Numerical and experimental study on dynamic characteristics of cavitation bubbles

2018 ◽  
Vol 70 (6) ◽  
pp. 1119-1126
Author(s):  
Feng Cheng ◽  
Weixi Ji
Keyword(s):  
Theoretical Model ◽  
Dynamic Characteristics ◽  
Water Pressure ◽  
Bubble Radius ◽  
Bubble Wall ◽  
Content Type ◽  
Cavitation Bubbles ◽  
Perturbation Frequency ◽  
Bubble Evolution ◽  
Evolution With Time

Purpose Cavitation bubbles cannot be avoided in the hydraulic system. Because of instability of flow and variation of water pressure, the jet often occurs in a bubble collapse. This study aims to accurately predict the shape, velocity and time of the resulting jet, so as to inhibit cavitation erosion. Design/methodology/approach In the study, a theoretical model of cavitation bubbles in the water has been developed by applying a periodic water film pressure into the Rayleigh–Plesset equation. A fourth-order in time Runge–Kutta scheme is used to obtain an accurate computation of the bubble dynamic characteristics. The behavior of the proposed theory is further simulated in a high-speed photography experiment by using a cavitation bubble test rig. The evolution with time of cavitation bubbles is further obtained. Findings A comparison with the available experimental results reveals that the bubble evolution with time has a duration of about 0.3T0, that well predicts the expanding and compressing process of cavitation bubbles. The results also show that the initial bubble radius in the water influences the moving velocity of the bubble wall, whereas the perturbation frequency of the water pressure has less effect on the velocity of the bubble wall. Originality/value A theoretical model well predicts dynamic characteristics of cavitation bubbles. The bubble evolution with time has a duration of about 0.3T0, Initial bubble radius influences the velocity of bubble wall. Perturbation frequency has less effect on the velocity of bubble wall.

Study of Cavitation Bubbles Evolution for High-Speed Water-Lubricated Spiral Groove Thrust Bearings

2019 ◽  
Vol 141 (5) ◽  
Author(s):  
Xiaohui Lin ◽  
Ruiqi Wang ◽  
Shaowen Zhang ◽  
Chibin Zhang ◽  
Shuyun Jiang
Keyword(s):  
Theoretical Model ◽  
High Speed ◽  
Groove Depth ◽  
Skewed Distribution ◽  
Outer Diameter ◽  
Spiral Groove ◽  
High Rotational Speed ◽  
Cavitation Bubbles ◽  
Bubble Evolution ◽  
Bubble Number

The purpose of this study is to investigate the evolution of cavitation bubbles for the high-speed water-lubricated spiral groove thrust bearing. A theoretical model of cavitation bubble evolution considering multiple effects (interface, breakage, and coalescence of bubbles) was established for the bearing. A high-speed experimental setup was developed to measure the distribution of bubbles. The theoretical model is verified by the experimental data. The results show that the Boltzmann-type bubble transport equation can be used to describe the bubble evolution of the bearing under the breakup and coalescence at high-speed conditions; the volume of the bubble group presents a skewed distribution in equilibrium; the number of small-sized bubbles is greater than that of large-sized bubbles at high rotational speed; the bubbles are mainly distributed at the inlets and outlets of spiral grooves; the bubble number density increases with the groove depth and spiral angle; more bubbles are generated near the outer diameter of the bearing. The study provides a theoretical and experimental basis for the bubble evolution of the water-lubricated spiral groove bearing under high speeds.

The Behavior of Bubbles in Non-Newtonian Lubricants

1977 ◽  
Vol 99 (4) ◽  
pp. 455-461 ◽  
Author(s):  
A. Shima ◽  
T. Tsujino
Keyword(s):  
Rheological Properties ◽  
Bubble Radius ◽  
Equation Of Motion ◽  
Crude Oils ◽  
Bubble Wall ◽  
Pressure Equation ◽  
Cavitation Damage ◽  
Lubricating Oils ◽  
Cavitation Bubbles ◽  
Impulse Pressure

The behavior of cavitation bubbles and the impulse pressure occurring from the bubble in non-Newtonian lubricants are analyzed as one of the studies on cavitation which is caused on the bearing metals and oil pressure valves. That is, the equation of motion for a bubble and the pressure equation can be derived by using the Sisko model which well represents the rheological properties of lubricants (lubricating greases, and crude oils in place of lubricating oils), and the variation with time of the bubble radius and the pressure and velocity at the bubble wall in greases and crude oils are numerically obtained. In consequence, it was found that the impulse pressure occurring from the collapse of comparatively large bubbles can be a cause for the cavitation damage.

Cavitation erosion of a single bubble in water as a kind of dynamic damage

2017 ◽  
Vol 231 (11) ◽  
pp. 1383-1389 ◽  
Author(s):  
Feng Cheng ◽  
Weixi Ji
Keyword(s):  
High Velocity ◽  
Cavitation Erosion ◽  
Water Pressure ◽  
Bubble Radius ◽  
Rotating Disk ◽  
Experimental Results ◽  
Single Bubble ◽  
Bubble Wall ◽  
Dynamic Damage ◽  
Disk Test

In this study, a rotating disk test rig was used for the cavitation test of the brass samples. A pit of single black dapple and a large pit of multiring black dapple were found on the sample surfaces after 30 h test. A cavitation model of the rotating disk test was further developed by applying a periodic water pressure into the Keller–Miksis equation, so as to obtain the bubble dynamic characteristics. A comparison with the available experimental results reveals that the velocity of the bubble wall is governed by the initial bubble radius, and the bubble collapsing mode has changed from single bubble compression with high velocity to multiple bubble compression, with a increase in the initial bubble radius. The results also show that the movement of the spherical bubble wall induces the formation of the micro-jet with high velocity, leading to cavitation erosion pits on the specimen surface in the rotating disk test, which are well verified by the present theoretical model as well as the available experimental results.

Farm wages and public works

2015 ◽  
Vol 8 (1) ◽  
pp. 19-72 ◽  
Author(s):  
Kanika Mahajan
Keyword(s):  
Theoretical Model ◽  
Wage Rate ◽  
Fixed Effects ◽  
Positive Impact ◽  
Wage Growth ◽  
State Level ◽  
Random Allocation ◽  
Farm Sector ◽  
Content Type ◽  
The Impact

Purpose – The purpose of this paper is to examine the impact of National Rural Employment Guarantee Scheme (NREGS) on farm sector wage rate. This identification strategy rests on the assumption that all districts across India would have had similar wage trends in the absence of the program. The author argues that this assumption may not be true due to non-random allocation of districts to the program’s three phases across states and different economic growth paths of the states post the implementation of NREGS. Design/methodology/approach – To control for overall macroeconomic trends, the author allows for state-level time fixed effects to capture the differences in growth trajectories across districts due to changing economic landscape in the parent-state over time. The author also estimates the expected farm sector wage growth due to the increased public work employment provision using a theoretical model. Findings – The results, contrary to the existing studies, do not find support for a significantly positive impact of NREGS treatment on private cultivation wage rate. The theoretical model also shows that an increase in public employment work days explains very little of the total growth in cultivation wage post 2004. Originality/value – This paper looks specifically at farm sector wage growth and the possible impact of NREGS on it, accounting for state specific factors in shaping farm wages. Theoretical estimates are presented to overcome econometric limitations.

Intention to adopt mobile payment in physical stores

2019 ◽  
Vol 33 (2) ◽  
pp. 285-308 ◽  
Author(s):  
Yonathan Dri Handarkho ◽  
Yulius Harjoseputro
Keyword(s):  
Theoretical Model ◽  
Technology Acceptance ◽  
Switching Behavior ◽  
Mobile Payment ◽  
Herd Behavior ◽  
User Intention ◽  
Consumer Innovativeness ◽  
Content Type ◽  
Use Of Technology ◽  
Acceptance Model

Purpose The purpose of this paper is to develop a theoretical model based on Push–Pull–Mooring (PPM) framework consisting of direct, indirect and moderating effects, derived from technology acceptance model, unified theory of acceptance and use of technology and other extended theory, to address the main factor influencing an individual in adopting mobile payment (MP) in physical stores. The research, therefore, utilized individual switching behavior as an underpinning to explain MP adoption in an offline context. Design/methodology/approach The theoretical model was tested by collecting data from 459 respondents in Indonesia through online self-administered questionnaires. Findings The finding indicated consumer innovativeness has the most influential direct effect on MP adoption, followed by deal proneness, perceived convenience and perceived herd behavior. Meanwhile, perceived enjoyment and subjective norms were found to have an indirect effect on the adaptation of MP through mediator convenience. Furthermore, age, gender, occupation and income did not have any moderating effect for all the direct influence of MP adoption. Originality/value Previous literature only focused on direct intention. However, this study observed the adoption of MP in a physical store by involving the switching behavior. It specifically puts concern and objective as the factors that influence user intention to switch from their old payment system to the MP system in bricks and mortar store using PPM framework.

Privacy helplessness on social media: its constituents, antecedents and consequences

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Hichang Cho
Keyword(s):  
Theoretical Model ◽  
Structural Equation ◽  
Factor Model ◽  
Measurement Model ◽  
Equation Modeling ◽  
Confirmatory Factor Analyses ◽  
Content Type ◽  
Internet Users ◽  
The Usa ◽  
Antecedents And Consequences

PurposeMany internet users exhibit signs of privacy helplessness and entirely give up online privacy management. However, we know little about what privacy helplessness is, when users are likely to experience it and its implications for privacy behavior. The objectives of this study were twofold: (a) the conceptual explication of privacy helplessness as a novel construct in privacy research and (b) the development of a theoretical model that specifies the antecedents and consequences of privacy helplessness.Design/methodology/approachA research model of privacy helplessness that contains three subcomponents of privacy helplessness, five antecedents and one outcome was developed. The model was empirically examined based on survey data collected from 589 Facebook users in the USA.FindingsThe results of exploratory and confirmatory factor analyses showed that privacy helplessness is adequately assessed by a three-factor model with affective, cognitive and motivational components. The results of structural equation modeling indicated that these three aspects of privacy helplessness are uniquely predicted by five theoretical factors: (a) prior experience of privacy risks, (b) personal mastery, (c) perceived costs of adaptive privacy actions, (d) perceived rewards of privacy inactions and (e) perceived vulnerability. Furthermore, it was found that helplessness as motivational deficits (and cognitive helplessness via this) impedes adaptive privacy actions, while cognitive helplessness promotes adaptive privacy actions when they do not result in motivational deficits.Originality/valueThis study pioneers investigation in understanding key constituents, attributes and processes underlying privacy helplessness. First, the present study developed the first theory-derived, successively validated measurement model of privacy helplessness. Second, this research proposed a theoretical model of privacy helplessness, specifying antecedents and consequences of privacy helplessness.

Research on mechanism configuration and dynamic characteristics for multi-split transmission line mobile robot

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Wei Jiang ◽  
Yating Shi ◽  
Dehua Zou ◽  
Hongwei Zhang ◽  
Hong Jun Li
Keyword(s):  
Mobile Robot ◽  
Transmission Line ◽  
Dynamic Model ◽  
Dynamic Characteristics ◽  
Transmission Lines ◽  
Dynamic Models ◽  
Working Environment ◽  
Joint Torque ◽  
Content Type ◽  
Working Space

Purpose The purpose of this paper is to achieve the optimal system design of a four-wheel mobile robot on transmission line maintenance, as the authors know transmission line mobile robot is a kind of special robot which runs on high-voltage cable to replace or assist manual power maintenance operation. In the process of live working, the manipulator, working end effector and the working environment are located in the narrow space and with heterogeneous shapes, the robot collision-free obstacle avoidance movement is the premise to complete the operation task. In the simultaneous operation, the mechanical properties between the manipulator effector and the operation object are the key to improve the operation reliability. These put forward higher requirements for the mechanical configuration and dynamic characteristics of the robot, and this is the purpose of the manuscript. Design/methodology/approach Based on the above, aiming at the task of tightening the tension clamp for the four-split transmission lines, the paper proposed a four-wheel mobile robot mechanism configuration and its terminal tool which can adapt to the walking and operation on multi-split transmission lines. In the study, the dynamic models of the rigid robot and flexible transmission line are established, respectively, and the dynamic model of rigid-flexible coupling system is established on this basis, the working space and dynamic characteristics of the robot have been simulated in ADAMS and MATLAB. Findings The research results show that the mechanical configuration of this robot can complete the tightening operation of the four-split tension clamp bolts and the motion of robot each joint meets the requirements of driving torque in the operation process, which avoids the operation failure of the robot system caused by the insufficient or excessive driving force of the robot joint torque. Originality/value Finally, the engineering practicability of the mechanical configuration and dynamic model proposed in the paper has been verified by the physical prototype. The originality value of the research is that it has double important theoretical significance and practical application value for the optimization of mechanical structure parameters and electrical control parameters of transmission line mobile robots.

The moderating role of cultural factors in the adoption of mobile banking in Brazil

2019 ◽  
Vol 11 (1) ◽  
pp. 63-81 ◽  
Author(s):  
Alexandre da C. Goularte ◽  
Silvia Novaes Zilber
Keyword(s):  
Theoretical Model ◽  
Behavioral Intention ◽  
Cultural Dimensions ◽  
Mobile Banking ◽  
Content Type ◽  
Five Dimensions ◽  
Cultural Variables ◽  
Use Of Technology ◽  
Country Culture ◽  
The Impact

Purpose This study aims to evaluate the impact of country culture, represented by Hofstede cultural dimensions, in the adoption of Brazilian mobile banking services. Design/methodology/approach Based on the replication of a theoretical model previously tested in Mozambique (Africa) that combines the extended version of the unified theory of acceptance and use of technology (UTAUT2) with the five Hofstede cultural dimensions, this study tested that model in another emerging country, Brazil, using partial least squares (PLS) as a modeling method. Findings Replication showed that the cultural dimensions do not present strong significance in the moderation of the use of mobile banking. In fact, out of the five dimensions tested, three were not significant and two showed weak significance (p < 0.10): collectivism and short-term orientation. Those results, contrasting with that one presented by Baptista and Oliveira (2015), made sense under Ajzen’s theory (1991) – the TPB, leading to the conclusion that the moderation of cultural dimensions on behavior use is not applicable. Originality/value The authors concluded that the tested model may not be adherent, finding a theoretical gap to be explored in future studies: the moderation of the behavioral intention by cultural variables proposed by Hofstede. That finding supported the proposition of a new theoretical model, which considers the moderation of cultural dimensions in another place: behavioral intention to use mobile banking instead of the behavior use, as proposed by Baptista and Oliveira (2015). So, based on the research results and based on some authors cited in this study (Choi et al., 2014; Chou, 2013; Srite and Karahanna, 2006), it is proposed to insert Hofstede cultural variables as moderators of independent variables on the behavioral intention.

Farm capital structure choice: theory and an empirical test

2014 ◽  
Vol 74 (1) ◽  
pp. 115-132 ◽  
Author(s):  
Feng Wu ◽  
Zhengfei Guan ◽  
Robert Myers
Keyword(s):  
Theoretical Model ◽  
Capital Structure ◽  
Credit Risk ◽  
Choice Theory ◽  
Empirical Test ◽  
Theoretical Framework ◽  
Comparative Statics ◽  
Content Type ◽  
Structure Choice ◽  
Capital Structure Choice

Purpose – The purpose of this paper is to provide a unified theoretical framework that explains farm capital structure choice. Design/methodology/approach – The framework accommodates different credit access scenarios and heterogeneous risk profiles of borrowers. It recognizes that the costs of capital are endogenously determined, reflecting the degree of credit risk and accessibility to credit markets. Based on the proposed model and the comparative statics derived thereof, the paper empirically tests the impacts of different factors on capital structure choice. Findings – Based on the theoretical framework, the paper derived the impacts of different factors on capital structure choice using comparative statics. Results suggest that the potential determinants of capital structure have varying effects at different ranges of leverage. Empirical evidence supports the theoretical model. Originality/value – Despite all of previous work on various aspects of farm capital structure choice, a framework that encompasses each of the different assumptions and scenarios is still lacking. The theoretical model integrates credit risk models and accommodates endogenous cost of capital, providing a comprehensive framework for studying farm capital structure choice and its determinants. The results provide insights that could help policy makers and lenders develop effective instruments to manage, monitor, and influence the financial leverage of farms at different quantiles of debt ratio.

scholarly journals A first-person theory of documentation

2019 ◽  
Vol 75 (1) ◽  
pp. 190-212 ◽  
Author(s):  
Tim Gorichanaz
Keyword(s):  
Theoretical Model ◽  
Design Methodology ◽  
Analytical Tool ◽  
First Person ◽  
Visual Artists ◽  
Art Making ◽  
Content Type ◽  
Person Perspective ◽  
Practical Implications ◽  
Person Experience

Purpose The purpose of this paper is to first articulate and then illustrate a descriptive theoretical model of documentation (i.e. document creation) suitable for analysis of the experiential, first-person perspective. Design/methodology/approach Three models of documentation in the literature are presented and synthesized into a new model. This model is then used to understand the findings from a phenomenology-of-practice study of the work of seven visual artists as they each created a self-portrait, understood here as a form of documentation. Findings A number of themes are found to express the first-person experience of art-making in these examples, including communicating, memories, reference materials, taking breaks and stepping back. The themes are discussed with an eye toward articulating what is shared and unique in these experiences. Finally, the themes are mapped successfully to the theoretical model. Research limitations/implications The study involved artists creating self-portraits, and further research will be required to determine if the thematic findings are unique to self-portraiture or apply as well to art-making, to documentation generally, etc. Still, the theoretical model developed here seems useful for analyzing documentation experiences. Practical implications As many activities and tasks in contemporary life can be conceptualized as documentation, this model provides a valuable analytical tool for better understanding those experiences. This can ground education and management decisions for those involved. Originality/value This paper makes conceptual and empirical contributions to document theory and the study of the information behavior of artists, particularly furthering discussions of information and document experience.

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