Linear Buckling topology optimization problem

 hello,

I need your help to solve a problem on linear buckling topology optimization

I am doing topology optimization for linear buckling case of simply supported I-section beam (slenderness ratio-120) having  compressive axial load. Beam is made up of shell elements. I have given base thickness 3mm and my design space thickness 6mm.

 

I have considered two cases

I-case

Objective- minimization of compliance

Constraints-  buckling and  volume fraction (0.4)

problem- Infeasible design , I am getting negative buckling eigenvalues and it violates my buckling constraints (lower bound=1). ( direction of my load cannot be reversed). I am applying load which are having magnitude below buckling load factor.

II- case 

  objective –minmax –objref-(minimizing the maximum buckling eigenvalue)  

constraints- volume fraction.

Problem- In second case I am getting positive eigen value but my volume fraction become so less in 4^th and 5^th  iterations (10^-2) .therefore I am not getting any topology

 

 

 

 

Also I have applied Topology optimization with minimum member size and 2-plane symmetry constraints in both cases.

i am attaching  *.out file.

Results are not satisfying , could you please help me out.

  

 

 

 

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