Unsteady flow in a collapsible tube subjected to external pressure or body forces

Flows in thin-walled, collapsible tubes are of fundamental importance to various physiologic phenomena and clinical devices.A one-dimensional, unsteady theory is developed for flows generated either by externally applied pressures or by body forces. Part 1 deals with small-amplitude, linearized flows, part 2 with large amplitude, nonlinear flows. Experimental results for a tube collapsing under external pressure are given in part 3, together with theoretical interpretations and comparative results of numerical simulations.Several new and unanticipated phenomena are revealed. These are in part associated with the highly nonlinear ‘equation of state’ (transmural pressure versus area) for a partially collapsed tube, and in part with whether the flow speed is sub- or supercritical relative to the speed of area waves. For instance, a flow produced by a spatially uniform external pressure applied to a limited region becomes choked at a flow-limiting throat at which point the fluid speed reaches the local wave speed. This throat forms at the edge of the pressurized region. The critical velocity can be exceeded with the application of certain types of spatially graded external pressures.

Download Full-text

Depressurization-Induced Nucleation in the “Polylactide-Carbon Dioxide” System: Self-Similarity of the Bubble Embryos Expansion

Polymers ◽

10.3390/polym13071115 ◽

2021 ◽

Vol 13 (7) ◽

pp. 1115

Author(s):

Dmitry Zimnyakov ◽

Marina Alonova ◽

Ekaterina Ushakova

Keyword(s):

Initial Rate ◽

Initial Pressure ◽

External Pressure ◽

Self Similarity ◽

Embryo Formation ◽

Linear Behavior ◽

Joint Influence ◽

External Pressures ◽

Adiabatic Cooling ◽

Self Similar

Self-similar expansion of bubble embryos in a plasticized polymer under quasi-isothermal depressurization is examined using the experimental data on expansion rates of embryos in the CO2-plasticized d,l-polylactide and modeling the results. The CO2 initial pressure varied from 5 to 14 MPa, and the depressurization rate was 5 × 10−3 MPa/s. The constant temperature in experiments was in a range from 310 to 338 K. The initial rate of embryos expansion varied from ≈0.1 to ≈10 µm/s, with a decrease in the current external pressure. While modeling, a non-linear behavior of CO2 isotherms near the critical point was taken into account. The modeled data agree satisfactorily with the experimental results. The effect of a remarkable increase in the expansion rate at a decreasing external pressure is interpreted in terms of competing effects, including a decrease in the internal pressure, an increase in the polymer viscosity, and an increase in the embryo radius at the time of embryo formation. The vanishing probability of finding the steadily expanding embryos for external pressures around the CO2 critical pressure is interpreted in terms of a joint influence of the quasi-adiabatic cooling and high compressibility of CO2 in the embryos.

Download Full-text

Pressure-flow relations in coronary circulation

Physiological Reviews ◽

10.1152/physrev.1990.70.2.331 ◽

1990 ◽

Vol 70 (2) ◽

pp. 331-390 ◽

Cited By ~ 294

Author(s):

J. I. Hoffman ◽

J. A. Spaan

Keyword(s):

Coronary Vessels ◽

Good Evidence ◽

The Body ◽

Vascular Compression ◽

Exact Nature ◽

Coronary Veins ◽

Collapsible Tubes ◽

External Pressures ◽

Flow Through

The blood vessels that run on the surface of the heart and through its muscle are compliant tubes that can be affected by the pressures external to them in at least two ways. If the pressure outside these vessels is higher than the pressure at their downstream ends, the vessels may collapse and become Starling resistors or vascular waterfalls. If this happens, the flow through these vessels depends on their resistance and the pressure drop from their inflow to the pressure around them and is independent of the actual downstream pressure. In the first part of this review, the physics of collapsible tubes is described, and the possible occurrences of vascular waterfalls in the body is evaluated. There is good evidence that waterfall behavior is seen in collateral coronary arteries and in extramural coronary veins, but the evidence that intramural coronary vessels act like vascular waterfalls is inconclusive. There is no doubt that in systole there are high tissue pressures around the intramyocardial vessels, particularly in the subendocardial muscle of the left ventricle. The exact nature and values of the forces that act at the surface of the small intramural vessels, however, are still not known. We are not certain whether radial (compressive) or circumferential and longitudinal (tensile) stresses are the major causes of vascular compression; the role of collagen struts in modifying the reaction of vessel walls to external pressures is unknown but possibly important; direct examination of small subepicardial vessels has failed to show vascular collapse. One of the arguments in favor of intramyocardial vascular waterfalls has been that during a long diastole the flow in the left coronary artery decreases and reaches zero when coronary arterial pressure is still high: it can be as much as 50 mmHg in the autoregulating left coronary arterial bed and approximately 15-20 mmHg even when the vessels have been maximally dilated. These high zero flow pressures, especially during maximal vasodilatation, have been regarded as indicating a high back pressure to flow that is due to waterfall behavior of vessels that are exposed to tissue pressures.(ABSTRACT TRUNCATED AT 400 WORDS)

Download Full-text

Steady compressible flow in collapsible tubes: application to forced expiration

Journal of Fluid Mechanics ◽

10.1017/s0022112089001515 ◽

1989 ◽

Vol 203 ◽

pp. 401-418 ◽

Cited By ~ 14

Author(s):

David Elad ◽

Roger D. Kamm ◽

Ascher H. Shapiro

Keyword(s):

External Pressure ◽

Forced Expiration ◽

Simple Description ◽

System Parameters ◽

Collapsible Tubes ◽

Influence Coefficients ◽

Cross Section Area ◽

Wall Stiffness ◽

Dependent Flow ◽

Flow Variables

Steady, one-dimensional flow of a compressible fluid through a collapsible tube is analysed. A general model is employed, incorporating axial variations in the parameters of the conducting system, such as the tube unstressed cross-section area and wall stiffness, the external pressure and energy exchange with the environment. The flow variables are described in differential form as functions of the conduit system parameters. A coupled set of equations for the dependent flow variables is summarized in a table of influence coefficients, which provides a clear and simple description of the effects produced by the system parameters. Examples of the effects of fluid compressibility in the respiratory system are presented for forced expiration manoeuvres. The effects are found to be generally small, but are most accentuated when breathing heavy gases and when the airways are pathologically stiffened.

Download Full-text

An Investigation of the Basic Physics of Irrigation in Urology and the Role of Automated Pump Irrigation in Cystoscopy

The Scientific World JOURNAL ◽

10.1100/2012/476759 ◽

2012 ◽

Vol 2012 ◽

pp. 1-6 ◽

Cited By ~ 6

Author(s):

Dwayne Chang ◽

Rustom P. Manecksha ◽

Konstantinos Syrrakos ◽

Nathan Lawrentschuk

Keyword(s):

Flow Rate ◽

External Pressure ◽

Flow Rates ◽

Pumping System ◽

External Pressures ◽

Basic Physics ◽

Traditional Irrigation ◽

Irrigation Solution ◽

Bladder Fullness

Objective. To investigate the effects of height, external pressure, and bladder fullness on the flow rate in continuous, non-continuous cystoscopy and the automated irrigation fluid pumping system (AIFPS).Materials. Each experiment had two 2-litre 0.9% saline bags connected to a continuous, non-continuous cystoscope or AIFPS via irrigation tubing. Other equipment included height-adjustable drip poles, uroflowmetry devices, and model bladders.Methods. In Experiment 1, saline bags were elevated to measure the increment in flow rate. In Experiment 2, saline bags were placed under external pressures to evaluate the effect on flow rate. In Experiment 3, flow rate changes in response to variable bladder fullness were measured.Results. Elevating saline bags caused an increase in flow rates, however the increment slowed down beyond a height of 80 cm. Increase in external pressure on saline bags elevated flow rates, but inconsistently. A fuller bladder led to a decrease in flow rates. In all experiments, the AIFPS posted consistent flow rates.Conclusions. Traditional irrigation systems were susceptible to changes in height of irrigation solution, external pressure application, and bladder fullness thus creating inconsistent flow rates. The AIFPS produced consistent flow rates and was not affected by any of the factors investigated in the study.

Download Full-text

Numerical solutions for unsteady gravity-driven flows in collapsible tubes: evolution and roll-wave instability of a steady state

Journal of Fluid Mechanics ◽

10.1017/s0022112099006084 ◽

1999 ◽

Vol 396 ◽

pp. 223-256 ◽

Cited By ~ 49

Author(s):

B. S. BROOK ◽

S. A. E. G. FALLE ◽

T. J. PEDLEY

Keyword(s):

Shallow Water ◽

Numerical Solutions ◽

Godunov Method ◽

Test Case ◽

Interesting Phenomenon ◽

One Dimensional ◽

Collapsible Tubes ◽

Highly Nonlinear ◽

Pressure Area ◽

The One

Unsteady flow in collapsible tubes has been widely studied for a number of different physiological applications; the principal motivation for the work of this paper is the study of blood flow in the jugular vein of an upright, long-necked subject (a giraffe). The one-dimensional equations governing gravity- or pressure-driven flow in collapsible tubes have been solved in the past using finite-difference (MacCormack) methods. Such schemes, however, produce numerical artifacts near discontinuities such as elastic jumps. This paper describes a numerical scheme developed to solve the one-dimensional equations using a more accurate upwind finite volume (Godunov) scheme that has been used successfully in gas dynamics and shallow water wave problems. The adapatation of the Godunov method to the present application is non-trivial due to the highly nonlinear nature of the pressure–area relation for collapsible tubes.The code is tested by comparing both unsteady and converged solutions with analytical solutions where available. Further tests include comparison with solutions obtained from MacCormack methods which illustrate the accuracy of the present method.Finally the possibility of roll waves occurring in collapsible tubes is also considered, both as a test case for the scheme and as an interesting phenomenon in its own right, arising out of the similarity of the collapsible tube equations to those governing shallow water flow.

Download Full-text

Managing External Pressures through Corporate Diplomacy

Journal of General Management ◽

10.1177/030630700703300103 ◽

2007 ◽

Vol 33 (1) ◽

pp. 33-50 ◽

Cited By ~ 6

Author(s):

Wolfgang Amann ◽

Shiban Khan ◽

Oliver Salzmann ◽

Ulrich Steger ◽

Aileen Lonescu-Somers

Keyword(s):

Case Studies ◽

Genetically Modified ◽

Food Products ◽

External Pressure ◽

Environmental Responsibility ◽

Genetically Modified Food ◽

Pressure Groups ◽

Tax Revenues ◽

External Pressures ◽

Public Pressure

Today's corporations face many demands from a plethora of different stakeholders, which are often incongruous. While shareholders demand a decent return on their investment, employees demand safe and well-paid jobs, communities stress upon their tax revenues and public pressure groups call for more social and environmental responsibility. Corporations thus require a great deal of corporate diplomacy to prioritise and – where necessary and possible – reconcile these different demands. This paper describes a framework for managerial/corporate attitudes and external pressure levels. Four case studies illustrate varying attitudes towards corporate diplomacy determine the outcome of controversies over genetically modified food products.

Download Full-text

Contribution of Inertia on Venous Flow in the Lower Limb during Stationary Gait

Journal of Applied Biomechanics ◽

10.1123/jab.20.2.115 ◽

2004 ◽

Vol 20 (2) ◽

pp. 115-128 ◽

Cited By ~ 1

Author(s):

Jean-Thomas Aubert ◽

Christian Ribreau

Keyword(s):

Blood Flow ◽

Gait Cycle ◽

Strong Dependence ◽

Venous Blood ◽

Kinematic Model ◽

The Body ◽

Axial Component ◽

Venous Blood Flow ◽

Collapsible Tubes ◽

Body Forces

Blood flows toward the heart through collapsible vessels, the veins. The equations of flow in collapsible tubes in motion show a strong dependence on body forces resulting from gravity and acceleration. This paper analyzes the contribution of body forces to venous blood flow during walking on level ground. It combines the biomechanics of gait and theory of collapsible tubes to point out that body forces due to gravity and limb acceleration cannot be overlooked when considering the determinants of venous blood flow during locomotion. The study involved the development of a kinematic model of the limb as a multi-pendulum arrangement in which the limb segments undergo angular displacements. Angular velocities and accelerations were determined and the body forces were calculated during various phases of the gait cycle. A vascular model of the leg's major venous system was also constructed, and the accelerations due to body and gravity forces were calculated in specific venous segments, using the data from the kinematic model. The results showed there were large, fast variations in the axial component (Gx–Mx) of the body forces in veins between the hip and the ankle. Acceleration peaks down to –2G were obtained at normal locomotion. At fast locomotion, a distal vein in the shank displayed values of (Gx–Mx)/G equal to –3.2. Given the down-to-up orientation of the x-axis, the axial component Mx was usually positive in the axial veins, and Mx could shift from positive to negative during the gait cycle in the popliteal vein and the dorsal venous arch.

Download Full-text

Structural, phase transition, mechanical and thermodynamic properties of TMNs under external pressures: A first-principles study

International Journal of Modern Physics B ◽

10.1142/s0217979218501813 ◽

2018 ◽

Vol 32 (15) ◽

pp. 1850181 ◽

Cited By ~ 3

Author(s):

Xin Tan ◽

Yinan Dong ◽

Yuan Ren ◽

Xuan Li ◽

Hui Qi ◽

...

Keyword(s):

Phase Transition ◽

Elastic Constants ◽

Density Functional ◽

Mechanical Stability ◽

Structural Phase ◽

Potential Method ◽

External Pressure ◽

Nanocomposite Films ◽

External Pressures ◽

Energy Relations

The plane-wave pseudo-potential method, which is based on density functional theory, is used to determine the structure, elastic constants and phase transition properties of transition metal nitride (TMN; TM = Ti, Zr, Hf, V, Nb and Ta) nanocomposite films under external pressures. Enthalpy–pressure and volume–energy relations of TMNs with different structures are calculated, and their relative stability is discussed. Mechanical stability of external pressure is calculated, and changes in elastic constants with external pressure are analyzed. The present study obtains influence of external pressure on the mechanical properties of material. By analyzing total energy–volume relation, enthalpy–pressure relation and mechanical stability, phase transition law of TMNs under external pressure is obtained.

Download Full-text

EXPERIMENTAL, NUMERICAL AND ANALYTICAL INVESTIGATIONS OF WIND-INDUCED NET PRESSURES FOR INDUSTRIAL BUILDINGS WITH ENVELOPE POROSITIES

Acta Polytechnica CTU Proceedings ◽

10.14311/app.2017.7.0058 ◽

2016 ◽

Vol 7 ◽

pp. 58

Author(s):

Vanessa Saubke ◽

Rüdiger Höffer

Keyword(s):

Spatial Distribution ◽

Numerical Model ◽

Wind Tunnel ◽

External Pressure ◽

Navier Stokes ◽

Industrial Building ◽

Wind Tunnel Experiments ◽

Industrial Buildings ◽

External Pressures

The magnitude and the spatial distribution of wind-induced net pressures (external and internal) on buildings are frequently discussed among research communities and construction industries. This paper deals with this topic based on a case study about an industrial building in Denmark, which was damaged due to the wind impact during a storm when a large part of the roof covering was blown off. In order to detect the reason for the damage the wind-induced loads were studied by i) wind tunnel experiments on the external pressures due to different wind directions, ii) analytical investigations of internal pressure due to envelope porosities and planned openings and iii) numerical analyses for the internal and the external pressure. The Reynolds averaged Navier-Stokes (RANS) method is employed to build a numerical model. The experimental, analytical and numerical results are compared with the indicated characteristic loads from the Eurocode.

Download Full-text

Determinants in detecting fraud triangle of financial statements on companies registered in Jakarta Islamic Index (JII) period 2012-2018

Journal of Islamic Accounting and Finance Research ◽

10.21580/jiafr.2020.2.1.4818 ◽

2020 ◽

Vol 2 (1) ◽

pp. 117

Author(s):

Iwan Budiyono ◽

Melati Sari Dewi Arum

Keyword(s):

Financial Stability ◽

Secondary Data ◽

Financial Statements ◽

External Pressure ◽

Financial Statement ◽

Fraud Triangle ◽

Analysis Model ◽

Financial Statement Fraud ◽

External Pressures ◽

Fraudulent Financial Statements

Purpose - The purpose of study was to examine the effect financial statement fraud based on the fraud triangle with a number of variables such as financial stability, external pressure, financial target, personal financial needs, opportunity and rasionalization in companies listed in Jakarta Islamic Index (JII) period 2012-2018.Method - The population are all companies listed in JII period 2012-2018. The sample is 6 companies that were feasible to analyze. The data used in this research is secondary data obtained from the annual report. The data analysis model applied multiple linier regression data panel using SPSS 25.Result - The results showed that the fraud triangle in the categories of financial stability, external pressure, financial targets, personal financial needs, opportunity and rationalization simultaneously affect the fraudulent financial statements. Furthermore financial stability, personal financial needs and opportunity partially negatively related and had no significant effect on financial statement fraud; while external pressures, financial targets and rationalization have positive and significant effects on financial statement fraud on companies listed in JII period 2012-2018.Implication - Companies Registered in JII are suggested to improve the financial performance in accordance with sharia principles.Originality - This research is the first study using multiple linier regression data panel.

Download Full-text