1,720,976 research outputs found
Multibody dynamics analysis of the human upper body for rotorcraft–pilot interaction
Get PDFThe study of the biodynamic response of helicopter passengers and pilots, when excited by rotorcraft vibrations that are transmitted through the seat and, for the latter, the control inceptors, is of great importance in different areas of aircraft design. Handling qualities are affected by the proneness of the aircraft to give rise to adverse interactions, an unwanted quality that can be captured by the so-called biodynamic feedthrough. On the other hand, the transmissibility of vibrations, especially from the seat to the head, affects the comfort of pilots and passengers during flight. Detailed and parametrised multibody modelling of the human upper body can provide a strong base to support design decisions justified by a first-principles approach. In this work, a multibody model of the upper body is formed by connecting a previously developed detailed model of the arms to a similarly detailed model of the spine. The whole model can be adapted to a specific subject, identified by age, gender, weight and height. The spine model and the scaling procedure have been validated using the experimental results for seat to head transmissibility. The coupled spine-arms model is used to evaluate the biodynamic response in terms of involuntary motion induced on the control inceptors, including the related nonlinearities
Evaluation of dynamic loads and performance indexes in tiltrotors using a mid-fidelity aeroservoelastic tool
Get PDFThis work presents a comprehensive numerical environment, obtained by the coupling of a mid-fidelity aerodynamic solver based on a vortex particle method with a multibody dynamics tool, for aeroelastic simulations suitable for the analysis and design of next-generation rotary-wing aircraft. Indeed, the presence of multiple propellers and rotors, together with interactional aerodynamics, have a strong impact on dynamic loads and performance indexes on rotorcraft. A mid-fidelity approach provides an ideal trade-off between the accuracy of the solution and the speed of execution required in the preliminary design phases of these vehicles.
A tiltrotor model representative of the Bell XV-15 with different levels of complexity is proposed as a test benchmark, whose characteristics can be similar to an eVTOL. The coupled solver shows the capability to determine the trim conditions in airplane mode and predicts steady and periodic trim loads. Transient analyses are presented as well, considering a roll maneuver and highlighting the importance of the accurate representation of rotary wing aerodynamics provided by the vortex particle method for load evaluation and vibrational assessment
Mid-fidelity numerical approach for the investigation of wing-propeller aerodynamic interaction
Get PDFThe present activity was aimed to validate the capability of a vortex particle-based mid-fidelity aerodynamics code for the study of the aerodynamic interaction between a wingtip-mounted propeller and a wing with a 25% chord flap. The wing-propeller model considered in this work was widely investigated in literature, both by experiments and high-fidelity CFD simulations and represented a benchmark case for this kind of aerodynamic study, reproducing a typical feature of tiltrotors and electrical distributed propulsion aircraft configurations. In particular, in the present activity results of simulations performed with DUST, the mid-fidelity aerodynamic solver of Politecnico di Milano were compared in terms of wing loads distributions, propeller airloads and flow fields with both experimental data and high-fidelity CFD simulations available in literature. Analyses on the upstream and downstream effects on the propeller and wing performance showed that the benefits arising from the installation of a wingtip-mounted propeller can be correctly predicted. Moreover, the significant lift and propeller performance enhancement as well as the interactional flow physics characterizing this configuration were accurately captured by the solver. Generally, this validation activity showed a quite good agreement with high-fidelity CFD results, thus confirming that the mid-fidelity numerical approach implemented in DUST is suitable for the investigation of wing-propeller aerodynamics interaction. The quite lower computational effort required by this mid-fidelity approach, while maintaining accuracy with respect to high-fidelity CFD methods opens a new scenario for the preliminary stage of design of novel tiltrotor or eVTOL aircraft characterized by complex interactional aerodynamic mechanisms
Rotorcraft stability analysis using Lyapunov characteristic exponents estimated from multibody dynamics
Get PDFStability analysis of complex, nonlinear dynamical systems is a challenge. The use of Lyapunov Characteristic Exponents through a Jacobian-less method is proposed as a means to identify the Maximum Lyapunov Characteristic Exponent, namely the fundamental stability indicator of a generic problem, solely from time series obtained through general-purpose multibody dynamics simulations of complex rotorcraft aeromechanics models. The method is first applied to a relatively simple scenario concerning the identification of ground resonance. Then, its application to more complex models is addressed by studying the aeroelastic stability and identifying the whirl flutter of the XV-15 tiltrotor using a comprehensive aeroelastic model
A numerical study of vibration-induced instrument reading capability degradation in helicopter pilots
Get PDFRotorcraft suffer from relatively high vibratory levels, due to exposure to significant vibratory load levels originating from rotors. As a result, pilots are typically exposed to vibrations, which have non-negligible consequences. Among those, one important issue is the degradation of instrument reading, which is a result of complex human-machine interaction. Both involuntary acceleration of the eyes as a result of biodynamics and vibration of the instrument panel contribute to a likely reduction in instrument reading capability, affecting flight safety. Therefore, being able to estimate the expected level of degradation in visual performance may give substantial benefits during vehicle design, allowing to make necessary adjustments while there is room for design changes or when retrofitting an existing aircraft to ensure the modifications do not adversely affect visual acuity and instrument reading ability. For this purpose, simulation is a very valuable tool as a proper model helps to understand the aircraft characteristics before conducting flight tests. This work presents the assessment of vibration-induced visual degradation of helicopter pilots under vibration exposure using a modular analysis environment. Core elements of the suggested analysis framework are an aeroelastic model of the helicopter, a model of the seat-cushion subsystem, a detailed multibody model of the human biodynamics, and a simplified model of ocular dynamics. These elements are combined into a comprehensive, fully coupled model. The contribution of each element to instrument reading degradation is examined, after defining an appropriate figure of merit that includes both eye and instrument panel vibration, in application to a numerical model representative of a medium-weight helicopter
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
A generalized Index for the assessment of helicopter pilot vibration exposure
Get PDFHelicopters are known to exhibit higher vibratory levels compared to fixed-wing aircraft. The consequences of vibrations depend on the affected helicopter component or subject. Specifically, pilots are in contact with several parts of the helicopter; vibrations can spoil the pilot-vehicle interaction. To evaluate the effects of vibration exposure on pilots, comfort levels resulting from whole-body vibration are computed. However, specific body parts and organs, e.g., hands, feet, and eyes are also adversely affected, with undesirable effects on piloting quality. Therefore, a detailed assessment is necessary for a more accurate estimation of pilot vibration exposure when comparing different configurations, tracking changes during design, and determining the safety of the flight envelope. A generalized assessment is presented by considering vibrations at the seat surface, hand-grip of controls, eyes, and feet. The suggested vibration measure includes comfort, handling, feet-contact, and vision in a single formulation. It is illustrated by coupling a high-fidelity biodynamic model of the pilot to a helicopter aeroservoelastic model in a comprehensive simulation environment. Using appropriate modeling techniques, vibration exposure of helicopter pilots could be evaluated during all stages of design, to achieve a more comfortable and safer flying environment
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