Pal Bergan - Academia.edu (original) (raw)

Papers by Pal Bergan

The paper describes briefly a method for nonlinear dynamic analysis of slender offshore structure... more The paper describes briefly a method for nonlinear dynamic analysis of slender offshore structures in an ocean environment. The method allows for large displacement and large rotational motion of bar and beam type structures. The computation of hydrodynamic loads is performed in deterministic as well as random waves. The nonlinear characteristics of the hydrodynamic loading in terms of the relative motion between the structure and the fluid as well as the moving free surface are accounted for. The extreme response of a flexible pipeline suspended between a fixed and a floating platform in random waves is computed and compared with the corresponding response in a deterministic wave.

Lecture notes in engineering, 1987

The paper gives a short introduction to the free formulation theory for finite elements, and indi... more The paper gives a short introduction to the free formulation theory for finite elements, and indicates how this theory also can be used for structural analysis including geometric and material nonlinearities. Some new flat, triangular shell elements have been developed using this theory. These elements are non-conforming, but satisfy the patch test. A novel feature is that these elements include the normal rotation as well as the conventional three translational and two rotations for flexure at the corner nodes. The drilling freedoms improve the membrane behaviour significantly and are particularly useful in making a complete set of rotational freedoms for shells. The high accuracy of the shell elements are documented through a series of linear and nonlinear examples.

Engineering mechanics, 1995

International Journal of Hydrogen Energy, Nov 1, 2022

A method of analysis for semielliptical, part-through surface cracks in thick plates are presente... more A method of analysis for semielliptical, part-through surface cracks in thick plates are presented. The finite element method involving a multilevel superelement technique is used for computation of stress intensity factors. The analysis procedure is based on the strain energy release rate, and the stress intensity factor is determined as a function of the crack geometry and the direction of propagation. The generality of the present approach allows it to be used for very complicated structures and complex loading conditions.

Engineering Computations, 1985

Nucleation and Atmospheric Aerosols, 2017

This paper presents the experimental results from the EnergyNest 2 x 500 kWh th thermal energy st... more This paper presents the experimental results from the EnergyNest 2 x 500 kWh th thermal energy storage (TES) pilot system installed at Masdar Institute of Science & Technology Solar Platform. Measured data are shown and compared to simulations using a specially developed computer program to verify the stability and performance of the TES. The TES is based on a solid-state concrete storage medium (HEATCRETE ®) with integrated steel tube heat exchangers cast into the concrete. The unique concrete recipe used in the TES has been developed in collaboration with Heidelberg Cement; this material has significantly higher thermal conductivity compared to regular concrete implying very effective heat transfer, at the same time being chemically stable up to 450 °C. The demonstrated and measured performance of the TES matches the predictions based on simulations, and proves the operational feasibility of the EnergyNest concrete-based TES. A further case study is analyzed where a large-scale TES system presented in this article is compared to two-tank indirect molten salt technology.

Journal of energy storage, Aug 1, 2019

The performance of a 2 × 500 kWh th thermal energy storage (TES) technology has been tested at th... more The performance of a 2 × 500 kWh th thermal energy storage (TES) technology has been tested at the Masdar Institute Solar Platform (MISP) at temperatures up to 380°C over a period of more than 20 months. The TES is based on a novel, modular storage system design, a new solid-state concrete-like storage medium, denoted HEATCRETE® vp1,-and has cast-in steel pipe heat exchangers. Measured data after specific intervals during various operation modes are analysed, and validation of system performance is done through direct comparison between measured values and numerically simulated performance. The demonstrated and measured long-term performance of the TES matches predictions based on performance simulations and proves the operational feasibility of the modular TES design. After accumulating close to 6 000 operational hours, inspection of extracted thermal elements prove that there is no degradation of the storage material, and no separation between steel pipes and storage material is observed. Measurements of core samples of the storage medium extracted from the TES confirms the material properties and stability. The thermal element design and storage material as demonstrated in the TES pilot has thus been proved to work in its final form with expected conditions and shows absolutely no sign of performance degradation. The modularity and simplicity of the TES design enables flexibility in scaling high temperature TES systems for among others industrial waste heat recovery, thermal power plants and concentrating solar power applications, thermal power plant.

International Journal of Offshore and Polar Engineering, May 26, 1996

This paper deals with a simplified, linear approach for analyzing the nonlinear creep effect of a... more This paper deals with a simplified, linear approach for analyzing the nonlinear creep effect of a composite steel-concrete structure by the use of any standard linear finite element program. The Heidrun concrete platform represents a novel concept in floating offshore platforms. In this challenging design, the affixing of the topside modules to the main support beams causes significant, secondary shear forces in the footings due to creep deformations. Creep effects in offshore structures are normally accounted for in linear analyses by modifying stiffness and loads. As a part of the design verification a separate verification study has been performed to see if there is reason for confidence in such a linear approach of including creep effects. Two alternative linear approaches are compared with a more comprehensive and accurate nonlinear method for analyzing creep effects. For the specific platform problem studied, the main conclusion is that one of the two linear methods is suitable for calculating creep forces transferred to the steel topside modules and may be used in design analyses.

Significant advances have been made over the last two decades in development of mathematical mode... more Significant advances have been made over the last two decades in development of mathematical models and analysis techniques for plain and reinforced concrete structures. A large number of rather comprehensive and complex models have been suggested for inelastic behaviour, cracking and complete failure of concrete during arbitrary loading conditions. Similarly, many sophisticated models for describing interaction between concrete and reinforcement have been developed. Some of these models have been implemented in finite element computer programs.

Springer eBooks, 1986

A new quadrilateral membrane element is derived using the socalled Free Formulation of the finite... more A new quadrilateral membrane element is derived using the socalled Free Formulation of the finite element method which has been proposed by the authors. The element has two translational and one rotational freedom per corner node. It is based on nonconforming displacement functions, still the element satisfies the convergence requirements including the patch test. Numerical studies show that the accuracy of the element is exceptionally good. It is particularly well suited for problems with extensive inplane bending (e.g. beams, webs, stiffeners) and as the membrane component in flat shell elements.

Design and Operation of Passenger Ships 2011, 2011

Safety and Reliability: Methodology and Applications, 2014

Volume 1: Offshore Technology, 2009

There is presently a growing demand for natural gas as a relatively clean energy resource. Major ... more There is presently a growing demand for natural gas as a relatively clean energy resource. Major gas reservoirs are often located far away from the major consumer markets; the need for safe end efficient transport across the oceans is growing rapidly. The preferred way of storing and transporting gas from gas fields that are not connected with pipe lines is by way of cooling down the gas to liquid state (LNG), storing it in insulated tanks, transporting it onboard ships, and unloading it at terminals. Recently there has also been an interest in offshore production of LNG onboard fixed or floating platforms or on floating production ships. Good technical solutions for storage of LNG has been available for decades, but there has recently been a growing need for tanks that are suited for transportation very large ships as well as suited for offshore storage and capable of dealing with partial degrees of filling during dynamic, floating conditions. The paper describes an entirely new co...