Flexible Tube ◽  
Proposed Model ◽  
Fluidelastic Instability

Fluidelastic instability remains the most devastating phenomenon in tube bundles subjected to cross-flow. Models have been developed to estimate the threshold of instability. Moreover, several time-domain models of fluidelastic instability have been developed to determine tube/support interaction parameters of tubes with loose supports. The present work deals with time domain modeling of fluid-elastic instability forces in a fully flexible tube array subjected to cross-flow. The model is based on the flow redistribution theory proposed initially by Lever and Weaver [1]. The proposed model utilizes fewer input parameters and can model various tube bundle geometries with any pitch-to-diameter ratio. Finite element method is used for solving the system response. The flow field inside the tube array is discretized into flow subdomains, each of which is surrounded by 4 tubes. The perturbation in the flow field, within each subdomain, is obtained by superimposing the effects of neighboring tube motions. The model has been applied to assess the response of a single flexible tube as well as multiple flexible tubes. It is shown that the single flexible model overestimates the stability threshold compared to the multiple flexible tube counterpart, especially at high mass-damping parameters. The results show a good agreement between the predicted and the experimental results. The proposed model does not assume any predetermined tube response or any tube motion pattern.

scholarly journals Classification of standing and sitting phases based on in-socket piezoelectric sensors in a transfemoral amputee

2020 ◽  
Vol 0 (0) ◽  
Author(s):  
Tawfik Yahya ◽  
Nur Azah Hamzaid ◽  
Sadeeq Ali ◽  
Farahiyah Jasni ◽  
Hanie Nadia Shasmin
Keyword(s):  
Time Domain ◽  
Classification Accuracy ◽  
Sensory System ◽  
Metabolic Energy ◽  
Support Vector ◽  
Data Set ◽  
Transfemoral Amputee ◽  
Sit To Stand ◽  
Optimal Classifier ◽  
The Impact

AbstractA transfemoral prosthesis is required to assist amputees to perform the activity of daily living (ADL). The passive prosthesis has some drawbacks such as utilization of high metabolic energy. In contrast, the active prosthesis consumes less metabolic energy and offers better performance. However, the recent active prosthesis uses surface electromyography as its sensory system which has weak signals with microvolt-level intensity and requires a lot of computation to extract features. This paper focuses on recognizing different phases of sitting and standing of a transfemoral amputee using in-socket piezoelectric-based sensors. 15 piezoelectric film sensors were embedded in the inner socket wall adjacent to the most active regions of the agonist and antagonist knee extensor and flexor muscles, i. e. region with the highest level of muscle contractions of the quadriceps and hamstring. A male transfemoral amputee wore the instrumented socket and was instructed to perform several sitting and standing phases using an armless chair. Data was collected from the 15 embedded sensors and went through signal conditioning circuits. The overlapping analysis window technique was used to segment the data using different window lengths. Fifteen time-domain and frequency-domain features were extracted and new feature sets were obtained based on the feature performance. Eight of the common pattern recognition multiclass classifiers were evaluated and compared. Regression analysis was used to investigate the impact of the number of features and the window lengths on the classifiers’ accuracies, and Analysis of Variance (ANOVA) was used to test significant differences in the classifiers’ performances. The classification accuracy was calculated using k-fold cross-validation method, and 20% of the data set was held out for testing the optimal classifier. The results showed that the feature set (FS-5) consisting of the root mean square (RMS) and the number of peaks (NP) achieved the highest classification accuracy in five classifiers. Support vector machine (SVM) with cubic kernel proved to be the optimal classifier, and it achieved a classification accuracy of 98.33 % using the test data set. Obtaining high classification accuracy using only two time-domain features would significantly reduce the processing time of controlling a prosthesis and eliminate substantial delay. The proposed in-socket sensors used to detect sit-to-stand and stand-to-sit movements could be further integrated with an active knee joint actuation system to produce powered assistance during energy-demanding activities such as sit-to-stand and stair climbing. In future, the system could also be used to accurately predict the intended movement based on their residual limb’s muscle and mechanical behaviour as detected by the in-socket sensory system.

scholarly journals Functional Modification of Cellulose Acetate Microfiltration Membranes by Supercritical Solvent Impregnation

Molecules ◽  
2021 ◽  
Vol 26 (2) ◽  
pp. 411
Author(s):  
Irena Zizovic ◽  
Marcin Tyrka ◽  
Konrad Matyja ◽  
Ivana Moric ◽  
Lidija Senerovic ◽  
...  
Keyword(s):  
Cellulose Acetate ◽  
Ion Beam ◽  
Antibacterial Properties ◽  
Cross Flow ◽  
Batch Mode ◽  
Impregnation Process ◽  
Supercritical Solvent ◽  
Cross Flow Filtration ◽  
Microfiltration Membranes ◽  
The Impact

This study investigates the modification of commercial cellulose acetate microfiltration membranes by supercritical solvent impregnation with thymol to provide them with antibacterial properties. The impregnation process was conducted in a batch mode, and the effect of pressure and processing time on thymol loading was followed. The impact of the modification on the membrane’s microstructure was analyzed using scanning electron and ion-beam microscopy, and membranes’ functionality was tested in a cross-flow filtration system. The antibiofilm properties of the obtained materials were studied against Staphyloccocus aureus and Pseudomonas aeruginosa, while membranes’ blocking in contact with bacteria was examined for S. aureus and Escherichia coli. The results revealed a fast impregnation process with high thymol loadings achievable after just 0.5 h at 15 MPa and 20 MPa. The presence of 20% of thymol provided strong antibiofilm properties against the tested strains without affecting the membrane’s functionality. The study showed that these strong antibacterial properties could be implemented to the commercial membranes’ defined polymeric structure in a short and environmentally friendly process.

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