Patrick T. Reardon

Improving Falling Ball Tests for Viscosity Determination

Laboratory experiments and numerical simulations are performed to determine the accuracy and reproducibility of the falling-ball test for viscosity determination in Newtonian fluids. The results explore the wall and end effects of the containing cylinder and other possible sources that affect the accuracy and reproducibility of the falling ball tests. A formal error analysis of the falling-ball method, an evaluation of the relative merits of calibration and individual measurements, and an analysis of reproducibility in the falling-ball test are performed. Recommendations based on this study for improving both the accuracy and reproducibility of the falling-ball test are presented.

Shear-thinning of polydisperse suspensions

The effects of the polydispersivity of the particle phase on the rheology of suspensions are studied with falling-ball rheometry. The model suspensions consist of large, neutrally buoyant spheres in a viscous Newtonian suspending fluid. The experiments determine the average velocity of the settling particle along the centreline or axis of the containing cylinders. The objective of this study was to determine the effects of the dispersivity of the particulate phase on the relative viscosity of the suspensions. In dilute and moderately concentrated suspensions, there is no statistically significant difference in the relative viscosity, ?r, between the model suspensions of spheres of uniform sizes and suspensions of spheres with polydisperse sizes for all settling sphere sizes examined. As increases to 0.5, suspensions made up of particles with very narrow size distributions have viscosities that are essentially shear-rate independent. As the standard deviation of the particle distribution normalized by the average particle size increases from 0.01 to 0.2, we find that ?r exhibits significant shear thinning with a power-law exponent, n, decreasing to 0.50 from the roughly Newtonian behaviour (n = 1). Over the range of our data, ?r increased as the degree of polydispersivity increased.

SPECIALIZED MACHINING TECHNIQUES FOR TARGET AND DIAGNOSTIC FABRICATION

Abstract During the course of machining targets for various experiments, it sometimes becomes necessary to take fixtures or machines that are designed for one function and adapt them to another function. When adapting a machine or fixture is not adequate, it may be necessary to acquire a machine specifically designed to produce the component required. In addition to the above scenarios, the features of a component may dictate that multistep machining processes are necessary to produce the component. This paper discusses the machining of four components where adaptation, specialized machine design, or multistep processes were necessary to produce the components.

Experimental observations of non-continuum effects in suspensions: Falling-ball versus towed-ball rheometry

Viscosity is an intrinsic material property of Newtonian liquids, independent of the fluid’s strain rate and state of stress. Experiments performed on a test sphere traversing a homogeneous Newtonian fluid should establish the same viscosity whether by measuring the force on a test sphere moving at a constant velocity or by measuring the velocity of a test sphere animated by a constant force. Here we report on the results of experiments designed to compare constant force and constant velocity experiments for test spheres translating through suspensions of non-colloidal, neutrally buoyant spheres dispersed in viscous Newtonian fluids. Measurements were made of the apparent viscosity of a suspension relative to that of the pure fluid using either a settling ball animated by a constant gravitational force (ηrF) or a towed ball translating with a constant velocity (ηrV). The primary experimental parameters were the solids fraction (ϕ) in the suspension, and the ratio of the radius of the suspended spheres, as...

Simulation works: a panel discussion

Construction operations are often repetitive not only in terms of time (the same tasks are performed over and over) but also in terms of space (the same tasks are repeated at several places, such as different floors in a high-rise building). Thus, construction simulation models in general must be cyclic to represent temporal repetitions, but also scaleable to represent spatial repetitions. This paper presents the mechanisms for preprocessor replacement and automatic code generation that have been designed and implemented to facilitate the development of scaleable simulation models in STROBOSCOPE, a general-purpose discrete-event simulation system developed by the authors. A relatively complex simulation model for the vertical transportation of people serves as an example to illustrate how to develop a completely scaleable model for the operation of an elevator in a building with any number of floors.

Pulsed Power Hydrodynamics: An Application of Pulsed Power and High Magnetic Fields to the Exploration of Material Properties and Problems in Experimental Hydrodynamics

Pulsed-power hydrodynamics (PPH) is an evolving application of low-impedance pulsed-power technology. PPH is particularly useful for the study of problems in advanced hydrodynamics, instabilities, turbulence, and material properties. PPH techniques provide a precisely characterized controllable environment at the currently achievable extremes of pressure and material velocity. The Atlas facility, which is designed and built by Los Alamos National Laboratory, is the worlds first, and only, laboratory pulsed-power system designed specifically for this relatively new family of pulsed-power applications. Atlas joins a family of low-impedance high-current drivers around the world, which is advancing the field of PPH. The high-precision cylindrical magnetically imploded liner is the tool most frequently used to convert electromagnetic energy into the hydrodynamic (particle kinetic) energy needed to drive strong shocks, quasi-isentropic compression, or large-volume adiabatic compression for the experiments. At typical parameters, a 30-g 1-mm-thick liner with an initial radius of 5 cm and a moderate current of 20 MA can be accelerated to 7.5 km/s, producing megabar shocks in medium density targets. Velocities of up to 20 km/s and pressures of > 20 Mbar in high-density targets are possible. The first Atlas liner implosion experiments were conducted in Los Alamos in September 2001. Sixteen experiments were conducted in the first year of operation before Atlas was disassembled, moved to the Nevada Test Site (NTS), and recommissioned in 2005. The experimental program resumed at the NTS in July 2005. The first Atlas experiments at the NTS included two implosion dynamics experiments, two experiments exploring damage and material failure, a new advanced hydrodynamics series aimed at studying the behavior of particles of damaged material ejected from a free surface into a gas, and a series exploring friction at sliding interfaces under conditions of high normal pressure and high relative velocities. Longer term applications of PPH and the Atlas system include the study of material interfaces subjected to multimegagauss magnetic fields, material strength at high strain rate, the properties of strongly coupled plasmas, and the equation of state of materials at pressures approaching 10 Mbar.

Pollution burdens associated with load/assemble/pack of an ap based MK-66 PIP motor by continuous and batch processing

Abstract The Clean Agile Manufacturing of Energetics (CAME) program was directed to identify major pollution sources and to propose life-cycle facility modifications which can reduce pollution burdens (Perry, W. J., Comprehensive Pollution Prevention Strategy—Memorandum for Secretaries of the Military Departments , et al., Department of Defense (11 August 1994). Potential avenues for pollution prevention are the use of advanced energetic and propellant materials, different product formulations, alternate chemical synthesis and load/assemble/pack (LAP) operations, and advanced demilitarization practices. The objective of this study was to compare batch and continuous processing of extruded composite propellant for the production of the motor for the MK-66 Safety Product Improvement Program (MK-66 PIP). The 2.75 inch motor uses an ammonium perchlorate based propellant formulation. Continuous processing of the motor is being developed and demonstrated as part of the Continuous Processing of Composite Propellant (CPOCP) program. The analysis compares an existing batch mixing and extrusion based production of 30,000 rocket motors to a proposed technology upgrade of continuous mixing and extrusion of the same composite propellant. Continuous processing offers a potentially lower cost and safer method of extrusion as the energetic material is subjected to high shear rates for a shorter period of time. Additional benefits include increased mixing efficiency, superior product homogeneity, and reduced wastes. The pollution burden was reduced using the proposed continuous process from 2.6 pounds of waste per pound of product to about one pound of waste per pound of product. This assumed that the product efficiency (number of motors produced to get the production goal of 30,000 certified motors) was the same for the batch and continuous processes. It was felt that the increased mixing efficiency and superior product homogeneity will make the continuous process more efficient.

Microrheological Origins of the Irreversible Flow of Suspensions

The hydrodynamic behavior observed for a sphere released under gravity in a Newtonian liquid is not consistent with that predicted by classical continuum theory when the sphere is near a solid wall. An irreversibility arises in the velocity of the sphere as it approaches and recedes from the plane that cannot be accounted for using continuum hydrodynamic equations alone. Earlier experiments on spheres falling from a plane were conducted under conditions such that this irreversibility could be attributed to the surface roughness of the spheres In this investigation, we extend these studies to situations where the pressure field between the receding sphere and the plane drops to the vapor pressure of the fluid and cavitation occurs. Experimental data support the theoretical prediction for a spheres motion based on the irreversible effect of cavitation and physical roughness in different flow regimes. The effects of these near‐contact irreversibilities on particle trajectories, shear‐induced self diffusion,...

A method to determine the effect of microscale heterogeneities on macroscopic web mechanics

The effect of a spatially heterogeneous density distribution on the development of defects during the transport of nonwoven webs through roller systems has been investigated numerically. A modeling approach has been developed by which the spatial heterogeneity in web mechanical properties can be characterized statistically and recreated for use in finite element simulations. The approach has been applied to model the transport of a carded nonwoven web, consisting of an agglomeration of polypropylene fibers bound together by a regular array of thermal bond points. The web was scanned optically to obtain a gray scale light distribution representing the local material density. Analysis of the local density distribution permitted the generation of “virtual webs” for use in heterogeneous finite element models, in which local mechanical properties were governed by local density. Virtual web response was investigated under two loading configurations; simple tensile testing, and web transport under tension through a three-roller system. The modeling approach provided results that were in good agreement with experimentally observed web mechanics, failure mechanisms, and processing instabilities. Spatial heterogeneity in material properties was found to strongly influence both general web behavior and the tendency for the web to incur manufacturing defects during transport through roller systems.