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The sinusoidal wavy cylinder of circular cross section is able to substantially reduce the fluid forces by effectively stabilizing the near wake in the subcritical flow regime. Based on the anechoic wind tunnel measurements and large eddy simulations (LESs), we investigate the capability of the sinusoidal wavy cylinder to reduce aeroacoustic noise as well as underlying flow physics. The wavy cylinder studied in this work covers a range of spanwise wavelength λ z = 1.8–6.0 D m and a range of wave amplitude a = 0.15–0.25 D m , where D m is the mean diameter of the wavy cylinder. The wind tunnel measurements are conducted at Reynolds number R e D m = 2.9–8.0 × 104, while LESs are conducted at R e D m = 3.0 × 104. It is observed that the wavy cylinder's configuration, determined by λ z and a , has a profound impact on the far-field sound pressure level (SPL) of both tonal and broadband noise. Compared with the baseline smooth cylinder, the wavy cylinder with λ z = 1.8 D m and a = 0.25 D m can reduce the peak value of SPL at the tonal frequency by up to 36.7 dB. The reductions in the overall SPL of the tonal and broadband noise are also tremendous, by up to 31.0 and 7.5 dB, respectively, by the wavy cylinder with the optimum wavelength. Consistent with observations on noise reduction are the significantly weakened near-wake structures and largely attenuated spanwise coherence, as well as substantially suppressed pressure fluctuations in the near wake and over the cylinder surface, based on the LES results. Dependence of the noise reduction on Reynolds number is discussed as well. [ABSTRACT FROM AUTHOR]

Quick and accurate crash detection is important for saving lives and improved traffic incident management. In this paper, a feature fusion-based deep learning framework was developed for video-based urban traffic crash detection task, aiming at achieving a balance between detection speed and accuracy with limited computing resource. In this framework, a residual neural network (ResNet) combined with attention modules was proposed to extract crash-related appearance features from urban traffic videos (i.e., a crash appearance feature extractor), which were further fed to a spatiotemporal feature fusion model, Conv-LSTM (Convolutional Long Short-Term Memory), to simultaneously capture appearance (static) and motion (dynamic) crash features. The proposed model was trained by a set of video clips covering 330 crash and 342 noncrash events. In general, the proposed model achieved an accuracy of 87.78% on the testing dataset and an acceptable detection speed (FPS > 30 with GTX 1060). Thanks to the attention module, the proposed model can capture the localized appearance features (e.g., vehicle damage and pedestrian fallen-off) of crashes better than conventional convolutional neural networks. The Conv-LSTM module outperformed conventional LSTM in terms of capturing motion features of crashes, such as the roadway congestion and pedestrians gathering after crashes. Compared to traditional motion-based crash detection model, the proposed model achieved higher detection accuracy. Moreover, it could detect crashes much faster than other feature fusion-based models (e.g., C3D). The results show that the proposed model is a promising video-based urban traffic crash detection algorithm that could be used in practice in the future. [ABSTRACT FROM AUTHOR]

This letter investigates an acoustic metamaterial exhibiting a unique sound pressure amplification mechanism for ultra-low frequency sound attenuation. The system is constructed by integrating a flexible panel into the side-branch duct of a Herschel-Quincke (HQ) tube. A new peak emerges in the Sound Transmission Loss (STL) at a frequency far lower than the frequencies of the HQ tube-induced STL peaks. It cannot, after careful comparisons, be attributed to any local resonances, including structural resonances of the flexible panel or air resonances inside the side-branch cavities. To explain the underlying physics, several numerical simulations are performed. The results reveal that analog to a mechanical inerter, a "push–pull" force is created by the sound pressure difference between the sub-cavities in which a pressure amplification mechanism is generated at the interface of the embedded panel. This force is large enough to activate an out-of-plane motion of the flexible panel, trapping the incident sound power in a circular flow around the duct-branch loop. The unique phenomenon is successfully reproduced in experiment, where the flexible panel is made of carbon fiber. The proposed acoustic metamaterial can be used as silencing components for ultra-low frequency noise control in duct. [ABSTRACT FROM AUTHOR]

This paper proposes a simulation approach for the optimal driving range of battery electric vehicles (BEVs) by modeling the driving and charging behavior. The driving and charging patterns of BEV users are characterized by reconstructing the daily travel chain based on the practical data collected from Shanghai, China. Meanwhile, interdependent behavioral variables for daily trips and each trip are defined in the daily trip chain. To meet the goal of the fitness of driving range, a stochastic simulation framework is established by the Monte Carlo method. Finally, with consideration of user heterogeneity, the optimal driving range under different charging scenarios is analyzed. The findings include the following. (1) The daily trip chain can be reconstructed through the behavioral variables for daily trips and each trip, and there is a correlation between the variables examined by the copula function. (2) Users with different daily travel demand have a different optimal driving range. When choosing a BEV, users are recommended to consider that the daily vehicle kilometers traveled are less than 34% of the battery driving range. (3) Increasing the charging opportunity and charging power is more beneficial to drivers who are characterized by high daily travel demand. (4) On the premise of meeting travel demand, the beneficial effects of increased fast-charging power will gradually decline. [ABSTRACT FROM AUTHOR]

Abstract This study investigates into the sound transmission through a periodic acoustic metamaterial grating of finite size. The single-layer grating is constructed by periodically arranging sub-wavelength unit cells in a slab, as a part of a large baffle between two acoustic domains. The metamaterial unit cell consists of an open duct decorated with coiled resonators, which intends to suppress sound transmission using its acoustic stop-band. The space-coiling structure allows the metamaterial to operate at low frequency with a compact size. Analytical approach to predict the sound transmission loss (STL) of the combined baffle is developed, which is employed to study its sound attenuation under normal and oblique incidence. Results show that the unit cell geometry, the periodicity of grating elements, and the angle of incidence significantly affect the STL. The STL behavior of the acoustic grating is mainly governed by three physical effects, including the acoustic stop-band, the edge diffraction, and the destructive radiation interference behind the acoustic grating. Detailed mechanism studies for these effects are discussed using numerical examples. Experiment is conducted to validate the proposed numerical approach. This paper presents a theoretical framework to predict and study the performance of acoustic gratings comprised of metamaterial unit cells, which can be further extended to study phase tailoring acoustic metasurface. [ABSTRACT FROM AUTHOR]

Abstract Experimental studies were conducted at an anechoic chamber to investigate the effectiveness of quarter flat tip, half flat tip and rectangular serrations on reducing propeller trailing edge noise. The experiments were conducted under four rotating speeds and the noise generated by the propeller was measured at four different positions. The thrust force produced by each propeller was also measured at each rotating speed. The performance of the quarter flat tip serrated propeller was poor at all rotating speeds and at all positions. The performance of the half flat tip serrated propeller was good at all rotating speeds and at all positions. It obtained overall noise reduction up to 5.8 dBA. For rectangular serrated propeller, its performance was only good at 2000 rpm at all positions and it obtained overall noise reduction up to 3.1 dBA. By overall, half flat tip serrated propeller had the best performance in term of noise attenuation compared to other two types of serrated propellers and its loss of thrust force was also 16.8% lower than that of rectangular serrated propeller. [ABSTRACT FROM AUTHOR]

The feasibility of using an acoustic metasurface (AMS) with acoustic stop-band property to realize sound insulation with ventilation function is investigated. An efficient numerical approach is proposed to evaluate its sound insulation performance. The AMS is excited by a reverberant sound source and the standardized sound reduction index (SRI) is numerically investigated. To facilitate the modeling, the coupling between the AMS and the adjacent acoustic fields is formulated using a sub-structuring approach. A modal based formulation is applied to both the source and receiving room, enabling an efficient calculation in the frequency range from 125 Hz to 2000 Hz. The sound pressures and the velocities at the interface are matched by using a transfer function relation based on “patches”. For illustration purposes, numerical examples are investigated using the proposed approach. The unit cell constituting the AMS is constructed in the shape of a thin acoustic chamber with tailored inner structures, whose stop-band property is numerically analyzed and experimentally demonstrated. The AMS is shown to provide effective sound insulation of over 30 dB in the stop-band frequencies from 600 to 1600 Hz. It is also shown that the proposed approach has the potential to be applied to a broad range of AMS studies and optimization problems. [ABSTRACT FROM AUTHOR]

Total variation and its variants have been widely used in the video/image restoration area in the past decades. Among them, the nonlocal total variation model introduces penalization on nonlocal gradients and demonstrates remarkable performance gain in many applications. However, this approach tends to suppress intensity-changes of visual contents, and hence cannot restore complicated visual contents well enough. To address this issue, this paper proposes a novel second order nonlocal total variation model for video restoration problems. Firstly, the directed space-time nonlocal gradients are defined in our model to formulate the spatio-temporal intensity-changes of video contents. Secondly, mean-value approximations of these nonlocal gradients are introduced into the model. Based on them, we build up a new model that consists of both first order and second order nonlocal regularization terms. Furthermore, for the purpose of adapting to specific visual contents, it is also augmented with a content-adaptive modification. These features make the proposed second order nonlocal total variation model a high order generalization of the original one. Experimental results on various video restoration problems show that the proposed model significantly improves the restoration qualities, compared with other state-of-the-art approaches. [ABSTRACT FROM AUTHOR]

This paper investigates the acoustic properties of a duct resonator tuned by an electro-active membrane. The resonator takes the form of a side-branch cavity which is attached to a rigid duct and covered by a pre-stretched Dielectric Elastomer (DE) in the neck area. A three-dimensional, analytical model based on the sub-structuring approach is developed to characterize the complex structure-acoustic coupling between the DE membrane and its surrounding acoustic media. We show that such resonator provides sound attenuation in the medium frequency range mainly by means of sound reflection, as a result of the membrane vibration. The prediction accuracy of the proposed model is validated against experimental test. The pre-stretched DE membrane with fixed edges responds to applied voltage change with a varying inner stress and, by the same token, its natural frequency and vibrational response can be tuned to suit particular frequencies of interest. The peaks in the transmission loss (TL) curves can be shifted towards lower frequencies when the voltage applied to the DE membrane is increased. Through simulations on the effect of increasing the voltage level, the TL shifting mechanism and its possible tuning range are analyzed. This paves the way for applying such resonator device for adaptive-passive noise control. [ABSTRACT FROM AUTHOR]

A membrane-based silencer using dielectric elastomer absorbers (DEAs) was developed and explored in the present study. Dielectric elastomer, a soft smart material, was used to fabricate this actuator. It has the characteristic of lightweight, high elastic energy density and large deformation under external direct current (DC) or alternating current (AC) voltages. The typical acoustic performances of this membrane-based silencer were experimentally identified using a transmission loss (TL) duct acoustic measurement system. It was found that the resonance peaks of this membrane-based silencer could be controlled by applying different external voltages, a maximum resonance frequency shift of 59.5 Hz for the resonance peaks was achieved which indicated that this membrane-based silencer could be adjusted to absorb the target noise without any addition mechanical part. Furthermore, the resonance shift and multiple resonances mechanisms using DEAs were proposed and discussed which was aiming to achieve multi-peaks noise reduction. The present results also provide insight into the appropriateness of the absorber for possible use as an acoustic treatment to replace the traditional acoustic treatment in the noise reduction technology. [ABSTRACT FROM AUTHOR]

A finite element acoustic model was proposed for investigating the characteristic of a novel non-locally reacting acoustic liner. This non-locally reacting acoustic liner was based on the so-called multiple cavity resonance mechanism which could broaden the absorption bandwidth. The basic idea of it was that when the back cavity of the liner was partitioned into sub-volumes of different size, multiple resonances relating to different length were produced so that the attenuation peaks came closer and worked jointly to provide high attenuation over a broad frequency band. There were strong coupling effects of the resonances inside the back cavities and in the duct when the sound propagated in the duct installed this non-locally acoustic liner. The proposed finite element acoustic model could simulate the entire sound field both in the duct and inside the back non-uniform cavities of the liner including the strong coupling effects. The comparison between the numerical and the experimental results demonstrated that, the finite element acoustic model was an accurate, stable and rapid method for investigating the acoustic characteristic of this novel non-locally reacting acoustic liner. The numerical study was also targeted for developing an optimal non-locally acoustic liner for engineering applications. [ABSTRACT FROM AUTHOR]

Road noise varies with the vehicles' load and speed, ranging from low to medium frequencies. The existing absorbers, including acoustic metamaterials, cannot fully mitigate the variable noise due to limited bandwidth. To target the variable noise but not occupy much space, this paper presents a tunable acoustic absorber that can transform from Helmholtz resonance to membrane resonance. This tunable absorber consist of double micro‐slit layers, namely an electro‐adhesive membrane and a flexible plate spaced closely in front of a shallow cavity. The boundary‐layer thick gap between the two forms a network of lateral orifices to enhance the acoustic damping at medium frequencies. When the gap closes under electrostatic attraction force, the membrane and plate zipped together and resonated like a drum at a much lower frequency. This transformation can shift the resonant frequency down by 1.6 octaves from 898 hetz (Hz) to 281 Hz, thanks to the structural resonance of the zipped parts. Interestingly, the peak absorption coefficient at the lowest tuned 281 Hz was as high as 0.93. Such distributed tunability based on a fault‐tolerant electro‐adhesive membrane will also be applicable to other acoustic meta‐materials that embody the components of micro‐perforated or micro‐slit panels. [ABSTRACT FROM AUTHOR]

Considerable efforts have been devoted to the development of dynamic origin-destination (OD) estimation models, which are a key step to realizing self-adaptive traffic control systems for urban traffic management. However, most of the models proposed to date estimate OD flows based on a single traffic data source, and their performance is limited by the coverage and accuracy of traffic sensors. The inherent difficulty in estimating the dynamic traffic assignment matrix means that dynamic OD estimation remains a challenge for real-life applications. This paper proposes the use of a Kalman filter for dynamic OD estimation using multi-source sensor data. The dynamic characteristic of changing OD flow over time is analyzed, and the problem of dynamic OD estimation is converted to a problem of estimating OD structural deviation. The resulting dynamic relationship between traffic volume and OD structural deviation is then used to establish the Kalman filter model. An improved traffic assignment approach is developed and embedded into the measurement equation of the Kalman filter model to enable dynamic updating of the traffic assignment matrix. A dual self-adaptive mechanism based on the Kalman filter is used to calibrate the model. The proposed method was implemented on a real-life traffic network in the downtown area of Kunshan City, China. The results show that the proposed method is more accurate than, and outperforms, the traditional link-volume-based and turning-movement-based methods. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The scroll-type compressor is the core component of the refrigeration system using the natural refrigerant carbon dioxide. An accurate scroll geometric theoretical model is essential for evaluating and enhancing compressor performance. The present paper proposed and validated an improved geometric theoretical model of a scroll compressor. A vector triangle method-based general piecewise function describes precisely the volume variation of the working chambers, based on which the transient throughflow modeling and performance evaluation of a carbon dioxide scroll compressor were conducted. The mechanisms and influencing factors of the suction precompression and the asymmetry discharging were analyzed. The results indicate that the strength of the suction precompression is mainly influenced by the suction vacuum under different rotating speeds, partly associated with the tangential leakage under low rotating speeds. The increasing initial suction pressure contributes to the linear raising of the pressure difference between suction initial and ending pressures, decreasing the precompression extension slightly. The variation of the discharge throughflow areas of two symmetric discharge chambers dominates the pressure asymmetry, which is gradually eliminated by the overlapping throughflow area. Compared with the circular discharge structure, the waist-shape port reduces the pressure asymmetry degree and shortens its duration. [ABSTRACT FROM AUTHOR]

In old video restoration, automatic detection of common defects, e.g., scratches and blotches, has always been emphasized. While prior thoughts mainly focus on detecting blotches and linear, vertical scratches separately, this paper contributes to a more generalized and challenging issue: simultaneous detection of blotches and complex scratches in video, with much less knowledge of them. We investigate the characteristics of blotches and scratches in space and time domain, and propose a novel detection method based on two main steps: cartoon-texture decomposition in the space domain and content-defect separation in the time domain. We then formulate it into convex optimization problems and develop corresponding algorithms. The experiment results demonstrate that the proposed method is of high detection accuracy, verifying the effectiveness of our detection via a video decomposition method. [ABSTRACT FROM PUBLISHER]

• Open-cell metallic foams with partially-open cell windows are developed and investigated. • A new microstructure-based fluid model is proposed to predict the flow characteristics across the porous medium. • The flow resistance and sound absorption performance are greatly enhanced while the foams maintain high porosity. • The predicted sound absorption coefficient shows excellent agreement with experiments. Metallic foams with high flow resistivity are of high interest as practical sound absorption materials. Herein, we report the novel open-cell metallic foams associated with a partially-open window morphology between interconnected pores for improved flow resistivity and sound absorption coefficient. Such a microstructure was produced through exploiting the shear thinning behavior of the metal slurry during the template replication fabrication process. A new microstructural model for permeability simulation is also developed for the new foam to account for the increased specific surface area from the windows. Input parameters to the model include cell geometries that are accessible via morphological characterization. Results showed that metallic foams with the window morphology have significantly increased flow resistivity (1.5 times) with little loss in porosity (< 2.3%). Impedance tube acoustic measurements confirmed such increments to improve the sound absorption coefficient (averaged as 0.2) throughout the entire frequency range. The concept explored in this study demonstrates a generic approach for the design of microstructure-specific foams with simultaneously increased flow resistance and a fully open-celled microstructure associated with high porosity (between 93%~97%). The proposed fluid model also has excellent potential to be adopted in a diverse range of applications for design and characterization. Image, graphical abstract [ABSTRACT FROM AUTHOR]

• Hygroscopic PEDOT:PSS electrodes and acrylic dielectric elastomer make a 'hygromophic' actuator • The current leaked via this constant-voltage activated capacitor surges with increasing humidity Many capacitive or resistive humidity sensors cannot accurately measure high humidity because of surface water condensation and saturation of hygrosopic material in the sensors. Here, we propose a novel method of high humidity measurement using a 'hydromorphic' dielectric elastomer actuator (DEA). This novel humidity sensor consists of a 'relatively water-inert' acrylic dielectric elastomer layer (3M VHB 4910) sandwiched by a pair of hygroscopic polymer electrodes. The hygroscopic polymer electrodes are made of poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS); they become softer upon moisture absorption while enabling moisture permeation into the dielectric elastomer substrate during electrical activation and read-out. While the dielectric elastomeric actuation (under constant voltage) enlarged with increasing humidity, the current leaked through it rose more significantly. This suggests a strong humidity dependence of dielectric resistivity. Experimental correlation showed the dielectric resistance be a piecewise linear function of humidity. Further, this DEA-based humidity sensor remained working when both its electrodes were sprayed with a mist of water droplets. [ABSTRACT FROM AUTHOR]

Membrane-type acoustic metamaterials (MAM) are novel, lightweight and compact materials that can be used to isolate the sound at low frequencies beyond the limits of conventional materials. MAMs open up many possibilities for creating a new generation of acoustic materials and sensor devices. In this paper, the acoustic-structural interaction of the MAM with eccentric masses is explored by employing finite element simulations that use multi-physics commercial software COMSOL with experimental validation. This scheme is set to optimize the distribution of eccentric masses (such as thickness, weight, shape, the split number, the size of the 'pocket' and the size of the ring mass) to improve acoustic performance. The mass added onto the membrane can change the membrane surface density, constrain membrane displacement and induce new anti-resonance modes. Combinations of these new anti-resonances can broaden sound insulation performance of the MAM. The 4-split ring mass configuration can significantly increase the 5 dB-TL band by 1325% compared to that of a single membrane in the low-frequency range (<300 Hz). The gap between the splits, called a 'pocket', is examined to further explore the membrane-acoustic interactions in order to obtain a better understanding of the physical mechanism. [ABSTRACT FROM AUTHOR]

Time-invariant (or mean) secondary flows, in terms of large-scale counter-rotating roll modes filling boundary layer, have been observed in turbulent boundary layer (TBL) flows over various spanwise-heterogeneous rough walls. Recent studies show that these mean secondary flows are inherently connected with instantaneous large-scale structures in TBL flows over such spanwise-heterogeneous rough walls. In this work, the technique of proper orthogonal decomposition (POD) is used to extract dominant energetic (and thus large-scale) structures from TBL flows over the surface with a spanwise-periodic converging/diverging riblets pattern, one of the spanwise-heterogeneous rough walls adopted previously. POD analyses are conducted on the three fluctuating components of velocities, measured by stereoscopic particle image velocimetry at Re θ = 13 000, in a cross-stream plane of the TBL flows over a spanwise section of the converging riblets pattern, where low-momentum eruptions consistently occur. It is found that first two POD modes with large temporal coefficients are linked to large-scale structures oscillating vigorously in the transverse direction within one section of the converging riblets. Superposition of these instantaneous large-scale structures reveals the observed pattern of mean secondary flows. Furthermore, these large-scale structures are associated with enhanced streamwise vortices and spanwise gradients of the streamwise velocity, compared with that in the smooth wall flow, thus rendering profound effects on the spatial correlations of velocities as well as the distributions of Reynolds stresses. [ABSTRACT FROM AUTHOR]

Macroscopic Fundamental Diagram (MFD) reveals the relationship between network accumulation and flow at the macroscopic level. The network traffic flow state analysis is a fundamental problem for the MFD-based applications. Theoretical and experimental investigations have provided insights into the dynamics and characters of traffic flow states. Although many empirical studies had been conducted in the field of MFD, few studies were dedicated to investigate the network traffic flow states with field data. This study aims to develop a data-driven method based on time series analysis of MFD state points to characterize critical transition state (CTS) of network traffic flow using field data. The proposed method was tested in a real network of Kunshan City, China. The test results showed that the CTS points can be well captured by the proposed method. The identified CTS points distinguished the traffic states between free-flow state and optimal accumulation state, and the optimal accumulation state was characterized. The day-to-day pattern of CTS points was investigated by the Gaussian Mixture Model-based clustering model. An extended application of real-time identification of CTS points was also discussed. The proposed method is helpful to understand the temporal evolution process of network traffic flow and provides potentials for developing more reliable network traffic flow management strategies, such as optimizing traffic signal plans and developing strategies for congestion tooling. [ABSTRACT FROM AUTHOR]

Acoustic absorbers, acoustic metamaterials, electro-adhesion, electrostatics, Helmholtz resonators, Helmholtz resonators, membrane resonators, self clearing, sound absorbers Transformation from Helmholtz to Membrane Resonance by Electro-Adhesive Zip of a Double-Layer Micro-Slit Acoustic Absorber (Adv. A transformable absorber that switches from the Helmholtz resonance at a medium frequency to the membrane resonance at a low frequency is developed. [Extracted from the article]

This paper presents an approach for data-driven modeling of aeroelasticity and its application to flutter control design of a wind-tunnel wing model. Modeling is centered on system identification of unsteady aerodynamic loads using computational fluid dynamics data, and adopts a nonlinear multivariable extension of the Hammerstein-Wiener system. The formulation is in modal coordinates of the elastic structure, and yields a reduced-order model of the aeroelastic feedback loop that is parametrized by airspeed. Flutter suppression is thus cast as a robust stabilization problem over uncertain airspeed, for which a low-order H ∞ controller is computed. The paper discusses in detail parameter sensitivity and observability of the model, the former to justify the chosen model structure, and the latter to provide a criterion for physical sensor placement. Wind tunnel experiments confirm the validity of the modeling approach and the effectiveness of the control design. [ABSTRACT FROM AUTHOR]

The noise sources are mainly associated with a turbulent flow (as in jet or boundary layer noise) or aerodynamic forces interacting with surfaces (as in airframe noise from high-lift devices and landing gear). This special collection presents the state of the art in theoretical, numerical, and experimental investigations of the source mechanisms and control methods of aerodynamic noise. The special collection on Source Mechanisms and Control Methods for Aerodynamic Noise is available in the ASCE Library https://ascelibrary.org/jaeeez/source mechanisms Aerodynamic noise, also known as aeroacoustic or flow noise, generally refers to the noise generated by unsteady flow. [Extracted from the article]

• Modal analysis revealed the vibrational modes of membrane-type acoustic metamaterials under different frequency excitations, offering profound insights into low-frequency sound insulation mechanisms. • By adjusting the shape, arrangement, radius, and material of the mass units, the transmission loss (TL) frequency of the acoustic metamaterials was successfully optimized. • By adding multiple loaded mass units and adjusting their positions and angles, collaborative resonance effects were achieved. Membrane-type acoustic metamaterials (MAM) represent a class of materials that are lightweight, compact, structurally simple, and simultaneously offer flexibility and moldability, all while demonstrating exceptional sound attenuation properties in the low-frequency range. As a continuation, this study focuses on membrane-based acoustic metamaterials with synergistic resonance of multiple loaded mass blocks. By varying the unit shape, arrangement method, radius and material of the loaded mass blocks, the low-frequency sound insulation performance of membrane-based acoustic metamaterials with synergistic resonance of multiple loaded mass blocks was calculated using a numerical model that are experimentally validated. The results indicate that the peak transmiss loss (TL) frequencies can be tuned to specific values. The optimized membrane-type acoustic metamaterial could achieve a TL bandwidth up to 844 Hz (>5dB) and a TL bandwidth up to 376 Hz (>10 dB) within the low-frequency range. Acoustic-membrane analysis further revealed the vibration patterns of the structure under different frequency excitations, providing profound physical insights into the mechanisms of low-frequency sound insulation. Moreover, by altering the relative angles between the loaded mass blocks could further broaden the effective noise reduction bandwidth which can benefit the understanding on the optimized membrane-acoustic interactions. [ABSTRACT FROM AUTHOR]

• A serration design of an owl-inspired propeller shows up to 4.4 dBA noise reduction. • A numerical model combining fluid and acoustic simulation is established. • The interactions between the flow characteristics and aerodynamic noise were obtained. • The experiment strikes a balance between increased power consumption and reduced noise. The present study investigates owl-inspired propellers with various serrated trailing edge configurations. An analysis utilizes a numerical model that integrates computational fluid dynamics (CFD) with Large Eddy Simulation (LES) and Lighthill acoustic analogy. The simulation aims to clarify the mechanism behind noise reduction in the bionic propeller by comparing tip vortices and wake region vortices with or without serrated trailing edge structures. Additionally, a thorough assessment of noise and aerodynamic performance is carried out on bionic propellers with varied serrated ratios, shapes, and coverage degrees, through experimental measurements conducted under varying rotation speeds and thrust levels. Experimental results demonstrated the significant noise reduction capabilities of sawtooth bionic structures across various rotation speeds. Notably, the bionic propeller with a round-serrated trailing edge, a serrated ratio of 0.9, an arc radius of 0.3 mm, and 50 % serration coverage achieves a noteworthy noise reduction of up to 4.4 dBA. The findings highlight a significant correlation between the propeller's flow structure and its aerodynamic noise characteristics. The findings highlight a correlation between the propeller's flow structure and its aerodynamic noise characteristics. Serrated trailing edges disrupt propeller tip vortices, expediting the vortex shedding and dissipation processes, thereby mitigating trailing edge noise. Additionally, a distinctive inward shift of the wake at the trailing edge promotes the intermixing of flow structures, enhancing collisions and mixing of vortices, ultimately resulting in a significant broadband noise reduction. [ABSTRACT FROM AUTHOR]

The sound absorption of vegetation with embedded periodic metamaterials is investigated numerically and experimentally. Acoustical property of the vegetation can be described as that in a porous material. The physical parameters of vegetation in the numerical study are obtained by fitting the measured reflection and transmission coefficients with the simulated results. The embedded metamaterial is composed of two-layer oppositely oriented split tubes, which can achieve two resonant absorption peaks at wavelengths much larger than its thickness. Both absorption peaks can be easily controlled by adjusting the width of the metamaterial while keeping its thickness unchanged. It is demonstrated that the absorption performance can be significantly enhanced by embedding periodic metamaterials into the vegetation. The results can be explained by coupling the viscous and thermal losses of vegetations with the resonance phenomenon arising from the metamaterials. Moreover, sound absorption increases with increased incidence angles and vegetation thickness. When more than one metamaterial per spatial period is considered, additional absorption peaks are observed which can further broaden the effective absorption bandwidth. [ABSTRACT FROM AUTHOR]

The sound absorption via an absorber constructed by a vegetation layer and a metasurface substrate (MS) is numerically and experimentally investigated. By combining the vegetation and MS, high-efficiency sound absorption (>90%) can be achieved in a broader frequency range (from 0.93 kHz to 1.15 kHz). The MS subunit is composed of two 180°-twisted ellipse-shaped split tubes, which can achieve high absorption at the resonance frequency. According to the applications, the resonance absorption peak can be controlled by adjusting the length of the semi-major axis of the elliptical subunit. The acoustical properties of the vegetation layer can be described as a porous material, and its parameters in the simulation are obtained by fitting the measured sound absorption coefficients. Integrating the vegetation layer into the proposed absorber can further improve the absorptions in a wide frequency range of interest while it does not affect the resonance frequency of the MS subunit. Five different subunits are selected to form a deep-subwavelength MS array which can extend the absorption bandwidth. The broadband sound absorption of the absorber is robust under oblique incidence even at large incident angles. The proposed absorber has potential applications in acoustic engineering such as traffic and building noise control as well as green façades and green walls. [ABSTRACT FROM AUTHOR]

Broadband absorption of the audible sound wave at low frequency has been achieved by using periodic acoustic metamaterial resonators (AMRs) embedded inside a porous layer. A single AMR embedded in a porous layer could reach perfect absorption (PA) at the resonance frequency, and it can be easily tuned by adjusting the inner radius of AMR. With four AMRs in the porous layer, a high absorption (>80%) is obtained in the frequency range from 180 Hz to 550 Hz, while the thickness of the porous layer is only 1 / 10 of the relevant wavelength at 300 Hz. The broadband and high absorption performances are due to the interferences of the low-frequency resonances of the AMRs and the energy trapping between the AMRs and the rigid backings. The finite element simulations are experimentally validated. Moreover, the broadband low-frequency absorption is robust under various oblique incidence even at large incident angles. The effects of the acoustic parameters of the porous layer on the absorption properties are also discussed. The absorbers should have high potential for the practical applications in buildings, aircrafts and automobiles due to their ease of fabrication, ultra-thin, and robust high-efficiency. [ABSTRACT FROM AUTHOR]

Determining spatiotemporal impact areas of incidents plays a significant role in incident impact analysis. Although existing empirical methods have proven to be promising, they suffer from the drawbacks that limit their wide applications in automated freeway safety management. This study presents a data‐driven approach to automatically determining the spatiotemporal impact areas of freeway incidents. The spatiotemporal contour plots were first constructed using three representative traffic measures. Next, a nonrecurrent congestion area identification method based on fuzzy clustering was developed. To distinguish possible multiple independent blocks in the nonrecurrent congestion area, a clustering algorithm based on graph theory was adopted. The incident impact areas were then determined by conducting a postprocessing strategy. The incident records and the associated traffic flow data, collected on I‐5 freeway segments in San Diego Region, CA, were used to evaluate the proposed approach. Experimental results show the proposed approach can automatically and properly determine incident impact areas while accounting for the uncertainty resulting from traffic variations. [ABSTRACT FROM AUTHOR]

Abstract Conventional sound barriers are constrained by fixed geometry which results in many limitations. In this research, origami , the paper folding technique, is exploited as a platform to design deployable and reconfigurable sound barriers, as well as to actively tailor the attenuation performance. As a proof of concept, a three-dimensional barrier structure is constructed based upon Miura-ori unit cells, whose shape can be significantly altered via folding with a single degree of freedom. Folding also generates periodic corrugations on the origami sheets, which can be exploited as backing cavities to form resonant sound absorbers with a micro-perforated membrane. The absorption performance of the constructed absorber and the insertion loss of the origami barrier are investigated using both numerical and experimental tools. The proposed origami barrier involves two fundamental mechanisms: sound reflection and absorption, and the origami offers unique tunability to enrich both mechanisms owing to the folding-induced geometric evolutions. Specifically, the sound reflection effect can be effectively tuned via changing the acoustic shadow zone and the diffracted sound paths by folding, and the sound absorption effect can also be regulated by altering the depth/shape of the backing cavities during folding. Overall, the results of this research offer fundamental insights into how folding would affect the acoustic performance and open up new opportunities for designing innovative origami-inspired acoustic devices. [ABSTRACT FROM AUTHOR]

• A theoretical method for predicting the acoustic impedance of rectangular micro-perforated membranes with membrane vibration. • Numerical modeling implements the linearized Navier-Stokes equations for coupled vibrations in the frequency domain. • The effects of membrane geometry parameters on the absorption performance of micro-perforated absorbers are investigated. A theoretical method base on the zero-slip boundary and a finite element model with thermoviscous membrane-acoustic interaction are proposed for investigating a viscously damped micro-perforated rectangular membrane. Both the theoretical and finite element methods well predicted the sound absorption performance of a dielectric elastomer micro-perforated membrane, and the results agree with those from experiments. The thermoviscous membrane-acoustic interaction is further explored. The properties which lead to better acoustic performance are studied using the developed numerical model. With the optimized parameters, a duct silencer with high transmission loss (>10 dB) and broad noise attenuation band (from 300 Hz to 1700 Hz) is designed, fabricated, and tested. The potential engineering application and the background physical mechanism are also addressed. [ABSTRACT FROM AUTHOR]

Vehicle trajectory data derived from automatic vehicle location (AVL) and automatic vehicle identification (AVI) systems provide critical support for intelligent transportation systems. However, the field-obtained vehicle trajectories are usually incomplete due to sensor malfunction or communication issues. To recover the incomplete data, the existing reconstruction methods have to impose strong assumptions on driver route choice behaviors (network level) and/or traffic dynamics (link level). With the tremendous data available, leveraging data-driven approaches to address the vehicle trajectory reconstruction problem with minimal assumptions is promising. This paper proposes a general dynamic sequential learning framework to reconstruct vehicle trajectory points for both AVL and AVI data. First, an Isolation Forest based ensemble learning model is developed to extract trajectory sequences attributed to different trips in an entire trip chain of a vehicle. Second, the dynamic recurrent neural network (dynamic RNN) is tailored to learn the underlying patterns from the complete AVL and AVI trajectories, respectively. Third, a sequential prediction scheme is customized to reconstruct AVL and AVI trajectories based on the trained networks. To validate the proposed method, two experiments are conducted. One is a simulation experiment with AVL data gathered from a well-calibrated simulation model. The other is a field experiment with AVI data collected from a real-world automatic license plate recognition (ALPR) system. The results show that the proposed method achieves superior performance for both AVL and AVI data compared with the traditional methods. The impacts of different sampling rates and traffic conditions on the model performance are also discussed. • A general learning framework for vehicle trajectory reconstruction is developed. • An Isolation Forest based model is adopted to extract trip trajectory sequences. • The dynamic RNN is tailored to learn the patterns from the complete trajectories. • A sequential prediction scheme is customized to reconstruct incomplete trajectories. • Two comparisons are conducted to demonstrate the effectiveness of the framework. [ABSTRACT FROM AUTHOR]