A quadratic viscous fluid law for ice deduced from Steinemann's uni-axial compression and torsion experiments

The response of ice to applied stress on ice-sheet flow timescales is commonly described by a non-linear incompressible viscous fluid, for which the deviatoric stress has a quadratic relation in the strain rate with two response coefficient functions depending on two principal strain-rate invariants I2 and I3. Commonly, a coaxial (linear) relation between the deviatoric stress and strain rate, with dependence on one strain-rate invariant I2 in a stress formulation, equivalently dependence on one deviatoric stress invariant in a strain-rate formulation, is adopted. Glen's uni-axial stress experiments determined such a coaxial law for a strain-rate formulation. The criterion for both uni-axial and shear data to determine the same relation is determined. Here, we apply Steinemann's uni-axial stress and torsion data to determine the two stress response coefficients in a quadratic relation with dependence on a single invariant I2. There is a non-negligible quadratic term for some ranges of I2; that is, a coaxial relation with dependence on one invariant is not valid. The data does not, however, rule out a coaxial relation with dependence on two invariants.

Silo discharge: influence of the particle shape on the velocity profiles

Experiments on the discharge of a silo with an inclined outlet are performed using flattened seeds in order to evaluate the validity of a previous theoretical formulation developed in our work group [1]. In that description, funnel flow regime is assumed to be based on a free fall parabolic arc. The shape of this arc is described with a parameter which is the only one involved in the flow rate formulation. An experimental analysis of the behavior of this parameter is carried out based on the geometry and shape of the grains within the silo. Also, video analysis of the silo discharge is performed in order to investigate the velocity profiles at the outlet of the hopper for these non-spherical particles. Experiments are contrasted with analytical predictions derived from the proposed formulation in order to assess and discuss its validity for the case of flattened particles.

The Impact of Rate Formulations on Stochastic Molecular Motor Dynamics

Cells are complex structures which require considerable amounts of organization via transport of large intracellular cargo. While passive diffusion is often sufficiently fast for the transport of smaller cargo, active transport is necessary to organize large structures on the short timescales necessary for biological function. The main mechanism of this transport is by cargo attachment to motors which walk in a directed fashion along intracellular filaments. There are a number of models which seek to describe the motion of motors with attached cargo, from detailed microscopic to coarse phenomenological descriptions. We focus on the intermediate-detailed discrete stochastic hopping models, and explore how cargo transport changes depending on the number of motors, motor interaction, system constraints and rate formulations, which are derived from common thermodynamic assumptions. We find that, despite obeying the same detailed balance constraint, the choice of rate formulation considerably affects the characteristics of the overall motion of the system, with one rate formulation exhibiting novel behavior of loaded motor groups moving faster than a single unloaded motor.

Effects of Primary and Secondary Creep Formulations on API 579-1 Residual Life Evaluation

A sound material constitutive equation is crucial for the residual life evaluation of pressure components operating in the creep range. In a previous work [1], the authors investigated how a secondary creep formulation encompassing both the dislocational and the diffusional range influences the assessment of damage according to API 579-1 [2] within the whole component stress range. In the present paper the work has been extended in order to include the effects of primary creep in the constitutive equation for the ASTM A335 P22 low-alloy steel used for the manufacturing of the HRSG header whose welded details were previously investigated. The creep damage was first calculated according to API 579-1 Section 10 via inelastic, time-dependent FEA and the Larson-Miller approach (LMP) with code-defined, minimum time-to-rupture data. This led to a first reckoning of the primary creep impact in terms of API 579-1 residual life for the components under evaluation. The API 579-1 time-to-rupture was then assessed with a detailed stress analysis implementing the Omega Method and its creep strain rate formulation. The obtained results were finally compared to those previously determined through the LMP procedure and the different creep correlations (secondary and primary+secondary).

Copper matte - slag reaction sequences and separation processes in matte smelting

While particle combustion and chalcopyrite oxidation in suspension smelting is well understood, few studies are available regarding the melt-melt reactions and the separation between copper matte and slag in matte smelting. In the present work, experimental investigations in air and argon atmosphere were conducted using a mixture of synthetic slag and chalcopyrite concentrate. The sequential reaction and separation processes occurring in matte smelting are outlined. Possible limiting factors in the overall process are also proposed. The result of the present work forms an important foundation for future work in the kinetic rate formulation of molten phase reactions between copper matte and slag in matte smelting.

Comparison of Convective and Radiative Heating Modes on the Thermophysical Changes of a Cerium Nitrate Droplet

In this paper, we try to establish the equivalence or similarity in the thermal and physiochemical changes in precursor droplets (cerium nitrate) in convective and radiative fields. The radiative field is created through careful heating of the droplet using a monochromatic light source (CO2 laser). The equivalence is also established for different modes of convection like droplet injected into a high-speed flow and droplet experiencing a convective flow due to acoustic streaming (levitated) only. The thermophysical changes are studied in an aqueous cerium nitrate droplet, and the dissociation of cerium nitrate to ceria is modeled using modified Kramers' reaction rate formulation. It is observed that vaporization, species accumulation, and chemical characteristics obtained in a convectively heated droplet are retained in a radiatively heated droplet by careful adjustment of the laser intensity. The timescales and ceria yield match reasonably well for both the cases. It is also noted that similar conclusions are drawn in both levitated droplet and a nonlevitated droplet.

Two-Dimensional Thermal Model of Asperity Heating in a Disk Pair in Dry Friction Between Two Rough Surfaces

In this paper, a formulation for the rate of heat generation due to the contact of one asperity with asperities on a second surface is proposed. A statistical approach is used to obtain the heat generation rate due to one asperity and employed to develop the equation for generation of heat rate between two rough surfaces. This heat rate formulation between the two rough surfaces has been incorporated into the 2D lumped parameter model of disk pair in dry friction developed by Elhomani and Farhang (2010, “A 2D Lumped Parameter Model for Prediction of Temperature in C/C Composite Disk Pair in Dry Friction Contact,” ASME J. Therm. Sci. Eng. Appl., 2(2), p. 021001). In this paper, the disk brake is viewed as consisting of three main regions: (1) the surface contact, (2) the friction interface, and (3) the bulk. Both surfaces of the disk brake are subjected to frictional heating. This model is considered to be a necessary step for simulating the aircraft braking system that consists of a stack of multiple disks.