Electric charges are often found in naturally or artificially formed droplets, such as raindrops and those generated by Kelvin's water dropper. In contrast to the impact of neutral droplets on a flat solid surface upon which a thin convex lens shape layer of the gas film is typically formed, I show that the delicate gas thin film can be fundamentally altered for even weakly charged droplets both experimentally and numerically. As the charge level is raised above a critical level of about 1% of the Rayleigh limit for representative impact conditions, the Maxwell stress overcomes the gas pressure buildup to deform the droplet bottom surface. A conical liquid tip forms and pierces Through the gas film, leading to a circular contact line moving outwards that does not trap any gas. The critical charge level only depends on the capillary number based on the gas viscosity. The deformation applies to common liquids and molten alloy droplets. Even dielectric surfaces can also induce conical deformation. The charged droplets can also deform upon hydrophobic surfaces, and increase the contact time on hydrophobic surfaces or even avoid bouncing. / Doctor of Philosophy / Electric charges are often found in naturally or artificially formed droplets, such as raindrops, waterfall, and inkjet printer. Neutral droplets impact on flat surfaces will usually trap a bubble inside because of the viscosity of air. The air bubble entrapped can be ignored if the droplet is water because the air bubble will eventually pinch-off. However, if the droplet is metal or some other viscous liquid, the air bubble will stay inside the liquid. This entrapped air bubble is undesired under some circumstances. For example, the existence of air bubble during metal 3D printing can influence the physical property. I show that the delicate gas thin film can be fundamentally altered for even weakly charged droplets both experimentally and numerically. As the charge level is raised above a critical level of about 1% of the maximum charges a droplet can carry for representative impact conditions, the electric stress will dominate the deformation of droplet. A conical liquid tip forms at the droplet bottom, avoiding the entrapment of air bubble. The critical charge level is experimentally proved to be only dependent on the gas viscosity and impact velocity. The deformation applies to common liquids and molten alloy droplets. Even dielectric surfaces can also induce conical deformation. The charged droplets can also deform upon hydrophobic surfaces, and increase the contact time on hydrophobic surfaces or even avoid bouncing.

Instability of humanoid robots is a common problem, especially given external disturbances or difficult terrain. Even with the robustness of most whole body controllers, instability is inevitable given the right conditions. When these unstable events occur they can result in costly damage to the robot potentially causing a cease of normal functionality. Therefore, it is important to study and develop methods to control a humanoid robot during a fall to reduce the chance of critical damage. This thesis proposes joint angular velocity strategies to reduce the impact velocity resulting from a lateral, backward, or forward fall. These strategies were used on two and three link reduced order models to simulate a fall from standing height of a humanoid robot. The results of these simulations were then used on a full degree of freedom robot, Viginia Tech's humanoid robot ESCHER, to validate the efficacy of these strategies. By using angular velocity strategies for the knee and waist joint, the reduced order models resulted in a decrease in impact velocity of the center of mass by 58%, 87%, and 74% for a lateral, backward, and forward fall respectively in comparison to a rigid fall using the same initial conditions. Best case angular velocity strategies were then developed for various initial conditions for each falling direction. Finally, these parameters were implemented on the full degree of freedom robot which showed results similar to those of the reduced order models. / Master of Science

Youth and varsity football helmets are currently designed similarly and tested to the same impact standards from the National Operating Committee on Standards for Athletic Equipment (NOCSAE). Youth players have differences in anthropometry, physiology, impact exposure, and potentially injury tolerance that should be considered in future youth-specific helmets and standards. This thesis begins by investigating the current standards and relating them to on-field data. The standard drop tests represented the most severe on-field impacts, and the performance of the youth and varsity helmet did not differ. There likely is not a need for a youth-specific standard as the current standard has essentially eliminated the catastrophic head injuries it tests for. As more is known about concussion, standards specific to the youth population can be developed. The second portion of this thesis compares the impact performance between 8 matched youth and varsity helmet models, using linear acceleration, rotational acceleration, and concussion correlate. It was found that helmet performance did not differ between the youth and varsity helmets, likely attributed to testing to the same standard. The final portion of this feature is aimed at advancing STAR for youth and varsity football helmets by including linear and rotational head kinematics. For varsity helmets, an adult surrogate is used for impact tests which are weighted based on on-field data collected from collegiate football players. For youth helmets, a youth surrogate is used and tests are weighted based on data collected from youth players. / Master of Science

One of the most important data elements recorded in the National Automotive Sampling System / Crashworthiness Data System (NASS/CDS) is the vehicle change in velocity, or ?V. ?V is the vector change in velocity experienced by a vehicle during a collision, and is widely used as a measure of collision severity in crash safety research. The ?V information in NASS/CDS is used by the U.S. National Highway Traffic Safety Administration (NHTSA) to determine research needs, regulatory priorities, design crash test procedures (e.g., test speed), and to determine countermeasure effectiveness. The WinSMASH crash reconstruction code is used to compute the ?V estimates in the NASS/CDS. However, the reconstruction accuracy of the current WinSMASH version has not previously been examined for side impacts. Given the importance of side impact crash modes and the widespread use of NASS/CDS data, an assessment of the program's reconstruction accuracy is warranted. The goal of this thesis is to quantify the accuracy of WinSMASH ?V estimations for side impact crashes, and to suggest possible means of improving side impact reconstruction accuracy. Crash tests provide a wealth of controlled crash response data against which to evaluate WinSMASH. Knowing the accuracy of WinSMASH in reconstructing crash tests, we can infer WinSMASH accuracy in reconstructing real-world side crashes. In this study, WinSMASH was compared to 70 NHTSA Moving Deformable Barrier (MDB) - to - vehicle side crash tests. Tested vehicles were primarily cars (as opposed to Light Trucks and Vans, or LTVs) from model years 1997 - 2001. For each test, the actual ?V was determined from test instrumentation and this ?V was compared to the WinSMASH-reconstructed ?V of the same test. WinSMASH was found to systemically over-predict struck vehicle resultant ?V by 12% at time of vehicle separation, and by 22% at time of maximum crush. A similar pattern was observed for the MDB ?V; WinSMASH over-predicted resultant MDB ?V by 6.6% at separation, and by 23% at maximum crush. Error in user-estimated reconstruction parameters, namely Principal Direction Of Force (PDOF) error and damage offset, was controlled for in this analysis. Analysis of the results indicates that this over-prediction of ?V is caused by over-estimation of the energy absorbed by struck vehicle damage. In turn, this ultimately stems from the vehicle stiffness parameters used by WinSMASH for this purpose. When WinSMASH was forced to use the correct amount of absorbed energy to reconstruct the crash tests, systemic over-prediction of ?V disappeared. WinSMASH accuracy when reconstructing side crash tests may be improved in two ways. First, providing WinSMASH with side stiffness parameters that are correlated to the correct amount of absorbed energy will correct the systemic over-prediction of absorbed energy when reconstructing NHTSA side crash tests. Second, providing some treatment of restitution in the reconstruction process will correct the under-prediction of ?V due to WinSMASH's assumption of zero restitution. At present, this under-prediction partially masks the over-prediction of ?V caused by over-prediction of absorbed energy. If the over-prediction of absorbed energy is corrected, proper treatment of restitution will correct much of the remaining error observed in WinSMASH reconstructions of NHTSA side crash tests. / Master of Science

When a gas turbine operates in a particle laden environment, such as a desert, small solid particles are ingested into the engine. The ingested sand particles can cause damage to engine components and reduce the service life of the engine. Particle ingestion causes the erosion of metal blades and vanes, and, if the firing temperature is hot enough, deposition of molten particles in the hot sections of the engine. Both deposition and erosion phenomena can severely reduce overall engine performance. The Coefficient of Restitution (COR) is a measure of the particle-wall interaction, and has been widely used to quantify particle rebound characteristics in past particle impact studies. This work investigates the effects of temperature on sand particle impact characteristics by measuring the COR and other deposition related impact parameters. The first study presented as part of the dissertation contains a description of a novel method used to measure COR using a Particle Tracking Velocimetry (PTV) method. This is combined with Computational Fluid Dynamics (CFD) flow field to allow for an accurate determination of the particle impact velocity. The methodology described in this paper allows for measurement of the COR in a wide range of test conditions in a relatively simple manner. The COR data for two different sizes of Arizona Road Dust (ARD) and one size of glass beads are presented in this paper. Target material was stainless steel 304 and the impact angle was varied from 25 to 85 degrees. The second study details the first quantification of the COR of san particles at elevated temperatures. Temperatures used in this study were 533 K, 866 K, and 1073 K. In this study the mass flow rate through the experimental setup was fixed. This meant that velocity and temperature were coupled. Target material for this study was stainless steel 304 and the impact angle was varied from 30° to 80°. The COR was found to decrease substantially at the temperatures and velocity increased. It was determined that the decrease in COR was almost certainly caused by the increase in velocity, and not the decrease in temperature. The third study contains COR results at elevated temperatures. Significant improvements from the method used to calculate COR in the first paper are described. The particle used for these tests was an ARD sand of 20-40 μm size. Target materials used were stainless steel 304 and Hastelloy X. The particles impinged on the target coupon at a velocity of 28m/s. Tests were performed at three different temperatures, 300 K (ambient), 873 K, and 1073 K to simulate temperatures seen in gas turbine cooling flows. The angle of impingement of the bulk flow sand on the coupon was varied between 30° and 80°. A substantial decrease in COR was discovered at the elevated temperatures of this experiment. Hastelloy X exhibited a much larger decrease in COR than does stainless steel 304. The results were compared to previously published literature. The final study also used the ARD size of 20-40 μm. The target material was a nickel alloy Hastelloy X. Experiments for this study were performed at a constant velocity of 70m/s. Various temperatures ranging from 1073 K up to and including 1323 K were studied. Particle angle of impact was varied between 30° and 80°. Significant deposition was observed and quantified at the highest two temperatures. The COR of the ARD sand at the highest temperatures was found not to change despite the occurrence of deposition. At elevated temperatures, many of the particles are not molten due to sand's non-homogenous and crystalline nature. These particles rebound from the target with little if any change in COR. / Ph. D.

In this thesis, the complete design, fabrication, and calibration of an instrumented drop weight impact tester is described. Included in this description are all the sketches and drawings that are needed to duplicate this project, if so desired. This impact tester was built for around $23,000 less than it would have cost to buy and modify a commercial tester for the intended research application. This tester, as designed, was intended to be used in the field of impact location detection using artificial neural networks. Even though this impact tester was built for a specific research application, the design concepts that are presented can easily be adapted to a variety of testing needs. This impact tester was built using an non-working milling machine for a base. This provides a rigid, stable base along with a moveable X-Y table. The tester itself has the capability for drop weights ranging from 3.518 Ib up to 15.408 lb, and impact energy levels ranging from 0.6 ft-lb up to 45.6 ft-lb. Also, it is capable of impacting multiple locations of large plates with variable boundary condition sizes up to 12" x 24". Furthermore, it uses a computer program written using a data acquisition software package to provide output plots for the impact event, including the force and energy applied to the specimen versus time and the force versus displacement. Finally, initial experimental results obtained from this tester agree very well with those obtained from a commercially available tester, allowing it to be used in future tests involving intelligent material systems. / Master of Science

This thesis examines the economic impact of two alternative canning plant sizes in Scott County, Virginia. The impacts of a community cannery as well as a commercial cannery are analyzed with respect to changes in output, employment, and income. Several uses for the commercial cannery are considered, such as specialization in different product categories. In both cases, an input-output model is used to evaluate the effects of the operation of the cannery in the county. The results indicate that the impact of the commercial cannery is significantly larger than the community cannery. Specialization of the commercial cannery in the Canned Specialties sector has the largest impact with respect to industry output and labor income while specialization in the Sausages and Other Prepared Meats sector has the largest impact with respect to employment. / Master of Science

Detailed information about negative effects of fine sediments on early life stages of brook trout (Salvelinus fontinalis) in southern Appalachian streams is lacking. Information on survival to different stages of egg and alevin development could indicate critical timing of sediment impacts. This study was designed to determine the effects of fine sediments (0.43-0.85 rom in diameter) on survival of brook trout eggs through early development stages under controlled laboratory and field conditions. Recently fertilized eggs were loaded into Whitlock-Vibert (W-V) boxes lined with 0.4 rom Nitex netting that contained mixtures of gravel and fine sediments. Survival to eyed, hatched, and emerged stages of development was determined for six amounts of fine sediment (0-25% by weight) in the laboratory study and for three amounts of fine sediment (0-20% by weight) in the field study. Survival in laboratory systems to each stage of development was inversely related to the percentage of fine sediment; even at low levels of fine sediment survival was reduced. In the field study, fine sediment may have played a role in the survival success of developing embryos, but determining a definitive relationship was confounded by effects of scouring flows and fungal infestations. The fungus Saprolegnia spp., may have increased the mortality rate of viable eggs and facilitated the disintegration of nonviable embryos, especially in the field study. Brook trout are sensitive to increasing levels of fine sediment through early development. However under field conditions such an effect may be difficult detect. / Master of Science

Mild traumatic brain injury in snowsports is a prevalent concern. With as many as 130,000 hospitalized injuries in the U.S. associated with snowsports in 2017, head injury constitutes about 28% and is the main cause of fatality. Studies have found that a combination of rotational and linear velocities is the most mechanistic way to model brain injury, but despite decades of research, the biomechanical mechanisms remain largely unknown. However, evidence suggests a difference in concussion tolerance may exist between athlete populations. To improve the ability to predict and therefore reduce concussions, we need to understand the impact conditions associated with head impacts across various sports. There is limited research on the conditions associated with head impacts in snowsports. These head impacts often occur on an angled slope, creating a normal and tangential linear velocity component. Additionally, the impact surface friction in a snowsport environment is highly variable, but could greatly influence the rotational kinematics of head impact. Currently helmet testing standards don't consider these rotational kinematics, or varying friction conditions that potentially occur in real-world scenarios. The purpose of this study is to investigate the head impact conditions in a snowsport environment to inform laboratory testing and evaluate snow helmet design. We determined head impact conditions through video analysis to determine the impact locations, mechanism of fall, and the kinematics pre-impact. We used these data to develop a test protocol that evaluates snowsport helmets in a realistic manner. Ultimately, the results from this research will provide snowsport participants unbiased impact data to make informed helmet purchases, while concurrently providing a realistic test protocol that allows for design interventions to reduce the risk of injury. / Master of Science / Mild traumatic brain injury in snowsports is a prevalent concern. With as many as 130,000 hospitalized injuries in the U.S. associated with snowsports in 2017, head injury constitutes about 28% and is the main cause of fatality. Studies have found that a combination of rotational and linear velocities is the most mechanistic way to model brain injury, but despite decades of research, the biomechanical mechanisms remain largely unknown. However, evidence suggests a difference in concussion tolerance may exist between athlete populations. To improve the ability to predict and therefore reduce concussions, we need to understand the impact conditions associated with head impacts across various sports. There is limited research on the conditions associated with head impacts in snowsports. These head impacts often occur on an angled slope, creating a normal and tangential linear velocity component. Additionally, the impact surface friction in a snowsport environment is highly variable, but could greatly influence the rotational kinematics of head impact. Currently helmet testing standards don't consider these rotational kinematics, or varying friction conditions that potentially occur in real-world scenarios. The purpose of this study is to investigate the head impact conditions in a snowsport environment to inform laboratory testing and evaluate snow helmet design. We determined head impact conditions through video analysis to determine the impact locations, mechanism of fall, and the kinematics pre-impact. We used these data to develop a test protocol that evaluates snowsport helmets in a realistic manner. Ultimately, the results from this research will provide snowsport participants unbiased impact data to make informed helmet purchases, while concurrently providing a realistic test protocol that allows for design interventions to reduce the risk of injury.

One of the most painful events in life that an adolescent can face is the loss of someone with whom they had a strong emotional attachment (Harvey, 2002). This loss could be a friend, relative, parent, or any person that was strongly attached to the adolescent. In today's literature, there is a lack of attention given to adolescents, college students in particular who experience loss. This retrospective study consisted of 224 university students who had lost someone during adolescence or preadolescence. I examined if the impact of the stress accompanied by the loss and the coping strategies used to deal with loss differed by gender and the time in which students experienced their loss. Results from this study indicate that gender plays a significant role in both coping behaviors and the impact of the loss on the individual. In particular, females were found have more coping behaviors and felt a higher degree of impact of the loss than males. Another variable that played a significant factor in this study was the time of loss, early or later in life. Those students who experienced their loss later in life (between 13-19) were impacted more than those who experienced their loss early in life (between 5-12). However, time of loss did not play a role in the individual coping behaviors exhibited. / Master of Science