An investigation of hydraulic-line resonance and its attenuation

An investigation of fluid resonance in high-pressure hydraulic lines has been made with two types of fluid dampers (or filters) installed in the line. One type involved the use of one or more closed-end tubes branching at right angles from a main line, and the other type was a fluid muffler installed in-line. These devices were evaluated in forced vibration tests with oscillatory disturbances over a 1000-Hz range applied to one end of the line and with oscillatory pressures measured at various stations along the main pipe. Limited applications of acoustic-wave theory to the branched systems are also included. Results show varying attenuations of pressure perturbations, depending on the number and location of branches and the type of muffler. Up to three branches were used in the branch-resonator study, and the largest frequency range with maximum attenuation was obtained for a three-branch configuration. The widest frequency ranges with significant attenuations were obtained with two types of fluid mufflers

Influence of thermally induced chemorheological changes on the torsion of elastomeric circular cylinders

When an elastomeric material is deformed and subjected to temperatures above some characteristic value T cr (near 100 ∘ C for natural rubber), its macromolecular structure undergoes time and temperature-dependent chemical changes. The process continues until the temperature decreases below T cr . Compared to the virgin material, the new material system has modified properties (reduced stiffness) and permanent set on removal of the applied load.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/46097/1/161_2006_Article_9.pd

Viscoelastic hinge formation in beams

A constitutive equation for nonlinear viscoelasticity is used to model the mechanical response of solid polymers such as polycarbonate. The nonlinearity arises from a reduced time variable which causes stress relaxation to occur faster as strain increases. This constitutive equation is used to study the consequences of the interaction of the acceleration of stress relaxation with strain and the spatial variation of strain within the context of the structural theory of beams undergoing small displacements.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/41706/1/707_2005_Article_BF01182510.pd

Exhibition Layout and Visitor Movement in Science Museums

Two arguments are made based on the analysis of traveling science exhibitions. First, sufficiently refined techniques of spatial analysis allow us to identify the impact of layout upon visitors' paths and behaviors even in moderately sized open plans which afford almost random sequences of movement and relatively unobstructed visibility. Specifically, contact with exhibits is associated with their relative accessibility while active engagement is associated with exhibit cross-visibility. Second, newly developed or adapted techniques of analysis allow us to make a transition from modeling the mechanics of spatial movement (the way in which movement is affected by the distribution of obstacles and boundaries) to modeling the manner in which movement registers additional aspects of visual information, particularly the arrangement of exhibits according to conceptual organizing themes. The advantages of such purely spatial modes of analysis extend into providing us with a sharper understanding of some of the underlying constraints within which exhibition content is conceived and designed

Degradation and healing in a generalized neo-Hookean solid due to infusion of a fluid

The mechanical response and load bearing capacity of high performance polymer composites changes due to diffusion of a fluid, temperature, oxidation or the extent of the deformation. Hence, there is a need to study the response of bodies under such degradation mechanisms. In this paper, we study the effect of degradation and healing due to the diffusion of a fluid on the response of a solid which prior to the diffusion can be described by the generalized neo-Hookean model. We show that a generalized neo-Hookean solid - which behaves like an elastic body (i.e., it does not produce entropy) within a purely mechanical context - creeps and stress relaxes when infused with a fluid and behaves like a body whose material properties are time dependent. We specifically investigate the torsion of a generalized neo-Hookean circular cylindrical annulus infused with a fluid. The equations of equilibrium for a generalized neo-Hookean solid are solved together with the convection-diffusion equation for the fluid concentration. Different boundary conditions for the fluid concentration are also considered. We also solve the problem for the case when the diffusivity of the fluid depends on the deformation of the generalized neo-Hookean solid.Comment: 24 pages, 10 figures, submitted to Mechanics of Time-dependent Material

Slow viscoelastic flow in tilted troughs

In viscoelastic flow of an incompressible fluid down a straight trough of arbitrary cross-section, the normal stress effect produces a distortion of the free surface. In slow flow, the shape is given in the lowest order of approximation in terms of the axial velocity for Newtonian flow. Equations governing the second-order perturbation are derived. Beim viskoelastischen Strömen einer inkompressiblen Flüssigkeit entlang einer geneigten geraden Rinne beliebigen Querschnittes erzeugt der Normalspannungseffekt eine Verzerrung der freien Oberfläche. Deren Form ist bei langsamer Strömung in erster Näherung durch die Axialgeschwindigkeit für Newton sche Strömung bestimmt. Die Gleichungen der Näherung zweiter Ordnung werden hergeleitet.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/41711/1/707_2005_Article_BF01176732.pd

New universal relations for nonlinear isotropic elastic materials

A nonlinear isotropic elastic block is subjected to a homogeneous deformation consisting of simple shear superposed on triaxial extension. Two new relations are established for this deformation which are valid for all nonlinear elastic isotropic materials, and hence are universal relations. The first is a relation between the stretch ratios in the plane of shear and the amount of shear when the deformation is supported only by shear tractions. The second relation is established for a thin-walled cylinder under combined extension, inflation and torsion. Each material element of the cylinder undergoes the same local homogeneous deformation of shear superposed on triaxial extension. The properties of this deformation are used to establish a relation between pressure, twisting moment, angle of twist and current dimensions when no axial force is applied to the cylinder. It is shown that these relations also apply for a mixture of a nonlinear isotropic solid and a fluid.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/42675/1/10659_2004_Article_BF00042450.pd

The influence of the representative volume element (RVE) size on the homogenized response of cured fiber composites

The influence of the representative volume element (RVE) size (in terms of fiber packing and number of fibers for a given fiber-volume fraction) on the residual stresses created during the curing process of a continuous fiber-reinforced polymer matrix tow is investigated with the ultimate goal of finding a minimum unit cell size that can be used later for a homogenization procedure to calculate the response of woven fiber textile composites and in particular, fiber tows. A novel network curing model for the solidification of epoxy is used to model the curing process. The model takes into account heat conduction, cure kinetics and the creation of networks in a continuously shape changing body. The model is applied to the curing of a fiber/matrix RVE. The results for the minimum size of the RVE, obtained on the basis of the curing problem, are compared with a similar RVE, modeled as an elastic–plastic solid subjected to external loads, in order to compare the minimum RVE sizes obtained on the basis of different boundary value problem solutions.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/98620/1/0965-0393_20_7_075007.pd

Barriers to Improving Primary Care of Depression: Perspectives of Medical Group Leaders

Using clinical trials, researchers have demonstrated effective methods for treating depression in primary care, but improvements based on these trials are not being implemented. This might be because these improvements require more systematic organizational changes than can be made by individual physicians. We interviewed 82 physicians and administrative leaders of 41 medical groups to learn what is preventing those organizational changes. The identified barriers to improving care included external contextual problems (reimbursement, scarce resources, and access to/communication with specialty mental health), individual attitudes (physician and patient resistance), and internal care process barriers (organizational and condition complexity, difficulty standardizing and measuring care). Although many of these barriers are challenging, we can overcome them by setting clear priorities for change and allocating adequate resources. We must improve primary care of depression if we are to reduce its enormous adverse social and economic impacts

Exploratory Design of Animal Habitats Within an Immersive Virtual Environment

One of the first useful applications of virtual environments (VEs) was the architectural walkthrough, in which users view buildings or other structures in a natural, interactive manner. The obvious next step is to allow the user to create or modify designs while immersed in the virtual world, but such "immersive design" systems have not generally been successful, because of a lack of constraints, the inability to perform precise input, the difficulty of performing tasks while immersed, and the fact that designers generally have not been trained to design in all three dimensions, especially in the beginning stages of a project. We present an immersive design application, aimed at university-level architecture students, which addresses these issues. Users of the system are immersed within an existing zoo habitat, and can make modifications and enhancements to the exhibit, using a set of efficient and complementary interaction techniques for navigation, object manipulation, and system control. A usability study has shown that because the students are not creating a complete design, but rather making constrained modifications to an existing one, interesting and unique designs can be achieved in a short time