A Possible Criterion for Cavitation Inception on Hemispherical Headforms

1981 ◽  
Vol 103 (4) ◽  
pp. 577-582
Author(s):  
B. R. Parkin

The present paper reviews several pertinent papers about the onset of bubble-ring cavitation on hemispherical headforms in which a laminar bubble is present. From this review, a likely sequence of events for cavitation inception, or desinence, can be discerned. When this sequence is postulated, the observational basis for each event is discussed. Once the physical aspects of the inception process have been noted, a mathematical formulation of key relationships required to establish an inception criterion can be undertaken. From these results, a quantitative criterion for the inception of bubble ring cavitation is stated and we give a discussion which interprets this possible inception criterion for future use. The use of this criterion in a theory of inception and a comparison of analytical and experimental results is left to a future publication.

Meccanica ◽  
2020 ◽  
Vol 55 (10) ◽  
pp. 1885-1902
Author(s):  
Yang Liu ◽  
Joseph Páez Chávez ◽  
Jiajia Zhang ◽  
Jiyuan Tian ◽  
Bingyong Guo ◽  
...  

Abstract The vibro-impact capsule system has been studied extensively in the past decade because of its research challenges as a piecewise-smooth dynamical system and broad applications in engineering and healthcare technologies. This paper reports our team’s first attempt to scale down the prototype of the vibro-impact capsule to millimetre size, which is 26 mm in length and 11 mm in diameter, aiming for small-bowel endoscopy. Firstly, an existing mathematical model of the prototype and its mathematical formulation as a piecewise-smooth dynamical system are reviewed in order to carry out numerical optimisation for the prototype by means of path-following techniques. Our numerical analysis shows that the prototype can achieve a high progression speed up to 14.4 mm/s while avoiding the collision between the inner mass and the capsule which could lead to less propulsive force on the capsule so causing less discomfort on the patient. Secondly, the experimental rig and procedure for testing the prototype are introduced, and some preliminary experimental results are presented. Finally, experimental results are compared with the numerical results to validate the optimisation as well as the feasibility of the vibro-impact technique for the potential of a controllable endoscopic procedure.


Author(s):  
Bernd Bachert ◽  
Bernhard Brunn ◽  
Bernd Stoffel

The aim of this work is to demonstrate the significant influence of liquid property on cavitation inception. The experimental results were obtained on two different test rigs, one with an axial test pump (nS = 180 min−1 in European Units or 9000 min−1 in US Units) and another one with a single hydrofoil configuration. To realize a variation of the gas content (nuclei content and distribution of nuclei) of the test water a special device, a so-called “micro bubble generator”, was developed and installed in the test rigs. The measuring of the tensile strength of the test water was also one point of the investigations of this work.


Geophysics ◽  
1968 ◽  
Vol 33 (3) ◽  
pp. 473-480 ◽  
Author(s):  
Fred Schwab ◽  
Robert Burridge

Many seismic problems involve interfaces. Seismic modeling provides a means of passing from the mathematical formulation to the solution of such problems when suitable analytical techniques are not available. Accurate interface formulations are necessary if modeling is to be as effective as possible in this role. Application of improved techniques has provided more accurate and detailed results than possible in the original work (Toksöz and Schwab, 1964) on model interface formulations. The present investigation was limited to butt‐joined, two‐dimensional models constructed with metallic sheets and epoxy bonding agents. Experimental results were first compared with those predicted by the simplest of “welded‐contact” theories—that which totally ignores the bonding layer. For a layer thickness of 0.007 cm, fair agreement was noted for frequencies below 125 kHz. New theoretical results were then predicted by taking the finite thickness and elastic properties of the bonding layer into consideration. The metal‐epoxy interfaces were assumed “welded‐contacts.” Irrespective of whether the formulation specified a perfectly elastic or an anelastic bonding material, the correlation between predicted and experimental results was quite poor. The disparity was much greater, over the entire frequency range, than that obtained from the formulation which totally ignored the bonding layer. All the welded‐contact interface formulations tested in this investigation were found unsatisfactory for highly accurate work. Based on the technique used to test the welded‐contact assumption, a mathematically accurate description of the interface was developed.


Author(s):  
L. P. Perera ◽  
V. Ferrari ◽  
F. P. Santos ◽  
M. A. Hinostroza ◽  
C. Guedes Soares

In this paper, experimental results on collision avoidance of autonomous ship manoeuvres are discussed. The collision avoidance experiments are conducted on a navigation & control platform that has been presented in a mathematical formulation as well as in an experimental setup. The mathematical formulation of collision avoidance consists of three systems: vessel traffic monitoring and information system (VTMIS), collision avoidance system (CAS), and vessel control system (VCS). The experimental platform of collision avoidance consists of a physical system that has been used to generate experimental results. The experimental platform is further divided into two sections: vessel model and navigation & control platform. The vessel model consists of a scale ship, where the CAS is implemented. The navigation & control platform consists of hardware structure and software architecture that supported for vessel model navigation. Two ship collision situations are considered in this study, where one ship is implemented under the vessel model and another ship is simulated. Finally, the successful collision avoidance results with respect various collision situations are presented.


2020 ◽  
Vol 68 (3) ◽  
pp. 801-832
Author(s):  
Viswanath Umashanker Trivedi ◽  
Amin Mawani

Using two experiments, this study examines taxpayers' decisions on how much income to report in the presence of tax auditors and post-reporting tax advisers, respectively. In the first experiment, we examine taxpayers' compliance in the presence and absence of corrupt auditors. In the second experiment, we examine taxpayers' compliance in the presence of corrupt tax auditors and compare it with their compliance in the presence of tax advisers retained by the taxpayers upon being audited. The bribes sought by corrupt auditors from audited taxpayers are expressed in the form of a percentage of taxes and penalties payable. The sequence of events in the first experiment is as follows: (1) the taxpayer decides what percentage of income to report to the tax authority; (2) the taxpayer finds out whether or not he or she is audited; and (3) the taxpayer pays any unpaid taxes and penalties if audited by a non-corrupt auditor, or decides whether to pay a bribe if the auditor is corrupt. In the second experiment, step 3 is replaced by the taxpayer having to decide whether to bribe the corrupt tax auditor without hiring a tax adviser, or to retain a (dispute resolution) tax adviser in the absence of a corrupt tax auditor to contest the penalties and underreporting of income. Participants' learning from earlier rounds of the experiment can affect their reporting choice in subsequent rounds. The results of our first experiment show that overall taxpayer compliance is reduced in the mere presence of a corrupt tax auditor, even when bribe-seeking may offer no net after-tax monetary benefits to the taxpayers. This demonstrates the corrosive effects of corrupt auditors. Taxpayer compliance declines even further when taxpayers receive net monetary benefits from bribing the corrupt auditor. The second experiment examines whether the involvement of a professional tax adviser increases or decreases the percentage of income reported compared to the baseline compliance in the presence of a corrupt tax auditor. If the tax adviser serves as a gatekeeper and moral authority, the percentage of income reported by the taxpayer client could increase in the presence of a tax adviser. However, if the tax adviser effectively serves to simply override the tax penalties imposed on the taxpayer, the percentage of income reported by the taxpayer client could decrease. Our experimental results show that in the absence of corrupt auditors, tax advisers are better at improving taxpayer compliance compared to the baseline compliance in the presence of a collusively corrupt tax auditor. This suggests that tax advisers do serve as moral gatekeepers for the tax system.


1998 ◽  
Vol 120 (2) ◽  
pp. 241-248 ◽  
Author(s):  
G. A. Ateshian ◽  
Huiqun Wang ◽  
W. M. Lai

Articular cartilage is the remarkable bearing material of diarthrodial joints. Experimental measurements of its friction coefficient under various configurations have demonstrated that it is load-dependent, velocity-dependent, and time-dependent, and it can vary from values as low as 0.002 to as high as 0.3 or greater. Yet, many studies have suggested that these frictional properties are not dependent upon the viscosity of synovial fluid. In this paper, a theoretical formulation of a boundary friction model for articular cartilage is described and verified directly against experimental results in the configuration of confined compression stress-relaxation. The mathematical formulation of the friction model can potentially explain many of the experimentally observed frictional responses in relation to the pressurization of the interstitial fluid inside cartilage during joint loading, and the equilibrium friction coefficient which prevails in the absence of such pressurization. In this proposed model, it is also hypothesized that surface porosities play a role in the regulation of the frictional response of cartilage. The good agreement between theoretical predictions and experimental results of this study provide support for the proposed boundary friction formulation.


Author(s):  
Hector J. Carlo ◽  
J. Patrick Spicer ◽  
Adamaris Rivera-Silva

The design of manufacturing systems is typically decoupled from ordering policy decisions. Traditionally, the system design decision is made to minimize the total investment cost given some system capacity requirements. Then, after the system is implemented, the ordering policy decisions are made. In this paper, a coupled approach is presented whereby the manufacturing system design is jointly developed with the ordering policy to minimize the total cost of inventory holding, setup, and equipment investment in a multiproduct system. The methodology is presented in the context of scalable-reconfigurable manufacturing systems (scalable-RMSs). First, a linear integer mathematical formulation to minimize investment cost in a single-product, multistage scalable-RMS is presented. The mathematical formulation is then extended to consider multiple products. Due to the nonlinear nature of the multiproduct formulation, an iterative algorithm is developed. Lastly, a mathematical formulation to simultaneously minimize the system investment and operating costs (i.e., the coupled approach) is presented. Given the complexity of the formulation, a genetic algorithm (GA)-based heuristic is proposed. Twenty four instances of the problem were generated to test the proposed methodologies. Experimental results indicate that the proposed GA-based heuristic is efficient in terms of solution quality and runtime. Further, experimental results indicate that the proposed coupled approach reduces the total costs by an average of 25% over the decoupled approach. It is concluded that the coupled approach (solved with the proposed GA-based heuristic) outperforms the decoupled approach (solved to optimality) in all instances considered.


Author(s):  
Alberto Di Matteo ◽  
Francesco Lo Iacono ◽  
Giacomo Navarra ◽  
Antonina Pirrotta

Very recently the tuned liquid column damper (TLCD) is receiving an increasing interest from researchers concerned with vibration control, to be considered an alternative device with respect to the tuned mass damper (TMD), since the former has low cost, easy adjustment, flexible installation. However, in recent studies the authors [1] have pointed out that for TMD the analytical formulation provides results that are in good agreement with the experimental ones, while for TLCD it has been deducted that the analytical formulation needs further investigation. In fact using the classical formulation of the problem, numerical results are very different from the experimental results obtained by the authors using the facilities at the experimental dynamic laboratory of University of Palermo. In particular it has been shown that the total liquid length should be corrected in an effective one, but in a different way from what has been done in literature, where only the variation of section of the vessel has been taken into account. On the other hand, from experimental investigations it is seen that the liquid moves more in the central area of the tube and less in the area in contact with the side walls. This aspect plays a fundamental role for capturing the real performance of TLCD. In fact, being the TLCD a special type of auxiliary damping device which relies on the inertia of liquid column in a U-tube to counteract the forces acting on the structure, then it is necessary to identify the effective moving liquid mass. To aim at this, in this paper the authors differentiate the total liquid mass into a liquid dead mass and a liquid dynamic mass, then introducing these values into a properly modified mathematical formulation numerical results match the experimental ones for all tests.


Author(s):  
R Balachandar ◽  
A S Ramamurthy

The study deals with the prediction of cavitation inception in the wake of two-dimensional bluff bodies subject to wall interference effects. Corrections are included in the model to account for flow entrainment effects and loss of circulation in the vortices shed from the bluff body. Experimental results are also presented to verify the proposed model over a range of blockages.


2014 ◽  
Vol 69 (3) ◽  
pp. 181-184 ◽  
Author(s):  
Mariusz Pietruszka ◽  
Krystyna Pazurkiewicz-Kocot

In context of a fairly concise review of recent literature and well established experimental results we reconsider the problem of action potential propagating steadily down the plant cell(s). Having adopted slightly modified Hodgkin-Huxley set of differential equations for the action potential we carried out the numerical investigation of these equations in the course of time. We argue that the Hodgkin-Huxley-Katz model for the nerve impulse can be used to describe the phenomena which take place in plants - this point of view seems to be plausible since the mechanisms involving active ionic transport across membranes from the mathematical point of view are similar. Besides, we compare in a qualitative way our theoretical outcomes with typical experimental results for the action potentials which arise as the reaction of plants to electrical, mechanical and light stimuli. Moreover, we point out the relevance of the sequence of events during the pulse with the appropriate ionic fluxes.


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