bluuebunny/crossref_metadata_2025 huggingface dataset:
The Application of Response Based Design in the Verification of the Banff Riser System
Authors: McCann David , Anderson Keith , Taylor Thomas S. , O’Brien Patrick
Published: March 2009

This paper details work that was conducted during the retrieval and subsequent re-installation of the Banff riser system between September 2000 and March 2001. Originally, deterministic methods were used to design the riser system. It is demonstrated that these methods may not be conservative when compared against stochastic techniques. To ensure a conservative design methodology it is necessary to fully account for the inherent dynamic frequency content of the riser. This is usually achieved using non-linear time domain irregular sea techniques. Time domain irregular sea analysis is computationally expensive in terms of resources and time. This paper presents the results of an alternative method of solution based on the frequency domain approach. Excellent agreement between the results of the time and frequency domain is observed.
Flexible Risers for the Future
Authors: Bindingsbo̸ Arne Ulrik , Slagsvold Lars
Published: March 2009

The offshore industry is often considered very conservative with respect to using new technology. The use of unbonded flexible risers is one of the few technology elements that have been introduced and accepted for use without being fully documented before use. The flexible riser is a great product and has made many field developments possible. When moving into deeper waters with high pressure wells the unbonded flexible riser becomes very heavy and introduces large hangoff forces on the vessel. Experience has indicated that is difficult to carry out proper inspection of these risers. We are therefore investigating riser concepts incorporating new materials and with a simpler cross section that can be used for floating production. Our requirement to a riser is excellent durability, possibility of inspection and installation by reeling. Advanced composite materials have properties such as, low weight, high strength, good durability and very good fatigue performance. These properties make risers manufactured from composite material very interesting. A composite riser can by made by either thermoset or thermoplastic materials. An internal liner must be used, as the composite itself may not be diffusion proof. This liner can be made of metal or plastic and a high quality material may be used, as the amount is modest. The requirement to installation by reeling rules out the metallic inner liner due great mismatch in properties between liner and composite. A very promising concept is the use of a thermoplastic liner together with a thermoplastic composite. This is a riser with excellent mechanical and durability properties and can be installed by the reeling method. An ongoing EU project, AURUM, is investigating this concept in detail. The project has a goal to manufacture an 8″ riser section and includes all the steps in a production process from fibre production to tape winding and analytical modeling.
On the Sensitivity of the Roll Motion of an FPSO
Authors: Kragtwijk Martijn H. J. , Vestbo̸stad Tone M. , Vugts Jan H. , Gudmestad Ove T.
Published: March 2009

This paper describes a theoretical model that has been used to investigate the roll motion of an FPSO. The Statoil operated Norne FPSO at Haltenbanken off central Norway has been used as a reference for the investigation. The model is based on linear potential theory. The viscous roll damping has been incorporated by linearizing the effect. Problems when simultaneously using various computer programs, textbooks and the theoretical model are highlighted. Also areas of caution when working with model tests are identified. The theoretical model has been used to investigate the sensitivity of the roll motion to certain key parameters. The theoretical model has further been compared with results from model tests and with full-scale measurements. The results of these comparisons are described and conclusions and recommendations following the investigation are presented.
Ultimate Strength and Structural Reliability Analysis of FPSO Hull Girder
Authors: Paul Eldho , Thavalingam Appapillal , Das Pumendu K.
Published: March 2009

The aim of this paper is to provide some results from an investigation on available simplified formulations for ultimate strength analysis of the gull girder and the possibility of extending these methods in order to couple with reliability computations. This particular study is based on an analytical method proposed by Paik and Mansour. The procedure is enhanced to include structural reliability analysis of FPSOs based on probabilistic approach where uncertainties for both capacity and loading of the structure are taken into account. The estimation of the Ultimate longitudinal capacity and the probability of failure of the FPSO are carried out by dividing the cross section of the hull girder into beam column elements considering the different loads acting on the hull. The limit state function is formulated considering the loads acting on the hull girder and ultimate capacity. The ultimate capacity of the hull is taken as a function of variety of random variable (e.g. area of cross section and yield stresses of the different ship components, etc). The loads acting on the hull girder, both still water and wave induced are calculated using IACS and DNV rules and margins are provided to take care of the long-term deployment of FPSO at sea. Some results from the sensitivity analysis are also provided which has been carried out to study the influence of several factors on the structural reliability of the ship under extreme wave induced bending moment loads.
Probabilistic Computations of Downtime for Inland Shipping in the Second Maasvlakte
Authors: Hurdle D. P. , Onassis J. , Veldman J. J.
Published: March 2009

This paper deals with the accessibility for inland shipping to several alternatives for the extension of the Maasvlakte in the Port of Rotterdam (Maasvlakte 2). The accessibility is governed by the risks associated with high wind and wave conditions, which can cause structural damage to the ship, excessive intake of water and high loads in the coupling cables of push-barge units. This paper discusses the computational methods for the following aspects: wave conditions in the port area; risk of failure in several failure modes and total downtime. The use of interviews with the skippers of the inland ships is discussed. A summary of the results of the study is also presented.
Consistent Design Codes for Anchors and Mooring Lines
Authors: Dahlberg Rune , Mathisen Jan
Published: March 2009

As the water depth of hydrocarbon discoveries becomes deeper, the technological challenges related to the design of mooring systems increases. Changing from steel catenary mooring systems (CMS) to fibre rope taut mooring systems (TMS) has been accompanied by an immense focus on how to qualify and approve fibre rope material for use in a TMS. This involves items related to specifications for manufacturing, handling and testing fibre ropes, as well as calibration of safety factors to use in the design of TMSs. One consequence of moving to a TMS is that the anchors will have to take more uplift load than in a conventional CMS, which makes the anchors a more critical component of the mooring system than before. The types of anchor normally available to the designer of a TMS are pile anchors, suction anchors and various types of plate anchors. Anchors of all types are designed and installed in ever-deeper water, but the safety of the designed mooring systems varies with the design code adopted. There is thus an obvious need for an industry standard, a design code for each anchor type that is calibrated based on structural reliability analysis using the current experience and knowledge in the industry. This paper compares anchor design codes that use total safety factors (TSF) with the DNV design code that uses partial safety factors and failure consequence classes. Examples of design codes for station-keeping systems that adopt the TSF format are API RP2SK and (assumed herein) the ISO code, which is under development. The comparison demonstrates that use of the safety format adopted in the DNV code provides more flexibility and ensures a uniform safety level of all components in a mooring system than the TSF format. If all types of anchor were designed to the same safety level it would be possible to compare anchors without worrying about differences in safety. A typical approach for calibration of a design code is described.
Reliability-Based Schemes for Control of Riser Response and Dynamic Positioning of Floating Vessels
Authors: Leira Bernt J. , So̸rensen Asgeir , Larsen Carl M.
Published: March 2009

Application of structural reliability methods in relation to online control of dynamic systems is considered. The particular case in focus is dynamic positioning of marine vehicles as related to mechanical limit states for the riser system. The magnitudes of top and bottom angles of the marine risers are considered. These angles are of crucial importance during e.g. drilling and workover operations. The relationship between surface floater motion and angle responses is first considered. The possibility of reducing the maximum angular response levels by dynamic positioning of the floater is then investigated. Typically, minimization of one of the riser top and bottom angles by adjusting the vessel position can only take place at the cost of increasing the other one. Hence, an optimum position should be defined by applying different weights for the two angles. Three different alternatives are considered: (I) The relative weights are kept fixed (II) The relative weights are determined as functions of the respective reliability indices for each of the two angles. (III) A loss function which is purely expressed in terms of reliability indices is introduced. The viability of different schemes of this type is explored by numerical simulation for a specific riser configuration.
Wave-Drift Added Mass of a Cylinder Array Free to Respond to the Incident Waves
Authors: Kinoshita Takeshi , Bao Weiguang , Yoshida Motoki , Ishibashi Kazuko
Published: March 2009

Conventional linear added mass and damping can be obtained when a floating body is forced to oscillate in the calm water. However, with the presence of the incident waves, there exists an alternative source of added mass and damping caused by the nonlinear interactions between waves and low-frequency oscillations. Proportional to the square of the wave amplitude, they are called the wave drift added mass and the wave drift damping. The problem of a circular cylinder array slowly oscillating in both diffraction and radiation wave fields is considered in the present work. The frequency of the low-frequency oscillation is assumed to be much smaller than the wave frequency. Perturbation expansion based on two time scales is performed to simplify the problem. Wave loads including the wave drift added mass are formulated by integration of the hydrodynamic pressure over the instantaneous wetted body surface.
Cost Effective Fabrication of Large Diameter High Strength Titanium Catenary Riser
Authors: Horn Agnes Marie , Hauge Mons , Ro̸stadsand Per-Arne , Bjo̸rnbakk Bjarne , Dahlberg Peer , Fossesholm Terje
Published: March 2009

A large diameter high strength titanium free-hanging catenary riser was evaluated by the Demo 2000 Ti-Rise project, from initiative of the Kristin Field development license. In order to reduce the uncertainties related to the schedule, cost, and special technical issues identified in the work related to a similar riser for future installation on the A˚sgard B semi-submersible platform, a fabrication qualification of a full scale riser in titanium was run. Several full-scale production girth welds were made in an in-situ fabrication environment. The welding was performed on extruded titanium grade 23 (ASTM) pipes with an ID of 25.5″) and wall thickness of 30 mm. The main challenge was to develop a highly productive TIG orbital welding procedure, which produced welds with as low pore content as possible. It is well known that sub-surface pores often are initiation sits for fatigue cracks in high strength titanium welds. This paper describes how a greatly improved productivity was obtained in combination with a high weld quality. NDT procedures were developed whit the main on the reliability to detect and locate possible sub-surface weld defects, volumetric defects such as pores and tungsten particles and planar defects such as lack of fusion. The results from the actual Non Destructive Testing (NDT), the mechanical testing, and the fatigue testing of the subjected welds are presented. The response of the catenary is optimised by varied distribution of weight coating along the riser’s length. A satisfactory weight coating with sufficient strength, bond strength, and wear properties was developed and qualified. The riser is planned to be fabricated from extruded titanium pipes, welded together onshore to one continuous piece. The field coating is added and the riser is loaded into the sea and towed offshore and installed.
Comparative Structural Analyses Between Sandwich and Steel Pipelines for Ultra-Deep Water
Authors: Pasqualino I. P. , Pinheiro B. C. , Estefen S. F.
Published: March 2009

Pipe-in-pipe systems are usually composed of two concentric metal pipes with or without an insulation material in the annulus region. Design requirements for ultra-deep water pipelines motivated the development of a new pipe-in-pipe conception in which the annulus is filled with materials that combine low cost, adequate thermal insulation properties and good mechanical resistance. The aim of this ongoing research project is to evaluate the structural performance of sandwich pipes with two different options of core material. Because of their wide availability and relatively low costs, the materials considered in this study were cement and polypropylene for the annulus, with pipes made of API X-60 grade steel. In this paper, a three-dimensional finite element model considering material and geometric nonlinear behavior was developed. This numerical model was used to perform a parametric study to determine the collapse envelopes of different pipe-in-pipe configurations under combined bending and external pressure. The collapse envelopes were compared with others obtained for steel pipelines of equivalent collapse pressure. The study showed that the pipe-in-pipe systems with either cement or polypropylene cores are feasible options to ultra-deep water pipelines fulfilling concomitantly both the requirements of structural resistance and thermal insulation.
Characteristic S-N Curves for Fatigue Design of Titanium Risers
Authors: Ronold Knut O. , Wa¨stberg Stig
Published: March 2009

A recommended practice for design of titanium risers is currently being developed as part of Det Norske Veritas’ series of standards and recommended practices for offshore structures. A recommendation is given herein for characteristic S-N curves for use in design of titanium risers against fatigue failure. As a basis for this recommendation, a set of statistical analyses of available fatigue test data have been carried out. Separate analyses have been carried out for base material and welds. The analysis results have been interpreted with respect to mean S-N curves as well as 97.7% lower tolerance bounds with 95% confidence. Characteristic S-N curves for base material and welds, which are not non-conservative with respect to these tolerance bounds, have been proposed. The paper presents the assumptions, the test data, the statistical analyses and their results, and the proposed characteristic S-N curves. The areas of application of the proposed curves are discussed with a particular view to stress range interval, material grade, weld position, temperature, and defect size.
Alternative Boundary-Integral Representations of Ship Waves
Authors: Noblesse Francis , Yang Chi , Hendrix Dane , Lo¨hner Rainald
Published: March 2009

The fundamental problem of determining the free-surface potential flow that corresponds to a given flow at a ship hull surface is reconsidered. Stokes’ theorem is used to transform the dipole distribution over the ship hull surface in the classical boundary-integral representation of the velocity potential. This Stokes’ transformation yields a weakly-singular boundary-integral representation that defines the potential in terms of the Green function G and related functions that are no more singular than G. Accordingly, the velocity representation only involves functions that are no more singular than ∇G.
Wave Trapping by Axisymmetric Concentric Cylinders
Authors: Shipway B. J. , Evans D. V.
Published: March 2009

It is both a pleasure and privilege to present a paper on the uniqueness of linearised water waves at this mini-symposium in honour of Professor John Wehausen whose classic review article Surface Waves (with E. V. Laitone) has done so much to influence workers in the field in the forty-two years since its publication. The question of the uniqueness of solutions to the linearised water wave equations was settled once and for all in a paper in the Journal of Fluid Mechanics by M. McIver (1996). She constructed a solution for the motion between a pair of fixed rigid surface-piercing cylinders in two dimensions which decayed at large distances from the cylinders. Soon after she was joined by P. McIver (1997) in producing an axisymmetric example in the form of a fixed rigid surface-piercing toroid of a special shape which supported an oscillatory motion in its interior fluid region whilst the motion in the exterior region decayed to zero. This wave trapping effect or non-uniqueness occurred for a particular relation between the wave frequency and the toroid geometry. In the present paper we show that such a phenomenon can occur for simple geometries also. In particular we show that wave trapping can occur in the annular region between two partially immersed vertical concentric circular cylindrical shells for particular values of radii and frequencies.
Thermal Analysis of Combined Active Heating and Passive Insulation of Deepwater Pipelines
Authors: Su Jian , Regis Clarissa R. , Botto Adriana
Published: March 2009

In this paper, we first present a global heat balance analysis of typical deepwater pipelines for oil and gas production and show that active heating is necessary for long pipelines due to technical limitations of passive thermal insulation systems. Two methods of combined active heating mid passive insulation are then considered. By the first method, active heating is provided by circulating hot water in annulus. Under certain simplifying hypothesis, we provide a close form analytical solution for the temperature profiles of the produced fluid and heat medium. By the second method, active heating is provided by electrical resistance on the inner steel pipe. For this case, we propose a heating method that minimises the power requirement for a given minimum temperature of produced fluid. Numerical results are shown for the second heating method. Significant reduction in power requirement is achieved.
Nonlinear Interaction of Submerged Cylinder With Free Surface
Authors: Makarenko Nikolai I.
Published: March 2009

The fully nonlinear problem on the unsteady water waves generated by submerged moving cylinder is considered. Using the analytic majorant method we prove local in time unique solvability of this problem. For the case when the dimensionless cylinder radius is small, the solution estimate obtained predicts rigorously dipole-like structure for the lowest order far field flow. The strength of dipole concentrated at the cylinder axis depends on the instantaneous wave form and fluid velocity at the free surface. Special case of the lifting accelerated cylinder starting from the rest is studied analytically in more detail.
A Model of Fracture Under Biaxial Loading
Authors: Grekov Mikhail A.
Published: March 2009

An influence of longitudinal load on the crack growth rate in an isotropic elastic-plastic body under biaxial loading is discussed. As a result, the relationship between the crack growth rate and maximum sizes of monotonic and cyclic plastic zones is derived from the dependence of the crack growth on alternating plastic strains near the crack edge. Comparison of the computational results and experimental data confirms this relationship for different cyclic loading conditions at infinity.
A Strongly-Nonlinear Model for Water Waves in Water of Variable Depth: The Irrotational Green-Naghdi Model
Authors: Kim J. W. , Bai K. J. , Ertekin R. C. , Webster W. C.
Published: March 2009

Recently, the authors have derived a new approximate model for the nonlinear water waves, the Irrotational Green-Naghdi (IGN) model. In this paper, we first derive the IGN equations applicable to variable water depth, then perform numerical tests to show whether and how fast the solution of the IGN model converges to the true solution as its level increases. The first example given is the steady solution of the progressive waves of permanent form, which includes the small amplitude sinusoidal wave, the solitary wave and the nonlinear Stokes wave. The second example is the run-up of a solitary wave on a vertical wall. The last example is the shoaling of a wave train over a sloping beach. In each numerical test, the self-convergence of the IGN model is shown first. Then the converged solution is compared to the known analytic solutions and/or solutions of other approximate models such as the KdV and the Boussinesq equations.
Coupled Nonlinear Motion of Floating Structures With Water Columns in Open-Bottom Tanks
Authors: Ma Q. W. , Patel M. H.
Published: March 2009

This paper examines the behaviour in ocean waves of floating structures that incorporate open-bottom tanks on their submerged hull geometry. These tanks contain water columns that can flow in or out through their open bottoms, and may also include a volume of trapped air on the top of such water columns. The trapped air acts as a spring with the motion of the floating structures in ocean waves being influenced by interactions between the vessel, the air springs and the water columns underneath them. During operations, the volume of air above the water columns can be trapped or allowed to flow freely to and from the atmosphere.
The Sinking of P-36
Authors: Barusco Filho Pedro Jose´
Published: March 2009

On March 14th, 2001, the semi submersible platform P-36, with production capacity of 180,000 bopd, which was in operation in Campos Basin in 1360 m of water depth, had a serious accident, which led to the sinking of the unit. This article addresses the reasons for the accident and further sinking, describes the investigation process and all the technical analyses done to support the most probable hypothesis for the event. The inquiry commission, in charge of performing the technical investigation, analyzed the operations on board of the unit, from December 2000 to the day of the accident, the actions the crew took to fight against the fire and the procedures they used to try to keep the stability previous to the abandonment. The commission used design documents, safety and operational files. They did several interviews, mainly with crewmembers, created many hypotheses for the event and performed technical computational analysis for explosion, gas dispersion and structural deformation. This article stresses the details of the most probable hypothesis of the accident and sinking and points out the main causes which were combined singularly, timely interconnected leading to the loss of the unit.
The Applicability of Online Monitoring for the Assurance of Fixed Jacket Structures’ Structural Integrity
Authors: Sanderson D. J. , Price A. G. , Nelson A. , Thurlbeck S. D. , Killbourn S. , Dougan A.
Published: March 2009

Online Monitoring (OLM) measures the acceleration response of platforms to the wave motion with damage being identified by a change in the measured response. This paper discusses a JIP instigated by EQE and Fugro to assess the applicability of OLM to different classes of North Sea jackets. Fugro studied ways of increasing the sensitivity of the method by improving the data collection and interpretation techniques, whilst EQE performed modal and pushover analyses in damaged and undamaged jackets to identify which jackets are suitable for OLM. The study showed that OLM is applicable to most 4-legged structures, but probably not 6- and 8-legged structures.
New Guidance on Fire and Explosion Engineering
Authors: Walker Steve , Corr Brian , Tam Vincent , O’Connor Pat , Bucknell Justin
Published: March 2009

This Paper describes a new approach to explosion loading and response developed by MSL as part of a project to develop Guidance for the Design and Assessment of Offshore Installations against Fire and Explosion accidental events. The Guidance document developed for BP is being considered as one of the source documents of the new Guidance Notes for the UK. This project is in progress and has been financed by UKOOA and the HSE. The Guidance document is based on the risk matrix approach described in API RP 2A (21st edition) and is being considered as one of the source documents for the development of the new API Recommended Practice on Fire and Explosion Engineering. This paper outlines the new thinking which is being incorporated into the new Guidance Notes and the new API standard. The paper concentrates on the areas of explosion loading and response and in particular the use of simplified methods in structural explosion assessment and design.
Remotely Sensed Wind, Wave, and Sea Level for European Sea Climatology
Authors: Bentamy Abderrahim , Hajji Hafedh , Soares Carlos Guedes
Published: March 2009

This paper provides an overview of the analysis of remotely sensed data that has been performed within the scope of a project aiming at obtaining a 40-year hindcast of wind, sea level and wave climatology for the European waters. The satellite data, including wind, wave and sea-level data, are collected for the same areas and are calibrated with available and validated measurements. It will be used to be compared with the hindcast results, so as to yield some uncertainty measures related to the data. This paper describes the type of data that will be used and presents the initial results, which concern mainly remote sensed wind data.
A Non-Linear Tubular Joint Response Model for Pushover Analysis
Authors: Dier Adrian F. , Hellan Oyvind
Published: March 2009

Pushover analyses are increasingly being used by the offshore industry in the assessment, and design, of offshore structures. Traditionally, such analyses are conducted on the basis that the tubular joints are assumed to be rigid. Whereas special finite elements for capturing the buckling behaviour of beam-columns have been in existence for some years, there has been no comparative approach for dealing with tubular joints, that is until the work reported in this paper. The work was carried out under the aegis of a major international Joint Industry Project concerned with the development, testing and calibration of an efficient analysis tool that allows the non-linear behaviour of tubular joints within a space frame structure to be appropriately accounted for. Pushover analysis incorporating proper joint behaviour can now be efficiently conducted with minimal user intervention. The paper describes the algorithms that were developed to simulate the non-linear behaviour of tubular joints under combined axial, in-plane and out-of-plane moment loads, across the full range of the load-deformation response. The (uncoupled) P-δ and M-θ responses were first represented by powerful, yet simple, equations whose coefficients were established by reference to test data. Coupling, for combined loads, was achieved by adapting plasticity theory algorithms. The interaction of chord loads on joint response and how the issue of joints having mixed K/X/Y classification is encompassed in the algorithms is addressed. Ductility limits and unloading behaviour are discussed. Finally, testing of the codified algorithms and calibration against frame test data are mentioned. The results demonstrate that frame response is more accurately captured when joint behaviour is taken into account.
Comparing Fatigue Strength From Full Scale Blade Tests With Coupon-Based Predictions
Authors: van Leeuwen Hans , van Delft Don , Heijdra John , Braam Henk , Jo̸rgensen Eric , Lekou Denja , Vionis Pantelis
Published: March 2009

In order to get a deeper understanding of the blade to blade variations and to determine the statistical distribution of the fatigue strength of rotor blades, 37 small rotor blades have been tested in static and fatigue loading. The blades are 3.4 m commercially available blades adapted to the needs of the project. Next to these blade tests, also coupons of identical material have been tested. The tests have encompassed static flapwise bending tests, flapwise fatigue tests at two different sections of the blade and edgewise fatigue tests. Since some blades could be re-used after a first test, a total number of 42 blade tests has been carried out in three different testing laboratories. The blades showed large deformation and development of creep. After correction for these phenomena, the fatigue strength of the blades seemed very good predictable with the classical Goodman relation using the well known slope parameter of 10.
Application of a Viscous Flow Methodology to the NREL Phase VI Rotor
Authors: Xu Guanpeng , Sankar Lakshmi N.
Published: March 2009

A numerical technique has been developed for efficiently simulating fully three-dimensional viscous fluid flow around horizontal axis wind turbines (HAWT). In this approach, the viscous region surrounding the blades is modeled using 3-D unsteady Navier-Stokes equations. The inviscid region away from the boundary layer and the wake is modeled using potential flow. The concentrated vortices that emanate from the blade tip are treated as piecewise straight line segments that are allowed to deform and convect at the local flow velocity. Biot-Savart law is used to estimate the velocity field associated with these vortices. Calculations are presented under axial wind conditions for a NREL two-bladed rotor, known as the Phase VI rotor, tested at the NASA Ames Research Center. Good agreement with the measurements is found. The computed results are used to develop improved engineering models for the loss of lift at the blade tip, and for the delay in the stall angle at inboard locations. The improved models are incorporated in a blade element-momentum (BEM) analysis to study the post-stall behavior of a three-bladed rotor tested at NREL.
Influence of Transition Modes and Gravity Loads on Rotor Fatigue and Power Control
Authors: Eggers A. J. , Moriarty P. , Chaney K. , Digumarthi R. , Holley W. E.
Published: March 2009

Two classes of transition modes are examined. The first class involves rotor start-up and shut-down in turbulent winds with rapidly varying mean wind speeds. In the start-up mode, coupling can occur between the mean and cyclic pitch control systems which leads to large peaks in blade flatwise moments. These peaks can substantially increase overall fatigue damage. They can be reduced by controlling blade pitch solely with the closed loop control system. Allowing the rotor to freely rotate at wind speeds below start-up eliminates blade moment peaks in the transition to low speed operation, with the result that closed loop control further increases blade fatigue life. These control alterations reduce power fluctuations but appear to have no significant effect on overall energy capture. Blade pitch control in the shutdown transition mode is restricted solely to mean pitch angle and no control coupling problems are encountered. The second class of transition modes studied is operation from below to above rated wind speed. This transition was previously idealized as an abrupt change from variable to constant rotor speed operation with mean blade pitch angle increased rapidly to hold mean power constant up to rotor shut down. This causes a very sharp peaking of mean moment at rated wind speed which increases blade fatigue damage. This peaking is reduced by smoothing the controlled variation of mean blade pitch angle over a range of wind speeds from below to above rated. As a result, rotor blade fatigue life is substantially increased, and energy capture is somewhat reduced in both open and closed loop operation. Thus there is a trade-off between energy capture and fatigue life which is examined. The comparative effects on blade fatigue life and weight of turbulence induced and 1P gravity loads are examined for large scale rotor blades. The bending strength of each blade in the out-of-plane and in-plane directions at the critical root location was assumed to be the same for full span pitch control requiring a cylindrical cross-section at the root. It is indicated that turbulence induced fatigue damage dominates over that due to gravity for rotor radii up to about 40m and near 2 MW rated power, depending on the number of rotor blades. This open loop result is unaltered in closed loop operation if blade weight is reduced to maintain the same fatigue life. Tradeoffs between rotor blade weight and energy capture in open and closed loop control operation are examined.
Predicting the Long Term Distribution of Extreme Loads From Limited Duration Data: Comparing Full Integration and Approximate Methods
Authors: Fitzwater LeRoy M. , Winterstein Steven R. , Cornell C. Allin
Published: March 2009

In this paper we present a methodology for proceeding from the short-term observations of extreme loads to the long-run load distribution of these extreme events, for both flap and edge loading in both operating and parked wind turbine conditions. First a general approach utilizing full integration, where numerical routines are used to directly integrate the conditional short-term load distribution over the annual occurrence of wind speeds and turbulence intensities, is presented. Then starting from this general approach, a qualitative analysis is undertaken to explore the extent of the contribution of each of the three variables, in the governing equation, to the variability in the long-term extreme load distribution. From this analysis, lower order models are considered, where instead of using the entire distribution of the variables, a constant fractile of the short-term extreme load distribution, turbulence intensity distribution, or both are used. Finally recommendations are given to guide the analyst to decide when simpler, yet robust, methods which account for sufficient variability in extreme load event may be employed with confidence.
System Control Based on a State Model Specifying, Design-In and Measuring of the Availability
Authors: Richters H. , Rademakers L. , Rajsekhar B. , Braam H. , Versteegh C. , Wubben F.
Published: March 2009

In the IEC 61400-12 standard “Wind turbine power performance testing”, the availability of a wind turbine is defined as: “the ratio of the total number of hours during a certain period, excluding the number of hours that the wind turbine could not be operated due to maintenance or fault situations, to the total number of hours in the period, expressed as a percentage” [1]. It seems to be a clear definition, however in practice all parties involved, and often commercially bounded by guarantees, cannot interpret it unambiguously. This has all to do with the fact that the actual measuring and tracking is not done in a structured manner, mainly because it is not clear what the various (sub-)states of a wind turbine can be, and which sub-states have to be considered as available or not, and also for discerning who is liable. Moreover, due to heavy operation conditions and potential unintended built-in weaknesses, the ultimate availability of a wind turbine measured over the lifetime of 20 years, can easily tail off by 10% to 25%. Directly related to availability, the return on investment (ROI) will even decrease with a higher proportional part. Consequently, availability is a serious issue for manufacturers and investors, and may have extensive commercial implications. To better understand and improve the availability, from the beginning of the design process, this article presents the ‘State Model for Wind Turbines’. It underpins the strategy to optimize the availability versus the total costs. Furthermore the article provides some practical tools for specifying, design-in and measuring of the final availability.
Load Control for Turbine Blades: A Non-Traditional Microtab Approach
Authors: Yen Nakafuji D. T. , van Dam C. P. , Michel J. , Morrison P.
Published: March 2009

Active flow control and load mitigation concepts developed for traditional aeronautical applications have potential to decrease torque, bending and fatigue loads on wind turbine blades and to help increase turbine life. Much of the early work in flow control focused on steady aerodynamic benefits. More recent technologies have focused on unsteady flow control techniques which require a deeper understanding of the underlying flow physics as well as sensors to record the various time-dependent aerodynamic phenomena and fast actuators for control. This paper identifies some developmental control concepts for load mitigation along with a new translational microfabricated tab concept available for active flow and load control on lifting surfaces and explores their applicability for wind turbine rotor blades. Specifically, this paper focuses on experimental results based on an innovative microtab approach for unsteady, active load control. Previous papers on this effort by Yen et al. focused on the multi-disciplinary design methodology and the significant lift enhancement achieved using these micro-scale devices. The current research extends the effort to include dynamic results with discontinuous tab effects, effects on drag, and lower (pressure side) and upper surface (suction side) tab deployment effects for the prototype airfoil as well as for the S809, a representative wind turbine airfoil. Results show that the microtab concept can provide macro-scale load changes and is capable of offering active control of lift and drag forces for load alleviation.
Inflow and the Fatigue of the LIST Wind Turbine
Authors: Sutherland Herbert J.
Published: March 2009

The Long-term Inflow and Structural Test (LIST) program is collecting long-term, continuous inflow and structural response data to characterize the spectrum of loads on wind turbines. A heavily instrumented Micon 65/13M turbine with SERI 8m blades is being used as the primary test turbine for this test. This turbine is located in Bushland, TX, a test site that exposes the turbine to a wind regime representative of a Great Plains commercial site. The turbine and inflow are being characterized with 60 measurements: 34 to characterize the inflow, 19 to characterize structural response, and 7 to characterize the time-varying state of the turbine. In this paper, the inflow and structural data from this measurement campaign are analyzed to determine the correlation of various inflow descriptors with fatigue loads. The inflow is described by various parameters, including the mean, standard deviation, skewness and kurtosis of the wind speed, turbulence intensity, turbulence length scales, Reynolds stresses, local friction velocity, Obukhov length and the gradient Richardson number. The fatigue load spectrum corresponding to these parameters is characterized as an equivalent fatigue load. A regression analysis is then used to determine which parameters are correlated to the fatigue loads. The results illustrate that the vertical component of the inflow is the most important of the secondary inflow parameters on fatigue loads. Long-term fatigue spectra illustrate that extrapolation of relatively short-term data to longer times is consistent for the data reported here.
Pollen viability of some Populus species as indicated by in vitro pollen germination and tetrazolium chloride staining
Authors: Rajora Om P. , Zsuffa Louis
Published: March 2009

The viability of pollen of Populus deltoides, P. maximowiczii, and P. nigra was assessed by in vitro germination and by use of 0.5% 2,3,5-triphenyl tetrazolium chloride (TTC) staining techniques. An agar medium with 10% sucrose resulted in maximum germination of P. deltoides and P. nigra pollen, while the medium with 20% sucrose was a optimal fo P. maximowiczii. Pollen staining in TTC for 1 h at 30 °C gave a good indication of pollen viability as determined by germination and seed set in poplar breeding programs. Significant differences in viability were observed among species, but not among clones and replications.
Interaction of calcium with indole-3-acetic acid and kinetin during the formation of local lesions in bean (Phaseolus vulgaris) by alfalfa mosaic virus
Authors: Tu J. C.
Published: March 2009

A study was conducted on the interaction of Ca2+ with 3-indoleacetic acid (IAA) and kinetin on local lesion formation by alfalfa mosaic virus on bean leaves. Local lesion number was reduced when IAA solutions alone were applied as postinoculation sprays, as compared with water sprays. The reduction was slight at 10−4 and 10−5 M but was large at 10−3 M. Although addition of 0.03 M CaCl2 to 10−4 and 10−5 M IAA sprays reversed the effect of IAA on local lesion formation, addition of the same concentration of calcium to 10−3 M IAA had little effect on local lesion production. Kinetin, except at the 10−4 M concentration, caused no increase in the number of local lesions, as compared with treatment with distilled water. However, with 0.03 M CaCl2 added, the local lesion production at all kinetin concentrations increased significantly over distilled water or 0.03 M CaCl2. The sizes of local lesions on leaves sprayed with 10−3, 10−4, and 10−5 M IAA were reduced by approximately 52, 26, and 10%, respectively, and on leaves sprayed with kinetin by approximately 44, 26, and 24%, respectively. Addition of 0.03 M CaCl2 to IAA and kinetin lessened their effect on the size of local lesions but did not eliminate the effect totally.
Flowering pattern and fruit production in the dioecious shrub Oemleria cerasiformis (Rosaceae)
Authors: Allen Geraldine A.
Published: March 2009

Male plants of Oemleria cerasiformis have a larger flower display and a longer flowering period than females, and tend to show greater phenological variability. Male inflorescences generally begin to flower sooner than females, but reach their peak and finish flowering later. Their longer blooming period is mainly the result of less synchronous flower opening in males. In both sexes flowering tends to be completed more rapidly in later inflorescences. Fruit set in females is positively correlated with time of flowering (r = 0.313) and inflorescence size (r = 0.421). Hand-pollination of female flowers increased fruit set in most inflorescences, indicating that reproductive success in female O. cerasiformis may be pollen limited.
A detailed procedure for the intranuclear microinjection of plant protoplasts
Authors: Reich Terry J. , Iyer V. N. , Scobie Bruce , Miki Brian L.
Published: March 2009

Procedures and equipment have been developed for the efficient intranuclear microinjection of plant protoplasts. The manipulation and culture of protoplasts was facilitated by the use of an environmentally controlled cabinet and video recording equipment. Microinjection rates of 80–100 nuclei/h were routine. The delivery of volumes as small as 10−17 L was easily controlled with a custom-designed microinjection syringe system. Individual protoplasts were recovered with 90% efficiency with the assistance of microscopie grid patterns photolithographically applied to cover slips.
A CELLULAR AUTOMATON MODELING THE STRUGGLE TO CONTROL THE MEDIA
Authors: BOCCARA N.
Published: March 2009

A free and fair press is an essential condition for democracy. In many western countries, the media production, distribution, ownership, and funding are dominated by corporations, and therefore governed by the idea of maximizing profits for the investors making freedom and fairness of the press very questionable. There exist, however, a number of political activists who, by writing books and articles, and giving talks, are fighting to free the media from the influence of big corporations. This paper presents a simple cellular automaton model of this struggle.
SCALINGS OF A MODIFIED MANNA MODEL WITH BULK DISSIPATION
Authors: CHEN CHIEN-FU , LIN CHAI-YU
Published: March 2009

This study incorporates bulk dissipation described by a losing probability f into a modified Manna model on an L × L square lattice. The crossover behavior between bulk and boundary dissipation is investigated using the characteristic lengths produced by bulk dissipation. The toppling number Nn and area Na are studied. For a probability distribution of Ns, [Formula: see text] where s = n or a, the scaling form including the finite-size scaling (f = 0) and the critical scaling (L → ∞) are determined. Subsequently, this paper investigates the joint probability distribution [Formula: see text] and provides the scaling relation between the toppling number and area.
A SIMPLE VARIATIONAL PRINCIPLE FOR CLASSICAL SPINNING PARTICLE WITH ANOMALOUS MAGNETIC MOMENTUM
Authors: POL'SHIN S. A.
Published: March 2009

We obtain Bargmann–Michel–Telegdi equations of motion of classical spinning particle using Lagrangian variational principle with Grassmann variables.
Human respiratory mechanics demonstration model
Authors: Anderson Janelle , Goplen Chris , Murray Lynn , Seashore Kristen , Soundarrajan Malini , Lokuta Andrew , Strang Kevin , Chesler Naomi
Published: March 2009

Respiratory mechanics is a difficult topic for instructors and students alike. Existing respiratory mechanics models are limited in their abilities to demonstrate any effects of rib cage movement on alveolar and intrapleural pressures. We developed a model that can be used in both large and small classroom settings. This model contains digital pressure displays and computer integration for real-time demonstration of pressure changes that correspond to the different phases of breathing. Moving the simulated diaphragm and rib cage causes a volume change that results in pressure changes visible on the digital sensors and computer display. Device testing confirmed the model's ability to accurately demonstrate pressure changes in proportion to physiological values. Classroom testing in 427 surveyed students showed improved understanding of respiratory concepts ( P < 0.05). We conclude that our respiratory mechanics model is a valuable instructional tool and provide detailed instructions for those who would like to create their own.