Strain Rate Components Research Articles

HYSTERESIS OF IMPLICIT EQUATIONS IN HYPOPLASTICITY FOR SOIL MATERIALS WITH GRANULAR HARDNESS DEGRADATION

We study a hypoplastic model for soil and granular materials stemming from geomechanical engineering which further incorporates effects of degradation of the granular hardness, therefore allowing for the description of environmental weathering. The governing system is described by a nonlinear system of transcendental-differential equations for stress and strain rate, which is investigated with respect to its long-time dynamic. Under deviatoric stress control, two different solutions of the underlying, implicit differential equations are constructed analytically. The spherical components of stress and strain rate converge asymptotically to an attractor and lead to the sparsification of material states. Whereas under cyclic loading-unloading carried out in a numerical simulation, finite ratcheting of the deviatoric strain rate is observed in the form of a square spiral.

Slip boundary condition near the wall-interface contact line in axial stratified two-phase flow

The behavior of the velocity and shear stresses in two-phase laminar stratified flow near a triple point (TP), formed in the flow cross-section by the intersection of the interface with the conduit wall, is reconsidered. Differently from the no-slip boundary condition that showed a possibility of diverging shear stresses upon approaching the TP, we allow a slip of the fluids at the wall that can be prominent in the TP region. The Navier's boundary condition is used, which considers a linear relationship between the slip velocity and the strain rate component perpendicular to the surface. The solution for the velocity field in the TP region is obtained in terms of a power series of the distance from the TP having a discrete set of powers. Similarly to the solution obtained with no-slip B.C., a so-called ‘characteristic equation’ is obtained. Its solution yields a discrete set of non-integer powers that are dependent on the dynamic viscosity ratio and the contact angle. However, contrary to the no-slip solution, with Navier's B.C, each of these powers introduces a tower of terms resulting from the relation between the slip velocity and the velocity derivative at the wall. In addition, the solution also includes a tower of integer powers. The solution yields the velocity and the shear stress fields, as well as the flux of the force per length that acts on an arbitrary surface in the flow field. The latter is obtained by considering an equivalent 2D representation of the stress tensor. These are examined in comparison to the corresponding results obtained when no-slip at the wall is imposed. The relaxation of the wall shear stresses in cases where the no-slip condition predicts diverging wall shear stresses at the TP is demonstrated. It is shown that if the local velocity in the TP region is a limit of a global no-slip solution, the scaled velocity field in the TP region is independent of the details of the global flow field.

The influence exerted by active cooling on the permanent connection formed as a result of electric arc welding

The problem of temperature stresses is solved in the work. The process of electric arc welding with guaranteed penetration of steel plates of various thicknesses is simulated. The possibility of reducing residual stresses formed as a result of welding by applying heat removal from the surface of the near-weld region of a steel plate is being investigated. The temperature distribution is determined by solving a non-linear heat equation, in which the specific heat and thermal conductivity depend on temperature. The heat source is modeled using the double ellipsoid method proposed by John A. Goldak. The horseshoe-shaped heat sink follows immediately after the anode spot and is set by the heat flux in such a way that the main temperature of the plate does not decrease below its initial temperature. This limitation reduces the level of the temperature gradient, thereby reducing the stresses in the metal plate. To illustrate the effect of active heat sink, the temperature distribution in the top layer at the moment of termination of welding is compared with and without active heat sink. The material is assumed to be elastoviscoplastic, the deformations are small and consist of reversible and irreversible ones. Reversible deformations are related to stresses by the Duhamel - Neumann law. Irreversible strains increase when the von Mises plastic flow condition is satisfied, in which there is a plastic strain rate component responsible for the plastic flow viscosity. The elastic moduli (Young's modulus, Poisson's ratio) and the yield strength are assumed to be temperature dependent. The solution of the mechanical part of the problem is found by the method of simple iterations. For plates with different thicknesses, diagrams of residual stresses are given, located in the center of the plate from the seam to the periphery. As a result of the work, according to the obtained distributions of residual stresses in the plate material, it is concluded that the use of an active horseshoe-shaped heat sink from the near-weld zone when welding thin steel plates reduces residual stresses, therefore it is recommended to use in the welding process. The use of an active heat sink on the reverse side of the plate leads to an increase in the stress level, therefore it is not recommended for use.

DNS analysis of turbulence modulation by lean premixed prevaporized spray flames in a model combustor

Turbulence modulation by lean premixed prevaporized (LPP) spray flames, which involve droplet motion, evaporation and gaseous reaction, is complicated and essential to organizing clean and efficient combustion. Direct numerical simulations of LPP combustion in a model swirling combustor under high pressure of 20 bar are performed. The gaseous flow is solved in the low-Mach-number limit, and the droplets are tracked as two-way coupled Lagrangian particles. The corrected infinite thermal conductivity model is adopted to describe droplet evaporation, and a reduced two-step kerosene/air chemistry mechanism is used to present combustion. Four cases, i.e., a non-reacting gaseous flow, a non-reacting spray flow and two reacting spray flows with different droplet sizes, are conducted to cover key features of LPP flame on turbulence modulation. The results show that the spray combustion significantly depresses the mean axial velocity on the centerline in the upstream, indicating an enhancement of the inner recirculation zone. The influence of droplets on the mean and fluctuating velocities is generally negligible except on the azimuthal modulation, while combustion can increase the velocities, which is more evident in downstream due to the pressure effect. In reacting cases, the turbulent kinetic energy (TKE) spectra in the shear layers reduce at high wavenumbers, reflecting the combustion-induced dissipation at small scales (below the laminar flame thickness scale). Besides, droplet evaporation can introduce energy at small scales while this modulation is balanced by combustion. Moreover, TKE budget analysis indicates that spray combustion mainly depresses the TKE and redistributes mean shear along the radial direction. Heat release increases the local fluid viscosity, depresses local turbulent transport, and increases viscous dissipation. Finally, the vortex stretching analysis shows that LPP combustion enhances the alignment with the intermediate strain rate component.

Modeling the Fourth Power Law Response of Viscoplastic Materials

A standard way to parametrize a steady structured shock going through a viscoplastic material, is by plotting the stress jump across the wave (Ds) as function of its maximum strain rate () plotted on a logarithmic scale. Doing this we usually get a straight line, which means that . Grady and coworkers noticed in the 1980s that for many materials b=4. Since then, several workers in the field tried to understand this unusual behavior, but they were not able to arrive at any plausible explanation. Recently, Grady revisited his fourth power law with an extensive review, including an outline of various mechanisms proposed as possible explanations of this law. But still, none of these mechanisms is able to explain the fourth power law response. In view of this background, we use here the fourth power law to calibrate the strain rate component of the constitutive response of Al 6061-T6. To this end, we integrate the steady viscoplastic equations (developed long ago) describing the propagation of a plane wave from the elastic precursor level to the stress plateau level. We find that in order to reproduce the fourth power law, the plastic deformation rate has to depend on the deviator overstress by: , with α=2.38. But for high shock levels, when the elastic precursor is overdriven, using this value of α leads to a higher value of the slope b, close to b=6. This result has yet to be verified experimentally.

Incremental diagnostic value of CMR-derived LA strain and strain rate in dialysis patients with HFpEF

ObjectivesTo test whether left atrial (LA) strain and strain rate add incremental value in the diagnosis of heart failure with preserved ejection fraction (HFpEF) in dialysis patients over clinical and conventional parameters only. BackgroundHFpEF frequently occurs in dialysis patients, however, the diagnosis of HFpEF is difficult. Although HFpEF is always companied with LA dysfunction, the performance of novel LA parameters, LA strain, and strain rate, in the diagnosis of HFpEF among dialysis patients remains unknown. MethodsIn the study, 153 dialysis patients (57 without HFpEF and 96 with HFpEF) and 52 healthy controls underwent cardiovascular magnetic imaging (CMR). Three components of LA strain and strain rate, including reservoir, contractile, and booster pump, were assessed via the CMR feature tracking module. Extra diagnostic value was examined by Harrell’s C-statistic. ResultsCompared with healthy controls and dialysis patients without HFpEF, dialysis patients with HFpEF had significantly impaired LA reservoir (εs) and contractile (εe) strain and strain rate (SRs, SRe), all p < 0.0001. Among these parameters, εs, εe, and SRe showed relatively high accuracy in diagnosing HFpEF among dialysis patients (areas under the curve: 0.84, 0.91, and 0.90, respectively). Reduction of εs, εe, and SRs provided incremental diagnostic value over conventional clinical and echocardiogram parameters. Combined with εs, εe or SRs, the diagnostic performance was further improved (Harrell’s C-statistic: 0.83 vs. 0.96, 0.97, and 0.97, respectively, all p < 0.0001). ConclusionsCMR-derived εs, εe, and SRs might add incremental diagnostic value over conventional indexes in diagnosing HFpEF among dialysis patients.

Left atrial booster-pump function as a predictive parameter for atrial fibrillation in patients with severely dilated left atrium.

Left atrial (LA) dimension ≥50 mm had approximately four times the risk of developing atrial fibrillation (AF). The aim of this study was to investigate whether the application of clinical and echocardiographic parameters could differentiate between the patients having severely dilated left atrium with and without AF. This retrospective cross-sectional study enrolled consecutive patients with LA dimension ≥50 mm and divided them into three groups: no AF (no-AF), paroxysmal AF (PAF) and non-paroxysmal AF (non-PAF) groups. For PAF and non-PAF groups, all patients underwent radiofrequency ablation, and the echocardiographic parameters were obtained on the next day after ablation. Our study population comprised 160 patients, including 80, 53, and 27 patients in the non-AF, PAF and non-PAF groups, respectively. The no-AF group had a significantly higher body mass index (kg/m2) (29.31±6.27, 27.58±4.12 and 26.57±2.81, P=0.01), and a higher prevalence of diabetes mellitus (DM) [31 (38.80%), 13 (25.00%) and 4 (14.80%), P=0.01] and hypertension [67 (83.80%), 34 (65.40%), and 19 (70.40%), P=0.04], but a lower prevalence of rheumatic heart disease (RHD) [3 (3.80%), 6 (11.50%) and 5 (18.50%), P=0.02] and sick sinus syndrome [0 (0.00%), 6 (11.50%) and 4 (14.80%), P=0.045]. Echocardiographic studies showed that the non-AF group had significantly smaller LA minimal volume index (24.89±9.74, 34.06±19.38 and 42.83±17.44 mL/m2, P<0.01), higher LA emptying fraction (51.99%±13.97%, 38.40%±15.96% and 33.89%±10.73%, P<0.01), longitudinal strain (23.87%±7.72%, 17.11%±8.52% and 12.38%±4.28%, P<0.01) and strain rate than the AF groups. The multivariate analysis showed that the late diastolic component of LA strain rate was the only independent factor associated with the presence of AF (odds ratio, 21.69; 95% CI, 9.77-48.13, P<0.01). LA function plays an important role in the absence of AF in patients with LA dimension ≥50 mm; the late diastolic component of LA strain rate was the only independent variable on multivariate analysis.

The impact of isometric handgrip testing in left atrial reservoir function

Abstract Funding Acknowledgements Type of funding sources: Public hospital(s). Main funding source(s): Fundação Adib Jatene Background Speckle tracking echocardiography (STE) allows accurate quantification of left atrial (LA) strain, thus allowing assessment of all phases of LA function (reservoir, conduit and contraction). Alterations in LA strain occur before changes in LA volumes, enabling early detection of LA dysfunction. In particular, the peak of LA strain during the reservoir phase (LASr) seems to be of prognostic value in heart failure. LASr is essential to pool enough blood volume to fill the LV during the subsequent diastole. The main determinants of LA reservoir function include blood volume arriving from the right ventricle, LA relaxation, and LA compliance. Still, changes in atrioventricular plane movement during the ventricular systole have been considered an additional factor influencing LASr. The relative contribution of left ventricular afterload to LASr, however, has yet to be clearly defined. Purpose We aimed to study the LA function during changes in LV afterload induced by the handgrip maneuver in subjects without heart disease, applying LASr and strain curve shape analysis. Material and Methods We studied 31 subjects (47 ± 15 years) without evidence of heart disease. A comprehensive 2D echocardiography was performed. We recorded 3 beat clips with standard STE views of LV and LA in baseline conditions and then during pressure overload-induced by left handgrip (42 ± 8 kg) combined with simultaneous pneumatic constriction of the right arm and both lower limbs. The LV GLS and LASr were calculated offline by a blinded examinator using commercially available software. Furthermore, we extracted the raw data of the strain curves and post-processed these signals using custom software. The global curves were split into different cardiac cycle phases using the valve opening and closure times(Figure 1). Quadratic functions estimated strain curves during the ejection phase due to the acceleration involved in the phenomenon. Quadratic function linear coefficients, a component of strain rate, were used to assess the shape of deformation curves. Results The handgrip maneuver caused mild reductions in LV strain: GLS baseline –19.07 % (±0.27) vs GLS handgrip -18.58% (±0.26) p = 0.02 (Figure 2A and C). Conversely, the LASr did not present significant changes: LASr baseline 33.82% (±0.84) vs LASr handgrip 32.96% (±0.85) p= 0.18 (Figure 2B and C). For the analysis of the shape of strain curves, we obtained data from 29 subjects. We found significant differences in LV ejection linear coefficient (ELC): LV ELC baseline –158.30 (±8.52) vs LV ELC handgrip –144.62 (±8.02) p = 0.02. For LA reservoir linear coefficient (RLC), we also found significant differences: LA RLC baseline 240.30 (±17.19) vs LA RLC handgrip 212.61 (±15.62) p = 0.03 (Figure 2D). Conclusion(s) The left atrial reservoir function is affected by changes in LV afterload induced by the handgrip maneuver. Our data suggest that LV pressure overload mainly impact the shape of LA strain curve rather than LASr. Abstract Figure 1 Abstract Figure 2

Evolutions of strain rate and dissipation rate of kinetic energy in turbulent premixed flames

The statistical behaviors of the evolutions of the components of the strain rate tensor and Favre-averaged dissipation rate of kinetic energy are analyzed using direct numerical simulations of statistically planar turbulent premixed flames propagating into forced unburned gas turbulence for different turbulence intensities spanning a range of different Karlovitz numbers. The pressure Hessian contribution and the combined molecular diffusion and dissipation terms are found to play dominant roles in the transport equations of diagonal strain rate components and the Favre-averaged dissipation rate of kinetic energy for flames with small Karlovitz numbers. By contrast, the leading order balance is maintained between the strain rate, vorticity, and molecular dissipation contributions for flames with large Karlovitz numbers, similar to non-reacting turbulent flows. The contributions of the terms arising from the correlation between pressure and density gradients and pressure Hessian in the strain rate and dissipation rate of kinetic energy transport equations weaken in comparison to the magnitude of the molecular dissipation contribution with an increase in Karlovitz number. These behaviors have been explained in terms of the alignments of vorticity, pressure gradient, and pressure Hessian eigenvectors with strain rate eigendirections. The magnitudes of the terms in the transport equation of the Favre-averaged dissipation rate of kinetic energy are also found to increase with increasing Karlovitz number, which is explained with the help of a detailed scaling analysis. This scaling analysis also explains the leading order contributions to the dissipation rate of kinetic energy for different combustion regimes.

Atrioventricular Longitudinal Mechanics Using Novel Speckle-Tracking Improved Risk Stratification Beyond Baseline Thyroid Hormone in Asymptomatic Subclinical Hypothyroidism.

Hypothyroidism is reportedly associated with increased cardiovascular risk and heart failure. We aimed to elucidate the mechanistic influence of atrio-ventricular deformations and their prognostic utilizations in asymptomatic subclinical hypothyroidism (SCH). We assessed speckle-tracking of deformations among 4173 population-based asymptomatic individuals classified as euthyroid (0.25< thyroid-stimulating hormone [TSH] ≤4.0 μIU/mL, n=3799) or having mild (4< TSH ≤10.0 μIU/mL, n=349) or marked (TSH >10 μIU/mL, n=25) SCH. We further related deformational indices to outcomes of atrial fibrillation and heart failure. Despite borderline differences in indexed left ventricular mass and left atrial volume (P=0.054 and 0.051), those classified as mild and marked SCH presented with modest but significant reductions of global longitudinal strain, and showed elevated E/tissue Doppler imaging (TDI)-e', markedly diminished peak atrial longitudinal strain and higher left atrial stiffness (all P<0.05) when compared with euthyroid subjects. A higher TSH level was independently associated with reduced TDI-s'/TDI-e', worse global atrio-ventricular strains (global longitudinal strain/peak atrial longitudinal strain), elevated E/TDI-e', and worsened left atrial strain rate components (all P<0.05). Over a median 5.6 years (interquartile range, 4.7-6.5 years) follow-up, myocardial deformations yielded independent risk prediction using Cox regression in models adjusted for baseline covariates, N-terminal pro-brain natriuretic peptide, E/e', and treatment effect. Incorporation of global atrio-ventricular strain (global longitudinal strain/peak atrial longitudinal strain) and strain rates further showed improved risk reclassification when added to the baseline TSH strata (classified as euthyroid and mild and marked SCH; all P<0.05). Cox regression models remained significant with improved risk reclassification beyond TSH-based strata by using slightly different deformational cutoffs after excluding marked SCH group. Hypothyroidism, even when asymptomatic, may widely influence subclinical atrio-ventricular mechanical functions that may lead to higher heart failure and atrial fibrillation risk. We proposed the potential usefulness and prognostic utilization of myocardial strains in such population.

Understanding Kinematics of the Orthogonal Cutting Using Digital Image Correlation—Measurement and Analysis

Abstract With the development of advanced image correlation and high-speed filming techniques, the kinematic field during the cutting process can be experimentally determined including the velocity and strain rate fields. As known, the setting parameters for the digital image correlation (DIC) as well as the optical parameters of the given camera and lighting system have a great influence on the spatial resolution and accuracy of the DIC results. In this study, the speckle pattern in terms of speckle size and intensity distribution are analyzed when using two different surface preparation methods. Moreover, the influences of the subset sizes for the image correlation on the strain rate are numerically studied. Interlaboratory measurements of the kinematic field during the orthogonal cutting of AISI 4140 were conducted with two different in-situ imaging setups. The material flow near the cutting tool edge determined from the velocity field is compared with the numerical simulation. The stagnation zone which is commonly found in the numerical simulation of the cutting process using a chamfered cubic boron nitride (CBN) tool was not observed in the experiments. Furthermore, slip-line fields were constructed from the experimentally determined strain rate components, from which the boundary conditions along the chip-free and chip-tool interface were derived.

Extensional gravity-rheometry (EGR) for yield stress fluids

In order to measure the extensional rheological properties of yield stress fluids, we developed a rheometrical approach based on the analysis of the deformations of a fluid extrudate flowing downward and breaking in successive elongated drops due to gravity. Assuming the gradients of longitudinal velocity in radial planes are negligible, the local instantaneous strain rate is deduced from the variations of the filament diameter in each cross section, while the normal stress is computed from the acceleration and weight of the material below this point. The observation of the filament profile in time allows us to identify a solid region, in which the deformations tend to saturate, and a liquid region, in which the deformations continuously increase. A further analysis allows us to distinguish the data for which pure elongational stress and strain rate components are effectively dominant so that the elongational flow curve of the material over several decades of the strain rate can be deduced. For two typical yield stress fluids (emulsion and clay suspension) with different internal structures, all the normal stress vs extensional rate data obtained under these different flow conditions fall along a single master curve for each material. This flow curve in elongation appears to be well represented by the standard 3D Herschel–Bulkley model under the condition that a slightly different power of the strain rate than in simple shear is used. For both material types, the elongational yield stress value found in this way is very close to the simple shear yield stress times the square root of 3.

Effects of Axial Casing Grooves on the Structure of Turbulence in the Tip Region of an Axial Turbomachine Rotor

Abstract Challenges in turbulence modeling in the tip region of turbomachines include anisotropy, inhomogeneity, and non-equilibrium conditions, resulting in poor correlations between Reynolds stresses and the corresponding mean strain-rate components. The geometric complexity introduced by casing grooves exacerbates this problem. Taking advantage of a large database collected in the refractive index-matched liquid facility at Johns Hopkins University (JHU), this paper examines the effect of axial casing grooves on the distributions of turbulent kinetic energy (TKE), Reynolds stresses, anisotropy tensor, and TKE production rate in the tip region of an axial turbomachine. The comparisons are performed at flowrates corresponding to prestall and best efficiency points of the untreated machine. Common features include high TKE near the tip leakage vortex center and in the shear layer connecting it to the blade suction side tip corner. The turbulence is highly anisotropic and inhomogeneous, with the anisotropy tensor shifting from one-dimensional (1D) to 2D and 3D structures over small distances. With the grooves, the flow structure, hence the distribution of Reynolds stresses, becomes more complex. Additional sites with elevated turbulence include the corner vortex that develops at the entrance to the grooves, and in the flow jetting out of the grooves into the passage. Consistent with trends of the production rates of normal Reynolds stress components, the grooves increase the axial but reduce the radial velocity fluctuations as the inflow and outflow from the groove interact with the passage flow. These findings might assist the development of Reynolds stress models suitable for tip flows.

An Exact Axisymmetric Solution in Anisotropic Plasticity

A hollow cylinder of incompressible material obeying Hill’s orthotropic quadratic yield criterion and its associated flow rule is contracted on a rigid cylinder inserted in its hole. Friction occurs at the contact surface between the hollow and solid cylinders. An axisymmetric boundary value problem for the flow of the material is formulated and solved, and the solution is in closed form. A numerical technique is only necessary for evaluating ordinary integrals. The solution may exhibit singular behavior in the vicinity of the friction surface. The exact asymptotic representation of the solution shows that some strain rate components and the plastic work rate approach infinity in the friction surface’s vicinity. The effect of plastic anisotropy on the solution’s behavior is discussed.

Solution Behavior Near Very Rough Walls under Axial Symmetry: An Exact Solution for Anisotropic Rigid/Plastic Material

Rigid plastic material models are suitable for modeling metal forming processes at large strains where elastic effects are negligible. A distinguished feature of many models of this class is that the velocity field is describable by non-differentiable functions in the vicinity of certain friction surfaces. Such solution behavior causes difficulty with numerical solutions. On the other hand, it is useful for describing some material behavior near the friction surfaces. The exact asymptotic representation of singular solution behavior near the friction surface depends on constitutive equations and certain conditions at the friction surface. The present paper focuses on a particular boundary value problem for anisotropic material obeying Hill’s quadratic yield criterion under axial symmetry. This boundary value problem represents the deformation mode that appears in the vicinity of frictional interfaces in a class of problems. In this respect, the applied aspect of the boundary value problem is not essential, but the exact mathematical analysis can occur without relaxing the original system of equations and boundary conditions. We show that some strain rate and spin components follow an inverse square rule near the friction surface. An essential difference from the available analysis under plane strain conditions is that the system of equations is not hyperbolic.

Associations of region‐specific visceral adiposity with subclinical atrial dysfunction and outcomes of heart failure

AimsExcessive visceral adiposity (VAT) plays an essential role in metabolic derangements with those close to heart further mediates myocardial homeostasis. The disparate biological links between region‐specific VAT and cardiometabolic profiles as mediators influencing atrial kinetics remain unexplored.Methods and resultsAmong 1326 asymptomatic individuals, region‐specific VAT including peri‐aortic root fat (PARF) and total pericardial fat (PCF) of cardiac region, together with thoracic peri‐aortic adipose tissue (TAT), was assessed using multiple‐detector computed tomography. VAT measures were related to functional left atrial (LA) metrics assessed by speckle‐tracking algorithm and clinical outcomes of atrial fibrillation (AF) and heart failure (HF). Multivariate linear regression models incorporating body fat, metabolic syndrome, and E/TDI‐e' consistently demonstrated independent associations of larger PARF/PCF with peak atrial longitudinal systolic strain (PALS) reduction, higher LA stiffness, and worsened strain rate components; instead, TAT was independently associated with cardiometabolic profiles. PARF rather than PCF or TAT conferred independent prognostic values for incident AF/HF by multivariate Cox regression (adjusted hazard ratio: 1.56, 95% confidence interval: 1.17–2.08, P = 0.002) during a median of 1790 days (interquartile range: 25th to 75th: 1440–1927 days) of follow‐up, with subjects categorized into worst PALS and largest VAT tertiles demonstrating highest events (all log‐rank P < 0.001). Mediation analysis showed that higher triglyceride and lower high‐density lipoproteins may serve as intermediary factors for effects between VAT and LA functional metrics, with lesser role by glucose level.ConclusionsVisceral adiposity surrounding atrial region was tightly associated with subclinical atrial dysfunction and incident AF or HF beyond metabolic factors. Instead, peri‐aortic adiposity may mediate their toxic effects mainly through circulating cardiometabolic profiles.

Modeling of creep deformation of a transversely isotropic rotating disc with a shaft having variable density and subjected to a thermal gradient

This study aims to develop the mathematical model of creep deformation of a transversely isotropic rotating disc with a shaft having variable density and subjected to a thermal gradient by using the transition theory of Seth and generalized strain measure theory. This theory of Seth requires no assumptions such as the creep deformation is infinitesimally small, creep strain laws and the associated flow rules, and is important for evaluating creep stresses and strain rates in a disc based on Lebesgue strain measure. The advantage of this theory is considering the nonlinear nature of the material. The combined impacts of density, temperature, and angular speed have been displayed numerically and graphically. Consequently, it is observed that the value of radial creep stress at the internal surface is maximum for the disc made of steel material in comparison to a disc made of titanium material. The values of the creep strain rate components increased at the internal surface with the introduction of thermal effects.

Heart failure with preserved ejection fraction or non-cardiac dyspnea in paroxysmal atrial fibrillation: The role of left atrial strain

BackgroundDiagnosis of heart failure with preserved ejection fraction (HFpEF) in patients with dyspnea and paroxysmal atrial fibrillation (AF) is challenging. Speckle tracking-derived left atrial strain (LAS) provides an accurate estimate of left ventricular (LV) filling pressures and left atrial (LA) phasic function. However, data on clinical utility of LAS in patients with dyspnea and AF are scarce. ObjectiveTo assess relationship between the LAS and the probability of HFpEF in patients with dyspnea and paroxysmal AF. MethodsThe study included 205 consecutive patients (62 ± 10 years, 58% males) with dyspnea (NYHA≥II), paroxysmal AF and preserved LV ejection fraction (≥50%), who underwent speckle tracking echocardiography during sinus rhythm. Probability of HFpEF was estimated using H2FPEF and HFA-PEFF scores, which combine clinical characteristics, echocardiographic parameters and natriuretic peptides. ResultsPatients with high probability of HFpEF were significantly older, had higher body mass index, NT-proBNP, E/e’, pulmonary artery pressure and larger LA volume index than patients in low-to-intermediate probability groups (all p < 0.05). All components of LAS and LA strain rate showed proportional impairment with increasing probability of HFpEF (all p < 0.05). Out of the speckle tracking-derived parameters, reservoir LAS showed the largest area under the curve (AUC = 0.78, p < 0.001) and the strongest independent predictive value (OR: 1.22, 95% CI 1.08–1.38) to identify patients with high probability of HFpEF. ConclusionsReservoir LAS shows a high diagnostic performance to distinguish HFpEF from non-cardiac causes of dyspnea in symptomatic patients with paroxysmal AF.

Strain Rate Contribution due to Dynamic Recovery of Ultrafine-Grained Cu–Zr as Evidenced by Load Reductions during Quasi-Stationary Deformation at 0.5 Tm

During quasi-stationary tensile deformation of ultrafine-grained Cu-0.2 mass%Zr at 673 K and a deformation rate of about e - 4 / s load changes were performed. Reductions of relative load by more than about 25% initiate anelastic back flow. Subsequently, the creep rate turns positive again and goes through a relative maximum. This is interpreted by a strain rate component ϵ ˙ - associated with dynamic recovery of dislocations. Back extrapolation indicates that ϵ ˙ - contributes the same fraction of ( 20 ± 10 ) % to the quasi-stationary strain rate that has been reported for coarse-grained materials with high fraction of low-angle boundaries; this suggests that dynamic recovery of dislocations is generally mediated by boundaries. The influence of anelastic back flow on ϵ ˙ - is discussed. Comparison of ϵ ˙ - to the quasi-stationary rate points to enhancement of dynamic recovery by internal stresses. Subtraction of ϵ ˙ - from the total rate yields the rate component ϵ ˙ + related with generation and storage of dislocations; its activation volume is in the order expected from the classical theory of thermal glide.

An application of tomographic PIV to investigate the spray-induced turbulence in a direct-injection engine

Fuel sprays produce high-velocity, jet-like flows that impart turbulence onto the ambient flow field. This spray-induced turbulence augments rapid fuel-air mixing, which has a primary role in controlling pollutant formation and cyclic variability in direct-injection engines. This paper presents tomographic particle image velocimetry (TPIV) measurements to analyze the 3D spray-induced turbulence during the intake stroke of a direct-injection spark-ignition (DISI) engine. The spray produces a strong spray-induced jet (SIJ) in the far field, which travels through the cylinder and imparts turbulence onto the surrounding flow. Planar high-speed PIV measurements at 4.8 kHz are combined with TPIV at 3.3 Hz to evaluate spray particle distributions and validate TPIV measurements in the particle laden flow. A comprehensive uncertainty analysis is performed to assess the uncertainty associated with individual vorticity and strain rate components.TPIV analyses quantify the spatial domain of the turbulence in relation to the SIJ and describe how turbulent flow features such as turbulent kinetic energy (TKE), strain rate (S) and vorticity (Ω) evolve into the surrounding flow field. Access to the full S and Ω tensors facilitate the evaluation of turbulence for individual spray events. TPIV images reveal the presence of strong shear layers (visualized by high S magnitudes) and pockets of elevated vorticity along the immediate boundary of the SIJ. S and Ω values are extracted from spatial domains extending in 1 mm increments from the SIJ. Turbulence levels are greatest within the 0–1 mm region from the SIJ boarder and dissipate with radial distance. Individual strain rate and vorticity components are analyzed in detail to describe the relationship between local strain rates and 3D vortical structures produced within strong shear layers of the SIJ. Analyses are intended to understand the flow features responsible for rapid fuel-air mixing and provide valuable data for the development of numerical models.