The method of fundamental solutions for the analysis of infinite 3D sonic crystals

[EN] The use of periodic structures in acoustic applications has interested the scientific community in the last two decades. Although in-depth research has been thoroughly performed, many issues have still not been solved. Computational analysis of sonic structures using realistic 3D models still poses significant problems, and most of the published results correspond to 2D problems. Analysing 3D problems of such structures using conventional methods demands large computational resources, which may be prohibitive. This paper proposes a new approach for such 3D problems making use of a highly efficient Method of Fundamental Solutions (MFS) approach to deal with sonic crystals made of 3D scatterers, infinitely repeated with constant spacing along one direction. The method makes use of a special form of the acoustic fundamental solutions which can be highly efficient in such analysis, while allowing just the cell that is repeated to be effectively modelled. Verification of the model is provided by first comparing its results with those from an ACA-MFS model. Results are compared with those from a FDTD algorithm, and a parametric study is presented revealing the 3D character of the computed responses, and evidencing the formation of acoustic band-gaps at specific frequency bands associated with the Bragg effect.The EU funding support in the scope of COST (European Cooperation in Science and Technology) through the COST ActionPlease check funding information and confirm its correctness. CA15125 - DENORMS: "Designs for Noise Reducing Materials and Structures" is here also acknowledged.Godinho, L.; Redondo, J.; Amado-Mendes, P. (2019). The method of fundamental solutions for the analysis of infinite 3D sonic crystals. Engineering Analysis with Boundary Elements. 98:172-183. https://doi.org/10.1016/j.enganabound.2018.09.015S1721839

A Hybrid Analytical-Numerical Model Based on the Method of Fundamental Solutions for the Analysis of Sound Scattering by Buried Shell Structures

Several numerical and analytical models have been used to study underwater acoustics problems. The most accurate and realistic models are usually based on the solution of the wave equation using a variety of methods. Here, a hybrid numerical-analytical model is proposed to address the problem of underwater sound scattering by an elastic shell structure, which is assumed to be circular and that is buried in a fluid seabed bellow a water waveguide. The interior of the shell is filled with a fluid that may have different properties from the host medium. The analysis is performed by coupling analytical solutions developed both for sound propagation in the waveguide and in the vicinity of the circular hollow pipeline. The coupling between solutions is performed using the method of fundamental solutions. This strategy allows a compact description of the propagation medium while being very accurate and highly efficient from the computational point of view

Particle Swarm Optimization for damage identification in beam-like structures

The main objectives of Structural Health Monitoring (SHM) are the characterization and the assessment of the health condition of structural systems. Combined with appropriate Damage Identification (DI) strategies, SHM aims to provide reliable information about the localization and quantification of the structural damage by using an inverse formulation approach, with the damage parameters being estimated from parametric changes in dynamic properties. Mathematically, an inverse problem consists of the optimization of a function which represents the "distance" between the experimental and the numerically-simulated features of the system. Such process requires the development of a mock-up numerical model fairly representative of the system and iteratively updated until a response, as close as possible to the experimental one, is provided. The minimization of the difference between measured and predicted features' values is the objective function, whose global minimum corresponds to the best adjustment of the model variables. Metaheuristics represent a large class of global methods for optimization purposes able to outperformtraditional methods in the following aspects: ease of implementation, time consumption, suitability for non-linear phenomena, black-box and high-dimensional problems. The present paper analyses, through a numerical experimentation approach, the suitability of one of the best-known metaheuristics, i.e. the Particle Swarm Optimization (PSO) algorithm, for DI of beam-like structures. Modal properties are used to define the objective function and various algorithm instances are tested across different problem instances to assess robustness and influence of the algorithm parameters.This work was supported by FCT (Portuguese Foundation for Science and Technology), within ISISE, scholarship SFRH/BD/115188/2016. This work was also financed by FEDER funds through the Competitivity Factors Operational Programme - COMPETE and by national funds through FCT - Foundation for Science and Technology within the scope of the project POCI-01-0145-FEDER-007633

East Asia Today

East Asia attracts growing interest in the West. Th e region is the world’s hotbed of economic growth, led by burgeoning China aided by more advanced Asian economies investing heavily in manufacturing and trading networks involving China. Western entrepreneurs clamor to join the China wave

The effect of tunnel construction on future underground railway vibrations

This paper investigates the effect of initial tunnel construction on the future ground vibration levels generated during underground railway line operation. This is important because tunnel construction results in soil disturbance, thus inducing high soil strain levels near the tunnel lining. The resulting soil stiffness degradation impacts the future generation of ground-borne traffic vibration and it's propagation to the foundations of nearby buildings, however has never been investigated. Therefore, to address this, this work develops a novel hybrid modelling approach, consisting of a construction simulation model and an elastodynamics model. First the convergence-confinement method is used to determine the stress state induced during tunnel construction using a tunnel boring machine (TBM). Next a 2.5D FEM-PML model consisting of vehicle-track-tunnel-soil is used to predict the vibration fields induced by underground trains. To link the approaches, the soil stiffness degradation contours computed from the tunnelling simulation act as inputs for the 2.5D underground railway model. This facilitates the assessment of the effect of tunnel construction on vibration levels. It is found that railway ground-borne vibration levels are underestimated if construction effects are ignored, with discrepancies of up to 10 dB found at higher frequencies. Therefore, when estimating future vibration levels during the underground railway design stage (e.g. for subway, metro, high-speed lines … etc), tunnel construction should be considered as an operational source of uncertainty

MAMMALS IN PORTUGAL : A data set of terrestrial, volant, and marine mammal occurrences in P ortugal

Mammals are threatened worldwide, with 26% of all species being includedin the IUCN threatened categories. This overall pattern is primarily associatedwith habitat loss or degradation, and human persecution for terrestrial mam-mals, and pollution, open net fishing, climate change, and prey depletion formarine mammals. Mammals play a key role in maintaining ecosystems func-tionality and resilience, and therefore information on their distribution is cru-cial to delineate and support conservation actions. MAMMALS INPORTUGAL is a publicly available data set compiling unpublishedgeoreferenced occurrence records of 92 terrestrial, volant, and marine mam-mals in mainland Portugal and archipelagos of the Azores and Madeira thatincludes 105,026 data entries between 1873 and 2021 (72% of the data occur-ring in 2000 and 2021). The methods used to collect the data were: live obser-vations/captures (43%), sign surveys (35%), camera trapping (16%),bioacoustics surveys (4%) and radiotracking, and inquiries that represent lessthan 1% of the records. The data set includes 13 types of records: (1) burrowsjsoil moundsjtunnel, (2) capture, (3) colony, (4) dead animaljhairjskullsjjaws, (5) genetic confirmation, (6) inquiries, (7) observation of live animal (8),observation in shelters, (9) photo trappingjvideo, (10) predators dietjpelletsjpine cones/nuts, (11) scatjtrackjditch, (12) telemetry and (13) vocalizationjecholocation. The spatial uncertainty of most records ranges between 0 and100 m (76%). Rodentia (n=31,573) has the highest number of records followedby Chiroptera (n=18,857), Carnivora (n=18,594), Lagomorpha (n=17,496),Cetartiodactyla (n=11,568) and Eulipotyphla (n=7008). The data setincludes records of species classified by the IUCN as threatened(e.g.,Oryctolagus cuniculus[n=12,159],Monachus monachus[n=1,512],andLynx pardinus[n=197]). We believe that this data set may stimulate thepublication of other European countries data sets that would certainly contrib-ute to ecology and conservation-related research, and therefore assisting onthe development of more accurate and tailored conservation managementstrategies for each species. There are no copyright restrictions; please cite thisdata paper when the data are used in publications.info:eu-repo/semantics/publishedVersio