SetFactory("OpenCASCADE");

h = 0.10;
eps = h/10;

Box(1) = { 1, 1, 0, 1, 1, h };    // Center box
Box(2) = { 0, 0, 0, 1, 1, h };    // Sponge bottom left
Box(3) = { 1, 0, 0, 1, 1, h };    // Sponge bottom center
Box(4) = { 2, 0, 0, 1, 1, h };    // Sponge bottom right
Box(5) = { 0, 1, 0, 1, 1, h };    // Sponge center left
Box(6) = { 2, 1, 0, 1, 1, h };    // Sponge center right
Box(7) = { 0, 2, 0, 1, 1, h };    // Sponge top left
Box(8) = { 1, 2, 0, 1, 1, h };    // Sponge top center
Box(9) = { 2, 2, 0, 1, 1, h };    // Sponge top right

Coherence;

bnd_bottom() = Surface In BoundingBox{-eps, -eps, -eps, 3+eps, 3+eps, eps};
bnd_top() = Surface In BoundingBox{-eps, -eps, h-eps, 3+eps, 3+eps, h+eps};
bnd_left() = Surface In BoundingBox{-eps, -eps, -eps, eps, 3+eps, h+eps};
bnd_right() = Surface In BoundingBox{3-eps, -eps, -eps, 3+eps, 3+eps, h+eps};
bnd_front() = Surface In BoundingBox{-eps, -eps, -eps, 3+eps, eps, h+eps};
bnd_back() = Surface In BoundingBox{-eps, 3-eps, -eps, 3+eps, 3+eps, h+eps};

Physical Volume("domain", 100) = {1};
Physical Volume("sponge_bl", 101) = {2};
Physical Volume("sponge_bc", 102) = {3};
Physical Volume("sponge_br", 103) = {4};
Physical Volume("sponge_cl", 104) = {5};
Physical Volume("sponge_cr", 105) = {6};
Physical Volume("sponge_tl", 106) = {7};
Physical Volume("sponge_tc", 107) = {8};
Physical Volume("sponge_tr", 108) = {9};

Physical Volume("all", 110) = {1,2,3,4,5,6,7,8,9};

Physical Surface("bottom", 100) = bnd_bottom();
Physical Surface("top", 101) = bnd_top();
Physical Surface("left", 102) = bnd_left();
Physical Surface("right", 103) = bnd_right();
Physical Surface("front", 104) = bnd_front();
Physical Surface("back", 105) = bnd_back();

Mesh.Algorithm3D = 10;

MeshSize{ PointsOf{ Volume{:}; } } = 0.11;