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
