Further Simple Features

Here we describe additional DELTAE features which are relevant to purely acoustic (not thermoacoustic) apparatus. A list of the purely acoustic segment types (including those introduced previously) is given below. More detailed descriptions of each are given in Chapter V.

TITLE

Required at the top; comment field is retained in all .DAT and .OUT files.

BEGIN

Required immediately after TITLE. This is the ``zeroth" segment. It defines global parameters such as mean pressure and frequency, and initial conditions for p and U .

ENDCAp

A surface area with oscillatory-pressure loss in its thermal penetration depth. Usually used at ends of ducts.

ISODUct

An isothermal duct, with losses. Separate entry of area and perimeter accommodates ducts of any cross-sectional shape.

ISOCOne

A cone to adapt between ducts of different sizes. Uses lossy Webster horn equation.

COMPLiance

A compliance. With oscillatory-pressure losses on surface.

IMPEDance

A lumped-parameter series impedance.

IDUCEr and VDUCEr

Current-driven and voltage-driven transducers, with parameters independent of frequency.

ISPEAker and VSPEAker

Current-driven and voltage-driven electrodynamic transducers, parameterized by mass, B-L product, etc., so that impedance coefficients depend on frequency.

BRANCh

A frequency-independent side-branch impedance.

OPNBRanch

A side-branch impedance with the characteristics of radiation impedance into solid angle.

HARDEnd

One of the allowed final segments. Used to set U = 0 through use of the inverse of the acoustic impedance in the TARGET vector.

SOFTEND

The other allowed final segment. Used to set p = 0 through use of the acoustic impedance in the TARGET vector. Very useful for defining mirror-image planes in symmetric apparatus with pressure nodes at center of symmetry.

The sameas nl feature allows reference to a value (either a number or a gas or solid type) in another segment. This helps prevent typographical errors in the input file, and is especially useful in linking dimensions of adjacent segments which you might want to vary all together while plotting, such as areas of all segments when increasing the size of the apparatus. You can give just the segment number, if the parameter letters are the same (e.g., ``sameas 0" is often the gas type in all segments after the zeroth segment), or segment number and line letter (e.g., ``sameas 3a"). If you try to use sameas for two different types of variables-making length the same as an area, for example-DELTAE will give an error message and abort. The following example is for a closed resonator composed of two ducts joined by a cone:

TITLE    illustrating use of sameas

BEGIN      Initial              0
  1.380E+06 a Mean P    Pa   
   132.     b Freq.     Hz   
   586.     c T-beg     K    
  6.639E+04 d |p|@0     Pa   
   .000     e Ph(p)0    deg  
   .000     f |V|@0    m^3/s 
   .000     g Ph(V)0    deg  
helium     Gas type

ENDCAP     Hot End              1
sameas 2a   a Area     m
sameas  0  Gas type

ISODUCT    Hot Duct             2
1.292e-2    a Area     m
   .403     b Perim    m   
1.0         c Length   m
sameas  0  Gas type

ISOCONE     adapter between ducts
sameas 2a   a AreaI   m^2
sameas 2b   b PerimI   m 
   .100     c Length   m   
sameas 4a   d AreaF   m^2 
sameas 4b   e PerimF   m 
sameas 0

ISODUCT    Cold Duct            4
0.323e-2  a Area      m^2
0.2015    b Perim      m
1.0       c Length     m
sameas 0

ENDCAP     Cold End             5
sameas  4a  a Area    m^2
sameas 0

HARDEND                         6
   .000     a R(1/Z)  
   .000     b I(1/Z)  
sameas 0

When you access a parameter specified by sameas using (m)odify, or (p)lot to make it an independent plot variable, or (u)se it in a guess vector, the sameas relationship is severed and the parameter is given its current actual value. This is required because the value at this point will be changed (either by you, or by DELTAE). But if a variable that is the root of several sameas references is caused to change in any of these three ways, all sameas references to this root within the model will change with it.