Acoustics simulation software SILDIS®: features

General information regarding the SILDIS® acoustics simulation software [0]  

The prediction of performances of products and construction systems for noise control engineering often requires an approach whose nature is computationally intensive, making its application difficult for most acoustics practitioners.

Several modules of a PC-based acoustics simulation tool for the assessment and optimization of materials and equipement for sound insulation and acoustic comfort improvement (walls and noise barriers, acoustic partitions, sound-absorbing coverings, silencers - including the evaluation of their aerodynamic performance) have been developed by ITS human resource in order to make possible such tasks without any computational effort from users, covering a wide range of industrial engineering and Research and development (R&D) purposes:  SILDIS® is an acoustic simulation software for performance prediction and sizing of soundproofing products and construction systems.

Regarding the multi-disciplinary scientific and technical background, suitable approaches of all times, able to be included in the general layout of the computation programs, have been selected and encapsulated in easy-to-use Excel based softwares using drop-down menus and providing results in tabular and graphical form (French or English language) with comprehensive input/output data on a unique printable simulation report. Almost all acoustics calculations are performed at single frequencies and displayed per 1/3 and/or 1/1 octave band (covering the 20 Hz – 20 kHz frequency range): global values with respect to a chosen reference spectrum are computed whenever it makes sense.

SILDIS® software publishing and engineering works carried out by ITS using SILDIS® software have been assessed to meet the requirements of standard ISO 9001.

This article illustrates various features of the software.

Main modules of SILDIS® acoustics simulation software 

Module 1 prediction of acoustic and aeraulic (aerodynamic) performance of silencers

The computations with SILDIS® acoustics simulation software concern either dissipative silencers or resonant silencers with a sound absorbing lining including up to 4 porous media, up to 4 series cloths, up to 4 series perforated protections selected among a library including for each kind of layer more than 20 referenced materials. In certain versions of the software, it is possible to account for liners with cavities and elastic plates (membranes), as well as non-linear effects resulting from high acoustic excitation levels (and also the case of asymmetric sound-absorbing packings i.e. differing in composition or thickness on either side of a given air gap).

Various calculation routines are implemented in the software to cover widely differing geometric configurations regarding the silencer's cross-section:

  • rectangular (including those with pinetree-style splitter baffles)
  • circular (with or without a central splitter/pod, with or without sound-absorbing lining in the form of concentric rings or transverse baffles)

The sophisticated modeling of the acoustic behavior of sound-absorbing packing is a key strength of the software. And the fact that it allows to perform sizing calculations that account, at all the appropriate modeling stages, for the effects of harsh operating conditions - complicating calculations and significantly impacting silencer performance - is another, not less important, when it comes to applications involving (very) high temperatures and (very) high fluid velocities.

Simulations can be performed not only for ordinary silencers (in terms of use and performance), such as those found in HVAC (Heating, Ventilation, and Air Conditioning) systems, but also for soundproofing equipment being more complex - or even out of the ordinary (e.g. combustion turbine exhaust silencers) -, for which performance requirements, namely for noise reduction and aerodynamics (both should be reconciled) are both rmajor stakes and technological challenges.

Regardless of the application's complexity, connoisseurs in silencer modeling will appreciate that using the SILDIS® software eliminates:

  • the need to create or import geometry and perform any meshing-related tasks (silencer geometries are pre-programmed)
  • the (sometimes interminable) waiting time for results to be dispalyed often associated with other computational tools (the kind used to design aircraft, submarines, and even rockets): with SILDIS®, simulation results are obtained almost instantly, even without a high-end computer

The main output data are (besides a skecth summarizing the entered dimensions):

  • insertion loss (reduction in sound power level compared to the "no silencer" configuration), per 1/3-octave and octave frequency band, such as by-pass correction and reflection loss (propagation loss is calculated per 1/21-octave band) and as an A-weighted overall value relative to a user-selected reference spectrum
  • sound power level of the flow noise, per 1/3-octave and octave frequency band, and as an A-weighted overall value
  • sound power level downstream of silencer, per 1/3-octave and octave frequency band, and as an A-weighted overall value
  • total pressure loss

The results of the calculations with SILDIS® acoustics simulation software (for cross sections possibly rectangular, square or circular) are comparable with the standardized measurement: cf. NF EN ISO 7235 Acoustics - Laboratory measurement procedures for ducted silencers and air terminal units- Insertion loss, flow noise and total pressure loss.

  • Characteristics

>> Module 1 Terminal 1
>> Module 1 Terminal 2
>> Module 1 Terminal 3
>> Module 1 Terminal 4
>> Module 1 Terminal 6

Module 1A prediction of acoustic and aeraulic (aerodynamic) performance of silencers with discontinued splitters

The main output data are:

  • insertion loss (reduction in sound power level compared to the "no silencer" configuration)
  • sound power level of the flow noise
  • sound power level downstream of silencer
  • total pressure loss

The results of the calculations with SILDIS® acoustics simulation software are comparable with the standardized measurement: see NF EN ISO 7235 Acoustics - Laboratory measurement procedures for ducted silencers and air terminal units- Insertion loss, flow noise and total pressure loss.

Module 1B prediction of acoustic and aeraulic (aerodynamic) performance of reactive silencers

Calculations performed using the SILDIS® acoustic simulation software cover reactive silencers (depending on the specific software version):

  • without perforated tubes, i.e. silencers operating exclusively through changes in internal geometry (using expansion chambers, and connecting tubes where multiple chambers are present) and wave reflections off the hard surfaces formed by the chamber extremities (ends)
    • 1 to 3 expansion chambers can be combined, with either axial or radial inlet configurations (12 configurations in total), plus 3 additional configurations involving flow reversals
  • with perforated tubes
    • 1 or 2 sub-chambers (the latter case being referred to as a "plug-silencer")
  • with shunt-branched (Helmholtz-type) resonators

The combination, in the sequence appropriate for each specific mounting (in the meaning of configuration/assembly: a cascaded arrangement of elements of various types) of transfer matrices for basic acoustic quantities is pre-programmed. The user, once having entered the thermodynamic fluid data corresponding to the silencer's operating conditions and selected a mounting, need only to input the dimensional parameters and make a very limited number of model choices for various calculation stages (without forgetting end corrections); if wished by him: utilizing a tuning feature to optimize acoustic performance across a broad frequency range, where such a feature is available for the considered mounting.

Just as with the dissipative silencers mentioned earlier, reactive silencers involve no complex tasks prior to the display (which is, again, instantaneous) of the calculation results.

The main output data are (besides a skecth summarizing the entered dimensions):

  • insertion loss (reduction in sound power level compared to the "no silencer" configuration), sound transmission loss (reduction in sound power level between the silencer inlet and outlet), noise reduction (decrease in sound pressure level at a specified location downstream of the silencer); per 1/3-octave and octave frequency band (calculated and dispalyed as a curve per 1/21-octave band) and as an A-weighted overall value relative to a user-selected reference spectrum
  • sound power level of the flow noise, per 1/3-octave and octave frequency band, and as an A-weighted overall value
  • sound power level downstream of silencer, per 1/3-octave and octave frequency band, and as an A-weighted overall value
  • total pressure loss

The results of the calculations with SILDIS® acoustics simulation software are comparable with the standardized measurement: see NF EN ISO 7235 Acoustics - Laboratory measurement procedures for ducted silencers and air terminal units- Insertion loss, flow noise and total pressure loss.

Module 2 prediction of acoustic performance of plane-flat partitions

The computations with SILDIS® acoustics simulation software concern an acoustic structure including up to 4 porous media, up to 4 series cloths, up to 4 series perforated protections, up to 4 sets of identical series thin plates with up to 1 complementary rear set of identical series thin plates selected among a library including for each kind of layer more than 20 referenced materials (with an atmospheric back or with an impervious rigid back).

This software module enables performance simulations regarding:

  • sound absorption (using 1 to 12 layers for the multilayer acoustic structure, potentially combining some or all of the other materials listed above); with a rigid, impermeable backing (e.g. for results comparable to standardized measurements) or an air gap (to simulate actual soundproofing panel installation conditions)
    • without considering thin plates within the multilayer acoustic structure; however, certain software versions allow for the inclusion of facings with elastic properties where all dimensions  - not just thickness, but also lateral dimensions, which are crucial for membrane resonance effects - are taken into account
    • in some software versions, it is possible to model sousn aborbing linings/liners - either without a membrane (Helmholtz resonator) or with one (hybrid resonator) - as well as non-linear effects resulting from high acoustic excitation levels
  • sound transmission loss (using 1 to 16 layers for the multilayer acoustic structure, potentially combining some or all of the other materials listed above; with the option of a 17th layer - a thin plate - at the rear); with a configurable atmosphere at the rear
    • including thin plates (in certain software versions: potentially laminated, with damping e.g. two- or three-layer configurations) within the multilayer acoustic structure, and potentially allowing for the simplified inclusion of a temperature gradient; the following terms - used since time immemorial and retained for the sake of consistency in the software documentation, even after various enhancements - should be lokked at in a special context:
      • the term "plane partition" or "flat partition", since calculations are possible (in certain software versions) by treating all or part of the plates as orthotropic (e.g. featuring corrugations, stiffeners, or a trapezoidal profile, such as certain types of cladding)
      • the term "thin plate" since calculations are possible for concrete walls with thicknesses measured in decimeters

The main output data are:

  • normal-incidence sound absorption coefficient, statistical (random) incidence sound absorption coefficient, Sabine absorption coefficient, per 1/3-octave and octave frequency band; weighted sound absorption coefficient αw, sound absorption class
  • sound reduction index, per 1/3-octave and octave frequency band, and as an A-weighted overall value relative to a user-selected reference spectrum; weighted sound reduction index Rw,

The results of the calculations with SILDIS® acoustic simulation software are comparable with the standardized measurement:

  • (in case of an atmospheric back) NF EN ISO 140-3 Acoustics - Measurement of sound insulation in buildings and of building elements – Part 3: Laboratory measurement of airborne sound insulation of building elements and ISO 717-1 Acoustics - Rating of sound insulation in buildings and of building elements - Part 1: Airborne sound insulation
  • (in case of rigid impervious back) NF EN ISO 354 Acoustics – Measurement of sound absorption in a reverberation room and also ISO 10534-1 Acoustics – Determination of sound absorption coefficient and impedance in impedance tubes – Part 1: Method using standing wave ratio.

Furthermore, the software enables performance simulations under conditions other than laboratory conditions (the latter involving ambient pressure and temperature) e.g. with very high temperatures.

Module 3 prediction of acoustic performance of duct walls

The computations with SILDIS® acoustics simulation software concern aeraulic systems or pressurized fluids networks; the ducts can have a rectangular or circular cross-section (including spiral-seam ducts/pipes), such as those found in HVAC (Heating, Ventilation, and Air Conditioning) systems. Performance simulation can address the sound waves path from the inside of the duct or conduit to the outside (break-out noise transmission) or the reverse path: from the outside of the duct or conduit to the inside (break-in noise transmission).

The main output data are: 

  • the sound reduction index, per octave frequency band and as an A-weighted overall value relative to a user-selected reference spectrum
  • the transmitted sound power level, per octave frequency band and as an A-weighted overall value 

The results of calculations using the SILDIS® acoustic simulation software are comparable to standardized measurements (depending on the context):

Module 4 prediction of acoustic performance of straight ducts

The computations with SILDIS® acoustics simulation software concern ducts (in duct systems) either with a rectangular cross section, or with a circular cross section:

  • such as for HVAC (Heating, Ventilation, and Air Conditioning) systems, including folded spiral seam ducts
  • such as for industrial stacks-chimneys (brick and steel can be distinguished, as well as the level of fouling)

The main output data are:

  • insertion loss (reduction in sound power level), per octave frequency band and as an A-weighted overall value relative to a user-selected reference spectrum
  • sound power level of the flow noise, per octave frequency band and as an A-weighted overall value 
  • sound power level downstream of the duct section, per octave frequency band and as an A-weighted overall value 

The results of calculations using the SILDIS® acoustic simulation software are comparable to standardized measurements (depending on the context):

  • for the sound power level downstream of the duct section

Module 5 prediction of break-out noise

The computations with SILDIS® acoustics simulation software concern either of straight ducts (with a rectangular cross section, or with a circular cross section - including folded spiral seam ducts) (in duct systems) or of silencers.

The main output data are:

  • the total sound power level: downstream of the duct section and transmitted through the walls, per octave frequency band and as an A-weighted overall value 

The results of calculations using the SILDIS® acoustic simulation software are comparable to standardized measurements (depending on the context):

  • for the sound power level downstream of the duct section and transmitted through the walls

Module 5A prediction of break-out noise of ducts with variable cross-section

The computations with SILDIS® acoustics simulation software concern in duct systems. Unlike those in Module 5, these have a variable cross-section e.g. transition pieces upstream and downstream of silencers, or ductwork upstream of a Heat Recovery Steam Generator (HRSG). In this case, the Module 5 methodology cannot be applied to the total duct length to directly evaluate overall performance; instead, it must be applied successively to individual duct segments (where the cross-section remains constant along the length of each segment, even if it differs from that of adjacent segments).

The main output data are: 

  • the transmitted sound power level, per octave frequency band and as an A-weighted overall value 

The results of calculations using the SILDIS® acoustic simulation software are comparable to standardized measurements (depending on the context):

  • for the transmitted sound power level

Module 6 prediction of acoustic performance of bends and junctions

The computations with SILDIS® acoustics simulation software concern elements (in duct systems): with a rectangular cross section, or with a circular cross section, or with mixed cross sections).

The main output data are:

  • insertion loss (reduction in sound power level), per octave frequency band and as an A-weighted overall value relative to a user-selected reference spectrum
  • sound power level of the flow noise, per octave frequency band and as an A-weighted overall value 
  • sound power level downstream of bends and junctions, per octave frequency band and as an A-weighted overall value 

The results of calculations using the SILDIS® acoustic simulation software are comparable to standardized measurements (depending on the context):

  • for the sound power level downstream of bends and junctions

Module 7 prediction of nozzle reflection

The main output data are:

  • insertion loss (reduction in sound power level), per octave frequency band and as an A-weighted overall value relative to a user-selected reference spectrum
  • sound power level downstream of nozzles, per octave frequency band and as an A-weighted overall value 

The results of calculations using the SILDIS® acoustic simulation software are comparable to standardized measurements (depending on the context):

  • for the sound power level downstream of nozzles

Module 8 prediction of the sound impact of duct systems

Calculations performed using the SILDIS® acoustic simulation software cover systems comprising components that can be modeled using Modules 1 through 7 e.g. regarding noise propagation to one end of the network:

  • silencers (dissipative or resonant) (cf. Module 1)
  • straight duct sections (cf. Module 3)
  • elbows and junctions with rectangular, circular, or mixed cross-sections (for certain components), as well as changes in cross-section (cf. Module 6)
  • nozzles (cf. Module 7)

The computations with SILDIS® acoustics simulation software concern components such as silencers (dissipative or resonant), straight ducts sections, bends with a rectangular cross section, or with a circular cross section, or with mixed cross sections (for some components).

The main output data are (taking into account the insertion loss and flow noise of the various cascaded components making up an air distribution system):

  • the sound power level, per octave frequency band and as an A-weighted overall value 
  • the sound pressure level at a specified location, per octave frequency band and as an A-weighted overall value 

The results of calculations using the SILDIS® acoustic simulation software are comparable to standardized measurements (depending on the context):

  • for the sound power level, per octave frequency band and as an A-weighted overall value 
  • for the sound pressure level at a specified location, per octave frequency band and as an A-weighted overall value 

In the specific case of stacks-chimneys (e.g. industrial ones), they are notably comparable to measurement results obtained in accordance with the standard ISO 10494:2018 Turbines and turbine sets - Measurement of emitted airborne noise - Engineering/survey method.

Module 8A prediction of stacks directivity

The main output data are:

  • the equidistant area
  • the directivity index
  • the sound pressure level at specified locations (when the sound power level is known), per 1/3-octave and octave frequency band, and 
  • the sound power level (when the sound pressure level at specified locations is known), per 1/3-octave and octave frequency band, and 

The results of calculations using the SILDIS® acoustic simulation software are comparable to standardized measurements (depending on the context):

  • for the sound power level
  • for the sound pressure level at specified locations

They are notably comparable to measurement results obtained in accordance with the standard ISO 10494:2018 Turbines and turbine sets - Measurement of emitted airborne noise - Engineering/survey method.

Some of the results of calculations with SILDIS® acoustics simulation software are comparable with some input data envisaged in standardized calculation: cf. NF EN ISO 9613-2 Acoustics - Attenuation of sound during propagation outdoors - Part 2: General method of calculation.

Module 8B prediction of atmospheric sound absorption

Some of the results of calculations with SILDIS® acoustics simulation software are comparable with some input data envisaged in standardized calculation: cf. NF EN ISO 9613-2 Acoustics - Attenuation of sound during propagation outdoors -- Part 2: General method of calculation.

Module 8C prediction of control valves aerodynamic noise

The results of calculations with SILDIS® acoustics simulation software are not comparable with standardized measurement due to the lack of documents formalizing corresponding measurement procedures.

Module 8D prediction of jet noise (including safety valves noise)

The results of calculations with SILDIS® acoustics simulation software are not comparable with standardized measurement due to the lack of documents formalizing corresponding measurement procedures.

Module 8E prediction of piping systems discharge parameters

The results of calculations with SILDIS® acoustics simulation software are not comparable with standardized measurement due to the lack of documents formalizing corresponding measurement procedures.

Module 8F determination of the performance and sizing of safety valves

The results of calculations with SILDIS® acoustics simulation software are not comparable with standardized measurement due to the lack of documents formalizing corresponding measurement procedures.

Module 8G simulation of the discharge of a fluid trough a valve vent stack

The results of calculations with SILDIS® acoustics simulation software are not comparable with standardized measurement due to the lack of documents formalizing corresponding measurement procedures.

Module 8H prediction of acoustic and aerodynamic performance of vent silencers for pressurized fluids

The results of calculations with SILDIS® acoustics simulation software are not comparable with standardized measurement due to the lack of documents formalizing corresponding measurement procedures.

Module 9 prediction of sound decay in enclosed spaces

The results of calculations with SILDIS® acoustics simulation software are comparable with standardized measurement NF EN ISO 3382-2 Acoustics -Measurement of room acoustics parameters- Part 2: reverberation time in ordinary rooms.

Module 9A prediction of sound spatial decay in open-plan offices

Some of the results of calculations with SILDIS® acoustics simulation software are comparable with standardized measurement NF EN ISO 3382-3 Acoustics -Measurement of room acoustics parameters- Part 3: Open plan offices.

Module 10 prediction of the noise emissions from buildings and other constructions

Module 10 of the SILDIS® simulation software is useful for assessing the impact, in terms of sound power level or sound pressure level at a specified location, of all or part of the construction elements making up a façade/partition (a wall or a roof):

  • an envelope (everywhere there is no opening, as detailed below)
  • openings (e.g. doors, windows, silencers; in quantities ranging from 1 to 5), considering (for each individually):
    • their sound reduction index - optionally using the software's library
    • an additional sound power upstream of the opening (i.e. "internal")
    • an additional sound power downstream of the opening (i.e. "external")
    • directivity 
    • a spatial sound decay model

Thus, for example, where an opening is equipped with a silencer, it is possible to account for (if required) additional sound powers to be added to the sound power resulting from the product of the internal acoustic field intensity and the area of the element (then: an opening), that characterize the sound transmission of any (other) facade/partition element:

  • fan noise (via an additional "internal" sound power)
  • silencer's self-generated noise (via an additional "external" sound power)

Depending on requirements, external noise sources (varying in number from 1 to 2) can be taken into account, considering the following for each one separately:

  • their sound power level 
  • their directivity 

Thus, for example, it is possible to simulate the presence of (often noisy) air-cooling equipment.

This is the software's strength: neither the building envelope, the openings, nor external noise sources are - a priori - assumed to be point sources when considered as a whole and consequently, SILDIS® prediction results avoid the approximate (or even completely erroneous) nature that might arise from the inappropriate use of such an assumption e.g. when the calculation points for sound pressure levels are located close to the facade/partition.

Of course, the point-source concept is essential for assessing sound levels at varying distances from a façade (whether or not additional external noise sources are present). However, it is applied - via specific calculation routines of SILDIS® software - to 5000 elementary noise sources that form a mesh covering the entire façade surface (this mesh is also used for external noise sources whenever their location partially aligns with these mesh elements). This makes all the difference:

  • regarding the software's potential applications: provided the characteristic dimension of an elementary mesh element (which represents only 1/5000th of the total façade area) is sufficiently small relative to the distance from the façade:
    • in practice, there are no real limitations regarding façade dimensions (even large ones) or the distance (even short ones) between the façade and the point where the sound pressure level is being evaluated
  • regarding calculation accuracy:
    • the calculations have undergone successful comparative testing as part of the software's validation process

The main outputs are (besides sketches summarizing the dimensions entered for the building envelope, openings, and external noise sources):

  • the sound power level of a façade or roof (and the contribution of its construction elements), per octave frequency band, and as an A-weighted overall value; with a noise map
  • the sound pressure level at specified locations (and the contribution of its construction elements), per octave frequency band, and as an A-weighted overall value; with a noise map

Graphs illustrate the contribution of each opening and each external noise source to the acoustic indicators applicable to the entire façade/partition, with A-weighted overall values

Some of the results of calculations with SILDIS® acoustics simulation software are comparable with results of calculations based on standard ISO ISO 12354-4 Building acoustics - Estimation of acoustic performance of buildings from the performance of elements - Part 4: Transmission of indoor sound to the outside.

  • Tutorial Module 10 (7 minutes)

Available packs for acoustics simulation software SILDIS®

Pack 1-8 = module 1 + module 2 + module 3 + module 4 + module 5 + module 6 + module 7 + module 8
Pack 1A = module 1A
Pack 1B = module 1B
Pack 5A = module 5A
Pack 8A = module 8A
Pack 8B = module 8B
Pack 8CDEFGH = module 8C + module 8D + module 8E + module 8F + module 8G + module 8H
Pack 9 = module 9
Pack 9A = module 9A
Pack 10 = module 10

Note: other modules/features exist for the software SILDIS®, allowing (namely) computations of sound propagation inside buildings, outdoor (including noise barrier sizing), from inside buildings to outside, etc... What follows is related to modules 1 to 9A exclusively (presentation preparation work of other modules in progress).

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