Changes between Version 4 and Version 5 of GuarDyan_VarRedu

Timestamp:

Feb 13, 2018, 4:21:29 PM (7 years ago)

Author:

dieda

Comment:

--

GuarDyan_VarRedu

@@ -7 +7 @@
 
 [[Image(TDMCC_varP_analog_vs_nonanalog.png​​, 400px)]]
-
-'' Figure 1.: Analog and non-analog simulation results for time dependent power evolution for a multiplying medium. Analog simulation produces an underestimate of the power ''
+\\'' Figure 1.: Analog and non-analog simulation results for time dependent power evolution for a multiplying medium. Analog simulation produces an underestimate of the power ''
 
 Biased sampling schemes are applied at fission yield, delayed neutron, interaction type sampling with ongoing development regarding path length sampling and angular biasing.
@@ -36 +35 @@
 
 
-== Event based and History based approach comparison: Test Case '''1'''
+=== Event based and History based approach comparison: Test Case '''1'''
 GUARDYAN has been recently validated against MCNP6 in a simplified setup assuming a monoenergetic neutron source inside a homogeneous sphere. 4 10^6^ neutrons were launched at energies 0.01eV , 1eV , 1keV , 1MeV and 18MeV , and tracked until either leaking out of the sphere or exceeding time boundary. The simulation was carried out for 412 isotopes and was used for validation of the code comparing the spectrum of leaking neutrons to MCNP6 results. Cross section library ENDF/B-VII.1 was used assuming temperature of 293:6K. Regarding our investigation of event-based tracking, wall-time was measured for both history-based (TH) and event-based (TE) simulations. In Fig. 2, histograms of simulation speedup are plotted for all starting energies. Speedup is simply defined by 
 
-Speedup= TE/TH
+ Speedup= TE/TH
 
 i.e. the ratio of wall-times. Fig. 2 shows that vectorization of the code resulted in faster execution time in most cases. Typical speedup was around 1:5-2, but longer simulation time was observed mainly when starting energy is below 1MeV .
 
 
- The efficiency loss was experienced in case of isotopes with high probability for fission around the starting energy. When the starting energy is low, neutrons released in fission take on much higher velocity than starters, thus leaking out of the system very fast. As a result, significant part of computational effort was spent on a few neutrons bouncing around in the system. Population drop caused vectorization gain to be cancelled due to the computational overhead of event-based tracking (particles need to be sorted by event type). On higher starting energies, no considerable speedup was observed in case of elements with low atomic numbers, the improvement from vectorization was more expressed when heavy elements were present. This is due to that the outgoing energy and angle of a neutron scattered on a light isotope are derived by simple laws of collision mechanics, while more complicated energy laws are applied when heavier isotopes are present . In GUARDYAN beside elastic scatter only ACE law 3 (inelastic discrete-level scattering) was used in the former case, and ACE law 4 (and 44) was additionally used in the latter. ACE law 4 represents a continuous tabular distribution, the outgoing energy is given as a probability distribution for every incoming energy. This sampling procedure takes considerably more time, contributing to thread divergence, and resulting in substantial efficiency boost for event-based tracking. 
+[[Image(event_vs_history_times_new.m.png​​, 800px)]]
+\\'' Figure 2.: Speedup figures for the simple spherical geometry ''
+
+The efficiency loss was experienced in case of isotopes with high probability for fission around the starting energy. When the starting energy is low, neutrons released in fission take on much higher velocity than starters, thus leaking out of the system very fast. As a result, significant part of computational effort was spent on a few neutrons bouncing around in the system. Population drop caused vectorization gain to be cancelled due to the computational overhead of event-based tracking (particles need to be sorted by event type). On higher starting energies, no considerable speedup was observed in case of elements with low atomic numbers, the improvement from vectorization was more expressed when heavy elements were present. This is due to that the outgoing energy and angle of a neutron scattered on a light isotope are derived by simple laws of collision mechanics, while more complicated energy laws are applied when heavier isotopes are present . In GUARDYAN beside elastic scatter only ACE law 3 (inelastic discrete-level scattering) was used in the former case, and ACE law 4 (and 44) was additionally used in the latter. ACE law 4 represents a continuous tabular distribution, the outgoing energy is given as a probability distribution for every incoming energy. This sampling procedure takes considerably more time, contributing to thread divergence, and resulting in substantial efficiency boost for event-based tracking. 
+