Finite Element Analysis of Von-Mises Stress Distribution in a Spherical Shell of Liquified Natural Gas (Lng) Pressure Vessels
This research work investigated the modeling of Von Mises stress in LNG Spherical Carbon Steel Storage tank using assumed displacement Finite Element analysis based on shallow shell triangular elements. Using equations of elasticity, constant thickness carbon steel spherical storage tanks were subjected to different loading conditions. This paper stresses the need for proper definition of shallow element using sector angles to obtain the shallowness. The shallow spherical triangular element has five degrees of freedom at each of its corner node, which are the essential external degrees of freedom. The assumed displacement fields of these shallow triangular elements satisfied the exact requirement of rigid body modes of motion. The FORTRAN 90 programming language was used for the programme coding to solve finite element equations resulting from the model while Von Mises stresses distribution within the spherical storage tank shell subjected to different internal pressures were determined. The results showed that the use of non-shallow elements due to improper sector angles resulted in unreliable results while real shallow elements produced results that tallied with ASME Section VIII Div 1, Part UG values.
Evaluation of the pressure-resisting capability of membrane-type corrugated sheet under hydrodynamic load
Abstract Fluid impact load-induced collapse of the corrugated sheet in the primary barrier of liquefied natural gas carrier (LNGC) cargo containment systems is recognized as one of the most dangerous deformation phenomena because it leads to catastrophic failure of the containment system. Thus, significant efforts have been dedicated to precisely evaluating the load-carrying capacity of the primary barrier. However, due to the lack of testing methods and the complex geometry of the corrugated primary barrier sheet, the structural behavior of the sheet under impact-induced pressure has rarely been investigated. The aim of this study is to develop design support methodology ensuring the integrity of the primary barriers in LNG cargo containment systems. A custom-built experimental facility was developed to create uniform pressurization on the primary barrier sheet. The out-of-plane deformations of the sheet were observed over time during the experiment. To create a reliable numerical method applicable in the design stage, a series of parametric studies using finite element analyses (FEA) were conducted. Based on the comparison between the numerical solutions and experimental results, a practical method to estimate the typical deflection patterns based on the corrugation type was developed. Thus, we demonstrate that the insights from experimental observations as well as FEA techniques can be used in the practical design support methodology.
Effects of reservoir volume on performance of pulse tube cooler.
A pulse tube cooler has the advantages of long-life and low-vibration over conventional cryocoolers such as G-M and Stirling coolers because of the absence of moving parts at low temperature. On the other hand, the combination of a reservoir and orifice is indispensable to optimize the performance of pulse tube coolers. In order to make the pulse tube cooler compact for practical applications, the volume of reservoir should be minimized. This paper analyzes the effects of the reservoir volume on the thermodynamic performance of various components in a simple orifice and a double-inlet pulse tube cooler by combining a linearized model with a thermodynamic analysis. Expressions of entropy production for those components are presented. The results show that the reservoir volume has a significant influence on the entropy production in the various components when the reservoir to pulse tube volume ratio is smaller than about 5. The ratio is important to determine the minimum reservoir volume for a pulse tube cooler. Optimum settings for a double-inlet pulse tube cooler are also discussed.