Pneumatic Rupture of a Brittle Pipe: The Depressurization Transient Adjacent to the Ruptured Zone

1981 ◽  
Vol 103 (3) ◽  
pp. 287-293 ◽  
Author(s):  
M. R. Baum ◽  
M. J. H. Elston
Keyword(s):  
Theoretical Model ◽  
Rupture Zone ◽  
Bursting Pressure ◽  
Pressure Transient ◽  
Adjacent Section ◽  
Comparison With Experiment ◽  
Simple Theoretical Model ◽  
Wide Range ◽  
Predicted Values

A simple theoretical model is developed to predict the pressure transient within a gas-pressurized pipe when an adjacent section shatters into many fragments. Comparison with experiment shows that the model correctly predicts the general form of the transient over a wide range of bursting pressure and rupture zone lengths, though the measured initial depressurization rates all fall below the predicted values.

scholarly journals Flow analysis of a set of ornamental chimney caps designed by Antoni Gaudí

2020 ◽  
Vol 8 (1) ◽  
Author(s):  
Albert Samper ◽  
Jordi Iglesias ◽  
Blas Herrera ◽  
Jordi Pallares
Keyword(s):  
Theoretical Model ◽  
Flow Analysis ◽  
External Flow ◽  
Pressure Reduction ◽  
Simple Theoretical Model ◽  
Wide Range ◽  
Wind Tunnel Measurements ◽  
The Individual ◽  
Antoni Gaudí ◽  
Flow Velocities

AbstractWe analyzed theoretically and experimentally the performance of the 19 different ornamental caps of the individual chimneys located on the terrace of Palau Güell (Barcelona, Spain) designed by Antoni Gaudí. This set of chimney caps has wide range of external geometries and different number and shapes of openings. Models of the chimney caps were obtained using photogrammetry and 3D printing. Wind tunnel measurements of the pressure inside the stack pipe connected to the cap were performed for different external and stack flow velocities. Two distinct orientations of the external flow with respect to the chimneys were considered. We derived a simple theoretical model, based on the potential flow theory, to relate the non-dimensional pressure reduction in the stack (chimney draft) with the ratio between the external and stack flow velocities. It has been found that the behavior of the chimneys caps predicted by this model is in agreement with the measurements. It has been found that the performance of the chimneys depends mainly on the number of supports of the conical cover of the cap and it is essentially independent on the shape of the cap and on the number and geometry of the openings located on the cap. These conclusions obtained for this particular set of chimneys can be useful for the design of caps for ornamental or general use.

A Structural Model for Molded Thermoplastic Ankle-Foot Orthoses

1987 ◽  
Vol 109 (4) ◽  
pp. 305-310 ◽  
Author(s):  
D. J. Leone
Keyword(s):  
Theoretical Model ◽  
Computer Aided Design ◽  
Structural Model ◽  
Structural Response ◽  
Leaf Spring ◽  
Simple Theoretical Model ◽  
Small Deflection ◽  
Predicted Values ◽  
Deflection Theory ◽  
Aided Design

The structural response of a posterior leaf spring, ankle-foot orthosis (AFO) was studied both experimentally and with a simple theoretical model. The theoretical model, which was compared with other analytical solutions and experimental data, predicted the bending and twisting of the AFO due to unit loads. The simple theoretical model utilized beam equations and small deflection theory. Excellent agreement between test and predicted values was achieved, indicating that the simple theoretical model, which was relatively easy to implement computationally, could serve as the major component of a computer-aided design program.

scholarly journals Incumbent and Entrant Bidding in Scoring Rule Auctions: A Study on Italian Canteen Services

2020 ◽  
Vol 0 (0) ◽  
Author(s):  
Riccardo Camboni ◽  
Paola Valbonesi
Keyword(s):  
Theoretical Model ◽  
Production Cost ◽  
Specific Information ◽  
Scoring Rule ◽  
The Public ◽  
Simple Theoretical Model ◽  
Original Dataset

AbstractWe empirically investigate incumbents’ and entrants’ bids on an original dataset of 192 scoring rule auctions for canteen services in Italy. Our findings show that winning rebates are lower (i.e., prices paid by the public buyer are higher) when the contract is awarded to the incumbent supplier. This result is not explained by the observable characteristics of the auction or the service awarded. We develop a simple theoretical model showing that the result is consistent with a setting in which the buyer exploits specific information on the incumbent supplier’s production cost.

scholarly journals Market Choices Driven by Reference Groups: A Comparison of Analytical and Simulation Results on Random Networks

Entropy ◽  
2021 ◽  
Vol 23 (8) ◽  
pp. 1007
Author(s):  
Michał Ramsza
Keyword(s):  
Theoretical Model ◽  
Reference Group ◽  
Third Party ◽  
Qualitative Behavior ◽  
Reference Groups ◽  
Group Influence ◽  
Simple Theoretical Model ◽  
High Connectivity ◽  
Simulation Results ◽  
Two Equilibria

The present paper reports simulation results for a simple model of reference group influence on market choices, e.g., brand selection. The model was simulated on three types of random graphs, Erdos–Renyi, Barabasi–Albert, and Watts–Strogatz. The estimates of equilibria based on the simulation results were compared to the equilibria of the theoretical model. It was verified that the simulations exhibited the same qualitative behavior as the theoretical model, and for graphs with high connectivity and low clustering, the quantitative predictions offered a viable approximation. These results allowed extending the results from the simple theoretical model to networks. Thus, by increasing the positive response towards the reference group, the third party may create a bistable situation with two equilibria at which respective brands dominate the market. This task is easier for large reference groups.

Measurements and Modeling of Ingress in a New 1.5-Stage Turbine Research Facility

2016 ◽  
Vol 139 (1) ◽  
Author(s):  
Marios Patinios ◽  
James A. Scobie ◽  
Carl M. Sangan ◽  
J. Michael Owen ◽  
Gary D. Lock
Keyword(s):  
Theoretical Model ◽  
Gas Turbines ◽  
Test Facility ◽  
Radial Clearance ◽  
Operating Life ◽  
The Core ◽  
Wide Range ◽  
Purge Flow ◽  
Rotor Disk ◽  
Engine Components

In gas turbines, hot mainstream flow can be ingested into the wheel-space formed between stator and rotor disks as a result of the circumferential pressure asymmetry in the annulus; this ingress can significantly affect the operating life, performance, and integrity of highly stressed, vulnerable engine components. Rim seals, fitted at the periphery of the disks, are used to minimize ingress and therefore reduce the amount of purge flow required to seal the wheel-space and cool the disks. This paper presents experimental results from a new 1.5-stage test facility designed to investigate ingress into the wheel-spaces upstream and downstream of a rotor disk. The fluid-dynamically scaled rig operates at incompressible flow conditions, far removed from the harsh environment of the engine which is not conducive to experimental measurements. The test facility features interchangeable rim-seal components, offering significant flexibility and expediency in terms of data collection over a wide range of sealing flow rates. The rig was specifically designed to enable an efficient method of ranking and quantifying the performance of generic and engine-specific seal geometries. The radial variation of CO2 gas concentration, pressure, and swirl is measured to explore, for the first time, the flow structure in both the upstream and downstream wheel-spaces. The measurements show that the concentration in the core is equal to that on the stator walls and that both distributions are virtually invariant with radius. These measurements confirm that mixing between ingress and egress is essentially complete immediately after the ingested fluid enters the wheel-space and that the fluid from the boundary layer on the stator is the source of that in the core. The swirl in the core is shown to determine the radial distribution of pressure in the wheel-space. The performance of a double radial-clearance seal is evaluated in terms of the variation of effectiveness with sealing flow rate for both the upstream and the downstream wheel-spaces and is found to be independent of rotational Reynolds number. A simple theoretical orifice model was fitted to the experimental data showing good agreement between theory and experiment for all cases. This observation is of great significance as it demonstrates that the theoretical model can accurately predict ingress even when it is driven by the complex unsteady pressure field in the annulus upstream and downstream of the rotor. The combination of the theoretical model and the new test rig with its flexibility and capability for detailed measurements provides a powerful tool for the engine rim-seal designer.

Measurements and Modelling of Ingress in a New 1.5-Stage Turbine Research Facility

2016 ◽  
Author(s):  
Marios Patinios ◽  
James A. Scobie ◽  
Carl M. Sangan ◽  
J. Michael Owen ◽  
Gary D. Lock
Keyword(s):  
Theoretical Model ◽  
Gas Turbines ◽  
Test Facility ◽  
Radial Clearance ◽  
Operating Life ◽  
The Core ◽  
Wide Range ◽  
Purge Flow ◽  
Engine Components ◽  
First Time

In gas turbines, hot mainstream flow can be ingested into the wheel-space formed between stator and rotor discs as a result of the circumferential pressure asymmetry in the annulus; this ingress can significantly affect the operating life, performance and integrity of highly-stressed, vulnerable engine components. Rim seals, fitted at the periphery of the discs, are used to minimise ingress and therefore reduce the amount of purge flow required to seal the wheel-space and cool the discs. This paper presents experimental results from a new 1.5-stage test facility designed to investigate ingress into the wheel-spaces upstream and downstream of a rotor disc. The fluid-dynamically-scaled rig operates at incompressible flow conditions, far removed from the harsh environment of the engine which is not conducive to experimental measurements. The test facility features interchangeable rim-seal components, offering significant flexibility and expediency in terms of data collection over a wide range of sealing-flow rates. The rig was specifically designed to enable an efficient method of ranking and quantifying the performance of generic and engine-specific seal geometries. The radial variation of CO2 gas concentration, pressure and swirl is measured to explore, for the first time, the flow structure in both the upstream and downstream wheel-spaces. The measurements show that the concentration in the core is equal to that on the stator walls and that both distributions are virtually invariant with radius. These measurements confirm that mixing between ingress and egress is essentially complete immediately after the ingested fluid enters the wheel-space and that the fluid from the boundary-layer on the stator is the source of that in the core. The swirl in the core is shown to determine the radial distribution of pressure in the wheel-space. The performance of a double radial-clearance seal is evaluated in terms of the variation of effectiveness with sealing flow rate for both the upstream and the downstream wheel-spaces and is found to be independent of rotational Reynolds number. A simple theoretical orifice model was fitted to the experimental data showing good agreement between theory and experiment for all cases. This observation is of great significance as it demonstrates that the theoretical model can accurately predict ingress even when it is driven by the complex unsteady pressure field in the annulus upstream and downstream of the rotor. The combination of the theoretical model and the new test rig with its flexibility and capability for detailed measurements provides a powerful tool for the engine rim-seal designer.

scholarly journals Theoretical Bounds on Electron Energy Filtering in Disordered Nanomaterials

2019 ◽  
Author(s):  
Amro Dodin ◽  
Brian F. Aull ◽  
Roderick R. Kunz ◽  
Adam Willard
Keyword(s):  
Theoretical Model ◽  
Electron Energy ◽  
Energy Levels ◽  
Additional Source ◽  
Discrete Energy ◽  
Energy Filtering ◽  
Simple Theoretical Model ◽  
Particle Polydispersity ◽  
Electron Energy Filtering ◽  
Individual Nanoparticles

This manuscript presents a theoretical model for determining the electron energy filtering properties of nanocomposite materials. Individual nanoparticles can serve as energy filters for tunneling electrons due their discretized energy levels. Nanomaterials comprised of many individual nanoparticles can in principle serve the same purpose, however, particle polydispersity can lead to an additional source of energetic broadening. We describe a simple theoretical model that includes the effects of discrete energy levels and inhomogeneous broadening. We use this model to identify the material parameters needed for effective energy filtering by quantum dot solids.

Prediction of the Condensation Coefficient on Horizontal Integral-Fin Tubes

1985 ◽  
Vol 107 (2) ◽  
pp. 369-376 ◽  
Author(s):  
R. L. Webb ◽  
T. M. Rudy ◽  
M. A. Kedzierski
Keyword(s):  
Surface Tension ◽  
Theoretical Model ◽  
Surface Tension Force ◽  
Tension Force ◽  
Condensation Coefficient ◽  
Film Drainage ◽  
Predicted Values ◽  
Experimental Values ◽  
Fin Tubes

A theoretical model is developed for prediction of the condensation coefficient on horizontal integral-fin tubes for both high and low surface tension fluids. The model includes the effects of surface tension on film drainage and on condensate retention between the fins. First, the fraction of the tube circumference that is flooded with condensate is calculated. Typically, the condensation coefficient in the flooded region is negligible compared to that of the unflooded region. Then the condensation coefficient on the unflooded portion is calculated, assuming that surface tension force drains the condensate from the fins. The model is used to predict the R-11 condensation coefficient on horizontal, integral-fin tubes having 748, 1024, and 1378 fpm. The predicted values are within ±20 percent of the experimental values.

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