Mechanical Engineering Commons^™

The Role Of Ball Backspin Alignment And Variability In Basketball Shooting Accuracy, Nathan Slegers, Dave Love

Faculty Publications - Biomedical, Mechanical, and Civil Engineering

Interaction between the shooting hand and ball at the moment a basketball is released generates a three dimensional backspin of the ball. This study is the first to investigate how characteristics of the backspin alignment and variability contribute to lateral shooting accuracy. Spin axis (SA) direction and backspin magnitude were measured on 25 shot attempts for 26 collegiate basketball players (male: n = 16, female: n = 10). The mean SA alignment, as viewed from the shooting hand side, was found to be tipped down and towards the target (p < 0.001). Standard deviations (SD) in the SA alignment were strong predictors of lateral accuracy (vertical SD: r = 0.80, p < 0.001, forward-backward SD: r = 0.51, p = 0.01), with variation in the vertical alignment being the best predictor. No significant correlation between mean SA misalignment and lateral accuracy was observed. However, intra-individual relationships between SA misalignment and lateral error revealed that individuals tended to have 0.17 degrees more misalignment for each cm of lateral error (p < 0.001, 95% CI: 0.24–0.09). These indicate that while an individual’s mean alignment may not predict lateral accuracy, improving one’s SA alignment and reducing alignment variability may increase lateral accuracy.

Factors Influencing Household Solar Adoption In Santiago, Chile, Jeffrey P. Walters, Jessica Kaminsky, Claudio Huepe

Faculty Publications - Biomedical, Mechanical, and Civil Engineering

In Santiago, Chile, the market conditions are seemingly excellent for the household adoption of photovoltaic (PV) technology, yet the uptake is negligible. To explore this paradox, the authors conducted a Delphi study to solicit the knowledge of a panel of Chilean PV experts. These efforts yielded 26 factors—both motivations and barriers—impacting the diffusion of PV in Santiago. Of the 26, experts were in consensus on the relative importance of 21. The literature suggests that diffusion of PV technologies is influenced by complex technical, economic, and social factors. Similarly, the experts saw influence from financial, environmental, and energy supply (e.g., electrical …

Gust Mitigation Of Micro Air Vehicles Using Passive Articulated Wings, Adetunji Oduyela, Nathan Slegers

Faculty Publications - Biomedical, Mechanical, and Civil Engineering

Birds and insects naturally use passive flexing of their wings to augment their stability in uncertain aerodynamic environments. In a similar manner, micro air vehicle designers have been investigating using wing articulation to take advantage of this phenomenon. The result is a class of articulated micro air vehicles where artificial passive joints are designed into the lifting surfaces. In order to analyze how passive articulation affects performance of micro air vehicles in gusty environments, an efficient 8 degree-of-freedom model is developed. Experimental validation of the proposed mathematical model was accomplished using flight test data of an articulated micro air vehicle …

High-Efficiency Thrust Vector Control Allocation, Jeb S. Orr, Nathan Slegers

Faculty Publications - Biomedical, Mechanical, and Civil Engineering

A generalized approach to the allocation of redundant thrust vector slew commands for multi-actuated launch vehicles is presented, where deflection constraints are expressed as omniaxial or elliptical deflection limits in gimbal axes. More importantly than in the aircraft control allocation problem, linear allocators (pseudoinverses) are preferred for large booster applications to facilitate accurate prediction of the control-structure interaction resulting from thrust vectoring effects. However, strictly linear transformations for the allocation of redundant controls cannot, in general, access all of the attainable moments for which there is a set of control effector positions thatsatisfles the constraints. In this paper, the control …

Learning From Failure In Systems Engineering: A Panel Discussion, Nathan Slegers, Ronald T. Kadish, Gary E. Payton, John Thomas, Michael D. Griffin, Dan Dumbacher

Faculty Publications - Biomedical, Mechanical, and Civil Engineering

This paper summarizes the discussion of the Learning from Failure in Systems Engineering panel that was held in Huntsville, AL on November 8, 2010. The panel objective was to discuss how systems engineers respond to and learn from failure and identify future directions important to the community. The panel consisted of four representatives with experience in government, industry, and academia: (1) Ronald Kadish from Booz Allen Hamilton and former director of the Missile Defense Agency, (2) Gary Payton, retired Deputy Under Secretary of the Air Force for Space Programs, (3) John Thomas from Booz Allen Hamilton and President-elect of INCOSE, …

Non-Isothermal Cool Flames In Unstirred Static Reactors: A Compressible Model With Global Kinetics, Michael R. Foster, Howard Pearlman

Faculty Publications - Biomedical, Mechanical, and Civil Engineering

A compressible model is developed with kinetics based on the Wang–Mou five-step global kinetic scheme and used to evaluate the temperature, concentration, and velocity fields characteristic of low temperature combustion in unstirred static reactors. This work relaxes the assumption of small exothermicity that enabled prior studies to employ the Boussinesq approximation, valid for cases where BT << 1, i.e., slow reactions and cool flames. In this study, the range of validity of the model is extended to cases with large temperature excursions, including multi-stage ignition. For the weakly exothermic cases considered, including modes of slow reaction and cool flames, the Boussinesq approximation is completely adequate. However, it overpredicts the density change and underpredicts the ignition delay time for high-temperature ignitions. Qualitative comparison with experimental results acquired at microgravity conditions are also discussed.

A Method For Defining Wind Turbine Setback Standards, Jonathan Rogers, Nathan Slegers, Mark Costello

Faculty Publications - Biomedical, Mechanical, and Civil Engineering

Setback distances established by regulatory authorities to minimize the probability of blade fragment impact with roads, structures and infrastructure can often have a significant impact on wind farm development. However, these minimum distance requirements typically rely on arbitrary rules of thumb and are not based on a physical or probabilistic analysis of blade throw. The work reported here uses a probabilistic approach to evaluate the effectiveness of current standards and to propose a new technique for determining setback distances. This is accomplished through the use of a dynamic model of wind turbine blade failure coupled with Monte Carlo simulation techniques …

Techniques From Workshops On Teaching: Implementing The Concepts And Evaluating Our Approaches, Michael R. Foster, Justin R. Vander Werff

Faculty Publications - Biomedical, Mechanical, and Civil Engineering

The challenges for new engineering educators abound and there are never enough hours in a day or days in a week. Young educators may lack confidence in course subject material given that they have never taught (the topic and/or in a classroom) before. In addition, their knowledge of teaching pedagogy and classroom management strategies often lacks refinement since their education is almost exclusively in a field of engineering rather than education. Teaching workshops have been developed to expose instructors in higher education to practical teaching pedagogy and effective classroom management. These workshops often emphasize research-based methods including use of clearly …

Modeling The Risk Of A Failed Wind Turbine Blade Impacting A Power Transmission Line, Nathan Slegers, Jonathan Rogers, Mark Costello, Maria Puga, Patricia Arons

Faculty Publications - Biomedical, Mechanical, and Civil Engineering

Wind turbine installations are generally situated in proximity to power transmission lines that integrate generated power into the grid. Failure of a wind turbine that results in a blade or blade fragment thrown from the rotor can result in impact with a transmission line and lead to significant transmission line damage. The work reported here creates a mathematical model to assess the risk of this type of failure event occurring as a function of wind turbine characteristics and the relative position of the power transmission line. A comprehensive rotor blade flight dynamic simulation tool comprised of a rigid body representation …

Detection Of Voids In Prestressed Concrete Bridges Using Thermal Imaging And Ground-Penetrating Radar, David G. Pollock, Kenneth J. Dupuis, Benjamin Lacour, Karl R. Olsen

Faculty Publications - Biomedical, Mechanical, and Civil Engineering

Thermal imaging and ground-penetrating radar was conducted on concrete specimens with simulated air voids. For the thermal imaging inspections, six concrete specimens were constructed during the month of June 2007 to simulate the walls of post-tensioned box girder bridges. The objective was to detect simulated air voids within grouted post-tensioning ducts, thus locating areas where the post-tensioning steel strands are vulnerable to corrosion. The most important deduction taken from these inspections was that PT-ducts and simulated voids were more detectable in the 20 cm (8 in.) thick specimens than in the 30 cm (12 in.) thick specimens. While inspections of …

The Role Of Diffusive Transport On Low And Intermediate Temperature Hydrocarbon Oxidation: Closed Reactor Experiments Using Equimolar N-Butane + Oxygen Premixtures At Reduced-Gravity, Howard Pearlman, Michael R. Foster

Faculty Publications - Biomedical, Mechanical, and Civil Engineering

Experiments were conducted in a closed, spherical reactor aboard NASA's KC-135 reduced-gravity aircraft using an equimolar n-C4H10 + 0 2 premixture ( Le = 1.3) at subatmospheric · pressures to compliment model predictions and further explore the reactive-diffusive structure of cool flames and ignitions. The pressure and radial temperature histories were recorded and analyzed for different initial conditions. In addition, the visible light emission from excited formaldehyde was recorded using an intensified video camera and was observed to be radially symmetric in all cases. Unexpectedly, however, the measured temperature distributions during (and after the passage of) the cool flames and …

Predictive Control Of A Munition Using Low-Speed Linear Theory, Nathan Slegers

Faculty Publications - Biomedical, Mechanical, and Civil Engineering

"Modified linear theory provides reasonable impact predictions at high speeds. However, for typical small UAS mission speeds, less than 20-m/s impact errors were substantial due to large angles of attack and pitch rates. Low-speed linear theory was developed by including higher-order terms involving w and q that modified linear theory neglects. As a result, the angle of attack, pitch, and yaw predictions are significantly improved, leading to accurate impact predictions even at very low speeds. A predictive control scheme was developed to reduce dispersion using control surfaces near the tail. The predictive controller uses low-speed linear theory to rapidly predict …

The Role Of Diffusive Transport On Low And Intermediate Temperature Hydrocarbon Oxidation: Numerical Simulations Using The Wang-Mou Mechanism, Howard Pearlman, Michael R. Foster

Faculty Publications - Biomedical, Mechanical, and Civil Engineering

The spatio-temporal temperature and species concentration distributions associated with low and intermediate temperature hydrocarbon oxidation are computed using a global thermo kinetic scheme augmented with diffusive transport. The scheme used for the computations was proposed by Wang and Mou and is extended to include diffusion of species and heat. The conservation equations for species and energy are then derived and solved for a one-dimensional and an axisymmetric, spherical domain for temperatures ranging from 540 to 660 Kat subatmospheric pressures. The predictions are then used to develop ignition diagrams for different Lewis ( Le) numbers. Increasing Le is found to promote …

Cool Flame Propagation Speeds, Michael R. Foster, Howard Pearlman

Faculty Publications - Biomedical, Mechanical, and Civil Engineering

Cool flames are studied at reduced-gravity in a closed, unstirred, spherical reactor to minimize complexities associated with natural convection. Under such conditions, transport is controlled by diffusive fluxes and the flames are observed to propagate radially outward from the center of the reactor toward the wall. Intensified video records are obtained and analyzed to determine the flame radius as a function of time for different vessel temperatures (593–623 K) and initial pressures (55.2–81.4 kPa) using an equimolar (Ø = 5) propane-oxygen premixture. Polynomial-fits are applied to the data and differentiated to determine the cool flame propagation speeds. In nearly …

Cool Flames At Terrestrial, Partial, And Near-Zero Gravity, Michael R. Foster, Howard Pearlman

Faculty Publications - Biomedical, Mechanical, and Civil Engineering

Natural convection plays an important role in all terrestrial, Lunar, and Martian-based, unstirred, static reactor cool flame and low-temperature autoignitions, since the Rayleigh number (Ra) associated with the self-heating of the reaction exceeds the critical Ra (approximately 600) for onset of convection. At near-zero gravity, Ra < 600 can be achieved and the effects of convection suppressed. To systematically vary the Ra without varying the mixture stoichiometry, reactor pressure, or vessel size, cool flames are studied experimentally in a closed, unstirred, static reactor subject to different gravitational accelerations (terrestrial, 1g; Martian, 0.38g; Lunar, 0.16g; a n dr e - duced gravity, ∼10−2g). Representative results show the evolution of the visible light emission using an equimolar n-butane:oxygen premixture at temperatures ranging from 320 to 350 ◦C (593–623 K) at subatmospheric pressures. For representative reduced-gravity, spherically propagating cool flames, the flame radius based on the peak light intensity is plotted as a function of time and the flame radius (and speed) is calculated from a polynomial fit to data. A skeletal chemical kinetic Gray-Yang model developed previously for a one-dimensional, reactive– diffusive system by Fairlie and co-workers is extended to a two-dimensional axisymmetric, spherical geometry. The coupled species, energy, and momentum equations are solved numerically and the spatio-temporal variations in the temperature profiles are presented. A qualitative comparison is made with the experimental results.

Transient Heat Partition Factor For A Sliding Railcar Wheel, T C. Kennedy, C Plengsaard, Robert F. Harder

Faculty Publications - Biomedical, Mechanical, and Civil Engineering

During a wheel slide the frictional heat generated at the contact interface causes intense heating of the adjacent wheel material. If this material exceeds the austenitising temperature and then cools quickly enough, it can transform into martensite, which may ultimately crack and cause wheel failure. A knowledge of the distribution of the heat partitioned into the wheel and the rail and the resulting temperature fields is critical to developing designs to minimize these deleterious effects. A number of theoretical solutions have appeared in the literature to model the thermal aspects of this phenomenon. The objective of this investigation was to …

An Existing Global Heptane Mechanism Augmented With Diffusive Transport, Michael R. Foster, Howard Pearlman

Faculty Publications - Biomedical, Mechanical, and Civil Engineering

The couplings between diffusive transport and the temperature and species concentration distributions associated with low and intermediate temperature heptane oxidation are explored using an existing four-step heptane mechanism, tuned for elevated pressures. The energy and species concentration equations are augmented with diffusive fluxes for heat and species and solved numerically in a one-dimensional domain. The ignition delay times are also tabulated and compared with the zero-dimensional data reported in the literature.

Cool Flames In Propane-Oxygen Premixtures At Low And Intermediate Temperatures At Reduced-Gravity, Howard Pearlman, Michael R. Foster, Devrez Karabacak

Faculty Publications - Biomedical, Mechanical, and Civil Engineering

No abstract provided.

Reliability Indices For Bolted And Nailed Connections In Wood Structures, David Pollock, Donald A. Bender

Faculty Publications - Biomedical, Mechanical, and Civil Engineering

Recently published test data for bolted and nailed connections was evaluated to assess the structural reliability inherent in current allowable stress design procedures for connections in wood structures. Reliability indices were determined for timber connections using standard firstorder, second moment (FOSM) procedures. For the connections considered in this study, reliability indices range from 2.6 to5.1, generally providing higher levels of safety than the structural members in timber structures.

Application Of Dynamic System Identification To Timber Beams - Part Ii, S T. Peterson, D I. Mclean, M D. Symans, David Pollock, W F. Cofer, R N. Emerson, Kenneth J. Fridley

Faculty Publications - Biomedical, Mechanical, and Civil Engineering

In a companion paper, a method of global nondestructive evaluation (NDE) for identifying local damage and decay in timber beams was developed and verified analytically using a finite-element model of a timber beam. The previously presented method of damage localization employs experimental modal analysis and an algorithm that monitors changes in modal strain energy between the mode shapes of a damaged beam with respect to the undamaged state of the beam. In this second part of a two-part paper, experimental laboratory tests on simply supported timber beams are presented to verify the capabilities and determine the limitations of the proposed …

Application Of Dynamic System Identification To Timber Beams - Part I, S T. Peterson, D I. Mclean, M D. Symans, David Pollock, W F. Cofer, R N. Emerson, Kenneth J. Fridley

Faculty Publications - Biomedical, Mechanical, and Civil Engineering

In this first part of a two-part paper, development of a method of dynamic system identification for timber beams is presented with an analytical verification of the method using a finite-element model. A method of global nondestructive evaluation for identifying local damage and decay in timber beams is investigated in this paper. Experimental modal analysis is used in conjunction with a previously developed damage localization algorithm. The damage localization algorithm utilizes changes in modal strain energy between the mode shapes of a calibrated model, representing the undamaged state of the beam of interest, and the experimentally obtained mode shapes for …

Bolt Bearing Behavior Of Engineered Wood Composites, Stephen J. Carstens, David Pollock

Faculty Publications - Biomedical, Mechanical, and Civil Engineering

The goal of this research was to gain a better understanding of the bolt bearing behavior of engineered wood composites made from yellow poplar lumber. Lumber specimens included in this study were laminated veneer lumber, strandbased lumber, yellow poplar lumber, and Douglas-fir larch lumber. Testing followed the half-hole and full-hole configuration as set forth in ASTM Standard D5764 (1998).

In a previous study by Wilkinson (1991), a strong correlation was shown between bearing strength perpendicular to grain and bolt diameter. This study supports Wilkinson's finding for bearing strength perpendicular-to-grain based on the half hole test configuration. Other findings in this …

Lateral Resistance Of Ring-Shank Nail Connections In Southern Pine Lumber, R D. Theilen, D A. Bender, David Pollock, S G. Winistorfer

Faculty Publications - Biomedical, Mechanical, and Civil Engineering

Ring-shank nails are used in engineered structures with lateral connection design values based on theoretically derived equations which were validated only for common nails. The goal of this study was to quantify the input parameters and lateral connection strength of several types of ring-shank nails in Southern Pine lumber and critically evaluate the applicability of the theoretical equations for ring-shank nails.

Two sizes of galvanized and ungalvanized, hardened steel ring-shank nails from two manufacturers were studied. The hardened, ring-shank nails carried significantly higher loads than the common wire nails studied. Because the current method of determining yield load does not …

Withdrawal Strength Of Ring-Shank Nails Embedded In Southern Pine Lumber, M J. Skulteti, D A. Bender, S G. Winistorfer, David Pollock

Faculty Publications - Biomedical, Mechanical, and Civil Engineering

Ring-shank nails are used extensively in post-frame construction due to their superior performance, yet surprisingly little testing has been done on nail sizes above 12d. Experience in the post-frame industry suggests that published allowable design values for ring-shank nails may be overly conservative and need revision. The goal of the research reported herein was to characterize the withdrawal strength of ring-shank nails embedded in Southern Pine lumber. Three sizes ofgalvanized and ungalvanized (bright) ring-shank nails from two manufacturers were studied. Ring-shank nails had approximately twice the withdrawal resistance of smooth-shank nails of the same diameter. Galvanizing slightly reduced withdrawal strength …

Threaded-Nail Fasteners - Research And Standardization Needs, B L. Wills, S G. Winistorfer, D A. Bender, David Pollock

Faculty Publications - Biomedical, Mechanical, and Civil Engineering

Threaded nail fasteners are commonly used in agricultural and commercial post-frame structures, yet there has been insufficient research to fully understand the effect of threads on withdrawal and lateral load resistance. The objective of this article is to review technical information on threaded nail fasteners and to identify problems facing manufacturers, designers, and users of threaded nail fasteners for engineering applications. Recommendations are given concerning research and standardization needs.

Ultrasonic Detection Of A Plastic Hinge In Bolted Timber Connections, David Pollock, Donald A. Bender, Don E. Bray, James T P Yao

Faculty Publications - Biomedical, Mechanical, and Civil Engineering

Connections between structural members are critical elements that typically govern the performance of structural systems; hence, techniques for monitoring the condition of connections are needed to provide early warning of structural damage. Plastic hinge formation in fasteners frequently occurs in timber connections when the yield capacity is exceeded. An innovative pulse echo testing technique was developed for detecting the formation of a plastic hinge in bolted timber connections and estimating the associated magnitude of connection displacement. A shift in overall signal centroid proved to be the best flTedictor of plastic hinge formation, with a coefficient of determination (R2) of 0.9. …

Finite Element Analysis Of Multipass Effects Of Vehicles On Soil Compaction, David Pollock, J V. Perumpral, T Kuppusamy

Faculty Publications - Biomedical, Mechanical, and Civil Engineering

Finite element procedure was used to simulate multiple wheel loading and to predict its effect on soil compaction. Results of nonlinear analysis, conducted using an incremental loading procedure, show effects of tire size, soil type, and number of passes on soil compaction. The results of the study also demonstrate the potential use of the procedure in compaction related studies. However, experimental verification of the model is necessary before the procedure can be recommended for wider use.