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Buckling of aboveground oil storage tanks under internal pressure
Shoichi Yoshida 국제구조공학회 2001 Steel and Composite Structures, An International J Vol.1 No.1
Overpressurization can occur due to the ignition of flammable vapors existing inside aboveground oil storage tanks. Such accidents could happen more frequently than other types of accident. In the tank design, when the internal pressure increases, the sidewall-to-roof joint is expected to fail before failure occurs in the sidewall-to-bottom joint. This design concept is the socalled “frangible roof joint” introduced in API Standard 650. The major failure mode is bifurcation buckling in this case. This paper presents the bifurcation buckling pressures in both joints under internal pressure. Elastic and elastic-plastic axisymmetric shell finite element analysis was performed involving large deformation in the prebuckling state. Results show that API Standard 650 does not evaluate the frangible roof joint design conservatively in small diameter tanks.
High-quality approximation of log-aesthetic curves based on the fourth-order derivative
Tsuchie Shoichi,Yoshida Norimasa 한국CDE학회 2022 Journal of computational design and engineering Vol.9 No.6
We propose a new method for approximating log-aesthetic curves ${\boldsymbol C}_{\mathrm{LA}}$ using high-degree Bézier curves. By leveraging the property that higher order derivatives are more sensitive to the quality of approximation, the method minimizes an objective function based on the fourth-order derivative; consequently, ${\boldsymbol C}_{\mathrm{LA}}$ is approximated with high accuracy. In addition, the proposed method is composed of two steps to ensure stable optimization so as not to be negatively affected because of a local minimum and to evaluate the fourth-order derivative. Furthermore, we reveal the difficulty in sufficiently approximating ${\boldsymbol C}_{\mathrm{LA}}$ with Bézier curves from two aspects. One aspect entails the uncertainty of how accurately the low-degree Bézier curves can approximate ${\boldsymbol C}_{\mathrm{LA}}$. The other aspect is the existence of a subset of ${\boldsymbol C}_{\mathrm{LA}}$ that is inherently difficult to approximate with such conventional parametric curves. The experimental results and comparisons demonstrated the validity of the proposed method.