.. _[t-wwbg]: [ T-WWBG ] section ================================================== This tally gives parameters used for the **[ww bias]** section. The tally serves as a Weight Window Bias Generator (WWBG) to automatically obtain effective settings of **[ww bias]**, which is used to bias **[weight window]**. The **[ww bias]** function is useful when the **[weight window]** parameters for a certain region are biased after automatically generating the **[weight window]** section by **[t-wwg]**. :numref:`fig-ww-wwbias` shows a flowchart of how to perform the transport calculation using **[weight window]** and **[ww bias]**. First, generate the **[weight window]** section by **[t-wwg]**. If the obtained parameters of **[weight window]** are enough to effectively use the variance reduction technique, the **[ww bias]** section is not needed. However, if they are not enough, the variance reduction technique can be used more effectively by biasing the **[weight window]** parameters for a certain region with **[ww bias]**. There are two methods to set the **[ww bias]** section: an automatic method using **[t-wwbg]**, which is a Weight Window Bias Generator (WWBG) and is explained below, and a manual method by a user. Only one **[t-wwbg]** section can be set in one input file. **[t-wwbg]** is effective only when **icntl=15** in **[parameters]**. For details of **[ww bias]**, see :numref:`sec-wwbias`. When performing a transport calculation with **[ww bias]** and **[weight window]**, set **icntl=0** and **iwwbias=1** in **[parameters]**. .. figure:: ./wwbias-e.png :width: 40em :name: fig-ww-wwbias :align: center The flowchart of the connection calculation between **[weight window]** and **[ww bias]**. .. figure:: ./twwbg1.png :width: 20em :name: fig-twwbg :align: center Parameters to define cylindrical regions. **[t-wwbg]** determines the bias values in stages of some cylindrical regions, which are with a central axis on a vector defined by two points **(x0,y0,z0)** and **(x1,y1,z1)**, shown in :numref:`fig-twwbg`. :numref:`fig-twwbg` shows a cross-section view of three different size cylinders. To define the cylindrical regions, the parameters **n-mesh**, **r-mesh**, **z-mesh**, and **f-mesh** are also required. **n-mesh** is the number of the cylinders. The differences of radii and heights of the cylinders are given by **r-mesh** and **z-mesh**, respectively. In these parameters, the same number of values as **n-mesh** must be given. The bias values can be set from the inside of the cylindrical regions in **f-mesh**. **f-mesh** must be set to **(n-mesh)+1**. The last value of **f-mesh** is the bias value in the outside of the cylinders. The cylindrical regions can be defined regardless of the geometry of the particle transport simulation. Note that if the defined cylindrical regions overlap the outer void given in **[cell]**, the outer void region can be extended by the **r-out** parameter. The **[t-wwbg]** parameters are formatted as follows. .. rst-class:: no-caption-number .. list-table:: **mesh** :header-rows: 0 * - value - explanation * - **reg, xyz, tet** - Mesh type. Only **reg**, **xyz**, and **tet** can be set. A mesh type subsection is required below this option. .. include:: ../commontally/part.rst .. include:: ../commontally/e-type.rst .. include:: ../commontally/t-type.rst .. rst-class:: no-caption-number .. list-table:: **axis** :header-rows: 0 * - value - explanation * - **xy, yz, xz, wwbg** - Restart calculation cannot be performed. When **xy**, **yz**, or **xz** is selected, the **rshow** option is needed. .. include:: ../commontally/file.rst .. include:: ../commontally/angel.rst .. include:: ../commontally/x-txt.rst .. include:: ../commontally/y-txt.rst .. include:: ../commontally/z-txt.rst .. rst-class:: no-caption-number .. list-table:: **rshow** :header-rows: 0 * - value - explanation * - **0** (default), **1, 2, 3** - When **mesh=xyz** and **axis=xy,yz,xz**, region border (1), material name (2), and region name (3) are plotted using this option. A **xyz** mesh section must be added below this option. .. rst-class:: no-caption-number .. list-table:: **resol** :header-rows: 0 * - value - explanation * - **1** (default) - This option multiplies the region line resolution by a factor of **resol** with the **rshow** option set to define the line thickness. .. rst-class:: no-caption-number .. list-table:: **width** :header-rows: 0 * - value - explanation * - **0.5** (default) - The option defines the line thickness. .. rst-class:: no-caption-number .. list-table:: **epsout** :header-rows: 0 * - value - explanation * - **0** (default), **1** - When **epsout=1**, results are plotted into eps files. The eps file is named by replacing the extension with ``.eps``. .. rst-class:: no-caption-number .. list-table:: **x0, y0, z0** :header-rows: 0 * - value - explanation * - - x, y, z coordinates of an initial point. .. rst-class:: no-caption-number .. list-table:: **x1, y1, z1** :header-rows: 0 * - value - explanation * - - x, y, z coordinates of a terminal point. .. rst-class:: no-caption-number .. list-table:: **n-mesh** :header-rows: 0 * - value - explanation * - n - The number of cylindrical regions. .. rst-class:: no-caption-number .. list-table:: **r-mesh** :header-rows: 0 * - value - explanation * - rm1, rm2, ..., rmn - The differences of radii of cylinders. The number of **n-mesh** values must be set. .. rst-class:: no-caption-number .. list-table:: **z-mesh** :header-rows: 0 * - value - explanation * - zm1, zm2, ..., zmn - The differences of heights of cylinders. The number of **n-mesh** values must be set. .. rst-class:: no-caption-number .. list-table:: **f-mesh** :header-rows: 0 * - value - explanation * - fm1, fm2, ..., fmn, fm(n+1) - Bias values in cylindrical regions. The number of **(n-mesh)+1** values must be set. .. rst-class:: no-caption-number .. list-table:: **r-out** :header-rows: 0 * - value - explanation * - (omissible, D=0) - Radius to extend the outer void [cm]. The same region specifications are required to use **[ww bias]** with **[weight window]** and therefore the same region definitions are required between **[t-wwg]** and **[t-wwbg]** to create **[weight window]** automatically using **[t-wwg]**. The following is an example of **[t-wwbg]**. .. code-block:: text :caption: Example of **[t-wwbg]** 1: [ T - WWBG ] 2: mesh = xyz 3: x-type = 2 4: nx = 30 5: xmin = -75 6: xmax = 75 7: y-type = 2 8: ny = 30 9: ymin = -75 10: ymax = 75 11: z-type = 2 12: nz = 40 13: zmin = 0.0 14: zmax = 200 15: axis = wwbg 16: file = wwbg.out 17: part = neutron 18: e-type = 1 19: ne = 2 20: 0.0 1e-3 1.0 21: x0 = 0.0 22: y0 = -20 23: z0 = 50 24: x1 = 0.0 25: y1 = 20 26: z1 = 150 27: n-mesh = 3 28: r-mesh = 10 10 10 29: z-mesh = 10 10 10 30: f-mesh = 1.0 0.5 0.1 0.05 31: r-out = 1000 In this example, the initial and terminal points are (0, -20, 50) and (0, 20, 150), respectively. The three cylindrical regions are defined with the central axis on the vector defined by the two points. :numref:`fig-twwbg2` shows a spatial distribution of the bias values given by the example input. The radii of the three cylinders are defined by **r-mesh**, and the differences of them are 10 cm. The heights of the cylinders increase by 20 cm, which is two times the 10 cm given by **z-mesh**. Bias values are given as 1.0, 0.5, 0.1, and 0.05 from the inside of the cylindrical regions. The change of the biases is shown in :numref:`fig-twwbg2`. .. figure:: ./twwbg2.png :width: 30em :name: fig-twwbg2 :align: center Spatial distribution of bias values given by the example of **[t-wwbg]**.