Comparison of Response Amplitude Operator Curve Generation Methods for Scaled Floating Renewable Energy Platforms in Ocean Wave Basin

2020 ◽  
Vol 1 (2) ◽  
Author(s):  
Deirdre O’Donnell ◽  
Jimmy Murphy ◽  
Vikram Pakrashi

Abstract Response amplitude operator (RAO) curves are commonly employed to assess the dynamic behavior of floating offshore structures in the frequency domain. There are multiple methods used to obtain RAOs for numerical models, scaled physical models, and full-scale tests. While for numerical modeling many studies detail the precise methods used, the literature around experimental RAO curves often do not detail them or leave methodological information incomplete. There exists inadequate experimental evidence in assessing the differences in results obtained by following different RAO generation methods from scaled physical testing. This paper addresses this gap by comparing two most popular RAO generation methods: the energy spectra (ES) and the cross spectral auto spectra (CSAS) method. These are experimentally compared on scaled semisubmersible and spar-buoy platforms in an ocean wave basin. Differences of heave and pitch RAOs generated by different methods are investigated. A method for reasonably collating multiple tests to create a representative RAO is also presented. RAO amplitudes vary significantly and how they decay off beyond certain frequencies is dependent on the method adopted to create them. This variation can be a source of significant uncertainty for floating structures for further analysis, design, control, or repair. Some RAOs (e.g., pitch) are sensitive to scaling and should be considered when converting scaled tests to full-scale equivalent. Detailing methods of RAO generation and comparing approaches of developing them can be important for crucial decisions from scaled physical testing of floating structures at design/development stages.

1998 ◽  
Vol 14 (04) ◽  
pp. 265-276
Author(s):  
Ivo Senjanovic

This review paper covers extensive investigations which were undertaken in order to verify the idea of launching of ships and other floating structures from a horizontal berth by a set of turning pads. This includes structural dynamics during launching, model tests and strength analysis of the structure and the launching system. The most important results, which were used for the design of the launching system, are presented. The preparation of a barge for side launching is described, and the full-scale measurement results are compared with the test results. The advantages of building ships and offshore structures on a horizontal berth are pointed out in the conclusion.


Author(s):  
Raed Lubbad ◽  
Sveinung Løset ◽  
Wenjun Lu ◽  
Andrei Tsarau ◽  
Marnix van den Berg

As offshore activities in the Arctic constitute a relatively new field with only a handful of relevant operations to draw experience from, and since full-scale trials are extremely expensive, there is an expressed need for much more extensive, detailed and cost-efficient analysis of concepts based on numerical simulations. However, until recently simulation tools of sufficient quality to perform such numerical analysis have not existed. The only verification available has been through a limited set of experiments in ice model basins. Today, this has changed, partly through the efforts at the Norwegian University of Science and Technology (NTNU) hosting SAMCoT (Centre for Research-based Innovation - Sustainable Arctic Marine and Coastal Technology), laying the foundation of a versatile and highly accurate high-fidelity numerical simulator for offshore structures in various ice conditions such as level ice, broken ice and ice ridges. Arctic Integrated Solutions AS (ArcISo) is a spin-off company from NTNU established in 2016 with the vision of increasing the technology readiness level of SAMCoT’s numerical models to become a professional software package for the analysis of sea ice actions and action effects on Arctic offshore and coastal structures. This software package is called Simulator for Arctic Marine Structures (SAMS) and it was first released in 2017. This paper introduces the software implementation and the theoretical basis of SAMS, and it discusses the use of full-scale data to validate the simulator.


2001 ◽  
Vol 123 (4) ◽  
pp. 170-176 ◽  
Author(s):  
Bertrand Bobillier ◽  
Subrata Chakrabarti ◽  
Poul Christiansen

Wind is an important environmental parameter that influences the design of floating offshore structures, particularly in harsh environment. Because wind spectrum is broad-banded, computation of wind load on the floating structure is complicated. Moreover, the wind-induced slow-drift oscillation is an important design criterion. Simulated environment in a model test often includes wind effect. Accurate modeling of wind in a laboratory environment is, however, a difficult task. The wind tunnel provides a steady load on the superstructure quite accurately, but fails to show the effect of the changing free surface as well as dynamic effect. Therefore, simultaneous simulation of wind in the wave basin is desirable. A weight representing the steady wind load with a string and pulley arrangement at the center of the application of the superstructure is inadequate since it fails to simulate the variation of the wind spectrum. The generation and control of the design wind spectrum by an overhead bank of fans facing the model superstructure is an extremely difficult task due to large windage area. This paper presents an accurate and highly controllable method of the generation of variable wind simultaneously with waves and current in the wave basin that can be used with a variety of floating structure model. The concept was originally proposed by Kvaerner Oil & Gas International and implemented by the offshore model basin (OMB). In this method, a fan equipped with a constant-speed motor and blades with an adjustable pitch angle is directly mounted on the model deck above water. A digital signal generated from the specified wind spectrum is used to run the fan much like the wavemaker. A feedback system ensures the proper generation of the wind with the model motion. The method was successfully applied in several model tests of deepwater floating structures in which broad-banded wind spectra were generated. An example from an earlier such test is given here. The importance of the effect of the simulated wind spectrum on floating structures should be clear to a design engineer from this example.


Author(s):  
Torbjørn Hals ◽  
Nils Albert Jenssen

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.


2017 ◽  
Vol 747 ◽  
pp. 694-701 ◽  
Author(s):  
Mustafa Hrasnica ◽  
Fadil Biberkic ◽  
Senad Medic

Unreinforced masonry structures are generally vulnerable to earthquake actions. Brittle masonry walls are very stiff and attract considerable seismic forces which cannot be sustained without cracking. In order to enhance ductility and load bearing capacity, certain strengthening techniques need to be applied. An experimental program concerning in-plane behavior of solid clay brick masonry walls was performed at the Institute for Materials and Structures, Faculty of Civil Engineering University of Sarajevo, in cooperation with Institute for Lightweight Structures and Conceptual Design, University of Stuttgart. The physical models include two unconfined unreinforced full scale masonry walls L/H/D=233/237/25cm and two strengthened full scale walls jacketed on both sides with 5cm thick concrete and reinforced with Q196 steel mesh. Twelve reduced scale walls L/H/D = 100/100/25cm were additionally constructed in order to test different strengthening methods which include one-or two-sided jacketing and CFK 150 strips. Specimens were exposed to cyclic shear as well as to monotonic push over loading program for different vertical stress levels with the aim to quantify shear strength, stiffness and energy dissipation. For lower vertical loads the tested walls exhibit rigid body rotation in each displacement cycle. For higher precompression mixed flexural and shear failure mode was registered, characterized by toe crushing and diagonal cracking. No separation of jacketing from the masonry was detected. Numerical models of tested wall panels were developed using finite element programs.


2019 ◽  
Author(s):  
Liwei Cao ◽  
Danilo Russo ◽  
Vassilios S. Vassiliadis ◽  
Alexei Lapkin

<p>A mixed-integer nonlinear programming (MINLP) formulation for symbolic regression was proposed to identify physical models from noisy experimental data. The formulation was tested using numerical models and was found to be more efficient than the previous literature example with respect to the number of predictor variables and training data points. The globally optimal search was extended to identify physical models and to cope with noise in the experimental data predictor variable. The methodology was coupled with the collection of experimental data in an automated fashion, and was proven to be successful in identifying the correct physical models describing the relationship between the shear stress and shear rate for both Newtonian and non-Newtonian fluids, and simple kinetic laws of reactions. Future work will focus on addressing the limitations of the formulation presented in this work, by extending it to be able to address larger complex physical models.</p><p><br></p>


Water ◽  
2021 ◽  
Vol 13 (4) ◽  
pp. 458
Author(s):  
Drew C. Baird ◽  
Benjamin Abban ◽  
S. Michael Scurlock ◽  
Steven B. Abt ◽  
Christopher I. Thornton

While there are a wide range of design recommendations for using rock vanes and bendway weirs as streambank protection measures, no comprehensive, standard approach is currently available for design engineers to evaluate their hydraulic performance before construction. This study investigates using 2D numerical modeling as an option for predicting the hydraulic performance of rock vane and bendway weir structure designs for streambank protection. We used the Sedimentation and River Hydraulics (SRH)-2D depth-averaged numerical model to simulate flows around rock vane and bendway weir installations that were previously examined as part of a physical model study and that had water surface elevation and velocity observations. Overall, SRH-2D predicted the same general flow patterns as the physical model, but over- and underpredicted the flow velocity in some areas. These over- and underpredictions could be primarily attributed to the assumption of negligible vertical velocities. Nonetheless, the point differences between the predicted and observed velocities generally ranged from 15 to 25%, with some exceptions. The results showed that 2D numerical models could provide adequate insight into the hydraulic performance of rock vanes and bendway weirs. Accordingly, design guidance and implications of the study results are presented for design engineers.


2020 ◽  
Vol 9 (1) ◽  
pp. 14
Author(s):  
Gianluca Zitti ◽  
Nico Novelli ◽  
Maurizio Brocchini

Over the last decades, the aquaculture sector increased significantly and constantly, moving fish-farm plants further from the coast, and exposing them to increasingly high forces due to currents and waves. The performances of cages in currents and waves have been widely studied in literature, by means of laboratory experiments and numerical models, but virtually all the research is focused on the global performances of the system, i.e., on the maximum displacement, the volume reduction or the mooring tension. In this work we propose a numerical model, derived from the net-truss model of Kristiansen and Faltinsen (2012), to study the dynamics of fish farm cages in current and waves. In this model the net is modeled with straight trusses connecting nodes, where the mass of the net is concentrated at the nodes. The deformation of the net is evaluated solving the equation of motion of the nodes, subjected to gravity, buoyancy, lift, and drag forces. With respect to the original model, the elasticity of the net is included. In this work the real size of the net is used for the computation mesh grid, this allowing the numerical model to reproduce the exact dynamics of the cage. The numerical model is used to simulate a cage with fixed rings, based on the concept of mooring the cage to the foundation of no longer functioning offshore structures. The deformations of the system subjected to currents and waves are studied.


2020 ◽  
Vol 12 (24) ◽  
pp. 10677
Author(s):  
Ronghui Ye ◽  
Jun Kong ◽  
Chengji Shen ◽  
Jinming Zhang ◽  
Weisheng Zhang

Accurate salinity prediction can support the decision-making of water resources management to mitigate the threat of insufficient freshwater supply in densely populated estuaries. Statistical methods are low-cost and less time-consuming compared with numerical models and physical models for predicting estuarine salinity variations. This study proposes an alternative statistical model that can more accurately predict the salinity series in estuaries. The model incorporates an autoregressive model to characterize the memory effect of salinity and includes the changes in salinity driven by river discharge and tides. Furthermore, the Gamma distribution function was introduced to correct the hysteresis effects of river discharge, tides and salinity. Based on fixed corrections of long-term effects, dynamic corrections of short-term effects were added to weaken the hysteresis effects. Real-world model application to the Pearl River Estuary obtained satisfactory agreement between predicted and measured salinity peaks, indicating the accuracy of salinity forecasting. Cross-validation and weekly salinity prediction under small, medium and large river discharges were also conducted to further test the reliability of the model. The statistical model provides a good reference for predicting salinity variations in estuaries.


2012 ◽  
Vol 10 (H16) ◽  
pp. 478-479
Author(s):  
Patrick Michel ◽  

AbstractNEOShield is a European-Union funded project coordinated by the German Aero-space Center, DLR, to address near-Earth object (NEO) impact hazard mitigation issues. The NEOShield consortium consists of 13 research institutes, universities, and industrial partners from 6 countries and includes leading US and Russian space organizations. The project is funded for a period of 3.5 years from January 2012 with a total of 5.8 million euros. The primary aim of the project is to investigate in detail promising mitigation techniques, such as the kinetic impactor, blast deflection, and the gravity tractor, and devise feasible demonstration missions. Options for an international strategy for implementation when an actual impact threat arises will also be investigated.The NEOShield work plan consists of scientific investigations into the nature of the impact hazard and the physical properties of NEOs, and technical and engineering studies of practical means of deflecting NEOs. There exist many ideas for asteroid deflection techniques, many of which would require considerable scientific and technological development. The emphasis of NEOShield is on techniques that are feasible with current technology, requiring a minimum of research and development work. NEOShield aims to provide detailed designs of feasible mitigation demonstration missions, targeting NEOs of the kind most likely to trigger the first space-based mitigation action.Most of the asteroid deflection techniques proposed to date require physical contact with the threatening object, an example being the kinetic impactor. NEOShield includes research into the mitigation-relevant physical properties of NEOs on the basis of remotely-sensed astronomical data and the results of rendezvous missions, the observational techniques required to efficiently gather mitigation-relevant data on the dynamical state and physical properties of a threatening NEO, and laboratory investigations using gas guns to fire projectiles into asteroid regolith analog materials. The gas-gun investigations enable state-of-the-art numerical models to be verified at small scales. Computer simulations at realistic NEO scales are used to investigate how NEOs with a range of properties would respond to a pulse of energy applied in a deflection attempt. The technical work includes the development of crucial technologies, such as the autonomous guidance of a kinetic impactor to a precise point on the surface of the target, and the detailed design of realistic missions for the purpose of demonstrating the applicability and feasibility of one or more of the techniques investigated. Theoretical work on the blast deflection method of mitigation is designed to probe the circumstances in which this last line of defense may be the only viable option and the issues relating to its deployment. A global response campaign roadmap will be developed based on realistic scenarios presented, for example, by the discovery of an object such as 99942 Apophis or 2011 AG5 on a threatening orbit. The work will include considerations of the timeline of orbit knowledge and impact probability development, reconnaissance observations and fly-by or rendezvous missions, the political decision to mount a mitigation attempt, and the design, development, and launch of the mitigation mission. Collaboration with colleagues outside the NEOShield Consortium involved in complementary activities (e.g. under the auspices of the UN, NASA, or ESA) is being sought in order to establish a broad international strategy.We present a brief overview of the history and planned scope of the project, and progress made to date.The NEOShield project (http://www.neoshield.net) has received funding from the European Union Seventh Framework Program (FP7/2007-2013) under Grant Agreement no. 282703.


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