非线性最小二乘法是不是指两个变量之间的关系为非线性?比如y=x^2,y=sinx等等?

用Mathematica 利用非线性最小二乘法 实现曲线拟合 盼您回信
数据{0,0},{0.115,0.11},{0.173,0.14},{0.231,0.24},{0.346,0.29},{0.461,0.31},{0.5,0.32} 模型是 D^2/[D^2 + (0.7 D + 2416.4)^2]*(Sin[0.5*x*Sqrt[D*D + (0.84 D + 2899.7)^2]])^2 ----3个方程合为一体 所以有点麻烦
Q1 利用非线性最小二乘法 实现曲线拟合
Q2 求出方程中 D的值
几个月前 经您指导 我照葫芦画瓢 写了代码 但是怎么也运行不了 请您指教
data = {{0,0},{0.115,0.11},{0.173,0.14},{0.231,0.24},{0.346,
0.29},{0.461,0.31},{0.5,0.32}};
model = D^2/[D^2 + (0.7 D + 2416.4)^2]*(Sin[0.5*x*Sqrt[D*D + (0.84 D + 2899.7)^2]])^2;
fit = FindFit[data,{model,{D >= 0}},{D},x]
modelf = Function[{x},Evaluate[model /.fit]]
Plot[modelf[x],{x,0,0.5},Epilog -> Map[Point,data]]
Methematica上面 提示的错误如下
Syntax::sntxf:"D^2/" cannot be followed by "[D^2+(0.7D+2416.4)^2]".
Syntax::tsntxi:"[D^2+(0.7D+2416.4)^2]" is incomplete; more input is needed.
Syntax::sntxi:Incomplete expression; more input is needed.

用Mathematica 利用非线性最小二乘法 实现曲线拟合
代码如下
data = {{0,0},{0.000115,0.09},{0.000173,0.13},{0.000231,0.17},{0.000346,0.23},{0.000461,0.25},{0.0005,0.24}};
model = D^2/(D^2 + (0.7 D + 2416.4)^2)*(Sin[0.5*x*Sqrt[D*D + (0.84 D + 2899.7)^2]])^2;
fit = FindFit[data,{model,{D >= 0}},{D},x]
modelf = Function[{x},Evaluate[model /.fit]]
Plot[modelf[x],{x,0,0.0005},Epilog -> Map[Point,data]]
数据 {{0,0},{0.000115,0.09},{0.000173,0.13},{0.000231,0.17},{0.000346,0.23},{0.000461,0.25},{0.0005,0.24}}
以方程D^2/(D^2 + (0.7 D + 2416.4)^2)*(Sin[0.5*x*Sqrt[D*D + (0.84 D + 2899.7)^2]])^2 为model 求出D的值并得出曲线拟合的图
但是用上面的代码计算出的D的值 有点问题（应该是几千的数值 但是结果才是1.03） 而且曲线拟合的图也不对