Total Shear Stress Research Articles

Variable-Order Fractional Models for Wall-Bounded Turbulent Flows.

Modeling of wall-bounded turbulent flows is still an open problem in classical physics, with relatively slow progress in the last few decades beyond the log law, which only describes the intermediate region in wall-bounded turbulence, i.e., 30–50 y+ to 0.1–0.2 R+ in a pipe of radius R. Here, we propose a fundamentally new approach based on fractional calculus to model the entire mean velocity profile from the wall to the centerline of the pipe. Specifically, we represent the Reynolds stresses with a non-local fractional derivative of variable-order that decays with the distance from the wall. Surprisingly, we find that this variable fractional order has a universal form for all Reynolds numbers and for three different flow types, i.e., channel flow, Couette flow, and pipe flow. We first use existing databases from direct numerical simulations (DNSs) to lean the variable-order function and subsequently we test it against other DNS data and experimental measurements, including the Princeton superpipe experiments. Taken together, our findings reveal the continuous change in rate of turbulent diffusion from the wall as well as the strong nonlocality of turbulent interactions that intensify away from the wall. Moreover, we propose alternative formulations, including a divergence variable fractional (two-sided) model for turbulent flows. The total shear stress is represented by a two-sided symmetric variable fractional derivative. The numerical results show that this formulation can lead to smooth fractional-order profiles in the whole domain. This new model improves the one-sided model, which is considered in the half domain (wall to centerline) only. We use a finite difference method for solving the inverse problem, but we also introduce the fractional physics-informed neural network (fPINN) for solving the inverse and forward problems much more efficiently. In addition to the aforementioned fully-developed flows, we model turbulent boundary layers and discuss how the streamwise variation affects the universal curve.

Comparison finite element analysis on duralium strength against multistage artificial aging process

Purpose: To analyze and estimate the strength of duralium rivets which had been treated by using multistage artificial aging compared with duralium that had not been treated. This processwas necessary to be conducted in riveting process effectively. Duralium has been widely used in aerospace industry, one of duralium usage in aerospace industry is aircraft fittings such as rivet. Riveting is one of method that used for joining airframe structural components. During riveting process, the load transfer causing stress that led to the fatigue. Riveting process also causes deformation on the rivet and sheet metal. Deformation that occurs on the rivet will affect the performance of rivet structure. Thus, duralium rivet was analyzed its total deformation, shear stress, and its equivalent stress Von Misses. Design/methodology/approach: that used in this study was finite element analysis. Geometry of rivet that used in this study was drawn by using Autodesk Inventor Professional 2018. While total deformation, shear stress and equivalent stress Von Mises on duralium rivets were found out by using ANSYS Workbench 18.1. Findings: Comparison result was obtained between duralium rivet with and without treatment of multistage artificial aging. The result shown that total deformation, shear stress and equivalent stress Von Mises which obtained by duralium rivet with multistage artificial aging had the lower value than duralium rivet without multistage artificial aging. Duralium rivet with multistage artificial aging could be used as aircraft fitting which had the higher strength. Research limitations/implications: Direct experiment on duralium rivet had not been done yet, this study only did simulation based on data that obtained form previous research that had been conducted by the researcher. Practical implications: Duralium rivet with multistage artificial aging had lower value on total deformation, shear stress, and equivalent stress Von Misses, thus duralium rivet with multistage aritificial aging had a higher strength.

Free surface flow over square bars at different Reynolds numbers

Large-eddy simulations of free surface flow over bed-mounted square bars are performed for laminar, transitional and turbulent flows at constant Froude number. Two different bar spacings are selected corresponding to transitional and k-type (reattaching flow) roughness, respectively. The turbulent flow simulations are validated with experimental data and convincing agreement between simulation and measurement is obtained in terms of water surface elevations and streamwise velocity profiles. The water surface deforms in response to the underlying bed roughness ranging from mild undulation for transitional roughness to distinct standing waves for k-type roughness. The instantaneous water surface deformations increase with an increase in Reynolds number. Contours of the mean streamwise and wall-normal velocities, the total shear stress and the streamfunction reveal the presence and extension of recirculation zones in the trough between two consecutive bars. The flow is governed by strong local velocity gradients as a result of the rough bed and the deformed water surface. The local Froude number at the free surface increases for low Reynolds number in the flow over transitional roughness and decreases for low Reynolds number in the flow over k-type roughness. The transitional and turbulent flows exhibit a very similar distribution of the pressure coefficient Cp in both cases, whilst Cp is generally lower for the laminar flow. Regarding the friction coefficient, Cf, it is significantly lower in the turbulent case than in the transitional and laminar cases. The bar spacing does not affect significantly the relative contribution of friction and pressure forces to the total force, neither does the Reynolds number. The friction factor is greater for transitional roughness and decreases with increasing Reynolds number.

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.

A modified Raupach's model applicable for shear‐stress partitioning on surfaces covered with dense and flat‐shaped gravel roughness elements

AbstractA commonly used measure to prevent soil wind erosion is to cover the surface with gravel. Gravel can inhibit soil erosion by covering the surface directly, changing the airflow field near the surface and sharing the shear stress of wind. Similar to other roughness elements, the protective effect of gravel on soil is usually expressed in terms of the ratio of the shear stress on the exposed soil surface to the total shear stress on the rough surface due to wind, i.e. through a shear‐stress partitioning model. However, the existing shear‐stress partitioning models, represented by Raupach's model (RM93), are only applicable when the lateral coverage of the roughness elements, λ < 0.10, and the applicability of the models to flat‐shaped roughness elements is unclear. The purpose of this study is to verify the applicability of RM93 for dense and flat‐shaped gravel roughness elements by using shear‐stress data from wind‐tunnel measurements pertaining to roughness elements with different densities (0.013 ≤ λ ≤ 0.318) and flat shapes (height‐to‐width ratios in the range 0.20 ≤ H/W ≤ 0.63), and to modify RM93 to enhance its predictive ability. The results indicate that RM93 cannot accurately predict the shear‐stress partitioning for surfaces covered by densely distributed and flat‐shaped gravel roughness elements. This phenomenon occurs because, when roughness elements are distributed densely or are flat‐shaped, the proportion of the shear stress on the top surface of the roughness elements (τc) to the total shear stress (τ) is large; in this case, τc plays a dominant role and serves as an essential component in the shear‐stress partitioning model. Consequently, RM93 is modified by incorporating τc into the calculation of τ. Under conditions of λ < 0.32 and H/W > 0.2, the modified RM93 can yield satisfactory predictions regarding the shear‐stress partitioning.

Experimental Study of Smooth Asymmetric Compound Channels Flow: An Investigation of the Interaction of Flow Using Scaling Argument for Prediction of Overall Discharge

A simple model for the apparent shear stress on the vertical interface between the floodplain and main channel in asymmetric smooth compound channels is proposed using experimental data obtained in this study. The turbulent structure, including Reynolds shear stress in asymmetric compound channel flows, is investigated for three different flow depths. The lateral distribution of the apparent shear stress obtained shows that the total apparent shear stress has a negative peak near the junction edge in the main channel. Furthermore, the intensity of the advection terms and the Reynold shear stress near the interface are investigated as the function of the bankfull height and floodplain width. The momentum transport due to Reynolds stress and secondary current between main channel and floodplain is finally modeled as depth ratio using scaling argument. The validation of the current model on three datasets shows an accurate prediction of overall discharge for the asymmetric smooth compound channels.

The Effect of Biofilms on Turbulent Flow Over Permeable Beds

AbstractDespite an increasingly large body of work advancing our understanding of flow interactions occurring at the interface of a turbulent flow overlying a permeable bed, little is known concerning how such flow may be affected by the presence of biofilms, which exist in nearly all aquatic environments. This study quantifies the effects on flow exerted by biofilms grown over experimental laboratory permeable beds until biofilm detachment, and then compares this to the residual effects after its detachment. The investigation is conducted in a flow channel by immersing two‐dimensional permeable beds with idealized geometry and different porosities in order to explore different bed permeabilities. Sequences of increasingly higher flow velocity conditions, followed by lower flow, were considered to explore the effect of detachment. Measurements were performed using particle image velocimetry. The total wall shear stress and friction velocity were found to increase in the presence of pregrown biofilm, and decrease after biofilm detachment, when compared at the same pump frequency. The dimensionless Reynolds stresses, at constant pump frequency, collapsed for different bed configurations in the outer layer, while for the inner layer, the presence of biofilm led to a decrease in dimensionless Reynolds stress. Quadrant analysis shows that this decrease was primarily due to a reduction in strong Q2 contributions. These results suggest that models for flow and transport over permeable media in aquatic environments cannot neglect the role of biofilms in modifying turbulence.

Shear models and parametric analysis of the PVC geomembrane-cushion interface in a high rock-fill dam.

As a type of flexible impermeable material, a PVC geomembrane must be cooperatively used with cushion materials. The contact interface between a PVC geomembrane and cushion easily loses stability. In this present paper, we analyzed the shear models and parameters of the interface to study the stability. Two different cushion materials were used: the common extrusion sidewall and non-fines concrete. To simulate real working conditions, flexible silicone cushions were added under the loading plates to simulate hydraulic pressure loading, and the loading effect of flexible silicone cushions was demonstrated by measuring the actual contact areas under different normal pressures between the geomembrane and cushion using the thin-film pressure sensor. According to elastomer shear stress, there are two main types of shear stress between the PVC geomembrane and the cushion: viscous shear stress and hysteresis shear stress. The viscous shear stress between the geomembrane and the cement grout was measured using a dry, smooth concrete sample, then the precise formula parameters of the viscous shear stress and viscous friction coefficient were obtained. The hysteresis shear stress between the geomembrane and the cushion was calculated by subtracting the viscous shear stress from the total shear stress. The formula parameters of the hysteresis shear stress and hysteresis friction coefficient were calculated. The three-dimensional box-counting dimensions of the cushion surface were calculated, and the formula parameters of the hysteresis friction were positively correlated with the three-dimensional box dimensions.

Transversal mass transfer and shear stress formation during rapid gravity flow of a granular medium

The micro structural models for shear stress generation during rapid gravity flow of granular materials on a rough chute are discussed. The mechanism of the shear stress formation, taking into account the tangential impulse formed under transversal mass transfer of particles, is suggested. The analogy between granular media during rapid shear deformation and dense gases is used to develop the suggested mechanism on the basis of kinetic theory. The total shear stress is determined as the sum of the stress components induced by collisions, transversal mass transfer and contact interactions of uniform cohesionless inelastic spherical particles. The mathematical models describing the components of shear kinetic stresses are developed as the functions of particle properties, structural and kinematical gravity flow characteristics. The equations of impulse and energy conservation in the course of rapid gravity flow of uniform cohesionless particles are formulated. A variant of the formulation of boundary conditions at the flow bottom is proposed for mathematical modeling of the dynamics of rapid gravity flows of granular materials on a rough chute. The variant assumes the displacement of the area with the most intense shear rate inside the flow and into its layers adjacent to the rough chute surface.

Turbulent flow characteristics over forward-facing obstacle

The local flow field and wake region over a forward-facing obstacle were experimentally investigated, when the water surface above the obstacle was dipped compared to flow further upstream and further downstream. The obstacle was modelled resembling the shape of an airfoil with a flat top having stoss-side slope and downstream lee-side slope designed for minimal flow separation. The submerged obstacle showed an evolutionary change in the flow field with a dipped water surface shape over the crest; and consequently three distinct flow regions were observed: upstream region, crest region and the downstream. The velocity data were recorded using a three-dimensional micro-acoustic Doppler velocimeter along the flume centreline for three flow Reynolds numbers and different localised Froude numbers. The paper highlights the flow and turbulence prime parameters: second-order statistics, turbulence kinetic energy, eddy viscosity, turbulence production, probability-density functions and the contributions of stress fraction into four quadrants to the total shear stress along the flow. The spectral analysis was performed to examine the energy distributions, vortex-shedding frequencies with corresponding Strouhal numbers. Variations of turbulence integral length scale along the flow passing over the obstacle were investigated to examine the eddy turnover scales. The turbulent features were fairly inspiring since it led to a pronounced acceleration on the crest location like a jet with a potential core region, and elongated deflection in the downside slope. The results provide a basic turbulence in natural environment for various phases of ebb and tide over a submerged smooth obstacle or mountain hills in river/ocean.

CFD numerical simulation of standalone sand screen erosion due to gas-sand flow

Solid particles entrained in produced gas cause erosive damage in production and transportation facilities, that may eventually impact any process safety. The main purpose of this research is to determine the point on the Standalone screen (SAS) surface, where erosion rate is critical and to evaluate the uncertainties in the calculations and predictions of sand screen erosion utilizing CFD numerical simulation. A k-epsilon model was implemented to solve gas flow behavior and Discrete Phase Model (DPM) was used to track solid particles. The results of DPM were then introduced to conduct erosion simulation on the SAS utilizing four erosion equations. A full presentation of particle velocity vectors, particle velocity streamlines, total pressure contours and wall shear stress contours on the screen surface are presented and discussed. Additionally, the particle traces and path-lines are also demonstrated based on particles residence time as part of the particles’ trajectories. The erosion rates and erosion patterns from the four erosion equations, have shown similarities in their response to the change of sand characteristics. Considering the change in solid particles properties, a good agreement between CFD predictions and published data is achieved. This research can be used as a basis to offer safe operating guidelines for wells that are completed using standalone sand screens (SAS).

The Influence of Ship Waves on Sediment Resuspension in the Large Shallow Lake Taihu, China.

Sediment resuspension induces endogenous nutrient release in shallow lakes, which has been demonstrated to be associated with eutrophication. In addition to natural wind-driven resuspension, navigable shallow lakes (such as Lake Taihu, China) also experience resuspension from human activities, such as ship waves. Both processes determine the intensity, frequency, and duration of sediment resuspension, and may consequently affect the pattern of cyanobacteria blooms in the lake. In this study, acoustic Doppler Velocimeter (ADV), Optical Backscatter Sensor (OBS), and temperature wave tide gauge (instrument model :RBR duo TD|wave) were placed in an observation platform in the lake to obtain high-frequency flow velocities, suspended sediment concentration (SSC), and wave parameters before, during, and after a cargo ship passed by. We found that the ship wave disturbance intensity is greatly influenced by the draft depth. The movement generated by ship disturbance is primarily horizontal rather than vertical. Compared with the wind-induced wave, the disturbance caused by the ship waves has a high intensity, short duration, and narrow range of influence. The maximum total shear stress under ship disturbance can reach 9~90 times the critical shear stress under a natural state. Therefore, the effect of ship waves on sediment resuspension near the channel of Lake Taihu is much greater than that of wind-induced waves. These findings represent an important step towards understanding the quantitative relationship between ship wave disturbance and sediment resuspension, and lay the foundation for future research in order to understand and control the eutrophication of shallow lakes.

RETRACTED: A novel rough-wall model for large eddy simulation of high-Reynolds-number flow

This study develops a novel rough-wall model for large eddy simulation (LES) based on recent work on wall-modelled LES. This approach is capable of solving for the basic flow character over a rough wall at high Reynolds numbers without resolving the details of the roughness elements. The wall-modelled LES approach on a smooth wall is proven to be sufficiently precise to predict the velocity profile and wall shear stress. The average roughness shear stress can be combined with the smooth-wall shear stress in the inner-layer wall model by defining a roughness shear stress ratio α. The instantaneous shear stresses caused by the roughness elements are calculated by the pressure projection and elevation fields. The total shear stress is fed back to the outer-layer LES mesh as a new boundary condition. The results of the wall-modelled LES correspond well with the experimental data. The comparison between the simulation and experiment reveals that the wall-modelled LES approach presented in this research is capable of predicting the flow in a rough-wall boundary layer without resolving the detailed roughness element geometries.

Interstitial fluid–solid interaction within aneurysmal and non-pathological human ascending aortic tissue under translational sinusoidal shear deformation

The interaction shear force between internal interstitial fluid motion and the solid circumferential-longitudinal medial lamellae helps generate the shear stress involved in dissection of human ascending aorta aneurysmal or non-pathologic tissue. Frequency analysis parameters from the total shear stress versus time response to translational 1 Hz sinusoidal shear deformation over 50 cycles measure the interaction with respect to the three factors: tissue type, sinusoidal deformation amplitude and direction of the shear deformation. Significant 1, 3, and 5 Hz components exist in this order of descending magnitude for shear deformation amplitudes of either 25% or 50% of the specimen length. Evaporation tests indicate that the amount of free water in both aneurysmal and non-pathological tissue is nearly the same. The interstitial fluid–solid interaction under shear deformation is visible in the shoulders of the total shear stress versus time response curve that are caused by the 3 Hz component. During a single deformation cycle, the ratio of the amplitudes of the 3 Hz and the 1 Hz components measures the normalized amount of interaction. Under translational sinusoidal shear deformation at 25% amplitude, this interaction ratio is statistically smaller in non-pathologic than in aneurysmal human ascending aortic tissue in the circumferential direction. The frequency analysis parameters provide evidence that the structural changes in aneurysmal tissue induce an increase in the interstitial fluid–medial solid interaction shear force which contributes to the propensity for aneurysmal rupture. Statement of significanceCircumferential shear force between the interstitial fluid and medial lamellae within the human ascending aortic wall is demonstrably greater in aneurysmal than non-pathologic tissue. This force likely increases with medial elastin degeneration and may facilitate the dissection propensity in aneurysmal tissue. The 3 Hz component in frequency analyses of the total shear stress versus time curve produced by 1 Hz sinusoidal translational shear deformation measures the fluid-solid interaction shear force that is otherwise difficult to isolate. This non-standard examination of the interstitial fluid interaction helps clarify clinical mechanical implications of structural differences between aneurysmal and non-pathologic human ascending aortic tissue. The aneurysmal dissection susceptibility does not appear to depend on the amount of interstitial fluid or the wall thickness compared to non-pathologic tissue.

A numerical study for heat and fluid flow of couple stress fluid over a spiraling disk by Legendre wavelet spectral collocation method

AbstractThis article aims to explore the spiraling motion of a couple stress fluid over a disk rotating and radially stretching simultaneously. The spiraling motion is developed through the uniform rotation of the disk in addition to radial stretching. The logarithmic spirals in the disk velocity are produced due to the combined effects of stretching and rotation. The similarity transformations are invoked to obtain the coupled ordinary differential equations representing the flow. A Legendre wavelet spectral collocation method (LWSM) is employed for obtaining numerical solutions to analyze the effects of the pertinent parameters on the flow. The quantities of physical interest, i.e., radial and azimuthal skin friction coefficients, the wall shear stress, and the heat transfer rate are computed for the various values of the spiral angle, spiraling parameter, and couple stress parameter. It is found that enhancing the spiral angle declines the radial skin friction while enhancing azimuthal skin friction and the total wall shear stress. The temperature of the fluid is decreased for increasing the spiraling parameter and spiral angle, but increases for large couple stress parameter.

Evaluation of stent-graft implantations for intramural hematoma based on fluid-solid interaction analysis

Endovascular stent-graft (SG) repair for patients with intramural hematoma (IMH) requires suitable SG deployment to avoid complications. In this paper, several SG implantation schemes are quantitatively evaluated by CFD tool, in which the mutual interactions between blood, SG and arterial wall are taken into account. Factors considered: (i) the depth d of SG implantation into the vascular wall; (ii) the deployment length L (exceeding O% of the lesion); (iii) the material of SG; (iv) the shape of SG. The total deformation, Von-Mises stress and wall shear stress (WSS) on arterial wall and stent are analyzed, and particularly the related fitting curves are displayed. The results show that the Von-Mises stress exerted on IMH wall increases with the increment in d or decrement in L, with remarkable variations at about d ∈ [0.2,0.4] or L ∈ [33.3%,60%]. The stress for IMH wall is linear inverse correlation with SG stiffness, and the stress discrepancy among different SGs is up to 37.6%. The Von-Mises stressmax for arterial wall and stent appears at the junction of healthy and IMH walls and the region where the SG curvature changes the most, respectively. Further, although the fluctuation of WSS is smaller than that of Von-Mises stress, the WSS remains linearly increasing with the decrement of L, d and material stiffness. Results obtained can potentially serve as the guideline to SG surgery for IMH patients.

The role of alongshore flows on inner surf and swash zone hydrodynamics on a dissipative beach

Cross-shore and alongshore velocities were measured over five high tide cycles in the swash and inner surf zones of a dissipative beach (significant wave height between 0.5 and 1.65 m; water levels between 0 and 0.87 m) using acoustic and electromagnetic current meters. Measurements are used to determine the importance of alongshore motions relative to cross-shore motions for bed shear stress; a parameter required for many sediment transport formulations. Velocities and water depths are infragravity dominated with running average (5 min) cross-shore and alongshore velocities being of similar magnitude near 0.25 m/s. Significant coherence squared between cross-shore velocity and water depth is found in an infragravity frequency range (0.0078 Hz–0.024 Hz). A narrower infragravity frequency range (0.012 Hz–0.022 Hz) of significant coherence squared is found between alongshore velocity and water depth. Near bed velocity profiles at high spatial resolution indicate the mean profile of cross-shore or alongshore velocity for different relative cross-shore positions are nearly depth uniform, suggesting, on average, a well-mixed water column. Time-averaged onshore-directed depth-averaged velocities are nearly constant as a function of mean water depth, whereas time-averaged offshore-directed depth-averaged velocity magnitudes decrease with an increase in mean depth. In contrast, mean alongshore depth-averaged velocity magnitudes increase with depth regardless of the corresponding cross-shore motion and were always southerly-directed. These variations result from changes in breaking wave forcing location (i.e. relative cross-shore position). Near instantaneous velocity profile data are used to estimate friction coefficients and the bed shear stress through the Law of the Wall assumption. Mean friction coefficients for alongshore flows are similar to those obtained for cross-shore flows and values of ~0.02 are appropriate for all phases of flow. Alongshore bed shear stresses are the dominant bed shear stress component for over 27% of the samples implying an enhancement of total bed shear stress through incorporation of alongshore motions. Neglecting these alongshore processes (even if alongshore uniform) in cross-shore sediment transport models will lead to errors in predicted sediment transport rates.

A smaller heart-aorta-angle associates with ascending aortic dilatation and increases wall shear stress

ObjectivesThe aim of this study was to evaluate whether the orientation of the heart, measured as an angle between the long axis of the heart and ascending aorta midline (heart-aorta-angle, HAA), associates with ascending aortic (AA) dilatation. Furthermore, the association between HAA and wall shear stress (WSS) was studied.MethodsHAA was retrospectively measured in 1000 consecutive coronary artery computed tomographic angiography (CCTA) images in patients with low-to-moderate pretest probability for coronary artery disease (CAD). To evaluate the effects of HAA on AA flow, 4D flow MRI was performed for 28 patients with AA dilatation (> 40 mm) and WSS was analyzed.ResultsThe mean age of patients undergoing CCTA was 52.9 ± 9.8 years; 66.5% were women. Their median HAA was 128.7° and interquartile range 123.3–134.1°. HAA was significantly smaller in patients with dilated AA (median 126.7° [121.3–130.8°]) compared with the patients with normal AA (median 129.5° [124.3–135.3°], p < 0.001). HAA was smaller in males (p < 0.001) and in patients with diabetes (p = 0.016), hypertension (p = 0.001), CAD (p = 0.003), hypercholesterolemia (p < 0.001), and bicuspid aortic valve (p = 0.025) than without these factors. In a subpopulation without any of these underlying diseases (n = 233), HAA was still significantly smaller in the patients with dilated AA (median 127.9° [124.3–134.3°]) compared with patients with normal AA (median 131.9° [127.6–136.9°], p = 0.013). In 4D flow MRI, a smaller HAA correlated with increased total WSS in the outer curvature of the proximal AA (r = − 0.510, p = 0.006).ConclusionA smaller HAA associates with AA dilatation and affects the blood flow in the proximal AA.Key Points• A smaller angle between the long axis of the heart and ascending aorta midline associated with ascending aortic dilatation.• A smaller heart-aorta-angle correlated with increased total wall shear stress in the outer curvature of the proximal ascending aorta.

Beton Dolgu Kompozit Levha Perde Duvaların Sonlu Elemanlar Metodu Kullanılarak İncelenmesi

Concrete filled compos ite plate shear wall is an innovative structural lateral force resisting system that is being investigated experimentally and numerically. It consists of pre-fabricated steel web plates that are spaced parallel to each other by having regularly spaced cross-connecting tie bars (rods) which is then filled with concrete . This paper make use of previously developed numerical models and extends the study to investigate different aspects of wall behavior. In this study, two of the previously tested wall models were used to investiagete percentage of steel plate yielding at certain wall elevations per certain drift levels, steel plate von-Mises stress contours, the distribution of cracks in concrete, relative contribution of steel plates and concrete to total wall base shear and axial stress distribution of steel plate and concrete. The study assumes fixed-based walls and describes the development of finite element models using LS-Dyna.

Is one dental mini-implant biomechanically appropriate for the retention of a mandibular overdenture? A comparison with Morse taper and external hexagon platforms

Statement of problemLimited information is available to clinicians on the use of dental mini-implants (MI) as opposed to standard-diameter implants (SDIs) for the stabilization of implant-retained mandibular overdentures (MOs). PurposeThe purpose of this in vitro and finite element analysis study was to analyze and compare the biomechanical behavior of MOs with either 1 or 2 implants with external hexagon (EH), Morse taper (MT) SDIs, and MIs. Material and methodsThirty photoelastic models (n=30) of each group (n=5) of SDIs (EH-1, EH-2, MT-1, MT-2) and MI (MI-1, MI-2) were fabricated for posterior, peri-implant, and total maximum shear stress evaluation by quantitative photoelastic analysis. One specimen of each group was further used to create the 6 computational models to be analyzed by finite element analysis. The maximum von Mises values and stress maps were plotted for each ductile component. Two types of load were applied to the overdenture: a150-N load bilaterally and simultaneously on the first molar and a 100-N load on the incisal edge of the central incisors at a 30-degree angle. The data were subjected to the 2-way ANOVA test and the Tukey honestly significant difference test (α=.05). ResultsThe EH-2 and MT-2 showed the lowest posterior (P<.001) and total (P<.05) mean shear stress values. For peri-implant shear stress, no difference was found among all groups (P>.05). Regardless of the loading area, the MI-1 and MI-2 groups showed the lowest von Mises stress values. However, for implant housing, the MI-1 group, under incisor loading, presented greater stress, followed by MT-1, EH-1, EH-2, MI-2, and MT-2. The attachment was the most overloaded structure, with high values under incisor loading, especially for the groups with 2 implants (MT-2, EH-2) as compared with the other models. ConclusionsBiomechanically, regardless of the implant number, MI is a promising rehabilitation method with similar peri-implant shear stress and lower von Mises stress on the implant when compared with SDIs for MOs.