Transient Shear Stress Research Articles

Friction relaxation model for fast transient flows application to water hammer in two-phase flow – The WAHA code

The paper deals with the problem of the wall shear stress during rapid transient 1D flows in a piping system caused by water hammers in two-phase flow induced by a fast valve closure. The evolution of the transient wall shear stress is interpreted in terms of two steps. The first step is a sudden and dramatic change of the wall shear stress due to the passage of the pressure wave. The second step is a relaxation process of the shear stress which is modeled from the Extended Irreversible Thermodynamics theory. The friction relaxation model (FRM) presented in the first part of this paper describes both steps of the evolution of the wall shear stress during water hammers. The second part of the paper deals with the application of the FRM model as a closure law in the WAHA code. The main purpose of the WAHA code is to predict various situations relative to single- and two-phase water hammer transients in piping systems. The last part of the paper deals with the simulation of several cases from the UMSICHT databank using the adapted WAHA computer code with the FRM model. The results of these simulations are systematically compared with the experimental data. It is concluded that the new FRM model has a clear effect on water hammer pressure wave damping and on the pressure wave propagation velocity.

Pipetting causes shear stress and elevation of phosphorylated stress‐activated protein kinase/jun kinase in preimplantation embryos

Shear stress at 1.2 dynes/cm(2) induces stress-activated protein kinase/jun kinase phosphorylation that precedes and causes apoptosis in embryos (Xie et al., 2006b, Biol Reprod). Pipetting embryos is necessary for many protocols, from in vitro fertilization to collecting embryos prior to analyzing gene expression by microarrays. We sought to determine if pipetting upregulates phosphorylated MAPK8/9 (formerly known as stress-activated protein kinase/jun kinase/SAPK/JNK1, 2). We found that phosphorylated MAPK8/9, a marker of MAPK8/9 activation, is upregulated in a dose-dependent manner by pipetting. Whereas embryos with the zona pellucida removed were more sensitive to stress-induced lethality mediated by 1.2 dynes/cm(2) shear force, phosphorylated MAPK8/9 was induced at lower numbers of pipet triturations in hatched embryos at E4.5. E4.5 embryos were more sensitive to induction of MAPK8/9 than unhatched embryos at E2.5 or E3.5. E3.5 embryos also showed a pipetting dose-dependent induction of FOS protein (formerly known as c-fos), a marker of shear stress in many cell types. Phosphorylated MAPK8/9 measured in ex vivo embryos from E1.5 to E4.5 were expressed at low levels. Embryos that had been pipetted sufficiently to induce phosphorylated MAPK8/9 and FOS had the same number of cells as untreated embryos 24 hr later. This suggests that rapid phosphorylation of MAPK8/9 due to transient shear stress does not mediate long-term negative biological outcomes. But, it is possible that techniques requiring multiple handling events would induce MAPK8/9 and cause biological outcomes or that other biological outcomes are affected by low amounts of transient shear stress. This study suggests that embryo handling prior to experimental measurement of signal transduction phosphoproteins, proteins and mRNA should be performed with care. Indeed, it is likely that shear stress may cause rapid transient changes in hundreds of proteins and mRNA.

Measurement modes of the response time of a magneto-rheological fluid (MRF) for changing magnetic flux density

The response of a magneto-rheological fluid (MRF) to a change of magnetic flux density is investigated by using a commercial plate–plate magneto-rheometer MCR501 (Anton Paar GmbH) at constant shear rate. The instrument was modified to allow an online determination of the transient flux density in the MRF. Both current and voltage imposition to the magneto-cell were applied by using a power operational amplifier to drive the electromagnet. Assuming a Maxwell behavior with switching time λ and a linear increase in shear stress with flux density, analytic relations for the transient shear stress are derived for sinusoidal and single exponential flux densities vs time. True switching times of a few milliseconds are only obtained if the low pass filter in the original MCR501 torque signal is surpassed by a firmware allowing a sampling rate of 0.1 ms. For a sinusoidal flux density, the switching time is derived from the modulation depth of the shear stress. An upper bound of λ < 3 ms for a flux density of 0.8 T was found. For step coil current imposition of 1 T magnitude, switching times of 2.8 ms (start-up) and 1.8 ms (shutdown) allowed to fit the transient torque signal more than 2/3 of the total change. Finally, the effect of a sigmoidal characteristic on the switching time determination is addressed.

Non-volcanic tremor driven by large transient shear stresses

Non-impulsive seismic radiation or 'tremor' has long been observed at volcanoes and more recently around subduction zones. Although the number of observations of non-volcanic tremor is steadily increasing, the causative mechanism remains unclear. Some have attributed non-volcanic tremor to the movement of fluids, while its coincidence with geodetically observed slow-slip events at regular intervals has led others to consider slip on the plate interface as its cause. Low-frequency earthquakes in Japan, which are believed to make up at least part of non-volcanic tremor, have focal mechanisms and locations that are consistent with tremor being generated by shear slip on the subduction interface. In Cascadia, however, tremor locations appear to be more distributed in depth than in Japan, making them harder to reconcile with a plate interface shear-slip model. Here we identify bursts of tremor that radiated from the Cascadia subduction zone near Vancouver Island, Canada, during the strongest shaking from the moment magnitude M(w) = 7.8, 2002 Denali, Alaska, earthquake. Tremor occurs when the Love wave displacements are to the southwest (the direction of plate convergence of the overriding plate), implying that the Love waves trigger the tremor. We show that these displacements correspond to shear stresses of approximately 40 kPa on the plate interface, which suggests that the effective stress on the plate interface is very low. These observations indicate that tremor and possibly slow slip can be instantaneously induced by shear stress increases on the subduction interface-effectively a frictional failure response to the driving stress.

Discrete element simulation of shock wave propagation in polycrystalline copper

The implementation of the characteristic of compressive plasticity into the Discrete Element Code, DM2, while maintaining its quasi-molecular scheme, is described. The code is used to simulate the shock compression of polycrystalline copper at 3.35 and 11.0 GPa. The model polycrystal has a normal distribution of grain sizes, with mean diameter 14 μm, and three distinct grain orientations are permitted with respect to the shock direction; 〈1 0 0〉, 〈1 1 0〉, and 〈1 1 1〉. Particle velocity dispersion (PVD) is present in the shock-induced flow, attaining its maximum magnitude at the plastic wave rise. PVD normalised to the average particle velocity of Δ u y / u ¯ P = 0.05 and Δ u y / u ¯ P = 0.087 are yielded for the 3.35 and 11.0 GPa shocks, respectively, and are of the same order as those seen in the experiment. Non-planar elastic and plastic wave fronts are present, the distribution in shock front position increasing with propagation distance. The rate of increase of the spread in shock front positions is found to be significantly smaller than that seen in probabilistic calculations on nickel polycrystals, and this difference is attributed, in the main, to grain interaction. Reflections at free surfaces yield a region of tension near to the target free surface. Due to the dispersive nature of the shock particle velocity and the non-planarity of the shock front, the tensile pressure is distributed. This may have implications for the spall strength, which are discussed. Simulations reveal a transient shear stress distribution behind the shock front. Such a distribution agrees with that put forward by Lipkin and Asay to explain the quasi-elastic reloading phenomenon. Simulation of reloading shocks show that the shear stress distribution can give rise to quasi-elastic reloading on the grain scale.

Oscillation superimposed on steady shearing: Measurements and predictions for wormlike micellar solutions

Measurements are made of the viscoelastic properties of a wormlike micellar solution undergoing steady shearing. The wormlike micellar solution has a clearly defined Maxwell response in oscillation. The features (for example, the plateau of the elastic modulus, G′, and the peak of the viscous modulus, G″) are extremely well defined, allowing the differences in elastic properties brought about by steady-shearing to be easily discerned. An important feature of the solution studied is that it displays a plateau-like region with almost constant shear stress over a range of steady shear rates. We find that as the steady shear rate is increased: (i) G′ becomes negative at low frequencies; (ii) the plateau value of G′ decreases; (iii) the frequency at which the plateau value of G′ is reached shifts to higher frequencies; (iv) the width of the G″ peak decreases; (v) the position of the G″ peak shifts to higher frequencies; and (vi) the height of the G″ peak increases then decreases. The constitutive equations of Bautista et al. [J. Non-Newtonian Fluid Mech. 80, 93–113 (1999)] and Boek et al. [J. Non-Newtonian Fluid Mech. 126, 39–46 (2005)] were used to fit and predict bulk rheology measurements. Neither model predicts the observed rise in normal stress, despite fitting the plateau region in the shear-stress versus shear-rate curve. It proved difficult to predict transient shear stress data when both increases and decreases in the shear rate were considered. The features found in combined steady and oscillatory flow are predicted qualitatively but not quantitatively. In particular, the reduction of the plateau of G′ is predicted to occur only at much higher shear rates than found experimentally. We also note that the commercial software controlling the rheometer does not interpret the raw data correctly in the regime where G′ is negative.

Pulsed Laser Microbeam-Induced Cell Lysis: Time-Resolved Imaging and Analysis of Hydrodynamic Effects

Time-resolved imaging was used to examine the use of pulsed laser microbeam irradiation to produce cell lysis. Lysis was accomplished through the delivery of 6 ns, λ = 532 nm laser pulses via a 40×, 0.8 NA objective to a location 10 μm above confluent monolayers of PtK 2 cells. The process dynamics were examined at cell surface densities of 600 and 1000 cells/mm 2 and pulse energies corresponding to 0.7×, 1×, 2×, and 3× the threshold for plasma formation. The cell lysis process was imaged at times of 0.5 ns to 50 μs after laser pulse delivery and revealed the processes of plasma formation, pressure wave propagation, and cavitation bubble dynamics. Cavitation bubble expansion was the primary agent of cell lysis with the zone of lysed cells fully established within 600 ns of laser pulse delivery. The spatial extent of cell lysis increased with pulse energy but decreased with cell surface density. Hydrodynamic analysis indicated that cells subject to transient shear stresses in excess of a critical value were lysed while cells exposed to lower shear stresses remained adherent and viable. This critical shear stress is independent of laser pulse energy and varied from ∼60–85 kPa for cell monolayers cultured at a density of 600 cells/mm 2 to ∼180–220 kPa for a surface density of 1000 cells/mm 2. The implications for single cell lysis and microsurgery are discussed.

Transient Flow in Rapidly Filling Air-Entrapped Pipelines with Moving Boundaries

A mathematical model is presented for transient flow in a rapidly filling pipeline with an entrapped air pocket. The influence of transient shear stress between the pipe wall and the flowing fluid is taken into account. A coordinate transformation technique is employed to generate adaptive moving meshes for the multiphase flow system as images of the time-independent computational meshes in auxiliary domains. The method of characteristics is used to reduce the coupled nonlinear hyperbolic partial differential equations governing the motion of the filling fluid, entrapped air, and blocking fluid to ordinary differential equations. Numerical solution of resulting equations shows that the transient shear stresses have only a small damping effect on the pressure fluctuations. The peak pressure in the entrapped air pocket decreases significantly with increasing initial entrapped air volume, but decreases slightly with increasing initial entrapped air pressure.

Application of Method-of-Lines to Charging-Up Process in Pipelines with Entrapped Air

A mathematical model is presented for the charging-up process in an air-entrapped pipeline with moving boundary conditions. A coordinate transformation technique is employed to reduce fluid motion in time-dependent domains to ones in time-independent domains. The nonlinear hyperbolic partial differential equations governing the unsteady motion of fluid combined with an equation for transient shear stress between the pipe wall and the flowing fluid are solved by the method of lines. Results show that ignoring elastic effects overestimates the maximum pressure and underestimates the maximum front velocity of filling fluid. The peak pressure of the entrapped air is sensitive to the length of the initial entrapped air pocket.

Rheostructural studies on a synthetic mesophase pitch during transient shear flow

The steady, shear viscosities of a synthetic mesophase pitch (Mitsubishi AR-HP) obtained from rate-sweep experiments at 0.1–10 s −1 exhibited shear-thinning (region I) and plateau responses (region II), but displayed a hysteresis during the decreasing rate sweep. Transient tests revealed that the shear stress (and consequently the shear viscosity) displayed a local maximum and a minimum before approaching a steady state. Following steady flow at 1 s −1, a reversal of flow direction or a very short interruption in flow did not lead to the maxima or minima in the transient shear stress, but the maxima and the minima reappeared in the transient stress after a rest time of ∼1000 s. An experimental protocol was developed to preserve the rheological samples, and their microstructure was characterized in three orthogonal planes for the initial and final states. The initial microstructure was found to have a weak, but preferred, orientation of mesophase layers in the radial direction of the rheometer cone-plate (due to the initial squeezing flow). The initial microstructure changed to a flow-aligned fibrous structure after shearing in the viscometric flow.

Pregnancy augments pressure‐induced calcium transients in endothelial cells of rat uteroplacental arteries

Normal pregnancy is characterized by augmented endothelium-dependent vasodilation in the maternal uteroplacental circulation, but the role of mechanical forces in modulating the endothelial function is not well understood. The objectives of the present study were to: (1) characterize endothelial cell (EC) [Ca2+]i changes in response to elevation of intraluminal pressure in uterine arteries of non-pregnant (NP) and late pregnant (LP) rats; (2) define the role of smooth muscle cell (SMC) Ca2+ signaling in mediating pressure-induced EC [Ca2+]i elevations. Uterine radial arteries were cannulated and pressurized to 10 mmHg. We performed fura 2-based measurements of changes in EC or SMC [Ca2+]i and arterial diameter in response to pressure elevation to 50 (60) mmHg. Basal levels of EC [Ca2+]i were significantly higher in vessels of LP compared to NP rats. Elevation of pressure resulted in a transient increase in EC [Ca2+]i that was markedly potentiated in late pregnancy (LP: 160 ± 16 nM; NP: 7 ± 2 nM). Pressure-induced elevations in SMC [Ca2+]i was significantly smaller compared to those in ECs indicating that Ca2+ diffusion from SMCs through gap junction is unlikely is a source of EC [Ca2+]i transients. Pressurization of the arteries from both sides to minimize the effect of shear stress resulted in 18 ± 3 % reduction in EC [Ca2+]i responses. In conclusion, late pregnancy is associated with a marked augmentation of EC [Ca2+]i transients in response to both arterial distension and transient shear stress, and might be an important adaptive mechanism that contributes to augmented vasodilation in the maternal uterine circulation. Supported by NIH HL067250

Shear-strain-governed transient compressive response of electrorheological fluid

Transient process of electrorheological (ER) fluids compressed between two parallel plates and applied a high square-wave voltage has been modeled based on transient shear strain constant and shear stress and experimentally verified. The transient compressive resistance is integrated from the pressure distribution at the middle plane between the plates. Employing transient shear strain constant derived from other experimental investigations of dynamic shearing of ER fluids to fit the tested compressive stress, good results have been obtained. The rising of compressive stress upon the sudden applying of an electric field showed to be governed by the experienced shear strain of the compressed ER fluid.

Simulation of a mechanical approach to treat aortic dissection

To evaluate the local hemodynamic effects of coronary artery balloon angioplasty, computational fluid dynamics was applied to representative stenoses geometry post-angioplasty (minimal lesion diameter dm=1.8mm which produced 64% mean area stenoses) based on a group of patients and measured values of coronary flow reserve (CFR) returning to a normal range (3.6±0.3). The computations were at mean flow rates (Q˜) of 50, 100, 150 and 170 ml/min. The study indicates changes in the hemodynamic conditions due to insertion of a guidewire, which can be used to determine the mean pressure drop (Δp˜) and fall in distal mean coronary pressure (p˜r), and thus give quantitative estimate of uncertainty expected in diagnosis of moderate lesions. The guidewire to minimal lesion diameter ratio is 0.26, causing tighter “artifactual” mean area stenoses of 65.5%. During hyperemia, p˜m dropped to 72 mmHg as compared to 75 mmHg under patho-physiological condition without guidewire. Q˜h (subscript h: hyperemia) decreased from 180 without guidewire to 170 ml/min with the guidewire present. Thus, there was a significant ∼43% increase in Δp˜h and a ∼51% increase in the hyperemic flow resistance (R˜h=Δp˜h/Q˜h) over the patho-physiological condition. This could cause an overestimation of the severity of the moderate stenoses. Transient and steady flow guidewire surface shear stress was 35–50% higher than corresponding values for arterial wall shear stress. The non-dimensional data given in tabular form may be useful in interpretation of clinical guidewire measurements for moderate lesions of similar geometry and size.

The relationship between shear stress and flow‐mediated dilatation: implications for the assessment of endothelial function

Endothelium-dependent flow-mediated dilatation (FMD) describes the vasodilatory response of a vessel to elevations in blood flow-associated shear stress. Nitric oxide (NO), one of many vasoactive substances released by the endothelium in response to shear stress, is of particular interest to researchers as it is an antiatherogenic molecule, and a reduction in its bioavailability may play a role in the pathogenesis of vascular disease. The goal of many human studies is to create a shear stress stimulus that produces an NO-dependent response in order to use the FMD measurements as an assay of NO bioavailability. The most common non-invasive technique is the 'reactive hyperaemia test' which produces a large, transient shear stress profile and a corresponding FMD. Importantly, not all FMD is NO mediated and the stimulus creation technique is a critical determinant of NO dependence. The purpose of this review is to (1) explain that the mechanisms of FMD depend on the nature of the shear stress stimulus (stimulus response specificity), (2) provide an update to the current guidelines for FMD assessment, and (3) summarize the issues that surround the clinical utility of measuring both NO- and non-NO-mediated FMD. Future research should include (1) the identification and partitioning of mechanisms responsible for FMD in response to various shear stress profiles, (2) investigation of stimulus response specificity in coronary arteries, and (3) investigation of non-NO FMD mechanisms and their connection to the development of vascular disease and occurrence of cardiovascular events.

Chronic Shear Stress Is Lethal to Preimplantation Mouse Embryos Acting Through SAPK/JNK Phospho and TUNEL, But Acute Mouth Pipetting Also Increases SAPK/JNK and c-Fos

To test for the effects of embryo movement creating shear stress. Observational laboratory study to test whether shear stress in a rotating wall vessel or during mouth pipetting can induce stress activated protein kinase/Jun kinase (SAPK/JNK) phosphorylation and mediate poor outcomes in the preimplantation embryo. Mouse embryos were shear stressed in laboratory experiments using a rotating wall vessel and a Synthecon rotational cell culture system (RCCS)-1 to produce shear stress estimated to be 1.2dynes/cm2 or by mouth pipetting and tested for induction of SAPK/JNK diphospho and c-Fos, and TUNEL/apoptosis assayed by immunocytochemical assays. Experiments were also done to test for the role of SAPK/JNK and the Zona pellucida in the shear stress pathway. Embryos developed time-dependent SAPK phosphorylation that preceded TUNEL/apoptosis and irreversible death occurring at 12hr. A marker of shear stress, c-Fos protein, was induced in the outer placental epithelial cells of the blastocyst within 0.5hr of the initiation of shear stress, and was greater than rotational control (RC), while static control (SC) embryos had only background levels of c-Fos protein. A SAPK inhibitor, SP600125 was able to inhibit a large fraction of the apoptosis, suggesting that SAPK is induced by shear stress and causal to increased TUNEL/apoptosis. In comparison with hyperosmolar stress, shear stress caused death faster than 2M sorbitol, a very high dose. Removal of the Zona pellucida also enhanced lethality (in speed and magnitude) in shear stress, but had no effect on embryos in SC. Mouth pipetting also induced SAPK/JNK phospho and c-Fos in a dose-dependent manner. Shear stress induces rapid c-Fos protein and SAPK phosphorylation, followed by TUNEL/apoptosis. The Zona pellucida delays the lethal effects of shear stress. Taken together, these data agree with an earlier report where the 8-cell stage embryo was also found to be most sensitive to lethality after removing the zone pellucida and re-implanting into the oviduct (Bronson and McLaren, 1970), conditions which would expose the embryo to low levels of shear stress. In this earlier report, removal of the Zona pellucida (an acellular protein coat without known function after fertilization), enhanced embryo lethality. This suggests that the function of the Zona after fertilization may be to prevent shear stress caused lethality. In addition, mouth pipetting E3.5 and E4.5 mouse embryos caused a rapid dose-dependent increase in c-Fos and SAPK/JNK phospho, suggesting that handling embryos can cause transient shear stress.

Effect of hydrodynamics on dynamics of phase separation in polystyrene/poly(vinyl methyl ether) blend

Polystyrene/poly(vinyl methyl ether) (PS/PVME) phase diagram was assessed by rheological tools and by on-line microscopy observations both under quiescent and shear flow conditions. Shear flow was found to induce both mixing and demixing of the mixture depending on the amplitude of the imposed shear rate. Viscoelastic properties of PS/PVME blends were also measured under steady shear flow near the phase separation temperature. At lower shear rate, flow enhances concentration fluctuation and induces phase segregation. At high shear rate, flow suppresses fluctuations and the polymer mixture keeps its miscible state. Several rheological signatures of phase transition were found. In steady shear flow, a secondary plateau in viscosity was observed when the temperature was close to Ts whereas, at the start-up shear flow, transient shear stress showed a second overshoot after a few minutes of shearing.

Transient Shear Stress Response After Flow Start-up and Flow Reversal in Low Molecular Weight Nematic Liquid Crystals

ABSTRACT Within the framework of the Leslie–Ericksen theory we develop a unified model for the interpretation the complex shear stress response of tumbling nematics after flow start-up and flow reversal. The model accounts quantitatively for: (i) the damping of the oscillations, the vanishing of the doublet structure and eventually a pronounced decay after flow start-up, and (ii) the progressive reappearance of the oscillations after flow reversal (echo phenomenon). Within this model the loss of director coherence, induced partially by noise and partially by a distribution of velocity gradients, is a significant additional cause of damping. A primary cause (but not sufficient) is the director drift towards the vorticity axis as pointed out by other authors. On the other hand, the reappearance of the oscillation is related to reversibility dictated by the mechanical Leslie–Ericksen equations combined with the velocity gradient distribution.

Transient response of an electrorheological fluid under square-wave electric field excitation

The transient process of an electrorheological (ER) fluid based on zeolite and silicone oil sheared between two parallel plates to which a square-wave electric field is applied has been experimentally studied. The transient shear stress response to the strain or time is tested. The characteristic constants of time under different applied electric fields and shear rates have been determined. The response time is found to be proportional to shear rate with an exponent of about −0.75 in the tested shear rate range, which agrees with the theoretical predictions made by others. But it only shows a small dependence on the strength of the applied electric field. The results show that the transient process of ER fluids is related to the structure formation in the shearing. When the required shear strain is reached, the shear stress rises to a stable value under constant electric field. Although the electric field strength greatly affects the yield strength, it shows little effect on the stress response time. Also, experiments showed the electric field-induced shear stress decreased with an increase of shear rate.

Formation Sand Liquefaction: A Mechanism for Explaining Fines Migration and Well Sanding

To understand the basic relationship between the rising water-cut, well sanding, and migration of fines, the author’s work led him to examine the mechanism of well sanding due to sand liquefaction in cases where the storm chokes in offshore wells were activated and when the production platform separator lines froze due to sudden cold weather. The author found that as the original water-oil contact plane rose above the original plane of contact, it caused a drastic change in water saturation and relative permeability. We show the increased water saturation decreases the resistance of the formation to stress by as much as 50%. This is one of the causes of sand liquefaction at or near the perforation cavities. The parameters affecting the process most are the fine-particle buoyancy, changes in the effective stress and the bulk density of the sand, the pore pressure buildup and changes in porosity near the perforation cavities, the induced transient shear stress resulting from the water-hammer total pressure wave, and the lack of adequate cohesive cement or interlocking contacts between the grains of the unconsolidated sand. The simple model calculations pointed to the conclusion that if the grains of the unconsolidated sand or the fine particles accelerated above the threshold limit of 0.19000g, the chances for fines migration and sand liquefaction were high. Furthermore, if, at the free face of the washed-out perf tunnels or the cavernous cavities of the unconsolidated sand, the total pressure wave magnitude exceeded the shear resistance of the sand, then sand liquefaction was certain to occur. The obvious outcome of this process is nothing but serious formation damage. Based on his models, the author’s recommendation for alleviating this type of damage, includes but is not limited to selective perforation, oriented perforation, gravel packing, frac packing, filter packing, trajectory planning for well reentries, and controlled drawdown.

Guidewire flow obstruction effect on pressure drop-flow relationship in moderate coronary artery stenosis

To evaluate the local hemodynamic effects of coronary artery balloon angioplasty, computational fluid dynamics was applied to representative stenoses geometry post-angioplasty (minimal lesion diameter d m = 1.8 mm which produced 64% mean area stenoses) based on a group of patients and measured values of coronary flow reserve (CFR) returning to a normal range ( 3.6 ± 0.3 ). The computations were at mean flow rates ( Q ˜ ) of 50, 100, 150 and 170 ml/min. The study indicates changes in the hemodynamic conditions due to insertion of a guidewire, which can be used to determine the mean pressure drop ( Δ p ˜ ) and fall in distal mean coronary pressure ( p ˜ r ), and thus give quantitative estimate of uncertainty expected in diagnosis of moderate lesions. The guidewire to minimal lesion diameter ratio is 0.26, causing tighter “artifactual” mean area stenoses of 65.5%. During hyperemia, p ˜ m dropped to 72 mmHg as compared to 75 mmHg under patho-physiological condition without guidewire. Q ˜ h (subscript h: hyperemia) decreased from 180 without guidewire to 170 ml/min with the guidewire present. Thus, there was a significant ∼ 43 % increase in Δ p ˜ h and a ∼ 51 % increase in the hyperemic flow resistance ( R ˜ h = Δ p ˜ h / Q ˜ h ) over the patho-physiological condition. This could cause an overestimation of the severity of the moderate stenoses. Transient and steady flow guidewire surface shear stress was 35–50% higher than corresponding values for arterial wall shear stress. The non-dimensional data given in tabular form may be useful in interpretation of clinical guidewire measurements for moderate lesions of similar geometry and size.