Numerical investigations about the sound transmission loss of a fuselage panel section with embedded periodic foams

The scope of this paper is to investigate the sound transmission loss of a typical fuselage panel section, as well as to propose solutions based on the inclusion of a periodic pattern inside its foam core, which aim at passively improving the acoustic performance in a mid-high range of frequencies. In detail, a new fuselage panel configuration is numerically studied, starting from the state of the art regarding the acoustic packages based on porous meta-materials. The main novelties of the present work are represented by the application of a meta-core solution inside an acoustic package of aeronautical interest, as well as a systematic investigation of the effects deriving from its geometrical parameters. In order to reach this goal, a numerical model of a fuselage panel section is studied, and the effect of several periodic patterns are simulated; more specifically, twelve configurations are taken into account, each with different radius of the inclusions and number of unit cells along the thickness. For each of these layouts, the mass increase of the so-called meta-core, compared to that of its classical homogeneous counterpart, is estimated, together with the associated mid-band frequency and amplitude of the sound transmission loss peak, which is caused by the additional acoustic modes excited by the periodic nature of the meta-core itself. Results are presented in terms of tables and graphs, which may constitute a good basis in order to perform preliminary design considerations that could be interesting for further generalizations

Use and Perceptions of a Campus Food Pantry Among Food Insecure College Students: An Exploratory Study from Appalachia

Introduction: Food insecurity has emerged as a public health problem among college students in Appalachia, jeopardizing their physical, mental, and emotional health and academic success. Campus food pantries have been established in this region, but no data are available concerning student use or perception of services. Purpose: This study measured use and perceptions of a campus food pantry by students at a mid-sized university in rural North Carolina. Methods: An online questionnaire collected behavioral and perceptual data, and follow-up interviews explored these variables. Descriptive statistics with significance at p\u3c0.05 and thematic analytical procedures were used. Results: Questionnaires were submitted by 896 of 6000 recruited students (14.9%), and four students granted interviews. Food insecurity affected 437 (48.8%) of participants, of whom 76 (17.4%) were pantry shoppers. Shoppers (n = 94) were 27.7% males, 65.1% females, and 7.2% non-cisgender, 63.8% non-Hispanic white, 84.5% undergraduate, and 14.3% graduate students. Reasons for non-pantry use by food insecure students included: others need it more (30.1%) and feel embarrassed (20.7%). Benefits of pantry use were: spent more on necessities (56.4%) and job performance improved (18.1%). Shoppers perceived the pantry’s physical environment most favorably and food offerings less favorably. Implications: The low use of the campus food pantry by food insecure students suggests that these students may be jeopardizing their physical and mental health and academic success. Greater efforts by faculty, academic advisers, and student leaders are needed to promote pantry use and decrease the associated stigma

Initial experimental investigations on natural fibre reinforced honeycomb core panels

The main attention of the present work is on eco-friendly honeycomb cores for sandwich panels. They are manufactured by combining flax fibres with polyethylene matrix; the analyses involve both reinforced and un-reinforced cores. Some experimental tests have been planned and carried out in order to qualify the modal characteristics of this important class of panels. Tests results, herein discussed, report a great improvement of reinforced cores (continuous-unidirectional and short-random) compared to un-reinforced ones in mechanical properties. An improvement in damping value is achieved by filling the core with wool fibres resulting in minimal weight increase. A summary of the impact and acoustic tests results of preview tests are also reported in order to have a global view of the behaviour of these sandwich panels

Time-resolved energy transfer from single chloride terminated nanocrystals to graphene

We examine the time-resolved resonance energy transfer of excitons from single n-butyl amine-bound, chloride-terminated nanocrystals to two-dimensional graphene through time-correlated single photon counting. The radiative biexponential lifetime kinetics and blinking statistics of the individual surface-modified nanocrystal elucidate the non-radiative decay channels. Blinking modification as well as a 4 times reduction in spontaneous emission were observed with the short chloride and n-butylamine ligands, probing the energy transfer pathways for the development of graphene-nanocrystal nanophotonic devices

Design of a tuned vbration absorber (TVA) for applications in transport engineering

The control of the response to tonal excitations or to broadband stochastic disturbances of a stiffened cylinder is investigated through the use of a Tuned Vibrating Absorber (TVA). In particular, the study considered both a purely passive device (Mechanical) and a semi-active one with shunt circuit (Electro-Mechanical) to evaluate the efficiencies and differences

A LINEAR TRANSFORMATION FOR THE RECONSTRUCTION OF THE RESPONSES BETWEEN SYSTEMS IN SIMILITUDE

The increasing attention towards the possibility of scaling structures and, therefore, systems in similitude in engineering field has led to plenty of methods which allow to reconstruct the response of a system, starting from that of a reference one. In fact, this approach would help to overcome the obstacles associated with full-scale testing, such as cost and setup. However, the associated predictions may not be fully reliable, due to some intrinsic limitations characterizing the traditional similitude methods (based on the definition of similitude conditions and scaling laws), such as: size effects, rate sensitivity phenomena, distorted similitudes. For this reason, a new method, called VOODOO (Versatile Offset Operator for the Discrete Observation of Objects), has been proposed; such a method is based on the definition of a transformation matrix which links the outputs between two sets of points belonging to a linear systems. The applications of VOODOO to plates and systems of plates demonstrate that an exact estimation of the frequency response is obtained when the degrees of freedom involved in the definition of the transformation are considered. Therefore, this work aims at investigating, by means of a sensitivity analysis, the method’s strengths and limitations when other degrees of freedom are considered, in order to identify the direction for further developments

Passive vibration control of tyres using embedded mechanical resonators

An investigation is carried out on structure-borne vibration and noise propagation of tyres’ models at low frequencies. The idea is to use embedded resonant meta-materials to damp the tyres’ vibrations and thus reduce the transferred energy to the main attached structures. A simplified tyre model is used, being the investigation of the effects of the embedded substructures the main target of the work; internal pressure and tyre rotation effects are neglected at this stage. Different configurations are tested targeting different natural modes of the tyre, while mechanical excitation is assumed on one section of the tyres. The results show how the proposed designs are a feasible solution for vibration control