The effects of particle shape on bedload transport and a wide range of bedload transport rates using both bed subsurface and surface layer based approaches are investigated using fractional transport analysis with a similarity approach. Bedload transport data from a stream containing flat, low density shale particles indicates that the reference transport critical shear stress for the median surface grain size is approximately 2 to 3 times higher than those for more spherical particles. This conclusion indicates a lower susceptibility of disc-like particles to initial entrainment and lower transport rates for given flow conditions than more rounded particles. Analysis of a wide range of transport rates verifies that the slope of the log-log bedload transport rate - bed shear stress relation decreases with increasing transport rate and becomes constant at very high transport rates. This result implies that the dependence of the transport rate on grain size decreases with increasing transport rate. Comparison of bed subsurface and surface layer based bedload transport approaches indicates that the two approaches produce similar transport - shear relations and reference shear stress values. / Master of Science / incomplete_metadata

A study was performed to investigate the factors that affect the accuracy of the procedures used by the Virginia Department of Transportation for design of drilled shaft sound wall foundations. Field load tests were performed on eight inch and nine inch diameter drilled shafts, and the results were compared to theoretical solutions for ultimate lateral load capacity. Standard Penetration Tests were run in the field and laboratory strength tests were performed on the soils from the test sites. It was found that published correlations between blow count and friction angle for sands and gravels can be used to estimate friction angles for the partly saturated silty and clayey soils encountered at the test sites. A spreadsheet program was developed to automate the process of determining design lengths for drilled shaft sound wall foundations. The spreadsheet was used to investigate the effects of different analysis procedures and parameter values on the design lengths of drilled shaft sound wall foundation. / Master of Science

Currently, pallets are designed assuming that the load is distributed evenly on the top of the pallet. When pallets are loaded with packages such as corrugated boxes or returnable plastic containers, due to their physical shape, packages, are not capable of deforming freely with the pallet and a bridging phenomenon occurs. During this load bridging phenomenon, a portion of the vertical forces are redistributed as horizontal forces which causes the redistribution of the vertical compression stresses on the pallet towards the support. As a result, the deflection of the pallet can decrease and the load capacity of the pallet can increase significantly. The second chapter of this paper investigates the effect of package content on pallet deflection. The study concluded that package content did not have a significant effect on pallet deflection within the boundary conditions of the experiment. The third part of this paper considers how a specific pallet characteristic could affect the way a corrugated box performs. Standard box design procedures include adjustments of estimated compression strength for relative humidity, overhang on pallets, vibration, and alignment of boxes. However, there is no adjustment factor for pallet stiffness. The objective of the study described in this thesis is to find an answer for how the compression strength of a box is affected by pallet stiffness and top deckboard twist. The study concluded that the pallet stiffness and top deckboard twist do not have an effect on the compression strength of the box until less than 12% of the area box is supported. / Master of Science

Helicopters have been used in applications where they need to carry a slung load for years. More recently, unmanned (UAV) helicopters are being used to deliver supplies to military units on the ground in theaters of war. This thesis presents a helicopter slung vehicle used to carry the payload and furthermore, provide a means of actuation for the payload. This provides more control authority to the system and may ultimately allow a helicopter to fly higher with a longer tether. The vehicle designed in this thesis was designed for use with 100kg class helicopters, such as the Yamaha RMAX operated by the Virginia Tech Unmanned Systems Lab. Each system on the vehicle was custom designed — including the propulsion system, wall detection / localization system, and controller. Three shrouded propellers provided thruster actuation. A scanning laser range finder and inertial measurement unit (IMU) were used to provide localization. A first attempt at a linear full state feedback controller with a complementary filter was used to control the vehicle. All of the systems were tested individually for functionality. The shrouded propellers met their design goals and were capable of producing .7lbf of thrust each. The wall detection system was able to detect walls and windows reliably and with repeatability. Results from the controller however were less than ideal, as it was only able to control yaw in an oscillatory motion, most likely due to model deficiencies. A reaction wheel was used to control yaw of the vehicle with more success. / Master of Science

The purpose of this study was to help explore the assumptions in job analysis literature involving whether holistic or decomposed job analysis items lead to a higher level of cognitive load for raters. The main study, involving 303 undergraduate university students, was a 2 (Type of measure: holistic or decomposed) X 2 (Level of extraneous cognitive load: additional load or no additional load) within-subjects design. The 160 decomposed items analyzed in this study were pilot tested to ensure that they would correlate with the 17 holistic items. Under the additional cognitive load condition, participants memorized an 8-digit number, and then were asked to recall and recognize this number upon the completion of the rating task (this manipulation was performed for both the holistic and decomposed measures). Stability of ratings across conditions and interrater agreement were used as dependent measures. Results indicated that the holistic items (r=.74) had higher levels of stability across cognitive load conditions than did the decomposed items (r=.66). The levels of interrater agreement were not significantly different between three of the four conditions. In partial support of Butler and Harvey (1988), the level of interrater agreement for the Holistic additional cognitive load condition (r*wg=.33) was significantly lower than the interrater agreement for the remaining three conditions. The pattern of results supported prior research (Cornelius & Lyness, 1980; Lyness & Cornelius, 1982) indicating that, depending on the criteria being used, holistic items do not necessarily cause a higher level of cognitive load for raters than do decomposed items. / Master of Science

The primary purpose of this study is to determine stability boundaries (interaction curves) for a three degree of freedom, shallow arch model under multiple dynamic loads. The model consists of four rigid bars connected by frictionless pins, with rotational springs and dashpots at the three interior joints, and a translational spring at the right hand exterior joint. Three independent loads (P₁, P₂, P₃) are applied to the model, one at each of the three interior joints. The model's equations of motion, which are derived from Lagrange's equations of motion, are numerically integrated, using the Newmark-Beta method (β = 1/4), to determine the buckling loads. The buckling loads are those loads for which the buckling criterion, the end bars simultaneously below the horizontal, is satisfied. The interaction curves and buckling loads are determined for a parabolic arch with damping under step loads, a parabolic arch without damping under step loads, an eccentric arch without damping under step loads, a parabolic arch without damping under impulse loads, and an / Master of Science

Pallets and corrugated boxes are ubiquitous in the global supply chain. However, the interactions that exist between the boxes and pallet are ignored during the pallet design process resulting in an over design of pallet performance and the waste of raw materials. The goal of this research is to understand how pallet performance is affected by headspace, box size, and base design across multiple support conditions using block class wooden pallets. Headspace and base design had no effect on pallet deflection for the experimental weights used throughout testing. The effect of box size was significant on pallet deflection across multiple support conditions. The effect was greatest for lower stiffness pallets and low stiffness support conditions (RAW) with up to a 50% reduction in pallet deflection observed by switching from small to large boxes on a very low stiffness pallet. Evaluation of pressure mat data showed an increase in the redistribution of pressure away from the center of the pallet and towards the supports as box size increased. The redistribution of pressure towards the supports is known as load bridging and validates the observed reduction in pallet deflection as a function of box size. The results indicate that incorporating the effect of packages into current pallet design practices could result more effective and cheaper pallet designs. / Master of Science / Transportation and storage of material goods at a national and international level is an integral part of our economy with pallets and corrugated boxes making up the majority of packaging materials. Currently, the interactions that exist between the boxes and pallet are ignored during pallet design resulting in an over design of pallet performance and a waste of raw materials. Understanding the interactions that exist in a unit load is important in optimizing pallet performance, reducing the amount of raw materials used, and ultimately reducing cost. This research project is specifically focused on the interactions between corrugated boxes and block class wooden pallets. The effect of headspace (the gap between the products and the top of the box) and box size was investigated as a function of pallet stiffness, support condition, and bottom deck design. Both pallet deflection and the pressure distribution on the top surface of the pallet were examined to evaluate pallet performance. It was found that headspace does not have an effect on pallet deflection unless the weight of the unit load exceeds 3,500 lbs. for small boxes and 1,750 lbs. for large boxes. Base design showed no significant effect on pallet deflection for all of the support conditions evaluated. The effect of box size had a major effect on the deflection of the pallet. Large boxes showed the greatest change especially when lower stiffness pallets were used. Increasing the box size can reduce the deflection of the pallet as much as 50% which means that pallets supporting larger boxes could support much more weight than currently estimated. Evaluation of pressure mat data showed that when the size of the boxes increased, more pressure is distributed towards the supports. More pressure is applied to the pallet section on the top of the supports; therefore, less pressure is available to cause pallet bending. This finding validates the observed reduction in pallet deflection as a function of box size. The obtained results help pallet designers to incorporate the interactions between the packages and the pallet into their design process which will allow them to reduce the amount material used for pallet.

GPU computing can significantly improve performance by taking advantage of massive parallelism of GPUs for data parallel applications. Computation in visualization applications is suitable for parallelization on the GPU, which can improve performance and interactivity in these applications. If used effectively, multiple GPUs can lead to a significant speedup over a single GPU. However, the use of multiple GPUs requires memory management, scheduling, and load balancing to ensure that a program takes full advantage of available processors. This work presents methods for data-driven and dynamic multi-GPU load balancing using a pipelined approach and a framework for use with different applications. Data-driven load balancing can improve utilization for applications by taking into account past performance for different combinations of input parameters. The dynamic load balancing method based on buffer fullness can adjust to workload changes at runtime to gain an additional performance improvement. This work provides a framework for load balancing to account for differing characteristics of applications. Implementation of a multi-GPU data structure allows for use of these load balancing methods in the framework. The effectiveness of the framework is demonstrated with performance results from interactive visualization that shows a significant speedup due to load balancing. / Master of Science

Pretesting prior to a study session has been shown to benefit memory for pretested information compared to traditional study. While previous research has not found a detriment to non-pretested but related material, it is possible that taxing attention by increasing the playback speed of presented material could reveal such impairments. The current study (N = 239) compared multiple-choice learning from educational videos at 1x, 1.5x, and 2x speeds. Three videos (one at each speed) were presented after a pretest, for which half of the tested material was pretested, and half was not (non-pretested related). Another three videos were presented without a pretest (non-pretested). Benefits from pretesting and impairments associated with increased playback speed were observed, but no evidence of impairments to non-pretested related information were observed even at an increased playback speed. These results are inconsistent with an attentional account of the pretesting effect.

In 2021, over three and a half million women entered the postpartum period in the United States [1]. Despite their prevalence, postpartum health is a largely overlooked area. After delivery, 25% of women within this population experience lumbopelvic or pelvic pain during the typical postpartum period [3], up to 8 weeks post-delivery, and research has found these women may continue to experience pain years after delivery [4]. Persistent pelvic region pain in postpartum women may result in lower limb load asymmetry. Additionally, external loading from carrying a child may alter the degree of asymmetric loading that exists in the lower limbs. Therefore, the first purpose of this study was to investigate the effect of daily tasks on lower extremity load symmetry using metrics that have successfully identified load asymmetry in other populations. Load symmetry was found to differ between task, with the largest asymmetry occurring between limbs during the sit-to-stand task for the peak impact force (PIF = 9.08% symmetry) and during the stair descent task for the average loading rate (ALR = 15.43% symmetry). The increase in asymmetry during these tasks may be attributed to increased muscle activation and force production. The second purpose of this study was to investigate the effect of an external child load on lower extremity load asymmetry during a 14-meter level walking task. A significant increase was found between the no load and both child load conditions for PIF and ALR (p <0.001 for both metrics). No statistically significant differences in symmetry were found between carrying the child centrally in a carrier and carrying on one side of the body without a carrier. The lack of difference in asymmetry during child carrying conditions may indicate mothers naturally compensate for the external child load as both ALR and PIF values increased during these conditions, but asymmetry was not impacted. Our results indicate the need to continue to examine different carrying conditions in postpartum women to better understand risk factors for pain or injury and provide evidence-based recommendations for postpartum activity progression. / Master of Science / In 2021, over three and a half million women entered the postpartum period in the United States [1]. Despite their prevalence, postpartum health is a largely overlooked area and 25% of women experience low back or pelvic pain past the typical postpartum period of 8 weeks post delivery [3]. Research has found women may continue to experience this pain years after delivery and result from the lower limbs being loaded unequally. The extra weight from carrying a child may also impact the amount of unequal loading placed onto the lower limbs. The first purpose of this study was to investigate the effect of daily tasks on load symmetry in the lower limbs using measures that have successfully identified unequal load distribution in non-pregnant individuals. Load symmetry was found to differ between task, with the largest asymmetry occurring between limbs during the sit-to-stand task for the force applied to lower limbs during initial contact of the feet and during the stair descent task for the rate that force was applied to lower limbs. The second purpose of this study was to investigate the effect of an external child load on lower extremity load asymmetry during a 14-meter level walking task. A significant increase was found between the no load and both baby load conditions for force applied during initial contact of the feet and rate this force was applied. No difference was found between child carrying external loading condition when evaluating asymmetry. Our results indicate the need to continue to investigate the unique loading patterns of postpartum women to better understand the specific risk factors for pain or injury development within this population.