Reduction In Shear Stress Research Articles

Two-dimension layered nanomaterial as lubricant additives: Covalent organic frameworks beyond oxide graphene and reduced oxide graphene

Abstract Two-dimension graphene-like covalent-organic frameworks (GCF) nano-sheets were successfully fabricated to evaluate the tribological behavior as lubricant additive in comparison to GO and rGO in PAO 10 oil. The exploration shows that conjugate system of GCF brings p-d feedback coordination to metal ions created by exoelectron, promoting the formation and stability of adsorbed film. The mechanical strength of covalent bond structure in-plane ensures carrying capacity and durability, and the ultrathin layered feature reduces shear stress due to slide effect. Eventually, the excellent reducing friction (up to 53.5%) and anti-wear (up to 95.4%) were achieved at an ultralow dosage of 0.008 wt%. By contrast, dissociation of C–O linkages of rGO and GO induced by tribo-stress and tribo-heat deteriorates its stability and durability.

Eight weeks of fish oil supplementation does not prevent sitting-induced leg endothelial dysfunction.

Prolonged sitting impairs leg endothelial function and this impairment is thought to be mediated by a sustained reduction in blood flow-induced shear stress. However, whether nutritional strategies can be used to prevent sitting-induced leg endothelial dysfunction remains unknown. Herein, we tested the hypothesis that 8 weeks of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) supplementation would prevent endothelial dysfunction associated with sitting. Nineteen healthy men were randomly assigned to a placebo group or EPA+DHA group in a double-blind fashion. The EPA+DHA group was administered EPA-rich fish oil, containing 600 mg EPA and 260 mg DHA per day for 8 weeks. The placebo group received matching capsules for the same duration of time. Popliteal artery flow-mediated dilation (FMD) was measured at baseline and before and after a 3-h sitting period. During sitting, blood pressure, popliteal artery diameter, and blood velocity were measured every hour. Throughout the sitting period, popliteal artery blood flow and shear rate were markedly and similarly reduced in both groups (P < 0.05). However, counter to the hypothesis, 3 h of sitting impaired popliteal artery FMD to the same extent in both groups (P < 0.05). In conclusion, daily EPA and DHA supplementation is not effective at preventing the detrimental effects of prolonged sitting on leg endothelial function. Novelty We provide evidence that sitting-induced leg endothelial dysfunction in young healthy subjects cannot be remediated by a nutritional strategy known to produce cardiovascular benefits. This could be partially due to the low total dose of EPA and DHA administered.

Jeffery orbits in shear-thinning fluids

We investigate the dynamics of a prolate spheroid in a shear flow of a shear-thinning Carreau fluid. The motion of a prolate particle is developed analytically for asymptotically weak shear thinning and then integrated numerically. We find that shear-thinning rheology does not lift the degeneracy of Jeffery orbits observed in Newtonian fluids, but the instantaneous rate of rotation and trajectories of the orbits are modified. Qualitatively, shear thinning has a similar effect to elongating the particle in a Newtonian fluid. The period of rotation increases as the particle slows down more when aligned with the flow due to a reduction in shear stresses. Unlike Jeffery orbits in Newtonian fluids, in shear-thinning fluids, the period of orbits depends on the specific trajectory (or initial orientation of the particle).

P2690Safety and effectiveness of thin-strut DES for bifurcated coronary lesions not involving left main: a RAIN (veRy thin stents for patients with left mAIn or bifurcatioN in real life) sub-analysis

Abstract Background Thinner stent struts of new DES (drug eluting stent) are associated with shorter time of reendothelialization, a reduction of shear stress and inflammation of coronary walls. Despite this great innovations their clinical safety and efficacy in challenging scenarios as non left main bifurcation coronary lesions has not been tested. Methods RAIN is a multicenter registry enrolling patients treated on bifurcated coronary lesions and left main with thin-strut DES. Baseline characteristics and procedural data were recorded. Target lesion revascularization (TLR) was the primary endpoint, whereas major adverse clinical events (MACE; composite of all-cause death, myocardial infarction (MI), target vessel revascularization (TVR), TLR and stent thrombosis (ST)) along with its single components were the secondary endpoints. A multivariate analysis to identify predictors of TLR and sub-analysis according to stenting strategy (provisional vs 2-stent technique), use of final kissing balloon (FKB) and IVUS/OCT optimization were performed. Results Data from 1803 patients (59% ACS, 61% stable CAD) treated on bifurcations were retrospectively evaluated. Follow up was available for 1685 (94%) patients for a median of 12 months (IQR 7–18). TLR occurred globally in 2.5% of cases (2.2% in provisional stenting, 3.5% in 2-stent technique). The rate of MACE was 9.4%, whereas all-cause death and MI, occurred in 4.1% and 3.2% of cases respectively. TVR and definite ST incidence were 3.7% and 1.1%. At multivariate analysis, chronic kidney disease (CKD) negatively influenced the main endpoint (HR 1.95, 95% CI 1.06–3.6, p=0.03), whereas post-dilatation (HR 0.56, 95% CI 0.3–0.93, p=0.04) and provisional stenting resulted being protective factors. FKB reduced TLR occurrence at FU only in 2-stent technique (p=0.03), whereas intracoronary imaging (performed in 29% of patients) were uninfluential. Conclusion Very thin-strut DES represents a highly effective solution in bifurcation lesions. The risk of TLR is reduced by post-dilatation and provisional stenting. FKB is recommended in 2-stent technique, whereas further studies are required to address the impact of intracoronary imaging in this setting.

Numerical investigation of seismic performance of high modulus columns under earthquake loading

This paper presents the result of two-dimensional finite element modeling studies in order to investigate the seismic behavior of high modulus columns in liquefiable soil. Particular attention was paid to the shear stress reduction mechanism of the high modulus columns and the shear strain distribution between soil and columns during earthquake motion. Numerical analyses were performed using a nonlinear elasto-plastic model in Plaxis 2016. The reliability of the numerical simulations was verified through the results of a centrifuge test model designed to investigate the contribution of high modulus columns in liquefaction mitigation. The capability of numerical simulations was assessed primarily through comparison of predicted acceleration-time histories, pore water pressures, and displacements with the measured counterparts. The results of the numerical analysis showed that the presence of the columns did not reduce seismic shear stresses in the soil when compared to the unimproved soil condition and pure shear behavior between soil and column did not develop as expected in the current design methodology.

Experimental and Modeling of Shear Mechanical Behavior of Soil Conditioned With Foaming Agent

Chemical foam is being used more frequently with Earth Pressure Balance (EPB) shields to achieve underground works, which present a rising interest in the excavation technique. During tunneling with an Earth Pressure Balance shield in clayey soil, clogging of the clay occurs, leading to blocking the cutting head and clog then the shield chambers. Surfactants are commonly used as conditioning agents to reduce clay stickiness. This treatment leads to a change in the mechanical properties of conditioned soil. This paper aims tostudy the shear strength behavior of foam-conditioned soil basing on triaxial tests in the undrained consolidated conditions. Experimental results are modeled using the finite element code COMSOL Multiphysics with the aim of analyzing the effect of the percentage of foam on the shear strength behavior. The soil mixture made from 40% of kaolinite and 60% of sand was conditioned with a foaming agent based on anionic surfactant. Consolidated undrained triaxial tests have been performed in order to explain the effect of foam. Results show that foam reduces the shear stress thanks to their weak stiffness. Shear strength stress is affected by the percentage of the foam in the mixture before shearing by reduce the shear strength of the conditioned soil. Soil-foam mixture has been modeled as a medium containing spherical pore inclusions with a low stiffness compared to the stiffness of unconditioned soil. Stiffness of bubbles inclusions was identified using one of the known homogenization models for composite materials. Results show that the reduce shear stress strength is affected by the percentage of inclusions in the matrix. It confirms the friction angle of composite material decrease as function of the percentage of gas bubbles inclusion in the matrix.

Hydrodynamic and thermodynamic enhancement of a solar chimney power plant

The present paper investigates the effect of geometrical parameters by using energy and exergy analysis and hydrophobic surfaces as an innovative method were proposed to enhance the performance of Solar Chimney Power Plant (SCPP). Furthermore, the best radiation model for SCPP simulation was represented. Hereupon, firstly large- scale SCPP using reverse fan model was validated based on Manzanares constructed power plant. For reducing the computational cost, nine different small scale 3-D models defined respect to prior experimental study under Tehran-Iran meteorological condition. The first and second laws of thermodynamics were studied, and an optimization was done for representing the best functional diameter, height and turbine pressure jump by the means of improvability rate and clarified optimization factor. Results show that the optimal state of chimney can be defined in relation to a certain condition; hence, the geometrical parameters under investigation should simultaneously be evaluated in system designs. Furthermore, applying the slip condition on walls to simulate hydrophobic surfaces was attempted to reduce shear stress on walls which led to roughly 11% performance enhancement. Consequently, Discrete Ordinates (DO) radiation model could be trusted based on its more factual outcomes with referred to prior experimental results of Heat flux method.

A load-transfer function for the side resistance of drilled shafts in soft rock

The shear stress and shear displacement relationship for the rock socket sidewalls is required for the calculation of the drilled shaft butt settlement under the service loads. This paper first introduces a comprehensive database of in situ axial load tests on drilled shafts, anchors and plugs that are embedded in different soft rock formations. The database includes measurements of (i) the initial shear stiffness, (ii) the peak shear stress and (iii) the post-peak reduction in shear stresses for the socket sidewalls. In addition to the load test results, information on soft rock mass mechanical properties and rock socket geometry is also included. It is found that (i) the initial shear stiffness is directly related to the deformation modulus of the soft rock mass and inversely proportional to the rock socket diameter and length, (ii) the mobilized peak shear stress is related to the drained friction angle of the rock mass and normal stress on the socket sidewalls at failure. The rock mass friction angle is related to the rock type and the geological strength index, and the normal stress at failure is directly related to deformation modulus of rock mass and inversely to the product of rock socket length and diameter, and (iii) the post-peak brittleness is related to the soft rock type and the post-peak shear displacement. An empirical framework for the prediction of the load-transfer function for side resistance of sockets in soft sedimentary and fine-grained rock is developed using the load test database introduced herein. The proposed framework accounts for the socket geometrical characteristics, and the rock mass engineering properties. The pre-peak range in the load-transfer function is modeled using a hyperbolic function, and the post-peak range is modeled using a brittleness index to account for the reduction in shear stresses with post-peak displacement.

A Virtual Comparison of the eCLIPs Device and Conventional Flow-Diverters as Treatment for Cerebral Bifurcation Aneurysms

PurposeEffective, consistent, and complication-free treatment of cerebral bifurcation aneurysms remains elusive despite a pressing need, with the majority of lesions presenting in such locations. Current treatment options focus either on aneurysm coil retention, supported by a stent-like device positioned in the parent vessel lumen, or intrasaccular devices that disrupt flow within the aneurysm dome. A third alternative, i.e., the use of conventional (intraluminal) flow-diverters to treat such bifurcation aneurysms raises the problem that at least one daughter vessel needs to be jailed in such a deployment. The eCLIPs is a stent-like device that offers the possibility of flow-diversion at the aneurysm neck, without the drawbacks of daughter vessel occlusion or those of intrasaccular deployment.MethodsIn this study the eCLIPs device was virtually deployed in five cerebral bifurcation aneurysms and compared with a conventional tubular flow-diverter device. Computational fluid dynamics (CFD) simulations of the aneurysm haemodynamic environment pre- and post-implantation were conducted, and focussed on metrics associated with successful aneurysm occlusion. Absolute and relative reductions in aneurysm inflow rate (Q) and time-averaged wall shear stress (TAWSS) were recorded.ResultsThe eCLIPs device was found to perform in a similar qualitative fashion to tubular flow-diverters, with overall reduction of metrics being somewhat more modest however, when compared to such devices. Aneurysm inflow reduction and TAWSS reduction were typically 10–20% lower for the eCLIPs, when compared to a generic flow diverter (FDBRAIDED) similar to devices currently in clinical use. The eCLIPs was less effective at diffusing inflow jets and at reducing the overall velocity of the flow, when compared to these devices. This result is likely due to the larger device pore size in the eCLIPs. Notably, it was found that the eCLIPs provided approximately equal resistance to flow entering and exiting the aneurysm, which was not true for the FDBRAIDED device, where high-speed concentrations of outflow were seen at the aneurysm neck along with local TAWSS elevation. The clinical implications of such behaviour are not examined in detail here but could be significant.ConclusionsOur findings indicate that the eCLIPs device acts as a flow-diverter for bifurcation aneurysms, with somewhat diminished occlusion properties comparing to tubular flow diverters but without the jailing and diminished flow evident in a daughter vessel associated with use of conventional devices.

The metalloproteinase ADAM15 is upregulated by shear stress and promotes survival of endothelial cells

Reduced shear stress resulting from disturbed blood flow can impair endothelial integrity and drive the development of vascular inflammatory lesions. Metalloproteinases of the ADAM family have been implicated in the regulation of cell survival and inflammatory responses. Here we investigate the mechanism and function of ADAM15 upregulation in primary flow cultured endothelial cells.Transcriptomic analysis indicated that within the ADAM family ADAM15 mRNA is most prominently upregulated (4-fold) when endothelial cells are exposed to physiologic shear stress. This induction was confirmed in venous, arterial and microvascular endothelial cells and is associated with increased presence of ADAM15 protein in the cell lysates (5.6-fold) and on the surface (3.1-fold). The ADAM15 promoter contains several consensus sites for the transcription factor KLF2 which is also upregulated by shear stress. Induction of endothelial KLF2 by simvastatin treatment is associated with ADAM15 upregulation (1.8-fold) which is suppressed by counteracting simvastatin with geranylgeranyl pyrophosphate. KLF2 overexpression promotes ADAM15 expression (2.1-fold) under static conditions whereas KLF2 siRNA knockdown prevents ADAM15 induction by shear stress. Functionally, ADAM15 promotes survival of endothelial cells challenged by growth factor depletion or TNF stimulation as shown by ADAM15 shRNA knockdown (1.6-fold). Exposure to shear stress increases endothelial survival while additional knockdown of ADAM15 reduces survival (6.7-fold) under flow conditions.Thus, physiologic shear stress resulting from laminar flow promotes KLF2 induced ADAM15 expression which contributes to endothelial survival. The absence of ADAM15 at low shear stress or static conditions may therefore lead to increased endothelial damage and promote vascular inflammation.

The Effect of the Slot Length on Beam Vertical Shear in I-Beams with Moment Connections

This paper evaluates the effect of slot existence with limited length between flanges and web junction of I-shaped beams at the region of moment connections on vertical force and shear stress distribution in beam flanges and web at connection section in comparison with classical theory of stress distribution. The main purpose of this research is to evaluate the efficiency of the slot in connections such as slotted web beam to column connection in modern age. The issue of the slot has many benefits but very little studies have been done on it. Accordingly, one hundred and twenty models with two moment connections under the concentrated static load in mid span have been made for doing parametric study in ANSYS Workbench finite element software. The linear static analysis was done on all constructed models. Variable parameters in these models for parametric study include slot length between flange and web junction in connection region (from 0 to 190 mm), beam length, beam section height and Poisson’s ratio of beam material. In all models the amount of shear stress in section height over the section vertical axis in connection region and also the devoted contribution from force which goes to flanges and web under the concentrated load on mid span have been calculated. Performed studies have shown that vertical shear stress distribution in beam to column connection section with moment connection differs a lot from what is stated in mechanics of materials equations. Practically the available equations in regulations which state that web receives the entire vertical shear and ignore the contribution of flanges are not reliable. In addition, studies have shown that the slot existence in junction of web and flanges in connection section with limited length can has great effect on the quality of vertical shear stress distribution over the section of connection and also the slot existence has great effect on the reduction of shear stress in flanges and increase in shear stress in web according to classical theory. As a total result, nowadays slotted web beam to column connection can be used as a fantastic and simple idea to improve modern connections behavior.

Comparison Of Endothelial-dependent Vasodilatory And Vasoconstrictor Responses Between Upper- And Lower-Limb Arteries In Older Adults

Low-flow mediated constriction (L-FMC) provides important information about the acute effects of reduced shear stress on endothelial function. L-FMC has been mainly tested in upper-limb arteries, where an inverse association with VO2peak has been observed in younger adults. It is unclear if an L-FMC response exists in lower limb arteries, which are exposed to larger fluctuations in shear stress during traditional modes of aerobic exercise than the upper-limb. Furthermore, it is uncertain whether the same inverse relationship between L-FMC and VO2peak exists in older adults (OA). PURPOSE: Based on known differences in flow-mediated dilation (FMD) between upper- and lower limbs, we tested the hypothesis that heterogeneous L-FMC responses exist between the brachial- (BA) vs. popliteal (POP) arteries. We also expected that OA with greater aerobic fitness would have larger L-FMC responses in both arteries. METHODS: FMD and L-FMC were assessed in 47 OA (67±5 yr; 30F) using high-resolution duplex ultrasonography with commercial edge-detection and wall-tracking software. L-FMC was defined as the % decrease in lumen diameter in response to 5-min of distal ischemia. FMD was calculated as the % increase in lumen diameter following a reactive hyperemia. RESULTS: Larger FMD responses were observed in the BA vs. POP (4.7±1.6% vs. 3.3±2.0%; P<0.001), which were moderately correlated to each other (r=0.54; P<0.001). When allometrically scaled, the BA exhibited a greater L-FMC response than the POP (-1.3±1.6% vs. -0.4±1.6%; P=0.03). L-FMC responses in the BA vs. POP were not correlated with each other (r=0.22; P=0.14). As expected, VO2peak was associated with both BA-FMD (r=0.59; P<0.001) and POP-FMD (r=0.48; P=0.001). VO2peak was moderately correlated to BA L-FMC (r=-0.52; P<0.001) but strongly correlated to POP L-FMC (r=-0.73; P<0.001). CONCLUSION: The heterogeneous L-FMC responses between the BA and POP indicates that upper limb L-FMC responses do not represent a systemic measure of vasoconstrictor capacity. The stronger association between VO2peak and POP L-FMC suggests that larger local shear stress responses, induced by traditional lower-limb modes of aerobic exercise, may result in greater adaptations to low flow-mediated endothelial vasoconstrictor responsiveness.

Examining the acute effects of retrograde versus low mean shear rate on flow-mediated dilation.

Arterial endothelial function is acutely and chronically regulated by blood flow-associated shear stress. An acute intervention employing modest forearm cuff occlusion to simultaneously increase retrograde and decrease mean brachial artery shear rate for 30 min evokes transient impairments in flow-mediated dilation (FMD). However, the independent influence of the low mean versus the retrograde shear stress components is unclear. Healthy young adults [n = 24 (12 women, 12 men); 22 ± 2 yr, body mass index = 25 ± 2 kg/m2 (mean ± SD)] completed three laboratory visits within 1 wk. Visits consisted of 45 min of supine rest followed by a brachial artery FMD test (duplex ultrasound) before and after a 30-min intervention: control (shear rate unchanged), cuff (mean shear rate decreased, retrograde shear rate increased), or arterial compression (mean shear rate decreased, no increase in retrograde shear rate). The mean shear rate on the compression visit was targeted to match that achieved on the cuff visit. Cuff and compression trials decreased mean shear rate to a similar extent (cuff: 43 ± 22 s-1, compression: 43 ± 21 s-1; P = 0.850) compared with control (65 ± 21 s-1; both P < 0.001), with the retrograde component elevated only in the former (cuff: -83 ± 30 s-1, compression: -7 ± 5 s-1; P < 0.001). FMD decreased by 29 ± 30% (P < 0.001) after the cuff intervention and 32 ± 24% (P < 0.001) after the compression trial but was unchanged on the control visit (-0.3 ± 18%; P = 0.754). This was not altered by accounting for the shear rate stimulus. An increased retrograde shear stress does not appear to be obligatory for the transient reduction in FMD achieved after a 30-min exposure to low mean shear stress. These findings provide novel mechanistic insight on the regulation of endothelial function in vivo. NEW & NOTEWORTHY Low mean and retrograde shear stress are considered atherogenic; however, their relative contribution to the acute regulation of endothelial function in humans is unclear. Matched reductions in mean shear stress (30 min), with and without increases in retrograde shear stress, elicited equivalent reductions in flow-mediated dilation in men and women. These findings afford novel insight regarding the shear stress components governing the acute (dys)regulation of conduit artery endothelial function in vivo.

Hemodynamic differences between Pipeline and coil-adjunctive intracranial stents

IntroductionModern coil-adjunctive intracranial stent designs have increased metal surface coverage to construct putative ‘flow diverter lights.’ This is rooted in the assumption that flow diversion is linearly correlated with metal...

One-dimensional coupled modeling of bed evolution and bank erosion processes in the Middle Yangtze River

After the operation of the Three Gorges Project, the Middle Yangtze River has continuously suffered from channel degradation, along with significant bank erosion processes in local subreaches, especially in the Jingjiang Reach, which may cause serious problems to channel stability, flood control management and navigation safety. In this study, a one-dimensional coupled morphodynamic model for bed evolution and bank erosion processes was proposed, including three modules for hydro- and sediment dynamics, groundwater flow and bank erosion, with the mode of plannar failure in the Upper Jingjiang Reach (UJR) and the mode of cantilever failure in the Lower Jingjiang reach (LJR) being considered. The proposed model was applied respectively to simulate the fluvial processes in the Jingjiang Reach in 2005, 2007 and 2010, in order to conduct a detailed process of model calibration and validation. These calculated results show that: (1) The proposed model accurately reproduced the flow and sediment transport processes, with the root mean squared errors of daily averaged discharge and suspended sediment concentration far less than the corresponding mean values. Besides, the model also predicted the major occurrence regions of serious bank erosion processes; (2) bank failure was mainly controlled by fluvial erosion in the Jingjiang Reach, with more than 50% of cantilever failure events in the LJR occurring during the flood period; and (3) the groundwater level variation was delayed, as compared with the river stage change, which could also obviously influence bank erosion processes in the UJR. Furthermore, multiple test runs were conducted to investigate the influences of the variations in outlet river stage and bank soil properties on the processes of bank erosion. These results from test runs indicate that: (1) If the outlet river stage was increased due to a higher lateral inflow from the Dongting Lake, the bank retreat width in the Jingjiang Reach would be decreased, resulting from the reduced longitudinal water surface slope and mean velocity in section; (2) the calculated bank retreat width at a section was most sensitive to an reduction in critical shear stress of bank soil, especially in the LJR. However, the calculated bank retreat width in the UJR was also sentitive to the change in bank soil cohesion, but it did not monototically decrease with an increase in soil cohesion. This is because the varitation in soil cohesion can lead to changes in the number, timing and individual failed block volumes of bank failure events. As the failure number keeps unchanged, an increase in soil cohesion would lead to a delayed occurrence of bank failure event and thus a larger failed block volume, which finally results in a larger total retreat width.

Wear performance of electrohydrodynamically atomized WS2 coatings deposited on biomimetic shark-skin textured surfaces

Abstract This paper aims to provide a method in improving tribological properties of Al2O3/TiC ceramics. Biomimetic shark skin was produced on Al2O3/TiC ceramic surfaces by laser surface texturing. Then WS2 coating was deposited on the biomimetic skin by electrohydrodynamic atomization and its dry friction behaviours and wear mechanisms were investigated. Results revealed that the synergy effect of biomimetic shark skin and WS2 coatings has an effective influence on the tribological properties of Al2O3/TiC ceramics. The friction coefficient reduced to ∼0.3 and ∼0.07 after texturing biomimetic shark skin and depositing WS2 coatings, which reduced by 29% and 84%, respectively, compared with those of only polished Al2O3/TiC ceramics. The contribution of biomimetic shark skin was primarily decreasing the friction surface, reducing shear stress and trapping wear debris. Moreover, the grooves acted as lubricant reservoir could keep a thicker trio-film and realize continuous lubrication for a longer friction time.

Energy efficiency in low consistency refining: a study using a Valley beater

Abstract The purpose of this work was to study the influence of pulp fiber suspensions refining operating variables on energy efficiency coefficient. Three chemical pulps with different average morphological characteristics were used, obtained from bleached kraft Pinus sylvestris, Eucalyptus globulus and Betula verrucosa. The final objective was to establish the chemical pulps refining efficiency parameters. Refining hydromechanics and energy consumption profiles were analyzed. Average normal and tangential forces on pulp suspension in the gap clearance, resulting rotor-stator distance and no-load and refining conditions power consumption were obtained. The refining trials took place in a laboratory Valley beater, and the manipulated variables were charge on the roll and rotor rotation speed. Global relationships for tangential stress and energy efficiencies in terms of rotation speed and rotor-stator gap were obtained. A relationship between energy efficiency and shear stress was obtained. The results have shown that in a Valley beater increased rotor-stator gaps reduce energy efficiency, concomitantly increasing apparent viscosity and reducing shear stress. No-load power was seen to increase with crowding factor, and thus with flocculation. Inversely, crowding factor and ultimately flocculation had an adverse effect on energy efficiency.

THE INVESTIGATION OF CONSTRUCTION TECHNIQUES AND MATERIAL USAGE OF HISTORICAL STONE BRIDGES IN ANATOLIA AND BALKANS

Aim: Historical bridges are important because of their construction techniques and historical heritage. Historical bridges must remain intact for many years. Therefore, material properties and construction techniques have to be known for their correct restorations. In this study, the bridges built between the Roman period and the end of the Ottoman period in Anatolia and the Balkans were investigated comparatively. The data obtained from this study is intended to provide a source for conservation applications. Method: In this study, related articles, books and archives were used. The stone bridges from the Roman period till the end of the Ottoman period are investigated in terms of their historical developments, alterations, material usages, construction techniques and structural properties. Findings: It has been determined that every period has specific characteristics. The timber pile system used in the construction of the Roman bridge and the use of iron clamps are also seen in the Seljuk and Ottoman bridges. In addition, it was observed that as you get closer to the present day both stone size decreased and workmanship's cares goes down. Conclusion: The construction techniques and materials were investigated from the Roman period till the end of the Ottoman period. Researches have shown that bridges have survived to the present day due to the application of rational solutions in the construction of bridges. The use of timber in bridge constructions and the reduction of shear stresses caused by weight loads also contributed positively to the effects of earthquakes. The use of iron elements ensures that the arches and foundations remain intact.

Two-Phase Nanofluid Thermal Analysis over a Stretching Infinite Solar Plate Using Keller Box Method (KBM)

In the present study, two-phase nanofluid flow in a three-dimensional system is modeled over a stretching infinite solar plate and the heat transfer analysis is performed for this problem. The governing equations are presented based on previous studies and the suitable solution method is recommended due to infinite boundary condition in the problem. Keller Box Method (KBM) using the Maple 15.0 mathematical software is applied as the solution method for the governing equation of the problem. The effect of some parameters existed in the equations (Pr (Prandtl number), Sc (Schmidt number), Nb (Brownian motion parameter), Nt (Thermophoresis parameter), λ=b/a (ratio of the stretching rate along y to x directions) and n (power-law index)), are discussed on the velocities, temperature, and nanoparticles concentration functions. As an important outcome, increasing both n and λ parameters, makes a reduction in shear stress, while it increase the Nusselt number function of heat transfer.

Calculation of the Unsteady Thermal Stresses in Elastoplastic Solids

The one-dimensional boundary problem of the theory of thermal stresses that simulates the shrink fit assembly of cylindrical parts is used to discuss a computational approach to predicting the evolution of the thermal stresses under piecewise-linear plasticity conditions. The solution of the problem is based on the classical maximum shear stress criterion (Tresca–Saint Venant yield criterion), and the maximum reduced shear stress criterion (Ishlinsky–Ivlev yield criterion) is only used to compare the calculation results. The application of piecewise-linear potentials in the theory of plastic flow is shown to allow equilibrium equations to be integrated in both the region of reversible deformation and various parts of a plastic flow region. The dependences thus obtained are important for a time-step calculation algorithm. This algorithm can trace the site and time of both nucleation and completion of plastic flows at each time step. The calculations demonstrate that, following temperature, the stresses in the assembly element materials can pass from correspondence to a certain face of a loading surface to correspondence to its edge and, then, to another face. This circumstance implies the division of the irreversible deformation region into parts, where a plastic flow obeys different sets of equations, which take into account the assignment of the state of stress to various faces and edges of the loading surface. The computational algorithm also makes it possible to trace the beginning of division of a flow region into parts and the motion of the part boundaries through irreversibly deformed materials, including the times of their coincidence (i.e., the disappearance of the parts of the calculation region). A repeated plastic flow is shown to appear. This flow nucleates when an assembly is cooled, i.e., when the assembly element materials return to reversible deformation conditions due to the evolution of the state of stress. Taking into account the change in plastic flow conditions that is caused by the use of piecewise-linear plastic potentials is found to substantially affect the level and the distribution of residual stresses and the final tightness of the assembly.