55 lines
1.7 KiB
Matlab
55 lines
1.7 KiB
Matlab
function [F,Elem] = intForcesUL(Model,Elem,U,D_U,update_angle)
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% Initialize global vector of internal forces
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F = zeros(Model.neq,1);
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for i = 1:Model.nel
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% Lengths: Beginning of step, current, and step increment
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L_1 = Elem(i).L_1;%每个增量步开始时进行更新
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L_c = elemLength(Elem(i),U);
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D_L = L_c - L_1;
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% 刚体位移角度增量（相对于增量步初始状态）
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rbr = elemAngleIncr(Elem(i),U,D_U);%rbr带有符号，增加正值，减少负值
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%rbr为相对荷载步初始转角的单元刚性转角，即当前构型与荷载步初始时的构型的整体转角差（梁单元轴向角度）
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angle = Elem(i).angle_1 + rbr;
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% 更新单元刚体转角
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if (update_angle)
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Elem(i).angle = angle;
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end
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% 局部坐标系-全局坐标系的坐标转换矩阵
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c = cos(angle);
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s = sin(angle);
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rot = [ c -s 0 0 0 0;
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s c 0 0 0 0;
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0 0 1 0 0 0;
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0 0 0 c -s 0;
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0 0 0 s c 0;
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0 0 0 0 0 1 ];
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% 形变转角，相对增量步初始构型
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r1 = D_U(Elem(i).n1.dof(3)) - rbr;
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r2 = D_U(Elem(i).n2.dof(3)) - rbr;
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% 局部坐标下的位移向量增量,相对增量步初始构型
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dl = [0; 0 ; r1; D_L; 0; r2];%没有y向变形，只有轴向和转动变形？？？因为y向的变形其实等同于转角，局部坐标系下不存在y向变形
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% 局部坐标系下内力向量增量
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D_fl = Elem(i).ke * dl;
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% 局部坐标系下总内力
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fl = Elem(i).fi_1 + D_fl;
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% 更新Elem中局部坐标系总内力
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Elem(i).fi = fl;
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% 内力从局部到全局的转换
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fg = rot * fl;
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% 单元内力组装到整体内力矩阵中
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gle = Elem(i).gle;
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F(gle) = F(gle) + fg;
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end
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end |