Influence Of Wall Friction Research Articles

Influence of wall friction on Active Earth Pressure in Model Test

Earth pressure theories occupy a paramount position in the field of geotechnical engineering. The knowledge of active earth pressure under static condition is essential in designing a retaining wall as the damage to such retaining structures may lead to disastrous failure. A retaining wall helps in maintaining the ground surface at different elevations on either side of it. Without such a structure, the soil at higher elevation would tend to move down till it acquires its natural, stable configuration. Laboratory model tests in geotechnical engineering are being performed in small steel test tanks to examine the lateral earth pressure on retaining walls. In present study laboratory model of retaining wall is cantilever type, having model tank of MS (1810 x 1210 mm) in plan and 1000 mm height. The MS plate (1210 x 1000 x 5 mm) acts as a retaining wall. Present work consists of evaluation of active earth pressure by conducting 18 tests on model with different frictional surfaces namely jute, geotextile, thick plastic sheet, cement bag and uniform surcharge of 2.0 kN/m2. All the tests are conducted on dry, cohesionless backfill. Test results show that, when frictional surfaces are attached on the side walls and retaining wall, the deflection of the retaining wall reduces and hence active earth pressure is also reduced. Earth pressure slightly reduces in case of frictional surfaces on side wall as well as on retaining wall as compared to that with frictional surface only on retaining wall. Further it is observed that the reduction of the active earth pressure depends on to the wall friction angle () of frictional surface. Increase in wall friction angle () of surface results in decrease in deflection and thereby corresponding decrease in active earth pressure. Earth pressure obtained in the present work agrees well with Culmann’s graphical method whereas earth pressure by coulomb method is slightly higher than that obtained experimentally.

Influence of wall friction on granular column**Project supported by the National Natural Science Foundation of China (Grant Nos. 11705256, 11772095, and 11572091) and the National Key Research and Development Program of China (Grant No. 2016YFB0700103).

Granular packings under gravity in frictional and frictionless silos were simulated and the influence of the wall friction on the normal force distribution was investigated. Although there is an obvious Janssen effect in frictional silos, only a slight influence on the geometry of packing was found. The law of normal force distribution is different for frictional and frictionless walls, which is related to the pressure profile. A modified formula with consideration of the pressure profile was well fitted to the simulation results.

Influence of wall friction on flow regimes and scale-up of counter-current swirl spray dryers

The structure of the vortex flow in swirl spray dryers is investigated after having fouled the walls with deposits typical of detergent manufacture. The range of Re and swirl intensity Ω characteristic of industry are studied using three counter-current units of varying scale and design. The friction with the deposits increases the flow turbulence kinetic energy and causes a drastic attenuation of the swirl and as a result, the vortex breaks down in the chamber forming recirculation regions (i.e. areas of reverse flow). Three flow regimes (1) no recirculation, (2) central and (3) annular recirculation have been identified depending on the swirl intensity. New control and scale up strategies are proposed for swirl dryers based in predicting the decay and the flow regime using the unit geometry (i.e. initial swirl intensity Ωi) and experimental decay rates function of the coverage and thickness of deposits. The impact in design and numerical modelling must be stressed. Adequate prediction of the swirl is vital to study fouling and recirculation, which surely play an important part in the dispersion and aggregation of the solid phase. Current models have no means to replicate these phenomena, and yet, in this case neglecting the deposits and assuming smooth walls would result in (a) over-prediction of swirl velocity up to 40−186% (b) under-prediction of turbulent kinetic energy up to 67−85% and (c) failure to recognise recirculation areas.

Influence of wall friction on settling behavior of loose-fill cellulose insulation material dependent on different surface roughness

As a preliminary test regarding the expected influence of wall friction on the settling behavior of loose-fill cellulose insulation (LFCI), a settling test was performed according to the draft ISO CD 18393, B. Two test boxes with different cavity depth were used with acrylic glass and soft board as two plank materials of different surface roughness. The wall elements were filled with LFCI and strained by drop off impacts. After 13 and 20 impacts, settling was measured and documented. Results of all four test variations show a clearly lower settling on the rougher surface consisting of soft board compared with the smooth acrylic glass. Concerning the different cavity depth, no obvious influence on wall friction is visible. Based on these results, a wall friction test with LFCI according to the Jenike test method was performed on three types of wood based panels with different roughness and acrylic glass as reference. Results show only little difference between the two rough surfaces. Under low normal stress, the three wood based surfaces are almost similar. Only acrylic glass as the smoothest surface of the test differs significantly from the others. On acrylic glass and oriented strand board, the coefficient of wall friction is rising with decreasing normal stress.

Study on continuous vortices induced by sub-microsecond pulsed surface dielectric barrier discharge plasma

The experiments to generate vortices continuously using sub-microsecond pulsed surface dielectric barrier discharge (SDBD) actuator are conducted by particle image velocimetry (PIV). The double-frequencies actuation mode is presented which includes repetitive pulse frequency and vortex frequency. It is found that the empty zone of PIV particles appears in the place where the particles are quite few even nil during the experiments. When discharges occur the primary empty zone is produced by the micro explosion due to the released heat of plasma, and when discharges end the secondary empty zone appears. The induced flow is farther apart form wall and the influence of wall friction should be suppressed due to primary empty zone. When the secondary empty zone on the left side of actuator exposed electrode is blown away completely, the next actuation can start. In order to control the flow more effectively, the pulse voltage with higher repetitive frequency should be applied. The pulse number during one vortex time should be more than 10. As the pulse number increases, the maximal velocity of induced flow increases but the momentum transfer efficiency decreases. The mechanisms releasing heat and body force can be triggered by using the sub-microsecond pulse SDBD actuator.

Estimation of Wall Friction of Chamber Box Using Consolidation Characteristic

An estimation of wall friction during the consolidation of kaolin in testing chamber using the consolidation characteristic is presented herein. A slurry of kaolin was consolidated one dimensionally in a testing chamber under Overconsolidation Ratio (OCR) of ten. The moisture content and undrained shear strength were determined after the consolidation completed. It was found that, the moisture content decreases and the undrained shear strength increases with chamber depth. The differences were observed in the moisture content and strength measurements with increasing depth due to the influence of wall friction during the consolidation process. By using consolidation characteristic of kaolin from the testing chamber and Rowe cell (supplementary test), estimation of wall friction was calculated. It was found that, the wall friction estimation provided differences less than 2.2% with the experimental test.

Wall friction effects and viscosity reduction of gel propellants in conical extrusion

Influence of wall friction on mean apparent viscosity reduction of gel propellants in conical radial flow extrusion is investigated analytically and numerically. A parametric study has been conducted to evaluate the effects of injector geometry, rheological constants, wall friction factor and volumetric flow rate on fluid viscosity profile. Gel propellants were modeled by the non-Newtonian power law constitutive relation. The influence of wall friction on the mean apparent viscosity, on wall slip and on pressure gradient is found to be substantial. Central results are supported by asymptotic analysis for small cone angles and low wall friction. Contact is made with lubrication type flow pattern.

Parametric investigation of particle acceleration in high enthalpy conical nozzle flows for coating applications

A modified cold gas-dynamic spray technique is under development by using shock tunnel technology, which can enhance the coating quality by increasing the solid particle velocity up to 1,500 m/s. The particle diameter typically amounts to 10 μm. A theoretical model based on gas-particle flows is employed to describe the behaviour of the flow and the solid particles. This quasi-1D model is capable to consider non-equilibrium effects of the gas phase due to high reservoir temperatures, and the influence of wall friction and heat transfer averaged over the nozzle cross section. This model is used for the design and optimization of the nozzle geometry by a parametric study, which results in a conical nozzle with a half opening angle of 2.8° and a length of 325 mm. Particles for coating are injected at about 55 mm downstream of the throat. A shock tunnel facility has been set up at the Shock Wave Laboratory for performing an experimental study of this new technique. The theoretical performance of this setup is evaluated by the KASIMIR simulation software and the quasi-1D method described in this paper. The high reservoir conditions required to achieve particle velocities of 1,500 m/s can be realized by using either a very high driver pressure of about 600 bar for air as driver gas or a relatively low driver pressure of about 200 bar for helium as driver gas.

A numerical examination of the direct shear test

The paper presents results of two-dimensional simulations of the direct shear test using the discrete element method (DEM). The heterogeneous distributions of stress and strain are illustrated and, taking advantage of the numerical technique, the evolution of the stress tensor and porosity changes in the shear zone are monitored. The results demonstrate that the dilation inside the shear zone is much greater than that deduced from boundary measurements. The stress ratio τ/σ calculated from the boundary forces is about 10% greater than that calculated in the shear zone. It is also demonstrated that coaxiality of stress and strain rate exists at the critical state. Further simulations show that the influence of wall friction along the vertical faces of the specimen can be minimised by adopting the ‘symmetrical arrangement’ suggested by Jewell, and that the actual stress–strain–dilation behaviour within the shear zone is unaffected by the detailed boundary conditions. Comparison with previously published simulations results suggests that, in laboratory experiments, more reliable data, in the context of both stress ratio and dilation, would be obtained if the shear box aspect ratio was reduced below the value of 1:2 adopted in the traditional Casagrande shear box.

Analysis of Two-Phase Homogeneous Bubbly Flows Including Friction and Mass Addition

The present work is a theoretical investigation of two-phase bubbly flows. The main objective is to get a better insight of the basic phenomena associated with such flows through nozzles via physical modeling and mathematical formulation. Introducing Mach number into the flow equations, we find novel, closed-form analytical solutions and expressions for homogeneous bubbly flows including the influence of wall friction and mass addition. The expressions obtained demonstrate an analogy to those of classical, single-phase gas flows. The study deals with homogeneous flows, however, its approach and results can also be applied to investigate flows with unequal phase velocities, to study instability phenomena, as well as to design and analyze water jet propulsion systems.

Explosive flow of boiling and degassing liquids out of pipes and reservoirs: the influence of wall friction

Explosive flow of boiling and degassing liquids out of pipes and reservoirs: the influence of wall friction

Atomization of liquids and suspensions with hollow cone nozzles

AbstractLarge centrifugal forces of rotational flow are used in hollow cone nozzles to form a thin liquid film in the outlet, which disintegrates into relatively small droplets. The flow in the nozzle can be calculated by means of simple physically meaningful balances, based on the cyclone theory. The influence of wall friction is taken into account via a wall friction coefficient which depends on the Reynolds number of the nozzle flow. The break‐up mechanism of the liquid film was investigated under the consideration of nozzle outlet velocity and film thickness as well as gas and liquid properties. With increasing velocity and film thickness, a transition from aerodynamic wave break‐up to turbulent atomization was observed to take place. Equations presented in this paper allow the calculation of mass flow rate, pressure drop and drop size distribution of hollow cone nozzles with any given geometry.

Analysis of earth pressure problems considering the influence of wall friction and wall deflection : Nakai, T Proc 5th International Conference on Numerical Methods in Geomechanics, Nagoya, 1–5 April 1985V2, P765–772. Publ Rotterdam: A. A. Balkema, 1985

Analysis of earth pressure problems considering the influence of wall friction and wall deflection : Nakai, T Proc 5th International Conference on Numerical Methods in Geomechanics, Nagoya, 1–5 April 1985V2, P765–772. Publ Rotterdam: A. A. Balkema, 1985

Compaction of till soils and growth tests with Norway spruce and scots pine

Five of the most common soils in forest areas in Sweden, viz., coarse sand, fine sand, coarse sandy till, medium sandy till and fine sandy till soil, were compressed at different loadings for 10 min. In the soils studied, it was found that the more fine material there was in the soil, the easier it compacted, and that till soils compacted much more than sediments of the same main particle class. The chosen compression time seemed to correspond well with an equilibrium level of static compaction. Influence of wall friction in compression tubes was found to be negligible for till soils. After compaction the soil cores were sown with Norway spruce ( Picea abies (L.) Karst.) or Scots pine ( Pinus sylvestris L.) and 16–20 days later the root lengths were recorded. Lengths of primary roots in per cent of the control were found to be almost inverse to the compaction of the soils; Norway spruce was more impeded than Scots pine. Thus, the bulk density alone is a poor indicator of the impact of soil compaction. Growth to 26, 33 and 120 days showed that the extension of secondary roots might be more impeded by compaction than the primary roots. Fertilization increased growth but did not decrease the growth difference between seedlings on unloaded and loaded soil cores.

Experiments on sedimentation beneath downward-facing inclined walls

It has been known since Boycott (1920) that sedimentation rates can be several times higher within inclined walls than in vertical vessels. Beneath the downward-facing inclined wall a thin boundary-layer of clear liquid is formed with an upward velocity. Mass continuity brings about the observed effect. Ponder (1925), and Nakamura & Kuroda (1937) proposed a global kinematic model without any detail of the flow field to predict the sedimentation rate. Recently, two asymptotic theories for describing the flow field became available. The investigation by Acrivos & Herbolzheimer (1979) requires both Re 2/ Gr and Re 4/ Gr to be small, with Re being a sedimentation Reynolds number and Gr a sedimentation Grashof number. The analysis due to Schneider (1982) is valid for small values of Re 2/ Gr and large values of Re 4/ Gr. This paper presents experimental sedimentation data in a 2/ Gr and large values of symmetrical, roof-shaped vessel. The experiments with spherical glass beads in a variable mixture of glycerine and water cover the whole parameter range from very small to very large values of Re 4/ Gr. Therefore, both theories could be verified. In the case of small values of Re 4/ Gr, strong waves beneath the downward-facing wall were observed and graphically evaluated in order to find a basis for further theoretical approach. Furthermore, an upward flow of particles in a sublayer of the boundary-layer leads te protruding “borns” and an oscillation of the originally horizontal discontinuity separating the suspension from the clear liquid. The measured particle distribution and deviations from a monodispersed suspension seems to be a possible explanation for this effect, which is investigated theoretically in a separate paper (Schaflinger 1984). A further experimental shortcoming, the shallow depth of the settling vessel, that was necessary for an optoelectronic measuring of the actual volume fraction solids within the bulk, may affect the convective motion when the sedimentation Reynols number is small. However, in this case the experimental data are in conformity with the theoretical predictions which do not consider the influence of wall friction on the sedimentation behaviour.

Einfluß der Wandreibung auf die Dimensionierung von Bunkern — Verfahrenstechnische und statische Gesichtspunkte

AbstractInfluence of wall friction on the design of silos – Aspects of process technology and statics. Mass flow and funnel flow are distinguished when considering the discharge of stored bulk solids. In order to cause mass flow to occur, i. e. the complete bunker filling is in motion, hopper walls need to be steep. Conditions close to the outlet are decisive, a large value of wall friction requiring steep hopper walls. For a safe design of bunker walls with respect to mechanical strength, DIN 1055, part 6 is commonly applied; it is currently being revised. From this regulation a strong influence of the angle of wall friction can be inferred, small values of the angle being associated with high horizontal pressures. In case the angle of wall friction depends on pressure and other parameters and safety factors are included there may be a considerable difference between the angle used by a process engineer and by a civil engineer.

Plastic boundary layers

Plastic boundary layers that develop in steady rectilinear flow of rigid/linear-hardening materials, near rough walls, are investigated. The general rectilinear flow problem is reduced to two semi-coupled partial differential equations. A few exact solutions for steady flow through simple cross sections are derived and used for a detailed study of plastic boundary layers. Material behaviour is governed by the usual von-Mises flow rule. The results reveal the influence of wall friction, wall pressure and material hardening on the boundary layers.

Deceleration Rate Parameter and Algebraic Prediction of Turbulent Boundary Layer

The deceleration rate θ1/λ, which is defined as the ratio of the momentum thickness to the distance where the free-stream velocity is reduced by 10 percent, is shown as an important and handy parameter to describe the development of turbulent boundary layer in an adverse pressure gradient. Using this parameter a simple calculation procedure of turbulent boundary layer is presented. In order to achieve a large inlet/exit velocity ratio, θ1/λ =0.02 may be recommended, where the influence of wall friction on the development of momentum loss is very small and the shape factor of boundary layer does not increase rapidly.

Analysis on the Heaps obtained at the Measurement of the Angle of Repose by Cohesion Parabola

A new apparatus was devised, having several favorable attributes, such as presentation of a drained angle without any influence of wall friction, and good reproducibility.The following facts were found;(1) The profiles of the heaps obtained with the apparatus well agreed with the cohesion parabola.(2) One could determine separately the coefficient of interparticle friction and the cohesion of granules and particles by cohesion parabola analysis.

One-Dimensional Magnetogasdynamic Flow with Wall Friction

The case of one-dimensional magnetogasdynamic flow under the influence of wall friction is investigated. In particular, the case of an infinitely conducting, compressible plasma is studied when the flow direction and the direction of the magnetic field are at right angles to one another. It is shown that all flow variables can be expressed as functions of the ratio of the local flow velocity to the Alfvén velocity. It is shown that the flow has a variety of regimes delineated by specific singularities and extremities. A typical magnetogasdynamic Fanno flow chart is presented and it is noted that the flow differs markedly from that encountered in classical gasdynamics.