ADAMOS (ADAptive MOdal Summation)
is a tool for dynamic analysis of piping systems
with gapped restraints. It is based upon a
piecewise linear approach in which the total
response is obtained as a summation of all the
modal responses and a correction for the left-out
modes (beyond the cut-off frequency of the
system). Piecewise linear means
that at time of impact or release of a gapped
restraint, the mode shapes and modal amplitudes
are recomputed. Between impacts or releases the
system behaves linearly. ADAMOS can be used with
applied force time-history loads at discrete
points, or with floor motion at a number of
support levels. In the development both cases are
dealt with simultaneously.
The
Response Spectrum method is the most commonly
used method for analyzing seismic events. It is
widely recognized that in some cases, when
so-called Twin Modes occur (in particular when
very small pipes are connected to bigger pipes or
when lines with similar eigenfrequencies are
connected together) the results obtained
with the Response Spectrum method are highly
exaggerated. Twin Modes may lead to seismic
responses that are up to 10 times higher
than reality. This in turns leads to large
numbers of redundant, but very expensive, seismic
restraints, that, in fact, never should have been
installed.
An
additional effect is that numerical instability
appears in the piping analysis: small changes in
the input data may have tremendous effects on the
results. This makes it impossible to adopt normal
design strategies for piping systems.
The Twin
Mode Rotation program provides an elegant
solution to the problem. Suspected Twin Modes
pairs are rotated before the seismic responses
are combined. The procedure is mathematically
rigorous for modes with very close frequencies.
It has been extended to include modes with
frequency differences up to 10 % by means of an
important validation program, which has led
to its acceptance by the Belgian Safety
Authorities.
THGE uses a probabilistic model
(inverse first crossing problems) to generate the
power spectral density of an equivalent
stationary Gaussian process having the design
spectrum as expected maximum response. This
process is then shaped to simulate a real
earthquake. A subsequent iterative process
refines the solution to match the target
spectrum. The Fast Fourier transform is
systematically used to connect the time and
frequency domains. Some additional features are
also included: imposed peak acceleration,
automatic correction to meet the SRP criteria,
transformation of the accelerogram into
PIPESTRESS format.
TRANSA allows the analysis of
thermal phenomena occuring in pipe walls during
fluid transients. TRANSA computes the temperature
history across the wall thickness and produces
the following output as required by the ASME
Boiler and Pressure Vessel code, Section III,
Division I, NB-3653.2 for Class I piping :
Mean wall
temperature
Equivalent
linear thermal gradient Delta T1
Non-linear
thermal gradient Delta T2
Thermal
stresses near gross structural or
material discontinuities
