Smiljko Rudan

Assessment of Geometry Correction Functions of Tanker Knuckle Details Based on Fatigue Tests and Finite-Element Analysis

The paper analyzes the fatigue crack growth of knuckle detail typical of tankers. An approach for evaluation of the fatigue life based on fracture mechanics is presented, where a Paris-Erdogan crack-growth law is applied. A geometry correction function is determined from fatigue test data. A closed-form equation is proposed for fatigue life estimation. The results obtained from a fatigue test and the calculated fatigue lives are compared. @DOI: 10.1115/1.1782643#

Ultimate hull-girder-strength-based reliability of a double-hull oil tanker after collision in the Adriatic Sea

ABSTRACT The aim of this paper is to present a methodology for the assessment of the structural reliability of an oil tanker damaged in a hypothetical collision accident in the Adriatic Sea. Monte Carlo simulation is employed to generate random damage scenarios. Assumption of the damage size is based on the numerical simulation of the ship–ship collision. Residual ultimate strength and still-water bending moment distribution are determined based on the size and location of the damage. Structural reliability analysis is employed to determine the safety index with respect to the ultimate hull-girder failure. Histograms of safety indices are thus obtained, representing new measures for the performance assessment of the damaged ship. If extended to more severe design wave environments and collision scenarios, the presented methodology may be used for general reliability-based comparison of different alternative designs of marine structures with respect to the accidental failure modes or for improvement of ship structural design rules.

Fiber optic vibration sensor for high-power electric machines realized using 3D printing technology

The objective of this work was to demonstrate a lightweight and inexpensive fiber-optic vibration sensor, built using 3D printing technology, for high-power electric machines and similar applications. The working principle is based on modulating the light intensity using a blade attached to a bendable membrane. The sensor prototype was manufactured using PolyJet Matrix technology with DM 8515 Grey 35 Polymer. The sensor shows linear response, expected bandwidth (< 150 Hz), and from our measurements we estimated the damping ratio for used polymer to be ζ ≈ 0.019. The developed prototype is simple to assemble, adjust, calibrate and repair.

Fatigue Analysis of Structural Details of an Oceangoing LPG Ship

Structural details of ship structures are prone to fatigue damage mainly due to high-cycle wave load and low-cycle cargo loading/unloading. Full stochastic fatigue analysis of selected structural details on an oceangoing 6500 cbm LPG ship is presented. A critical Y-joint of longitudinal bulkhead and bilobe tank shell as well as double-bottom girder details are selected due to different reasons. The eccentricity of the Y-joint, leads to significant stress concentration. Saddle supports of gas tanks cause stress concentration in ship double bottom due to weight and dynamic loads. Wave load on ship structure is calculated using linear strip theory for ship in ballast condition and full ship. Wave load is transferred to ship finite element model and notch structural stresses are determined using finite element analysis. Stochastic fatigue analysis is then performed, taking into account sailing route and other ship operational parameters. Finally, fatigue damage summation is done and results are discussed.

Finite element study of residual ultimate strength of a double hull oil tanker with simplified collision damage and subjected to bi-axial bending

ABSTRACT The aim of the study is assessment of the residual strength of the double hull oil tanker damaged in collision, which the accidental limit states foreseen by International Association of Classification Societies in their new Common Structural Rules. Collision damage is idealised as a ‘rectangular box’, assuming to start from the main deck downwards. Nonlinear finite element method with the explicit dynamic integration method implemented in LS-Dyna is employed. Such approach enables a systematic investigation of ship residual strength under combined horizontal and vertical bending moments that has not been performed previously. As a result of the study, residual strength interaction diagrams are developed with the purpose of rapid residual ultimate longitudinal strength assessment of the damaged oil tanker. Interaction diagrams may be useful for classification societies when developing rules regarding accidental limit states, as well as for a fast assessment of the hull girder residual strength in accidental situations.

Conforming shear-locking-free four-node rectangular finite element of moderately thick plate

Abstract An outline of the modified Mindlin plate theory, which deals with bending deflection as a single variable, is presented. Shear deflection and cross-section rotation angles are functions of bending deflection. A new four-node rectangular finite element of moderately thick plate is formulated by utilizing the modified Mindlin theory. Shape functions of total (bending+shear) deflections are defined as a product of the Timshenko beam shape functions in the plate longitudinal and transversal direction. The bending and shear stiffness matrices, and translational and rotary mass matrices are specified. In this way conforming and shear-locking-free finite element is obtained. Numerical examples of plate vibration analysis, performed for various combinations of boundary conditions, show high level of accuracy and monotonic convergence of natural frequencies to analytical values. The new finite element is superior to some sophisticated finite elements incorporated in commercial software.

Fiber-optic vibration sensor for high-power electric machines

We demonstrate a fiber-optic sensor for monitoring mechanical vibrations in high-power electric machines built using 3D-printing. We describe the design, mechanical and optical modeling, and the results of its preliminary characterization. The measurements show linear sensor response in the frequency range 10 to 150 Hz.

Crashworthiness of type C tanks in LPG ship

Liquefied Petroleum Gas (LPG) ships carry a liquefied gas either pressurized, refrigerated or both at the same time. Due to that, among the other cargo containment solutions on LPG ships, type C tanks may be distinguished: they are independent tanks built as conventional pressure vessels. A single hull design of such ships is common and a question of their crashworthiness arises. In particular, the safety of the cargo may be of concern in the case of high energy collision event. In a previous study, crashworthiness of both common and novel sandwich hull design of an LPG ship was studied. In both cases, cargo tank was damaged. It is the aim of this work to study this damage in detail. An LPG ship and ferry collision event was modeled and studied by the means of nonlinear FEM. Collision parameters were altered to study their influence on the resulting collision damage on both ships. Bi-lobe cargo tank crashworthiness is analyzed and the possibility of cargo spill examined.Copyright

Remedy for misalignment of hemispherical head of bilobe cargo tank in liquefied petroleum gas carrier

This work describes the remedy for a misalignment at the joint of two segments of hemispherical heads in a bilobe cargo tank. The misalignment is the result of a relatively thin spherical shell and production difficulties. Measurements of out-of-roundness show a rather large deviation of meridional camber and variation of radius in the head cross-section plane. At the ends of the segments the spherical form changes into a conical one. As a result a peak occurs in the meridional generatrix, which causes high stress concentration. The cross-section of the hemisphere at the segment joint is reinforced with a ring in order to overtake the bending moment caused by the variation of circular radius. The ring dimensions are determined based on an approximate consideration. Stress concentration at the segment joint is reduced by two additional rings connected with a set of bars in the meridional direction. Angular distance between the bars is specified in such a way that the strength criteria, i.e. stress and fatigue requirements according to the Classification Rules, are satisfied. Stress distribution in the actual imperfect and reinforced structure is determined by the finite element method. Total static plus dynamic tank pressure is taken into account.