source: palm/trunk/DOC/tec/topography_flags.html @ 1320

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second preliminary update for turbulent inflow

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13  <title>PALM chapter 3.8</title><meta name="GENERATOR" content="StarOffice 7 (Win32)">
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17  <meta name="AUTHOR" content="Siegfried Raasch">
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41<h3 style="line-height: 100%;">Topography flags</h3>
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44<p style="line-height: 100%;">Starting from version 3.4a
45a flag array has been introduced in PALM for representing the topography. The new array<span style="font-family: Courier New,Courier,monospace;">&nbsp;flags </span>is a 3D-<span style="font-family: Courier New,Courier,monospace;">INTEGER</span> array dimensioned (<span style="font-family: Courier New,Courier,monospace;">nzb:nzt+1,nys-1:nyn+1,nxl-1:nxr+1</span>) where each value describes the features of the respective grid point with respect to the topography. Strictly speaking,&nbsp;<span style="font-family: Courier New,Courier,monospace;">flags</span> is a <span style="font-family: Courier New,Courier,monospace;">POINTER</span> which by default points to the real array<span style="font-family: Courier New,Courier,monospace;"> wall_flags_1</span>. In case of using the multigrid method as pressure solver, additional arrays<span style="font-family: Courier New,Courier,monospace;"> wall_flags_2</span>,<span style="font-family: Courier New,Courier,monospace;"> wall_flags_3</span>,
46etc. are used containing the respective flag informations for the
47coarser grids. (Attention: The finest grid always has the largest
48number, i.e. if four multigrid levels are used, then the flags for the
49finest grid are stored in array<span style="font-family: Courier New,Courier,monospace;"> wall_flags_4</span>.)</p><p style="line-height: 100%;">Each
50INTEGER value has to be interpreted bitwise. As to the FORTRAN model
51bits are counted from right to left starting with bit 0. So far, the
52first seven bits are used for storing the following informations (a bit value of "<span style="font-style: italic;">1</span>" means that the appropriate flag is set):</p><br><table style="text-align: left; height: 220px; width: 496px;" border="1" cellpadding="2" cellspacing="2"><tbody><tr><td style="width: 85px; text-align: center;"><span style="font-weight: bold;">bit position</span></td><td style="width: 393px;"><span style="font-weight: bold;">meaning</span></td></tr><tr><td style="width: 85px; text-align: center;">0</td><td style="width: 393px;">wall to the bottom</td></tr><tr><td style="width: 85px; text-align: center;">1</td><td style="width: 393px;">wall to the top &nbsp;(this cannot be used in the code so far)</td></tr><tr><td style="width: 85px; text-align: center;">2</td><td style="width: 393px;">wall to the south</td></tr><tr><td style="width: 85px; text-align: center;">3</td><td style="width: 393px;">wall to the north</td></tr><tr><td style="width: 85px; text-align: center;">4</td><td style="width: 393px;">wall to the left</td></tr><tr><td style="width: 85px; text-align: center;">5</td><td style="width: 393px;">wall to the rigth</td></tr><tr><td style="width: 85px; text-align: center;">6</td><td style="width: 393px;">inside topography / building</td></tr></tbody></table><p style="line-height: 100%;"><span style="font-weight: bold;">Example:</span><br>If a gridpoint has two neighbouring walls to the bottom and to the left, then the flag bit value is "<span style="font-style: italic;">...010001</span>" which gives the<span style="font-family: Courier New,Courier,monospace;"> INTEGER </span>value "<span style="font-style: italic;">17</span>" = 1*2<sup>4</sup>+1*2<sup>0</sup>.</p><p style="line-height: 100%;">For a gridpoint in the free flow without any neighbouring wall no bits are set, i.e. the<span style="font-family: Courier New,Courier,monospace;"> INTEGER </span>value of the respective array element of<span style="font-family: Courier New,Courier,monospace;"> flags </span>is "<span style="font-style: italic;">0</span>".</p><p style="line-height: 100%;">The intrinsic FORTRAN functions <span style="font-family: Courier New,Courier,monospace;">IBSET</span>, <span style="font-family: Courier New,Courier,monospace;">IBITS</span>, <span style="font-family: Courier New,Courier,monospace;">IAND</span>, <span style="font-family: Courier New,Courier,monospace;">IOR</span>, etc. can be used to manipulate the bits.</p><p style="line-height: 100%; font-weight: bold;"></p><p style="line-height: 100%; font-weight: bold;">Examples:</p><div style="margin-left: 40px;"><span style="font-family: Courier New,Courier,monospace;">flags(k,j,i) = IBSET( flags(k,j,i), 6 )</span></div><p style="line-height: 100%;">sets the sixth bit of array element <span style="font-family: Courier New,Courier,monospace;">(k,j,i)</span> to "<span style="font-style: italic;">1</span>".</p><div style="margin-left: 40px; font-family: Courier New,Courier,monospace;">IBITS( flags(k,j,i), 4, 1 )</div><p style="line-height: 100%;">gives the<span style="font-family: Courier New,Courier,monospace;"> INTEGER </span>value "<span style="font-style: italic;">1</span>" if the fourth bit of array element <span style="font-family: Courier New,Courier,monospace;">(k,j,i)</span> is "<span style="font-style: italic;">1</span>", otherwise "<span style="font-style: italic;">0</span>".</p><p style="line-height: 100%;">Here is an example from routine <span style="font-family: Courier New,Courier,monospace;">redblack</span> (within <span style="font-family: Courier New,Courier,monospace;">poismg.f90</span>) which shows how <span style="font-family: Courier New,Courier,monospace;">IBITS</span> is used for implicit setting of Neumann boundary conditions:</p><p style="line-height: 100%; margin-left: 40px; font-family: Courier New,Courier,monospace;">p_mg(k,j,i+1) + IBITS( flags(k,j,i), 5, 1 ) * &amp;<br>&nbsp; &nbsp;&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; ( p_mg(k,j,i) - p_mg(k,j,i+1) )&nbsp;</p><p style="line-height: 100%;">If there is no wall to the right of gridpoint <span style="font-family: Courier New,Courier,monospace;">(k,j,i)</span> the term results to <span style="font-family: Courier New,Courier,monospace;">p_mg(k,j,i+1)</span>, otherwise it gives <span style="font-family: Courier New,Courier,monospace;">p_mg(k,j,i)</span>.</p><br>The flag array <span style="font-family: Courier New,Courier,monospace;">flags</span> is calculated in routine <span style="font-family: Courier New,Courier,monospace;">init_grid</span> using the topography information stored in <span style="font-family: Courier New,Courier,monospace;">nzb_local</span>.
53Here also the flag arrays for the coarser grids needed for the
54multigrid scheme are calculated. This requires informations from a
55distance of more than one grid spacing away from the current gridpoint.
56Therfore, array <span style="font-family: Courier New,Courier,monospace;">nzb_local</span> had to be extended for further ghost point levels (see <span style="font-family: Courier New,Courier,monospace;">init_grid</span>).</body></html>
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