Merge pull request #1940 from ojschumann/time-src

Time distribution for source.

docs/source/usersguide/settings.rst

@@ -174,10 +174,11 @@ create an instance of :class:`openmc.Source` and use it to set the
 varying source strengths, :attr:`Settings.source` should be set to a list of
 :class:`openmc.Source` objects.
 
-The :class:`openmc.Source` class has three main attributes that one can set:
+The :class:`openmc.Source` class has four main attributes that one can set:
 :attr:`Source.space`, which defines the spatial distribution,
-:attr:`Source.angle`, which defines the angular distribution, and
-:attr:`Source.energy`, which defines the energy distribution.
+:attr:`Source.angle`, which defines the angular distribution,
+:attr:`Source.energy`, which defines the energy distribution, and
+:attr:`Source.time`, which defines the time distribution.
 
 The spatial distribution can be set equal to a sub-class of
 :class:`openmc.stats.Spatial`; common choices are :class:`openmc.stats.Point` or
@@ -210,14 +211,23 @@ distribution. This could be a probability mass function
 specified, a Watt fission spectrum with :math:`a` = 0.988 MeV and :math:`b` =
 2.249 MeV :sup:`-1` is used.
 
+The time distribution can be set equal to any univariate probability
+distribution. This could be a probability mass function
+(:class:`openmc.stats.Discrete`), a uniform distribution
+(:class:`openmc.stats.Uniform`), or a tabular distribution
+(:class:`openmc.stats.Tabular`). By default, if no time distribution is
+specified, particles are started at :math:`t=0`.
+
 As an example, to create an isotropic, 10 MeV monoenergetic source uniformly
-distributed over a cube centered at the origin with an edge length of 10 cm, one
+distributed over a cube centered at the origin with an edge length of 10 cm, and
+emitting a pulse of particles from 0 to 10 µs, one
 would run::
 
   source = openmc.Source()
   source.space = openmc.stats.Box((-5, -5, -5), (5, 5, 5))
   source.angle = openmc.stats.Isotropic()
   source.energy = openmc.stats.Discrete([10.0e6], [1.0])
+  source.time = openmc.stats.Uniform(0, 1e-6)
   settings.source = source
 
 The :class:`openmc.Source` class also has a :attr:`Source.strength` attribute

include/openmc/source.h

@@ -42,13 +42,13 @@ public:
 };
 
 //==============================================================================
-//! Source composed of independent spatial, angle, and energy distributions
+//! Source composed of independent spatial, angle, energy, and time distributions
 //==============================================================================
 
 class IndependentSource : public Source {
 public:
   // Constructors
-  IndependentSource(UPtrSpace space, UPtrAngle angle, UPtrDist energy);
+  IndependentSource(UPtrSpace space, UPtrAngle angle, UPtrDist energy, UPtrDist time);
   explicit IndependentSource(pugi::xml_node node);
 
   //! Sample from the external source distribution
@@ -64,6 +64,7 @@ public:
   SpatialDistribution* space() const { return space_.get(); }
   UnitSphereDistribution* angle() const { return angle_.get(); }
   Distribution* energy() const { return energy_.get(); }
+  Distribution* time() const { return time_.get(); }
 
 private:
   ParticleType particle_ {ParticleType::neutron}; //!< Type of particle emitted
@@ -71,6 +72,7 @@ private:
   UPtrSpace space_;                               //!< Spatial distribution
   UPtrAngle angle_;                               //!< Angular distribution
   UPtrDist energy_;                               //!< Energy distribution
+  UPtrDist time_;                                 //!< Time distribution
 };
 
 //==============================================================================

openmc/source.py

@@ -22,6 +22,8 @@ class Source:
         Angular distribution of source sites
     energy : openmc.stats.Univariate
         Energy distribution of source sites
+    time : openmc.stats.Univariate
+        time distribution of source sites
     filename : str
         Source file from which sites should be sampled
     library : str
@@ -43,6 +45,8 @@ class Source:
         Angular distribution of source sites
     energy : openmc.stats.Univariate or None
         Energy distribution of source sites
+    time : openmc.stats.Univariate or None
+        time distribution of source sites
     file : str or None
         Source file from which sites should be sampled
     library : str or None
@@ -56,11 +60,12 @@ class Source:
 
     """
 
-    def __init__(self, space=None, angle=None, energy=None, filename=None,
+    def __init__(self, space=None, angle=None, energy=None, time=None, filename=None,
                  library=None, parameters=None, strength=1.0, particle='neutron'):
         self._space = None
         self._angle = None
         self._energy = None
+        self._time = None
         self._file = None
         self._library = None
         self._parameters = None
@@ -71,6 +76,8 @@ class Source:
             self.angle = angle
         if energy is not None:
             self.energy = energy
+        if time is not None:
+            self.time = time
         if filename is not None:
             self.file = filename
         if library is not None:
@@ -104,6 +111,10 @@ class Source:
     def energy(self):
         return self._energy
 
+    @property
+    def time(self):
+        return self._time
+
     @property
     def strength(self):
         return self._strength
@@ -142,6 +153,11 @@ class Source:
         cv.check_type('energy distribution', energy, Univariate)
         self._energy = energy
 
+    @time.setter
+    def time(self, time):
+        cv.check_type('time distribution', time, Univariate)
+        self._time = time
+
     @strength.setter
     def strength(self, strength):
         cv.check_type('source strength', strength, Real)
@@ -178,6 +194,8 @@ class Source:
             element.append(self.angle.to_xml_element())
         if self.energy is not None:
             element.append(self.energy.to_xml_element('energy'))
+        if self.time is not None:
+            element.append(self.time.to_xml_element('time'))
         return element
 
     @classmethod
@@ -229,6 +247,10 @@ class Source:
         if energy is not None:
             source.energy = Univariate.from_xml_element(energy)
 
+        time = elem.find('time')
+        if time is not None:
+            source.time = Univariate.from_xml_element(time)
+
         return source
 
 

src/settings.cpp

@@ -459,9 +459,12 @@ void read_settings_xml()
   // If no source specified, default to isotropic point source at origin with
   // Watt spectrum
   if (model::external_sources.empty()) {
+    double T[] {0.0};
+    double p[] {1.0};
     model::external_sources.push_back(make_unique<IndependentSource>(
       UPtrSpace {new SpatialPoint({0.0, 0.0, 0.0})},
-      UPtrAngle {new Isotropic()}, UPtrDist {new Watt(0.988e6, 2.249e-6)}));
+      UPtrAngle {new Isotropic()}, UPtrDist {new Watt(0.988e6, 2.249e-6)},
+      UPtrDist {new Discrete(T, p, 1)}));
   }
 
   // Check if we want to write out source

src/source.cpp

@@ -46,11 +46,12 @@ vector<unique_ptr<Source>> external_sources;
 // IndependentSource implementation
 //==============================================================================
 
-IndependentSource::IndependentSource(
-  UPtrSpace space, UPtrAngle angle, UPtrDist energy)
-  : space_ {std::move(space)}, angle_ {std::move(angle)}, energy_ {
-                                                            std::move(energy)}
-{}
+IndependentSource::IndependentSource(UPtrSpace space, UPtrAngle angle, UPtrDist energy, UPtrDist time)
+  : space_{std::move(space)},
+    angle_{std::move(angle)},
+    energy_{std::move(energy)},
+    time_{std::move(time)}
+{ }
 
 IndependentSource::IndependentSource(pugi::xml_node node)
 {
@@ -140,6 +141,17 @@ IndependentSource::IndependentSource(pugi::xml_node node)
       // Default to a Watt spectrum with parameters 0.988 MeV and 2.249 MeV^-1
       energy_ = UPtrDist {new Watt(0.988e6, 2.249e-6)};
     }
+
+    // Determine external source time distribution
+    if (check_for_node(node, "time")) {
+      pugi::xml_node node_dist = node.child("time");
+      time_ = distribution_from_xml(node_dist);
+    } else {
+      // Default to a Constant time T=0
+      double T[] {0.0};
+      double p[] {1.0};
+      time_ = UPtrDist {new Discrete{T, p, 1}};
+    }
   }
 }
 
@@ -224,6 +236,9 @@ SourceSite IndependentSource::sample(uint64_t* seed) const
       break;
   }
 
+  // Sample particle creation time
+  site.time = time_->sample(seed);
+  
   return site;
 }
 

tests/regression_tests/source/inputs_true.dat

@@ -121,6 +121,7 @@
         </dist>
       </pair>
     </energy>
+    <time parameters="2 5" type="uniform" />
   </source>
   <source strength="0.1">
     <space origin="1.0 1.0 0.0" type="cylindrical">
@@ -144,5 +145,6 @@
         </dist>
       </pair>
     </energy>
+    <time parameters="2 5" type="uniform" />
   </source>
 </settings>

tests/regression_tests/source/test.py

@@ -65,14 +65,16 @@ class SourceTestHarness(PyAPITestHarness):
         energy3 = openmc.stats.Tabular(E, p, interpolation='histogram')
         energy4 = openmc.stats.Mixture([1, 2, 3], [energy1, energy2, energy3])
 
+        time1 = openmc.stats.Uniform(2, 5)
+
         source1 = openmc.Source(spatial1, angle1, energy1, strength=0.3)
         source2 = openmc.Source(spatial2, angle2, energy2, strength=0.1)
         source3 = openmc.Source(spatial3, angle3, energy3, strength=0.1)
         source4 = openmc.Source(spatial4, angle3, energy3, strength=0.1)
         source5 = openmc.Source(spatial5, angle3, energy3, strength=0.1)
         source6 = openmc.Source(spatial5, angle3, energy4, strength=0.1)
-        source7 = openmc.Source(spatial6, angle3, energy4, strength=0.1)
-        source8 = openmc.Source(spatial7, angle3, energy4, strength=0.1)
+        source7 = openmc.Source(spatial6, angle3, energy4, time1, strength=0.1)
+        source8 = openmc.Source(spatial7, angle3, energy4, time1, strength=0.1)
 
         settings = openmc.Settings()
         settings.batches = 10