Damping Estimation Methods Applied to in Service Measurements of a 350 Metre Container Ship

2021 ◽  
Author(s):  
R. B. Hageman ◽  
A. Andoniu ◽  
A. Benhamou
Keyword(s):  
Bending Moment ◽  
Vertical Vibration ◽  
Estimation Methods ◽  
Vibration Modes ◽  
Container Ship ◽  
Hull Girder ◽  
Stochastic Subspace Identification ◽  
Twist Mode ◽  
The Time Domain ◽  
Frequency Domain Decomposition

Abstract Large modern container ships feature an open cross section which results in a low stiffness of the vessel to global hull excitation. The contribution of whipping is a significant portion of the overall acceleration and stress response of such a vessel. Whipping results in an increase of the maximum hull girder bending moment experienced by the vessel as well as an increase in the fatigue accumulation of critical details. In this research, we present damping estimates based on in-service measurements from a container ship. An array of accelerometers was used to derive the first three vertical and first twist vibration modes. The flexural vibrations were isolated using two different methods: first, the Enhanced Frequency Domain Decomposition and secondly, the time domain Stochastic Subspace Identification. Both methods were applied to four representative voyages of the vessel covering a variety of environmental and loading conditions. On the two- and three-node vertical vibration modes, consistent results between both methods have been obtained. Both the four-node vertical vibration mode and the twist mode showed larger deviations between the two methods. On the vertical vibration modes, the damping is between 0.5 and 2%. On the twist modes, the damping is significantly larger at 5% and up. A correlation between the combined damping and the significant wave height was observed for the different flexural modes.

Strength of a Container Ship in Extreme Waves Obtained by Nonlinear Hydroelastoplasticity Dynamic Analysis and Finite Element Modeling

2016 ◽  
Vol 138 (3) ◽  
Author(s):  
Weiqin Liu ◽  
Xuemin Song ◽  
Weiguo Wu ◽  
Katsuyuki Suzuki
Keyword(s):  
Finite Element ◽  
Nonlinear Dynamic ◽  
Structural Response ◽  
Bending Moment ◽  
Dynamic Responses ◽  
Container Ship ◽  
Extreme Waves ◽  
Wave Models ◽  
The One ◽  
The Time Domain

Extreme waves have caused a lot of ship accidents and casualties. In this paper, a two-dimensional (2D) hydroelastoplasticity method is proposed to study the nonlinear dynamic responses of a container ship in extreme waves. On the one hand, the traditional ultimate strength evaluation is mainly performed using a quasi-static assumption without considering the dynamic wave effect. On the other hand, the dynamic response of a ship induced by a wave is studied based on hydroelasticity theory, which means the ship structural response to large waves is linear. Therefore, a 2D hydroelastoplasticity method that accounts for the coupling between the time-domain wave and ship beam for nonlinear vertical bending moment (VBM) is proposed. In addition, a nonlinear dynamic finite element method (FEM) is also applied for the nonlinear VBM of ship beam. The computational results of the FEM, including the nonlinear VBM and deformational angle, are compared with the results of the 2D hydroelastoplasticity and hydroelasticity. A number of numerical extreme wave models are selected for computations of hydroelasticity-plasticity, hydroelasticity, and FEM. A difference is observed between the nonlinear VBM calculated by FEM and linear VBM calculated by hydroelasticity, and conclusions are drawn.

Time Domain Comparison With Experiments for Ship Motions and Structural Loads on a Container Ship in Abnormal Waves

2011 ◽  
Author(s):  
Suresh Rajendran ◽  
Nuno Fonseca ◽  
C. Guedes Soares ◽  
Gu¨nther F. Clauss ◽  
Marco Klein
Keyword(s):  
Time Domain ◽  
Bending Moment ◽  
Green Water ◽  
Ship Motions ◽  
Container Ship ◽  
Wave Elevation ◽  
Strip Theory ◽  
The Time Domain ◽  
Vertical Bending Moment ◽  
Comparison With Experiments

The paper presents experimental results from model tests with a containership advancing in abnormal wave conditions and comparisons with numerical simulations. A nonlinear time domain method based on strip theory is used for the calculation of vertical ship responses induced by abnormal waves. This code combines the linear diffraction and radiation forces with dominant nonlinear forces associated with vertical response arising from Froude-Krylov forces, hydrostatic forces and shipping of green water. The time domain simulations are compared directly with experimental records from tests with a model of a container ship in deterministic waves for a range of Froude numbers. Extreme sea conditions were replicated by the reproduction of realistic abnormal waves like the New Year Wave and abnormal wave from North Alwyn. Head sea condition is considered and the comparisons include the wave elevation, the vertical motions of the ship and the vertical bending moment at midship.

Dynamic Ultimate Strength of a Container Ship Under Sagging Condition

2020 ◽  
Author(s):  
George Jagite ◽  
Hervé le Sourne ◽  
Patrice Cartraud ◽  
Fabien Bigot ◽  
Quentin Derbanne ◽  
...  
Keyword(s):  
Ultimate Strength ◽  
Dynamic Load ◽  
Research Work ◽  
Structural Response ◽  
Bending Moment ◽  
Container Ship ◽  
Wave Loads ◽  
Hull Girder ◽  
Load Factors ◽  
Collapse Effect

Abstract When technically specifying ships for the future, the following aspects are examples of what we will have even more focus on than today: bigger, lighter, and faster. Thereby, the hydro-elastic type of structural response will be more and more significant. In addition, some of the recent container ships’ designs are with very low values of the “minimum hogging still water bending moment.” Combined with high whipping induced sagging moments, it casts some doubts on the probability of buckling appearance in the upper structure. Therefore, the objective of the research work presented in this paper is to investigate the dynamic ultimate strength of the entire hull girder section, subjected to sagging bending moment associated with wave loads and whipping response. The dynamic ultimate strength is computed and compared with the quasi-static ultimate strength, in order to derive the dynamic load factors, which can be used as an estimator of the dynamic collapse effect.

A Novel Solution to Compute Stress Time Series in Nonlinear Hydro-Structure Simulations

2015 ◽  
Author(s):  
Fabien Bigot ◽  
François-Xavier Sireta ◽  
Eric Baudin ◽  
Quentin Derbanne ◽  
Etienne Tiphine ◽  
...  
Keyword(s):  
Time Series ◽  
Frequency Domain ◽  
Time Domain ◽  
Hot Spot ◽  
Structural Response ◽  
Container Ship ◽  
Time Step ◽  
Computation Cost ◽  
Hull Girder ◽  
Non Linear

Ship transport is growing up rapidly, leading to ships size increase, and particularly for container ships. The last generation of Container Ship is now called Ultra Large Container Ship (ULCS). Due to their increasing sizes they are more flexible and more prone to wave induced vibrations of their hull girder: springing and whipping. The subsequent increase of the structure fatigue damage needs to be evaluated at the design stage, thus pushing the development of hydro-elastic simulation models. Spectral fatigue analysis including the first order springing can be done at a reasonable computational cost since the coupling between the sea-keeping and the Finite Element Method (FEM) structural analysis is performed in frequency domain. On the opposite, the simulation of non-linear phenomena (Non linear springing, whipping) has to be done in time domain, which dramatically increases the computation cost. In the context of ULCS, because of hull girder torsion and structural discontinuities, the hot spot stress time series that are required for fatigue analysis cannot be simply obtained from the hull girder loads in way of the detail. On the other hand, the computation cost to perform a FEM analysis at each time step is too high, so alternative solutions are necessary. In this paper a new solution is proposed, that is derived from a method for the efficient conversion of full scale strain measurements into internal loads. In this context, the process is reversed so that the stresses in the structural details are derived from the internal loads computed by the sea-keeping program. First, a base of distortion modes is built using a structural model of the ship. An original method to build this base using the structural response to wave loading is proposed. Then a conversion matrix is used to project the computed internal loads values on the distortion modes base, and the hot spot stresses are obtained by recombination of their modal values. The Moore-Penrose pseudo-inverse is used to minimize the error. In a first step, the conversion procedure is established and validated using the frequency domain hydro-structure model of a ULCS. Then the method is applied to a non-linear time domain simulation for which the structural response has actually been computed at each time step in order to have a reference stress signal, in order to prove its efficiency.

On the Effect of Hull Girder Flexibility on the Vertical Wave Bending Moment for Ultra Large Container Vessels

2012 ◽  
Author(s):  
Ingrid Marie Vincent Andersen ◽  
Jørgen Juncher Jensen
Keyword(s):  
Bending Moment ◽  
Main Concern ◽  
Hull Girder ◽  
Numerical Predictions ◽  
Strip Theory ◽  
Reliability Method ◽  
Non Linear ◽  
Large Container ◽  
The Waves ◽  
Good Agreement

Currently, a number of very large container ships are being built and more are on order, and some concerns have been expressed about the importance of the reduced hull girder stiffness to the wave-induced loads. The main concern is related to the fatigue life, but also a possible increase in the global hull girder loads as consequence of the increased hull flexibility must be considered. This is especially so as the rules of the classification societies do not explicitly account for the effect of hull flexibility on the global loads. In the present paper an analysis has been carried out for the 9,400 TEU container ship used as case-ship in the EU project TULCS (Tools for Ultra Large Container Ships). A non-linear time-domain strip theory is used for the hydrodynamic analysis of the vertical bending moment amidships in sagging and hogging conditions for a flexible and a rigid modelling of the ship. The theory takes into account non-linear radiation forces (memory effects) through the use of a set of higher order differential equations. The non-linear hydrostatic restoring forces and non-linear Froude-Krylov forces are determined accurately at the instantaneous position of the ship in the waves. Slamming forces are determined by a standard momentum formulation. The hull flexibility is modelled as a non-prismatic Timoshenko beam. Generally, good agreement with experimental results and more accurate numerical predictions has previously been obtained in a number of studies. The statistical analysis is done using the First Order Reliability Method (FORM) supplemented with Monte Carlo simulations. Furthermore, strip-theory calculations are compared to model tests in regular waves of different wave lengths using a segmented, flexible model of the case-ship and good agreement is obtained for the longest of the waves. For the shorter waves the agreement is less good. The discrepancy in the amplitudes of the bending moment can most probably be explained by an underestimation on the effect of momentum slamming in the strip-theory applied.

Hull-Girder Reliability of a Chemical Tanker

2009 ◽  
Vol 46 (04) ◽  
pp. 192-199
Author(s):  
Jôsko Parunov ◽  
Maro Corak ◽  
C. Guedes Soares
Keyword(s):  
International Association ◽  
Progressive Collapse ◽  
Bending Moment ◽  
Single Step ◽  
Hull Girder ◽  
Structural Rules ◽  
Term Operation ◽  
Reliability Method ◽  
Reliability Bound ◽  
Oil Tanker

The aim of the paper is to calculate hull-girder reliability of chemical tanker according to the reliability model proposed by International Maritime Organization (IMO). The probability of hull-girder failure is calculated using a first-order reliability method for two operational profiles—one typical for oil tanker and the other one modified in order to reflect differences between oil tanker and chemical tanker. The evaluation of the wave-induced load effects that occur during long-term operation of the ship in the seaway is carried out in accordance with International Association of Classification Societies (IACS) recommended procedure. The stillwater loads are defined on the basis of a statistical analysis of loading conditions from the loading manual. The ultimate collapse bending moment of the midship cross section, which is used as the basis for the reliability formulation, is evaluated by progressive collapse analysis and by single-step procedure. The reliability analysis is performed for "as-built" ship and for "corroded" ship according to corrosion deduction thickness from new Common Structural Rules for double-hull oil tankers. It is shown that hull-girder failure probability of "as-built" chemical tanker is well above the upper reliability bound proposed by IMO, while the "corroded" ship is slightly unconservative since the reliability index is lower than IMO lower reliability bound.

Experimentelle Bestimmung der Dämpfung eines Bauwerkes am Beispiel einer Fußgängerbrücke – Worauf man achten sollte

Bauingenieur ◽  
2016 ◽  
Vol 91 (04) ◽  
pp. S 2-S 9
Author(s):  
Rune Brincker ◽  
Anela Bajric ◽  
Reto Cantieni
Keyword(s):  
Domain Decomposition ◽  
Frequency Domain ◽  
Subspace Identification ◽  
Stochastic Subspace Identification ◽  
Frequency Domain Decomposition ◽  
Enhanced Frequency Domain Decomposition

Am Beispiel der experimentellen Untersuchung der dynamischen Eigenschaften einer Fußgängerbrücke werden Probleme bei der Bestimmung der Dämpfungskapazität eines Ingenieurtragwerkes diskutiert. Aus Gründen der Verständlichkeit wird zunächst relativ ausführlich auf diese Experimente, die für die Identifikation der modalen Eigenschaften der Brücke benützten Methoden und die dabei verwendeten Parameter eingegangen.   Solange man sich für die Bestimmung der Dämpfung auf dem Boden analoger Zeitsignale bewegt, sind keine gröberen Fehler zu erwarten. Die manuelle Untersuchung eines freien, rein harmonischen Ausschwingvorganges ist zwar auch nicht vor Ungenauigkeiten gefeit. Da es die „lineare, rein viskos gedämpfte“ Struktur nicht gibt, gibt es auch den rein exponentiellen Ausschwingvorgang nicht. Der aus dem Beginn eines Ausschwingvorganges bestimmte Dämpfungswert wird nicht mit jenem übereinstimmen, der sich aus der Auswertung des Endes des Vorganges ergibt [1]. Man wird sich aber in einem begrenzten Bereich bewegen, maximal vielleicht +/- 30...50 % des „wahren“ Wertes.   Nach der Beschreibung der Versuche wird auf die Probleme eingegangen, die zwangsweise auftreten, wenn für die Bestimmung der Dämpfung ein gemessenes Zeitsignal digitalisiert, in den Frequenzbereich und wieder zurück in den Zeitbereich transformiert wird. Der dabei auftretende, systematische Fehler kann für tiefe Frequenzen exorbitante Ausmaße annehmen. Dass dies hier am Beispiel der im ARTeMIS Softwarepaket angebotenen EFDD-Methode (EFDD = Enhanced Frequency Domain Decomposition, [2]) vorgeführt wird, ist Zufall. EFDD wird auch in anderen Softwarepaketen verwendet. Das gleiche gilt auch für das hier nur am Rand diskutierte Problem, dass auch bei Verwendung der in der Wissenschaft populären SSI Methode (SSI = Stochastic Subspace Identification) unter Umständen sehr grobe Fehler an der identifizierten Dämpfung auftreten können. Am Rand wird dieses Problem hier diskutiert, weil der Grund für solche Fehler noch nicht wissenschaftlich dokumentiert ist.   Der praktisch tätige Ingenieur sollte sich darauf verlassen können, dass die Anwendung eines kommerziell vertriebenen Softwarepaketes für die Auswertung seiner Experimente brauchbare Werte für die Dämpfung liefert. Die Kenntnis der Dämpfungskapazität ist von zentraler Wichtigkeit, wenn es darum geht, die möglichen Auswirkungen von Resonanzzuständen (oder resonanzähnlichen Zuständen) zu beurteilen. Dies trifft gerade für die ersten, tieffrequenten Eigenschwingungen eines Tragwerkes zu. Für exorbitante, systematische Fehler der Auswertemethoden ist hier kein Platz. Wenn man diese aber kennt, kann ihnen aus dem Weg gegangen werden.

The Effect of Sloshing in Tanks on Motions and Hull Girder Responses of Damaged Vessels

2011 ◽  
Author(s):  
Huirong Jia ◽  
Torgeir Moan
Keyword(s):  
Reliability Analysis ◽  
Structural Reliability ◽  
Bending Moment ◽  
Roll Motion ◽  
Multimodal Approach ◽  
Rectangular Shape ◽  
Hull Girder ◽  
Structural Reliability Analysis ◽  
Oil Tankers

The structural reliability analysis of damaged vessels has up to now commonly been investigated by neglecting the effect of sloshing. This paper deals with the effect of sloshing in tanks on motions and hull girder responses of oil tankers in various damage conditions and represents a part of a study to assess the effect of sloshing on hull girder failure of damaged vessels, The flooded tanks are assumed to have a of rectangular shape and linear multimodal approach is adopted to deal with sloshing. It is concluded that even though the effect of sloshing in tanks on the roll motion of vessels can be neglected in certain damage conditions, the effect of sloshing on the horizontal bending moment cannot be neglected, especially when resonance motion occurs.

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