Numerical Analysis of Filament Wound Cylindrical Composite Pressure Vessels Accounting for Variable Dome Contour

In this work, the stress distribution along cylindrical composite pressure vessels with different dome geometries is investigated. The dome contours are generated through an integral method based on shell stresses. Here, the influence of each dome contour on the stress distribution at the interface of the dome-cylinder is evaluated. At first, the integral formulation for dome curve generation is presented and solved for the different dome contours. An analytical approach for the calculation of the secondary stresses in a cylindrical pressure vessel is introduced. For the analysis, three different cases were investigated: (i) a polymer liner; (ii) a single layer of carbon-epoxy composite wrapped on a polymer liner; and (iii) multilayer carbon-epoxy pressure vessel. Accounting for nonlinear geometry is seen to have an effect on the stress distribution on the pressure vessel, also on the isotropic liner. Significant secondary stresses were observed at the dome-cylinder interface and they reach a maximum at a specific distance from the interface. A discussion on the trend in these stresses is presented. The numerical results are compared with the experimental results of the multilayer pressure vessel. It is observed that the secondary stresses present in the vicinity of the dome-cylinder interface has a significant effect on the failure mechanism, especially for thick walled cylindrical composite pressure vessel. It is critical that these secondary stresses are directly accounted for in the initial design phase.

“N”-shaped Y/X coda spectral ratio observed for in-line-type OBS networks; S-net and ETMC: interpretation based on natural vibration of pressure vessel

We have identified “N”-shaped Y/X amplitude spectral ratios in S-coda records from a significant number of OBSs (ocean bottom seismometers) belonging to in-line-type ocean bottom networks of S-net and ETMC deployed around the Japan Trench and Sagami Trough, respectively. The “N”-shape reflects a sharp peak and notch at approximately 5–13 Hz and 10–23 Hz, respectively. This shape does not characterize OBSs belonging to node-type ocean bottom network of DONET deployed near the Nankai Trough. For S-net stations, the “N”-shape is not clearly formed for stations installed within grooves dug in the seafloor. We interpret the “N”-shaped Y/X amplitude spectral ratio is caused by the natural vibrations of a cylindrical pressure vessel that is placed sideways (long-axis lies in the horizontal plane) on the seafloor. The notch and peak frequencies in the Y/X amplitude spectral ratio likely correspond to natural frequencies of longitudinal (X-direction) and torsional and/or bending (Y-direction) vibrations, respectively. These natural vibrations are not observed for buried OBSs or those installed within grooves in the seafloor probably because they are better coupled to the seafloor. We propose a simple model to evaluate the extent to which the peak and notch have formed, which depends on the natural frequencies and coupling of the pressure vessel. We suggest users of in-line-type OBSs carefully examine if there are different responses between the X and Y components when frequencies about > 3 Hz are used. When installing OBS networks in the future, installing OBSs and cables within grooves dug in the seafloor or by burial will be effective in suppressing such natural vibrations.

Some classical problems in rate-independent plasticity

This chapter presents analytical solutions to some classical problems in rate-independent plasticity. Solutions are presented for the elastic-plastic torsion of a round bar, including spring back; for the elastic-plastic response of a thick-walled spherical pressure vessel, including initial yield, partial yield, full yield, and unloading; for the incompressible elastic-plastic response of a plane-strain thick-walled cylindrical pressure vessel, including initial yield, partial yield, and full yield.

Investigation of the Stresses and Interaction Effects of Nozzle-Cylinder Intersections When Subject to Multiple External Loads

Analyzing and solving the problem of practical cylinder-cylinder pressure vessel intersections is challenging when using a finite element approach. Although numerous theoretical and finite element solutions have been developed for the cylinder-cylinder intersection problem, there remains the requirement for an updated, innovative model which takes account of all practical as-fabricated features including fillets and crotch corner ground radii. This study presents the development of a suitable model, based on the results of a parametric macro study, which is able to compare all of these operations on a single, high fidelity model. This study considers a cylindrical pressure vessel with a single nozzle connection without reinforcement plate and examines the maximum stress values in the nozzle-shell intersection area (crotch corner) under the various loads applied to the nozzle. Additionally, internal pressure and external load actions on the nozzle, including effects of circumferential, torsional, and longitudinal moments are compared using a suitable finite element approach. Furthermore, equations and solutions for external loads in spherical and cylindrical shells are given in WRC Bulletins 107 and 537. Therefore, comparisons with the results obtained from these are made for validation purposes and the overall impact of the new as-built approach is presented.

Dynamic Stress Analysis of Multilayered Structure With Radial Gaps of Cylindrical Pressure Vessel Under Plane Strain Conditions

Radial gaps were found in multilayered cylindrical vessels which experience inner explosion accidents in chemical plants in the past few years worldwide. It is necessary to investigate the dynamic response of multilayered structures with radial gaps to ensure the vessel safety. This paper presented a numerical modeling of the dynamic response of a multilayered structure with radial gaps of cylindrical pressure vessel under plane strain conditions by using the ANSYS/ls-dyna package. The effects of the dynamic loading profile and the radial gap height are considered in the investigation. The stress spatial distribution, the stress and the plastic deformation variation curves with time are emphatically analyzed. The results show that the stress variation of the entire loading process can be divided into four stages: the oscillation stage, the yield stage, the fast increase stage, and the redistribution stage. The layer stress distributes discontinuously at the gaps between layers and distributes unevenly in any single layer. The inner layer stress is not always larger than the outer layers' during the whole loading process. The effect of loading profile on the dynamic response is not as obvious as the gap height. As the gap height increases, the stress oscillation stage is suppressed and becomes shorter. While the loading recovers to the operation pressure, the stress and the plastic deformation of inner layers increases and vice versa for the outer layers.