Dear experts, I’ve encountered issues while using the FW-CADIS (Random Ray) method.
I tried to use the random_ray to reproduce the literature ”Application of the Random Ray Method to Global Variance Reduction in Radiation Shielding Problems”.The model is shown below. The source is a 2 MeV isotropic neutron source, uniformly distributed in the red area. The gray region represents concrete, and the light blue region represents air.
While using FW-CADIS, the majority of the mesh tallies yield a flux of zero, with only a few meshes showing non-zero values. Furthermore, the resulting weight window lower bounds are all -1.0. I suspect the issue may lie either with the multi-group cross sections (which I generated using the MAGIC method in OpenMC) or with the configuration of the Random Ray method. Below are my settings.：
def create_settings(materials):
“”“创建模拟设置”“”
settings = openmc.Settings()
# 2 MeV neutron source
source = openmc.IndependentSource()
source.space = openmc.stats.Box([-320, -120, 0],[320, 120, 340])
source.energy = openmc.stats.Discrete([2.0e6], [1.0])
source.angle = openmc.stats.Isotropic()
source.particle = 'neutron'
#source.domain = materials[0]
random_ray_source = openmc.IndependentSource()
random_ray_source.space = openmc.stats.Point((200, 0, 120)) # central point
random_ray_source.energy = openmc.stats.Discrete([2.0e6], [1.0]) # 2 MeV neutron
random_ray_source.angle = openmc.stats.Isotropic()
settings.source = random_ray_source
# 网格通量计数器
mesh = openmc.RegularMesh()
mesh.dimension = [32, 12, 17] # 20cm网格
mesh.lower_left = [-320, -120, 0]
mesh.upper_right = [320, 120, 340]
settings.energy_mode = 'multi-group' # 关键：设置多群模式
settings.photon_transport = False
#settings.inactive = 200
settings.particles = 10000 # 先减少粒子数测试
settings.run_mode = 'fixed source'
settings.random_ray = {
'distance_active': 600.0,
'distance_inactive': 100.0,
'ray_source': source,
'volume_normalized_flux_tallies': True
}
settings.batches = 1000 # 先小批量测试
weight_window_gen2 = openmc.WeightWindowGenerator(
mesh=mesh,
#energy_bounds=energy_bounds,
particle_type='neutron', # 应用于中子
method='fw_cadis', # 使用MAGIC方法生成权重窗口
max_realizations=settings.batches, # 最多5个实现
update_interval=5, # 每10个批次更新一次
on_the_fly=True # 启用实时权重窗口
)
settings.weight_window_generators = [weight_window_gen2] #magic方法开始加入网格了
return settings,mesh
“source“ describes the whole region,which is used in settings.random_ray['ray_source']. while “random_ray_source” is used because the program encounters a segmentation fault if settings.sourceare set as box source