A User's Manual for DELSOL3 - prod.sandia.gov - Sandia National ...

optimum for any power level is 13. Then when doing the next tower height, which
might be THT = 160, DELSOL will start to search at receivers of size 12.
The second assumption of smart optimization, that optimum tower height and
receiver size increase with power level, allows DELSOL to use the minimum opti-
mum receiver size at a lower power level as the starting point for the next power
level. DELSOL also applies this to optimize a single power level in that once an
optimum receiver is found, receivers with smaller areas are not examined, except
that the optimization always starts with the next smaller area. This limitation on
area is also not used on cavity receivers where the depth is being optimized, since
the power is calculated at the aperture and remains constant as heat absorber
area increases, or decreases slightly due to increased receiver losses.
DELSOL’s “smart” optimization also includes several checks to try to ensure
that the correct optimum system is chosen. One such check is that if a minima is
found on the first try for a variable whose minima had previously been found to
be one larger, the starting point for that iteration will be lowered and the itera-
tion will be Started again. This’means that DELSOL may check the same system
twice, once due to reducing the starting point here and again as it begins increas-
ing the variable again until energy costs start increasing again. Despite this du-
plication, “smart” optimization will still examine many fewer systems than if ev-
ery possible combination allowed is examined. Because of the assumptions made
in “smart” optimization, it is possible that DELSOL will miss the best system.
However, the difference in energy cost between the chosen system and the best
system will be srnall, and the user can easily check for the better system by doing
a more limited optimization with IALL=1 around the system which the “smart”
optimization previously found to be optimum.
Flux limited receiver designs complicate the “smart” optimization search
strategy. None of the methods for restricting the search can be applied until the
flux constraint is satisfied. For example, DELSOL will increase the receiver size
as long as a flux limit is exceeded even though energy costs may be increasing. In
many respects, exceeding a flux limit is treated similarly to not reaching a design
point power of interest. Thus, flux limited receiver optimizations have to search
over more cases than the corresponding non-flux limited receiver “smart” opti-
mizations. It is very important when optimizing with a flux limit to use
a two step coarse grid/fine grid strategy. A search over a coarse grid of op-
timization variables locates an approximate optimum design rapidly. This is fol-
lowed by a search over a fine grid of optimization variables centered on the coarse
grid optimum. Thus a large range can be looked at without examining a large
number of systems.
A detailed summary of the optimization search is provided as output. The
user can follow the optimization strategy by analyzing this information. In addi-
tion, the information on the search can give a good indication of the sensitivity
of the energy costs, performances, etc. to variation of the design parameters. For
example, if a 150 meter tower is optimum but the user would like to know what
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