mm-bem v2.0

This is a web-based demonstration of the mm-bem code, which calculates acoustic scattering patterns from mesh defined targets using Boundary Element Method (BEM)¹ and Method of Fundamental Solution (MFS). The BEM algorithm uses classical P0 elements, while the MFS algorithm uses source points that are located inside the mesh on the element normals at a distance of 0.05λ. The demo runs entirely within modern web browsers and allows calculating scattering patterns for pressure released (soft) targets modeled by not more than 5000 triangular elements. It requires no third-party libraries and can operate offline on any client machine. It is dedicated to compute target strength TS of swimbladdered fish across multiple frequencies commonly used in fisheries acoustics, provided the wavelength to element size ratio condition is fulfilled.

The Input parameters section gives user interface for configuring simulations. Users can specify: (1) target mesh (2) plane wave direction angles θ₀ and φ₀ (3) its frequency f₀ and (4) sound speed c₀ in water (located in Configuration section). The target mesh could be selected from dropdown menu containing cannonical examples and swimbladder models. The mesh is displayed in the Data Visualisation section on the left 3D panel (Ctrl-H for help). The results of BEM calculations are shown in the right panel as 2D polar plot of the scattering pattern. In fishery acoustics wave directions for calculating TS includes dorsal aspect (θ₀=270°), ventral aspect (θ₀=90°) and lateral aspect (θ₀=0° with φ₀=90° or 270°). The angles could be also set into scanning modes enabling calculations over a full angular range. When both angles are set into scanning mode, the output represents 3D backscattering length distribution, which is visualized in 3D View, replacing original mesh. The frequency parameter could be also set into scan mode across predefined frequency range (up to 360 kHz). In such a case the results are visualised also in the polar plot with angular values representing frequencies in kHz. See Gallery section for examples.

The fish swimbladder models included in the demo are sourced from (1) scientific studies^2,3 (2) the echoSMs initiative (3) the NOAA Fisheries KRM model webpage. Users may also enter custom target meshes in one of the following formats: GMSH MSH 2.0 with triangular elements or STL or in the echoSMs JSON data structure. Additionally, it is possible to use fish shape models from echoSMs anatomical data store after importing in Configure section. You can also generated the echoSMs json file with outline from two swimbladder crosssection images*. These images could be derived from radiographs or CT scans **.

Full mm-bem package contains source codes in different programming languages for several cases using also the other BEM algorithms. For more detailed information, please refer to the readme and the github repository.

Target:
or

Plane wave: θ₀ = φ₀ =

Frequency: f₀ =

Add data:
or

Fig.1. Low resolution model of sphere with radius r=1.905 cm inside wave-length box with a size of 38kHz wavelength.	Fig.2. Scattering pattern at 38kHz obtained for low resolution model of a soft sphere with radius r=1.905 cm along with exact solution (dashed-blue).
Fig.3. Target strength pattern at 38kHz obtained for low resolution model of a soft sphere with radius r=1.905 cm along with exact solution (dashed-blue).	Fig.4. 3D Backscattering length pattern at 38kHz for low resolution model of a sphere with radius r=1.905 cm.
Fig.5. Target strength frequenecy dependance for low resolution model of a soft sphere with radius r=1.905 cm along with exact solution (dashed-blue). The angular axis values corespond to frequencies in kHz.	Fig.6. 3D backscattering length pattern at 38kHz for a soft sphere with radius r=1.905 cm (exact solution).
Fig.7. High resolution model of a sphere with radius r=1.905 cm. Wave-length box is set for 70 kHz and is fully inside the sphere.	Fig.8. Scattering length pattern at 70kHz for high reolution model of a sphere with radius r=1.905 cm along with exact solution.
Fig.9. Scattering length pattern at 120kHz for high reolution model of a sphere with radius r=1.905 cm along with exact solution.	Fig.10. Target strength frequency dependence for high resolution model of the soft sphere with radius r=1.905 cm along with exact solution (dashed-blue). The angular axis values corespond to frequencies in kHz.
Fig.11. The visualisation of the exact sphere, for which calculations are based on theoretical equations.	Fig.12. Scattering length for of the exact sphere for three frequencies: 38 kHz (dashed-blue), 120 kHz (dashed-blue) and 200 kHz (red).
Fig.13. The model of Yellowfin tuna swimbladder conatining 1500 triangles. The green dot represents wave direction from dorsal aspect (from up).	Fig.14. Scattering strength from dorsal aspect (θ₀=270ˆ φ₀=0ˆ) of Yellowfin tuna swimbladder model at 38 kHz.
Fig.15. The model of Yellowfin tuna swimbladder conatining 1500 triangles. The green dot represents wave direction from lateral aspect (from one side).	Fig.16. Scattering strength from lateral aspect (θ₀=0ˆ φ₀=90ˆ) of Yellowfin tuna swimbladder model at 38 kHz.
Fig.17. Two target strengths patterns of Yellowfin tuna swimbladder model at 38 kHz obtained as 15ˆ scan along φ₀=0 (dashed-blue) and φ₀=90 (red).	Fig.18. 3D backscattering length pattern at 38kHz of the Yellowfin tuna swimbladder model obtained as 10ˆ scan along both direction angles.
Fig.19. The model of Gadus morhua swimbladder from echoSMs github repository.	Fig.20. 3D backscattering length pattern at 38kHz of the Gadus morhua swimbladder model obtained as 10ˆ scan along both direction angles.
Fig.21. The model of Cod swimbladder from KRM model web-page.	Fig.22. 3D backscattering length pattern of the Cod swimbladder model at 38kHz obtained as 10ˆ scan along both direction angles.

Calculation method: Solver:

Calculations rule:

Sound speed: c₀ =

Source distance (0-plane wave): r₀ = λ

EchoSMs anatomical data store endpoint URL*: