Effect Of Body Force Research Articles

117 回転二重円筒間を旋回する二液流れにおける界面振動と混合現象 : 動粘度の影響と体積力の影響について(GS1-2 壁面間流れ,界面挙動,火災,一般セッション:GS1 流体工学)

117 回転二重円筒間を旋回する二液流れにおける界面振動と混合現象 : 動粘度の影響と体積力の影響について(GS1-2 壁面間流れ,界面挙動,火災,一般セッション:GS1 流体工学)

Carbon nanoparticle-filled polymer flow in the fabrication of novel fiber composites

During the fabrication process of advanced composites using nanoparticle-filled matrices, many problems potentially could arise. One such problem is the clogging of the channels of the microfiber matrix used due to strong interactions between the nanoparticle additives and the matrix walls. In the present paper, a two-dimensional simulation model based on an Eulerian multiphase flow approach is introduced to investigate and predict the flow characteristics of carbon nanoparticle-filled fluid around carbon microfiber matrix. The interactions between the microfiber matrix walls and the nanoparticle additives have been studied, and an energy “imbalance” technique has been applied between the fluid and the microfiber walls to prevent any potential sticking of the nanoparticle additives on the microfiber matrix walls during the flow process. The concept of phasic volume fractions is utilized, and the effects of external body forces, lift forces, and virtual mass forces are introduced into the momentum equations. The phase coupled SIMPLE algorithm is employed to solve the model.

Elasticity solutions for plane anisotropic functionally graded beams

This paper considers the plane stress problem of generally anisotropic beams with elastic compliance parameters being arbitrary functions of the thickness coordinate. Firstly, the partial differential equation, which is satisfied by the Airy stress function for the plane problem of anisotropic functionally graded materials and involves the effect of body force, is derived. Secondly, a unified method is developed to obtain the stress function. The analytical expressions of axial force, bending moment, shear force and displacements are then deduced through integration. Thirdly, the stress function is employed to solve problems of anisotropic functionally graded plane beams, with the integral constants completely determined from boundary conditions. A series of elasticity solutions are thus obtained, including the solution for beams under tension and pure bending, the solution for cantilever beams subjected to shear force applied at the free end, the solution for cantilever beams or simply supported beams subjected to uniform load, the solution for fixed–fixed beams subjected to uniform load, and the one for beams subjected to body force, etc. These solutions can be easily degenerated into the elasticity solutions for homogeneous beams. Some of them are absolutely new to literature, and some coincide with the available solutions. It is also found that there are certain errors in several available solutions. A numerical example is finally presented to show the effect of material inhomogeneity on the elastic field in a functionally graded anisotropic cantilever beam.

Modelling filament stretching flows with strain-hardening models and sub-cell approximations

This article analyses the transient viscoelastic response of strain-hardening fluids in filament stretching flows. We utilise an arbitrary Lagrangian/Eulerian temporal approach (ALE), coupled with a particle-tracking procedure for free-surface movement and a hybrid finite volume/element method upon the domain. We are able to contrast findings between Oldroyd, Giesekus and linear Phan-Thien/Tanner models, and distinguish between single and multi-mode implementations. In this manner, we identify the impact that greater severe strain hardening has in this transient flow context. Contributions from shear-thinning rheology may be gathered in particular by comparing single-mode solution response between a shear-thinning Giesekus and a constant shear viscosity Oldroyd-B model. A parameter study on body force and surface tension effects has been undertaken, where we isolate the occurrence of asymmetries in the flow under certain conditions, leading to the onset and formulation of bead-like structures. This elucidates the specific localised influence that surface tension and gravitational forces have upon some stretching filament flows.

Body force effect on consolidation of porous elastic media due to pumping

In this study, the linear poro‐elasticity theory is applied to examine the body force effect on consolidation of porous media due to pumping. The steady‐state solutions of displacement and incremental effective stress for a stratum of clay sandwiched between sandy strata are analytically given. The effect of body force could be represented by the body force number that depends on Lame's constants, porosity, and the thickness of porous media. The consolidation of clay is significantly related not only to the body force number but also to the ratio of water table depression in upper and lower sandy strata due to pumping. The neglect of body force will severely underestimate the displacement and incremental effective stress when porous media are soft or thick, or both. This might lead to potential flaws in engineering practice, such as the calculation of soil settlement.

A boundary integral formulation of quasi-steady fluid wetting

This paper considers the motion of a liquid droplet on a solid surface. When capillary relaxation is much faster than the motion of the contact line, the fluid geometry and its dynamical evolution can be characterized in terms of the contact line alone. This problem can be cast in terms of boundary integral equations involving a Dirichlet–Neumann map coupled to a volume conservation constraint. A computational method for this formulation is described which has two principal advantages over approaches which track the entire free surface: (1) only the curve which describes the contact line is computed and (2) the resulting method exhibits only mild numerical stiffness, obviating the need for implicit timestepping. Effects of both capillary and body forces are considered. Computational examples include surface inhomogeneities, topological transitions and cusp formation.

Effects of body forces on electro- and magnetorheological fluids

Body forces in electro- and magnetorheological fluids are typically small compared to the magnitudes of the field-induced electric and magnetic forces. Using particle-level simulations, we show that these relatively small forces can have large effects on the rheological response of these fluids in shear flow.

중력식 콘크리트 댐에 작용하는 양압력이 응력확대계수에 미치는 영향

The modeling of uplift pressure within dam, on the foundation on which it was constructed, and on the interface between the dam and foundation is a critical aspect in the analysis of concrete gravity dams, i.e. crack stability in concrete dam can correctly be predicted when uplift pressures are accurately modelled. Current models consider a uniform uplift distribution, but recent experimental results show that it varies along the crack faces and the procedures for modeling uplift pressures are well established for the traditional hand-calculation methods, but this is not the case for finite element (FE) analysis. In large structures, such as dams, because of smaller size of the fracture process zone with respect to the structure size, limited errors should occur under the assumptions of linear elastic fracture mechanics (LEFM). In this paper, the fracture behaviour of concrete gravity dams mainly subjected to uplift Pressure at the crack face was studied. Triangular type, trapezoidal type and parabolic type distribution of the uplift pressure including uniform type were considered in case of evaluating stress intensity factor by surface integral method. The effects of body forces, overtopping pressures are also considered and a parametric study of gravity dams under the assumption of LEFM is performed.

Peeling, Healing, and Bursting in a Lubricated Elastic Sheet

We consider the dynamics of an elastic sheet lubricated by the flow of a thin layer of fluid that separates it from a rigid wall. By considering long wavelength deformations of the sheet, we derive an evolution equation for its motion, accounting for the effects of elastic bending, viscous lubrication, and body forces. We then analyze various steady and unsteady problems for the sheet, such as peeling, healing, levitating, and bursting, using a combination of numerical simulation and dimensional analysis. On the macroscale, we corroborate our theory with a simple experiment, and, on the microscale, we analyze an oscillatory valve that can transform a continuous stream of fluid into a series of discrete pulses.

A Method for Assessing the Importance of Body Force on Flow Boiling CHF

Experiments were performed to examine the effects of body force on flow boiling CHF. FC-72 was boiled along one wall of a transparent rectangular flow channel that permitted photographic study of the vapor-liquid interface just prior to CHF. High-speed video imaging techniques were used to identify dominant CHF mechanisms corresponding to different flow orientations and liquid velocities. Six different CHF regimes were identified: Wavy Vapor Layer, Pool Boiling, Stratification, Vapor Counterflow, Vapor Stagnation, and Separated Concurrent Vapor Flow. CHF showed significant sensitivity to orientation for flow velocities below 0.2 m/s, where extremely low CHF values where measured, especially with downward-facing heated wall and downflow orientations. High flow velocities dampened the effects of orientation considerably. The CHF data were used to assess the suitability of previous CHF models and correlations. It is shown the Interfacial Lift-off Model is very effective at predicting CHF for high velocities at all orientations. The flooding limit, on the other hand, is useful at estimating CHF at low velocities and for downflow orientations. A new method consisting of three dimensionless criteria is developed to determine the minimum flow velocity required to overcome body force effects on near-saturated flow boiling CHF.

Prediction of the deflection and residual stress in controlled cooling of hot-rolled steel beams including load and arbitrary support: Part I. Computational model

The computation of deflection and residual stress in hot-rolled beams subject to controlled cooling on the run-out table, to produce predetermined properties, is described. The inclusion of self-load and arbitrary contact with the supporting table and provision for inclusion of applied stress represents an extension of published analyses. The present analysis is based on the generalised plane-strain model of Abouaf, Chenot and Marcelin which is extended to include the effect of body forces (the weight of the beam) which requires removal of the assumption of constant curvature and thence permits inclusion of applied load. The present analysis also provides for improved representation of the coefficient of thermal expansion of the beam by deriving it as a function of temperature and the kinetics of phase transformation. Experiments to validate the model by comparing computed and measured residual stresses in beams are described.

Seismic bearing capacity of foundations on slopes

The effect of pseudo-static horizontal earthquake body forces on the bearing capacity of foundations on sloping ground has been assessed using the method of stress characteristics. Two failure mechanisms were considered, based on the extension of the characteristics from the ground surface towards the footing base from either one side or both sides. The magnitude of Nγ based on the both-sides failure mechanism, for smaller values of earthquake acceleration coefficient (αh), has been found to be significantly smaller than that obtained using the single-side mechanism; however, in the presence of αh the both-sides mechanism becomes kinematically inadmissible in many cases for higher values of ϕ. Only the single-side mechanism was found statically admissible for computing the bearing capacity factors Nc and Nq on sloping ground. All the bearing capacity factors reduce considerably with increase in αh for various ground inclinations.

Seismic bearing capacity of rough footings on slopes using limit equilibrium

For foundations placed on horizontal ground surfaces, incorporating the effects of earthquake body forces, investigations have been performed by using the method of slices (Sarma & Iossifelis, 1990), limit equilibrium (Budhu & Al-Karni, 1993), the upper bound limit analysis (Richards et al., 1993; Dormieux & Pecker, 1995; Soubra, 1997, 1999) and the method of characteristics (Kumar & Mohan Rao, 2002a). For sloping ground surfaces, on the basis of limit analysis Zhu (2000) has reported an earthquake reduction factor for the bearing capacity factor,$ N_{y}$. By using the method of characteristics, Kumar & Mohan Rao (2002b) have established the variation of the bearing capacity factors with changes in horizontal earthquake acceleration coefficient, h, for different ground inclinations. Two different failure mechanisms (single side and both sides) were used in the analysis. It was indicated that, in the presence of \alpha h, only the single-side failure mechanism remains statically admissible for the computation of Nc and Nq. By contrast, in finding$ N_{y}$, for smaller values of \alpha h and _ both mechanisms were shown to remain statically admissible. As compared with the single-side mechanism, the bearing capacity factor $N_{y}$ was shown to become much smaller on the basis of the both-sides mechanism, especially for very small values of \alpha h and _. It was also indicated that the single-side mechanism remains kinematically admissible in all those cases where no slip has been allowed along the footing–soil interface (rough foundations). Although the approach was quite rigorous, however, it was assumed that the ratio of shear to normal stresses along the foundation–soil interface remains constant. Since the limit equilibrium technique does not require this assumption, it was intended to use this method to determine the seismic bearing capacity of rough foundations on sloping ground. It was simultaneously ensured that the solution remains kinematically admissible in all the cases. The results were thoroughly compared with those reported previously.

A state space formalism for anisotropic elasticity.: Part II: Cylindrical anisotropy

A state space formalism for thermoelastic analysis of a cylindrically anisotropic elastic body is developed. By proper grouping of the stress and taking rσ ij instead of σ ij as the stress variables, the three-dimensional equations of elasticity in the cylindrical coordinates are concisely formulated into a state equation and an output equation using matrix notations. The general solution for the generalized plane problems is derived in a simple manner. Effects of extension, torsion, bending, temperature change and body force are accounted for systematically. The eigen relation arising from the solution process and the degenerate cases of repeated eigenvalues are examined. To demonstrate the power of the formalism, exact solutions to extension, torsion, bending and thermo-mechanical loading of a general cylindrically anisotropic circular tube or bar are obtained. The surface tractions and temperature field may vary in θ but not in z. Displacement as well as traction boundary conditions are considered. It appears that many problems of anisotropic elasticity are best viewed and treated in the state space framework.

Experimental assessment of the effects of body force, surface tension force, and inertia on flow boiling CHF

The interfacial instabilities important to the modeling of critical heat flux (CHF) in reduced-gravity systems are sensitive to even minute body forces, especially for small coolant velocities. Understanding these effects is of paramount importance to both the reliability and safety of two-phase thermal management loops proposed for future space and planetary-based thermal systems. Unfortunately, reduced gravity systems cannot be accurately simulated in 1 g ground-based experiments. However, ground-based experiments can help isolate the effects of the various forces (body force, surface tension force and inertia) which influence flow boiling CHF. In this project, the effects of the component of body force perpendicular to a heated wall were examined by conducting 1 g flow boiling experiments at different orientations. Boiling experiments were performed using FC-72 in vertical and inclined upflow and downflow, as well as horizontal flow, and with the heated surface facing upward or downward relative to gravity. CHF was very sensitive to orientation for flow velocities below 0.2 m/s and near-saturated flow; CHF values for downflow and downward-facing heated surface were much smaller than for upflow and upward-facing surface orientations. Increasing velocity and subcooling dampened the effects of flow orientation on CHF. For saturated flow, the vapor layer characteristics fell into six different regimes: wavy vapor layer, pool-boiling, stratification, vapor stagnation, vapor counterflow, and vapor concurrent flow. The wavy vapor layer regime encompassed all subcooled and high-velocity saturated conditions at all orientations, as well as low-velocity upflow orientations. Prior CHF correlations and models were compared, and shown to predict the CHF data with varying degrees of success.

Accounting for Buoyancy Effects in the Explicit Algebraic Stress Model: Homogeneous Turbulent Shear Flows

Most explicit algebraic stress models are formulated for turbulent shear flows without accounting for external body force effects, such as the buoyant force. These models yield fairly good predictions of the turbulence field generated by mean shear. As for thermal turbulence generated by the buoyant force, the models fail to give satisfactory results. The reason is that the models do not explicitly account for buoyancy effects, which interact with the mean shear to enhance or suppress turbulent mixing. Since applicable, coupled differential equations have been developed describing these thermal turbulent fields, it is possible to develop corresponding explicit algebraic stress models using tensor representation theory. While the procedure to be followed has been employed previously, unique challenges arise in extending the procedure for developing the algebraic representations to turbulent buoyant flows. In this paper the development of an explicit algebraic stress model (EASM) is confined to the homogeneous buoyant shear flow case to illustrate the methodology needed to develop the proper polynomial representations. The derivation is based on the implicit formulation of the Reynolds stress anisotropy at buoyant equilibrium. A five-term representation is found to be necessary to account properly for the effect of the thermal field. Thus derived, external buoyancy effects are represented in the scalar coefficients of the basis tensors, and structural buoyancy effects are accounted for in additional terms in the stress anisotropy tensor. These terms will not vanish even in the absence of mean shear. The performance of the new EASM, together with a two-equation (2-Eq) model, the non-buoyant EASM of Gatski and Speziale (1993) and a full second-order model, is assessed against direct numerical simulations of homogeneous, buoyant shear flows at two different Richardson numbers representing weak and strong buoyancy effects. The calculations show that this five-term representation yields better results than the 2-Eq model and the EASM of Gatski and Speziale where buoyancy effects are not explicitly accounted for.

Seismic bearing capacity factors for spread foundations

The effect of horizontal earthquake body forces on the bearing capacity of foundations has been examined computationally in a rigorous manner by employing the method of stress characteristics. The bearing capacity factors Nc, Nq and Nγ, due to the components of soil cohesion, ground surcharge pressure and soil unit weight respectively, have been plotted as a function of earthquake acceleration coefficient (αh) for different values of soil friction angle (ϕ). The inclusion of earthquake body forces causes a considerable reduction in the bearing capacity factors. The bearing capacity factors Nc and Nq are seen to be approximately of the same magnitude as those reported in the literature on the basis of different solution methods. However, the obtained values of Nγ are found to be significantly smaller than the available results. The nature of the pressure distribution along the footing base and the geometry of the observed failure patterns vary with the consideration of earthquake body forces.

1116 外力を伴う格子乱流場における乱流混合反応機構の解明

1116 外力を伴う格子乱流場における乱流混合反応機構の解明

The body-force effect on the cell formation of premixed flames

The body-force effect on the cell formation of premixed flames at Lewis number unity is investigated by two-dimensional (2-D) and three-dimensional (3-D), unsteady calculations of reactive flows. To investigate the body-force effect on intrinsic instability, the relation between the growth rate and the wave number, i.e., the dispersion relation, is obtained. When premixed flames are propagated downward (upward), the growth rate decreases (increases) and the unstable range narrows (widens) with an increase in acceleration. Positive growth rates induced by hydrodynamic and body-force effects form a cellular flame. To investigate the cell formation due to intrinsic instability, the disturbance with the linearly most unstable wavelength is superimposed on a planar flame. The superimposed disturbance evolves, and eventually a cellular flame front is formed. When the flame is propagated downward, the spacing between cells is almost constant and the cell depth becomes smaller as the acceleration increases. When the flame is propagated upward, on the other hand, the former becomes smaller and the latter becomes larger. In addition, the cell depth and flame-surface area of 3-D flames are larger than those of 2-D flames. This is caused by the difference in spacing between cells and disposition of cells.

Micron-scale tensiometry for studying density-matched and highly viscous fluids — with application to bitumen-in-water emulsions

Measuring the interfacial tension (IFT) between density-matched fluids has been a serious challenge in the study of tensiometry. These measurements can be further complicated when one or both of the fluids possess high viscosities. In this study, a micron-scale technique is developed to circumvent such difficulties. This microscopic technique involves stretching an otherwise spherical drop, of diameter ∼10 μm in an aqueous medium, with the use of two suction micropipettes; one of the pipettes is shaped as a cantilever to allow for measurement of the stretching force. It is shown that, for mechanical experiments conducted on the 1–10 μm scale, as in the present application, the gravitational body force and viscous effects can be neglected (provided relaxation times of several seconds are allowed). The Young–Laplace equation, which describes the force-drop deformation relation, is utilized to determine the equilibrium IFT. The system of present interest was that of bitumen drops in water at room temperature, in which the densities of the two phases are nearly equal (to within 1%) and the viscosity of bitumen is extremely high (more than 10 5 times that of water). This is the first study of bitumen–water (IFT) at room temperature over a range of pH.