bluuebunny/crossref_metadata_2025 huggingface dataset:
Arctic Pipeline Design Considerations
Authors: DeGeer D. , Nessim M.
Published: July 2009

Since the discovery of reserves in arctic regions, operators have been faced with a number of challenges, including assessing appropriate methods of transporting produced hydrocarbons to market. For pipeline systems, designers are required to deal with a number of unique environmental conditions not normally present in other regions of the world. These include ice scour, permafrost thaw and/or frost heave, leak detection and containment, and installation techniques. For offshore applications, novel design alternatives that have been considered to address these issues include pipe-in-pipe systems, non-bonded flexible pipes, composite wrapped pipes, and hybrid pipes. Each alternative offers strengths and weaknesses, depending on the specific hazards or failure event consequences that may exist at the location of interest. For buried onshore pipelines, the key design issue is the potential for high bending strains resulting from frost heave and thaw settlement. For both onshore and offshore pipelines, possible ways to address these issues includes the use of pressure and diameter combinations that lead to thick walls, integration of in-service inspection and maintenance within the design philosophy, stringent quality control for girth welds, and selection of materials with appropriate post yield behaviour. Because of the lack of traditional design solutions to these challenges, limit state, reliability-based and strain-based design methods are now preferred for arctic applications. The implementation of these methods requires a good understanding of linepipe material behaviour, soil loading conditions, ice loading mechanisms, and the consequences associated with product release. They allow the integration of analytical and experimental assessments into the overall design philosophy, which has been shown to improve design concept confidence and reduce overall uncertainty. This paper describes some of the key challenges facing the design of both onshore and offshore pipelines. It describes some of the current design options and how reliability-based and strain-based methods can be used to integrate essential information from a number of analytical and experimental sources into an overall framework that addresses the challenges and leads to optimal design decisions. It discusses the state of the art in this area and identifies knowledge gaps that need to be filled.
Real Time Wave Forecasting for Real Time Ship Motion Predictions
Authors: Naaijen Peter , Huijsmans Rene´
Published: July 2009

This paper presents results of a validation study into a linear short term wave and ship motion prediction model for long crested waves. Model experiments have been carried out during which wave elevations were measured at various distances down stream of the wave maker simultaneously. Comparison between predicted and measured wave elevation are presented for 6 different wave conditions. The theoretical relation between spectral content of an irregular long crested wave system and optimal prediction distance for a desired prediction time is explained and validated. It appears that predictions can be extended further into the future than expected based on this theoretical relation.
Effects of Structural Material Damping on Nonlinear Seismic Response of Offshore Piles
Authors: Kimiaei Mehrdad
Published: July 2009

Nonlinear response of pile foundations is the most important part of potential nonlinear response of pile supported offshore platforms to seismic excitations. Soil nonlinearity, soil radiation damping and structural material damping are the main sources of energy dissipation in seismic behavior of offshore piles. In this study, a practical BNWF (Beam on Nonlinear Winkler foundation) model is used to compute the nonlinear lateral response of piles, embedded in layered soil deposits, subjected to seismic loading. The results of equivalent linear and nonlinear earthquake free field ground motion analyses are used as the input excitations at support nodes of the model. Sensitivity of the pile seismic responses to structural material damping ratios are discussed and addressed in this paper. Numerical results are compared with centrifuge test results.
Managing Ageing Flexible Pipe Assets
Authors: Botto Adriana , O’Sullivan Enda , Banti Ce´line
Published: July 2009

The population of flexible pipes is increasing exponentially and by definition it is ageing. Over the coming years an increasing number of flexible pipes will reach the end of their design life, therefore prudent operators should focus on understanding the integrity status of their flexible pipes. Understanding and effectively managing the integrity of flexible pipes is necessary to prevent, predict, or detect the presence of any loss of integrity. A detailed understanding of the manufacturing history, operational conditions, any previous repairs and inspection or test history are all required to gain a full insight of the flexible pipe fitness and assess its suitability for continued operation and for any potential life extension beyond the initially intended service life. This paper presents guidelines for developing and implementing an integrity management strategy, which utilises the correct mix of inspection and assessment tools (degradation of internal pressure sheath, fatigue assessment, corrosion and annulus condition monitoring etc.) and operating procedures that will allow the operator to assess the opportunity for life extension of flexible pipes.
Spectral Properties of Cyclone-Generated Waves in Deep and Shallow Water
Authors: Xu Fumin , Perrie Will
Published: July 2009

Juan is recorded as one of the most damaging storms in the modern history of Nova Scotia, Canada. In this paper, the spectral evolution characteristics of waves generated by hurricane Juan are studied, based on the observed 1D wave spectra along Juan’s track in deep open ocean waters (buoy 44137) and the 2D wave spectra in shallow coastal waters at the directional waverider (DWR) location. Valuable results are obtained for cyclone-generated wave spectral properties, in both deep and shallow waters. In deep water, as illustrated at buoy 44137, the spectral variation, spectra pattern development, spectral peak frequency, cut-off frequency coefficient and high frequency spectral tail of the wave spectra are analyzed, before, during and after the cyclone’s passing. Thus, the spectral variation characteristics during the entire cyclone processe are obtained. Properties of the high frequency spectral tail are discussed, using average frequency and peak frequency as the cut-off frequency parameters under different cut-off coefficient conditions, respectively. We suggest reasonable values for the cut-off frequency parameter. Cyclone-generated 2D wave spectra in shallow water (at DWR location) are investigated, shoaling effects, 2D spectral pattern variations, swell and wind waves spectral evolution. Our study shows the invalidity of presently accepted spectral formulae, in describing cyclone-generated waves.
Tsunami Hazards in the Northwestern Indian Ocean
Authors: Heidarzadeh Mohammad , Pirooz Moharram D. , Zaker Nasser H.
Published: July 2009

Although northwestern Indian Ocean has experienced some deadly tsunamis in the past, this region remains one of the least studied regions in the world and little research work has been devoted to its tsunami hazard assessment. In this study, we compile and analyze historical tsunami in the northwestern Indian Ocean and present a tsunami list for this region. Then, a deterministic method has been employed to give a preliminary estimation of the tsunami hazard faced by different coastlines in this region. Different source scenarios are considered and for each scenario, numerical modeling of tsunami is performed. For each case, the maximum positive tsunami wave heights along the coasts are calculated which provide a preliminary estimation of tsunami hazard and show which locations face the greatest threat from a large tsunami.
A Review of Ship Surveys Practices and of Marine Casualties Partly Due to Aging Effects
Authors: Rizzo Cesare Mario , Lo Nigro Angelo
Published: July 2009

The first part of this paper overviews the present international regulatory regime and the future expected developments of ship surveys, from the viewpoint of methods and criteria, identifying different degradation phenomena mainly related to aging of structures and hull equipment. The current onboard practice is recalled, both of mandatory surveys (including class surveys and particularly the new requirements introduced by the IACS Common Structural Rules) and of non mandatory industry-driven inspections. Then, reviews of few databases of marine casualties, available to authors, are presented aiming at assessing the role of aging effects in the marine accidents. Even if it should be admitted that available statistical samples are not always complete and accurate, the intent is to identify trends in the pattern of structural failures and to develop recommendations for improving the inspection regimes and procedures for condition assessment analyses by which to reduce the number and severity of such occurrences.
Use of Hydroelastic Analysis for Verification of Towed Equipment for Acquisition of Seismic Data
Authors: Berstad Are Johan , Tronstad Harald
Published: July 2009

This paper presents how analysis can be used in the design and the design verification process for towed equipment. Analysis of a seismic gun array has been carried out and points out the challenges that need to be addressed in order to obtain an assessment of the system. It is shown how analysis should be carried out to obtain proper design verification. Applicable rules and design criteria are presented and discussed. The work shows the importance of carrying out a coupled hydroelastic analysis of towed equipment. The strong effect of waves and currents to positioning of equipment is shown.
Evaluation of the Potential of Wave Energy in Chile
Authors: Mona´rdez Patricio , Acun˜a Hugo , Scott Doug
Published: July 2009

In Chile, incentives have been created during the past years for the installation of non-conventional renewable energy plants (NCRE). It is within this context that wave energy can be transformed into a feasible alternative for electrical power generation in the near future within the country. This work corresponds to the first approach to quantify the wave energy resources in Chile based in a technically superior manner. The first step in the assessment of a wave energy plant is to quantify the available resources, therefore the wave climate was obtained for various sites along the Chilean coastline and a deterministic assessment was made of the power of the waves and their main characteristics, especially the variability under different time horizons. In order to convert the mechanical energy of the waves into electrical power, an assessment was made of various offshore devices existing on the market. An estimate was made of the output power of these conversion devices based on the wave climate and on the energy conversion matrixes that define them, performing an analysis that is completely analogue to that of wave power. Waves in the Chilean coast arrive year in and year out with scarce variation during the various seasons, are very regular, with low directional dispersion and high periods. This determines the low seasonal variability of the power and the high capacity factors that conversion devices can develop. The characteristics of waves in Chile are due mainly to the presence of swell usually found in great oceans, which makes Chilean territory one of the most appropriate sites in the world for the generation of electrical power with energy from the waves.
The Effect of Bottom Damage Size of Stranded Ship on Ultimate Strength
Authors: Rim Chae Whan , Lee Tak Kee , Han Dae Suk , Kim Byung Hyun , Lee Jae Myung , Kim Ki Sup
Published: July 2009

Ships operating in littoral sea are likely to be subjected to accidental loads especially stranding. Once she has damage on the hull structure, her ultimate strength will be reduced. This paper is to investigate the effect of stranding damage size on the ultimate strength of ship structure by using a series of collapse tests. For the experiment, five box-girder models of 720mm × 720mm in section and 900mm in length were prepared. Of the five, one has no damage and each four have a diamond shaped damage of different size which represents the shape of rock section in seabed. Among the damaged models, three were made by cutting the plate and one by pressing to represent stranding damage. Experiments were carried out under pure bending load and the applied load and displacements were recorded. The ultimate strength is reduced as the damage size increases, as expected. The largest damaged model has the damage size of 30% of breadth and its ultimate strength is reduced by 21% than that of no damaged one. The pressed one has lower ultimate strength than cut one. This might be due to the fact that the plate around the pressed damage area effect unfavorably on the ultimate strength. The models are analyzed with LS-DYNA and the results are compared with the results from the experiments. From the intact model, buckling occurred in the analysis but not in the experiment. The ultimate strengths of other models from the analysis are fairly close to those from the experiments. The errors are within 10%. With the results from the experiments and analysis, an estimation method of ultimate strength of damaged ship on bottom is derived.
Long-Term Tidal Water Level Measurements in Abu Dhabi Emirate
Authors: Mohamed Khaled A.
Published: July 2009

Abu Dhabi Emirate, United Arab Emirates has a unique tidal system. Understanding the tidal hydrodynamics in Abu Dhabi waters is very important for the design of the hydraulic structures and in the marine environmental studies. The objective of this study is to investigate the tidal water levels and tidal motion in Abu Dhabi, making use of the long-term water levels available. To achieve the aim of the study, the National Energy and Water Research Center (NEWRC) of Abu Dhabi Water and Electricity Authority installed tidal gauges at different locations in Abu Dhabi waters to obtain long-term water level measurements. At present, long-term water level measurements for at least 3 years period are available at different locations in Abu Dhabi waters. Tidal analysis was carried out on the available data to determine the characteristics of the tidal wave in Abu Dhabi Emirate and to get the main tidal constituents affecting the tidal motion. The obtained tidal constituents are used in updating and improving the boundary conditions of the numerical hydrodynamic models simulating the flow pattern in Abu Dhabi waters. The set up of the water level measurement program in Abu Dhabi waters and the results of the tidal analysis are presented and discussed in the paper.
Centrifuge Modelling of Pipe Penetration Due to Dynamic Lay Effects
Authors: Cheuk C. Y. , White D. J.
Published: July 2009

On-bottom pipelines are subjected to small-amplitude oscillations during installation due to dynamic motion of the pipe within the touchdown zone. This motion is driven by the movement of the lay vessel and hydrodynamic excitation of the suspended length of pipe. The increase in as-laid embedment caused by these dynamic lay effects has a significant influence on various aspects of the performance of the pipeline. A series of centrifuge model tests was conducted to assess the change in embedment of an unburied pipeline subjected to small-amplitude horizontal oscillations. Two clay samples were used — kaolin clay and a soft high plasticity clay recovered from offshore Angola. Dynamic lay effects were simulated by applying a constant vertical load to the model pipeline then imposing packets of cycles of horizontal motion, representing the pipe movement within the touchdown zone. The results demonstrate that a few (<5) small amplitude cycles (±0.05D) can double or triple the pipe embedment, and a number of cycles that might represent the entire lay process (∼100) could increase the pipe embedment by up to 8 times relative to the static embedment under the same vertical load. The amount of penetration is governed by the vertical load level relative to the bearing capacity, and the oscillation amplitude. Significant differences were observed between the two clays. The high plasticity clay was much more susceptible to softening and increased embedment under dynamic loading.
Experimental Analysis of High-Efficient Centrifugal Gas-Liquid Separators
Authors: Zhao Lixin , Zhu Baojun , Wang Yue
Published: July 2009

Application background of gas-liquid separators is introduced. Centrifugal gas-liquid separators have many advantages, which are analyzed by comparing with normal gravity settling facilities. Experimental research was carried out. Test rig and facilities are described. Test prototypes are transparent plexi-glass separators. Through transparent prototypes, interior flow field can be observed clearly. Experimental phenomena of different structure plexi-glass prototypes are compared with and analyzed, some test photos were recorded. Test data of plexi-glass prototypes were obtained. Results show that the separating performance of the centrifugal gas-liquid separators is satisfactory. The structural scheme of high-efficient separator design is concluded.
A Generalized Strip Theory for Curvilinear Motion in Waves
Authors: Sutulo Serge , Guedes Soares C.
Published: July 2009

A simulation-oriented mathematical model for a slender ship manoeuvring in waves was devised as a fusion of two classic linear strip theory implementations used separately in manoeuvring and seakeeping. Two basic requirements were formulated: the generalized model must reduce to the popular Salvesen–Tuck–Faltinsen seakeeping model in the particular case of the rectilinear base motion (constant speed advance) and to the Munk theory in absence of waves and wave-induced motions. It was assumed that the generalized model will then be reasonably consistent in intermediate regimes. The primary problem formulation was performed under the assumption that small-amplitude oscillations with the encounter frequency in regular seas are superimposed with the arbitrary base manoeuvring motion characterized by slowly-varying kinematic parameters. After the velocity potential’s decomposition into the quasi-steady and substantially unsteady parts, application of the Bernoulli equation, and further integration over the wetted surface (which can be taken in its equilibrium or instantaneous position) result in the representation of hydrodynamic forces in the frequency domain through longitudinal distributions of the sectional complex added masses and their longitudinal derivatives. The frequency-dependent coefficients are then approximated with rational fractions and, further, subjected to the Fourier transform. As a result, a set of ordinary differential equations for the time-dependent hydrodynamic forces and auxiliary state variables were obtained. The model was implemented as part of a manoeuvring simulation code and some time histories of various components of the hydrodynamic forces are given as illustrations.
A Practical Method for the Prediction of Planing Craft Motions in Regular and Irregular Waves
Authors: Sebastiani Luca , Bruzzone Dario , Gualeni Paola , Rambaldi Guido , Ruscelli Danilo , Viviani Michele
Published: July 2009

Leisure boats market has constantly grown during the recent years, entailing an increasing need of design tools. This seems particularly urgent for seakeeping and hydrodynamic performance prediction in the field of planing boats. Numerical methodologies are almost consolidated instruments for conventional displacement ships, while some shortcomings are still to be faced and overcome concerning planing craft, due to the high complexity of the hydrodynamic problem. The present paper describes a simplified methodology for the prediction of pitch, heave and roll motions of a planing boat, in regular and irregular waves. In the formulation, a 2D approach is adopted, based on ‘momentum theory’; various aspects of the wedge-theory are used in order to model the sectional characteristics, with particular attention to the added mass. A validation of the proposed methodology concerning vertical motions is presented against data available in literature.
Partial Safety Factors Assessment for Double Hull Tankers Following the New Common Structural Rules
Authors: Hussein Arwa W. , Guedes Soares C.
Published: July 2009

The partial safety factors are calculated for three double hull tankers of different size, designed according to the new IACS Common Structural Rules and based on load models estimated from the rule design values. The ultimate strength is calculated using progressive collapse method based on the net scantlings +50% of the corrosion addition, tnet+50, and applying the failure modes defined in the new rules defined in the Common Structural Rules. For one of the tankers the load models are calculated based on the actual load manual data. The still water bending moment is calculated for full load condition and the wave bending moment is based on direct calculations of wave induced load, determining the extreme value. The calculated loads are compared with the rule design values. Another load modeling based on the rule design values is calculated. The reliability and partial safety factors are calculated for both cases to show how the load models affect the values of partial safety factors. Sensitivity analysis is made to study the importance of the variables. The reliability of the three takers is calculated based on the rule design values and the corresponding partial safety factors are assessed. To achieve a certain pre defined level of reliability, a design modification factor is applied to the deck plating to adjust the ultimate strength. The loads are assumed to remain unchanged by the design modification factor.
Collapse Strength of Stiffened Panels With Local Dent Damage
Authors: Witkowska Malgorzata , Guedes Soares C.
Published: July 2009

In this study the behaviour and ultimate strength of damaged stiffened panels is investigated. The damage is in a form of local imperfection and represents a dent that could be caused by a fall or strike of an object. The model used is a panel made of five plates joined transversally with four longitudinal flat-bar stiffeners. Finite element non-linear analysis of panels having different geometrical properties is carried out. The influence of several parameters has been studied in order to establish their interaction with the presence of the local dent. It has been found that stiffened panels present quite good performance while subjected to the local damage, however, depending on geometrical characteristics, a problem of stiffener deformations may occur, significantly lowering the ultimate strength.
Adaptable Measuring Instrument for Wireless Dynamic Strain Monitoring on Moving Objects
Authors: Dzˇapo Hrvoje , Stare Zoran , Bobanac Nenad
Published: July 2009

Dynamic strain monitoring provides valuable information about behavior and condition of mechanical parts subjected to the load either under test or realistic working conditions. In many occasions, test points for strain measurement are not easily accessible for temporary or permanent wired connection with standard test and measurement equipment, especially for measurements on moving objects. We developed a configurable portable dynamic strain monitoring system, which is particularly suitable for short-term installations and adaptable for wide range of expected strain values. The high-accuracy measuring module, attached to the test point along with the strain gage sensor, digitizes and transmits measured data over the license-free ISM radio-frequency band to the receiving unit for further signal processing and results representation. The calibration procedure is highly simplified due to the specific design of the input analog measuring chain, which eliminates the need, in several commercially available similar instruments, for manual sensor calibration. The accuracy and the bandwidth of the input measuring chain were optimized to provide means for high quality spectral analysis of acquired dynamic strain waveforms. The system may be simply extended for dynamic torque, power and rotational speed measurements on revolving shafts, by connecting to the inductive proximity switch to the receiver module. Receiving unit also provides means for connection with other test and measurement equipment by standard analog and digital industrial communication protocols (4–20 mA current loop, RS485). The overall system was designed to accommodate to wide variety of test and research applications, as well as monitoring parameter ranges.
Experiments on VIV Under Frequency Modulation and at Constant Reynolds Numbers
Authors: Franzini Guilherme R. , Pereira Adriano A. P. , Fujarra Andre´ L. C. , Pesce Celso P.
Published: July 2009

The present paper presents a new mechanical apparatus, specially designed for investigating fundamental aspects of VIV in a Towing Tank. An electrically driven movable spring-leaf system was conceived and constructed to deal with elastic mounted cantilevered cylinders, either rigid or flexible ones. The apparatus has low structural damping and allows the excitation of VIV under continuously modulated spring rigidity, aiming at investigating the effect of natural frequency modulation on the response. The experiments were carried out at IPT Towing Tank, which is 280m long, 6m wide and 4m deep. Both rigid and flexible cantilevered cylinders mounted on the new apparatus were studied. In this paper, some results on the rigid cylinder are presented. A striking feature of such apparatus is the possibility to obtain the whole VIV amplitude and frequency response curves from a single run, under a single towing velocity, therefore at the same Reynolds number. This is possible as the reduced velocity varies along that particular constant velocity run, according to the natural frequency modulation.
Free Surface Flow Around Ship Hulls Using an Interface-Capturing Method
Authors: Ciortan C. , Guedes Soares C. , Wanderley J.
Published: July 2009

In the present paper, a compressible free surface code is used for simulating the flow around ship hulls. The code simulates both turbulent and laminar, free-surface flow around ship hulls, using the Slightly Compressible Flow formulation. The runs were performed for a Series60, Cb = 0.6 hull in standard conditions of Froude numbers and the results were compared against experimental and numerical results. The turbulence model used is Baldwin-Lomax. The numerical scheme was marched in time using the 2nd order, explicit Runge-Kutta. For the time being, the code uses a fixed grid on which the kinematic free surface equation is solved. Several boundary conditions were implemented and their behaviour assessed. The results show fair agreement with the experimental results.
Vortex Induced Motions of the Horn Mountain Truss Spar
Authors: Irani Mehernosh , Perryman Steve , Brewer Jonathan , McNeill Scot
Published: July 2009

Vortex Induced Motion (VIM) of a Spar platform is an important consideration in the design of Spar moorings and risers. During the design phase, the VIM characteristics of a Spar configuration are evaluated by hydrodynamic model testing. The basis for hydrodynamic model testing is that geometric and dynamic similitude between prototype and model parameters is preserved. Reynolds number and Froude number scaling are the two relevant scaling parameters for Spar VIM model testing. However, simultaneously satisfying Reynolds and Froude scaling for the model and prototype conditions is practically impossible. This leads to compromises in model test Reynolds number scaling and inherent uncertainties in extrapolating the model test VIM predictions to full-scale design conditions. Hence measurement of full-scale Spar VIM responses provides valuable data for validation of design assumptions. BP’s integrity management efforts for its Gulf of Mexico deep water production facilities include monitoring of the environmental conditions, and response of the hull, mooring and riser systems. Field measured data for VIM of BP’s Horn Mountain Truss Spar, presented in this paper, shows that the Horn Mountain Truss Spar VIM response is within original design assumptions. The maximum VIM measured in the field (A/D ≈ 0.26) is well below the acceptable design value of A/D = 0.5. The field data is analyzed and results presented in the form of Spar VIM response time traces, Spar VIM response versus Reduced Velocity and variation of period of VIM oscillation with Spar offsets. The field data shows VIM response characteristics consistent with model test observations.
Scale Effects: Correlation of Fatigue Capacity for Full-Scale Pipes and Samll-Scale Specimens
Authors: O̸rjasæter Oddvin L. , Knagenhjelm Han Olav , Haagensen Per J.
Published: July 2009

Increasing a component’s size is known to have detrimental effect on the fatigue performance. To account for this, reduction factors are given in several design codes. Away from plate products, there is no general consistency between the various correction procedures. The main causes of the scale effects can be divided into three phenomenon: Statistical effects (probability for defects that initiate cracks), technological effects (differences in material and production procedures for large and small components), and stress gradient effects (scaling differences for stress level for (small) cracks). In this paper the main factors influencing the scale effect is reviewed and correction rules are discussed. Fatigue data for 30” and ID6” pipes with girth welds are analysed and compared with medium sized sector specimens cut out from pipes. Also effects of weld quality and pipe alignment (hi/lo and angular distortion) in this context are discussed. On this basis, recommendations for applying the scale correction procedures for welded pipes are proposed.
Fatigue Life Prediction Due to Slug Flow in Extra Long Submarine Gas Pipelines
Authors: Kansao Rabih , Casanova Euro , Blanco Armando , Kenyery Frank , Rivero Mayela
Published: July 2009

Some offshore production fields require transporting of production fluids through very long submarines pipelines without a previous separation process. In the case of gas production, condensate will appear in the pipeline due to the pressure losses and low temperatures. For some production conditions a slug flow pattern may then develop in the pipeline, and because of the irregular sea bottom profile, there may be pipe unsupported spans of even hundreds of meters long. Therefore, slugs traveling in the pipeline will act as moving loads for the unsupported pipe, producing a dynamic response that in some cases might reduce the fatigue life of the pipeline. In this work, a finite element (FE) model of a pipeline transporting slugs has been developed and used to assess the fatigue life of a horizontal pipeline. Slug hydrodynamic characteristics have been obtained using Taitel & Barnea’s model. The structural FE model is based in Bernoulli beam elements where slugs, once they have been geometrically characterized, are input as moving loads traveling in the pipeline. The system dynamic response was calculated for different spans conditions and slugs characteristics corresponding to different gas-liquid ratios typical from gas field production conditions. Once a steady state condition was obtained in the dynamic response, mean and alternating stress levels were obtained for each analyzed case and introduced in fatigue formulae to obtain the fatigue life of the pipeline. Results show that for some production conditions and free span longitudes, fatigue life of pipeline may experience important reductions due to slug flow. These free spans are obviously most likely to happen in extra long submarines pipelines.
Enhancement of High Damping VIV Through Roughness Distribution for Energy Harnessing at 8×103 < Re < 1.5×105
Authors: Raghavan Kamaldev , Bernitsas Michael M.
Published: July 2009

Vortex Induced Vibration (VIV) of a circular cylinder in a steady flow is enhanced using distributed surface roughness. VIV enhancement is needed in harnessing clean and renewable energy from ocean/river currents using the VIVACE (VIV for Aquatic Clean Energy) Converter (Bernitsas et al. 2006a, 2006b; Raghavan et al. 2007). High damping is mandatory in energy harnessing and higher Reynolds numbers are required to reach the high lift TrSL3 regime. Roughness is added to the surface of the cylinder in the form of sandpaper strips to achieve three goals: (1) Trip separation in a controlled manner. (2) Fully correlate the flow regardless of the Reynolds number regime. (3) Energize the boundary layer, thus inducing higher vorticity and circulation and consequently lift. Our experiments show that it is possible to achieve all three goals and reach VIV amplitudes of 2.1 to 2.7 diameters under high damping. The range of synchronization increased dramatically but its end was not observed within the capabilities of our experimental facility.
Numerical Simulation of Oscillatory Shallow-Water Flow Around a Conical Headland Using the K-E and Algebraic Stress Turbulence Models
Authors: Hakimzadeh Habib
Published: July 2009

Oscillatory shallow-water flows around a headland of conical form have been investigated numerically using the k-ε and algebraic stress closure models of turbulence. The turbulent flow behind the headland was driven by oscillatory current in a tidal basin. Emphasis has been focused on comparing the more sophisticated turbulence models including: the k-ε and algebraic stress models to predict accurately the flow patterns within such tidal basins. The governing equations have been discretized using the finite difference method. The difference equations were then solved using the ADI algorithm. The advective terms in the k-ε equations were treated using the exquisite scheme. As for the experimental results, the numerical model tests have shown that the structure of eddy shedding was dependent on the Keulegan-Carpenter number. The experimental data from the UKCRF were used to check the numerical model results and it was found that both of the closure models of turbulence generally produced reasonable results for the tests considered within the coastal basin.
The Equivalent Design Pressure of Ship Frame Structures Under Bottom Slamming Loads
Authors: Wang Hui , Gu Xuekang , Shen Jinwei
Published: July 2009

Two-dimensional model drop tests were carried out to investigate slamming phenomena of a flat-inclined ship bottom in different drop heights. The water-entry velocities of the model, slamming pressures on the bottom and the resultant dynamic strains in the structures were recorded and the characteristic of the loads and structural responses were analyzed. To deduce design pressures for the frame structures, structural responses of the model under evenly distributed static pressures were calculated with the finite element method. Then, the experimental and calculated responses of the structures are compared with each other and a reduction factor is introduced to represent the relations of the two pressures. This reduction factor is linearly related to water-entry velocity and deadrise angle, and it could be used in the transformation of the measured slamming pressure peaks to equivalent design pressures in designing the frame structures of the bottom frames.
Dynamics of Boat Seine Fishing Using a Net Geometry Simulator
Authors: Suzuki Katsuya , Takagi Tsutomu
Published: July 2009

Boat seine fishing is used to catch mainly demersal species; it has many benefits such as reduced energy and labor costs, and low damage to the sea bottom if it is controlled. This fishing technique has complex motion between the seine boat and the supple net over large operating areas; therefore, the dynamics of its operating processes during fishing are unknown. To investigate the dynamics of boat seine fishing in detail, we calculated its dynamics during a fishing operation using a net geometry simulation system that we developed. Two experimental surveys were carried out in January 2007 at Hokkaido, Japan. Latitude, longitude, and depth were measured in 10 places, from casting the anchor buoy to picking up the seine net. Depth sensors were installed at the top and bottom of the seine net mouth to record a time series of net shape during fishing. Using our net geometry simulator, we simulated net shape and the dynamics of boat seine fishing based on ship position and net depth. Very close agreement was observed between the experimental and simulated depths of the top and bottom of the net mouth during fishing. Three-dimensional visualization of the simulation results showed the capture processes of this fishing technique in a large scale operation. This study shows that our method is valid for modeling fishing operations to better implement smart fishing.
Reduction/Suppression of VIV of Circular Cylinders Through Roughness Distribution at 8×103 < Re < 1.5×105
Authors: Bernitsas Michael M. , Raghavan Kamaldev
Published: July 2009

Vortex Induced Vibration (VIV) of a circular cylinder in a steady flow is reduced using distributed surface roughness. VIV reduction is needed in numerous applications where VIV is destructive. Roughness is distributed to the surface of the cylinder in the form of sandpaper strips to achieve three goals: (1) Trip separation in a controlled manner so that some uncertainties are removed and the flow becomes more predictable. (2) Reduce spanwise correlation, which is strongly linked to VIV. (3) Select roughness grit size to achieve the first goal without energizing too much the boundary layer, which would induce higher vorticity and circulation, and consequently lift. Our experiments show that it is possible to reduce VIV amplitude and synchronization range. More tests are needed to achieve full suppression. Our experiments are conducted in the TrSL2 and TrSL3 flow regimes.
Extreme Value Statistics of Wind Speed Data by the POT and AER Methods
Authors: Naess A. , Haug E.
Published: July 2009

The paper describes a new method for predicting the appropriate extreme value distribution derived from an observed time series. The method is based on introducing a cascade of conditioning approximations to the exact extreme value distribution. This allows for a rational way of capturing dependence effects in the time series. The performance of the method is compared with that of the peaks over threshold method.
Recent Advances in In-Situ Ocean Observation
Authors: Shih H. H.
Published: July 2009

Ocean observation has evolved tremendously, from collection and exchange of weather and sea state information by ocean going ships in the late 19th century to today’s multisensor, multi-platform, multi-disciplinary, large scale observation networks. Data are now transmitted and disseminated automatically in real-time to a variety of user groups with significant social and economical implications. This paper provides an overview of representative advances in in-situ ocean observation during the past decade. Major driving forces and representative advances and trends in in-situ observation are described. Advances are discussed under the categories of observation infrastructure and major measurement system components including sensor, platform, data collection and telemetry, and power supply. The U.S. National Oceanic and Atmospheric Administration (NOAA) is a major participant of the global ocean observation programs and examples of its contributions and activities are introduced.
An Experimental Study of Negative Drift Force Acting on a Floating OWC “Backward Bent Duct Buoy”
Authors: Imai Yasutaka , Toyota Kazutaka , Nagata Shuichi , Setoguchi Toshiaki , Oda Junko , Matsunaga Narimasa , Shimozono Takafumi
Published: July 2009

The utilization of renewable energy is required immediately since emissions of carbon dioxide are being restricted. To this end, we are investigating the ocean wave energy converter, especially the floating OWC “Backward Bent Duct Buoy” (BBDB). The BBDB, proposed by Masuda in 1986, is a wave energy converter of the ‘moored floating oscillating water column’ type that is composed of an air chamber, an L-shaped bent duct, a buoyancy chamber, and a turbine. The BBDB has certain positive characteristics. Firstly, the primary conversion performance of the BBDB is better than other floating OWCs. Secondly, the length of the BBDB is shorter than other floating OWCs. Thirdly, as the BBDB advances in the incident wave direction with slow speed waves because of the negative wave drift force, the mooring cost can be reduced. In this research, experiments under a various wave periods were carried out to clarify the characteristics and cause of the generation of negative drift force acting on a BBDB in regular waves with a two-dimensional wave tank at Saga University. The length of the BBDB model is 85cm. To measure the wave drift force, the model is moored with horizontal wire-springs. The motions of the BBDB, such as surge, heave, and pitch, are measured by remotely using image processing. The fluid velocity around the BBDB is measured by using particle image velocimetry (PIV). Motion tests of the BBDB without mooring are also carried out to measure the horizontal velocity of the BBDB in waves. From the experimental results, the characteristics and causes of the generation of negative drift force acting on the BBDB in regular waves are discussed.
On the Use of Belleville Washers to Reduce Relaxation in Bolted Flange Joints
Authors: Bouzid Abdel-Hakim , Nechache Akli
Published: July 2009

Bolted flange joints are prone to leakage when exposed to high temperature. In most cases this is due to relaxation that takes place as a result of material creep. One way to solve this problem is to use Belleville spring washers or longer bolt with spacers. However, there is practically no reliable analytical model that can evaluate the exact number of washers or length of the bolts required to reduce relaxation to a target minimum level. This paper describes an analytical model based on the flexibility and displacement interactions of the joint different elements including the axial rigidity of the flange and bolts, used to evaluate relaxation. The developed analytical flange model can accommodate either Belleville spring washers or longer bolts with spacer tubes to reduce the bolt load loss to a maximum target value. This model is validated by comparison with the more accurate FEA findings. Calculation examples on a bolted flanged joint are presented to illustrate the suggested analytical calculation procedure.
On the Application of Mindlin’s Plate Theory to Free Vibration Analysis of Piezoelectric Coupled Circular FGM Plate
Authors: Ebrahimi Farzad , Rastgoo Abbas
Published: July 2009

In this paper, a free vibration analysis of moderately thick circular functionally graded (FG) plate integrated with two thin piezoelectric (PZT4) layers is presented based on Mindlin plate theory. The material properties of the FG core plate are assumed to be graded in the thickness direction while the distribution of electric potential field along the thickness of piezoelectric layers is simulated by sinusoidal function. The differential equations of motion are solved analytically for two boundary conditions of the plate: clamped edge and simply supported edge. The analytical solution is validated by comparing the obtained resonant frequencies with those of an isotropic host plate. The emphasis is placed on investigating the effect of varying the gradient index of FG plate on the free vibration characteristics of the structure. Good agreement between the results of this paper and those of the finite element analyses validated the presented approach.
Some Topics in the Modal FRS Method
Authors: Ly B. L. , Sun L.
Published: July 2009

The following five common topics in the modal Floor Response Spectrum (FRS) method are examined: 1) The relationship between the effective mass and the total mass; 2) Estimation of the base shear; 3) Identification of a local mode; 4) The uniform acceleration to be applied in the equivalent static analysis method; 5) Correction for the residual rigid modes. This paper shows the usage of effective mass in determining the base shear. A quantitative method based on the ranking of the importance of a mode and the importance of a mass in a mode is given, in addition to graphic animations, to exclude a local mode. It also provides a more realistic static method with a less overly conservative acceleration.
Investigation on the Mechanisms of Strain Growth in Cylindrical Containment Vessels Subjected to Internal Blast Loading
Authors: Dong Q. , Li Q. M. , Zheng J. Y.
Published: July 2009

Strain growth is a phenomenon observed in the elastic response of containment vessels subjected to internal blast loading. The local dynamic response of a containment vessel may become larger in a later stage than its response in the earlier stage. In order to find out the possible mechanisms of the strain growth phenomenon, the natural frequencies and mode shapes of various vibration modes in cylindrical shells with different boundary conditions are obtained theoretically and numerically. The dynamic elastic responses of cylindrical shells subjected to internal blast loading are studied by theoretical analysis and finite element simulation using LS-DYNA. It is found that strain growth in cylindrical containment vessels is mainly caused by linear modal superposition and nonlinear modal coupling. The effects of the reflected blast shock waves and structural perturbation are discussed. The proposed theory for the strain growth mechanisms may guide the safe design of cylindrical containment vessels.
Effect of Crack Detection Performance and Sizing Accuracy on Reliability of Piping With Stress Corrosion Cracks
Authors: Machida Hideo , Yamashita Norimichi
Published: July 2009

Integrity assessment of primary recirculation system (PLR) piping with stress corrosion cracks is one of the recent interests in Japanese BWR plants. Crack detection performance and a sizing error in non-destructive test (NDT) have a great influence on the integrity assessment of piping. This paper presents effects of crack detection performance and sizing accuracy on the reliability of PLR piping with stress corrosion cracks. Failure probability (leak and break) of PLR piping maintained according to the rules in Fitness-For-Service (FFS) Codes of JSME was analyzed using a probabilistic fracture mechanics (PFM) code which could analyze initiation and growth behavior of stress corrosion cracks. For the reliability of PLR piping, reducing oversight of cracks and crack sizing error are effective, and detectable crack size has not much influence on reliability of piping. For the higher reliability, reducing oversight of cracks is more important than the improvement of the detectable crack size in NDT, and the qualified inspectors should be employed for sizing of detected cracks in order to be suitable measurement in NDT.