• norsk
    • English
  • English 
    • norsk
    • English
  • Login
View Item 
  •   Home
  • Fakultet for ingeniørvitenskap (IV)
  • Institutt for bygg- og miljøteknikk
  • View Item
  •   Home
  • Fakultet for ingeniørvitenskap (IV)
  • Institutt for bygg- og miljøteknikk
  • View Item
JavaScript is disabled for your browser. Some features of this site may not work without it.

Force and response estimation on bottom-founded structures prone to ice-induced vibrations

Nord, Torodd Skjerve
Doctoral thesis
Thumbnail
View/Open
Fulltext (PDF) available (24.41Mb)
URI
http://hdl.handle.net/11250/2372706
Date
2015
Metadata
Show full item record
Collections
  • Institutt for bygg- og miljøteknikk [5150]
Abstract
Various types of bottom-founded structures, including lighthouses, quay structures,

mono-pod platforms, multi-legged platforms, caisson-retained islands and bridges, are

located in ice-infested waters. Level ice can interact with bottom-founded structures in

various manners, and over fifty years of extensive measurement campaigns has brought

attention to ice-induced vibrations. This phenomenon is caused by repeated ice crushing

failures across the ice-structure interface and may entail violent vibrations of the

structure, thereby potentially harming the structural integrity, secondary installations

and operational safety. Such ice-induced vibrations are commonly divided into three

regimes:

1) Intermittent crushing

2) Frequency lock-in

3) Continuous brittle crushing

in which the ice velocity increase from regime 1 to regime 3. The ice conditions leading

to each of the three regimes are not yet fully understood. Therefore, measurement

campaigns both in the field and in the laboratory must address these regimes, wherein

two of the major ingredients are the ice force and the structural response.

A laboratory-scale ice-induced vibration measurement campaign was conducted at the

Hamburg Ship Model Basin during August-September 2011, from which data were

obtained for this thesis. Data measured at the Nordströmsgrund lighthouse in Sweden

during the winter of 2003 and structural information on the Hanko-1 channel marker in

Finland constitute the full-scale basis in this thesis.

The ice forces present during ice-induced vibrations are traditionally measured by load

panels or inverse techniques. Load panels are expensive; thus, inverse techniques are

favorable. This thesis assessed a deterministic-stochastic framework to identify both the

ice forces and responses at both the model scale and full scale. All of the considered

data were limited to scenarios of ice-induced vibrations, and the considered ice

conditions were primarily level ice. The framework as it is applied in this thesis consists

of a joint input-state estimation algorithm, a model of the structure and a set of response

measurements. Both full-order finite element models and modally reduced order models

were used in this thesis.

Using the laboratory measurements, the force and response identification was

performed by employing two different full-order finite element models. One model was

entirely based on the blueprints of the structure. The other model was tuned to more

accurately reproduce the measured first natural frequency. The results were presented

for two different regimes of ice-induced vibrations: the intermittent crushing regime and

the continuous brittle crushing regime. The accuracy of the identified forces using the

joint input-state estimation algorithm was assessed by comparing the forces with those

obtained by a frequency-domain deconvolution method based on experimentally

obtained frequency response functions. The results demonstrated the successful

identification of the level-ice forces for both the intermittent and continuous brittle

crushing regimes even when significant modeling errors were present. The responses

(displacements) identified in conjunction with the forces were also compared to those

measured during the experiment. Here, the estimated response was found to be sensitive

to the modeling errors in the blueprint model. Simple tuning of the model, however,

enabled high-accuracy response estimation.

The joint input-state estimation algorithm was further used as a means to analyze the

laboratory data, from which the global structural response was simultaneously identified

with the forces. Novel insights into ice-induced vibration phenomena were obtained by

comparing, on different time scales, measured and estimated response quantities and

forces/pressures. First, the identified forces, ice velocities and time-frequency maps of

the measured responses were presented for a series of ice-induced vibration tests. It was

shown that the ice forces excited more than one mode of the structure and that the

transition ice velocity at which the vibrations shifted from the first mode to the second

mode increased with decreased foundation stiffness and superstructure mass. Second, a

detailed analysis of the interaction between the structure and the ice edge was

performed on a smaller time scale by comparing the locally measured pressures at the

ice-structure interface to the identified structural responses and forces. It was shown that

structural vibrations at a frequency that is higher than the dominant vibration frequency

caused cyclic loading of the ice edge during intermittent crushing. These vibrations led

to an increasing loading rate prior to ice failure. During an event that showed the

tendencies of frequency lock-in vibrations, the structural response was dominated by a

single vibration frequency.

At full scale, a comparison between the measured and identified dynamic ice forces

acting on the Nordströmsgrund lighthouse is presented. The dynamic ice forces were

identified from the measured responses using the joint input-state estimation algorithm

in conjunction with a reduced-order finite element model. A convincing agreement

between the measured and identified forces was found. The algorithm was further used

to estimate the response of the structure at unmeasured locations, including the iceaction

point. The structural velocity amplitudes when the structure was subject to

frequency lock-in vibrations were occasionally higher than the ice velocity and within

the range of observations for other structures.

A measurement campaign at the Hanko-1 channel marker in the Gulf of Finland is

planned to monitor the forces leading to ice-induced vibrations via force identification.

The ice forces are to be identified using the joint input-state estimation algorithm in

conjunction with a modally reduced order model. Recently developed guidelines were

used to determine the optimal response measurement types and locations that ensure the

identifiability of the dynamic ice forces from only a limited number of sensors and a

selection of vibration modes.
Has parts
Paper 1: Nord, Torodd Skjerve; Maattanen, Mauri Pellervo; Øiseth, Ole. Frequency domain force identification in ice-structure interaction. I: The proceedings of the 22nd International Conference on Port and Ocean Engineering under Arctic Conditions. : Port and Ocean Engineering under Arctic Conditions 2013

Paper 2: Nord, Torodd Skjerve; Lourens, Eliz-Mari; Øiseth, Ole; Metrikine, Andrei. Model-based force and state estimation in experimental ice-induced vibrations by means of Kalman filtering. Cold Regions Science and Technology 2015 ;Volum 111. s. 13-26 http://dx.doi.org/10.1016/j.coldregions.2014.12.003 The article in is reprinted with kind permission from Elsevier, sciencedirect.com

Paper 3: Nord, Torodd Skjerve; Lourens, Eliz-Mari; Maattanen, Mauri Pellervo; Øiseth, Ole; Høyland, Knut Vilhelm. Laboratory experiments to study ice-induced vibrations of scaled model structures during their interaction with level ice at different ice velocities. Cold Regions Science and Technology 2015 ;Volum 119. s. 1-15 http://dx.doi.org/10.1016/j.coldregions.2015.06.017 The article in is reprinted with kind permission from Elsevier, sciencedirect.com

Paper 4: Nord, T.S., Lourens, E.-M., Øiseth, O. Ice force identification on the Nordströmsgrund lighthouse. © 2016. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/ The final version is avialable at http://dx.doi.org/10.1016/j.compstruc.2016.02.016

Paper 5: Nord, Torodd Skjerve; Øiseth, Ole; Petersen, Øyvind Wiig; Lourens, Eliz-Mari. Sensor network for dynamic ice-force identification: The Hanko-1 Channel Marker case study. Proceedings - International Conference on Port and Ocean Engineering under Arctic Conditions 2015
Publisher
NTNU
Series
Doctoral thesis at NTNU;2015:217

Contact Us | Send Feedback

Privacy policy
DSpace software copyright © 2002-2019  DuraSpace

Service from  Unit
 

 

Browse

ArchiveCommunities & CollectionsBy Issue DateAuthorsTitlesSubjectsDocument TypesJournalsThis CollectionBy Issue DateAuthorsTitlesSubjectsDocument TypesJournals

My Account

Login

Statistics

View Usage Statistics

Contact Us | Send Feedback

Privacy policy
DSpace software copyright © 2002-2019  DuraSpace

Service from  Unit