Transmission Loss Model Research Articles

Hydroacoustic Evidence for Offshore Lava Emplacement During the 2018 Kīlauea Eruption

AbstractDuring the 2018 Kīlauea eruption, over half the erupted lava was deposited on the seafloor. Lava flows crossing the shoreline generated sounds that were recorded by a network of hydrophones. We show that short‐duration, broadband signals associated with lava‐water interactions occurred throughout the eruption but increased in number when the Ahalanui ocean entry initiated on July 11. These terminated in early August coincident with the eruption's end. We compare hydroacoustic data with transmission loss models and eruption photographs to show that coastal explosive activity was poorly recorded by the hydrophone network. Similarly, strong hydroacoustic signals did not correlate with observed activity. These results suggest that acoustic signals were generated by lava flowing up to 100 s of meters offshore. Offshore lava flows can be hazardous to boaters, but hydrophones provide a means by which these hazards can be detected.

A vibroacoustic model for low-frequency sound transmission loss in circular membranes with added strip mass

Noise control strategies involve physical barriers in the transmission path. Conventional barriers conform to the mass law which states an inverse relation between sound transmission, barrier mass, and incident frequency. Practical scenarios for low-frequency noise attenuation require prohibitively thick barriers making them infeasible. Mass-loaded membranes exhibit marked differences in their dynamic nature from that of bare membranes as they do not necessarily conform to the mass law. Being thin, compact, and lightweight makes them geometrically ideal for most applications. The paper presents an analytical model based on the Newtonian approach for the vibroacoustic behavior of a pre-stretched elastic circular membrane with rigidly attached strip mass under normal incidence. The point collocation approach distributes the effect of the strip mass on the membrane as a collection of discretized concentrated loads along the interfacial boundary resulting in a summation that is easier to solve. The peak and dip frequencies of sound transmission are determined for circular membranes with eccentric and central strip mass. The present study evaluates strip mass-loaded membranes' capability to attenuate noise at low frequencies as an unconventional physical barrier.

Acoustic optimization design for the laying schemes on the composite roof structure of high-speed train

ABSTRACT If the weak sound insulation in the roof during high-speed train travel through tunnels can be addressed by adjusting the order of materials, this will meet design requirements for both economy and lightweight construction. This paper studies this problem. First, a prediction model for sound transmission loss (STL) of the roof was established to investigate the impact of different material placement schemes and optimize their arrangement. Then, the optimal placement schemes between the roof and floor were compared using STL tests. Finally, this study also examined how an optimal scheme mitigates power radiation from the roof into the train interior under typical mechanical excitations. The results indicate that the optimal laying scheme for the roof differs from that of the floor. By placing sound absorption materials on the inner side of aluminium extrusion and sound insulation materials on decorative plate, it effectively enhances vibro-acoustic characteristics of the roof.

Modelling the Acoustic Properties of Baffles Made of Porous and Fibrous Materials

The research described in the article addresses the problem of measurement, prediction and practical use of the acoustic properties of materials determined in an impedance tube. The aim of the research was to develop a simple calculation model for the insertion loss of small machinery enclosures, based on the normal incidence sound transmission loss and the normal incidence sound absorption coefficient of porous and fibrous materials. Both experimental and model tests were carried out on materials such as mineral wool, melamine foam and rebonded polyurethane foam. Assessing the absorption properties of the tested porous and fibrous materials was performed using selected theoretical models, relating the calculations of the normal incidence sound absorption coefficient to measurements of this parameter conducted using an impedance tube. The application of the modified Allard and Champoux model brought the best results with the smallest discrepancies of the obtained results in relation to the experimental tests. Assessing the sound-insulating properties of the tested mineral wool was carried out using the proposed calculation model for the normal incidence sound transmission loss, relating the obtained results to measurements conducted using an impedance tube. The assessment of the sound-insulating properties of porous and fibrous materials was performed using the proposed calculation model for insertion loss, which was validated using two prototype test stands for determining the insertion loss of cubic enclosures, in this case with walls made of porous and fibrous materials. Satisfactory results were obtained for engineering applications in the calculation results using the proposed models with respect to measurements. The results may have practical applications in assessing the effectiveness of acoustic enclosures, in which the basic construction material is an appropriate porous or fibrous plate, selected to have both sound-absorbing and sound-insulating properties.

Design strategies of cementitious metamaterials (CMs) with tunable bandgaps: Density customization and geometric optimization

The propagation of low-frequency elastic waves may exert significant stress on both human health and environmental safety. This study presents a new kind of cementitious metamaterials (CMs) characterized by tunable bandgaps for efficient absorption of low-frequency elastic waves. A dynamic system model is employed to examine and analyze the eigenfrequencies of these CMs. Herein, the porous alkali-activated municipal solid waste incineration fly ash (AAFMs) is modulated with customed density and then combined with rubber for generating CMs. Two distinct strategies are proposed to modulate the bandgap properties of the CMs: density customization and geometric optimization. The AAFMs' density is meticulously regulated by altering the foaming aluminum content, allowing the customization of CMs' bandgaps. Additionally, the CMs' bandgaps can also be tailored through geometric optimization, a process that involves a numerical method focused on examining the impact of varying inclined angles in inner and outer re-entrant structures. A transmission loss model is also developed to validate the bandgap characteristics of these CMs. Overall, the study explores the potential applications of these CMs, with a specific focus on their efficacy in mitigating low-frequency vibrations and attenuating noise. The successful utilization of these materials in such domains holds promising prospects for substantial advancements across diverse industrial sectors.

An enhanced strain gradient model for temperature-dependent sound transmission loss in double-walled functionally graded microplates

With the growing use of functionally graded (FG) microplates in structural acoustic metamaterials for aerospace and automotive applications, accurate modeling of sound transmission loss is critical for effective vibration and noise control engineering. In this study, a theoretical model is formulated based on the first-order shear deformation theory (FSDT) to estimate sound transmission loss (STL) through air-filled rectangular double-walled FG microplates with simply supported boundary conditions. The microplates are subjected to a nonlinear thermal environment, and the modified strain gradient theory (MSGT) is employed, incorporating three material length scale parameters to account for the size effect. The material properties are temperature-dependent and vary across the thickness following a power-law distribution. Size-dependent coupled vibroacoustic equations are derived utilizing the sound velocity potential, normal velocity continuity conditions, and Hamilton's principle, and are subsequently solved using the Galerkin method. Comparative analysis is performed by contrasting the results obtained from the MSGT model with those from the modified couple stress theory (MCST) and classical continuum theory (CCT) models, allowing for the assessment of the accuracy and precision of the proposed solution. Additionally, the influence of various parameters, such as gradient index, length scale parameters, temperature variation, incident angles, and acoustic cavity depth, on the STL is investigated. Key findings demonstrate that in the stiffness-controlled region, length scale parameters significantly enhance STL, while power-law index and temperature variation reduce it.

Information geometry approach to model reduction

Information geometry combines the fields of information theory and differential geometry. In information geometry, a model is interpreted as a Riemannian manifold, referred to as the model manifold, where distance on the model manifold corresponds to statistical distinguishability. Boundaries on the model manifold are reduced-order models where a parameter or parameter combination is taken to an extreme limit and drops out of the model. Therefore, by locating the model manifold boundaries, simpler models with fewer parameters can be obtained. A model reduction algorithm which exploits this insight is the Manifold Boundary Approximation Method, or MBAM, which locates manifold boundaries by calculating geodesics on the surface of the model manifold. This can be done iteratively to find increasingly simple reduced models. We demonstrate this method for model reduction using the Pekeris waveguide transmission loss model. A machine learned surrogate model for the Pekeris waveguide is constructed so that the necessary derivatives for calculating geodesics can be easily obtained using automatic differentiation. [Work supported by the Office of Naval research Grant N00014-21-S-B001.]

High spatial resolution long-term temperature profiling to inform near-shore atmospheric sound propagation

Atmospheric sound propagation depends on factors such as surface characteristics and meteorological parameters. Effective numerical modeling of atmospheric sound propagation requires reliable and realistic input parameters. One of the most influential factors is the air temperature profile. This work examines the application of experimentally determined air temperature profiles in acoustic modeling of littoral environments. Long term measurements of near-surface air temperature profiles over water and marsh grass are presented. Data have been recorded using temperature loggers affixed to two permanent 7 m masts. The loggers were positioned with a 1 m vertical spacing. A common approach to characterize the near-surface boundary layer uses Monin–Obukhov Similarity Theory (MOST). This work compares high spatial resolution air temperature measurements with measurement-informed profiles based on MOST. The development of a more experimentally grounded set of assumptions will ultimately contribute to the improvement of atmospheric acoustic transmission loss models in near shore environments.

Basin scale propagation modeling of MLS signals from the Kauai Beacon source

Long distance underwater acoustic propagation is of interest for a variety of applications including underwater navigation, yet modeling such propagation is challenging due to the large degree of environmental uncertainty. In this presentation, the propagation of 75Hz center frequency maximum length sequence (MLS) signals emitted from a submerged source near Kauai and received at various sites throughout the Pacific Ocean Basin is modeled with the Bellhop ray tracing [1] and Monterey-Newport Parabolic Equation [2] models. Sites such as the Monterey Accelerated Research System (MARS) observatory and the Comprehensive Nuclear Test Ban Organization (CTBTO) hydroacoustic monitoring station near Wake Island are included in the discussion. The range-dependent environment is based on historical profiles from the World Ocean Atlas database and reanalysis data from the hybrid coordinate ocean model (HYCOM) [3]. Bathymetry profiles along the axis of propagation are interpolated from the General Bathymetric Chart of the Oceans (GEBCO) 2021 database [4]. Simulated broadband channel impulse responses transmission loss levels in the modeled environment are compared to selected receptions of the signal at the hydrophone sites. Additionally, fluctuations of the modeled transmission loss in the presence of an internal wave model [5] are discussed.

Behavioural responses of male killer whales to a ‘leapfrogging’ vessel

The research and whalewatching communities of Johnstone Strait, British Columbia, Canada have worked closely together to identify whalewatching practices that minimise disturbance to northern resident killer whales. Local guidelines request that boaters approach whales no closer than 100m. Additionally, boaters are requested not to speed up when close to whales in order to place their boat in a whale’s predicted path: a practice known as ‘leapfrogging’. A land-based study was designed to test for behavioural responses of killer whales to an experimental vessel that leapfrogged a whale’s predicted path at distances greater than 100m. Ten male killer whales were repeatedly approached and the animals responded on average by adopting paths that were significantly less smooth and less straight than during preceding, control conditions. This adoption of a less ‘predictable’ path is consistent with animals attempting to evade the approaching boat, which may have negative energetic consequences for killer whales. The results support local consensus that leapfrogging is a disruptive style of whalewatching, and should be discouraged. Similarly, as the experimental boat increased speed to overtake the whale’s path, the source level of engine noise increased by 14dB. Assuming a standard spherical transmission loss model, the fast-moving boat would need to be 500m from the whale for the received sound level to be the same as that received from a slow-moving boat at 100m. Whalewatching guidelines should therefore encourage boaters to slow down around whales, and not to resume full speed while whales are within 500m.

Machine learning a surrogate model for transmission loss on a Pekeris waveguide

The connection between ocean environmental parameters and transmission loss (TL) can be modeled using sound propagation models. We can analyze and improve these models using information theoretic tools such as the Fisher information matrix (FIM) and methods for model reduction, where we identify parameters that can be removed from a model without sacrificing accuracy. Critical to these methods for model reduction is the ability to evaluate derivatives of the model predictions of TL with respect to model parameters. Calculating derivatives of TL models using finite difference methods with sufficient accuracy is challenging due to the complexity of sound fields in an ocean environment; instead, we train a surrogate machine learning model to which we can apply automatic differentiation (AD). We propose a general method for model reduction in which a ML model is used as a surrogate model for physical sound propagation ocean models, which is then used to find potential simplifications of the original model. We demonstrate this method using the Pekeris waveguide model of the ocean, which calculates underwater acoustic TL in an ocean environment due to seafloor characteristics. [Work supported by Office of Naval Research]

Air temperature profiling over different littoral surfaces

There are many factors that must be considered in the study of atmospheric sound propagation over long distances; these include surface characteristics as well as wind speed and air temperature profiles. This work presents measurements of air temperature profiles over various surfaces. Building a catalogue of this type can enable more realistic case assumptions to be made in an atmospheric acoustic transmission loss model. Accurate air temperature profiles are critical because of the potentially significant impact on the transmission loss predictions. Air temperature profile measurements have been collected by solar radiation shielded temperature loggers mounted 1 m apart on a 7 m mast. Long duration measurements were taken to capture the variability in day and nighttime temperature differentials present over surfaces such as: gravel, vegetated shoreline, marsh grass, lawn grass, water, and asphalt. In particular, measurements performed off shore were done by placing the sensor array on the deck of a pontoon boat. The initial results revealed that this configuration captures a very low elevation warming due to re-radiation from the deck of a boat instead of the true over water temperature. This study highlights the influence of wind speed on the development of the near surface temperature inversions.

MPC Trajectory Feasibility Constraints for Self-Powered Control Systems

A self-powered control system derives the energy to power its operation entirely from the dynamics of the plant in which it is embedded. Each actuator is a transducer capable of injecting energy into, as well as removing energy from, the plant. Removed energy is stored for reuse in rechargeable energy storage subsystems. Control inputs are physically constrained by the requirement that the system does not exhaust these energy storage subsystems. This article analyzes model-predictive control (MPC) trajectory feasibility for self-powered control systems. Specifically, we examine the case in which the MPC algorithm formulates a discrete-time zero-order-hold control trajectory, for which the energy constraints are approximately enforced by using response information only at discrete sample times. It is shown that continuous-time control feasibility can be ensured by conservatively overbounding the transmission loss model. The analysis is conducted both for the case in which future disturbances are known deterministically and the case in which they are uncertain but bounded. The methodology is demonstrated on an example pertaining to vibration control.

Large-scale monitoring of Indo-Pacific finless porpoises (Neophocaena phocaenoides) using multiple static acoustic sensors

The distribution of Indo-Pacific finless porpoise (IPFP, Neophocaena phocaenoides) around the Hainan Island (China) is unknown, but evidences for a resident population have recently emerged. Passive acoustic data were collected from 10 locations along the south-west area of the island using static sensors (about 200 km of coastline), over a total period of 476 days from 25th February 2018 to 16th June 2019 (154,884 5-min recordings). A supervised machine learning technique was used to classify IPFP clicks and acoustic features were measured for 2,654 short-narrowband pulses detected within 47 days across the 10 sites. Detections were verified by a trained operator using spectrogram analysis and the detection range of the clicks was estimated using a Transmission Loss (TL) model. The animals were not detected at all locations and the site with the highest number of detections was characterized by low levels of ambient noise, abundance of soniferous fishes and the presence of another marine mammal species, the Indo-Pacific humpback dolphin (Sousa chinensis). The northernmost region had no detections and only two recorded files containing IPFP clicks were found at the two nearby locations (one file each). In general, the low number of detections in the study area are most likely a result of the limited detection range (about 200 m) of IPFP echolocation signals. This is a nationally protected species and the Hainan population is increasingly subject to many threats. The large-scale and long-term monitoring approach provides information regarding the spatial acoustic occurrence of this vulnerable, nearshore and small-size cetacean.

Investigation and development of an empirical model for transmission loss of acoustic windows in alleviating road traffic noise impact

An Acoustic Window is comprised of a horizontal sliding window at the inner layer, and a side-hung window, which can be pushed to open, on one side of the outer layer, and a fixed glazing on the other side. The glazing of the sliding inner window serves as a “baffle” for screening off the noise passing through the opened outer window when it is slid behind the opened outer window. This baffle-type acoustic window is proved to reduce up to 8 dB(A) road traffic noise and is gaining popularity in residential developments of Hong Kong, particularly for those located in difficult sites in close proximity to heavily trafficked roads. This paper presents the experimental results from a study looking into the acoustical transmission loss of Acoustic Windows with respect to changes in window configuration and setting of line sources. Based on the experimental results, empirical models for noise reduction of Acoustic Windows are developed and investigated to assist quick design of Acoustic Windows for planning residential developments.

An energy-mix model for round-the-clock power supply in a decarbonized electricity generation scenario: case study of South India

There is increasing urgency towards integration of renewable sources into electricity generation so as to minimize greenhouse gas (GHG) emissions. Renewable power sources are highly specific in prevalence, both regionally and temporally, and their utilization at utility scale for round-the-clock power supply poses the problem of matching power generation capacity and power demand at every instant of time. In the present work, we propose a model that integrates geographically distributed and diverse power sources with geographically spread-out power consumption centres and distributed and diverse electrical energy storage systems through transmission and storage loss models. For a regional electricity grid, the model computes, over a given day, the minute-by-minute power demand from and power generation in all districts, extracts matching power from a hierarchy of power sources so as to minimize transmission and storage losses, and stores/draws excess power in/from a variety of power storage options. For the specific case of the South Indian Power Grid (catering to about 285 million people in South India), the model shows that about 240 GWh of new electrical storage is required for round-the-clock power supply from non-GHG power sources.Graphical abstract

Acoustic transmission loss and noise from Kevlar wind tunnel walls

In this paper we will develop a model for the acoustic transmission loss and self-noise generated by a Kevlar wind tunnel wall. It is shown that the porosity of the fabric is the most important controlling factor of the transmission loss, and the effect of wind tunnel flow speed is to increase the losses, as observed in experiments. In addition, a model is developed for the weave noise generated by a Kevlar wind tunnel wall, which is found to be caused by the pumping of the fluid through the pores in the Kevlar and depends on their open area ratio. The mechanism for this sound generation is similar to the roughness noise mechanism for a turbulent boundary layer in that the pore spacing couples with the small wavelength disturbances in the boundary layer to cause acoustic radiation at the sum and difference frequencies.

Estimation of High-Frequency Auditory Masking in Beluga Whales by Commercial Vessels in Cook Inlet, Alaska

Industrial development in Cook Inlet, Alaska, has raised concerns about the decline of the resident beluga whale ( Delphinapterus leucas) population over the past decades. Anthropogenic noise sources, such as commercial vessels, can cause auditory masking of cetacean vocalizations used in communication, navigation, and foraging. This study includes a source-level spectrum of a containership, positioned in Cook Inlet within the primary shipping channel, and audiograms obtained from a live, stranded beluga calf in Cook Inlet, in sound transmission loss modeling. The model uses a hybrid parabolic equation/raytracing solution to determine underwater sound pressure levels. Whereas the communication band of belugas can be fully masked by ambient noise and underwater radiated noise from a containership positioned at 5,000 m, the echolocation band (for navigation) is only partially masked at shorter ranges (≤2,500 m). Increased multipath reflections from the propagation of underwater noise in the upslope direction contributes significantly to the attenuation of high frequencies and minimizes masking in the echolocation band of the beluga whale. To assess the complex task of auditory masking, critical ratios were used to determine the difference between the energy of a pure tone and the noise in the masking band. A successful strategy to reduce underwater radiated noise must consider the interactions and contributions of mitigation measures that have already been shown to be effective. The technical and economic profitability of these measures will largely depend on the design, operating parameters, and mandatory requirements for a particular vessel.

Coupled modeling of the seasonal transmission loss in the Beaufort Sea

An eight-element drifting vertical line array was deployed overwinter 2019–20 in the Beaufort Sea to record transmissions from two moored 35 Hz sources deployed as part of the Coordinated Arctic Acoustic Thermometry Experiment (CAATEX), and seven 925 Hz sources deployed by the Arctic Mobile Observing Systems (AMOS) experiment. Transmissions were received every day on the array at ranges of 10 to 850 km. A probabilistic rough-ice canopy was integrated to a Parabolic Equation code to predict the propagation loss. Sound speed profiles and percent ice cover along the propagation paths were obtained at daily resolution from data-assimilative Global Ice Ocean Prediction System (GIOPS, 20 km spatial resolution). Sea ice roughness and keel properties are empirically determined from the GIOPS ice thickness. The ice roughness is generated using a random pulse-train model with a characteristic wavenumber spectrum slope determined by ice age. Empirical probability distributions of ice keel depth, slope, and spatial densities are used to randomly add keels. Spatial averaging is used to account for signal bandwidth and uncertainty in receiver positions. The environment files and modeling are performed in piece-wise steps to manage memory footprints over long ranges. Modeled propagation losses compare well with the data and reproduce the seasonal variability observed in the measured results.

Environmentally constrained modeling of mid-frequency transmission loss and reverberation measured during the Target and Reverberation Experiment 2013

The goal of the Target and Reverberation Experiment (TREX13) was to make contemporaneous measurements of mid-frequency (1.5–4 kHz) transmission loss and reverberation with extensive environmental measurements so detailed model/data comparison can be achieved and important environmental factors can be identified for different applications. APL-UW collaborated with ARL-Penn State, led by John R. Preston, to deploy the Five Octave Research Array (FORA) on a “clothesline” about 2.1 m above the seafloor. This fixed-source/receiver configuration helped eliminate uncertainties from the motion of a towed array and allow reverberation measurement along a narrow, 7-km-long section of seafloor. The experiment site had a fairly complex spatial distribution of both sediment type and sediment scattering properties and keeping the FORA in a fixed position was instrumental in understanding and modeling the reverberation. While soft sediments make up only 27% of the sediments by area at the site, it is necessary to account for this spatial dependence so that both transmission loss and reverberation can be modeled using a consistent set of environmental inputs. These models and their implications for our understanding of the environmental factors which most impact mid-frequency reverberation will be discussed. [Work supported by the U.S. Office of Naval Research.]