bluuebunny/crossref_metadata_2025 huggingface dataset:
Restraint System Markings and Occupant Kinematics in Crash Tests With Disabled Seat Belt Restraint Systems
Authors: Welsh Kevin J. , Struble Donald E. , Struble John D.
Published: May 2009

This paper presents an observational study that sought to explore the question of what type of evidence, if any, would be visible on a belt system after a crash at a low severity, or after a crash in which some aspect of the belt system was disabled. Such evidence could be added to the practical knowledge available to the investigator tasked with making a determination of whether a belt system has been used, misused, or has malfunctioned in some way. The study entailed frontal impacts into a barrier angled 30 degrees counter-clockwise. However, to reflect the larger angularity often seen in field accidents, compared to standard laboratory angled-barrier tests, the vehicle was also rotated 30 degrees counter-clockwise, similar to the impactor orientation in the FMVSS 214D test procedure. As with the 214D test, such a configuration re-creates the structural engagement and angularity of the striking vehicle involved in a typical perpendicular intersection collision with both vehicles moving. This common impact mode produces simultaneous lateral and longitudinal loading of the front structure, and much more angular occupant motions as compared to typical laboratory crash tests. A series of three repeated impact crash tests was run, in which the same test vehicle was used for all three tests, rather than using three separate vehicles. Each test included a 50th male dummy in the left front seat and a 5th female dummy in the left rear seat, for a total of six occupant exposures. Each dummy was restrained with a new replacement belt system for each test. In the first test, at 13 mph, both dummies were restrained with a normally functioning seat belt system, with the objective of documenting any marks generated at this lower crash severity. In the second test, at 23 mph, both dummies were fitted with belt systems with defeated buckles. In the third test, at 29 mph, both dummies were fitted with belt systems with disabled retractors. The tests illustrate the effects of crash severity, air bag deployments and belt malfunctions. The resulting physical evidence was documented for each crash test. Occupant kinematics are discussed. When either the buckle or the retractor was disabled, both occupant kinematics and occupant/belt interactions were fundamentally different from what occur under normally restrained conditions. Of course, the specifics of the resulting physical evidence will depend on the nature of the crash, the vehicle (a used 2002 Chevrolet Cavalier in this instance), the occupants, and the belt systems. However, the basic mechanics of the belt/occupant interaction, and the resulting markings documented herein, will help investigators determine whether a hypothesis about belt use, misuse, or malfunction is supported by the physical evidence being examined.
System Identification for Air/Fuel Ratio Modeling Using Switching Sensors
Authors: Hu Yiran , Rajagopalan Sai S. V. , Yurkovich Stephen , Guezennec Yann
Published: May 2009

Modeling the internal combustion engine for air-to-fuel ratio (AFR) control has been widely studied and several methodologies have been adopted toward the end goal of applying model based control schemes. In this paper, an online binary sensor identification (BID) technique using switching sensors is adopted for modeling the response from fuel input to AFR output of a spark-ignited, internal combustion engine, to be used in AFR control. In general terms, the algorithm identifies the impulse response of a linear time invariant (LTI) system by choosing an optimal sequence of inputs. The entire modeling process is done online with a four-cylinder engine in a test cell, using typical production switching sensors. Finite impulse response (FIR) linear time invariant (LTI) models are identified at prescribed operating points of the engine (specified by engine speed and the manifold air pressure). The validity of the resulting model is then tested on separate data streams with AFR measured from a wide-range sensor output. By scheduling the coefficients of the FIR models based on the operating condition, it is possible to identify a linear parameter varying AFR model for the appropriate operating regions of the engine.
Robust Fault Detection Filter Design With Applications to Steer-by-Wire Vehicles
Authors: Gadda Christopher D. , Laws Shad M. , Gerdes J. Christian
Published: May 2009

This paper presents a method for designing robust, model-based fault detection filters for linear systems with bounded parametric uncertainty. The approach maximizes the theoretical channel capacity of the system and diagnostic filter together, regarding the fault condition as an input to a hypothetical communication channel and the resulting residual as the output, with sensor noise, disturbances, and system input as sources of interference. This results in a robust residual that is both sensitive to faults and insensitive to noise and disturbances. The effectiveness of the technique is demonstrated in the design of a fault detection filter for use with a diagnostic system for a steer-by-wire vehicle.
Diagnostic Train for High Speed Line: A Tool for Improving Vehicle and Track Maintenance
Authors: Diana Giorgio , Cheli Federico , Belforte Paolo , Resta Ferruccio , Elia Michele , Favo Francesco
Published: May 2009

During 2005, the Italian railway Network Operator (RFI – Rete Ferroviaria Italiana) realized two ETR500 train sets completely dedicated to diagnostic operation on the new high speed lines being built in Italy. During 2006, these train were equipped with a complete acceleration measuring system for test activities on new Italian high speed line Turin – Novara and Rome – Neaples. A complete accelerometric measurement set up has been installed for track investigation. To this aim, the experimental set up is able to identify vertical profile of track geometry, without the limitation to 25 – 30 m, typical of the traditional measuring methods. On the other hand, a tool for predictive identification of hunting instability has been developed. For each run, it is possible to define a map, highlighting all the irregularity wavelengths involved as a function of the space: for high speed application wavelength over 100 m can become really important both for comfort and safety, because they are able to interest low frequency dynamic (around 0.8 – 1.5 Hz). Moreover, with the aim of identifying the beginning of hunting instability, a tool has been developed in order to identify yaw instability vibration mode and thus its non-dimensional damping, just by bogie yaw acceleration measurement. Both this tools have been developed by means of comparison between numerical multi body simulations and experimental measurements. Numerical simulation have been used to simulate a wide range of operating condition, that was of fundamental importance in tuning of such tools. Full evidence on these method will be given in the paper, together with an example of the obtained results.
Effect of Independently Rotating Wheels on the Dynamic Performance of Railroad Vehicles
Authors: Zaazaa Khaled E. , Whitten Brian
Published: May 2009

In recent decades, there has been a considerable effort in improving railroad vehicle dynamic performance. This involves high operational speed with stable behavior, better curving performance, better ride quality, and increased life of the wheel and rail profiles. To achieve this goal, the use of independently rotating wheels (IRW) is proposed as one potential option. Using IRW either partially or totally decouples the pitch rotation of the two wheels of the “wheelset”, thereby reducing or eliminating the longitudinal creepage and thus wheelset hunting motion. On the other hand, the longitudinal creepage is no longer available to provide steering assistance in curves, and continuous flange contact during curving is expected. However, by judicious choice of wheel profile and careful truck design, the lateral force between wheel and rail during curving can be reduced, decreasing the wear on both the wheel and rail profiles. Therefore, such solution is assumed to achieve higher stable operational speed and improved curving behavior. In this paper, the effect of using IRW on railroad vehicle performance is examined. The equations of motion of a single wheelset model and a suspended wheelset model that use IRW are presented and compared with those for similar models that use a rigid wheelset. Using a newly developed general multibody code, a complete vehicle model that uses IRW is examined and compared with one that uses rigid wheelsets. The effect of the IRW system on vehicle dynamic performance is quantitatively presented. In addition, the ability of the contact formulations used in this multibody code for modeling the IRW system is confirmed.
Aluminium Tubes in an Under Ride Protection Device
Authors: Henning Petrus F. J. , Pretorius Leon , Laubscher Rolf
Published: May 2009

Aluminum tubes were investigated numerically and experimentally, and a comparison was made between the obtained results. From the comparison an energy absorber was conceptually designed for application in the transport industry.
Development of a Finite Element Model for Simulation of Rollover Crashes
Authors: Hu Jingwen , Ma Chunsheng , Yang King H. , Chou Clifford C. , King Albert I. , McCoy Robert W. , Chen Roger J.
Published: May 2009

Rollover crashes are complex by their very nature, and have stimulated many researches aimed at improved occupant safety. In order to investigate the vehicle crashworthiness during rollovers, several test modes are generally used to replicate different real world rollover scenarios. However, such tests are very expensive, especially during the development stage of a new car line. Computer modeling is a cost-effective way to study rollover crashes. However, a survey of literature showed that only rigid-body dynamics based models have been used for rollover simulations. It is well known that this class of models cannot be used to simulate component deformation and structural collapses. Finite element (FE) method, which has been widely used to simulate frontal and side crashes, was rarely used for simulating rollover crashes, due mainly to the relative long duration of a rollover crash. The objective of this study was to develop an FE model for investigating vehicle crashworthiness during three commonly used rollover tests. An FE model of an SUV was developed in this study. Several sub-models, namely the vehicle structure sub-model, the tire sub-model, the suspension system sub-model, the restraint system sub-model, and the dummy model were generated and integrated together. The structure model was first used to simulate the roof crush test as prescribed in FMVSS 216. The resulting load versus roof crush curve matched well against test results. The integrated model was then used to simulate three laboratory-based rollover test modes, namely the SAE J2114 dolly test, curb-trip test, and corkscrew test. For each test mode, up to 1.5 seconds of simulation time (about 1 full vehicle roll) were computed. The vehicle kinematics, including the angular velocity, lateral acceleration, and vertical acceleration during these three test modes were computed and compared with experimental data. The simulated dummy head accelerations, timing and location of the most severe impact to the dummy’s head were also compared with the experimental results. Results showed very good agreement between the tests and simulations. In order to reduce the computational time, multiple CPUs were used. Approximately ten hours were required to run a 1.5 second rollover simulation on eight CPUs. Thus, simulating rollovers using FE method is quickly becoming a reality.
Load-Sharing Marine Drilling Riser Pipe Tension Slope
Authors: Chang Roger , Fisher Ed
Published: May 2009

Marine drilling riser using a load sharing flange design as the coupling connector is getting popular as people venture into the ultra deep water, 10,000 ft and more. The advantage and goal is the reduction in riser pipe wall thickness; hence, the riser system weight saving. The float (gap) value between the auxiliary lines’ coupling and the flange cut-out pocket is diligently designed in the engineering phase and carefully maintained in the manufacturing phase so that auxiliary lines start sharing the load at the desired tension magnitude. Two slopes of riser pipe tension curve, riser pipe carrying the full load then sharing with auxiliary lines, is well accepted and used in the design. However, it is found by finite element analysis that the riser pipe tension has a third slope when the auxiliary lines are pressurized. This paper presents the works done in deriving this finding and the associated fatigue problem needs to be considered in the load sharing flange design.
Vibration Damping and Active Noise Control in Ships and Floating Structures
Authors: Olunloyo Vincent O. S. , Osheku Charles A. , Agboola Femi
Published: May 2009

Vibration and noise reduction in ships and floating structures can significantly enhance dynamic stability and improve hydrodynamic performance during navigation, exploration and exploitation of deep and ultra-deep offshore geo-resources. In this paper, slip damping with sandwich composite elastic beam-plate smart structures for dissipation of vibration and active noise control mechanism is investigated analytically. For this problem, a boundary value partial differential equation is formulated for linear and non-linear hydrodynamic wave loading. In particular the effect of interfacial pressure distribution variation at the interface of the layered smart structures on the energy dissipation, logarithmic damping decrement and spatial transfer function is analyzed and presented for design application and selection of stabilizers.
Numerical Simulation of Roll Damping of a FPSO
Authors: Wanderley Juan B. V. , Ramiro Andre´ , Reis Thiago , Fernandes Antonio Carlos , Levi Carlos
Published: May 2009

The viscous flow problem of roll damping of a FPSO is investigated by means of numerical solution of the unsteady two-dimensional Navier-Stokes equations. The finite volume method using unstructured grid is used to solve the integral form of the governing equations. The cross section of the FPSO hull with an initial roll displacement is left free to oscillate in roll, heave and sway in an initially still fluid. The numerical simulation provides a realistic picture of the physics of the phenomenon, capturing the vortex formation around the bilge keel. The numerical results are compared with experimental data showing a fairly good qualitative and quantitative agreement of the motion damping.
Time-Varying Wave and Current-Induced Scour Around Offshore Wind Turbines
Authors: Nielsen A. W. , Hansen E. A.
Published: May 2009

The paper presents the engineering model, WiTuS (Wind Turbine Scour), which uses the results of several previous published physical experiments with scour around cylinders to determine the time development of the scour hole around the pile due to the actual and the previous wave and current climate. The WiTuS includes: • Time-varying water level, sea states and current. • Seabed material properties. • Description of the scour geometry around the pile. Simulations presented in the paper show that for typical North Sea conditions the scour depth will be around 0.3 times the pile diameter in periods with larger waves, which is a significant reduction from 1.3 times the pile diameter which is often seen as the industry standard.
Development of Oil-Water Separation Hydrocyclones for Oilfield Produced-Fluid Pre-Treatment
Authors: Jiang Minghu , Zhao Lixin , Li Feng , Zhang Yong
Published: May 2009

Research background is first introduced, and the structural type of the hydrocyclone used for produced-fluid pre-separation is defined. The effect of geometric parameters on separation performance is studied and analyzed. The parameters include nominal diameter, inlet size and its shape, overflow tube diameter and its length, overall length, cone angle, and tail tube length, etc. Oilfield experiments were carried out. By oilfield pilot test, the results of both parallel-type hydrocyclones and vessel-type hydrocyclones were tested and contrasted. By using vessel-type hydrocyclones, 5000m3/d scale oilfield experiments were taken. The industrial experimental results show that the studied hydrocyclones are feasible for oilfield produced-fluid pre-treatment. When the water-cut of produced-fluid is above 85%, by two-stage hydrocyclonic separation, the water-cut of the first oil outlet can be dropped down to 30%, and at the same time the oil-cut of the second water outlet can be treated to below 1000mg/L.
Laterally Loaded Piles With Bulge
Authors: Grabe Ju¨rgen , Du¨hrkop Jan
Published: May 2009

This paper contains several investigations on the behaviour of bulged piles. Bulge means the application of vertical steel plates somewhere near ground surface to improve the lateral bearing capacity. The results of small scale tests in sand are illustrated, which demonstrate the effectiveness of such bulge. Some theoretical investigations are presented trying to apply standard methods like the p-y-curve procedure to the design of bulged piles. An outline of possible calculation methods is given. Investigations on two different exemplary pile systems demonstrate the behaviour of the bulged structure and give an idea of the advantages of this innovative system.
Finite Element Validation Studies of BS7910 FAD Method Applied to Welded SHS Joints
Authors: Yang Zhengmao , Lie Seng Tjhen , Gho Wie Min
Published: May 2009

The failure assessment diagram (FAD) has now been widely accepted and used for the assessment of defects found in metallic structures. In BS7910 (2005), the use of this method for offshore structures has been validated for a range of joint geometries. But these validations are only applicable for circular hollow section (CHS) welded joints. For rectangular or square hollow section (RHS or SHS) joints, there are very few references available in the literature. In this paper, systematic investigations have been carried out for the validation and verification of the FAD curves for SHS T-joints. FAD curves for a wide range of welded SHS T-joints containing surface cracks have been established using the fracture mechanics data generated from the finite element analyses. The range of β ratio of these joints is from 0.3 to 0.8. Therefore, the failure mode is constrained in the chord face yielding. The influence of residual stresses on the plastic collapse load and the FAD curves has also been analyzed. The reduction factor used to calculate the plastic collapse load of the SHS T-joints containing cracks have been quantitatively examined, and the use of the BS7910 (2005) Level 2A FAD for SHS joints containing surface cracks has been validated accordingly.
An Experimental Investigation of the Flow Around Straked Cylinders
Authors: Korkischko Ivan , Meneghini Julio R. , Gioria Rafael S. , Jabardo Paulo J. , Casaprima Enrique , Franciss Ricardo
Published: May 2009

This paper presents experimental results concerning the response of circular cylinders with and without strakes. The longitudinal and transverse fluid forces (drag and lift), amplitude response and wake structures of plain and helically straked cylinders are compared. Six different configurations of straked cylinders with pitches (p) equal to 5D, 10D and 15D and heights (h) equal to 0.1D and 0.2D are investigated. Measurements on the dynamic response oscillations of an isolated plain and straked cylinders and flow visualization employing a PIV system are shown. Fixed cylinder drag measurements are also shown. The models are mounted on an elastic base fitted with flexor blades and instrumented with strain gauges or in an air bearing base. The base is fixed on the test-section of a water channel facility. The flexor blades possess a low-damping and the flexor blades base an the air bearing base are free to oscillate only in the cross-flow direction. The Reynolds number of the experiments ranges from 2000 to 10000, and reduced velocities, based on natural frequency in still water, vary up to 13. The drag coefficient is increased by 20% for the h = 0.1D cylinder, and 60% for the h = 0.2D cylinder, comparing both with the plain cylinder. The smaller height strokes (h = 0.1D) do not prevent vortex formation in the region very close to the body, resulting in a decrease of about 50% of the amplitude response compared with the plain cylinder. Lowest amplitude response was found to the p = 10D and h = 0.2D case. The analysis of the vorticity contours shows that the shear layer does not roll close to the body (same result for the other cases with h = 0.2D).
Hydrodynamic and Thruster Model Validation for Autonomous Underwater Vehicles
Authors: Chyba M. , Haberkorn T. , Smith R. N. , Choi S. K. , Weatherwax Scott
Published: May 2009

From Pontryagin’s Maximum Principle to the Duke Kahanamoku Aquatic Complex; we develop the theory and generate implementable time efficient trajectories for a test-bed autonomous underwater vehicle (AUV). This paper is the beginning of the journey from theory to implementation. We begin by considering pure motion trajectories and move into a rectangular trajectory which is a concatenation of pure surge and pure sway. These trajectories are tested using our numerical model and demonstrated by our AUV in the pool. In this paper we demonstrate that the above motions are realizable through our method, and we gain confidence in our numerical model. We conclude that using our current techniques, implementation of time efficient trajectories is likely to succeed.
ECA Methodology for Fatigue Design of Risers and Flowlines
Authors: Luk C. H. , Wang T. J.
Published: May 2009

Engineering Criticality Assessment (ECA) is a procedure based on fracture mechanics that may be used to supplement the traditional S-N approach and determine the flaw acceptance and inspection criteria in fatigue and fracture design of risers and flowlines. A number of design codes provide guidance for this procedure, e.g. BS-7910:2005 [1]. However, more investigations and example studies are still needed to address the design implications for riser and flowline applications. This paper provides a review of the existing ECA methodology, presents a fracture mechanics design method for a wide range of riser and flowline fatigue problems, and shows flaw size results from steel catenary riser (SCR) and flowline (FL) examples. The first example is a deepwater SCR subjected to fatigue loads due to vessel motion and riser VIV. The second example is a subsea flowline subjected to thermal fatigue loads. The effects of crack re-characterization and material plasticity on the Level-2 and Level-3 ECA results of the SCR and flowline examples are illustrated.
Experimental Study of Wave Forces on Vertical Cylinders in Shallow Waters
Authors: Ma Rujian , Li Guixi , Zhao Dong , Wang Jungang
Published: May 2009

An experimental study of wave forces on the vertical cylinders in shallow waters was carried out in a wave channel. The wave parameters, wave forces and wave pressures are measured and studied in the paper. The study indicates that the distribution of wave pressures of the shallow water waves can be described by an exponential function with respect to water depth. The maximum surface elevation for shallow water waves can be estimated using the significant wave height. The wave pressure around circumference can be expressed as a simple form of cosine function. An experimental formula for the calculation of wave forces on vertical cylinders is proposed. As compared with test data, the predicted wave forces showed good agreement and high reliability. The calculated wave forces by different wave theories are less than those of the proposed method. Therefore, the wave force calculation method for shallow water waves should be modified for engneering applications.
Strength and Fatigue Analysis of VIM Suppression Strakes for Large Diameter Spars
Authors: Tallavajhula Sudhakar , Wang Jim , Solberg Inge
Published: May 2009

The efficiency of spar vortex induced motion (VIM) suppression strakes has been found to be dependent upon the height of the strakes, the number of strakes in the helix, the pitch of the helix and the extent of strake coverage. As spars have increased in diameter, the height of the VIM suppression strakes has grown to maintain strake efficiency. This has introduced new challenges to the structural design of the strakes as a result of the increased hydrodynamic pressure loads on the strakes and the effect of global bending of the spar hull. The connection of the strakes to the hard tank outer shell often has high stress concentration, which in combination with the cyclic hydrodynamic loading, tends to result in fatigue considerations governing the design of these connections. As a result, finite element models, both global and local, are required to perform detailed stress analysis for the structural strength and fatigue assessment of the strakes and surrounding hard tank structures. This paper will use a generic, large diameter truss spar as an example to outline the methodology and key elements used for strength and fatigue analyses of the strakes. In particular, an efficient unit load method will be presented, which has been used to de-couple the finite element stress analysis and the actual hydrodynamic pressure load analysis for fatigue damage calculation. This method incorporates a time domain global analysis of spar hull global bending loads, and a frequency domain analysis of wave induced hydrodynamic pressure loads on the strakes. Final fatigue damage is calculated based on combined principal stresses using the spectral method. Analysis results and findings are presented for both the in-place condition and the wet tow condition. By applying this procedure, Technip has been able to repeatedly design robust and reliable VIM suppression strakes in a cost efficient process, within the constraints of tight fabrication schedules.
Modeling of Tsunami Propagation in the Vicinity of the Southern Coasts of Iran
Authors: Heidarzadeh Mohammad , Pirooz Moharram D. , Zaker Nasser H. , Mokhtari Mohammad
Published: May 2009

The extensive death toll and sever economical damages brought by the 2004 Indian Ocean tsunami has emphasized the urgent need for assessing the hazard of tsunami in this ocean, and determining the most vulnerable coastlines to the impact of possible tsunami. In this paper the hazard of tsunami for southern coasts of Iran bordering the Indian Ocean is discussed. At first, historical data of tsunami occurrences on the Iranian southern coasts are collected, described and analyzed. Then, numerical simulation of potential tsunamis in the Makran subduction zone is performed and the tsunami wave height distribution along the Iranian coast is calculated. The Makran subduction zone is among two main tsunamigenic zones in the Indian Ocean. In this zone the Oman oceanic plate subducts beneath the Iranian Micro-plate at an estimated rate of about 19 mm/yr. Historically, there is the potential for tsunami generation in this region and several tsunamis attacked the Makran coastlines in the past. The most recent tsunami in this region has occurred on 28 November 1945 which took the lives of more than 4000 people in the coasts of Iran, Pakistan, India, and Oman. Here we examine the seafloor uplift of the Makran zone and its potential for generating destructive tsunamis in the southern coastlines of Iran. Several earthquake scenarios with moment magnitudes ranging between 6.5 and 8.5 are used as initial conditions for analysis. For scenario of an earthquake with magnitude of 8.0, propagation of tsunami waves on coastlines and wave time histories in selected reference locations are calculated.
Three Phase Flow Simulations of an Oil Recovery Ship in Various Sea States
Authors: Clauss Gu¨nther F. , Sprenger Florian , Kosleck Sascha , Stu¨ck Robert
Published: May 2009

The analysis of local flow phenomena, in particular the analysis of the oil flow and the oil-water separation process in a three phase flow simulation (air, water, oil), including the free water surface, is a basic need for the development of an efficient oil recovery system such as the Seaway Independent Oilskimming System (SOS). As the oil separation process is highly dependent on the ships motions, its seakeeping behaviour needs to be simulated accurately. The paper presents two-phase flow simulations (air, water) of the seakeeping behaviour in three and six degrees of freedom (two- and three-dimensional — 2D/3D). The vessel motions simulated in various sea states are validated by model tests conducted in a physical wave tank. The grid resolution as well as the flow parameters of the simulation have been varied to find a fast and reliable solution. The need for three dimensional simulation runs is questioned, as two dimensional simulations give nearly the same results and are far less time intensive. Oil is introduced as the third phase. The associated analysis illustrates the oil-water separation process and yields the systems efficiency in dependency of the sea state conditions. Based on the results of three-phase simulations, the operational range of the Seaway Independent Oilskimmer is determined and recommendations for the system optimization can be made.
Experimental Investigation of Vortex-Induced Vibration on an Inclined Circular Cylinder
Authors: Fujarra Andre´ L. C. , Meneghini Ju´lio R. , Franciss Ricardo , Franzini Guilherme R. , Korkischko Ivan
Published: May 2009

This paper presents experimental results of vortex-induced oscillations of an inclined circular cylinder mounted on an elastic base. Models are mounted on an air-bearing elastic base, instrumented with strain gages, accelerometers and a load cell. The experiments were carried out on a water channel facility at NDF-EPUSP. The elastic base has low structural damping and is free to oscillate only in the cross-flow direction. The cylinder axis is inclined in relation to the current. New measurements on the dynamic response oscillations of this inclined cylinder, due to vortex-induced vibrations (VIV), are compared with previous experiments on a vertical cylinder. VIV is investigated by conducting experiments in two ways: first, the cylinder is maintained vertical on the elastic base, with a uniform current normal to its axis, and the response curve is obtained; subsequently, the investigation is carried out changing the angle of inclination from 0 to 45 degrees in relation to vertical. The results for a vertical cylinder are in accordance with other literature measurements for mass ratio m*=2. For the inclined model, using the decomposition of the flow on the direction normal to cylinder axis, the results for amplitude, drag and lift coefficients are consistent with the vertical cylinder.
An Alternative Top Termination for a Steel Catenary Riser
Authors: Li Yousun , Lo King Him , Zhang Heping
Published: May 2009

Flexible joints and tapered stress joints are the commonly used top terminations for deepwater steel catenary risers (SCR). A flexible joint, by design, can accommodate large angular motions between the floating host and the SCR. A tapered stress joint, on the other hand, is a more rigid termination for the SCR and cannot easily accommodate large host angular motion. Recent activities in potentially hot and sour fields, however, have posed new challenges and requirements on the ability of a flexible joint to sustain long-term operations. A tapered stress joint can be an attractive alternative to a flexible joint for hot and sour operations. However, excessive large bending moments could be induced by the tapered stress joint onto the host structure. In this paper, an alternative approach to SCR top termination is proposed, which utilizes a combination of riser guide and stress joint to provide the required top termination flexibility. The SCR is connected to the host at the riser top, and is allowed to slide along and rotate about a riser guide fixed onto the host at some distance below the top support. The flexibility of the proposed top termination is realized by the riser pipe deflection between the top support and the riser guide. A stress joint is used to alleviate the high riser stress at the riser guide, without increasing the lateral load on the guide. The proposed top termination thus provides a flexible connection as well as a continuous conduit for the fluid stream. It is an attractive option for high temperature and pressure operations, especially in the presence of higher concentrations of sour elements. For applications that are not driven by hot and sour conditions, the new approach to SCR top termination seems to have the potential to be more cost effective, especially for application to larger diameter deepwater SCRs. Numerical simulations were used to demonstrate the feasibility of the proposed top termination for deepwater SCRs.
Floating Wave Energy Device With Two Oscillating Water Columns
Authors: Hong D. C. , Hong S. Y.
Published: May 2009

The absorbed power, motion and drift force of a floating wave energy device with two oscillating water column (OWC) chambers are studied taking account of the interaction between two chambers within the scope of the linear wave theory. The oscillating surface-pressure in the OWC chamber is represented by a product of the air-flow velocity and an equivalent linear damping parameter. The two-dimensional potential problem is formulated as a hybrid Green integral equation using the Rankine Green function inside the chamber and the finite-depth free-surface Green function outside respectively. The present numerical method makes it possible to tune the OWC and the floating body motions to the incident waves that is essential to maximize the absorbed power. The absorbed powers are calculated by both the near-field and far-field methods for various values of the linear damping parameter in two chambers. The reflection and transmission coefficients of the body are also presented. The numerical results for one OWC devices where the OWC is placed in a backward and forward bent duct buoys (BBDB and FBDB) are also presented for comparison of the performance. The present floating wave energy devices can also be served as a good floating breakwater having small drift force. The present numerical results show that the existence of reverse time-mean horizontal wave drift force is not contradictory to the principle of wave energy conservation.
A Methodology to Analyze, Treat and Guarantee Attendance to Legal Requirements of Light Ship Modifications on Floating Production Units
Authors: Nogueira Se´rgio , Ayres Raphael d’Andre´a
Published: May 2009

The constant modifications that are done aboard floating units have direct impact on the safety requirements regarding stability. With few exceptions these modifications imply on onboard construction (e. g. process plant upgrade), and the correspondent rise of light ship weight. The consequence will be negative effect on stability, a reduction of the capacity for future modifications that will probably be necessary as well as the ability to deballast to lower drafts. According the Rules applicable [1], the modification of the light ship weight that surpasses a defined limit must be checked through an Inclining Test that can only be executed with the unit in sheltered waters. For a Floating Production Unit (FPU) this test is unfeasible because of the operational procedure (the need to disconnect anchor lines and risers, tow and reconnect) and the production downtime. The alternative is to negotiate with the Regulatory Bodies a penalty for the light ship modifications that imply in a further reduction on the range of stability and the correspondent capacity of the unit to undergo further and necessary modifications. The motivation of this work is to develop and test a methodology where the light ship modifications that were done through the years undergo audit and the data generated is statistically treated considering the conditions and objectives of the Classification Society’s stability criteria. The result is an acceptable alternative to the inclining test that is consistent with the stability rules that apply, that permits a reduction on the penalties and consequently permits further and most necessary modifications aboard. This methodology has been applied to a semi submersible floating production unit (FPU) operating and going through light ship modifications for 15 years, with very good results. The whole procedure was approved by the Classification Society of the unit.
Horizontal Capacity of Embedded Suction Anchors in Clay
Authors: Bang S. , Jones K. , Kim Y. S. , Cho Y.
Published: May 2009

An analytical solution has been developed to estimate the horizontal pullout capacity of embedded suction anchors in clay seafloor. Validation has been made through comparisons with the centrifuge model test results. The results indicate that the horizontal pullout capacity of the embedded suction anchor in clay increases, reaches its peak and then starts to decrease as the point of the load application moves downward. The effect of flanges on the horizontal pullout capacity is also found to be significant.
Numerical Validation of the Goda Spread Parameter of Extreme Wave Height Distribution
Authors: Benassai G. , Chianese E.
Published: May 2009

Starting from the definition of the Goda spread parameter γ50 and from the verification of the spatial homogeneity hypothesis, the 50-year significant wave height H50 was obtained for a sea area characterized by a limited wave observation period. The procedure was applied for the location of Cetraro in the Southern Tyrrhenian Sea starting from the waves recorded offshore Ponza, provided that the spatial homogeneity hypothesis was verified. This hypothesis was not verified, however, between the wave measurement stations of Crotone or Catania and two wave measurement stations recently installed by Calabria Region in the Ionian Sea. In the Southern Tyrrhenian Sea the results of H50 were compared with the ones obtained with the method of fetch transposition of De Girolamo & Contini (1998).
Estimating Extreme Response of Drag Dominated Offshore Structures From Simulated Time Series of Structural Response
Authors: Naess A. , Gaidai O. , Haver S.
Published: May 2009

The paper presents a study of extreme response statistics of drag dominated offshore structures, showing a pronounced dynamic behaviour when subjected to harsh weather conditions. The key quantity for extreme response prediction is the mean up-crossing rate function, which can be simply extracted from simulated stationary response time histories. Present practise for obtaining adequate extremes for design purposes requires a number — say 20 or more — of 3-hour time domain analyses for several extreme sea states. For early phase considerations, it would be convenient if extremes of a reasonable accuracy could be obtained based on shorter and fewer simulations. It is therefore of interest to develop specific methods which make it possible to extract the necessary information from relatively short time histories. The method proposed in this paper opens up the possibility to predict simply and efficiently long-term extreme response statistics, which is an important issue for the design of offshore structures. A short description of this is given, but in the present paper the emphasis is on short-term analyses. The results presented are based on extensive simulation results for the Kvitebjo̸rn jacket structure, in operation on the Norwegian Continental Shelf. Specifically, deck response time histories for different sea states simulated from a MDOF model were used as the basis for our analyses.
Structural Safety Assessment of Damaged Ships
Authors: Khan Imtaz A. , Das Purnendu K.
Published: May 2009

In the design of ships, structural strength is generally assessed for the intact condition. In intact condition, the critical load case for mono-hull ship is the vertical bending moment, which reaches its maximum in head seas. Both horizontal bending moment and torsional load may play insignificant role. The torsion is considered only when there are large opening on ships. This methodology has been successfully applied to ship design for many years. But when a ship is damaged the whole scenario for the safety assessment changes. In damaged condition its floating condition could be changed dramatically. Its draught is increased and it may heel. It could also have large holes in the structure. So the load combination becomes very essential part of structural safety assessment in damaged scenario. Different damage scenarios in two tankers have been studied. A rational way to combine the vertical, horizontal wave-induced bending moments and still water bending moment is presented. For the deterministic analysis a rational interaction equation, combining vertical and horizontal bending moments is discussed. The reliability index and the probability of failure at different damage scenario are studied. The combined effect of torsional, vertical and horizontal bending moments is discussed. Finally the survivability of the damaged ships is discussed.
High Cycle Fatigue of Pipelines With Plain Dents: Simulations, Experiments and Assessment
Authors: Cunha Se´rgio B. , Pinheiro Bianca C. , Pasqualino Ilson P.
Published: May 2009

The objective of this work is to propose a methodology for assessing the fatigue life of dented pipelines according to the current high cycle fatigue theory. The proposed methodology employs S-N curves obtained from tensile test material properties and includes an expression to estimate stress concentration factors for spherical dents. Finite element analyses are carried out to determine stress concentration factors for different pipe and dent geometries. Using the numerical results, an expression to estimate stress concentration factors of dented pipelines is developed. Additionally, fatigue tests are conducted with the application of cyclic internal pressure on small-scale dented steel pipe models. Different pressure levels are employed, resulting in failures ranging from around 6000 to more than 106 cycles, enabling the determination of the endurance limit and of the finite life behavior of dented pipes. Furthermore, the Goodman and Gerber criteria to account for the mean stress are evaluated in view of the experimental results. The fatigue test results are used to validate the proposed assessment methodology for the analyzed conditions.
Soil Loads on Polyethylene Natural Gas Pipelines Subjected to Relative Axial Ground Displacements
Authors: Weerasekara Lalinda , Wijewickreme Dharma
Published: May 2009

The performance of buried natural gas pipeline systems in areas subjected to permanent ground displacements is an important engineering consideration since geotechnical hazards can be a major cause of damage to these utilities. Although pipe-soil interaction models exist, there is only limited experience with pipeline materials other than steel, and particularly in relation to polyethylene (PE). With this background, a detailed research program involving full-scale physical model testing of buried pipeline systems was undertaken, and performance of straight PE pipes subject to relative axial soil movement was investigated as a part of this work. A closed-form solution was derived to account the nonlinear material response of MDPE pipes subject to relative axial soil movement, and the analytical results are compared with the results obtained from the full-scale testing. This closed-form solution provides a rational framework to estimate the response of the pipe (level of strain, force) and even the mobilized frictional length along the pipe for a known amount of ground displacement. The approach, in turn, could be used in estimating the relative axial soil displacement needed for pipe failure, which is an important consideration in the evaluation of the field performance of MDPE pipe systems located in areas of potential ground movement.
Second-Order Hydrodynamic Resonances on a Compound Truncated Cylinder Floating Near the Free Surface
Authors: Chatjigeorgiou Ioannis K. , Mavrakos Spyros A.
Published: May 2009

The present work treats the problem of possible hydrodynamic resonances that may occur when a compound-truncated floating axisymmetric body is subjected to monochromatic incident waves. The analysis that is conducted in the paper, utilizes both linear and nonlinear potential theory. The solution of the second-order hydrodynamic problem is derived using semi-analytical formulations for the double frequency velocity potentials. The work emphasizes on the conditions under which the resonance phenomena could be excited, how they are reflected on the wave elevation and the induced hydrodynamic loading, and finally, on the physical and mathematical justification of such occurrences.
The Effect of Bow Shape on the Springing/Whipping Response of a Large Ocean-Going Vessel: Investigated by an Experimental Method
Authors: Storhaug Gaute , Moan Torgeir
Published: May 2009

Wave induced vibrations often referred to as springing and/or whipping increase the fatigue and extreme loading in ship hull girders. Both effects are disregarded in current ship rules. Various numerical codes exist for predicting the wave induced vibrations, but so far they are not considered reliable. Another means to investigate the importance of the high frequency response, although more resource demanding, is to carry out full scale measurements and/or model tests. Recently, full scale measurements of blunt ships have been carried out by DNV, and in this paper one of these ships was considered and tested in a towing tank to evaluate the additional fatigue damage due to the wave induced vibrations. Different excitation sources may excite the 2-node vertical vibration mode depending on ship design, and it is not straight forward to determine which is more important. The relative importance of the excitation mechanisms are investigated by two approaches in this paper. The first approach separates the whipping from springing to illustrate their relative importance based on basic theory in combination with model test results. The linear and second order transfer functions are utilized in this procedure. The second approach deals with the effect of the bow design on the additional fatigue damage. Three different bows were tested. The first bow design is identical to the real ship. The second bow design is a simplified version of the first one, by removing the bulb and flare. The third bow is fundamentally different from the two former blunt bows. Bow three is sharp pointed with a vertical sharp stem and vertical ship sides. The results indicate that the importance of whipping depends on the sea state, but that it is of similar importance as springing for the sea states that contributes most to the fatigue damage. Moreover, the difference in the additional fatigue damage due to wave induced vibrations for different bow shapes is moderate. This indicates that vessels with pointed bows and without pronounced bow flare, such as LNG vessels, may have a similar contribution from wave induced vibrations. Modern container vessels, which are more slender, but with pronounced bow flares should be further investigated.
CFD High L/D Riser Modeling Study
Authors: Constantinides Yiannis , Oakley Owen H. , Holmes Samuel
Published: May 2009

Fully three dimensional fluid flow simulations are used with a simple structural model to simulate very long risers. This method overcomes many shortcomings of methodologies based on two dimensional flow simulations and can correctly include the effects of three dimensional structures such as strakes, buoyancy modules and catenary riser shapes. The method is benchmarked against laboratory and offshore experiments with model risers of length to diameter ratios up to 4,000. RMS values of vortex induced vibration motions are shown to be in good agreement with measurements. The resources needed to model ultra deep water drilling and production risers are estimated based on current computer technology.