Ultimate Strength Assessment of Steel-Welded Hemispheres under External Hydrostatic Pressure

This paper focusses on steel-welded hemispherical shells subjected to external hydrostatic pressure. The experimental and numerical investigations were performed to study their failure behaviour. The model was fabricated from mild steel and made through press forming and welding. We therefore considered the effect of initial shape imperfection, variation of thickness and residual stress obtained from the actual structures. Four hemisphere models designed with R/t from 50 to 130 were tested until failure. Prior to the test, the actual geometric imperfection and shell thickness were carefully measured. The comparisons of available design codes (PD 5500, ABS, DNV-GL) in calculating the collapse pressure were also highlighted against the available published test data on steel-welded hemispheres. Furthermore, the nonlinear FE simulations were also conducted to substantiate the ultimate load capacity and plastic deformation of the models that were tested. Parametric dependence of the level of sphericity, varying thickness and residual welding stresses were also numerically considered in the benchmark studies. The structure behaviour from the experiments was used to verify the numerical analysis. In this work, both collapse pressure and failure mode in the numerical model were consistent with the experimental model.

Small-Scaled Experimental Research on the Buckling of Steel Containment Under Axial Compression

Focusing on the general and localized elastoplastic buckling of the cylindrical section of steel containment under axial pressure, nonlinear finite element method (FEM) and small-scaled experiments are applied to analysis. First, FEM analysis is conducted considering nonlinear items caused by geometric shape imperfection and elastoplastic constitutive model by the arc-length method RIKS procedure. Parameter sensitivity of the buckling is revealed. Then, small-scaled experiments are carried out. Buckles status is observed, and key geometrical parameters’ influence are found. The results show that cylindrical buckling under axial pressure is sensitive to geometrical parameters and imperfection. It is necessary to employ more realistic parameters to the FEM analysis via accurate geometrical measurement. This research has reference value for the design and fabrication of AP series steel containment vessel.

INFLUENCE OF SHAPE IMPERFECTION ON DYNAMICS OF VORTEX SPIN-TORQUE NANO-OSCILLATOR

The dynamics of vortex gyration under spin-polarized current in a spin-torque nano-oscillator with axial symmetry violated by shape imperfection has been studied by micromagnetic modeling. We have considered the following kinds of shape: the displacement of the nanodisks centers, the pyramidal shape and the shape with several small cutouts. The corresponding frequency spectra of the vortex oscillations are presented. We found that shape imperfection can influence not only fundamental frequency but also can genarate second and higher harmonics. The impact of different types of shape on the vortex dynamics has been analyzed qualitatively. New ideas of microwave signal arising by artificial nonidealities of structure were proposed.