Model Tests With a Compliant Cylindrical Structure to Investigate Ice-Induced Vibrations

2016 ◽  
Vol 138 (4) ◽  
Author(s):  
Gesa Ziemer ◽  
Karl-Ulrich Evers
Keyword(s):  
Natural Frequency ◽  
Structural Response ◽  
Model Tests ◽  
Ice Thickness ◽  
Cylindrical Structure ◽  
Ice Drift ◽  
Wide Range ◽  
Dynamic Forces ◽  
Dynamic Amplification ◽  
Ice Model

A compliant cylindrical structure has been built and tested in a series of model tests in ice in the Large Ice Model Basin at HSVA. The structure's stiffness in ice plane is higher in ice drift direction than crosswise, enabling the model to vibrate in different geometrical oscillation patterns. In total, four ice sheets have been used to perform tests in different ice thickness, covering a wide range of ice drift velocities between 0.005 and 0.15 m/s in model scale. Several events of ice-induced vibrations were observed throughout the test campaign. Oscillations are found to reach different types of beginning steady states, depending on ice drift velocity and ice thickness. Dynamic amplification of structural response in ice plane as well as ratio of static and dynamic forces is highly dependent on the type of vibration. While the dynamic amplification is highest when the ice load's frequency equals the first natural frequency of the structure, the highest dynamic forces occur when the crushing frequency is an integer fraction of the natural frequency. The paper describes the design of the test setup, instrumentation and calibration, performance and analysis of conducted tests, and general findings.

Ice Model Tests With a Compliant Cylindrical Structure to Investigate Ice-Induced Vibrations

2014 ◽  
Author(s):  
Gesa Ziemer ◽  
Karl-Ulrich Evers
Keyword(s):  
Natural Frequency ◽  
Structural Response ◽  
Model Tests ◽  
Ice Thickness ◽  
Cylindrical Structure ◽  
Ice Drift ◽  
Wide Range ◽  
Dynamic Forces ◽  
Dynamic Amplification ◽  
Ice Model

A compliant cylindrical structure has been built and tested in a series of model tests in ice in the Large Ice Model Basin at HSVA. The structure’s stiffness in ice plane is higher in ice-drift direction than crosswise, enabling the model to vibrate in different oscillation patterns. In total, 4 ice sheets have been used to perform tests in different ice thickness, covering a wide range of ice drift velocities between 0.005 and 0.15 m/s in model scale. Several events of ice-induced vibrations were observed throughout the test campaign. Oscillations are found to reach different types of beginning steady-state, mainly depending on ice drift velocity and ice thickness. Dynamic amplification of structural response in ice plane as well as ratio of static and dynamic forces is highly dependent on the type of vibration. While the dynamic amplification is highest when the ice load’s frequency equals the first natural frequency of the structure, the highest dynamic forces occur when the crushing frequency is an integer fraction of the natural frequency. The paper describes the design of the test set-up, instrumentation and calibration, performance and analysis of conducted tests, and general findings.

scholarly journals neXtSIM: a new Lagrangian sea ice model

2016 ◽  
Vol 10 (3) ◽  
pp. 1055-1073 ◽  
Author(s):  
Pierre Rampal ◽  
Sylvain Bouillon ◽  
Einar Ólason ◽  
Mathieu Morlighem
Keyword(s):  
Sea Ice ◽  
Arctic Sea Ice ◽  
The Arctic ◽  
Dynamical Response ◽  
Ice Dynamics ◽  
Ice Drift ◽  
Wide Range ◽  
Arctic Sea ◽  
Sea Ice Drift ◽  
Ice Model

Abstract. The Arctic sea ice cover has changed drastically over the last decades. Associated with these changes is a shift in dynamical regime seen by an increase of extreme fracturing events and an acceleration of sea ice drift. The highly non-linear dynamical response of sea ice to external forcing makes modelling these changes and the future evolution of Arctic sea ice a challenge for current models. It is, however, increasingly important that this challenge be better met, both because of the important role of sea ice in the climate system and because of the steady increase of industrial operations in the Arctic. In this paper we present a new dynamical/thermodynamical sea ice model called neXtSIM that is designed to address this challenge. neXtSIM is a continuous and fully Lagrangian model, whose momentum equation is discretised with the finite-element method. In this model, sea ice physics are driven by the combination of two core components: a model for sea ice dynamics built on a mechanical framework using an elasto-brittle rheology, and a model for sea ice thermodynamics providing damage healing for the mechanical framework. The evaluation of the model performance for the Arctic is presented for the period September 2007 to October 2008 and shows that observed multi-scale statistical properties of sea ice drift and deformation are well captured as well as the seasonal cycles of ice volume, area, and extent. These results show that neXtSIM is an appropriate tool for simulating sea ice over a wide range of spatial and temporal scales.

Different Ways of Modeling Ice Drift Scenarios in Basin Tests

2013 ◽  
Author(s):  
Andrea Haase ◽  
Peter Jochmann
Keyword(s):  
Sea Ice ◽  
Relative Motion ◽  
Development Project ◽  
Model Tests ◽  
Contact Forces ◽  
Second Phase ◽  
Offshore Structure ◽  
Ice Drift ◽  
Ice Field ◽  
Ice Model

One known scenario from full scale sea ice investigations is a drifting managed ice field. This ice field may be driven by winds or currents or both and may eventually hit a vessel or an offshore structure. In case of a moving vessel the relative motion between vessel and ice may be determined by the vessels direction of motion or even its ambition to hold position against the drifting ice. All the above described scenarios deal with relative motions between several bodies. Along with the relative motion come the contact forces between the interacting bodies and last but not least the question of the failure of either of the bodies. As ice model tests are in general state of the art procedures to investigate the behavior of a vessel and the related loads in sea ice the question of how to model drift scenarios is of relevance here. Typically in ice model tests a drifting managed ice field is simulated by moving a model ship through a resting ice field. This paper addresses the differences in modeling the ice drift as described above and when moving the floes against a stationary vessel. For this purpose ice model tests of each kind are investigated and theoretical efforts are made to enlighten the topic. Also it is distinguished between the vessel being driven by its own propulsion system or by an external force. In summer 2011 and 2012 a comprehensive set of ice model tests was performed in the large ice tank of the Hamburg Ship Model Basin (HSVA). The tests are related to the research and development project DYPIC — Dynamic Positioning in Ice. Within the project two phases of model tests have been performed. The first phase has been documented and presented in [1] while the second phase is presented in [2]. The model setups described and analyzed in this paper all relate to tests performed within the scope of DYPIC.

scholarly journals neXtSIM: a new Lagrangian sea ice model

2015 ◽  
Vol 9 (5) ◽  
pp. 5885-5941 ◽  
Author(s):  
P. Rampal ◽  
S. Bouillon ◽  
E. Ólason ◽  
M. Morlighem
Keyword(s):  
Sea Ice ◽  
Arctic Sea Ice ◽  
The Arctic ◽  
Dynamical Response ◽  
Ice Dynamics ◽  
Ice Drift ◽  
Wide Range ◽  
Arctic Sea ◽  
Sea Ice Drift ◽  
Ice Model

Abstract. The Arctic sea ice cover has changed drastically over the last decades. Associated with these changes is a shift in dynamical regime seen by an increase of extreme fracturing events and an acceleration of sea ice drift. The highly non-linear dynamical response of sea ice to external forcing makes modelling these changes, and the future evolution of Arctic sea ice a challenge for current models. It is, however, increasingly important that this challenge be better met, both because of the important role of sea ice in the climate system and because of the steady increase of industrial operations in the Arctic. In this paper we present a new dynamical/thermodynamical sea ice model, called neXtSIM in order to address this. neXtSIM is a continuous and fully Lagrangian model, and the equations are discretised with the finite-element method. In this model, sea ice physics are driven by a synergic combination of two core components: a model for sea ice dynamics built on a new mechanical framework using an elasto-brittle rheology, and a model for sea ice thermodynamics providing damage healing for the mechanical framework. The results of a thorough evaluation of the model performance for the Arctic are presented for the period September 2007 to October 2008. They show that observed multi-scale statistical properties of sea ice drift and deformation are well captured as well as the seasonal cycles of ice volume, area, and extent. These results show that neXtSIM is a very promising tool for simulating the sea ice over a wide range of spatial and temporal scales.

Model Testing of Ice Barriers Used for Reduction of Design Ice Loads

2003 ◽  
Author(s):  
Peter Jochmann ◽  
Karl-Ulrich Evers ◽  
Walter L. Kuehnlein
Keyword(s):  
Bending Strength ◽  
Model Tests ◽  
Individual Model ◽  
Mean Values ◽  
Drilling Rig ◽  
Design Load ◽  
Ice Load ◽  
Ice Drift ◽  
Ice Loads ◽  
Ice Model

The drilling rig Sunkar, owned and operated by Parker Drilling under contract to Agip KCO, was the first drilling rig in the North Caspian Sea. In this area sea ice may occur between November and April. The original ice protection concept of the drilling rig was based on the fact that ice loads were partly taken and/or reduced by two rows of heavy piles. As an alternative concept ice model tests for Sunkar with installed ice barriers (Ice Rubble Generators) around the rig were carried out in the Large Ice Model Basin of HSVA in order to establish the design ice loads and to prove that the design forces can be reduced significantly by using these ice barriers. The test series were carried out in 1.3 m thick level ice with a bending strength of 770 kPa. Ice drift angle, ice drift speed, spacing between the ice barriers, as well as the angle of the ice barriers were varied. The design water level simulated in the model tests was about 4 m. As maximum measured ice load values are a result of coincidental ice failure occurrences these values are much more scattered than the mean values of ice model tests. Even if an individual model test could be repeated exactly, i.e. exactly within measurable limits, the maximum load would be different. Therefore the design load needs to be obtained by using a sophisticated statistical approach. To establish the design load an extreme value distribution, a Gumbel-Probability-Distribution (GPD) for each individual model run has been applied. The ice model tests have shown that a significant ice force reduction can be achieved if the drilling rig Sunkar is protected with ice barriers. The reduction of the maximum horizontal global ice load amounts to approx. 63% when Sunkar is protected by ice barriers. The ice barriers initiate ice rubble and areas of rafted ice as well as ice accumulation between the barriers, which lead to ice bridging with a spacing of 60 to 80 m between the ice barriers. As a final result it was found that the stability of Sunkar will be sufficient under any angle of drifting ice if ice barriers are installed.

DP Ice Model Test of Arctic Drillship and Polar Research Vessel

2012 ◽  
Author(s):  
Torbjørn Hals ◽  
Nils Albert Jenssen
Keyword(s):  
Numerical Models ◽  
Offshore Structures ◽  
Model Tests ◽  
Full Scale ◽  
The Arctic ◽  
Research Vessel ◽  
Station Keeping ◽  
Ice Drift ◽  
Ice Conditions ◽  
Ice Model

The paper presents the results from a series of ice model tests performed as part of the DYPIC (Dynamic Positioning in Ice Conditions) research program. DYPIC is a research and development project within the EU’s ERA NET MARTEC project. The major purpose of the DYPIC project is development of equipment and methods for DP Ice Model testing which allows the prediction of station keeping capability of different vessel types and offshore structures under various ice conditions. The first DYPIC model tests performed in 2011 was conducted with two significantly different vessel sizes, a 68.0000 m3 volume displacement arctic drillship and an 8.600 m3 polar research vessel. The model scale was 1/30 for the arctic drillship and 1/18.6 for the Polar Research Vessel. The model tests were performed in the ice model basin at HSVA using vessel models equipped with thruster capacity similar to full scale operation according to DP class 2 / 3 operations. The DP control system was also modified from normal open water DP operations in order to cope with the highly varying ice drift loads acting on the vessel. The test program gave data supporting the development of numerical models of ice loads from managed ice, see reference [6]. The main focus in this paper is on the station keeping performance and associated thrust utilization as a function of varying ice drift loads. The results and data collected in the first year of the DYPIC program demonstrates that DP ice model tests will be a valuable tool for evaluation of vessel performance prior to moving on to full scale arctic DP operations.

Model Tests: LNG-Carriers in Ice

2006 ◽  
Author(s):  
Jens-Holger Hellmann ◽  
Karl-Heinz Rupp ◽  
Walter L. Kuehnlein
Keyword(s):  
Natural Gas ◽  
Model Tests ◽  
Ice Thickness ◽  
New Developments ◽  
Ship Building ◽  
Future Performance ◽  
Level Ice ◽  
Ice Navigation ◽  
Parental Level ◽  
Ice Model

Approximately on third of the world’s known and not yet exploited reserves of natural gas are in Russia. The overwhelming majority of these reserves are in Artic and Subarctic areas. But not only in Russia, also in other areas like Canada and USA, natural gas reserves are found in harsh and ice covered environments. As a consequence, the LNG ship technology is going towards Arctic LNG-Carriers. New developments in ice navigation, winterization and ship sizes are generating a new exiting challenge for shipping and ship building industries all over the world. Existing ice class regulations should be only considered as a first guide for designing ice-going vessels. Because the future performance in ice covered waters of new developed LNG-Carriers needs to be investigated in much more detail, therefore ice model tests are imperative. It is common practice guiding ships in ice-covered waters by using one or two icebreakers for wider LNG-Carriers. The LNG-Carrier is following in the broken channel of about 1.25 to 2 times the widths of its beam. For the model tests a parental level ice sheet of target ice thickness will be prepared according to HSVA’s standard model ice preparation procedure. In order to obtain a defined friction coefficient between the ice and the model hull, HSVA applies a special paint composition to the models of ice-going vessels. The channel will be broken with the help of two stock icebreakers towed through the level ice generating the most realistic wide ice channel. The prime objectives of such ice model tests are: • Evaluation of the icebreaking performance in a wide ice channel, • Propeller-ice-interactions and • how the ice is transferred aside and below the vessel.

Influence of the distribution of the shear walls on the seismic response of the buildings

2020 ◽  
Vol 15 (1) ◽  
pp. 37-44
Author(s):  
El Mehdi Echebba ◽  
Hasnae Boubel ◽  
Oumnia Elmrabet ◽  
Mohamed Rougui
Keyword(s):  
Structural Analysis ◽  
Seismic Response ◽  
Natural Frequency ◽  
Structural Design ◽  
Structural Response ◽  
Shear Walls ◽  
Structural Elements ◽  
Analysis Software ◽  
Ansys Apdl ◽  
The Impact

Abstract In this paper, an evaluation was tried for the impact of structural design on structural response. Several situations are foreseen as the possibilities of changing the distribution of the structural elements (sails, columns, etc.), the width of the structure and the number of floors indicates the adapted type of bracing for a given structure by referring only to its Geometric dimensions. This was done by studying the effect of the technical design of the building on the natural frequency of the structure with the study of the influence of the distribution of the structural elements on the seismic response of the building, taking into account of the requirements of the Moroccan earthquake regulations 2000/2011 and using the ANSYS APDL and Robot Structural Analysis software.

Model Tests in Brash Ice Channels

2005 ◽  
Author(s):  
Jens-Holger Hellmann ◽  
Karl-Heinz Rupp ◽  
Walter L. Kuehnlein
Keyword(s):  
Perforated Plate ◽  
Ice Sheet ◽  
Open Water ◽  
Model Tests ◽  
Ice Thickness ◽  
Special Device ◽  
Level Ice ◽  
Set Up ◽  
Parental Level ◽  
Oil Tankers

According to the present Finnish-Swedish Ice Class Rules (FSICR) the formulas for the required main engine power for tankers led to much bigger main engines than it is needed for the demanded open water speed. Therefore model tests may be performed in order to verify the vessel’s capability to sail with less required power in brash ice channels compared to the calculations. Several model test runs have been performed in order to study the performance of crude oil tankers sailing in brash ice. The tests were performed as towed propulsion tests and the brash ice channel was prepared according to the guidelines set up by the Finnish Maritime Administration (FMA). The channel width was 2 times the beam of the tanker. The model tests were carried out at a speed of 5 knots. For the tests a parental level ice sheet of adequate thickness is prepared according to HSVA’s standard model ice preparation procedure. After a predefined level ice thickness has been reached, the air temperature in the ice tank will be raised. An ice channel with straight edges will be cut into the ice sheet by means of two ice knives. The ice stripe between the two cuts will be manually broken up into relatively small ice pieces using a special ice chisel and if required the brash ice material will be compacted. Typically the brash ice thickness will be measured prior the tests at 9 positions across the channel and every two meter over the entire length of the brash ice channel with a special device, which consists of a measuring rule with a perforated plate mounted under a right angle at the lower end of the rule. As a result of the tests it could be demonstrated that tankers with a capacity of more than 50 000 tons require 50% and even less power compared to calculations using the present FSICR formulas.

The NREL Large-Scale Turbine Inflow and Response Experiment: Preliminary Results

2002 ◽  
Author(s):  
Neil Kelley ◽  
Maureen Hand ◽  
Scott Larwood ◽  
Ed McKenna
Keyword(s):  
Wind Turbine ◽  
Large Scale ◽  
Structural Response ◽  
Technology Center ◽  
Operating Environments ◽  
Sonic Anemometers ◽  
Wide Range ◽  
Scaling Parameters ◽  
Planar Array ◽  
Turbulence Scaling

The accurate numerical dynamic simulation of new large-scale wind turbine designs operating over a wide range of inflow environments is critical because it is usually impractical to test prototypes in a variety of locations. Large turbines operate in a region of the atmospheric boundary layer that currently may not be adequately simulated by present turbulence codes. In this paper, we discuss the development and use of a 42-m (137-ft) planar array of five, high-resolution sonic anemometers upwind of a 600-kW wind turbine at the National Wind Technology Center (NWTC). The objective of this experiment is to obtain simultaneously collected turbulence information from the inflow array and the corresponding structural response of the turbine. The turbulence information will be used for comparison with that predicted by currently available codes and establish any systematic differences. These results will be used to improve the performance of the turbulence simulations. The sensitivities of key elements of the turbine aeroelastic and structural response to a range of turbulence-scaling parameters will be established for comparisons with other turbines and operating environments. In this paper, we present an overview of the experiment, and offer examples of two observed cases of inflow characteristics and turbine response collected under daytime and nighttime conditions, and compare their turbulence properties with predictions.

Sign in / Sign up

Export Citation Format

Share Document