Industrial Sources

The general source types, such as point, line and area sources (horizontal and vertical), are used to model a variety of noise sources including also the building radiation. Moreover, they may have an individual directivity (see Directivity at Industrial Sources).

When applying these sources to model the sound radiation from buildings the object snap is activated in order to place them in front of the building’s facade at a distinct distance (see Object Snap). This prevents from the source being placed inside the building.

see Common Input Data for detailed information on the common parameters of the general sound sources.

Point Source

A point source is entered at the position of the mouse pointer with a mouse click at the desired location. The point source is represented by a cross.

Point sources are noise sources whose dimensions are small in comparison to the distance to the receiver points. Examples are ventilation openings, pumps, motors, and people shouting.

Line Source

Line sources are modelled as open polygons. Line sources have one dimension only, while the dimensions in the other two orthogonal dimensions are small compared with the distance to the receiver points. Examples are pipelines, conveyor belts, and traffic routes on a factory site.

Upon calculation, CadnaA subdivides the line source in a two-step procedure. First, the line source is subdivided into sections being screened and sections not being screened by any obstacles lying between the receiver and the sub-source (see Projection at extended Sound Sources). In a second step, the distance between the receiver and each section is determined and a further subdivision is required if the section length exceeds the minimum distance criterion.

Area Source

Area sources are modelled as closed polygons. They are noise sources extending in two dimensions while the third dimension perpendicular to its area is small in relation to the receiver distance.

CadnaA subdivides upon calculation the area sources into sufficiently small sub-areas. In the centre of each sub-source a point source with the appropriate partial sound power is placed. This procedure results in a fine grid of point sources, the total emission of which represents the area source.

horizontal Area Source

Horizontal area sources are inserted by entering their horizontal projection.

Examples of area sources are parking lots (see Parking Lots), sports facilities, and even entire industrial or commercial areas.

vertical Area Source

Vertical area sources are inserted by entering their horizontal projection as an open polygon line.

Upon calculation, CadnaA subdivides the area source in a two-step procedure. First, the area source is subdivided into partial areas being screened and partial areas not being screened by any obstacle lying between the receiver and the source (see Projection at extended Sound Sources). Then, in the second step, the distance between the receiver point and each partial area is determined and a further subdivision is required if the largest dimension of a partial area exceeds the minimum distance criterion.

Geometric definition of the vertical area source

In order to enter a window (as illustrated above) as a sound-radiating area, enter a vertical area source as a polygon line in xy-plane at a short distance in front of the facade. For a clear distinction, a distance of approximately 0.05 m is used. This distance is automatically set via the dialog Object Snap (Options menu) prior to the input of the vertical area source (see Object Snap).

Vertical area source in front of a facade

On the edit dialog of the vertical area source specify the position of the top edge via button Geometry. As with any other object, this height may be defined as relative or absolute value, or with respect to the roof of a building. The latter is particularly convenient when entering e.g. ventilators placed onto a roof. The lower edge of the vertical area is specified as „z-dimension“ downwards from the top edge. More complicated outlines of vertical sound-radiating areas can be approximated by several rectangular areas.

Upon calculation, the vertical area source is replaced by a series of line sources with a spacing of 1 m. These are subdivided into sections as described above.

Note

The subsequent chapters are specific for each standard or guideline available in CadnaA. These specifications do not represent a copy of the standardized procedures, rather the way they are implemented.