Engineering Commons^™

Internally Constrained Mixtures Of Elastic Continua, Stephen M. Klisch

Mechanical Engineering

A treatment of internally constrained mixtures of elastic continua at a common temperature is developed. Internal constraints involving the deformation gradient tensors and the common mixture temperature are represented by a constraint manifold, and an internally constrained mixture of elastic continua is associated with each unique equivalence class of unconstrained mixtures. The example of intrinsic incompressibility of each constituent first proposed by Mills is discussed.

Application Of A Fiber-Reinforced Continuum Theory To Multiple Deformations Of The Annulus Fibrosus, Stephen M. Klisch, Jeffrey C. Lotz

Mechanical Engineering

Accurate tissue stress predictions for the annulus fibrosus are essential for understanding the factors that cause or contribute to disc degeneration and mechanical failure. Current computational models used to predict in vivo disc stresses utilize material laws for annular tissue that are not rigorously validated against experimental data. Consequently, predictions of disc stress resulting from physical activities may be inaccurate and therefore unreliable as a basis for defining mechanical–biologic injury criteria. To address this need we present a model for the annulus as an isotropic ground substance reinforced with two families of collagen fibers, and an approach for determining the …

A Compensated Acoustic Actuator For Systems With Strong Dynamic Pressure Coupling, Charles Birdsong, Clark J. Radcliffe

Mechanical Engineering

This study improves the performance of a previously developed acoustic actuator in the presence of an acoustic duct system with strong pressure coupling. The speaker dynamics and the acoustic duct dynamics are first modeled separately. The two systems are then coupled, and the resulting system is modeled. A velocity sensor is developed and used in feedback compensation. The resulting speaker system has minimal magnitude and phase variation over a 20–200 Hz bandwidth. These conclusions are verified through experimental results.

Use Of Polyurethane Material Models For Simulating Leg-Form Impact In Different Explicit Finite Element Codes, Joe Hassan, Peter Schuster, G. Frederick

Mechanical Engineering

Compressible plastic foams are used throughout the interior and bumper systems of modern automobiles for safety enhancement and damage prevention. Consequently, modeling of foams has become very important for automobile engineers. To date, most work has focused on predicting foam performance up to approximately 80% compression. However, in certain cases, it is important to predict the foam under maximum compression, or 'bottoming-out.' This paper uses one such case-a thin low-density bumper foam impacted by a pedestrian leg-form at 11.1 m/s-to investigate the 'bottoming-out' phenomenon. Multiple material models in three different explicit Finite Element Method (FEM) packages (RADIOSS, FCRASH, and LS-DYNA) …

Determination Of Bumper Styling And Engineering Parameters To Reduce Pedestrian Leg Injuries, Peter J. Schuster, Bradley Staines

Mechanical Engineering

The European Commission is proposing legislation aimed at reducing the severity of injuries sustained by pedestrians in the event of an impact with the front-end of a motor vehicle. One aspect of this proposed legislation is reducing the pedestrian's leg injuries due to contact with the bumper and frontal surfaces of a vehicle, assessed using a 'pedestrian leg impact device,' or 'leg-form.'

This proposed legislation presents the challenge of designing a bumper system which achieves the required performance in the leg-form impact-without sacrificing the bumper's primary function of vehicle protection during low-speed impacts. The first step in meeting this challenge …

Distributed Activation Energy Model Of Heterogeneous Coal Ignition, John C. Chen

Mechanical Engineering

We present a model that simulates the conventional tube-furnace experiment used for ignition studies. The Distributed Activation Energy Model of Ignition accounts for particle-to-particle variations in reactivity by having a single preexponential factor and a Gaussian distribution of activation energies among the particles. The results show that the model captures the key experimental observations, namely, the linear increase in ignition frequency with increasing gas temperature and the variation of the slope of the ignition frequency with oxygen concentration. The article also shows that adjustments to the model parameters permit a good fit with experimental data.

Observation Of Laser Ignition And Combustion Of Pulverized Coals, John C. Chen, Masayuki Taniguchi, Kazuyuki Ito

Mechanical Engineering

Direct observation of pulsed-laser ignition and combustion of pulverized coals with a high speed video has been made. A dilute stream of particles was dropped into a laminar, upward-flow wind tunnel with a quartz test section. The gas stream was not preheated. A single pulse from a Nd:YAG laser was focused through the tunnel and ignited several particles. The transparent test section and cool walls allowed for optical detection of the reaction sequence. The ignition and combustion behaviours of amorphous carbon spheres and an anthracite were as expected for heterogeneous ignition and reaction. Surprisingly, the reaction of a high volatile …

Optimization Of Expanded Polypropylene Foam Coring To Improve Bumper Foam Core Energy Absorbing Capability, Gregory Frederick, Gregory A. Kaepp, Conrad M. Kudelko, Peter J. Schuster, Friedrich Domas, Udo G. Haardt, Werner Lenz

Mechanical Engineering

To design a cost, weight, and energy efficient bumper foam energy absorber, it is important to consider optimizing the shape of coring employed in the design of the system. In this paper, a number of foam coring patterns are studied by both empirical and analytical methods. The size and shape of proposed core designs are studied in detail with consideration given to several different densities of expanded polypropylene (EPP) foam. Using the finite element method of structural analysis, it is possible to have an inside look at the stress distribution during deformation of foam structures. An optimization study using the …

Ignition And Combustion Properties Of Pulverized Coal Suspended In Laminar Upward Flow Under High Heating Rate Condition, Masayuki Taniguchi, John C. Chen, Kiyoshi Narato, Kazuyuki Ito, Hiroshi Miyadera, Kazuhiko Kudo

Mechanical Engineering

Ignition and combustion behaviors were observed for pulverized coal particles which were suspended in a laminar upward flow and were heated by a single pulse Nd : YAG laser. The surface temperature of the particles was estimated to increase at a rate of about 10⁶K/s. For a bituminous coal, observations with high-speed video revealed that the coal particles ignited heterogeneously 1-2ms after the laser pulse operation and this was followed by the evolution of volatile materials and their combustion in the gas phase. A rate constant of surface oxidation reaction of the bituminous coal at a temperature range …

A Radiant Flow Reactor For High-Temperature Reactivity Studies Of Pulverized Solids, John C. Chen, Stephen Niksa

Mechanical Engineering

Our radiant two‐phase flow reactor presents several new possibilities for high‐temperature reactivity studies. Most importantly, the thermal histories of the suspension and entrainment gas can be independently regulated over wide ranges. At low suspension loadings, outlet temperatures can differ by hundreds of degrees and gas temperatures are low enough to inhibit hydrocarbon cracking chemistry, so primary products are quenched as soon as they are expelled. With coal suspensions, tars were generated with the highest H/C ratio and lowest proton aromaticity ever reported. Alternatively, particles and gas can be heated at similar rates to promote secondary chemistry by increasing particle loading. …

Suppressed Nitrogen Evolution From Coal-Derived Soot And Low-Volatility Coal Chars, John C. Chen, Stephen Niksa

Mechanical Engineering

This laboratory study uses a novel furnace to resolve nitrogen evolution during the three stages of pulverized coal combustion: primary devolatilization, secondary pyrolysis, and combustion. The behavior of six coals depicts continuous rank variations, as well as suppressed nitrogen evolution from low volatility coals. During primary devolatilization of any coal, aromatic compounds in tar and oils are virtually the only shuttles for nitrogen out of the coal matrix. The small amounts of HCN observed while primary devolatilization winds down probably come from the char, because char particles are significantly hotter than tar in these experiments. Secondary pyrolysis promotes additional HCN …

The Use Of A High Level Cfd Code In Engineering Education, J.E.S. Venart, P. Lemieux, A.C.M. Sousa, D. Tatchell

Mechanical Engineering

An advanced multipurpose Computational Fluid Dynamics (CFD) code, FloSYS, developed for use in a CAD/CAE environment has been utilized in undergraduate and graduate courses in heat transfer. Problems are introduced at an introductory level in: -steady 2- and 3-dimensional conduction, -transient 1-, 2-, and 3-dimensional conduction, -free convective cavity flow with conjugate heat transfer, and -turbulent flows with heat transfer. More sophisticated problems, related to the use of porous media concepts for modelling heat exchangers, and compartment fire modelling are introduced at a more senior level. After one year's experimental use, the CFD code is being recommended for use in …