Cavitation in Hydraulic Machines: Measurement, Numerical Simulation and Damage Patterns

2020 ◽  
Author(s):  
Helmut Benigni
Keyword(s):  
Single Phase ◽  
Rapid Assessment ◽  
Vapor Bubbles ◽  
Test Rig ◽  
Liquid Media ◽  
Histogram Method ◽  
Pressure Drops ◽  
Physical Limit ◽  
Hydraulic Machines ◽  
Multi Phase

Abstract Cavitation is a phenomenon that occurs in liquid media when the pressure drops below the vapor pressure. Cavitation is accompanied by damage when the imploding vapor bubbles implode in the vicinity of components. Cavitation is known in all hydraulic machines, be it a pump or a turbine, and it can occur within all components that are flowed through and have a low-pressure side or area. In the last 100 years, a lot has been done to understand the damage caused by cavitation, and cavitation has been classified within the entire range of component-damaging mechanisms. Nevertheless, users are now interested in the behavior of different machine types and different specific speeds and need information for a particular installation situation, while hydraulic developers are interested in a methodology for the rapid assessment of CFD results. This paper presents examples of damage to all kinds of hydraulic machines as well as numerical simulations of cavitation. Cross-comparisons between single-phase numerical calculations are realized with the histogram method, and multi-phase calculations are carried out and then compared with test rig investigations. Often, it is not possible or economically feasible to completely avoid cavitation. With the help of dimensionless values and the assumption of complete cavitation, a generally valid physical limit curve can be specified for turbines.

The Work Hardening of Single Phase and Multi-Phase Aluminium Alloys

2006 ◽  
Vol 519-521 ◽  
pp. 71-78 ◽  
Author(s):  
J. David Embury ◽  
Warren J. Poole ◽  
David J. Lloyd
Keyword(s):  
Work Hardening ◽  
Aluminium Alloys ◽  
Single Phase ◽  
Dynamic Recovery ◽  
Uniform Elongation ◽  
Strengthening Mechanisms ◽  
Plastic Response ◽  
Spring Back ◽  
Hardening Process ◽  
Multi Phase

The process of work hardening in aluminum alloys is important from the viewpoint of formability and the prediction of the properties of highly deformed products. However the complexity of the strengthening mechanisms in these materials means that one must carefully consider the interaction of dislocations with the detailed elements of the microstructure and the related influence of the elements on dislocation accumulation and dynamic recovery. In addition, it is necessary to consider the influence of the work hardening process at various levels of plastic strain. This permits the possibility of designing microstructure for tailored plastic response, e.g. not simply designed for yield strength but also considering uniform elongation, spring-back, ductility etc. This presentation will explore the concept of identifying the various interactions which govern the evolution of the work hardening and their possible role in alloy design.

Abstract 77: Ongoing Leakage Revealed by Second Phase Spot Sign Volume Expansion in Multi-Phase Computed Tomography Angiography Strongly Predicts Intracranial Hemorrhage Growth

Stroke ◽  
2020 ◽  
Vol 51 (Suppl_1) ◽  
Author(s):  
Abdulaziz Al Sultan ◽  
Ericka Teleg ◽  
MacKenzie Horn ◽  
Piyush Ojha ◽  
Linda Kasickova ◽  
...  
Keyword(s):  
Volume Expansion ◽  
Single Phase ◽  
Meta Analysis ◽  
Hematoma Expansion ◽  
Second Phase ◽  
Hematoma Volume ◽  
Spot Sign ◽  
Time Resolved ◽  
Multi Phase

Background: CTA spot sign is a predictor of intracerebral hemorrhage (ICH) expansion. This sign can fluctuate in appearance, volume, and timing. Multiphase CTA (mCTA) can identify spot sign through 3 time-resolved images. We sought to identify a novel predictor of follow up total hematoma expansion using mCTA. Methods: This cohort study included patients with ICH between 2012-2019. Quantomo software was used to measure total hematoma volume (ml) from baseline CT & follow-up CT/MRI blinded to spot sign in 3 mCTA phases. Spot sign expansion was calculated by subtracting 1 st phase spot sign volume from 2 nd phase spot sign volume measured in microliters. Results: 199 patients [63% male, mean age 69 years, median NIHSS 11, IQR 6-20] were included. Median baseline ICH volume was 16.1 ml (IQR 5-29.9 ml). Amongst all three mCTA phases, spot sign was best detected on the 2nd phase (23% vs 17.5% 1 st phase vs 22% 3 rd phase). In multivariable regression, spot sign expansion was significantly associated with follow up total hematoma expansion (OR: 1.03 per microliter of spot sign expansion, p=0.01). Figure 1 shows the predicted total hematoma expansion by spot sign expansion. mCTA spot sign had a higher sensitivity for predicting total hematoma volume expansion than single-phase CTA (reported in meta-analysis of 14 studies), 86% vs 53%, respectively, while both having similar specificity, 87% vs 88%, respectively. Conclusion: Spot sign expansion on mCTA is a novel predictor of total hematoma expansion and could be used to select patients for immediate therapeutic intervention in future clinical trials. Using mCTA improves sensitivity while preserving specificity over single-phase CTA.

scholarly journals Outcome Prediction Using Perfusion Parameters and Collateral Scores of Multi-Phase and Single-Phase CT Angiography in Acute Stroke: Need for One, Two, Three, or Thirty Scans?

2018 ◽  
Vol 20 (3) ◽  
pp. 362-372 ◽  
Author(s):  
Katharina Schregel ◽  
Ioannis Tsogkas ◽  
Carolin Peter ◽  
Antonia Zapf ◽  
Daniel Behme ◽  
...  
Keyword(s):  
Acute Stroke ◽  
Ct Angiography ◽  
Single Phase ◽  
Outcome Prediction ◽  
Multi Phase

scholarly journals A Multi-Phase Assessment of the Effects of COVID-19 on Food Systems and Rural Livelihoods in Zimbabwe

2021 ◽  
Author(s):  
Vine Mutyasira
Keyword(s):  
Food Systems ◽  
Smallholder Farmers ◽  
Rapid Assessment ◽  
Policy Research ◽  
Rural Livelihoods ◽  
Mitigation Strategies ◽  
Sub Saharan Africa ◽  
Response Measures ◽  
Sub Saharan ◽  
Multi Phase

The COVID-19 pandemic has continued to affect agri-food systems around the world and lay bare its fragility, worsening the welfare of millions of smallholder farmers whose livelihoods are anchored on agricultural activities. For the vast majority of sub-Saharan Africa, COVID-19 has coincided with a number of other macroeconomic shocks, which have also exacerbated the impacts of the pandemic on food security, nutrition and general livelihoods, as well curtailed policy responses and mitigation strategies. In Zimbabwe, the COVID-19 pandemic struck at a time the country was experiencing a worsening economic and humanitarian situation. This study focused more on community and household dynamics and response measures to cope with the pandemic. This paper presents a summary of findings emerging from a series of rapid assessment studies undertaken by the Agricultural Policy Research in Africa (APRA) Programme in Mvurwi and Concession areas of Mazowe District in Zimbabwe to examine how COVID-19 is affecting food systems and rural livelihoods in our research communities.

Design Parameters of Brush Seals and Their Impact on Seal Performance

2012 ◽  
Author(s):  
H. Schwarz ◽  
J. Friedrichs ◽  
J. Flegler
Keyword(s):  
Steam Turbine ◽  
Gas Turbine ◽  
Large Scale ◽  
Design Parameters ◽  
Test Rig ◽  
Pressure Drops ◽  
Seal Design ◽  
Brush Seal ◽  
Extreme Load ◽  
Brush Seals

Brush seals, which were originally designed for gas turbine applications, have been successfully applied to large-scale steam turbines within the past decade. From gas turbine applications, the fundamental behavior and designing levers are known. However, the application of brush seals to a steam turbine is still a challenge. This challenge is mainly due to the extreme load on the brush seal while operating under steam. Furthermore, it is difficult to test brush seals under realistic conditions, i.e. under live steam conditions with high pressure drops. Due to these insufficiencies, 2 test rigs were developed at the University of Technology Braunschweig, Germany. The first test rig is operated under pressurized air and allows testing specific brush seal characteristics concerning their general behavior. The knowledge gained from these tests can be validated in the second test rig, which is operated under steam at pressure drops of 45 bar and temperatures up to 450 °C. Using both the air test rig and the steam test rig helps keep the testing effort comparably small. Design variants can be pre-tested with air, and promising brush seal designs can consequently be tested in the steam seal test rig. The paper focuses on a clamped brush seal design which, amongst others, is used in steam turbine blade paths and shaft seals of current Siemens turbines. The consequences of the brush assembly on the brush appearance and brush performance are shown. The clamped brush seal design reveals several particularities compared to welded brushes. It could be shown that the clamped bristle pack tends to gape when clamping forces rise. Gapping results in an axially expanding bristle pack, where the bristle density per unit area and the leakage flow vary. Furthermore, the brush elements are usually assembled with an axial lay angle, i.e. the bristles are reclined against the backing plate. Hence, the axial lay angle is also part of the investigation.

Eco-driving control of electric vehicle with battery dynamic model and multiple traffic signals

2021 ◽  
pp. 095440702110374
Author(s):  
Hafiz Muhammad Yasir Naeem ◽  
Aamer Iqbal Bhatti ◽  
Yasir Awais Butt ◽  
Qadeer Ahmed
Keyword(s):  
Life Cycle ◽  
Boundary Value Problem ◽  
Single Phase ◽  
Boundary Value ◽  
Optimization Technique ◽  
Traffic Signals ◽  
Multiple Shooting ◽  
Point Boundary ◽  
Phase Problem ◽  
Multi Phase

Limited capacity and short life cycle of a battery are the major impediments in development of practical Electric Vehicles (EVs). Eco-driving is an optimization technique through which a velocity trajectory that consumes minimum energy is advised to the driver. However, presence of traffic signals to control large traffic network degrades the performance of eco-driving; as applying brakes to stop and then maximum re-acceleration to restart a trip consumes lot of energy. Eco-driving problem with multiple traffic signals and static model of battery has been proposed as Two Point Boundary Value Problem (TPBVP). TPBVP fails to solve multi-phase problem as a single phase due to discontinuity of the co-states at the junction, that is, start of a new phase. This paper investigates an optimal solution with both EV and battery dynamics in the presence of multiple traffic signals as Multi Point Boundary Value Problem (MPBVP) using multiple shooting technique. Traffic signals come at some intermediate points of a trip. MPBVP ensures continuity at the junction to solve the multi-phase problem as a single phase through inter dependencies between each phases. Goal of this work is not only to solve constrained eco-driving problem with traffic signals but also include charging and discharging limits on battery that indirectly improves battery’s life cycle. Results indicate that EV has crossed all the traffic signals during their green duration without applying brakes with also satisfying all the other constraints and continuity condition. Moreover, it can be seen that energy consumption using MPBVP is also marginally lesser as compared to TPBVP.

Analytical Electrical Conductivity Models for Single-Phase and Multi-Phase Fractal Porous Media

Fractals ◽  
2021 ◽  
Author(s):  
Wenhui Song ◽  
Masa Prodanovic ◽  
Jun Yao ◽  
Kai Zhang ◽  
Qiqi Wang
Keyword(s):  
Electrical Conductivity ◽  
Porous Media ◽  
Single Phase ◽  
Multi Phase ◽  
Conductivity Models

scholarly journals Dynamic behavior of coalbed methane flow along the annulus of single-phase production

2019 ◽  
Vol 6 (4) ◽  
pp. 547-555 ◽  
Author(s):  
Xinfu Liu ◽  
Chunhua Liu ◽  
Guoqiang Liu
Keyword(s):  
Water Column ◽  
Dynamic Behavior ◽  
Coalbed Methane ◽  
Single Phase ◽  
Compressibility Factor ◽  
Production Performance ◽  
Flow Rates ◽  
Pressure Drops ◽  
Bottom Hole ◽  
Gravitational Gradients

Abstract Dynamic behavior of coalbed methane (CBM) flow will provide the theoretical basis to optimize production performance for a given well. A mathematical model is developed to simulate flowing pressures and pressure drops of CBM column from well head to bottom hole. The measured parameters and independent variables of flow rates, flowing pressures and temperatures are involved in CBM producing process along the annulus. The developed relationships are validated against full-scale measured data in single-phase CBM wellbores. The proposed methodology can analyze the dynamic behavior in CBM reservoir and process of CBM flow with an overall accuracy of 2%. The calculating process of flowing pressures involves friction factor with variable Reynolds number and CBM temperature and compressibility factor with gravitational gradients. The results showed that the effect of flowing pressure on CBM column was more obvious than that on CBM and water column accompanied by an increase of dynamic water level. The ratios of flowing pressure on increment of CBM column to the whole column increased with the declined flow rates of water column. Bottom-hole pressure declined with the decreased flowing pressure of CBM column along the annulus. It will lead to the results of the increased pressure drop of CBM column and CBM flow rate in single-phase CBM wellbores.

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