Modelling Bending Wave Transmission across Coupled Plate Systems Comprising Periodic Ribbed Plates in the Low-, Mid-, and High-Frequency Ranges Using Forms of Statistical Energy Analysis

Prediction of bending wave transmission across systems of coupled plates which incorporate periodic ribbed plates is considered using Statistical Energy Analysis (SEA) in the low- and mid-frequency ranges and Advanced SEA (ASEA) in the high-frequency range. This paper investigates the crossover from prediction with SEA to ASEA through comparison with Finite Element Methods. Results from L-junctions confirm that this crossover occurs near the frequency band containing the fundamental bending mode of the individual bays on the ribbed plate when ribs are parallel to the junction line. Below this frequency band, SEA models treating each periodic ribbed plate as a single subsystem were shown to be appropriate. Above this frequency band, large reductions occur in the vibration level when propagation takes place across successive bays on ribbed plates when the ribs are parallel to the junction. This is due to spatial filtering; hence it is necessary to use ASEA which can incorporate indirect coupling associated with this transmission mechanism. A system of three coupled plates was also modelled which introduced flanking transmission. The results show that a wide frequency range can be covered by using both SEA and ASEA for systems of coupled plates where some or all of the plates are periodic ribbed plates

Wave propagation in one-dimensional nonlinear acoustic metamaterials

The propagation of waves in the nonlinear acoustic metamaterials (NAMs) is fundamentally different from that in the conventional linear ones. In this article we consider two one-dimensional NAM systems featuring respectively a diatomic and a tetratomic meta unit-cell. We investigate the attenuation of the wave, the band structure and the bifurcations to demonstrate novel nonlinear effects, which can significantly expand the bandwidth for elastic wave suppression and cause nonlinear wave phenomena. Harmonic averaging approach, continuation algorithm, Lyapunov exponents are combined to study the frequency responses, the nonlinear modes, bifurcations of periodic solutions and chaos. The nonlinear resonances are studied and the influence of damping on hyper-chaotic attractors is evaluated. Moreover, a "quantum" behavior is found between the low-energy and high-energy orbits. This work provides an important theoretical base for the further understandings and applications of NAMs

Structure-borne sound transmission between isotropic, homogeneous plates and periodic ribbed plates

The prediction of sound and vibration transmission in built-up structures is important for human comfort, health and safety. For structural reasons, engineering structures often incorporate periodic ribbed plates to increase stiffness and stability whilst reducing the weight. However, vibration propagation on periodic ribbed plates is complex due to the existence of stop/pass bands. This thesis is concerned with predicting vibration transmission between isotropic, homogeneous plates and periodic ribbed plates. The objectives are to investigate the use of Statistical Energy Analysis (SEA) and develop and validate advanced SEA (ASEA) using ray tracing to incorporate tunnelling mechanisms. Two approaches were considered for modelling the periodic ribbed plate: either representing it as a single subsystem or representing each bay as a single subsystem in the high-frequency range (above the fundamental local mode of the bay). In the low-frequency range (below the fundamental local mode of the bay) Finite Element Methods (FEM) and laboratory experiments show that the periodic ribbed plate can be adequately modelled in SEA using wave approaches from periodic structure and orthotropic plate theories. In the high-frequency range a significant decrease in energy along successive bays was identified using FEM leading to the conclusion that it is not appropriate to model a periodic plate as a single subsystem. SEA models were therefore investigated that treated each bay as an individual subsystem using wave theory. For different L-junctions formed from an isotropic, homogeneous plate and a periodic ribbed plate, SEA significantly underestimated the response in the bays. Experimental SEA (ESEA) was used to investigate these discrepancies which confirmed the existence of tunnelling mechanisms between physically unconnected subsystems. In contrast to SEA which gave errors up to 60 dB for the furthest bay from the junction, ASEA gave errors less than 6 dB when the mode count for the bay was greater than five. A range of two- and three- plate structures with different periodic ribbed plates or periodic folded plate have been modelled with ASEA. The results all lead to the conclusion that ASEA can successfully incorporate tunnelling mechanisms and provide a significantly more accurate approach to predicting high-frequency vibration transmission across periodic ribbed plates than SEA

Effective Action Recognition with Embedded Key Point Shifts

Temporal feature extraction is an essential technique in video-based action recognition. Key points have been utilized in skeleton-based action recognition methods but they require costly key point annotation. In this paper, we propose a novel temporal feature extraction module, named Key Point Shifts Embedding Module ($KPSEM$), to adaptively extract channel-wise key point shifts across video frames without key point annotation for temporal feature extraction. Key points are adaptively extracted as feature points with maximum feature values at split regions, while key point shifts are the spatial displacements of corresponding key points. The key point shifts are encoded as the overall temporal features via linear embedding layers in a multi-set manner. Our method achieves competitive performance through embedding key point shifts with trivial computational cost, achieving the state-of-the-art performance of 82.05% on Mini-Kinetics and competitive performance on UCF101, Something-Something-v1, and HMDB51 datasets.Comment: 35 pages, 10 figure

STAR (Saving Time, Adding Revenues) STAR: (Saving Time, Adding Revenues) Boarding/Deboarding Strategy

Summary Our goal is a strategy to minimize boarding/deboarding time. • We develop a theoretical model to give a rough estimate of airplane boarding time considering the main factors that may cause boarding delay. • We formulate a simulation model based on cellular automata and apply it to different sizes of aircraft. We conclude that outside-in is optimal among current boarding strategies in both minimizing boarding time (23-27 min) and simplicity to operate. Our simulation results agree well with theoretical estimates. • We design a luggage distribution control strategy that assigns row numbers to passengers according to the amount of luggage that they carry onto the plane. Our simulation results show that the strategy can save about 3 min. • We build a Áexible deboarding simulation model and fashion a new insideout deboarding strategy. • A 95% conÀdence interval for boarding time under our strategy has a halfwidth of 1 min. We also do sensitivity analyses of the occupancy of the plane and of passengers taking the wrong seats, which show that our model is robust