The Buckling and Postbuckling of Fibrils Adhering to a Rigid Surface

2013 ◽  
Vol 80 (4) ◽  
Author(s):  
Sebastian Stark ◽  
Matthew R. Begley ◽  
Robert M. McMeeking
Keyword(s):  
Aspect Ratio ◽  
Numerical Results ◽  
Rigid Surface ◽  
Displacement Control ◽  
Load Displacement ◽  
Adhesive Performance

Recent experiments in which arrays of compliant fibrils are compressed axially against a rigid surface and then released have shown that there is load-displacement hysteresis during this process, accompanied by buckling and unbuckling of the fibrils. Furthermore, the adhesive performance of the system is decreased by such prior buckling. We present a model describing the buckling and postbuckling characteristics of a fibril with an aspect ratio of 10 or greater. The possibility during buckling of partial detachment of the end of the fibril is taken into account. The results are presented and discussed for both load and displacement control and the load-displacement hysteresis is identified. It is found that due to instabilities sudden spreading and shrinkage of the adhered area at the end of the fibril can accompany the hysteresis. Numerical results are provided to substantiate the findings and possible reasons for the observed influence of buckling on adhesive performance are reviewed.

scholarly journals Numerical and Experimental Analysis of Secondary Flow in Modern State-of-the-Art Low Pressure Guide Vane Rows

1995 ◽  
Author(s):  
Ernst Lindner
Keyword(s):  
Aspect Ratio ◽  
Secondary Flow ◽  
Total Pressure ◽  
Guide Vane ◽  
Numerical Results ◽  
Flow Behaviour ◽  
Inlet Guide Vane ◽  
Streamwise Vorticity ◽  
Pressure Losses ◽  
Turbine Guide Vane

To enhance the performance of the inlet guide vane and the annular duct of a jet engine, a detailed investigation of annular cascades with two different types of turbine guide vane rows is made. The first one is a leaned guide vane with an aspect ratio of two and a half and a transition duct ahead of the vane. To avoid the losses associated to the decelerating transition duct an alternative vane is designed and investigated with the same inlet and exit conditions. In this case the chord of the vane is increased to the effect that the vane begins immediately at the enterance of the diverging annulus and so a continuously accelerated flow is achieved. To maintain a good performance for this configuration a bowed-type vane with an aspect ratio of one is designed. The aim of the investigation is to obtain detailed informations on the secondary flow behaviour with particular regard to the development of the total pressure losses and the streamwise vorticity of the vortices inside and behind the blade rows. In the first step a three-dimensional, structured, explicit finite-volume flow-solver with a k–ε turbulence model is validated against the measurements, which were made in cross-sections behind the blades. Having proved that the numerical results are very close to the experimental ones, the secondary flow behaviour inside and behind the blade rows is analysed in the second step. By calculating the streamwise vorticity from the numerical results the formation of horse-shoe vortex, passage-vortex and the trailing edge vortex shed is investigated. The differences of the vortical motion and the formation of the total pressure losses between the two configurations of turbine guide vane rows are discussed.

Investigation on the load-displacement curves of a human healthy heel pad: In vivo compression data compared to numerical results

2012 ◽  
Vol 34 (9) ◽  
pp. 1253-1259 ◽  
Author(s):  
C.G. Fontanella ◽  
S. Matteoli ◽  
E.L. Carniel ◽  
J.E. Wilhjelm ◽  
A. Virga ◽  
...  
Keyword(s):  
Numerical Results ◽  
Heel Pad ◽  
Compression Data ◽  
Load Displacement

Correlations for Natural Convection Between Heated Vertical Plates

1991 ◽  
Vol 113 (1) ◽  
pp. 97-107 ◽  
Author(s):  
S. Ramanathan ◽  
R. Kumar
Keyword(s):  
Rayleigh Number ◽  
Aspect Ratio ◽  
Prandtl Number ◽  
Vertical Direction ◽  
Numerical Results ◽  
Maximum Temperature ◽  
Parallel Plates ◽  
Plate Temperature ◽  
Aspect Ratios ◽  
Prandtl Numbers

This paper presents the numerical results of natural convective flows between two vertical, parallel plates within a large enclosure. A parametric study has been conducted for various Prandtl numbers and channel aspect ratios. The results are in good agreement with the reported results in the literature for air for large aspect ratios. However, for small aspect ratios, the present numerical results do not agree with the correlations given in the literature. The discrepancy is due to the fact that the published results were obtained for channels where the diffusion of thermal energy in the vertical direction is negligible. The results obtained in this paper indicate that vertical conduction should be considered for channel aspect ratios less than 10 for Pr = 0.7. Correlations are presented to predict the maximum temperature and the average Nusselt number on the plate as explicit functions of the channel Rayleigh number and the channel aspect ratio for air. The plate temperature is a weak function of Prandtl number for Prandtl numbers greater than 0.7, if the channel Rayleigh number is chosen as the correlating parameter. For Prandtl numbers less than 0.1, the plate temperature is a function of the channel Rayleigh number and the Prandtl number. A correlation for maximum temperature on the plate is presented to include the Prandtl number effect for large aspect ratio channels.

Investigation of a Flexible Disk Rotating Near a Rigid Surface

1988 ◽  
Vol 110 (4) ◽  
pp. 664-669 ◽  
Author(s):  
M. Carpino ◽  
G. A. Domoto
Keyword(s):  
Reynolds Equation ◽  
Numerical Results ◽  
Inertial Effects ◽  
Rigid Surface ◽  
Close Proximity ◽  
Flexible Disk

A flexible disk rotating in close proximity to a flat rigid surface has been studied experimentally and theoretically. A bump is located on the surface to create a non-axisymmetric disturbance. The gas film between the disk and the rigid surface is represented by an incompressible Reynolds equation with inertial effects included. The general equations of a disk including both membrane and bending effects with displacement dependent tension distributions are presented. Numerical results are developed where the effects of displacement on the tension distributions and of bending in the disk are not included.

Viscous flow in a channel with periodic cross-bridging fibres: exact solutions and Brinkman approximation

1991 ◽  
Vol 226 ◽  
pp. 125-148 ◽  
Author(s):  
Ruey-Yug Tsay ◽  
Sheldon Weinbaum
Keyword(s):  
Aspect Ratio ◽  
Drag Coefficient ◽  
Viscous Flow ◽  
Velocity Component ◽  
Stokes Equations ◽  
Interpolation Formula ◽  
Numerical Results ◽  
Brinkman Equation ◽  
Capillary Endothelium ◽  
Channel Height

A general solution of the three-dimensional Stokes equations is developed for the viscous flow past a square array of circular cylindrical fibres confined between two parallel walls. This doubly periodic solution, which is an extension of the theory developed by Lee & Fung (1969) for flow around a single fibre, successfully describes the transition in behaviour from the Hele-Shaw potential flow limit (aspect ratio B [Lt ] 1) to the viscous two-dimensional limiting case (B [Gt ] 1, Sangani & Acrivos 1982) for the hydrodynamic interaction between the fibres. These results are also compared with the solution of the Brinkman equation for the flow through a porous medium in a channel. This comparison shows that the Brinkman approximation is very good when B > 5, but breaks down when B [les ] O(1). A new interpolation formula is proposed for this last regime. Numerical results for the detailed velocity profiles, the drag coefficient f, and the Darcy permeability Kp are presented. It is shown that the velocity component perpendicular to the parallel walls is only significant within the viscous layers surrounding the fibres, whose thickness is of the order of half the channel height B′. One finds that when the aspect ratio B > 5, the neglect of the vertical velocity component vz can lead to large errors in the satisfaction of the no-slip boundary conditions on the surfaces of the fibres and large deviations from the approximate solution in Lee (1969), in which vz and the normal pressure field are neglected. The numerical results show that the drag coefficient of the fibrous bed increases dramatically when the open gap between adjacent fibres Δ′ becomes smaller than B′. The predictions of the new theory are used to examine the possibility that a cross-bridging slender fibre matrix can exist in the intercellular cleft of capillary endothelium as proposed by Curry & Michel (1980).

scholarly journals Investigation of the effects of main geometric parameters and flow characteristics on secondary flow losses in a turbine cascade

2021 ◽  
Vol 2131 (3) ◽  
pp. 032081
Author(s):  
M Mesbah ◽  
V G Gribin ◽  
K Souri
Keyword(s):  
Mach Number ◽  
Aspect Ratio ◽  
Total Energy ◽  
Flow Characteristics ◽  
Numerical Results ◽  
Energy Losses ◽  
Inlet Flow ◽  
Flow Angle ◽  
Flow Losses ◽  
Exit Mach Number

Abstract This paper presents numerical simulation results of a three-dimensional (3D) transitional flow in a stator cascade of an axial turbine. The influences of the main geometric parameters and flow characteristics including, the blade aspect ratio, pitch-to-chord ratio, inlet flow angle, and exit Mach number, on secondary flows development and end-wall losses, were studied. The numerical results were validated by the results of experiments conducted in the laboratory of the steam and gas turbine faculty of the Moscow Power Engineering Institute. The maximum difference between computed and experimental results was 2.4 %. The total energy losses decrease by 20 % when the exit Mach number changes from 0.38 to 0.8. Numerical results indicated that the blade aspect ratio had the most effect on secondary flow losses. The total energy losses increase by 46.6 % when the aspect ratio decreases from 1 to 0.25. The total loss of energy by 13.2 % decreases by increasing the inlet flow angle from 60 degrees to 90 degrees. Then by increasing the inlet flow angle from 90 to 110 degrees, the total loss rises by 3.6%. As the pitch-to-chord ratio increases from 0.7 to 0.75, the total energy losses are reduced by 12.2 %. Then by increasing the pitch-to-chord ratio from 0.75 to 0.8, the total energy losses increase by 6 %. As with experimental data, the numerical results showed that the optimal inlet flow angle and relative pitch for the cascade are 90 degrees and 0.75, respectively.

scholarly journals Experimental Study and Mechanism Analysis of Concrete-Filled Square Steel Tubular Columns Reinforced by Rhombic Stirrups Under Axial Compression

2021 ◽  
Vol 8 ◽  
Author(s):  
Zongping Chen ◽  
Fan Ning ◽  
Linlin Mo
Keyword(s):  
Aspect Ratio ◽  
Bearing Capacity ◽  
Failure Mode ◽  
Axial Compression ◽  
Failure Process ◽  
Steel Tube ◽  
Mechanism Analysis ◽  
Steel Ratio ◽  
Load Displacement ◽  
Square Steel Tube

The square steel tube component has a beautiful appearance, simple joint connection, and it is widely available. However, the uneven distribution of effective constraints in the cross-section of a square steel tube hinders its application. A novel concrete-filled square steel tubular column was tested under axial compression. There were 11 specimens [10 concrete-filled square steel tube columns reinforced with rhombic stirrups with 90-degree internal angle (SSSC specimens) and 1 concrete-filled square steel tube column (SC specimen)]. The load-displacement curves, the law of failure process, failure mode, mechanism analysis, energy consumption, ductility, and stiffness degradation were described, we then investigated the influence of stirrup diameter, stirrup side length, stirrup spacing, steel tube thickness, aspect ratio, and steel ratio on the mechanical properties of the specimens. The results show that the failure process of the SSSC specimens was basically the same. The ultimate failure mode of the specimens with an aspect ratio of 4 was local buckling failure. The specimens with an aspect ratio of 5 and 6 failed due to bending failure in the plastic stage. The steel tube bulged out in different degrees in most of the debonding areas. The longitudinal bars also produced outward bending deformation in the larger bulging area of the steel tube. Some of the stirrups were broken in the later stage of loading. The characteristics of load-displacement curve changed with the changing of stirrup spacing. The strength of longitudinal constraint had an obvious influence on the bearing capacity. In a certain range of steel ratio (ρs = 8.97% ∼ 9.05%), the weakening of the lateral restraint of the stirrup cage had a greater adverse effect on the bearing capacity than the weakening of the effective restraint of the corner. In a certain range of steel ratio (ρs = 8.97% ∼ 9.49%), strengthening the effective corner constraint of stirrups improved the stiffness of the specimen, however, the ductility performance was reduced. The opposite was true for strengthening the lateral constraint of the stirrup cage.

scholarly journals Comparison of OpenFOAM and EllipSys3D for neutral atmospheric flow over complex terrain

2016 ◽  
Vol 1 (1) ◽  
pp. 55-70 ◽  
Author(s):  
Dalibor Cavar ◽  
Pierre-Elouan Réthoré ◽  
Andreas Bechmann ◽  
Niels N. Sørensen ◽  
Benjamin Martinez ◽  
...  
Keyword(s):  
Aspect Ratio ◽  
Roughness Length ◽  
Numerical Results ◽  
Function Approach ◽  
Navier Stokes ◽  
Wall Function ◽  
Atmospheric Flow ◽  
Cell Height ◽  
Order Of Magnitude ◽  
Near Wall

Abstract. The flow solvers OpenFOAM and EllipSys3D are compared in the case of neutral atmospheric flow over terrain using the test cases of Askervein and Bolund hills. Both solvers are run using the steady-state Reynolds-averaged Navier–Stokes k–ϵ turbulence model. One of the main modeling differences between the two solvers is the wall-function approach. The OpenFOAM v.1.7.1 uses a Nikuradse's sand roughness model, while EllipSys3D uses a model based on the atmospheric roughness length. It is found that Nikuradse's model introduces an error dependent on the near-wall cell height. To mitigate this error the near-wall cells should be at least 10 times larger than the surface roughness. It is nonetheless possible to obtain very similar results between EllipSys3D and OpenFOAM v.1.7.1. The more recent OpenFOAM v.2.2.1, which includes the atmospheric roughness length wall-function approach, has also been tested and compared to the results of OpenFOAM v.1.7.1 and EllipSys3D. The numerical results obtained using the same wall-modeling approach in both EllipSys3D and OpenFOAM v.2.1.1 proved to be almost identical. Two meshing strategies are investigated using HypGrid and SnappyHexMesh. The performance of OpenFOAM on SnappyHexMesh-based low-aspect-ratio unstructured meshes is found to be almost an order of magnitude faster than on HypGrid-based structured and high-aspect-ratio meshes. However, proper control of boundary layer resolution is found to be very difficult when the SnappyHexMesh tool is utilized for grid generation purposes. The OpenFOAM is generally found to be 2–6 times slower than EllipSys3D in achieving numerical results of the same order of accuracy on similar or identical computational meshes, when utilization of EllipSys3D default grid sequencing procedures is included.

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