Always LOAD into an output variable! That will make your code much more reliable, and makes this task easier.
Method 1: the simplest approach is to use LOAD's syntax which already supports regular expressions:
fnm = sprintf('%s.mat',fileName);
raw = load(fnm,'-regexp','^Fsim');
myData = struct2cell(raw)
Method 2: check the output variable's fieldname:
raw = load(fnm);
fld = fieldnames(raw);
assert(numel(fld)==1,'You said only one variable!')
idx = startsWith(fld,'Fsim'); % or STRNCMP
if idx
myData = raw.(fld{1}); % dynamic fieldname
end
Method 3: use STRUCT2CELL and some indexing, e.g.:
obj = struct2cell(raw);
myData = obj(idx);
