scholarly journals Critical Flow Velocities for Collapse of Reactor Parallel-Plate Fuel Assemblies

1960 ◽  
Vol 82 (2) ◽  
pp. 83-91 ◽  
Author(s):  
D. R. Miller
Keyword(s):  
Flow Velocity ◽  
Critical Velocity ◽  
Parallel Plate ◽  
Reactor Fuel ◽  
Critical Flow ◽  
Small Deflection ◽  
Fuel Assemblies ◽  
Flow Velocities

Theoretical formulas are presented for prediction of the flow velocity at which collapse occurs in long parallel-plate assemblies. Beyond the critical velocity the pressure-unbalance forces, developed as a consequence of a small deflection, exceed the corresponding elastic restraining forces, and the plates collapse. Both flat and curved-plate assemblies are considered, and the applicability of the formulas to design of reactor fuel-plate assemblies is discussed.

scholarly journals Hybrid Scour Depth Prediction Equations for Reliable Design of Bridge Piers

Water ◽  
2021 ◽  
Vol 13 (15) ◽  
pp. 2019
Author(s):  
Hossein Hamidifar ◽  
Faezeh Zanganeh-Inaloo ◽  
Iacopo Carnacina
Keyword(s):  
Flow Velocity ◽  
Critical Velocity ◽  
Depth Estimation ◽  
Hybrid Models ◽  
Velocity Estimation ◽  
Bridge Piers ◽  
Critical Flow ◽  
Scour Depth ◽  
Critical Flow Velocity ◽  
Estimation Equations

Numerous models have been proposed in the past to predict the maximum scour depth around bridge piers. These studies have all focused on the different parameters that could affect the maximum scour depth and the model accuracy. One of the main parameters individuated is the critical velocity of the approaching flow. The present study aimed at investigating the effect of different equations to determine the critical flow velocity on the accuracy of models for estimating the maximum scour depth around bridge piers. Here, 10 scour depth estimation equations, which include the critical flow velocity as one of the influencing parameters, and 8 critical velocity estimation equations were examined, for a total combination of 80 hybrid models. In addition, a sensitivity analysis of the selected scour depth equations to the critical velocity was investigated. The results of the selected models were compared with experimental data, and the best hybrid models were identified using statistical indicators. The accuracy of the best models, including YJAF-VRAD, YJAF-VARN, and YJAI-VRAD models, was also evaluated using field data available in the literature. Finally, correction factors were implied to the selected models to increase their accuracy in predicting the maximum scour depth.

Vibrations of a Simply Supported Cross Flow Heat Exchanger Tube With Axial Load and Loose Supports

2017 ◽  
Vol 12 (5) ◽  
Author(s):  
Anwar Sadath ◽  
V. Vinu ◽  
C. P. Vyasarayani
Keyword(s):  
Flow Velocity ◽  
Axial Load ◽  
Galerkin Approximation ◽  
Period Doubling ◽  
Critical Flow ◽  
Axial Loads ◽  
Critical Flow Velocity ◽  
Delay Differential ◽  
Loose Support ◽  
Flow Velocities

In this work, a mathematical model is developed for simulating the vibrations of a single flexible cylinder under crossflow. The flexible tube is subjected to an axial load and has loose supports. The equation governing the dynamics of the tube under the influence of fluid forces (modeled using quasi-steady approach) is a partial delay differential equation (PDDE). Using the Galerkin approximation, the PDDE is converted into a finite number of delay differential equations (DDE). The obtained DDEs are used to explore the nonlinear dynamics and stability characteristics of the system. Both analytical and numerical techniques were used for analyzing the problem. The results indicate that, with high axial loads and for flow velocities beyond certain critical values, the system can undergo flutter or buckling instability. Post-flutter instability, the amplitude of vibration grows until it impacts with the loose support. With a further increase in the flow velocity, through a series of period doubling bifurcations the tube motion becomes chaotic. The critical flow velocity is same with and without the loose support. However, the loose support introduces chaos. It was found that when the axial load is large, the linearized analysis overestimates the critical flow velocity. For certain high flow velocities, limit cycles exist for axial loads beyond the critical buckling load.

HIPPO – In situ device to monitor the remobilization process of fine sediments

2021 ◽  
Author(s):  
Tim Kerlin ◽  
Mark Musall ◽  
Peter Oberle ◽  
Franz Nestmann
Keyword(s):  
Flow Velocity ◽  
Measurement System ◽  
Measuring System ◽  
Critical Flow ◽  
Sampling Area ◽  
Critical Flow Velocity ◽  
Fine Sediments ◽  
Flow Velocities

<p>Within the joint project Integrated Water Governance Support System (iWaGSS) funded by the German Federal Ministry for Education and Research (BMBF, reference numer: 02WGR1424C) the Institute of Water and River Basin Management (IWG) of the Karlsruhe Institute of Technology (KIT) developed a benthic flume. The benthic flume HIPPO (Hydro-morphological Investigation of riverbed Particle Performance On-site) is an adjustable in situ device to reliably determine the start of erosion of fine sediments.</p><p>In advance 3D-CFD simulations have been carried out to optimize the components and the setup of the measurement system. The final product is primarily a benthic flume, which has a downwardly opened sampling area at the bottom and is placed on the river or reservoir bed. This underwater flow channel can be adapted to the local conditions with further components and is connected via a tube system to a measurement boat or raft. On the boat a pump creates a steady flow velocity in the system. The velocity in the benthic flume is gradually increased at fixed time intervals and is monitored using a built-in flow velocity meter (Acoustic Doppler Velocimeter). In addition the entire erosion process is recorded visually with video cameras. Also the turbidity of the water flowing through the system is continuously measured by a turbidity probe installed behind the pump. The amount of flow induced by the pump is controlled by a valve close to the end of the system. With the pump currently installed flow velocities of up to v = 0.8 m/s at the sampling area can be achieved, which is sufficient for the determination of the critical flow rate for erosion of most types of clay, silty and fine sandy sediments. During the process of erosion also the remobilization of fluid mud can be monitored. The critical flow velocity for the start of sediment transport is determined on the basis of the turbidity of the pumped water and data from the flow velocity probe and is verified using the camera system.</p><p>In addition to the critical threshold flow velocities, the critical bed shear stress is often required as input or evaluation variables for morhpodynamic numerical models. The conversion can be made, for example, using the quadratic velocity approach originally used in pipe hydraulics. The determination of the required resistance coefficient λ is based on the Moody Chart. However, it should be considered that this procedure entails some uncertainties with regard to the measurement system presented here. Still for cohesive sediments, the natural values measured in this way represent a significant added value compared to common estimates based on only partially known bed parameters, since factors such as vegetative cover, consolidation or even a developed biofilm can influence the timing of erosion. Especially against this background, possible effects of the change of hydraulics by the measuring system (geometry, velocity profile) seem to be small compared to the uncertainties of contemporary morphodynamic analyses.</p>

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