Average Shear Stress Research Articles

Quantitative Assessment of Changes in Hemodynamics After Obliteration of Large Intracranial Carotid Aneurysms Using Computational Fluid Dynamics.

Background: It was speculated that the alteration of the geometry of the artery might lead to hemodynamic changes of distal arteries. This study was to investigate the hemodynamic changes of distal arterial trees, and to identify the factors accounting for hyperperfusion after the obliteration of large intracranial aneurysms.Methods: We retrospectively reviewed data of 12 patients with intracranial carotid aneurysms. Parametric models with intracranial carotid aneurysm were created. Patient-specific geometries were generated by three-dimensional rotational angiography. To mimic the arterial geometries after complete obliteration of the aneurysms, the aneurysms were virtually removed. The Navier–Stokes equations were solved using ANSYS CFX 14. The average wall shear stress, pressure and flow velocity were measured.Results: Pressure ratio values were significantly higher in A1 segments, M1 segments, and M2 + M3 segments after obliteration of the aneurysms (p = 0.048 in A1 segments, p = 0.017 in M1 segments, p = 0.001 in M2 + M3 segments). Velocity ratio values were significantly higher in M1 segments and M2 + M3 segments after obliteration of the aneurysms (p = 0.047 in M1 segments, p = 0.046 in M2 + M3 segments). The percentage of pressure ratio increase after obliteration of aneurysms was significantly correlated with aneurysmal angle (r = 0.739, p = 0.006 for M2 + M3).Conclusions: The pressure and flow velocity of distal arterial trees became higher after obliteration of aneurysms. The angle between the aneurysm and the parent artery was the factor accounting for pressure increase after treatment.

Influence of aortic valve tilt angle on flow patterns in the ascending aorta

Transcatheter aortic valve implantation (TAVI) has become the alternative procedure to high-risk patients who are diagnosed with aortic valve stenosis. Differently from the traditional open-chest surgical procedure, a small variation on the prosthetic aortic valve deployment angle is expected with the TAVI procedure. The hemodynamic patterns of the blood flow in the ascending aorta are related to the development of many cardiovascular diseases. There are, however, few data available in the literature correlating the aortic valve tilt angle to hemodynamic effects. In this work, a 3D printed aorta model made of a transparent silicon resin was produced, based on the anatomy of a specific patient submitted to a TAVI procedure. The stereoscopic Particle Image Velocimetry technique was employed to measure three-component velocity fields at closely spaced cross-sectional planes, along the ascending aorta. The measurements were performed for a constant flow rate corresponding to the peak of the systolic phase of the cardiac cycle. Averaged velocity fields and turbulent quantities were determined for both, the base case, with no valve tilt, and for cases with an inclination of 4° and 8°, oriented at the four anatomical directions of the human body reference system, namely anterior, posterior, right and left. The results revealed the dominant flow patterns in the ascending aorta formed by a jet-like inlet flow impinging on the curved aorta right wall, inducing a significant eccentricity on the axial velocity profile. Regions of reverse flow were identified and linked to the abrupt area change associated with the typical reduced inlet diameter of TAVI implants. The impinging flow and wall curvature effects established circulation patterns defining a helical flow structure. The influence of the inlet flow orientation on the flow turbulent characteristics was assessed by the spatial evolution of the turbulent kinetic energy (TKE), Reynolds and viscous stresses. The maximum values of TKE were found around the inlet jet boundaries and concentrated in the neighborhood of the right aorta wall where the eccentric axial flow prevailed. Spatial distributions of the maximum Reynolds stresses were similar to the TKE distributions and presented maximum stresses typically one order of magnitude higher than the maximum average viscous shear stresses. Maximum average viscous stress distributions were revealed at the jet-like flow boundaries and in the vicinity of the right wall, displaying moderate stress levels that, according to the literature, can be sufficient to produce cell damage and platelet activation. The complex nature of the flow field was revealed by streamlines obtained from the measured flow fields, allowing the identification of the influence of the inlet flow orientation and tilt angle on the position of the stagnation point on the aorta right wall, as well as the angle of incidence of the jet-like flow on the wall. A simple model based on momentum balance was used to estimate the pressure increment on the wall due to flow impingement. The model captured the influence of the inlet flow orientation, indicating that pressure increases of the order of 40% in relation to the base case condition were obtained for the 8°, left inlet flow orientation.

In Vivo Function of Flow-Responsive Cis-DNA Elements of eNOS Gene: A Role for Chromatin-Based Mechanisms.

eNOS (endothelial nitric oxide synthase) is an endothelial cell (EC)-specific gene predominantly expressed in medium- to large-sized arteries where ECs experience atheroprotective laminar flow with high shear stress. Disturbed flow with lower average shear stress decreases eNOS transcription, which leads to the development of atherosclerosis, especially at bifurcations and curvatures of arteries. This prototypic arterial EC gene contains 2 distinct flow-responsive cis-DNA elements in the promoter, the shear stress response element (SSRE) and the KLF (Krüppel-like factor) element. Previous in vitro studies suggested their positive regulatory functions on flow-induced transcription of EC genes including eNOS. However, the in vivo function of these cis-DNA elements remains unknown. Insertional transgenic mice with a mutation at each flow-responsive cis-DNA element were generated using a murine eNOS promoter-β-galactosidase reporter by linker-scanning mutagenesis and compared with episomal-based mutations in vitro. DNA methylation at the eNOS proximal promoter in mouse ECs was assessed by bisulfite sequencing or pyrosequencing. Wild type mice with a functional eNOS promoter-reporter transgene exhibited reduced endothelial reporter expression in the atheroprone regions of disturbed flow (n=5). It is surprising that the SSRE mutation abrogated reporter expression in ECs and was associated with aberrant hypermethylation at the eNOS proximal promoter (n=7). Reporter gene silencing was independent of transgene copy number and integration position, indicating that the SSRE is a critical cis-element necessary for eNOS transcription in vivo. The KLF mutation demonstrated an integration site-specific decrease in eNOS transcription, again with marked promoter methylation (n=8), suggesting that the SSRE alone is not sufficient for eNOS transcription in vivo. In wild type mice, the native eNOS promoter was significantly hypermethylated in ECs from the atheroprone regions where eNOS expression was markedly repressed by chronic disturbed flow, demonstrating that eNOS expression is regulated by flow-dependent DNA methylation that is region-specific in the arterial endothelium in vivo. We report, for the first time, that the SSRE and KLF elements are critical flow sensors necessary for a transcriptionally permissive, hypomethylated eNOS promoter in ECs under chronic shear stress in vivo. Moreover, eNOS expression is regulated by flow-dependent epigenetic mechanisms, which offers novel mechanistic insight on eNOS gene regulation in atherogenesis.

Device for Testing at Combined Cyclic Fatigue Loading by Tensile and Torsion, Attachable to the Universal Testing Machine

To designing various types of components that work in operation under the simultaneous effect of normal stresses, σ, and shear stresses, τ, is important to determine and know the behavior of materials under fatigue compound stress states. A device constructed to introduce into a specimen a state composed of normal and shear stresses is presented herein. The device is intended for performance under fatigue tests under combined tensile and torsional loading and can be mounted on a monoaxial fatigue machine. Variation of the combinations of normal and shear stresses is given by the possibility to change the cams to different inclination angles. We present a method of calculating the normal and shear stresses based on the parameters provided by a universal testing machine. Fatigue data for 6061 aluminum alloy are presented for several combinations of tensile and torsional loading. The fatigue limits, σ0–τ0, obtained by biaxial testing of the cylindrical specimens, were used to construct the σ–τ diagram. The calculation relations resulting from the use of the device for normal and shear stresses are deduced and presented. The calibration of the device is presented by means of a sample on which two electrotensometric transducers are mounted. The main feature of the device is its simplicity, based on the original idea of using a rigid cam that forces the central shaft to transform a translational movement received from the testing machine into rotational and translational movements using the inclined channel in the cam.

Prediction of the bending and out-of-plane loading effects on formability response of the steel sheets

Failure in sheet metal forming can occur by necking, fracture or wrinkling. By using a forming limit diagram (FLD) as a powerful tool to prevent sheets metal failures in the forming process, provides parameters controlling throughout forming. There are different developed methods for predicting FLDs, which estimate sheet metal forming strains limits. Assessment of FLD estimation reveals that there is a dependency between the effect of several factors containing normal stress, shear stress, sheet thickness, mechanical properties, metallurgical properties, yield function, strain path, and bending with formability. In this research, the effects of bending via two finite element models are investigated. In the first method, the out-of-plane deformation is applied by increasing punch displacement to study the effects of bending. In the second method, the effect of bending is investigated via changing punch diameter (25, 50, 70 and, 100 mm). The Marciniak–Kuczynski (M–K) theory is used to predict the time of localized necking in finite element simulations. Furthermore, a novel method for the determination of the inhomogeneity coefficient is presented in M–K model to simulate the groove width for M–K model. To verify finite element simulation results, Nakazima tests with 50 and 100 mm punch diameters were done as experimental studies. The comparison of experimental results and finite element analysis illustrates that the increasing bending or the out-of-plane loading can improve formability. At the end, the effect of bending on FLD is reported as an equation based on minor and major strains.

BiLSTM-Based Soil–Structure Interface Modeling

Deep learning (DL) algorithm bidirectional long short-term memory (BiLSTM) neural network is employed to model behaviors of the soil–structure interface in this study, as a pioneer research work to investigate the feasibility of using DL to model interface behaviors. Datasets are collected from 12 constant normal stress and 20 constant normal stiffness sand–structure interface tests. A modeling framework with the integration of BiLSTM is thereafter proposed. The results indicate that the BiLSTM-based model can accurately capture the responses of interface behaviors including volumetric dilatancy and strain hardening on the dense samples and volumetric contraction and strain softening on the loose samples, respectively. The effects of surface roughness, soil relative density, and normal stiffness on the interface behaviors are also investigated using the BiLSTM-based model. The predicted normal stress, shear stress, and normal displacement show good agreement with measured results.

Investigation on large elastoplastic deformation in expansion and springback for a composited bioresorbable stent

Mechanical performances for a composited bioresorbable stent were investigated by using the finite element method, which concerns the elastoplastic large deformation of expansion and springback during stent implantation. The introduced stent is composited by the outer layer of poly-L-lactic acid (PLLA) and the core of magnesium alloy (Mg alloy). As comparisons, meanwhile two single-material stents of PLLA and Mg alloy with the same geometric structures as the composited stent were considered. The numeric simulation results indicated that, the wrapping of PLLA can make the maximum Mises stress locate at the interior, it is beneficial to slow down the earlier surface degradation of stents caused by stress concentration. Also, the variation of residual deformation and stress distribution in Mg alloy core after PLLA outer layer degraded entirely are analyzed. The distributions of normal and total shear stresses on the interface of two materials were also calculated for the cases of expansion and springback. In addition, the analysis reveals the radius of implanted stent is in approximate linearly related to the expansion displacement load.

Computational hemodynamics and thermal analysis of laminar blood flow for different types of hypertension

Computational hemodynamics (CHD) is a promising engineering technique that has allowed doctors to learn a lot about patients’ conditions in various diseases such as cardiovascular disease (CVD) and even surgery. In industrialized countries, hypertension is becoming a widespread public health issue, resulting in death in extreme cases. A successful method for investigating hypertension in both diastolic and systolic conditions is to use the finite volume method (FVM) to incorporate velocity and pressure. Due to the use of Magnetic Resonance Image (MRI) and Digital Imaging and Communications in Medicine (DICOM), the 3D geometry has an acceptable accuracy, and the geometry has been created based thereon. The flow of blood is regarded as steady, lamina, incompressible, and non-Newtonian. Herein, all the age groups have their unique effect on the parameters reported, including Nusselt number and dimensionless numbers, e.g., average wall shear stress (AWSS), temperature, and pressure drop. In such a numerical simulation, all the results revealed that the parameters improved by increasing diastolic and systolic blood pressure. Nevertheless, the patient is recommended to see a doctor urgently in case of a hypertensive situation.

Effect of hydrodynamic cavitation water treatment on Pseudomonas aeruginosa quorum-sensing molecules

Hydrodynamic cavitation treatment was used for the functional inactivation of quorum-sensing lactone molecules of Pseudomonas aeruginosa. Hydroxyl radicals formed as well as the shear effects during the cavitation process induced the inactivation of the signal molecules through hydrolysis reaction coupled with bacterial destruction. Concentration of two different types of homoserine lactones(HSL) molecules was tested after the treatment at various rotational speeds. It was found that the strongest effects can be achieved at speeds > 2000 rpm. This value is considered as an onset speed of dominant cavitation, and it is in agreement with literature data. The experimental trends were in agreement with the calculations based on the finite element modelling, which show a significant increase in average shear stress at higher rotational speeds. Overall, the work has demonstrated the possible effects of hydrodynamic cavitation on the quorum-sensing molecules of Pseudomonas aeruginosa for the first time.

A Mechanistic Model for Wellbore Cleanout in Horizontal and Inclined Wells

Summary The accumulation of rock cuttings, proppant, and other solid debris in the wellbore caused by inadequate cleanout remarkably impedes field operations. The cuttings removal process becomes a more challenging task as the coiled-tubing techniques are used during drilling and fracturing operations. This article presents a new hole cleaning model, which calculates the critical transport velocity (CTV) in conventional and fibrous water-based fluids. The study is aimed to establish an accurate mechanistic model for optimizing wellbore cleanout in horizontal and inclined wells. The new CTV model is established to predict the initiation of bed particle movement during cleanout operations. The model is formulated considering the impact of fiber using a special drag coefficient (i.e., fiber drag coefficient), which represents the mechanical and hydrodynamic actions of suspended fiber particles and their network. The dominant forces acting on a single bed particle are considered to develop the model. Furthermore, to enhance the precision of the model, recently developed hydraulic correlations are used to compute the average bed shear stress, which is required to determine the CTV. In horizontal and highly deviated wells, the wellbore geometry is often eccentric, resulting in the formation of flow stagnant zones that are difficult to clean. The bed shear stress in these zones is sensitive to the bed thickness. The existing wellbore cleanout models do not account for the variation in bed shear stress. Thus, their accuracy is limited when stagnant zones are formed. The new model addresses this problem by incorporating hydraulic correlations to account for bed shear stress variation with bed height. The accuracy of the new model is validated with published measurements and compared with the precision of an existing model. The use of fiber drag and bed shear stress correlations has improved model accuracy and aided in capturing the contribution of fiber in improving wellbore cleanout. As a result, for fibrous and conventional water-based fluids, the predictions of the new model have demonstrated good agreement with experimental measurements and provided better predictions than the existing model. Model predictions show a noticeable reduction in fluid circulation rate caused by the addition of a small quantity of fiber (0.04% w/w) in the fluid. In addition, results show that the existing model overpredicts the cleaning performance of both conventional and fibrous water-based muds.

The Effects of Upstream Wall Roughness on the Spatio-Temporal Characteristics of Flow Separations Induced by a Forward-Facing Step

Abstract Separating and reattaching turbulent flows induced by a forward-facing step submerged in thick oncoming turbulent boundary layers (TBL) developed over smooth and rough upstream walls were investigated using time-resolved particle image velocimetry. The examined upstream walls resulted in smooth, transitionally rough, and fully rough wall conditions. The upstream boundary layer thicknesses were 4.3 and 6.7 times the step height in the smooth and rough wall cases, respectively. The Reynolds number based on the step height and freestream velocity was 7800. The effects of upstream wall roughness on the mean flow characteristics, Reynolds stresses defined in both Cartesian and curvilinear coordinate systems, as well as the unsteadiness of the turbulent separation bubbles were critically examined. The results show that upstream wall roughness increases the boundary layer thickness and turbulence intensity and consequently, promotes early mean flow reattachment over the step. Distinct regions of significantly elevated vertical Reynolds normal stress and Reynolds shear stress were observed upstream of the step in the fully rough wall case compared to the smooth wall case. Proper orthogonal decomposition (POD) and the reverse flow area over the step were employed to investigate the unsteadiness of the separation bubbles. The first POD mode coefficient and the reverse flow area over the step were strongly correlated and exhibited the same dominant frequency.

Laboratory Investigation on the Interface Bonding between Portland Cement Concrete Pavement and Asphalt Overlay

The interface bonding between Portland cement concrete (PCC) pavement and hot-mix asphalt (HMA) overlay plays an important role in the performance of the composite pavement. This research conducted a series of comprehensive laboratory studies to investigate the influence factors of the interface bonding strength using a self-designed direct shear test apparatus that can simultaneously apply normal stress and shear stress on a specimen. Four kinds of commonly used tack coat materials were systematically tested and compared under various combinations of normal stress and temperature. Then, coupling effects of the normal stress and temperature on the interface bonding between PCC and HMA were analyzed. The test results show that temperature has a significant impact on the adhesion of the tack coat. Emulsified asphalt was considered the optimal tack coat material because of its simple construction method. In addition, it was found that a damaged interface could still provide considerable bonding strength. Normal stress generated by traffic loads was beneficial to the interface bonding strength, especially at lower temperatures. The temperature had a significant effect on interface bonding and played a leading role in the failure mode of interface bonding.

Combining Invasive Cardiopulmonary Exercise Testing with Computational Fluid Dynamics to Better Understand LVAD Fluid Mechanics during Exercise

<h3>Purpose</h3> Invasive cardiopulmonary exercise testing (iCPET) is helpful in evaluating dyspnea but is infrequently utilized in patient supported by left ventricular assist devices (LVAD). Computational fluid dynamics (CFD) allows for a more thorough analysis of fluid mechanics including shear stress (SS) and shear rate (SR). The additive information from iCPET and CFD may allow for optimal understanding of the pump-patient interaction during exercise. <h3>Methods</h3> Hemodynamic and ventilatory gas measurements were recorded as part of an iCPET study on a patient with a HeartMate 3 (HM3). Exercise using a bicycle ergometer by increments of 20 watts every 2 minutes was performed. An anatomical model of the vasculature was reconstructed from computed tomography (CT) images, and the LVAD outflow cannula was used as the inflow boundary. The LVAD outflow was calculated separately using a lumped-parameter-model (LPM) of the circulation. Ventricular volumes were reconstructed from CT and the patient's hemodynamic tracings. The contribution of flow from the HM3 was implemented in the LPM via published H-Q curves. CFD simulations were then carried out over the stages of exercise. Blood velocities, SS and SR were quantified in the vascular beds. <h3>Results</h3> Compared to rest, blood volume exposed to SR >1000 s⁻¹ increased 2.8 fold (0.47 to 1.31 cm³), while average SS increased 1.45 fold (2.61 to 3.79 Pa) in the cannula, 1.48 fold (0.89 to 1.31 Pa) in the ascending aorta, and 1.61 fold (0.67 to 1.08 Pa) in the aortic arch and cerebral circulation. Compared to rest, peak velocities increased nearly 5 fold in the aortic arch. <h3>Conclusion</h3> CFD applied to iCPET provides valuable information about variations in flow to the vasculature with exercise as well as shear rate and shear stress augmentation. This patient-specific information may help with optimization of LVAD speeds to meet the physiological needs of exercise.

Experimental and numerical study of optimum functionally graded Aluminum/GFRP adhesive lap shear joints using Epoxy/CTBN

Abstract Failure in adhesive joints is usually the result of a non-uniform distribution of stress, which is observed with maximum values near the two ends of the overlap, and the central parts have a minor overall load-bearing contribution. In the joint of two dissimilar materials, the stress fields are asymmetric and the optimum grading of the adhesive properties will not be symmetric. The main objective of this work was to study the performance of optimum functionally graded joints (OFGJ) to maximize the ultimate loading capacity of a lap shear joint. The adherends were aluminum 7075-T6 and unidirectional glass-epoxy composite. The study has been performed considering a grading strategy based on mixtures of an epoxy resin with different values of liquid rubber to obtain the properties variations. First, the mono-adhesive joints with homogeneous bond-line and then symmetrical graded joints with equal bands were investigated. A compliance-based optimization method with the normalized shear stress distribution was used to obtain the best properties along the bond-line. The elastic-plastic model and mixed-mode cohesive damage model were used to obtain the stress distribution and failure prediction, respectively. By grading the overlap symmetrically, the stress distribution has become more uniform and the failure load compared to the base specimen (with a shear strength of 6 kN), increased by 206%. Optimization of adhesive properties using normalized shear stress distribution has positive effects on modifying stress distribution, non-shear forces elimination, improvement of the load-bearing contribution, failure mode alteration, and delay on adhesive joints failure. Therefore, there is a high increase in shear load strength of optimum graded specimen by a significant amount of 299%.

Computational Evaluation of Venous Graft Geometries in Coronary Artery Bypass Surgery

Cardiothoracic surgeons are faced with a choice of different revascularization techniques and diameters for saphenous vein grafts (SVG) in coronary artery bypass graft surgery . Using computational simulations, we virtually investigate the effect of SVG geometry on hemodynamics of both venous grafts and the target coronary arteries. We generated patient-specific 3-dimensional anatomic models of coronary artery bypass graft surgery patients and quantified mechanical stimuli. We performed virtual surgery on 3 patient-specific models by modifying the geometry vein grafts to reflect single, Y, and sequential surgical configurations with SVG diameters ranging from 2 mm to 5 mm. Our study demonstrates that the coronary artery runoffs are relatively insensitive to the choice of SVG revascularization geometry. We observe a 10% increase in runoff when the SVG diameter is changed from 2 mm to 5 mm. The wall shear stress of SVG increases dramatically when the diameter drops, following an inverse power scaling with diameter. For a fixed diameter, the average wall shear stress on the vein graft varies in ascending order as single, Y, and sequential graft in the patient cohort. The runoff to the target coronary arteries changes marginally due to the choice of graft configuration or diameter. The shear stress on the vein graft depends on both flow rate and diameter and follows an inverse power scaling consistent with a Poiseuille flow assumption. Given the similarity in runoff with different surgical configurations, choices of SVG geometries can be informed by propensity for graft failure using shear stress evaluations.

Shear strength properties of hybrid (hinoki cypress and Japanese cedar) cross-laminated timber

In this study, the out-of-plane shear strength of hybrid cross-laminated timber (CLT) with outer layers of hinoki (hinoki cypress, Chamaecyparis obtusa) and inner layers of sugi (Japanese cedar, Cryptomeria japonica) is investigated for four different layer configurations. To investigate the influence from rolling shear properties of cross layers on the shear strength of CLT, stress analysis was conducted using the shear analogy method. The nominal shear strength, the maximum shear force divided by the cross-section of CLT, was in the 1.0–2.1 MPa range. Using the shear analogy method, the rolling shear modulus in the cross layer was determined as 72.9 MPa, which was comparable with the value obtained for laminae in previous study as well as the value confirmed by strain measurements in the present study. The magnitude of rolling shear stress in the cross layer was 0.9–1.1 times the average shear stress, which was negatively correlated with the nominal shear strength. From the regression line between the nominal shear strength and the magnitude of the shear stress in the cross layer, the mean shear strength of the cross layer was estimated to be 1.33 MPa.

COMPUTATIONAL STUDY OF GEOMETRIC EFFECTS OF BOTTOM WALL MICROGROOVES ON CELL DOCKING INSIDE MICROFLUIDIC DEVICES

Cells docking inside microfluidic devices is effective in studying cell biology, cell-based biosensing, as well as drug screening. Furthermore, single cell and regularly cells docking inside the microstructure of microfluidic systems are advantageous in different analyses of single cells exposed to equal drug concentration and mechanical stimulus. In this study, we investigated bottom wall microgrooves with semicircular and rectangular geometries with different sizes which are suitable for single cell docking along the length of the microgroove in [Formula: see text]-direction and numerous cells docking regularly in one line inside the microgroove in a 3D microchannel. We used computational fluid dynamics to analyze the fluid recirculation area inside different microgrooves. The height of recirculation area in the bottom of microgroove could affect the cell’s attachment, and also materials delivery to attached cells, so the height of recirculation area may have optimum value. In addition, we analyzed the fluid drag force on cell movement toward the microgroove. This parameter was proportional to the fluid velocities in [Formula: see text] and [Formula: see text] directions in different microgrooves geometries. In different microgrooves’ geometries the fluid velocity in [Formula: see text]-direction did not change, but the fluid velocity in [Formula: see text]-direction decreased inside the microgroove. Therefore, the cell movement time inside the microgroove increased, and also the drag force in [Formula: see text]-direction could push the cells toward the bottom due to the lower drag force in [Formula: see text]-direction. The percentages of negative shear stress and average shear stress on the adhered cell surface were also calculated. The lower average shear stress, and negative shear stress around 50% on the cell surface were against cell detachment from the substrate. The results indicated that at the constant fluid inlet velocity and microchannel height, microgroove geometry and ratio of cell size to the microgroove size play pivotal roles in the cell initial adhesion to the substrate as well as the cell detachment.

Design and Analysis Methods for Composite Bonded Joints

Abstract A literature review on existing design and analysis methods for composite adhesively bonded joints has been conducted. Methods that might form a basis for development of practical engineering methodology for adhesively bonded joints were selected and described. Starting from the simplest and the fastest analytical methods (closed-form solutions): average shear stress, shear lag model and adhesive beam model through more complex and more time consuming numerical methods supported by finite element analysis: global models, local models, cohesive zone models. Assumptions and applicability of each method was discussed. Simple and fast methods in order to be reliable have to include many conservative assumptions and therefore may lead to over-designed structure (weight penalty). Structural optimization and weight reduction require the usage of more complex and time consuming methods. Therefore, selection of adequate methods should always be balanced against strength, durability, costs and weight.

Crustal Deformation and Fault Strength of the Sulawesi Subduction Zone

AbstractThis paper investigates the seismicity and rheology of the North‐Sulawesi subduction zone. Body‐wave modeling is used to estimate focal mechanisms and centroid depths of moderate magnitude (M5–M6.5) earthquakes on the North Sulawesi megathrust and surrounding region. The slip vectors of megathrust earthquakes radiate outward from Sulawesi, indicating motion that is incompatible with the relative motion of two rigid plates. Instead, the observed deformation implies lateral spreading of high topography, controlled by gravitational potential energy contrasts. This finding suggests that the observed deformation of Sulawesi results from stresses transmitted through the lithosphere, rather than basal tractions due to circulation in the mantle. Our modeling of the force balance on the megathrust shows that the subduction megathrust is weak, with an average shear stress of ∼13 MPa and an effective coefficient of friction of 0.03. Elsewhere in Sulawesi, slip vectors of other earthquakes suggest similar potential‐energy‐driven deformation is present, but at significantly slower rates. Our results show the importance of lateral rheology contrasts in determining deformation rate, and hence seismic hazard, in response to a given driving force.

Study on Drag and Noise Reduction of Bionic Blade of Centrifugal Pump and Mechanism

In order to study the relationship between the important parameters of internal flow and the effect of drag and noise reduction, the internal flow field and sound field characteristics of bionic centrifugal pump are studied in this paper. Based on the methods of theoretical analysis, numerical simulation and test, the relationship between wall average shear stress, drag reduction rate, increasing efficiency and noise reduction rate of internal sound field is studied. Internal flow parameters to judge and predict the effect of drag and noise reduction are revealed. The results show that the bionic pit can effectively increase the thickness of the boundary layer and reduce the Reynolds stress on the wall. The resistance on the wall is reduced and the hydraulic efficiency of the centrifugal pump is increased. The noise reduction rate is basically consistent with the changing trend of the drag reduction rate, increasing efficiency and wall average shear stress in the flow field. Wall average shear stress can reveal the effect of drag and noise reduction, so the effect of drag and noise reduction can be predicted and judged by the change of wall average shear stress.