bluuebunny/crossref_metadata_2025 huggingface dataset:
Predicting the Fatigue Life of Long Dents in Petroleum Pipelines
Authors: Rinehart Adam J. , Keating Peter B.
Published: March 2009

A full scale experimental study has demonstrated that long, unrestrained pipeline dents typically experience fatigue cracking in the dent contact region and have significantly shorter fatigue lives compared to other dent types studied. Furthermore, these dents often fully reround under normal pipeline operating pressures, making them difficult to reliably detect and assess using existing depth-based approaches. Several conditions unique to the dent contact region accelerate fatigue damage accumulation and are considered in a case-specific long dent fatigue life prediction method. First, the contact region develops significant bending stresses that contribute to a higher rate of fatigue crack growth. Second, history dependent, thru-thickness residual bending stresses that may have a significant influence on fatigue behavior are present in the contact region as a result of plastic deformation associated with dent formation and subsequent rebounding. A method for predicting the fatigue life of long dents that accounts for these factors is presented here and is used to analyze specific cases for which laboratory data is available. Nonlinear finite element modelling of the dent life cycle, including the indentation and rebounding phases, is used to determine local stress range behaviors and residual stress distributions. The application of appropriate fracture mechanics based models of fatigue is discussed and demonstrated. Fatigue life predictions are made on a case by case basis for situations studied in the laboratory so that the validity and accuracy of the approach presented here may be studied.
An Efficient Finite Element for the Study of Drag Chains for a Floating Pipeline
Authors: Mainc¸on Philippe , Passano Elizabeth , Nielsen Finn-Gunnar
Published: March 2009

In areas with very uneven ocean bottom topography, the floating pipeline concept may be used. An example is the Ormen Lange gas field west of Norway. The floating pipeline has positive buoyancy and is moored to the seafloor at regular intervals by tethers. Before the tethers are installed, drag chains will keep the pipeline in position. To study the effect of the drag chains on the pipe installation, its static configuration and its dynamic behavior, it would be very inefficient to model each drag anchor using cable elements. This would require a very high number of elements and small time-steps, while the details of the forces in the chain are not critical in the pipeline design. Instead, a non-linear element has been developed that precisely represents the quasi-static behavior of a complete drag chain. To determine reaction forces at the top end of the chain given displacements of the top, the length of dragging chain necessary to balance the forces acting on the top is found by iteration. Proof is provided that the iteration is unconditionally stable. This iteration makes use of the classical catenary solution for the hanging part of the chain, combined with a model of the configuration of the fraction of the chain resting on the seabed. This configuration can be arbitrary, so that any combination of straight chain, heaps and coils resulting from the history of the displacement chain is accounted for. The element behaves in a coherent way also if the whole length of chain is being dragged on the seabed, lifted clear of the seabed, or landed back on the seabed. The incremental stiffness matrix is found by numerical derivation of the reaction forces with respect to the displacements. The element is designed for use in non-linear static or non-linear time domain analyses. It has been implemented in the riser and pipeline analysis program RIFLEX and successfully tested.
Coupled Mooring Analysis and Large Scale Model Tests on a Deepwater Calm Buoy in Mild Wave Conditions
Authors: Bunnik T. H. J. , de Boer G. , Cozijn J. L. , van der Cammen J. , van Haaften E. , ter Brake E.
Published: March 2009

This paper describes a series of model tests aimed at gaining insight in the tension variations in the export risers and mooring lines of a CALM buoy. The test result were therefore not only analysed carefully, but were also used as input and to validate a numerical tool that computes the coupled motions of the buoy and its mooring system. The tests were carried out at a model scale of 1 to 20. Captive tests in regular and irregular waves were carried out to investigate non-linearities in the wave forces on the buoy for example from the presence of the skirt. Decay tests were carried out to determine the damping of the buoy’s motions and to obtain the natural periods. Finally, tests in irregular waves were carried out. The dynamics of the mooring system and the resulting damping have a significant effect on the buoy’s motions. A numerical tool has been developed that combines the wave-frequency buoy motions with the dynamical behaviour of the mooring system. The motions of the buoy are computed with a linearised equation of motion. The non-linear motions of the mooring system are computed simultaneously and interact with the buoy’s motions. In this paper, a comparison is shown between the measurements and the simulations. Firstly, the wave forces obtained with a linear diffraction computation with a simplified skirt are compared with the measured wave forces. Secondly, the numerical modelling of the mooring system is checked by comparing line tensions when the buoy moves with the motion as measured in an irregular wave test. Thirdly, the decay tests are simulated to investigate the correctness of the applied viscous damping values. Finally, simulations of a test in irregular waves are shown to validate the entire integrated concept. The results show that: 1. The wave-exciting surge and heave forces can be predicted well with linear diffraction theory. However, differences between the measured and computed pitch moment are found, caused by a simplified modelling of the skirt and the shortcomings of the diffraction model. 2. To predict the tension variations in the mooring lines and risers (and estimate fatigue) it is essential that mooring line dynamics are taken into account. 3. The heave motions of the buoy are predicted well. 4. The surge motions of the buoy are predicted reasonably well. 5. The pitch motions are wrongly predicted.
Investigating the Response of Offshore Foundations in Soft Clay Soils
Authors: Byrne B. W. , Cassidy M. J.
Published: March 2009

A series of tests were conducted in a drum centrifuge with the aim of investigating the performance of typical offshore foundations on soft normally consolidated clay. The foundations consisted of spudcan footings and suction caissons. These types of foundations are being considered for use in various offshore applications including as foundations for mobile drilling rigs (jack-ups) and offshore wind turbines. A special loading device was designed so that combined loading could be applied to the footing. This device could apply the same ratio of horizontal to moment loading as that applied to the foundations of mobile drilling units. The main aim of the investigation was to compare how the performance changes as the foundation is varied. This is important when considering the use of a jack-up rig for a permanent facility, a concept that is increasingly being considered. In such a case there are concerns about the long-term suitability of the spudcan footing, with the amount of sustainable rotational fixity being of particular interest. A total of 64 experiments were carried out investigating areas that include a) comparing the vertical loading response in both compression and tension, b) using a fixed arm to apply predominantly horizontal loading, and c) using a hinged arm to apply a distinct ratio of horizontal to moment loading. Interestingly in the case of the spudcan footing considerable back-flow of the soil was observed during the installation phase. The combined load response of spudcans under these conditions is an area that has not been investigated thoroughly.
Integrity Monitoring of Flexible Risers by Optical Fibres
Authors: Berg Arne , Risho̸j-Nielsen Niels Jo̸rgen
Published: March 2009

The use of fibre optic sensing technology for integrity monitoring of flexible risers has been demonstrated. A technique for integration of the sensors along the tensile armouring has been developed and used in testing of a full-scale riser where the strain in the tensile armour was measured. The integration technique is also applicable to fibre optic sensors for other measurands. The test riser was exposed to a fatigue test of 612 000 bending cycles. The strain measurements provided new and important data about the conditions in the annulus of a riser during operation. The small diameter of optical fibres (OD = 0.125mm) and the multiplexing features of sensors based on fibre Bragg gratings (FBG) make it possible to realise various sensing systems in the riser annulus. A possible combination of different fibre optic sensors is outlined.
Modeling of Seabed Liquefaction and Other Processes Responsible for Mine Burial
Authors: Brandes Horst G. , Riggs H. Ronald
Published: March 2009

A new Office of Naval Research Program is focusing on developing new mine burial prediction models for a number of processes that have been identified for shallow water environments. These processes are briefly reviewed and preliminary modeling aspects and numerical computations for seabed liquefaction due to surface water waves are presented. Both a deterministic and a possible empirical approach are discussed.
Flexure Behavior of Composite Spoolable Tubes
Authors: Ochoa Ozden O. , Rodriguez Douglas E.
Published: March 2009

Composite tubes are a realistic alternative to metals in many offshore applications, offering high specific stiffness and strength as well as tailorability to sustain environmental loads [1]. Furthermore the manufacturing options that are available enable them to be coiled onto spools for ease of storage, handling, and ease of installation. Some current applications of inland spoolable composite tubulars include buried and above ground flowlines, pipeline relining applications, and downhole injection strings [2]. Our objective is to develop a synergistic methodology that integrates testing and computational modeling to identify the minimum spool radius for storage without introducing damage in the composite tube. Four-point flexure tests are conducted to simulate the spooling conditions. The computational models are based on the two dimensional shell elements of ABAQUS finite element package. These models incorporate non-linear geometry effects as well as a user material subroutine with residual stresses to predict damage progression. Parametric studies are conducted to assess the effects of lay-up, geometry, and constitutive material on the flexural behavior of the composite tubes and compared with the experimental data.
A Universal Reduced Damping Parameter for Prediction of Vortex-Induced Vibration
Authors: Vandiver J. Kim
Published: March 2009

A dimensionless parameter, Su, is proposed which enables a clear presentation of vortex-induced vibration response data in sheared and uniform flows. The ability of the parameter to account for the effects of damping, flow velocity and power-in length is demonstrated with response data from an unusual set of experiments conducted by SHELL Development Co. The historical relationship of the new parameter to the earlier work of Owen Griffin is also presented.
Prediction of Slamming Occurrence on Catamaran Cross Structures
Authors: Grande Kristoffer , Xia Jinzhu
Published: March 2009

In this paper, we study the problem of wave slamming on the cross structures of both fast ferry type catamarans and ocean going racing sailing catamarans. The emphasis is given to the prediction of the statistical distributions of slamming occurrence and slamming pressure magnitudes in a random seaway. A partly non-linear high-speed strip theory sea-keeping program is used to calculate the vessel motions and the relative motions between any part of the hull and the sea surface, including slamming impact velocity. Impact velocities are classified in 5 groups, and slamming pressures calculated for each group. To calculate vessel motions of heeled sailing catamarans a strip method for an asymmetric multi-hull is developed; the theory and initial results are presented. An investigation into the effect of sail forces on motions and slamming occurrence is also performed. The sail forces are found to be an important factor in predicting motions of sailing catamarans. The procedure proposed in this paper gives the necessary information to estimate the maximum slamming pressures the vessel is likely to encounter and equally importantly the expected frequency of lighter slams, which is useful for fatigue calculations.
Ocean Nutrient Enhancer: Creation of Fishing Ground Using Deep Ocean Water
Authors: Ouchi Kazuyuki , Ogiwara Seiko , Kobayashi Eiichi , Fukumiya Kenji , Yonezawa Masayuki , Kato Ken
Published: March 2009

The project to create the fishing ground in the open ocean by rising Deep Ocean Water (DOW) and discharging it in the euphotic layer where photosynthesis can be done by DOW’s rich nutrient salt has been carried out since April 2000, sponsored by Japanese Government Fisheries Agency and Marino-Forum 21. The name of this machine is called Ocean Nutrient Enhancer (ONE for short). As the output of the first year research which includes tank tests, computer simulations and feasibility studies, following outline of the ONE’ concept is proposed. • Rising DOW of 500m depth and 500,000m3/day with the special impeller which makes density current in the euphotic region. • Power for driving the impeller is supplied by OTEC (Ocean Thermal Energy Conversion) engine using a cold characteristics of DOW. • Adopting the configuration of submerged spar type as a floating construction to work safely and continuously against the rough sea. • Upending of the riser pipe is considered for the reliable and cost-effective setting up operation. From the above research, the ONE’s effectiveness is confirmed significantly.
Experimental and Numerical Study of Damaged Tubular Members Under Lateral Loads
Authors: Ruggieri Claudio , Ferrari Jose´ Alfredo
Published: March 2009

Structural behavior of dent damaged tubular members by local indentation remains a key issue for the safety and failure assessment of critical structures, including marine and nuclear facilities, oil and gas pipelines. This failure mode most often arises from very large localized plastic deformations caused mainly by excessive or accidental loads such as, for example, during the collision of adjacent risers in deepwater floating production systems (FPS). The complex interaction between the local deformation in the dented region and global bending of the tubular member may severely reduce the plastic collapse load while, at the same time, strongly affecting its load-deflection behavior. This study presents an experimental and numerical investigation of the structural behavior of a dented tubular member under lateral load which is applicable to marine risers. Experimental load-deflection curves measured using a 4 1/2″ O.D. (114 mm) API N80 pipe (580 MPa yield stress) with varying length characterize the plastic response during local indentation and global bending. 3D finite element models are employed to generate numerical solutions describing the large deformation, non-linear behavior for the tested pipes. The experimental results agree well with the numerical results. The analyses provide further insight into the structural response of tubular members and risers which dent damage effects.
Deep Draft Semi Submersible
Authors: Bindingsbo̸ Arne Ulrik , Bjo̸rset Arve
Published: March 2009

High Pressure and High Temperature wells together with harsh environmental conditions puts a tough challenge on the flowline and riser design. The flexible riser which has been the favorite choice for many field developments with subsea wells have several technical limitations. Large gas fields such as Ormen Lange require large bore export risers. Steel risers are the preferred solutions with respect to durability and cost. Unfortunately, it is difficult for steel risers to accommodate the vessel motions of a semi submersible or ship. Heave restricted vessels such as TLP or SPAR are used together with toptensioned risers and surface trees. Based on the limitations of flexible risers Hydro is pursuing extensive research on riser and floater technology. As part of this research program a study on the effect on riser design caused by reducing vessel motions. The main goal is to introduce steel catenary risers (SCR) on semi submersible platforms. The typical draft of a semi submersible production platform is 20–25 m. By reengineering the design of such a platform and increasing the draft from 21 m to 40 m the vessel motions were reduced significantly. Hence, an opening for novel riser solutions was made. ULS and FLS analyses for 10″ and 30″ SCR in 300 and 1000 m water depth were carried out. The key result is that the 10Prime; riser satisfies both the ULS and FLS requirement for both vessel drafts and water depth and the 30Prime; riser satisfies the both the ULS and FLS requirement for the 40 m vessel draft at 1000 m water depth.
Effective Riser Solutions for a Deepwater FPSO
Authors: Zimmermann Charles-Alexandre , Petruska David , Duggal Arun S.
Published: March 2009

With the recent increase of discoveries in the deepwater Gulf of Mexico (GoM) and the rapid deployment of deepwater floating production systems, the design of dynamic risers to produce and export to and from these FPS has quickly evolved in complexity and variety. As one of the attractive solutions for the development of these deepwater discoveries, the Floating Production, Storage and Offloading (FPSO) system offers a serious challenge to the riser system designer. This paper presents detailed results of a three steel risers systems design study to a turret moored FPSO system in 1,370 meters (4,500 feet) water depth in the GoM. The three riser systems considered are the Steel Lazy Wave Riser (SLWR) system, the Tension Leg Riser (TLR) system and the Single Leg Hybrid Riser (SLHR) system. The three riser concepts are shown to be feasible. The paper shows that for the diameter, number of risers and water depth considered, the SLWR is the preferred option. However, under different parameters, the TLR or SLHR may be preferred since they fully decouple the steel portion of the riser from the vessel motions via flexible jumpers. Very often, riser feasibility can only be demonstrated by doing a complete and thorough evaluation as demonstrated in the paper. The results of this paper demonstrate that steel riser options are available and present effective solutions for use on an FPSO system in the GoM.
Sensitivity and Uncertainty Studies for the Modelling of Marine Growth Effect on Offshore Structures Loading
Authors: Schoefs Franck
Published: March 2009

Structural response to extreme events or fatigue loadings and structural integrity are major criteria to be quantified in a rational process of reassessment. It is now well established that the probabilistic mechanics approach gives an efficient means for measuring the relative changing in safety level compared to a predefined requirement. To this aim, effects of marine growth have been largely studied during the last two decades. This natural process of structural colonization is particularly hard to embrace because it leads to various consequences as over-loading effect coming from screen and drag effects, bio-chemical attacks of materials and mask effects for inspections methods. Only effects on loading are studied here. These effects are particularly hard to quantify because of the bio-variety of marine growth, season conditioning, natural cleaning or death of species, severe competition leading to replacement of some species and of course local hydrodynamic conditions. As in situ data collection through inspections is hard to practice and very expensive, lot of works propose experiments respecting scale effects and numerical modelling. Both are needed to perform uncertainty and sensitivity analyses. This paper proposes a numerical analysis of marine growth effects based on Response Surface Methodology. This method is here suggested to provide explicit approximations of load variables acting on offshore structures submitted to extreme events or fatigue loading as Jacket platforms. Then, from a sensitivity analysis, main factors conditioning load effects are pointed out. From a physical analysis of hydrodynamics parameters affecting these dominant variables, their probabilistic modelling is then suggested using available published experiments for several probabilistic characteristics.
Risk-Based Inspection Planning for Mooring Chain
Authors: Mathisen Jan , Larsen Kjell
Published: March 2009

The use of risk-based inspection planning for offshore structural components is becoming quite familiar. This paper describes an application of this technique to mooring chain. In many cases, the technique is based on probabilistic modelling of fatigue crack growth in the structural components, and updating of the failure probability on the basis of inspections. The extension of this basis from a single component to very many components is necessary to tackle series systems, such as mooring chain, where a fatigue fracture can arise in any chain link. The theoretical basis for the analysis is described, including details of the model for stochastic dependency between the chain links. Results are shown that compare failure probabilities for a single chain link and a chain segment. The effects of various levels of inspection coverage are illustrated. An example of a cost optimal inspection plan is developed for mooring chain on an FPSO in the northern North Sea.
Wave Crest Sensor Intercomparison Study: An Overview of WACSIS
Authors: Forristall George Z. , Barstow Stephen F. , Krogstad Harald E. , Prevosto Marc , Taylor Paul H. , Tromans Peter
Published: March 2009

The Wave Crest Sensor Intercomparison Study (WACSIS) was designed as a thorough investigation of the statistical distribution of crest heights. Measurements were made in the southern North Sea during the winter of 1997–1998 from the Meetpost Noordwijk in 18 m water depth. The platform was outfitted with several popular wave sensors, including Saab and Marex radars, an EMI laser, a Baylor wave staff and a Vlissingen step gauge. Buoys were moored nearby to obtain directional spectra. Two video cameras viewed the ocean under the wave sensors and their signals were recorded digitally. The data analysis focused on comparisons of the crest height measurements from the various sensors and comparisons of the crest height distributions derived from the sensors and from theories. Some of the sensors had greater than expected energy at high frequencies. Once the measurements were filtered at 0.64 Hz, the Baylor, EMI and Vlissingen crest height distributions matched quite closely, while those from the other sensors were a few percent higher. The Baylor and EMI crest distributions agreed very well with the statistics from second order simulations, while previous parameterizations of the crest height distribution were generally too high. We conclude that crest height distributions derived from second order simulations can be used with confidence in engineering calculations. The data were also used in investigations of crest and trough shapes and the joint height/period distribution.
Reliability Assessment of a Generic Jacket: Effects of Airgap Choices and Current Modelling
Authors: Haver Sverre , Eik Kenneth Johannesen , Nygaard Einar
Published: March 2009

A simplified reliability assessment is carried out for a generic jacket at 200m water depth. The purpose is to indicate the sensitivity of the annual failure probability to the selected airgap and current design profile. Two example cases are considered. For one case the required airgap is defined by the 10−4 wave crest height, while for the other the required airgap is defined from the 10−2 wave crest height plus an uncertainty margin taken to be 10% of the crest height. For both cases, the required minimum design base shear capacities are determined both using the 10-year current profile (earlier practice at the Norwegian Continental Shelf) and the associated current profile (i.e. the current profile which when used in combination with the n-year wave height yields the n-year load). The investigation shown herein clearly demonstrates that the chosen airgap is a crucial parameter regarding the annual probability of structural failure. It is, furthermore, demonstrated that if a wave-deck impact is required in order to fail the structure (which will be the case for most jackets), the current modeling is not very important. However, if the structure is designed such that failure may occur for wave heights not reaching deck level (either due to a highly utilized design or a very generous initial airgap), the current modeling (both in terms of selected design profile and joint description of wave height and current speed) may be far more important.
Combined Loading Criteria for Titanium Risers
Authors: Aamlid Olav , Aronsen Kristoffer , Ronold Knut Olav , Mo̸rk Kim , Baxter Carl
Published: March 2009

DNV has, in cooperation with partners from the industry, carried out a joint industry project with the aim to develop recommended practice with respect to the design of titanium risers. As a part of this work, calibrated design formulae for combined loading have been established. The considered load situation is a combination of internal overpressure, bending moment and axial force. The data basis for the calibration study encompasses results from 12 finite element simulations with varying diameter to thickness ratio and internal pressure exposed to bending moment and axial force. With the design equation for steel risers, taken from the DNV Offshore Standard (OS-F201) Dynamic Risers, as a basis, the titanium data basis was investigated using state-of-the art methodology with an uncertainty modeling for load effects in compliance with recent research and development projects for risers and pipeline design. The outcome of this work is a design equation with reliability based calibration of safety factors that comply with the overall safety objective in the above offshore standard.
On the Interaction of Waves With Intake/Discharge Flows Originating From a Freely-Floating Body
Authors: Padmanabhan B. , Ertekin R. C.
Published: March 2009

This work is motivated by the many instances of intake/discharge flows from openings on floating or submerged ocean vessels and structures that may affect the wave field around them. Damaged vessels may release oil, or water may enter these vessels through openings. In oil skimming operations, for example, a very thin layer of oil must be skimmed off a large surface area, and therefore, oil skimming vessels require large intakes. Floating OTEC plants also require large intake and discharge volumes to sustain their operations. A linear theory is developed to obtain the motions of a 2-dimensional, freely floating body (from which steady intake/discharge flows originate) that encounters incoming waves. The boundary-value problem is formulated within the assumptions of linear potential theory by decomposing the total potential into its oscillatory and steady components. The steady potential is further decomposed into the double-model and perturbation potentials. The time-harmonic potential is coupled with the steady potential through the free-surface condition. The potentials are obtained by use of the quadratic boundary-element method based on the Rankine source. The effect of the steady intake/discharge flows on the diffraction loads, hydrodynamic force coefficients, as well as the motions of a 2-dimensional prismatic body floating on the free surface are presented. It is shown that the exciting wave forces and the hydrodynamic coefficients other than the damping coefficients are not appreciably affected by the intake/discharge flows of low Froude number for a 100MW floating OTEC plant.
Overview of the FPSO: Fatigue Capacity JIP
Authors: Bergan Pa˚l G. , Lotsberg Inge , Fricke Wolfgang , Franc¸ois Michel , Pisarski Henryk
Published: March 2009

This paper presents an overview of a joint industry project carried out in the period 2001 – 2003 to address the Fatigue Capacity of FPSOs. Numerical investigations and fatigue testing is performed in order to improve the accuracy, robustness and efficiency of finite element modeling and hot spot stress evaluation for typical FPSO details. Design criteria will be developed for fatigue crack growth from the root of fillet welds in typical details in FPSOs including fillet welds around attachments and fillet welds around pipes penetrating deck plates. Fatigue analysis methods for FPSOs with guidelines on determination of side pressures in the water line will be developed. This work will be supported by assessment of actual measurement data from the field and testing in a tank. Methods for planning in-service inspection of FPSOs based on a fracture mechanics and reliability analysis will be developed. Also a procedure for repair of a fatigue crack while the FPSO is on station in the field will be developed.
Experimental Investigation of Airfoil Subject to Harmonic Translatory Motions
Authors: Gaunaa Mac , So̸rensen Jens N.
Published: March 2009

This paper concerns an experimental investigation of a NACA 0015 airfoil subject to harmonic one-degree-of-freedom translatory motion. Specifically, unsteady pressure distributions were measured at a range of incidences and movement directions at reduced frequencies matching real life conditions for the lead-lag motion of wind turbine rotors. From the experimental results, hysteresis loops and aerodynamic damping were computed and compared to results from linear quasi-stationary theory and unsteady potential flow theory. The maximum negative aerodynamic damping was found to take place at moderate stall and an incidence of about 15°, at a movement direction close to the chordwise direction. Comparison with unsteady potential flow theory showed excellent agreement with the experimental data for incidences up to 5°. Linear quasi-stationary theory failed to reproduce the overall features of the aerodynamic damping for incidences above 12°.
Aero-Acoustic Computations of Wind Turbines
Authors: Shen Wen Zhong , Michelsen Jess A. , So̸rensen Jens No̸rkær
Published: March 2009

A numerical algorithm for acoustic noise generation is extended to 3D flows. The approach involves two parts comprising a viscous incompressible flow part and an inviscid acoustic part. In order to simulate noise generated from a wind turbine, the incompressible and acoustic equations are written in polar coordinates. The developed algorithm is combined with a so-called actuator-line technique in which the loading is distributed along lines representing the blade forces. Computations are carried out for the 500kW Nordtank wind turbine equipped with three LM19 blades.
Design of State-Space-Based Control Algorithms for Wind Turbine Speed Regulation
Authors: Wright Alan D. , Balas Mark J.
Published: March 2009

Control can improve the performance of wind turbines by enhancing energy capture and reducing dynamic loads. At the National Renewable Energy Laboratory, we are beginning to design control algorithms for regulation of turbine speed and power using state-space control designs. In this paper, we describe the design of such a control algorithm for regulation of rotor speed in full-load operation (region 3) for a two-bladed wind turbine. We base our control design on simple linear models of a turbine, which contain rotor and generator rotation, drivetrain torsion, and rotor flap degrees of freedom (first mode only). We account for wind-speed fluctuations using disturbance-accommodating control. We show the capability of these control schemes to stabilize the modeled turbine modes via pole placement, while using state estimation to reduce the number of turbine measurements that are needed for these control algorithms. We incorporate these controllers into the FAST_AD code and show simulation results for various conditions. Finally we report conclusions to this work and outline future studies.
Cogging Torque Reduction in a Permanent Magnet Wind Turbine Generator
Authors: Muljadi E. , Green J.
Published: March 2009

Most small wind turbines use permanent magnet (PM) generators. The generators are usually direct-drive (i.e., no gearbox is required). Direct-drive PM generators are characterized by low maintenance and high efficiency. Small wind turbines are usually self-starting and require very simple controls. Cogging torque is an inherent characteristic of PM generators and is caused by the geometry of the generator. Cogging torque affects self-start ability and produces noise and mechanical vibration. Thus, minimizing cogging torque is important in improving the operation of small wind turbines. In this paper, we investigate three design options to minimize cogging torque: uniformity of air gap, pole width, and skewing. Although the design improvement is intended for small wind turbines, it is also applicable to larger wind turbines.
Ultrastructure of acridone alkaloid idioblasts in roots and cell cultures of Ruta graveolens
Authors: Eilert U. , Wolters B. , Constabel F.
Published: March 2009

Histological analysis of Ruta graveolens L. roots and in vitro grown cell suspensions revealed idioblasts with vacuoles containing clusters of droplets thought to be the storage compartment of acridone alkaloids. These idioblasts contained numerous vacuoles of varying sizes rather than the large, single, central vacuole characteristic of most adjacent parenchyma cells. The structure of idioblasts in roots and suspension cultures was identical. Treatment of suspension cultures with fungal elicitors known to increase alkaloid accumulation greatly did not affect the structure of idioblasts.
Le système endophytique d'Arceuthobium oxycedri. I. Organisation, étude cytologique et cytochimique
Authors: Sadik A. , Rey L. , Renaudin S.
Published: March 2009

In the endophytic system or haustorial apparatus that Arceuthobium oxycedri develops inside the parasitized branch of Juniperus, the present work shows that the cortical strands which connect the haustoria are either longitudinal or circular, that they always occur in the host secondary phloem, and that the smallest ones do not contain tracheids. Contrary to the secondary haustoria, in which parenchyma cells and tracheids are irregularly distributed, the primary haustoria have a more elaborate structure. At the ultrastructural level, the endophytic system is characterized by the presence of chloroplasts in all parts, including the tip of the haustoria, where these are, however, less differentiated. These plastids contain starch, but the cells are mainly rich in lipidic inclusions, especially in the deeper parts of the haustoria. Cell walls are always thick and endoplasmic reticulum profiles are locally abundant. In comparison with the corresponding healthy tissues, the host tissues neighbouring the endophytic system also become richer in starch and lipid inclusions.
Pleomorphism and conidiogenesis in Rhinocladiella atrovirens isolated from beetle galleries
Authors: Tsuneda A. , Murakami S. , Nishimura K. , Miyaji M.
Published: March 2009

Three pleomorphic strains of Rhinocladiella atrovirens, a fungus identified as the normally blastic-sympodial anamorphic species, were examined. When freshly isolated from beetle galleries, an Exophiala synanamorph was dominant in cultures, but with repeated transfers it tended to become progressively less prominent, and a Rhinocladiella morph took over. The relative dominance was also influenced by culture media. Various intermediate or reduced forms of these two major synanamorphs appeared in culture. Apparently, interconversion of the Rhinocladiella-type and Exophiala-type proliferation in conidiogenous cells occurred. Transmission electron microscopy of the Exophiala morph revealed that its conidium development and secession differed from the typical enteroblastic-annellidic mode; annellationlike scars on generative pegs were very thin and fragile, and conidium secession was by the development of a separation line resembling a hilum in the nonlayered conidium-delimiting wall. The Phialophora morph reported previously was not encountered in the present study, but a morph resembling Chloridium occasionally occurred on Sabouraud dextrose agar.
Control of fusiform initial orientation in the vascular cambium of Abies balsamea stems by indol-3-ylacetic acid
Authors: Zagórska-Marek B. , Little C. H. A.
Published: March 2009

Fusiform initial reorientation, deduced from changes in tracheid arrangement, was investigated in helical bridges left after Abies balsamea stems were girdled. The first responses included an increase in the number of S- and Z-oriented anticlinal divisions without any change in their ratio, a decrease in fusiform initial length, and the formation of traumatic resin canals. Subsequently, normal tracheid differentiation resumed, the frequency of anticlinal divisions further increased, and there was an increase in the number of oriented intrusive growth events. The orientations of the anticlinal wall and of the intrusive growth were predominantly in the direction that eventually would result in the fusiform initials being aligned parallel to the bridge angle. The application of exogenous indol-3-ylacetic acid to the upper edge of a helical bridge inhibited fusiform initial reorientation, mainly by decreasing the frequency of oriented intrusive growth events. However, immediately below the application point, exogenous indol-3-ylacetic acid also induced the fusiform initials to begin temporarily to realign so as to be perpendicular to the bridge angle. The transport of a pulse of [1-14C]indol-3-ylacetic acid applied to the shoot apex was inhibited 1 day after girdling in both helical and longitudinal bridges, particularly the former, whereas it was inhibited only in helical bridges at the end of a subsequent 11-week growing period. The degree of inhibition in the helical bridges was greater the day after girdling than at the end of the growing period, during which interval fusiform initial reorientation occurred at the bottom of the bridge width. The results support the conclusion that the orientation of fusiform initials is parallel to the direction of indol-3-ylacetic acid transport.
The marine algae of British Columbia and northern Washington: division Rhodophyta (red algae), class Rhodophyceae, order Palmariales
Authors: Hawkes Michael W. , Scagel Robert F.
Published: March 2009

This is a floristic treatment of benthic marine red algae (Rhodophyta) in the order Palmariales that occur in British Columbia and northern Washington. Seven species (including one new species of Palmaria) in four genera are recorded as follows: Halosacciocolax kjellmanii Lund, Halosaccion glandiforme (S. G. Gmelin) Ruprecht, Palmaria callophylloides Hawkes et Scagel, sp. nov., P. hecatensis Hawkes, P. mollis (Setchell et Gardner) van der Meer et Bird, Rhodophysema elegans (P. L. et H. M. Crouan ex J. Agardh) P. S. Dixon, and R. georgii Batters. Rhodophysema minus Hollenberg et Abbott is treated as a taxonomic synonym of R. elegans. An historical background of the Palmariales is provided. Also provided are revised circumscriptions of the family Palmariaceae and genera Palmaria, Halosaccion, and Rhodophysema based on recent life-history studies by other workers that demonstrate the presence of sexual reproduction in several palmarialean taxa. Keys to and descriptions of taxa (at the ordinal, familial, generic, and specific levels), as well as information on synonyms, location of type specimens, type localities, and what is known about the life histories, distribution, seasonality, and habitats of all taxa, are provided. References are given, and representative specimens are cited that document our concept of the taxa and their morphological variability, seasonality, and geographical distributions.
The ecology of Ramalina menziesii. IV. In situ photosynthetic patterns and water relations of reciprocal transplants between two sites on a coastal–inland gradient
Authors: Matthes-Sears U. , Nash III T. H. , Larson D. W.
Published: March 2009

The lichen Ramalina menziesii shows a clear coast–inland gradient in morphology. To investigate whether functional differences in the field were imposed by the environment or were relatively stable phenotypic characteristics, reciprocal transplants were made between coastal and inland habitats in central California. Patterns of gross photosynthesis and thallus water content, together with the driving environmental variables, were measured simultaneously on indigenous and transplanted samples. The comparison showed that thallus water content of the two morphological forms was not significantly different when atmospheric humidity was low. In a humid atmosphere, however, the coastal samples maintained a slightly higher hydration level than the inland samples. This resulted in slightly higher photosynthetic rates when water content was low. At higher hydration levels, the inland samples photosynthesized at a higher rate than the coastal samples. It is possible that these differences are an effect of increased salt load in coastal thalli.
The major weedy biotypes of proso millet (Panicum miliaceum) in Canada
Authors: Bough Marguerite , Colosi Joseph C. , Cavers Paul B.
Published: March 2009

Proso millet, Panicum miliaceum L., has become a problem weed in corn-growing areas of Canada over the last 15 years. Several different biotypes of this weed exist, and one of the features by which they may be distinguished from one another is seed colour. Those plants with dark olive – bronze – black seeds that shatter readily are the most difficult to control. Part of their success as weeds is due to their ability to form a long-term viable seed bank in the soil, making quick elimination from an area impossible. Other biotypes closely resemble crop types and have little dormancy or ability to form a long-term seed bank. Between these two extremes are 'crown' and some 'golden' biotypes, some populations of which have weedy characteristics that may make them more aggressive weeds as the selection process continues. Some biotypes are more readily controlled than others by a combination of management practices, including rotation and spraying. Good chemical control is available for use in some broad-leaved crops (e.g., soybeans), but consistently effective control of this weed in corn has not yet been achieved. Thus, a knowledge of the ecology of the weed can assist in other forms of management. Each biotype that has been discovered in Canada is described and illustrated, together with an outline of ecological characteristics that may aid in its identification and control.
Subcuticular growth of Alternaria brassicae in rapeseed
Authors: Tewari J. P.
Published: March 2009

The early stages of infection by Alternaria brassicae (Berk.) Sacc. in the leaves of the susceptible rapeseed cultivar Candle (Brassica campestris L.) and the moderately susceptible cultivar Altex (B. napus L.) were studied by transmission electron and light microscopy. The pathogen became subcuticular after direct penetration. This was followed by colonization of the epidermal and the mesophyll cells. The histology of early stages of infection was found to be similar in the two cultivars. It is concluded that the basis of differential susceptibility of B. campestris and B. napus to A. brassicae does not reside in the early stages of host–pathogen interaction.
Qualitative and quantitative effects of acid misting and two air pollutants on foliar structures of Liriodendron tulipifera
Authors: Crang Richard E. , McQuattie Carolyn J.
Published: March 2009

One-year-old seedlings of Liriodendron tulipifera (yellow poplar) were exposed to a daily misting regime at pH levels of 5.6, 4.6, 3.6, or 2.6 for a period of 8 weeks. Identical misting conditions supplemented with either a 0.1 ppm fumigation of ozone or NO2 were established for additional treatments. Leaf samples were prepared for light and transmission electron microscopy and light micrographs were used for quantitative analyses of transectional cellular and air-space areas. Leaves exposed to acid misting alone exhibited a cellular collapse at pH 2.6. With increasing acidity, a steady decline in mesophyll air space, an increase in dense inclusion bodies, and a decline in plastid starch content were observed. Plants that received supplemental ozone fumigation during misting exhibited cellular swelling at all pH levels and an increase in total mesophyll area from pH 5.6 to 3.6. While mesophyll cell transectional areas were virtually unchanged from pH 3.6 to 2.6, the air space was significantly reduced. Distinctive differences in apparent cell wall thickness were noted between palisade and spongy cells at pH 3.6 and 2.6. Leaves exposed to NO2 fumigation plus mist macroscopically appeared vigorous and generally showed increased blade thickness with increasing acidity primarily because of changes in mesophyll cell content. Chloroplasts showed prominent stroma protrusions into the cytoplasm. Thus, this study reveals distinctively different quantitative and morphological foliar responses to the misting and fumigation regimes.
The genus Phaeocollybia (Agaricales) in eastern Canada and its biological status
Authors: Redhead S A. , Malloch D. W.
Published: March 2009

Phaeocollybia christinae (Fr.) Heim and P. jennyae (Karst.) Heim are described and illustrated from eastern Canadian collections. Basidiomes of Phaeocollybia christinae have been traced to a narrow attachment point on senescent primary rootlets of spruce. Circumstantial evidence suggests that it is a root parasite.
A HYPERCHAOTIC SYSTEM WITH A FOUR-WING ATTRACTOR
Authors: HU GUOSI , YU BO
Published: March 2009

Recently, there are many methods for constructing multi-wing/multi-scroll or hyperchaotic attractors; however, it has been noticed that the attractors with both multi-wing topological structure and hyperchaotic characteristic rarely exist. A new chaotic system, obtained by making the change on coordinate to the Hu chaotic system, can generate very complex attractors with four-wing topological structure and three positive Lyapunov exponents over a wide range of parameters. The influence of parameters varying to system dynamics is analyzed, computer simulations and bifurcation analysis is also verified in this paper.
LEPTON FLAVOR CONSERVING Z BOSON DECAYS AND SCALAR UNPARTICLE
Authors: ILTAN E. O.
Published: March 2009

We predict the contribution of scalar unparticle to the branching ratios of the lepton flavor conserving Z → l+l- decays and we study the discrepancy between the experimental and the QED corrected standard model branching ratios. We observe that these decays are sensitive to the unparticle scaling dimension du for its small values, especially for heavy lepton flavor output.
AN ALGEBRAIC APPROACH TO THE q-DEFORMED MORSE POTENTIAL
Authors: SETARE M. R. , HATAMI O.
Published: March 2009

We have obtained the creation and annihilation operators directly from the eigenfunction for the general deformed morse potential in one-dimensional Klein–Gordon equation with equally mixed vector and scalar potentials and also in the Schrödinger equation, we show that these operators satisfy the commutation relation of the SU(1, 1) group. Then we have expressed the Hamiltonian in terms of the su(1, 1) algebra.