bluuebunny/crossref_metadata_2025 huggingface dataset:
A Study of Joints Suitable for Lamina Emergent Mechanisms
Authors: Winder Brian G. , Magleby Spencer P. , Howell Larry L.
Published: July 2009

One way to save space and reduce cost in a competitive environment is to use ortho-planar compliant mechanisms which can be made from sheets of material, or lamina emergent mechanisms (LEMs). One major challenge associated with LEM design, however, is creating joints with the desired motion characteristics, especially where complex spatial mechanism topologies are required. This paper presents some important considerations for designing joints for LEMs. A technique commonly used in robotics, using serial chains of revolute and prismatic joints to approximate the motion of complex joints, is presented for use in lamina emergent mechanisms. Important considerations such as linkage configuration and simple prototyping are also discussed.
Fabrication and Design of a Nanoparticulate Enabled Micro Forceps
Authors: Aguirre M. E. , Hayes G. , Frecker M. , Adair J. , Antolino N.
Published: July 2009

A novel fabrication process and design optimization method for a micro forceps is presented. This work is part of a larger research effort to design and fabricate nanoparticulate enabled surgical instruments. The micro forceps is a monolithic compliant mechanism that due to its two-dimensional design can be manufactured using the new fabrication process. The process begins with fabrication of an array of molds on refractory substrates using a modified UV lithography technique. In parallel, engineered ceramic nanocolloidal slurries are prepared for gel-casting into the molds. Mold infiltration takes place via a squeegee technique adapted from screen printing with excess slurry removed using an ethanol wipe. Finally, the photoresist molds are removed with a reactive ion etch (RIE) step, and ceramic parts sintered to full density. Employing this manufacturing technique for the compliant micro forceps design is advantageous because a large number of parts can be produced with a large aspect ratio (≥40:1), sharp edges (∼ 1 μm), and a resolution of 2 μm. Two optimization problems are formulated to determine the effect of dimensional parameters and material strength on the performance of the compliant micro forceps. First, performance is sensitive to small changes in the geometry, indicating that dimensions and shrinkage rates must be carefully controlled during processing. Second, performance can also be improved by using very large aspect ratios and/or improvements in material strength. A sample part manufactured using the new process is presented.
Development of a Compliant Rotary-to-Translational Transmission Mechanism for a Micro-Parallel Kinematic Mechanism
Authors: Bronson Jessica R. , Wiens Gloria J. , Fassi Irene
Published: July 2009

This paper presents the integrated design of an electrostatic comb-drive rotary actuator and a compliant slider-crank mechanism to transmit the motion from a rotary actuator into translational motion. This integrated design yields a transmission exhibiting minimal sliding contact with supporting substrate. This design is applicable to micro-Parallel Kinematic Mechanisms (PKM) for micro/nano positioning and manipulation of optical components including lenses and mirrors. For a 3 degree of freedom micro-PKM, the rotational motion of three electrostatic torsion actuators is converted into translational motion through a compliant transmission device. The compliant transmission is based on a slider-crank mechanism that uses flexible beams for the linkages. The input of the rotary motion through the transmission’s crank yields translational motion of the slider component. The slider is supported via a Roberts straight-line mechanism which yields a suspended slider design and therefore reduced friction and wear within the transmission. Furthermore, the slider component of the transmission provides a linear force-displacement relationship beneficial for embedded sensing. This paper describes the design of the actuation and transmission system and its integration into the kinematics of the micro PKM motion.
Development of a Multi-Project Production Planning and Scheduling System With Agent Technology
Authors: Zhang Xutang , Liu Xinhua , Peng Gaoliang
Published: July 2009

This study intends to propose an intelligent system with agent technology in order to realize integration and cooperation of multi-project production planning and scheduling process. The agent-based system framework, in which various intelligent agents worked together to perform multi-project production planning and scheduling tasks in an autonomous and collaborative way, is put forward. The system consists of three categories of agents and functional definition of each intelligent agent is presented. Moreover, agents communication mechanism and cooperation sequence diagram are proposed. Furthermore, an intelligent algorithm based on fuzzy comprehensive evaluation is designed to resolve competition conflicts among the agents. Finally, an experiment example was illustrated and the algorithm was demonstrated feasible and efficient.
Minimum Vibration Mechanism Design via Convex Programming
Authors: Lim Bokman , Park Frank C. , Yoo Seungjin
Published: July 2009

One means of designing reduced vibration mechanisms is to ensure that the mechanism’s natural frequency be sufficiently greater than the driving frequencies of the actuators. In this paper we consider the problem of determining a mechanism’s mass, inertial, and joint stiffness parameters so as to maximize the lowest natural frequency of the mechanism. We show that this leads to a convex programming problem, which is characterized by global optima that can be found with efficient interior point algorithms. Several case studies involving closed chain mechanisms and hydraulically actuated excavators demonstrate the viability of the design methodology.
Analytical and Experimental Characterization of Parasitic Motion in Flexure-Based Selectively Compliant Precision Mechanisms
Authors: Patil Chinmaya B. , Sreenivasan S. V. , Longoria Raul G.
Published: July 2009

Flexure-based selectively compliant mechanisms with less than six degrees of freedom are capable of meeting the demanding requirements of ultra precision positioning and scanning systems. However, machining imperfections induce undesirable motion and limit the mechanisms precision capability. A spatial kinematics based kinetostatic model is presented here that not only enables determination of inherently spatial parasitic motion due to machining imperfections, but also offers critical geometric insight into the motion characteristics of flexure mechanisms. The analytical development reveals that the geometric errors induced by machining imperfections perturb the special screw systems of motion of ideal flexure mechanisms to their corresponding general screw systems. This insight leads to clearly defined metrics that can capture the non-ideal behavior using screw system theory and is applicable to all selectively compliant mechanisms. This result is illustrated using one and two DOF mechanisms as examples. In the case of rotational DOF flexure mechanisms, the pitch of twist of motion captures the difference between the special and general screw systems and represents the intrinsic parasitic motion. The machining imperfections are regarded as Gaussian random variables with known variance, and the model is used to determine the variance of the pitch of twist via Monte Carlo simulation, leading to determination of the precision capability of the flexure mechanisms. The modeling and analysis is illustrated using one and two DOF rotation flexure mechanisms. Finally, the details of a test setup built to determine the parasitic motion of the one DOF rotational mechanism are presented. Experimental results indicate that the one DOF flexure mechanism is indeed executing screw motion rather than pure rotation.
Geometric Constraint Solving With Solution Selectors
Authors: Kale Vaibhav , Bapat Vikram , Bettig Bernie
Published: July 2009

Current parametric CAD systems are based on solving equality type of constraints between geometric objects and parameters. This includes algebraic equations constraining the values of variables, and geometric constraints, constraining the positions of geometric objects. However, to truly represent design intent, next-generation CAD systems must also allow users to input other types of constraints such as inequality constraints. Inequality constraints are expressed as inequality expressions on variables or as geometric constraints that force geometric objects to be on specific sides or have specific orientations with respect to other objects. To solve problems involving constraints, we use a graph-based constraint solving algorithm that can be used in CAD/CAM/CAE applications. This graph-based constraint solving algorithm, called the Modified Frontier Algorithm with Solution Selection (MFASS), has been implemented at Michigan Technological University to solve equality based constraints in a CAD/CAM/CAE testbed application. The objective of this research was to investigate whether the Frontier Algorithm can be extended to solve geometry positioning problems involving systems of equality and inequality based declarations in which the inequality based declaration are used as solution selectors to choose from multiple solutions inherently arising from these systems. It is hypothesized that these systems can be decomposed by the Frontier Algorithm in a manner similar to purely equality-based constraint systems however they require tracking and iterating through solutions and in many cases may require backtracking through the solution sequence. This capitalizes on the strength of the Frontier Algorithm which solves only one small subsystem at a time with resulting short processing times compared to alternative algorithms. In this research we generate a new algorithm/DR planner for handling inequality constraints, both theoretically and through implementation in a testbed to demonstrate the working of the algorithm.
Computational Analysis of Self-Healing in a Polymer Matrix With Microvascular Networks
Authors: Martinez Lucci Jose , Amano R. S. , Rohatgi Pradeep
Published: July 2009

For the last decade, many researchers have been working to develop self-healing materials, and have obtained good results in the field of polymers, these components with microencapsulated healing agent have exhibited noticeable mechanical performance and regenerative property The research described in this paper applies the concept of self healing to simulate self healing polymer matrix composites, with the aid of models developed by the authors for the manufacturing processes and self-healing behavior. The development of self-healing is a novel idea that has not been totally explored in great detail yet. The concept of self-healing described in this paper consists of simulation of a healing agent dicyclopentadiene (DCPD) inside of a microvascular network within a polymer matrix coating with catalyst forming a self-healing composite (SHC). When this SHC is damaged or cracked, the healing agent by capillary action will flow inside of the microvascular network; when the liquid enter in contact with the catalyst will form a polymer structure and sealing the crack. The study consists of theoretical analysis and Computational Fluid Dynamics of a self-healing polymer. The objective of the study reported here was to find the influence and efficiency of the microvascular network in healing a polymer matrix. To check this effect a computational model was created to simulate the healing treatment, thus a crack was created on the matrix surface piercing the microvascular network filled with healing agent and the method to simulate healing behavior of the composite allows assessment of the effects of the autonomously repairing repeated damage events.
Performance Monitoring of Deepwater Risers
Authors: Thethi Ricky , An Pei
Published: July 2009

Deepwater risers are complex dynamic structures subject to extreme events in the Gulf of Mexico such as hurricanes and high currents. The offshore industry in the Gulf of Mexico is aggressively moving into the ultra deep and developing challenging fields with high pressure, high temperature conditions and corrosive production fluids. Floating production vessels such as semi-submersibles and FPSOs are being selected for these developments and these vessels typically have higher motions than Spars and TLPs used to date. Consequently, the risers become increasingly challenging to engineer and design margins can be significantly reduced. Uncertainties in design basis data, actual response in the field, and component degradation with time can be effectively managed by monitoring the performance of the riser system in service through direct structural monitoring on the riser in conjunction with vessel and environmental monitoring. Such a system forms an integral part of the integrity management program and can allow anomalies to be identified ahead of time to prevent catastrophic riser failure. This paper puts forward the benefits of riser performance monitoring and describes system based architectures for various development scenarios utilizing dry tree vertical top tensioned risers, wet trees with SCRs, and wet trees with free-standing risers.
Time-Dependent Solution for Linear Water Waves by Expansion in the Single-Frequency Solutions
Authors: Meylan Michael H.
Published: July 2009

We consider the solution in the time-domain of water wave scattering by fixed bodies (which may or may not intersect with the free surface). We show how the the problem with arbitrary initial conditions can be found using the single-frequency solutions. This result relies on a special inner product and is known as a generalized eigenfunction expansion (because the operator has a continuous spectrum). We also show how this expansion should be modified when trapped modes are present.
A Three-Dimensional Numerical Modelling Study of the Sound Velocity Profiles in the Persian Gulf
Authors: Sadrinasab Masoud , Kenarkoohi Karim
Published: July 2009

The Persian Gulf connects to the Indian Ocean via the Strait of Hormuz. In this study, a three-dimensional hydrodynamic model (COHERENS) is employed in a fully prognostic mode to derive sound velocity profiles in the Persian Gulf, an evaporation-driven inverse estuary that is governed by import of surface water from the adjacent ocean and export of saline bottom gulf water through the Strait of Hormuz. During spring and summer, a cyclonic overturning circulation establishes along the full length of the Gulf. During autumn and winter, this circulation breaks up into mesoscale eddies, laterally stirring most of the Gulf’s surface waters. Output of the model shows that sound velocity in the Persian Gulf depends mainly on the temperature in the surface layer whereas the bottom layer as well as the southern part of the Gulf depends on temperature and salinity. Maximum sound velocity occurs during summer in the Persian Gulf which decreases gradually moving from Strait of Hormuz to the north western part of the Gulf. A gradual decrease in sound velocity profiles with depth was commonly observed almost at all stations in the Gulf. However, an exception occurred in Strait of Hormuz during winter. The results of the model are very close to previous observations.
Corrosion Fatigue of Steel Catenary Risers in Sweet Production
Authors: Pargeter Richard , Baxter David , Holmes Briony
Published: July 2009

Steel catenary risers (SCRs) are commonly used for deepwater oil and gas developments and the most economic material of construction is generally carbon manganese (C-Mn) steel. These risers suffer cyclic loading principally due to vessel movements, and vortex induced vibration (VIV) from passage of marine currents. For this reason, close attention is paid to fatigue design and girth weld quality, and fatigue testing is commonly carried out on procedure test welds. A further advantage of C-Mn steel is that good quality welds can readily be made, and more importantly, freedom from defects can be assured by reliable ultrasonic inspection. In sweet corrosive environments, when significant hydrogen effects would not be anticipated, a range of environmental effects on fatigue could be envisaged under different conditions, and at different stages of fatigue crack growth. For example, in early stages of growth, corrosion could blunt crack tips, and therefore slow the growth rate, whereas under other circumstances, or later in life, corrosion could provide additional crack extension, and accelerate growth. It has been demonstrated in this programme of fatigue crack growth rate and endurance testing that the most aggressive conditions in terms of corrosivity may not give shortest fatigue lives in testing. The results of tests comparing behaviour in air and in a very highly corrosive aqueous environment at 60°C saturated with CO2 (conditions which could not be sustained in production) have been explained by reference to competing effects of fatigue and corrosion. Comparison has been made with other published data. Important safety implications surrounding conditions for project-specific corrosion fatigue testing for riser design are considered.
The Behaviour of Shallow Cracks in a Pipeline Steel Operating in a Sour Environment
Authors: Holtam C. M. , Baxter D. P. , Ashcroft I. A. , Thomson R. C.
Published: July 2009

Setting conditions for the avoidance of in-service crack growth in aggressive corroding environments has long been a major challenge due to the number of variables that have a significant effect on material behaviour. One area where both experimental data and a validated assessment methodology are lacking is the behaviour of shallow cracks. This paper describes the early results of an ongoing research programme aimed at addressing the shortfall in experimental data to characterise material behaviour in the shallow crack regime, with the long-term aim of improving the understanding and assessment of the early stages of environment assisted cracking (EAC). There is an industry need for a better understanding of material behaviour under these conditions, and for the development of a more robust assessment methodology. API 5L X65 pipeline steel parent material was tested in a sour environment with initial flaw sizes in the range 1–2 mm. Fatigue crack growth rate (FCGR) tests have been performed to investigate the influence of crack depth on crack growth rate (da/dN). Initial results suggest that crack growth rates for deep flaws can increase by a factor of 5–100 compared to air depending on the applied stress intensity range (ΔK). Shallow cracks have been shown to grow up to 130 times faster in a sour environment than in air and up to an order of magnitude faster than deep cracks in a sour environment at the same value of ΔK. Constant load tests have also been performed to investigate the influence of crack depth on the threshold stress intensity factor for stress corrosion cracking (KISCC). Preliminary results suggest that in this case there is no crack depth dependence in the range of flaw sizes tested. While further experimental work is required, the results obtained to date highlight the potential non-conservatism associated with extrapolating deep-crack data. Guidance is therefore provided on how to generate appropriate experimental data to ensure that subsequent fitness for service assessments are conservative.
Construction of the Mega-Frame Platforms Based on Topological Optimization
Authors: Zhao Dong , Zhang Mingzhe , Cai Dongmei , Cai Shaoli
Published: July 2009

The mega-frame platform (MFP) is a new type of antivibration platform using the mega-frame theory. Its construction, or layout, doesn’t have the international, national or industry de facto standards to be referred to. In order to increase the MFP’s performance and decrease its steel consumption, the topological optimization whose purpose is to find out the best use of material is used in the construction of the mega-frame platform. Firstly, the MFP is built with uniform thickness slab. Four pieces of the slabs constitute a huge frustum of rectangular pyramid which is the same function with the jacket for the common jacket platform. When the MFP’s global stiffness which is the objective criterion taking an extreme value subject to the volume reduction under the given loads, the mega-frame platform has the best topological shape. Some material of the huge frustum of rectangular pyramid is removed. And the prismoid’s walls become netlike structures. Secondly, equivalent stiffness dimensional trellis trusses are chosen as the substitute for the reserved material that constituted the netlike structure. Thirdly, the new platform is mode analyzed. The analyses show that the platform has no mode shape distortion and the best static and dynamic performance. Lastly, vibration control simulations of megaplatforms subject to random excitation wave loads are done using FEM software. Results show that the new MFP has better vibration control effect than the traditional jacket platform under the same out loads.
A Comparative Study on the Plastic Formulations of Ship Shell Plating Under Patch Loading
Authors: Hong Lin , Amdahl Jo̸rgen
Published: July 2009

The purpose of the present study is to further develop the response formulation of ship shell plating under general patch loading, considering the effect of finite, permanent deformation. A comparative study is conducted between various formulations for the load-carrying capacity of laterally patch loaded plates with the aid of nonlinear finite element method. The increasing public interest of transportation and resource exploitation in Arctic area gives rise to advances in ice strengthening of ship structures. As a result, the subject of ship shell plating under ice loads has been extensively studied. Similar to ice loads, wave slamming loads, wheel loads of vehicles and accidental loads, e.g. collision and grounding, are all likely to take place over a limited area of the plate, and can be termed as ‘patch loading’. Consequently, the resistance of ship shell plating under ‘patch loading’ is of significant interest. In this study, a recently developed plastic formulation for patch loaded plates is further extended for general patch loading condition, i.e. patch load with limited extension in both length and height direction. After a brief review of the development of the response and design formulations for plates under uniform lateral load and patch load, comparative studies are made in cases of limited and finite permanent deformation with the aid of nonlinear finite element methods. By allowing a certain level of permanent deformation, significant weight savings can be achieved. Some main findings will be concluded from the comparative study. The present formulation may be used as a versatile tool for predicting the resistance of plates under various types of patch loads, notably when finite, permanent deformations are accepted, e.g. in the Accidental (Abnormal) Limit States design.
Study on Salinity Stratification and Distribution in Lingding Yang Estuary
Authors: Yang Mingyuan , Zhang Wei
Published: July 2009

Ling Ding Yang (LDY) estuary is one of the main parts of the whole Zhujiang estuary, which lies in the south sea, China. It is about 60km wide from Hong Kong in the east to Macao in the west and the water areas are approximately 2110 km2. The mixing process of salt water and fresh water in the estuary is influenced by many factors, such as the estuarine geometry, tidal range and ravine flows, etc. In this paper, based on the data from the tidal gauge stations and synchronously surveyed data during July 2003, a study on the temporal and spatial distribution characteristics of salinity was made. According to the observation data, in wet season, the fresh water and salt water mixes with the N parameter between 0.21 and 1.63. The distribution of salinity concentration in the east part of LDY is due to coriolis’ force. The salinity concentration decreases from the sea to the estuary, and there exists apparent division point, Nei Lingding Island. To the south of Nei Lingding Island, it is almost partially mixed, and to the north of Nei Lingding Island, it belongs to highly stratification. At the same time, the stratification parameter and the vertical mean velocity in wet season are compared. The N parameter changes with the velocity of tide flow in a tidal cycle. The value of N in a flood tide is usually larger than that is in an ebb tide. That is to say, the mix intensity is much bigger in the flood tide.
Envelope and Phase Statistics of Large Waves
Authors: Tayfun M. Aziz , Fedele Francesco
Published: July 2009

A theoretical expression derived previously for describing the joint distribution of the envelope and phase of nonlinear waves is verified with wind-wave measurements collected in the North Sea. The same distribution is explored further to derive the marginal and conditional distributions of wave envelopes and phases. The nature and implications of these are examined with emphasis on the occurrence of large waves and associated phases. It is shown that the wave-phase distribution assumes two distinct forms depending on whether if envelope elevations exceed the significant envelope height or not. For envelope elevations sufficiently larger than this threshold, the wave-phase distribution approaches a simple limit form, indicating that large surface displacements can occur only above the mean sea level. Comparisons with the North Sea data confirm these theoretical results and also suggest that large surface displacements and thus large wave heights arise from the constructive interference of spectral components with different amplitudes and phases. Further, large waves with high and sharp crests do not display any secondary maxima and minima. They appear more regular or narrow-banded than relatively low waves, and their heights and crests do not violate the Miche-Stokes type upper limits.
Hydrodynamic Forces and Motion Responses of Feeding Platform and Sea Cages
Authors: Ito Sho , Kinoshita Takeshi , Kitazawa Daisuke , Tsunoda Tomoyuki , Bao Weiguang , Itakura Hiroshi , Fujino Masatoshi
Published: July 2009

With the increasing world demand for seafood and environmental problems in coastal aquaculture, offshore area has been increasingly expected to be utilized for aquaculture. The offshore aquaculture system has fewer effects on the surrounding marine environment through the rapid diffusion of organic wastes from the cultured fish than the coastal one. The offshore area then provides clean waters for cultured fish. On the other hand, the offshore aquaculture system is subject to the harsh natural condition such as typhoon attack. Actually, in the current aquaculture system, the offshore fish cages are submerged every time around 10m below the sea surface to escape from high waves and strong currents. However, the safety of the sea cage against the incident wave has not been examined, while that against the water current has been analyzed by tank model test and numerical simulation. In the present study, therefore, the hydrodynamic forces on the submerged sea cage from the incident wave were investigated by the tank model test, and the motion of the submerged sea cage was observed. As a result of the forced oscillation test, the numerical values of the added mass and damping coefficient of the sea cage scatter according to the wave amplitude for the same frequency of the forced oscillation. The difference in the added mass may be attributed to the effects of ladder and the bending of the net. The current analysis is focused on modeling of the bending of the net. Then the difference was also found in the damping coefficient at the same frequency of the forced oscillation. The damping coefficient based on viscosity was separated by the equivalent linearization using the equation of Morison’s drag force. As a result, the scattering of the damping coefficient was reduced, adjusting the drag coefficient. It is a future study to examine the relationship between each mode of the motion of the sea cage and the adjusted drag coefficient. As for the experiment of the mooring system, the larger mooring force worked on the rope between the cushion float and anchor than that between the cushion float and frame rope of the sea cage. The motion of the submerged sea cage was suppressed so that the mooring force between the cushion float and frame rope was reduced. However, the mooring force depends on the initial tension of the mooring rope, therefore the relationship between the initial tension and the mooring force should be examined as future studies.
Station Keeping Study for WEC Devices Including Compliant Chain, Compliant Hybrid and Taut Arrangement
Authors: Johanning Lars , Smith George H.
Published: July 2009

This paper presents results from the third phase of large scale mooring investigation at the Scapa Flow in Orkney, Scotland, for wave energy applications. It considers the suitability of three slack mooring line configurations, namely, i) compliant chain, ii) complaint hybrid and iii) taut fibre rope arrangement. This investigation is extended with a numerical study analysing the station keeping criteria for the three slack line configurations and that of a taut system for wave energy converter installations. The results are used to discuss the suitability of the individual mooring line configurations and that of the taut arrangement. This paper is partially to provoke a discussion on the advantages of a taut mooring system and raise the issues that need to be solved if they are to be practicable.
Bending Stiffeners: A Parametric Structural Analysis
Authors: de Souza Jose´ R. , Ramos Roberto
Published: July 2009

The bending stiffeners discussed in this paper are ancillary structural components installed on flexible lines at their connections with floating units in offshore oil production systems. The configuration of these accessories must provide the installation with a gradual variation of the bending stiffness near the line’s attaching point, smoothing the curvature and avoiding that the structural bending limit of the flexible line be exceeded, and thus reducing the stress field of the compliant structure therein fixed. Generally modeled as having a simple conical shape, in practice, however, bending stiffeners geometries are not so simple. Indeed, units consisting of four different sections are common. This paper presents a parametric structural analysis of these components by means of an analytically formulated model, which results in a second order non-linear differential equation with variable coefficients. The ensuing mathematical boundary value problem is solved numerically with a code developed in Matlab®, using an internal program based on a collocation method — as opposed to a shooting method. Bending stiffener design and normative issues are also briefly discussed. Finally, solutions obtained previously both analytically and by finite element discretizations are used to validate the analytical solutions obtained herein.
Spatial Evolution of an Extreme Sea State With an Embedded Rogue Wave
Authors: Clauss Gu¨nther F. , Klein Marco , Testa Daniel
Published: July 2009

In the last years the existence of freak waves has been affirmed by observations, registrations and severe accidents. Many publications investigated the occurrence of extreme waves, their characteristics and their impact on offshore structures, but their formation process is still under discussion. One of the famous real world registration is the so called “New Year Wave”, recorded in the North Sea at the Draupner jacket platform on January 1st, 1995. Since there is only a single point registration available, it is not possible to draw conclusions on the spatial development in front of and behind the measurement point which would be indispensable for a complete understanding of this phenomenon. This paper presents a spatial development of the “New Year Wave” being generated in a model basin (L = 120 m, W = 8 m, d = 1 m, scale 1:70). To transfer the recorded “New Year Wave” into the wave tank, an optimization approach for the experimental generation of wave sequences with predefined characteristics is applied. The method is utilized to generate scenarios with a single high wave superimposed to irregular seas. At the end of this optimization process, a control signal for a deterministic wave sequence is obtained. The generated sea state with the embedded “New Year Wave” is measured at different locations in the tank, in a range from 2163 m (full scale) ahead of to 1470 m behind the target position — altogether 520 registrations. The focus lies on a detailed description of a possible evolution of the “New Year Wave” over a large area and time interval. It is observed that the extreme wave at the target position develops mainly from a wave group of three smaller waves. In particular the group velocity, wave propagation and the energy flux of the wave group is analyzed. In addition, the WAVE FORECAST METHOD is applied. This method is based on linear wave propagation and provides a prediction of the wave train a few minutes in advance from a single surface elevation snap shot. The capability of the prediction of approaching extreme wave heights is shown.
Active Control of Vertical Risers Undergoing Vortex-Induced Vibrations
Authors: Fortaleza Eugenio , Creff Yann , Le´vine Jean
Published: July 2009

This paper presents a first control strategy to reduce the vortex induced vibrations (VIV). First, the system equations and an associated modal analysis are presented. This modal analysis shows that, for low damped resonant frequencies, there is a phase shift of ±90° between a periodic external force at the riser’s top, and the generated vibration along the structure. This phase shift is used in the design of the control law to reduce the VIV along the structure. For some operating conditions, simulations show that the control system attenuates the VIV and reduces the vortex shedding synchronism along the structure. Simulations are presented with two different kinds of sea current profiles. The advantages of this strategy are the small external force required to reduce VIV, and the fact that no structural change is required along the structure submerged part. But a displacement sensor near the structure bottom is needed.
Added Resistance of Moonpools in Calm Water
Authors: van ‘t Veer Riaan , Tholen Haye Jan
Published: July 2009

The additional ship resistance due to water oscillations in an open moonpool as constructed in drillships can be obtained through model tests. The oscillation has a dominant frequency and character, and the amplitude increases with forward speed. The resonant oscillation mode can be piston or sloshing. Recent measurements show that both types of oscillation can increase ship resistance to the same magnitude. The sloshing mode dominates in longer moonpools, while piston mode oscillations are dominant in shorter moonpools. Based on two model tests series carried out at Delft University of Technology, a resistance prediction model is constructed for piston type oscillations. The model was verified with a resistance measurement performed at MARIN in the past, showing fair agreement between the predicted and measured resistance increase.
A Procedure for Evaluation, Assessment, and Improvement of Added Mass and Radiation Damping of Floating Structures
Authors: Cao Yusong
Published: July 2009

Currently, the linear diffraction-radiation wave theory is still most-widely used by naval architects and ocean engineers to obtain wave loads on floating structures. The hydrodynamic coefficients (added mass and radiation damping coefficients, wave excitation force transfer functions, second-order wave force functions, etc.) depend only on the shape of the underwater portion of the hull, the wave direction and frequency, and the motion modes. They only need to be evaluated once and stored as a database which can be repeatedly used to calculate the wave loads in different environmental conditions. It is therefore very important to ensure a high quality of the database covering the whole range of wave frequency. This paper presents a practical procedure for the evaluation, assessment and improvement of the added mass and radiation damping coefficients. An accurate semi-analytical method is introduced for the evaluation of the retardation functions and time domain added mass. The quality of the added mass and damping is then assessed using Kramer-Kronig relations. Finally, an iterative method is presented for improving (re-constructing) the added mass and radiation damping so that Kramer-Kronig relations are better satisfied.
Condition Management of HP/HT Pipelines: A New Approach
Authors: Nes Hroar , Etterdal Birger , Svardal Stian
Published: July 2009

StatoilHydro operates a large number of High Pressure/High Temperature (HP/HT) pipeline systems in the Norwegian Sea. These lines connect remote subsea templates to floating processing and storage units. Flowlines are designed for a maximum temperature up to 155 °C and a pressure in the range of 390–500 bar. Design pressure for injection lines are in general 500 bar. In addition to high operating loads, the infield lines are exposed to challenging seabed conditions and a potential for interference with on-bottom trawl gear. The objective of this paper is to present the principles and the methodology used for integrity assessment of the HP/HT lines, which provides the basis for specification of optimum maintenance requirements. The risk of integrity failure, associated with any hot-spot location, is consistently estimated based on safety margins predicted for the actual design criterion and as a function of the pre-defined Safety Class. The developed methodology assumes that the pipeline configuration and associated response parameters are accurately determined for relevant operating conditions. This requires finite element models that are calibrated according to survey data and corresponding operating parameters. A cyclic load history is applied to the post-buckled pipeline model in order to simulate actual operating conditions. Design criteria for relevant degradation and failure modes are established for a wide range of operating configurations and conditions. These criteria are used both to identify potential hot-spots and to estimate the relative utilization. The relative utilization may be estimated for an extreme single event, i.e. a design condition, or due to long term degradation. The risk of integrity failure is then determined as a function of the Safety Class and the relative utilisation, expressing the consequences and the probability of failure, respectively. A risk matrix, configured according to design safety principles, determines the risk of integrity failure. A software interface has been developed to compare and to visualize pipeline simulation results, survey data and corresponding design criteria. This information is used for documentation of the pipeline operating condition, and finally, for specification and follow-up of maintenance measures. The new integrity assessment methodology has been implemented as part of the condition management system for more than 30 HP/HT pipelines operated by StatoilHydro.
On the Use of Linear and Weakly Nonlinear Wave Theory in Continuous Ocean Wave Spectra: Convergence With Respect to Frequency
Authors: Johannessen Thomas B.
Published: July 2009

The basic principle of wave superposition in the analysis of irregular linear wave problems such as the analysis of the wave surface itself or forces on large volume or slender structures, has been used for more than fifty years. Also the extension of the perturbation solution to second and in some cases third order is well known. In the nonlinear extension of the perturbation scheme, the basic idea is that nonlinear interaction between two or, in the third order case, three wave components can take place. The solution may therefore be found for two or three wave components and extended to the interaction of all wave components without further calculation. Whereas this superposition idea is an efficient and accurate method to determine wave loads and properties, the convergence properties with respect to the high frequency tail of the spectrum is often neglected. Many of the terms arising in practical applications increase rapidly as the frequency increases so that their convergence properties in a continuous wave spectrum are strongly dependent on the tail of the wave spectrum. The lack of convergence with respect to frequency will typically lead to a choice of: • Using an equivalent regular wave to represent the problem knowing that a regular wave cannot represent all the relevant physical and statistical properties of the wave field; • Make a sensible truncation of the wave spectrum knowing that the chosen truncation frequency affects the results; • Resort to an engineering solution such as the Wheeler (1970) stretching technique for crest kinematics above the crest. It is the object of the present paper to investigate the requirements to linear and second order problems to converge with respect to frequency. Using the Lindgren (1970) properties of a wave crest in a linear wave field and linear Monte Carlo simulations, it is found that requirements to convergence in a spectrum with an ω−4 and ω−5 tail is very strict indeed. It is further found that it is convenient to distinguish between problems where the linear component itself is not defined and problems where the linear component is defined but where the higher order component is not defined. It is shown that the latter problem may be overcome and an example of this is given.
Numerical Simulations of Ocean Drilling System Behavior With a Surface or a Subsea BOP in Waves and Current
Authors: Morooka Celso K. , Tsukada Raphael I. , Brandt Dustin M.
Published: July 2009

Subsea equipment such as the drilling riser and the subsea Blow-Out Preventer (BOP) are mandatory in traditional systems used in deep sea drilling for ocean floor research and petroleum wellbore construction. The drilling riser is the vertical steel pipe that transfers and guides the drill column and attached drilling bit into a wellbore at the sea bottom. The BOP is used to protect the wellbore against uncontrolled well pressures during the offshore drilling operation. Presently, there is a high level of drilling activity worldwide and in particular in deeper and ultra-deeper waters. This shift in depth necessitates not only faster drilling systems but drilling rigs upgraded with a capacity to drill in the deep water. In this scenario, two general drilling systems are today considered as alternatives: the traditional system with the subsea BOP and the alternate system with the surface BOP. In the present paper, the two systems are initially described in detail, and a numerical simulation in time domain to estimate the system behavior is presented. Simulations of a floating drilling rig coupled with the subsea and surface BOP in waves and current are carried out for a comparison between the two methods. Results are shown for riser and BOP displacements. Critical riser issues for the systems are discussed, comparing results from both drilling system calculations. Conclusions are addressed showing advantages and disadvantages of each drilling system, and indicating how to correct the problems detected on each system.
Detection of Jacket Member Severance Using Structural Instrumentation
Authors: Killbourn Stuart D.
Published: July 2009

Fixed-jacket offshore platforms are susceptible to damage below the water line which may be difficult to observe except by underwater inspections that can be up to several years apart. An instrumentation system installed at deck-level can be used to detect the severance of a jacket member by continuous monitoring of the structural response due to ambient wave loading. Data is presented during a brace failure event that occurred on a North-Sea platform and also for subsequent repair work. The observed changes in structural response are compared to those predicted by finite-element modelling. The ability of this method to detect jacket member failure within hours of severance is an important factor in assessing the risks to personnel as well as maintaining structural integrity. In the case of this jacket member failure, the provisions made by the platform operator meant that the incident was anticipated, planned for and ultimately managed in a way that enabled production at the platform to continue without interruption.
Risk Based Inspection Planning of Ageing Structures
Authors: So̸rensen John Dalsgaard , Ersdal Gerhard
Published: July 2009

There are an increasing number of older installations in use on the Norwegian Continental shelf. Inspections are a key issue in ensuring the safety of an older installation, and the inspection intervals, inspection methods and its reliability are clearly influencing the safety of the installations. Different approaches for updating inspection plans for older installations are considered in order to achieve decreased inspection intervals as the structure are ageing. The most promising method consists in increasing the rate of defects / crack initiation at the end of the expected lifetime. Different system aspects are considered incl. assessment of the acceptable annual probability of failure for one component dependent on the number of critical components. Information obtained from inspection of one component can be used not only to update the inspection plan for that component, but also for other nearby components. An example indicates that a high degree of correlation between the uncertain parameters in different components is needed in order to obtain substantial information which can be used in inspection planning. Fatigue failure of one (or more) components does not necessary imply total collapse of the structure. The importance of each component can be measured by the RIF (Residual Influence Factor) for each component and is illustrated by examples. When an installation becomes older then the number of fatigue critical components can be expected to increase. If the maximum acceptable annual system probability of failure is the same as for a new installation, this implies that the acceptable annual fatigue probability of failure decrease, which again implies more inspections.
Structural Integrity Management Framework for Fixed Jacket Structures
Authors: Stacey A. , Birkinshaw M. , Sharp J. V. , May P.
Published: July 2009

In recent years, a significant amount of effort has been expended by HSE and the offshore industry on the development of good practice for structural integrity management in the new code for offshore structures, ISO 19902. However, a review of the structural integrity management of fixed offshore installations operated on the UKCS has indicated that duty holders adopt varying approaches, in terms of both the methods used and effectiveness. The elements of a framework for the management of the structural integrity of fixed jacket structures are presented.
Ageing of Materials
Authors: Ho¨rnlund Erik , Sævik O̸ystein , Hinderaker Rolf H. , Ersdal Gerhard
Published: July 2009

A considerable part of the structures in the Norwegian part of the North Sea have passed or are close to their design lifetime. Degradation of materials will play an important role in the ageing of these structures and the evaluation of their safety. Hence, Petroleum Safety Authority Norway has initiated several research projects to investigate into the ageing of materials, and how to ensure robust materials also for life extension. The present paper gives a summary of these research projects.