Rod Velocity Research Articles

Piston rod seal and scraper ring interaction in hydraulic cylinders

In this work the problem of hydrodynamic cooperation and the inter action of piston rod seals and scraper rings is treated. The theory used is an extention of the hydrodynamic theory for single-seal elements presented earlier by the author. This theory is in turn based on the inverse hydrodynamic theory. A computer program, SIMPROS, for simulation of the performance of different seal element combinations has been developed. The following data are input data to the program: data describing running conditions such as sealed pressure, fluid viscosity and piston rod velocity; data describing the geometry of the surroundings of the seal elements; the static pressure distribution in the two seal contacts. The program considers the possibilities of cavitation, starvation and pressure build-up, and the following results are presented after a program run: leakage flow and total frictional force; fluid film thickness distributions in the two seal contacts; “cavitation degrees” and pressures in the parallel clearances. The function of the program is demonstrated with a test example.

The transport properties of rod-like particles via molecular dynamics. I. Bulk fluid

Molecular dynamics studies of pure bulk fluids of hard, infinitely thin rods are reported. In the semidilute fluid above 70 rods/L3, the rotational diffusion coefficient scales with concentration, with an exponent approaching, but not reaching −2, the value predicted by the Doi–Edwards theory. We estimate the semidilute transition concentration to be at least 70 rods/L3, a concentration twice as large as previously reported from simulations of this rod fluid, but more consistent with recently published theoretical estimates. In the Doi–Edwards theory, a given rod executes a series of step rotations through a sequence of ‘‘cages’’ formed by neighboring rods. Using the simulation results, we estimate a value of τt, the average lifetime of a cage. As one would expect from the Doi–Edwards theory, we find that τt decreases sharply when we turn off the hard core repulsive interactions between the rods which comprise the cages. This result is in disagreement with a recently published Brownian dynamics study. In a previous molecular dynamics study of this model rod fluid, the translational self-diffusion coefficient was observed to increase with concentration above 30 rods/L3; an increase attributed in the theory of Frenkel and Maguire to the decreasing amount of rotational motion. Our results confirm the increase above 30 rods/L3. However, at higher concentrations the theory is inadequate; it underestimates the diffusivity and the lifetime of the rod velocity along its axis.

Finite hard rod systems and their thermodynamic limit. II. Ergodic properties, pair distribution function, and equation of state

Generalizing a trick used previously for one- and two-particle systems we obtain closed expressions for the positions and velocities of the hard rods as functions of time and the initial conditions. Using the corresponding solution of Liouville’s equation we show which ensembles can be used to calculate time averages and discuss the conditions under which an expectation value tends toward a stationary value. We also calculate the pair distribution function for almost all stationary distributions and the pressure, defined as the time average of the force exerted onto a specified particle by its left neighbor, for three kinds of stationary ensembles (smallest stationary, microcanonical, and canonical).

Coefficient of Dynamic Friction Via Analog Computer Data Reduction

This paper describes a technique to determine the effective coefficient of dynamic friction from experimental data. The experiment consists of a rod that is being inserted in a test vessel which is subjected to a sinusoidal vibration input. The rod is impacted by three bushings. The actual impact forces are measured with three strain bolts per bushing. These nine impact forces, as well as rod position, are recorded continuously on an FM magnetic tape for playback and analysis. The data reduction is performed on an analog computer. All pertinent forces affecting vertical rod motion, i.e. gravity, fluid drag, buoyancy, and friction, as well as rod position and velocity, are included in this simulation. The end result of the analysis is the value of the effective coefficient of dynamic friction during a sinusoidal excitation. The analysis is straightforward and based on first principles. Results to date show excellent repeatability and accuracy.

Analytical investigation of a one-dimensional homogenized model for a pressurized water reactor core

A one-dimensional homogenized model for dynamic fluid-structure interaction in a pressurized water reactor core is used to study the influence of the virtual density and spacer's stiffness. The model consists of a linear system of partial differential equations for fluid velocity, rod velocity and pressure. For these equations analytical solutions are deduced for boundary conditions prescribing either periodic wall oscillations or linearly growing wall accelerations from rest. The theoretical model for the virtual density is verified by comparison to an experiment. For zero spacer stiffness, purely acoustic oscillations appear. For positive spacer stiffness, additional oscillations arise with relative rod motions. The wavelengths of the latter oscillations are small for weak spacers. Large numerical effort would be required in a more complete three-dimensional core-model to resolve such short wave lengths. In fact in a typical core the spacer's stiffness c s is small in comparison to the fluid bulk modulus K. For c s K ⩽0.1 it might be appropriate to neglect the influence of the spacers.

Laminar flow between a circular tube and a cylindrical eccentric capsule

AbstractThe fully‐developed laminar flow between a circular tube and an eccentric moving cylindrical rod is predicted for eccentricities between zero and unity. For eccentricities less than unity, an earlier solution is extended to account for arbitrary rod (capsule) velocities; useful shear force expression in closed form are given. An entirely new solution for the fully eccentric case is presented.

Comparison of Two- and Three-Dimensional Calculations of Super Prompt Critical Excursions

Calculations of super prompt critical excursions induced by ramp variation of absorption cross sections are performed in various geometries (r, xy, rz, xyz). The time behavior of neutron flux and fuel temperature is analyzed, especially with regard to their dependence on geometry and rod velocity. The evaluations establish the need for genuine three-dimensional calculations to correctly predict peak flux and temperature distributions for situations where space-dependent feedback effects are essential.

Falling coaxial cylinder viscometry of polymer melts

AbstractThis article considers possible erxors in experiment or analysis and alternative methods of data treatment for a falling coaxial cylinder viscometer. The viscometer uses a weighted rod falling into a polymer melt contained in a closed end concentric cylinder. Flow relations can be solved for non‐Newtonian fluid response in steady, simple shearing flow. Although the rod fall is found not to be steady, as assumed, this produces negligible error in the computed flow curves. Consistent flow curves which were independent of apparatus geometry were obtained by a method in which instantaneous rod velocities were estimated graphically from raw data and an end correction was taken into account.

Particle motions in non-Newtonian media

An experimental study of the behaviour of rigid and deformable particles suspended in pseudoplastic and elasticoviscous liquids undergoing slowCouette flow was undertaken. The velocity profiles deviated slightly from those obtained forNewtonian fluids, but the measured angular velocities of rigid spheres showed that the rotation of the field was equal to half the velocity gradient. While the measured angular velocities of rods and discs were in accord with theory applicable toNewtonian liquids, in both non-Newtonian media there was a steady drift in the orbit towards an asymptotic value corresponding to minimum energy dissipation in the flow. Furthermore, discs in elasticoviscous solutions of polyacrylamide at higher shear stresses aligned themselves in the direction of the flow and ceased to rotate.

Particle Motions in Non-Newtonian Media. II. Poiseuille Flow

The behavior of rigid and deformable particles suspended in pseudoplastic and elasticoviscous liquids undergoing tube flow was studied. The velocity profiles were more blunted than those obtained for Newtonian fluids and, as in Couette flow, the measured angular velocities of rigid spheres, rods, and discs were in accord with the theory for Newtonian liquids. There was also a drift in the orbit of the cylinders to limiting values corresponding to minimum energy dissipation in the flow. In elasticoviscous liquids, rigid particles migrated across the planes of shear towards the tube axis whereas in pseudoplastic liquids, the opposite was observed, rigid spheres actually coming in contact with the wall. The lateral migration of deformed liquid drops in elasticoviscous fluids was, as in Newtonian systems, towards the tube axis whereas in pseudoplastic liquids the drops attained an equilibrium position between the tube wall and axis. An accumulation of rigid spheres behind an advancing suspension-air meniscus was observed in elasticoviscous media at all initial volume concentrations, the rates of accumulation increasing with flow rate and particle size. In the pseudoplastic fluids, however, there was a dilution at concentrations less than 10% followed by an accumulation at higher values but the rates of accumulation decreased with increasing flow rate and particle size. As in the Couette flow of non-Newtonian suspension, it was not possible to interpret the observed radial migration of the particles in terms of the known rheological properties of the suspending fluids.

Spherical Waves Coupled to a One-Dimensional Wave Guide

An approximate expression is derived for the disturbance in a one-dimensional wave guide resulting from an expanding spherical wave which is loosely coupled to the wave guide at all points along its length. For the case of a slender rod immersed in a fluid, curves are presented showing axial strain for three ratios of rod velocity to fluid velocity.

Spherical Waves Coupled to a One-Dimensional Wave Guide

Expressions are derived for the disturbance in a one-dimensional wave guide resulting from an expanding spherical wave which is loosely coupled to the wave guide at all points along its length. The example treated is a slender solid rod immersed in a fluid, and curves are presented showing axial stress, strain, and particle velocity due to an expanding step function rise in pressure. When rod velocity is higher than fluid velocity the first signal observed follows the refraction path, and the onset of a secondary signal coincides with the passage of the pressure front in the fluid. When the two velocities are equal, only one signal is observed, and its amplitude increases with distance from the source. When rod velocity is smaller, the first signal coincides with the passage of the pressure front, and a weak secondary signal appears to travel from the point nearest the source at rod velocity. These results are an extension of the approximate theory presented by White [J. Acoust. Soc. Am. 25, 906 (1953)].

Account of a new steam, and heated air engine

The behaviour of an elastomeric seal for a pneumatic cylinder piston is analysed in this work. The aim of the paper is to validate experimentally a numerical approach to evaluate seal performance, in actual working conditions.The friction force between seal and the cylinder bore is evaluated through experimental tests and numerical simulations, using a finite element model. Working conditions are simulated for different piston rod velocity and cylinder supply pressure, both in dry conditions, boundary and fluid lubrication conditions. Simulation is obtained by an iterative process that uses the friction coefficient, experimentally measured, as a function of speed and lubrication conditions. Results obtained from experimental tests and numerical simulation are compared to determine the friction force between seal and cylinder bore.