Effect Of Shear Stress Research Articles

Analysis of lateral behaviour of monopiles considering principal stress rotation under coupled loading in sand

Monopiles for offshore wind turbine foundations are often subjected to vertical-horizontal combined loading. For the analysis of piles subjected to horizontal loads in sand, the p-y curve method based on the Winkler model is usually employed, where p is the soil resistance of the pile per unit length and y is the local horizontal displacement of the pile or the soil compression at the point of study. As the load bearing properties of horizontally loaded piles depend on the ultimate resistance P u of the soil around the pile in the shallow soil layer, it is important to determine P u of the shallow soil accurately. In this paper, the wedge model is employed to calculate P u. The effect of vertical shear stress along the pile on the principal stress direction which decides the bottom angle of the wedge is taken into account. Then, the effects of the vertical loads on the p-y curves, P-Δ effect, M R effect is considered in the horizontal equilibrium equation of the pile. The shear-displacement method is employed to calculated the vertical responses of the pile. The shear stress and horizontal soil resistance were redistributed when the coupled effect of the vertical load and the horizontal load is considered. Then, the horizontal responses of the monopile under vertical load, horizontal load and moment simultaneously can be calculated. Finally, the proposed method is used to calculate a centrifuge model test where a piles is subjected to coupled loads in sandy soils. The results showed that the pile moment curve after considering the bottom angle of the wedge β modification is closer to the experimental results than without the β modification, so it makes the modified β more reasonable in analyzing the behavior of laterally loaded single piles in sand. At the same time, the β modification is not required for pure horizontal loading.

EXPERIMENTAL STUDY ON THE DYNAMIC SHEAR MODULUS AND DAMPING RATIO OF SATURATED SAND UNDER CYCLIC LOADING

Initial shear stress is inevitable in actual engineering slopes, subgrades and foundations, and soils exhibit different dynamic characteristics under the influence of initial shear stress. Using a dynamic triaxial test system, this study explores the dynamic shear modulus and damping ratio of saturated sand from Wenchuan, investigates the effects of the initial shear stress and vibration frequencies on the dynamic shear modulus and damping ratio of saturated sand and proposes a normalised dynamic shear modulus formula that considers the initial shear stress and vibration frequency. Results show a threshold dynamic shear strain of the saturated sand. When the dynamic shear strain is below this threshold, the dynamic shear modulus significantly increases with the initial shear stress and vibration frequency. Otherwise, the influence of the initial shear stress and vibration frequency gradually decreases and eventually stabilises. The initial shear stress significantly affects the normalised dynamic shear modulus/strain curves where a larger initial shear stress corresponds to a higher curve. Meanwhile, the vibration frequency only exerts a slight influence. The curves under different frequencies are generally within the same band and fall near the Seed upper envelope. The initial shear stress also has a significant influence on the damping ratio where a larger initial shear stress corresponds to a smaller damping ratio. On the basis of the experimental results, a normalised dynamic shear modulus/shear strain formula that considers the influence of the initial shear stress and vibration frequency is established. Fitting results indicate that this formula shows good agreement with the test data.

Stress field analysis of an infinite plate with a central closed inclined crack under uniaxial compression

In view of the shortcomings of existing studies, the mechanical behavior of the closed crack under uniaxial compression is studied. Based on the far-field and the crack surface stress boundary conditions, Kolossoff-Muskhelishvili stress function of an infinite plate with a central closed inclined crack is derived with Muskhelishvili complex theory. Then the calculation methods of the stress components, stress intensity factors and T-stress at the crack tip are proposed. The mainly findings are as follows. First of all, the crack surface stress boundary conditions vary with variation of the far-field stress condition from tension to compression, so it’s false to directly introduce the theory for the crack under tension to that for the closed crack under compression. Next, it is found that there is no KI singular term at the crack tip and meanwhile KII and T-stress are influenced by the effective shear stress on the crack surface. When the effective shear stress is zero, there are two T-stress components (i.e. Tx and Ty, which are parallel and perpendicular to the crack surface respectively). While the effective shear stress is greater than zero, the third T-stress component (namely Txy which is along the xy direction) also exists. Finally, the theoretical predictions with the proposed method are verified with the isochromatic fringe patterns of photoelasticity experiment near the crack tip under uniaxial compression. Meanwhile the distribution of each stress component around the crack is effected obviously by the friction coefficient of the crack surface and the dip angle of crack, but the distribution tendency of these stress components is similar.

Study on the maximum tangential strain criterion for the initiation of the wing-crack under uniaxial compression

The global stress field function of an infinite plate with a closed inclined crack under uniaxial compression is presented, then the stress field at the crack tip is obtained, namely the formulae of KI, KII and T-stress are obtained. A new maximum tangential strain (MTSN) criterion is proposed to predict the initiation of the crack under compression by considering singular and non-singular terms based on the classical MTSN criterion. The influence factors on KII are analyzed and the effects of T-stress on the tangential strain at the crack tip under different critical plastic zones (rc), dip angel of crack (β), friction coefficients of crack surface (f) and Poisson’s ratio (ν) are studied. The comparison of the wing-crack initiation angle measured from the experimental results and predicted by the proposed criterion and other researchers’ models are made. The following findings are obtained. First of all, the proposed global stress field function satisfies the far-field and crack surface stress boundary conditions. The singular term of KII and non-singular term of T-stress vary with the effective shear stress along the crack surface. When the effective shear stress is zero, there is still singularity at the crack tip, which is completely opposite to the classical theory, and there are two components of T-stress (i.e. Tx and Ty, which is parallel and perpendicular to the crack surface respectively). While there is a third component of T-stress (i.e. Txy, which along the xy direction) when the effective shear stress is greater than zero. Next, the comparison of the wing-crack initiation angle measured from the experimental results and predicted by the proposed criterion and other researchers’ models are made. The results of the proposed method are consistent with the experiments very well, especially when the effective shear stress decreases to zero with the increase of friction coefficient (f). Finally, the tangential strain field at the crack tip are effected significantly by the critical plastic zones (rc), dip angel of crack (β), friction coefficients of crack surface (f) and Poisson’s ratio (ν).

Climate Change Impacts on Coastal Wave Dynamics at Vougot Beach, France

Wave dynamics contribute significantly to coastal hazards and were thus investigated at Vougot Beach by simulating both historical and projected future waves considering climate change impacts. The historical period included a major storm event. This period was projected to the future using three globally averaged sea level rise (SLR) scenarios for 2100, and combined SLR and wave climate scenarios for A1B, A2, and B1 emissions paths of the IPCC. The B1 wave climate predicts an increase in the occurrence of storm events. The simulated waves in all scenarios showed larger relative changes at the beach than in the nearshore area. The maximum increase of wave energy for the combined SLR and wave scenarios was 95%, while only 50% for the SLR-only scenarios. The effective bed shear stress from waves and currents showed different spatial variability than that of the wave height, emphasizing the importance of interactions between nearshore waves and currents. Increases in the effective bed shear stress (combined scenarios: up to 190%, and SLR-only scenarios: 35%) indicate that the changes in waves and currents will likely have significant impacts on the nearshore sediment transport. This work emphasizes that combined SLR and future wave climate scenarios need to be used to evaluate future changes in local hydrodynamics and their impacts. These results provide preliminary insights into potential future wave dynamics at Vougot Beach under different climate change scenarios. Further studies are necessary to generalize the results by investigating the wave dynamics during storm events with different hydrodynamical conditions and to evaluate potential changes in sediment transport and morphological evolution due to climate change.

Hemodynamic Analysis on the Anastomosis Angle in Arteriovenous Graft Using Multiphase Blood Model

Numerical analysis was performed for the effect of the venous anastomosis angle in a forearm arteriovenous graft for hemodialysis using a multiphase blood model. The geometry of the blood vessel was generated based on the patient-computed tomography data. The anastomosis angles were set at 15°, 30°, and 45°. The hematocrit was set at 34%, 45%, and 58%. The larger anastomosis angle, high wall shear stress area >11 Pa, increases to the side of the vein wall away from the anastomosis site. Further, the relatively low wall shear stress area, <3 Pa, occurs near the anastomosis site in larger anastomosis angles. Therefore, the effect of high wall shear stress has advantages in the vicinity of the anastomosis, as the anastomosis angle is larger, but disadvantages as the distance from the anastomosis increases. Moreover, patients with low hematocrit are advantageous for WSS area.

Effect of Shear Stresses on Asphalt Pavement Performance and Evaluating Debonding Potential under Repeated Loading: Numerical Study

The primary of this paper is to evaluate the potential of shear failure in asphalt pavement with the primary focus on the layer interface debonding. To fulfill this objective, a three-dimensional (3D) finite-element (FE) model is developed to calculate the stress state within the asphalt pavement structure. Five different cases of vehicle maneuvering where shear forces acting on the surface layer were selected, and pavement responses were obtained and analyzed under 100 loading cycles at three different temperatures. Results show that maximum shear stress occurred on top of the surface layer, and with receding from the surface, the stresses reduced significantly along the pavement depth. The case where the vehicle moves along the curved road section induced the highest transverse shear stress, whereas braking action caused the highest longitudinal shear stress both within the pavement layer and at the layer interface. Moreover, the maximum shear stress in both directions and all studied cases took place in somewhere within the tire imprint area. With increasing temperature, the pavement responses increased in all cases accordingly. In addition, pavement responses at the bottom of the binder course were significantly lower than those of at the bottom of the surface layer. In general, pavement responses in pavement layers were larger than their counterparts at the layer interface. Finally, the concept of interface shear ratio (ISR) is presented to evaluate the potential of debonding at the layer interface under repeated loading. According to initial results, the ISR could be considered as a promising criterion for assessing shear failure potential at layer interface.

Applications of Second Log-Wake Law for Turbulent Velocity Distributions in Laboratory Flumes and Natural Rivers

AbstractNatural river velocity distributions are often studied by laboratory flume flows because of similarities of the bed shear stress effects between the two flows. Nevertheless, the velocity di...

Finite element analysis of smart composite plate structures coupled with piezoelectric materials: Investigation of static and vibration responses

This research presents a generalized-energy-based finite element modeling of smart composite plates with distributed piezoelectric materials for the static and vibration responses under electrical and mechanical loading. The zigzag kinematics in conjunction with a non-polynomial higher-order shear deformation theory is used to derive the model. The plate theory accounts for the non-linear variations of the transverse shear strains across the thickness of the plates and also accommodates the inter-laminar continuity effects of transverse shear stresses at the interfaces. Eight noded isoparametric serendipity elements are used to discretize the physical domain. The solutions in the time domain are obtained from the discretized system of ordinary differential equations with Newmark’s time integration scheme. Several numerical examples are solved for different types of smart composite plates with various piezoelectric materials, boundary conditions, static and dynamic loadings. The classical negative feedback controller is used for deriving the suppressed and controlled vibration responses of the smart composite plates with distributed actuators and sensors. A comparison of the present FE solutions with the elasticity and other analytical and numerical solutions shows good agreement, thereby ensures the applicability of the present finite element model for studying the coupled electromechanical problems of piezoelectricity.

Numerical modelling of osteocyte growth on different bone tissue scaffolds

The most common solution for the regeneration or replacement of damaged bones is the implantation of prostheses comprising ceramic or metallic materials. However, these implants are known to cause problems such as post-operative infections, collapse of the prosthesis, and lack of osseointegration. Consequently, bone tissue engineering was established because of the limitations of such implants. Osteogenic implants offer promising solutions for bone regeneration; however, three-dimensional scaffolds should be used as supportive structures. It is challenging to correctly design these structures and their compositions or properties to provide a microenvironment that promotes tissue regeneration and expedites bone formation. Computational fluid dynamics can be used to model the main phenomena that occur in bioreactors, such as cell metabolism, nutrient transport, and cell culture growth, or to model the influence of several key mechanisms related to the fluid medium, in particular, the wall shear stress. In this work, a new numerical bone cell growth model was developed, which considered the oxygen and nutrient consumption as well as the wall shear stress effect on cell proliferation. The model was implemented using 35 three-dimensional scaffolds of different porosities, and the effect of the main geometrical parameters involved in each scaffold type was analysed. The porosity plays an important role, however, a similar porosity did not guarantee similar shear stress or cell growth among the scaffolds. Randomised trabecular scaffolds, that more closely resembled trabecular bone, showed the highest cell growth values, so these are the best candidates for cell growth in a bioreactor.

Undrained Cyclic Response and Resistance of Saturated Calcareous Sand considering Initial Static Shear Effect

Sand elements in the natural or manmade field have often undergone initial static shear stresses before suffering cyclic loading. To explore the effect of static shear stress, a series of undrained cyclic triaxial tests were performed on dense and loose calcareous sand under different initial and cyclic shear stresses. The triaxial test results are used to describe the effect of static shear stress on the cyclic response of the calcareous sand with different relative density. Cyclic mobility, flow deformation, and residual deformation accumulation are the three main failure modes under varying static and cyclic shear stress levels. The cyclic resistance of dense sand is greater than that of loose sand, but the initial static stress has different effects on the cyclic resistance of the two kinds of sand. The dense sand owns a higher cyclic resistance with SSR increasing, while for the loose sand, 0.12 is the critical SSR corresponding to the lowest value of the cyclic resistance. The dense sand has more fast accumulation of dissipated energy, compared with loose sand. Additionally, an exponential relationship is established between static shear stress, relative density, and normalized energy density.

Erythrocytes, a New Contributor to Age-Associated Loss of Blood-Brain Barrier Integrity.

Blood exchanges between young and old partners demonstrate old blood has a detrimental effect on brain health of young animals. Previous studies primarily investigate soluble blood factors, such as transforming growth factor‐beta, on the brain and the blood–brain barrier (BBB). However, the role of blood cellular components, particularly erythrocytes, has not been defined. Erythrocyte morphology and rigidity change as mammals age, altering their transport within the capillary bed. This impacts downstream biological events, such as the release of reactive oxygen species and hemoglobin, potentially compromising the BBB. Here, a micro electrical BBB (µE‐BBB), with cocultured endothelial and astrocytic cells, and a built‐in trans‐endothelial electrical resistance (TEER) system is described to monitor the effect of capillary shear stress on erythrocytes derived from young and old mice and people and the subsequent effects of these cells on BBB integrity. This is monitored by the passage of fluorescein isothiocyanate‐dextran and real‐time profiling of TEER across the BBB after old and young erythrocyte exposure. Compared to young erythrocytes, old erythrocytes induce an increased permeability by 42% and diminished TEER by 2.9% of the µE‐BBB. These results suggest that changes in circulating erythrocytes are a biomarker of aging in the context of BBB integrity.

An analytical model for mass transport calculations in a viscous muddy layer

This study aims to present analytical solutions to the interactions between waves, currents, and the muddy bed layer and compare the results for different constant, linear, and second-order current profiles. The effects of mean shear stress and its variations on wave dispersion relations as well as mud (particle and mass transport) velocities are investigated. It is found that the second-order profile presents the maximum effects on the wave field (wave dissipation and mud mass transport velocities) compared to the constant and linear current profiles. However, assuming the constant current profile, frequently applied in the literature models, results in the minimum effects. A local peak exists in the mud mean discharge over the current profile curvature. The mud velocity induced by the linear current profile presents the closest value to the particle velocity for the no-current case. Additionally, the second-order current profile provides slightly better results for the mud mass transport velocity rather than the constant current profile when comparing the results with the laboratory data.

Numerical Investigation of Wall Shear Stress under Single-Phase and Two-Phase Flow in the Electrical Submersible Pump

The effects of the wall shear stress on an Electrical Submersible Pump (ESP) was investigated in this paper. A CFD model in ANSYS Fluent was proposed to simulate actual single-phase and two-phase flow. The bottom hole pressure was minimized by utilizing the artificial lift methods. The flowing fluids in pumps and pipes causes shear stress on surface interacting. In multiphase flow application pump damages on head degradation as well as shear stress affects. The K-ω turbulence model and the multiphase Mixture approach with the sliding technique used to solve the Navier-Stokes equation. To study the effects of gas-liquid (air-water) flow on the ESP and the pump handle ability, the rotation speeds were varied while the other parameters were kept constant. The rotation speeds simulated were at 500, 900, 1500, 2000 and 2500 rpm meanwhile the water flow rate and gas flow rate were kept constant with 20 L/min and 1% fraction, respectively. The results obtained show that as the rotation speeds were increased, the less concentration of the bubbles were observed, moreover the wall shear stress (WSS) increases. Although, the wall shear stress in both single-phase and two-phase flow were tend to increase as the blades length increased, however for the single-phase flow the WSS was found higher in all the simulated rotational speeds.

A new flux prediction model for laminar and turbulent flow regimes in constant pressure cross-flow microfiltration

Cross-flow filtration mode can greatly alleviate the membrane fouling due to the presence of shear stress. In this paper, a new flux prediction model for steady cross-flow microfiltration has been established by considering the effect of shear stress as function of the geometry of filtration module and the suspension properties in the particle mass balance. The results showed that this model possessed higher accuracy in both laminar and turbulent flow regime (relative error σ = 4.43%/1.91%) than Glen Bolton’s model (σ = 11.88%/6.42%) and Makardij’s model (σ = 9.44%/12.92%). Meanwhile, the validity of the proposed model was approved by using other suspensions (yeast suspension and activated sludge suspension) (σ < 3.43%) and other membranes (PVDF and PES microfiltration membrane) (σ < 4.63%). Moreover, new criterion relationships between Sherwood number (Sh), Reynolds number (Re) and Schmidt number (Sc) in both laminar and turbulent flow regime were also established.

Effect of initial water content and shear stress on immersion-induced creep deformation and strength characteristics of gravelly mudstone

Soft sedimentary rocks undergo deterioration due to weathering induced by dry–wet cycles in a process known as slaking. To investigate the effect of the initial water content and shear stress on the immersion-induced creep deformation and strength characteristics of gravelly mudstone (slaking index = 1 and 2), creep tests were conducted using a modified direct-shear-test apparatus under different creep-stress ratios. Crushed mudstone with different degrees of compaction and initial water content was subjected to immersion under the creep-shear-stress conditions. After the creep shear and vertical displacements stabilized, a monotonic shear loading was applied. During creep immersion, the increment in the creep-shear displacement increases as the creep-stress ratio increases and the initial water content and/or degree of compaction decrease. Retaining a high initial water content in crushed mudstone is recommended to maintain its shear-stress stability. Under the same density, the peak shear strength decreased with an increase in the increment of the creep-shear displacement during creep immersion. The results indicate that the occurrence of immersion-induced creep deformation in addition to slaking can result in the deterioration of slope stability.

A novel yielding anisotropy and corresponding lattice evolution mechanism in CP-Ti achieved via pulsed electric current

We report a novel yielding anisotropy in commercially pure titanium (CP-Ti) and provide fundamental insights into its texture evolution and the corresponding lattice evolution mechanism. Herein, yielding anisotropy was attained by an α ↔ β cyclic phase transformation (CPT) treatment via pulsed electric current (PEC). After the three-cycle CPT treatment, the CP-Ti perpendicular to the PEC direction exhibited the maximum value of (0002) plane in the X-ray diffraction intensity and of {0001} pole figure for electron backscatter diffraction analysis. The three-cycle-treated CP-Ti presented a significant yielding anisotropy which was the far greater yield strength (297.5 MPa) than that of the other treated specimens. This is attributed to the preferential activation of basal <a> slip with a higher effective critical resolved shear stress in the three-cycle-treated CP-Ti, compared with the preferential activation of prismatic <a> slip for the other treated specimens. Fundamentally, the lattice evolution mechanism and orientation relationship ({0001}α//{001}β and <112¯0>α//<1¯00>β) responsible for this yielding anisotropy were proposed. Under the PEC, the (0001) plane in HCP structure transformed in parallel to the (001) plane in BCC structure, and followed by the transformation of the (110) plane in the BCC to the (0001) plane in the HCP under cooling when the PEC was switched off.

Effects of shear stress on differentiation of stem cells into endothelial cells.

Stem cell transplantation is an appealing potential therapy for vascular diseases and an indispensable key step in vascular tissue engineering. Substantial effort has been made to differentiate stem cells toward vascular cell phenotypes, including endothelial cells (ECs) and smooth muscle cells. The microenvironment of vascular cells not only contains biochemical factors that influence differentiation but also exerts hemodynamic forces, such as shear stress and cyclic strain. More recently, studies have shown that shear stress can influence the differentiation of stem cells toward ECs. A deep understanding of the responses and underlying mechanisms involved in this process is essential for clinical translation. This review highlights current data supporting the role of shear stress in stem cell differentiation into ECs. Potential mechanisms and signaling cascades for transducing shear stress into a biological signal are proposed. Further study of stem cell responses to shear stress will be necessary to apply stem cells for pharmacological applications and cardiovascular implants in the realm of regenerative medicine.

The effects of solid shear stress and wall roughness on the simulation of cylindrical hydrocyclone classification

Reasonable numerical conditions are critical for the precision and accuracy of the numerical consequences of hydrocyclones. In this paper, the effects of resistance coefficient, wall roughness, and friction packing limit on particle velocity and distribution as well as the separation behaviors were studied in a cylindrical hydrocyclone using the two-fluid model. The results show that the friction packing limit and wall roughness can significantly influence the numerical results, whereas the effect of the resistance coefficient is negligible. As the friction packing limit increases from 0.4 to 0.55, the cut size gradually decreases with improving separation sharpness, and it reaches the minimum when the friction parking limit is 0.5. The wall roughness monotonously increases the cut size and reduces the separation sharpness. Simulation results were also compared with experimental data, and a reasonable prediction can be obtained with resistance coefficient, friction packing limit, and wall roughness height of 0.95, 0.5, and 50 μm, respectively.

Performance tests and microstructure‐based sigmoid model for a three‐coil magnetorheological damper

Magnetorheological (MR) damper is one of the most promising smart devices for dissipating seismic energy and reducing structural vibrations. The MR dampers with multiple coils are widely adopted to enhance the output damping forces and seismic performance. In order to study the dynamic characteristics of multicoil MR dampers from a micro to macro viewpoint, a three-coil MR damper was designed and manufactured in this paper. The performance tests of the three-coil MR damper under different excitation currents, displacement amplitudes, frequencies, and coil combinations were conducted. Assuming that the distance between two adjacent ferromagnetic particles meets chi-square distribution, the two-column micromodel for the MR fluid was modified by introducing a distribution parameter. The modified MR fluid micromodel was verified by comparing the damping forces calculated by this model with experimental data. Combining the modified micromodel for the MR fluid and the double-sigmoid model for MR dampers, a mathematical model for the three-coil MR damper was proposed. The microstructure-based sigmoid model considers the effects of yield shear stress of the MR fluid and internal magnetic induction intensity on the damping force. The comparison of the proposed model and the performance test data shows that the microstructure-based sigmoid model can finely describe the dynamic characteristics and magnetic saturation properties of the three-coil MR damper under different excitation currents and loading conditions, which provides a good basis for control strategies and dynamic analysis of structures with multicoil MR dampers.