The SILDIS software (in Excel format) enables the modeling of sound emissions from buildings and other constructions as illustrated by a tutorial concerning a heterogeneous façade (i.e. one with elements differing in nature and, consequently, in acoustic performance - sound reduction and/or directivity -) to determine (and compare against targeted values):
- the sound power level (in dB ref. 1 pW):
- of each element, considered individually
- total, for the façade
- the sound pressure level (expressed in dB ref. 2×10⁻⁵ Pa) at a specified location:
- resulting from noise transmission through each element, considered individually
- total, for the façade, combining the effects of the various elements
In the above context, the term "construction" is to be understood in the broadest possible sense, encompassing all structures or assemblies for which acoustic insulation or noise reduction performance is required and must be quantified (e.g. enclosures, casings, soundproofed hangars, as well as silencer walls and other large-scale air-handling system components - including those for flue gas exhaust -).
Certain results obtained using the SILDIS acoustic simulation software are comparable to those derived from calculations based on the ISO 12354-4 standard Building acoustics - Estimation of acoustic performance of buildings from the performance of elementsPart 4: Transmission of indoor sound to the outside.
However, the software goes much further, as its primary outputs include not only sound levels (per octave frequency band and as A-weighted overall values, eventually compared against a target limit to assess any exceedances or noise emergence -) but also:
- noise maps (in color), allowing visualization of the impact of each element considered individually
- graphs showing the respective contribution or comparative performance of the various elements, considered both individually and as a collective whole
It is therefore a comprehensive tool for analyzing sound transmission and emission through the facades (walls or roofs) of buildings and other structures.
Regarding the interior of the building or structure, the modeling is based on:
- an average sound pressure level inside the structure, close to the surfaces (if this is not explicitly known, a supplementary Excel spreadsheet included in the module allows for its estimation in various scenarios, based on a sound power level or a sound pressure level at a specified distance from a source, the latter being known)
- a model of the acoustic field's diffusivity within the structure (depending on the shape of the rooms and the varying amounts of sound-absorbing materials present)
The modeling can also account for (without dimensional limitations) the presence of:
- envelope elements (masonry, cladding, panel-based metal structures, or of any other type, provided the sound reduction index is known)
- openings (e.g. doors, windows, silencers; in quantities ranging from 1 to 5), considering (for each individually):
- their sound reduction index, in dB - optionally using the software's library
- an additional sound power (expressed as a level, i.e. in dB ref. 1 pW) upstream of the opening (i.e. "internal"), added to the sound power resulting from the product of the internal sound field intensity and the opening area (this allows for accounting - when required - for the sound power of one or more ventilation system fan(s))
- an additional sound power (expressed as a level, i.e. in dB ref. 1 pW) downstream of the opening (i.e. "external"), added to the sound power resulting from the product of the internal sound field intensity and the opening area (this allows for accounting - when required - for the self-generated sound power of one or more silencer(s))
- directivity in dB
- a spatial sound decay model
- external noise sources (in quantities ranging from 1 to 2), considering (for each individually) - which is useful, for example, for simulating the presence of air-cooled condensers -:
- their sound power level in dB ref. 1 pW
- their directivity in dB
The difference between the sound power level and the sound pressure level at a specified location (for predictive calculation or noise measurement) in relation to a façade element, as mentioned above - and even more so in relation to the entire façade - can only be validly determined using simplified formulas if the ratio of the characteristic dimension of the element (or façade) to the distance from the measurement point is sufficiently small (this corresponds to the point-source assumption, where the wavelength associated with the frequency in question is a relevant factor).
This assumption does not hold true, at least not for the facade viewed as a whole, when the specified locations are at a short distance, and even less so if the facade in question is large. For noise control projects (not limited to industrial applications) where a maximum noise level is prescribed (often one that must be guaranteed), distances as short as one meter (or at least in that order of magnitude) are frequently used as the reference for specified locations (as they allow the influence of background noise to be limited when assessing only the emissions from a specific noise source) relative to:
- partitions/walls e.g. of an equipment enclosure, of a machine housing, of a building, and even of ducts walls - the surface area of the ductwork at the inlet of a Heat Recovery Steam Generator (HRSG), for instance, can run into the hundreds of square meters -
- openings e.g. air intakes for high-capacity compressors or combustion turbines - areas can range in the tens of square meters -, not to mention the intake and discharge areas of air-cooled condensers and cooling towers, which can - again - reach hundreds of square meters
Discretizing the surface using a mesh (based on 5000 cells, even for small-scale structures) forms the basis of the approach used with SILDIS software, of which prediction results are in pratice - ipso facto - valid for all noise impact studies (regarding the surrounding environment, even at very close range) involving walls or roofs encountered to date, representing the state of the best practice in this field.
Furthermore, Module 10 of the SILDIS software for modeling buildings and other constructions combines ease of use, rapid simulation[1], and reliability[2] (qualities that serve as its hallmark).
As for the software's features and calculation methods, it takes little time to grasp the essentials, given that the tutorial linked below lasts less than 8 minutes.
Tutorial (8 minutes)
[1] based on Excel, the software allows the user to enter simulation parameters into designated cells and to select models from drop-down menus for various stages of the calculations. No geometry input or import is required - quite the opposite: a diagram of the façade, including a representation of its components, is generated as an output by the software - and calculation results are obtained almost instantly, as demonstrated in the tutorial
[2] numerous comparisons between the results of modeling with SILDIS software and results of predictions obtained via other methods/of measurements have been made, yielding conclusive results (software development and validation regularly certified as compliant with the ISO 9001 Quality Management standard)