Effects of Spin on Tennis Ball Aerodynamics: An Experimental and Computational Study

The aerodynamic behaviour of a tennis ball is very complex and significantly differs from other sports balls due to its surface structures (fuzz, seam orientation etc). Relatively high rotational speeds (spin) make the aerodynamic properties of tennis balls even more complex. Although several studies have been conducted on drag and lift in steady state condition (no spin involved) by the author and others, little or no studies have been conducted on spin effects. The so called Magnus effect on a sphere is well known in fluid mechanics. It is believed that the spinning can affect aerodynamic drag and lift of a tennis ball thus the motion and flight path of the ball. Therefore, the primary objectives of this work are to study the spin effects using both experimental and computational methods. In order to achieve these objectives, a series of tennis balls were used to measure their aerodynamics forces as a function of wind speeds, seam orientation and spins. The experimental study was conducted in the RMIT Industrial Wind Tunnel. A computational study of a simplified tennis ball was also studied using commercial software ‘FLUENT’. The CFD results were compared with the experimental findings. Flow around the ball was visualised with smoke

Alexithymia may explain the relationship between autistic traits and eating disorder psychopathology

Background: Autistic people are disproportionately vulnerable to anorexia nervosa and other eating disorders (ED), and within the general population, autistic traits correlate with ED psychopathology. A putative mechanism which may underpin this heightened risk is alexithymia, a difficulty identifying and describing emotional states which is observed in both autism and ED. In two experiments with independent non-clinical samples, we explored whether alexithymia might mediate the heightened risk of eating psychopathology in individuals high in autistic traits. Methods: Our first experiment used the PROCESS macro for SPSS to examine relationships between alexithymia (measured by the Toronto Alexithymia Scale (TAS-20)), autistic traits (autism quotient (AQ)), and eating psychopathology (Eating Attitudes Test (EAT-26)) in 121 participants. Our second experiment (n = 300) replicated and furthered this analysis by examining moderating effects of sex and controlling for anxiety and depression as covariates. We also included an additional performance-based measure of alexithymia, the Levels of Emotional Awareness Scale (LEAS). Results: Study 1 suggested that TAS-20 scores mediated the relationship between heightened autistic traits and eating psychopathology. Replication and further scrutiny of this finding, in study 2, revealed that this mediation effect was partial and specific to the female participants in this sample. The mediation effect appeared to be carried by the difficulty identifying feelings subscale of the TAS-20, even when depression and anxiety were controlled for. LEAS scores, however, were not significantly related to autistic traits or eating psychopathology. Limitations: Cross-sectional data prevents any conclusions around the direction and causality of relationships between alexithymia, autistic traits, and eating psychopathology (alongside depression and anxiety), necessitating longitudinal research. Our non-clinical sample was predominantly Caucasian undergraduate students, so it remains to be seen if these results would extrapolate to clinical and/or autistic samples. Divergence between the TAS-20 and LEAS raises crucial questions regarding the construct validity of these measures. Conclusions: Our findings with respect to autistic traits suggest that alexithymia could partially explain the prevalence of ED in autistic people and may as such be an important consideration in the pathogenesis and treatment of ED in autistic and non-autistic people alike. Further research with clinical samples is critical to explore these ideas. Differences between men and women, furthermore, emphasize the importance of looking for sexspecific as well as generic risk factors in autistic and non-autistic men and women

Alexithymia, emotional awareness and perceived dysfunctional parental behaviors in heroin dependents

© Springer Science+Business Media New York 2013The original publication is available at www.springerlink.com © Springer Science+Business MediaThe aim of this study was to analyse alexithymia and deficits in emotional awareness, in heroin addicts, and their relationship with perceptions of early parental interactions. The sample included 99 opiate dependent outpatients and 43 healthy controls. Assessment was performed using the Toronto Alexithymia Scale, the Levels of Emotional Awareness Scale, the Inventory for Assessing Memories of Parental Rearing Behavior, the Mini-Mental State Examination and the Hospital Anxiety and Depression Scale. Findings suggest parental representations, which were mostly characterized by emotional unavailability and a rejection interaction pattern, significantly related to alexithymia. Emotional awareness was associated with the number of years of drug use and methadone level. Negative affect was associated with alexithymia but not to emotional awareness. Regression analyses emphasized the influence of perceived dysfunctional parenting behaviors in alexithymia and difficulties in identifying feelings, particularly an interaction with paternal rejection, moderated by self-reported anxiety. These results are discussed addressing comprehensive issues of emotion regulation and treatment strategies in heroin dependence

Design and materials in snowboarding

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A comparative study of aerodynamic forces of time trial bicycle helmets

The aerodynamic efficiency becomes essential design criterion for time trial bicycle helmets as small time difference can make the winner. Currently numerous manufacturers market time trial helmets claiming to have superior aerodynamic efficiency. Unfortunately, the aerodynamic performances of these helmets were not well publicised and in most cases data is kept in house. Additionally, no comparative study of aerodynamic performance of various time trial helmets has been reported in the open literature. Therefore the primary objectives of this research were to study the aerodynamic performance of several time trial helmets that currently used in time trial racing in Australia and elsewhere. The helmets were tested on a mannequin in the time trial head positions over a range of yaw angles and wind speeds. The results indicated that there was a significant variation in aerodynamic performances of these helmets. However, their performances varied depending on yaw and pitch angles

Virtual design of efficient twin-screw superchargers for sustainable power management in engines

The concept of sustainability has gained increased importance in recent years as the planet's living systems have declined and many of its vital resources depleted. Vehicle design is changing to reflect this paradigm shift, and motor vehicles are required to meet severe requirements for fuel consumption and exhaust gas. To meet these requirements, motor engines equipped with superchargers are being introduced to the market. In this study, a CFD approach to predict the leakage flow in twin-screw superchargers is described. It allows creating an integrated CAD/CFD design environment, which can address aspects of fluid and geometry requirements for the future designs

Modelling and analysis of alternative face guard designs for cricket using finite element modelling

In professional cricket, where bowlers can bowl balls that reach speeds of up to 160 km h-1, effective head protection is vital. Current head protection equipment typically consists of a helmet with a high impact grade polypropylene shell, a high density EPS liner, and a metal face guard. Most of the weight in existing helmets is attributed to the steel grill used as the face guard. We present a virtual design approach to the development and evaluation of new face guards made from alternative materials. In particular, we investigate a face guard design for cricket made from polycarbonate rather than steel using an explicit dynamic finite element analysis (FEA) approach. The FEA model developed for this purpose incorporates the headform, helmet, polycarbonate face guard and the impacting ball. ABAQUS CAE was used for FEA. HyperMesh and SolidWorks were used to develop the geometric model. This work identifies appropriate modelling and simulation strategies, and key design attributes for the development of new face guards using alternative materials. A preliminary study shows that by using polycarbonates it is possible to reduce the mass of the face guard by 20%, thus contributing to greater comfort of the players without compromising their safety. The key criteria for reduction of ball deceleration by at least 25% at each test site were satisfied, with deceleration reduction values ranging from 44% to 87% from those due to ball impact with the bare head

Evaluation of different gyroscope sensors for smart wheelchair applications

Inertial sensors have been used extensively in recent years for measuring and monitoring performance in many different sports except in wheelchair sports. Mounting an accelerometer directly on a wheelchair frame and determining performance parameters from linear acceleration measurements can provide valuable insight into wheelchair sports performance. However, the processing required for this purpose is tedious. With improvements in the accuracy and measuring range of MEMS gyroscopes, it is now possible to mount a gyroscope on a wheelchair racing wheel and measure speeds close to 30m/s. This paper evaluates and compares angular velocity measurements from a custom built wireless gyroscope sensor, a commercial inertial sensor and an iPod Touch 4 device. With effective filtering, gyroscope sensors provide a suitable tool for performance analysis in wheelchair sports

Non-linear rolling friction of a tyre-caster system: analysis of a rugby wheelchair

Tyre-caster systems such as wheelchairs consist of several components with different bearing and rolling friction, with the latter depending on the tyre pressure. The aim of this study was to determine the rolling friction of a rugby wheelchair with deflated and maximally inflated tyres. The rolling friction was determined with coast-down tests by instrumenting the wheelchair with an accelerometer. As the energy loss of coasting down comes primarily from the rolling friction and aerodynamic drag, the latter (including the lift) was determined using wind tunnel experiments. The ratio of the sum of horizontal forces (drag and inertial) to the sum of vertical forces (lift and gravitational) determined the rolling friction coefficient. The rolling friction coefficient expressed as a function of the velocity was found to be highly non-linear, consisting of an initial viscous spike at low velocities, a constant component, and a parabolic component increasing with velocity. Therolling friction coefficient of the wheelchair with deflated tyres was on average three times higher than the one with maximally inflated tyres