bluuebunny/crossref_metadata_2025 huggingface dataset:
On the Use of Blades Stagger and Stacking in Turbine Stage Optimization
Authors: Arabnia Mohammad , Ghaly Wahid
Published: January 2011

The flow in modern turbines is highly three dimensional and fairly complex. This paper presents a practical and effective optimization approach to minimize 3D-related flow losses by re-staggering and re-stacking the blades. This approach is applied to the redesign of a low speed high subsonic single stage turbine, that was designed and tested in Hannover, Germany. The optimization is performed at the design point and the objective function is given by a weighted sum of individual objectives, namely stage efficiency and streamwise vorticity downstream of the rotor and stator, and is penalized with one constraint, namely the design mass flow rate. A Genetic Algorithm (GA) is coupled with a Response Surface Approximation (RSA) of the Artificial Neural Network (ANN) type. A relatively small data set of high fidelity 3D flow simulations that is obtained using Fluent, is used to train and test the ANN model. The variation of stagger angle and stacking are parametrically represented using a quadratic rational Bezier curve (QRBC). The QRBC parameters are directly related to the design variables, namely the rotor and stator lean & sweep angles, and their stagger distribution. Moreover, it results in eliminating infeasible shapes and in reducing the number of design variables to a minimum while providing a wide design space for the blade shape. This optimization approach results in an improvement of 1.74% to 1.91% in stage efficiency. This optimization approach is found to be helpful in understanding the physical implications of the design variables and in interpreting their effect on the stage performance.
Vibrations of the LH2 Turbine Rotor During the Vinci Engine Test: Tip Timing Measurements and Predictions
Authors: Andersson Clas , Grasbon Peter , Merchant Simon
Published: January 2011

A test campaign with the purpose of demonstrating new technologies introduced in the Vinci engine was performed in 2008. One of these new technologies is the blisk technology included in the LH2 fuel and LOX oxidizer pump turbines, for which Volvo Aero Corporation has the design responsibility. A challenge with blisks in rotating machinery is the risk of large amplitude vibrations due to low damping. To address the mechanical integrity of the Vinci LH2 turbine rotor blisk with respect to vibrations, an advanced blade vibration measurement system using the blade tip timing method was designed and implemented in close cooperation with the subcontractor AGILIS. The implementation of tip timing for measuring the blade vibrations of the Vinci LH2 blisk was recognized as a challenging application for this kind of measurement system. The conditions in the LH2 turbine are harsh with temperatures down to about 80 K with high pressure and hydrogen environment. Nevertheless, these challenges were systematically investigated rendering a successful implementation. The detailed analysis of the tip timing test data provided unique information for validation. More resonances than expected were confirmed. The responses, however, were modest rendering a low risk for HCF in the test. The most severe resonance in the test with respect to HCF was excited by the second stator harmonics. It was excited several times in the test campaign at about 69200 rpm. This resonance was also pointed out in the design process as being the worst one with respect to HCF. Hence, even though the test data revealed more resonances than expected, the most critical one was identified by the VAC design tool prior to the test. The agreement in predictions and test results for the critical mode was very good with respect to both frequency and response. This statement of very good agreement also applies to the frequencies associated with the other resonances in the test.
Full Scale Wind Turbine Flowfield Measurements Using a 7-Sensor Fast Response Probe
Authors: Mansour M. , Kocer G. , Lenherr C. , Chokani N. , Abhari R. S.
Published: January 2011

The unsteady wind profile in the atmospheric boundary layer upstream of a modern wind turbine is measured. The measurements are accomplished using a novel measurement approach that is developed and demonstrated for wind energy applications. The measurements of the unsteady 3D velocity field have to be resolved in a low dynamic head environment and over large flow angles around a modern wind turbine (rotor diameter 80–120m and tower height 60–100m). The novel measurement approach is comprised of an autonomous Uninhabited Aerial Vehicle (UAV) that is equipped with a seven-sensor fast-response aerodynamic probe (F7S-UAV). The autonomous UAV enables high spatial resolution (∼9% of rotor diameter) measurements, which hitherto have not been accomplished around full-scale wind turbines. The 7-sensor fast-response aerodynamic probe developed at ETH Zurich is the key-enabling technology for the measurements. This measurement system is realized as a light, compact measurement chain that conforms to the limited payload area and weight restrictions of the UAV. The time-averaged wind profile from the F7S-UAV probe is found to be in very good agreement to an independently measured profile using the UAV. This time-averaged profile, which is measured at a wind turbine that is located in moderately complex terrain, differs by as much as 30% from the wind profile that is extrapolated from a logarithmic height formula; therefore the limited utility of extrapolated profiles, which are commonly used in site assessments, is made evident. The time-varying wind profiles show that, at a given height, the velocity fluctuations can be as much as 44% of the time-averaged velocity, therefore indicating that the wind turbine and its components, notably the gearbox, will experience substantial loads that may impact the fatigue life of the components. Furthermore, the shear in the velocity profile also subjects the fixed pitch blade to varying incidences and loading. Analysis of the associated velocity triangles indicates that the sectional lift coefficient at mid-span of this modern turbine would vary by 12% in the measured time-averaged wind profile. These variations must be accounted in the structural design of the blades. Thus the measurements of the unsteady wind profile accomplished with this novel measurement system, demonstrate that it is a cost effective complement to the suite of available site assessment measurement tools.
Comparison of Gas-Oil and Bio-Oil Spray Performance for Use in a Gas Turbine
Authors: Crayford Andrew P. , Bowen Philip J. , Kay Peter J. , Laget Hannes
Published: January 2011

This study forms part of an ongoing program to investigate the feasibility of substituting a bio-oil for gas-oil in gas turbine applications. In this paper, the influence of the change of fluid properties on spray characteristics is presented and analyzed. It was not feasible to characterize the spray at full-scale operating conditions, and so a scaling methodology was adopted using published correlations. The study was conducted in three stages; a scaled nozzle was selected utilizing a published correlation to ensure the spray characteristics match the critical characteristics of the full-scale nozzle. The scaled nozzle was then characterized with a gas-oil as a benchmark for comparison with the bio-oil tests. Finally bio-oil tests were conducted at elevated fuel preheat temperatures and the spray characteristics compared to the benchmark case. The objective of the program was to provide an insight into the effect of fuel preheat on spray characteristics. The results of this program helped determine scaled operating conditions for a subsequent atmospheric combustion program, not presented in this paper. The spray characterization was conducted in the atmospheric spray rig (ASR) located at Cardiff University’s GTRC, at Port Talbot, UK. The experiments presented were conducted using bio-oil at elevated fuel preheat temperatures. The spray structure and mean droplet sizes are measured for a bio-oil at various initial pre-heat temperatures and compared with the benchmark gas-oil case. Operating conditions were chosen to maintain an equivalent thermal load of approximately 1.5 MW. Good quality PDA data were recorded for all cases and demonstrated that primary spray characteristics for bio-oil could be optimized and matched to those of gas-oil utilizing the same fuel delivery system. This was achieved by implementing a fuel pre-heat of 80 °C, thereby changing the delivery conditions of the bio-oil.
Numerical and Experimental Investigation of Turning Flow Effects on Innovative Pin Fin Arrangements for Trailing Edge Cooling Configurations
Authors: Bianchini C. , Facchini B. , Simonetti F. , Tarchi L. , Zecchi S.
Published: January 2011

The effect of the array configuration of circular pin-fins is investigated from a numerical and experimental point of view reproducing a typical cooling scheme of a real high pressure aeroengine blade. The airstream enters the domain of interest radially from the hub inlet and exits axially from the trailing edge (TE) outlet section. More than one hundred turbulators are inserted in the wedge shaped TE duct to enhance the heat transfer: a reference array implementing 7 rows of staggered pins is compared with an innovative pentagonal arrangement. Investigations were made considering real engine flow conditions: both numerical calculations and experimental measurements were performed fixing Re = 18000 and Ma = 0.3 in the TE throat section. The effect of the tip mass flow rate was also taken into account, investigating 0% and 25% of the TE mass flow rate. The experimental activity was aimed at obtaining detailed heat transfer coefficient maps over the internal pressure side (PS) surface by means of the transient technique with thermochromic liquid crystals. Particle Image Velocimetry measurements were performed and surface flow visualizations were made by means of the oil & dye technique on the PS surface. Steady-state RANS simulations were performed with two different CFD codes: the commercial software Ansys CFX® 11.0 and an in-house solver based on the opensource toolbox OpenFOAM®, to compare the performance and predictive capabilities. Turbulence was modeled by means of the k–ω SST model with an hybrid near wall treatment allowing strong clustering of the wall of interest as well as quite coarse refinement on the other viscous surfaces.
Overhaul and Uprate of Industrial Gas Turbines by an Alternate Service Provider
Authors: Arnal Michel
Published: January 2011

This paper reviews specific methods used by Wood Group Gas Turbine Services for boosting power output and improving heat rate for existing industrial gas turbines. The methods employed allow operators to make the most of existing equipment as a cost-effective alternative to the replacement of a complete engine. The article summarizes experience with the service and uprate of General Electric Frame 6B gas turbines using the company’s Advanced Parts Manufacture (APM™) turbine parts. A comparison of output and heat rate before and after service allows estimates of the performance improvement for individual components and combinations of hot gas path parts. Such comprehensive upgrades can be implemented only in older generation gas turbines that are part of a model line which the original equipment manufacturer (OEM) has redesigned. An ideal example of such a gas turbine model is the General Electric Frame 6B series. Wood Group Gas Turbine Services has extensive experience in overhauling and uprating the complete range of Frame 6B gas turbines. The company’s replacement parts have been installed in all stages of the hot gas path both as complete sets and in stages in combination with OEM parts in neighboring stages. Examples of components which can be upgraded include: • Turbine vanes and blades; • Combustion Lines and transition pieces; • Heat shields / shroud blocks; • Seals and clearances. All of these can be installed to increase the engine firing temperature and improve performance. The performance data is corrected to ISO conditions to enable a fair and meaningful comparison. The different configurations employed for the overhauls also permit estimates of the contribution of the replacement parts to the overall improvement in performance. Design details of the advanced technology parts are described as needed to provide understanding for the improvements in engine efficiency.
Composition Dependent Model for the Prediction of Syngas Ash Deposition With Application to a Leading Edge Turbine Vane
Authors: Sreedharan Sai Shrinivas , Tafti Danesh K.
Published: January 2011

An improved physical model to predict flyash deposition is developed and discussed in this paper. This model differs from its predecessor [1, 2] by accounting for deposition of syngas ash particles below the ash softening temperature. The modified deposition model is based on the critical viscosity approach. To test this model, deposition of ash particles impacted on a flat, 45° wedge shape geometry is computed and the results obtained from the numerical model are compared to Crosby et al. [3]. Large Eddy Simulation (LES) is used to model the flow field and flyash particles are modeled using a discrete Lagrangian framework. Results quantify deposition for 4 pm particles of various ash composition samples. Most of the deposition occurs at the stagnation region of the target plate. At 1456K, out of all the ash samples considered in this study, ND ash sample shows the highest capture efficiency (8.84%) and HNP01 ash sample exhibits the lowest capture efficiency (3.61%). In general, capture efficiencies for all ash samples followed an exponential trend with temperature. Additionally, this model is also compared to results obtained from the flat plate deposition experiments conducted here at Virginia Tech using PVC particles [4]. In the case of PVC particles, the sticking probability in the deposition model assumed an exponential increase in deposition rate with temperature and was calibrated with one experimental data point. The results obtained from this model for PVC particles showed excellent agreement with the experimental measurements over a range of temperatures.
Wet Compression Analysis Including Velocity Slip Effects
Authors: White A. J. , Meacock A. J.
Published: January 2011

Injection of water droplets into industrial gas turbines in order to boost power output is now common practice. The intention is usually to saturate and cool the intake air, especially in hot and dry climates, but in many cases droplets carry over into the compressor and continue to evaporate. Evaporation within the compressor itself (often referred to as “overspray”) is also central to several advanced wet cycles, including the Moist Air Turbine (MAT) and the so-called TOPHAT cycle. The resulting wet compression process affords a number of thermodynamic advantages, such as reduced compression work, and increased mass flow rate and specific heat capacity of the turbine flow. Against these benefits, many of the compressor stages will operate at significantly off-design flow angles, thereby compromising aerodynamic performance. The current paper describes wet compression calculations including velocity slip and many of the associated phenomena (e.g., blade deposition and film evaporation). The calculations also allow for a poly-dispersion of droplet sizes and droplet temperature relaxation effects (i.e., the full droplet energy equation is solved rather than assuming that droplets adopt the wet-bulb temperature). The latter is important for sprays produced by “flashing” since the resulting droplets are initially much hotter than the surrounding gas. The method has been applied to a “generic” twelve stage compressor to ascertain to the impact slip effects have on the wet compression process.
Investigating the Transient Flooding and Sloshing in Internal Compartments of an ITTC Damaged Ro-Ro Passenger Ferry: Part II—Experimental Analysis
Authors: Khaddaj-Mallat Chadi , Vadeboin Fabienne , Davoust Laurent , Pettinotti Bruno , Alessandrini Bertrand , Rousset Jean-Marc , Ferrant Pierre
Published: January 2011

Passenger Ro-Ro ferries have proved to be extremely vulnerable regarding their hydrostatic stability when damaged. This is not only due to the design of their car decks. After an abrupt ingress of water caused by a maritime accident, the spaces below the car deck can experience dangerous intermediate flooding stages that might lead the ship to sink. The intermediate flooding stages depend upon hosts of factors that are interdependent. Some of them eventually interact during the flooding. An experimental campaign using the midsection of the PRR02 - ITTC/SiW passenger Ro-Ro ferry was devoted to provide a thorough insight to the flooding physics and to quantify these interactions using a novel-to-ocean-engineering methodology, the so-called DOE method. The physical background and the experimental set up of this campaign are presented in the previous one (OMAE2010-20047). This paper is devoted to presenting the experimental methodology and the first findings. The flooding is found a complex phenomenon in which a strong interaction between water and air occurs, also in coupling with the hydrodynamic efforts. Model tests based on one-factor-at-a-time experiments highlights the importance of the damage area and the time of damage creation in the ship behavior during the transient phase. We advocate the use of the DOE methodology to deal with stability problems and to find a model quantifying the intermediate flooding stages.
The Influence of Seabed Response on Fatigue Performance of Steel Catenary Risers in Touchdown Zone
Authors: Shiri Hodjat , Randolph Mark
Published: January 2011

The significant influence of the riser-seabed interaction on the fatigue performance of steel catenary risers is now widely accepted. Most design, however, is still carried out using linear seabed springs, and assuming a flat seabed. Improved nonlinear hysteretic seabed models have recently been proposed, which automatically simulate the different stiffness in the seabed response through the touchdown zone. A further consideration, however, is the influence of the trench that forms at the seabed. ROV surveys have shown that trenches several diameters deep can develop beneath the riser in the early stages of the SCR life, and a critical question is how this affects the fatigue life. A non-linear soil hysteretic model has been used to model gradual trench development in the touchdown zone. Initially, the seabed model parameters are adjusted to allow trenches of varying depth to be developed over a moderate number of displacement cycles of the SCR. Design wave spectra are then applied, simulating a generic Spar system, after correcting the model parameters to more typical values normal range. The paper presents results that show the impact of trenches of different depths on the fatigue performance of SCRs in the touchdown zone.
Second-Order Diffraction and Radiation of a Floating Body With Small Forward Speed
Authors: Shao Yan-Lin , Faltinsen Odd M.
Published: January 2011

The formulation of the second-order wave-current-body problem in the inertial coordinate system involves higher-order derivatives in the body boundary condition. A new method taking advantage of the body-fixed coordinate system in the near field is presented to avoid the calculation of higher-order derivatives in the body boundary condition. The new method has advantage over the traditional method when the body surface is with sharp corner or high curvature. The nonlinear wave diffraction and forced oscillation of floating bodies are studied up to second order in wave slope. A small forward speed is taken into account. The results of the new method are compared with that of the traditional method based on a formulation in the inertial coordinate system. When the traditional method applies, good agreement has been obtained.
Coupling Effects Between Tank Sloshing and Motions of a LNG Carrier
Authors: Clauss Gu¨nther F. , Testa Daniel , Sprenger Florian
Published: January 2011

Free liquid surfaces inside the cargo tanks of seagoing ships not only reduce the initial stability but also influence the sea-keeping characteristics, in particular roll motions. Due to the increasing demand of liquefied natural gas (LNG), the concept of offshore processing or receiving terminals will gain in importance. Since pipelines are not economic for long distances, LNG is transported by shuttle carriers from remote marine locations for onshore energy supply. The loading/unloading procedure of an average carrier vessel takes 18 to 24 hours — a time span where the tanks are partially filled and feature free liquid surfaces. Depending on the filling level, the wave incident angle as well as the phase shift of tank sloshing and body motions, the characteristics of the vessel’s response amplitude operators (RAO), especially the roll motion, are altering. This is ascribed to coupling effects between the moving liquid and the hull motions. Hence, the seakeeping characteristics have to be reappraised for each case. A 138,000 m3 LNG carrier with four membrane tanks is numerically analysed with a potential theory based software at different filling levels and wave incident angles in frequency domain. For experimental validation, the tanks are filled with water. Optical motion sensors and transient wave packages are used to determine the RAOs in six degrees of freedom. Additionally, the forces and moments induced by the sloshing liquid are measured by six-component force sensors. On this basis, further computations with LNG are conducted. The focus of the investigations lies on the influence of sloshing on the surge and roll motions of the exemplarily chosen LNG carrier. Instead of one single resonance peak as for the solid filling case, the roll RAO of the dual-mass system features two peaks, whose magnitude and position depends on the filling level of the cargo tanks. But coupling effects due to resonant sloshing also affect longitudinal body motions. The knowledge of the altered seakeeping characteristics of LNG carriers due to free liquid surfaces is essential for save offshore transfer operations.
Nonlinear Dynamics of a Floating Wave Energy Converter Reacting Against the Sea Bottom Through a Tight Mooring Cable
Authors: Vicente Pedro C. , Falca˜o Anto´nio F. O. , Justino Paulo A. P.
Published: January 2011

Tightly moored single-body floating devices are an important class of offshore wave energy converters. Examples are the devices under development at the University of Uppsala, Sweden, and Oregon State University, USA, prototypes of which were recently tested off the western coast of Sweden and off the Oregon coast, respectively. These devices are equipped with a linear electrical generator. The mooring system consists of a cable that is kept tight by a spring or equivalent device. This cable also prevents the buoy from drifting away by providing a horizontal restoring force. The horizontal and (to a lesser extent) the vertical restoring force are nonlinear functions of the vertical and horizontal displacements of the buoy, which makes the system a nonlinear one (even if the spring and damper are linear), whose modelling requires a time-domain analysis. Such an analysis is presented, preceded by a simpler frequency-domain approach. Numerical results (motions and absorbed power) are shown for a system consisting of a hemispherical buoy in regular and irregular waves, a tight mooring cable and a power take-off system consisting of a linear spring and a linear damper.
Wave Diffraction by a Harbour With Circular Arc Profile by Scaled Boundary FEM
Authors: Tao Longbin , Song Hao
Published: January 2011

In this paper, wave diffraction by a harbour is studied by the scaled boundary finite-element method (SBFEM). The semi-analytical approach, with the combined advantages of both finite-element and boundary-element methods, is based on linear wave theory and is applicable to harbours of circular arc profile. The whole solution domain is divided into one unbounded subdomain and one bounded sub-domain by the profile of the harbour. The effects of the incident wave angle and the opening angle of the harbour are discussed. Discretising only the circumference of the harbour, the current semi-analytical SBFEM model exhibits excellent computational accuracy and efficiency. The technique can be extended to solve more practical wave-structure interaction problems with increased complexity.
Research on Corner Structure Under Explosive Loading for War-Ship Cabin
Authors: Kong Xiangshao , Xu Shuangxi , Wu Weiguo , Li Xiaobin , Zheng Yuanzhou
Published: January 2011

For the warship cabin under explosive loading, the detail structure in cabin corner can easily be torn by the high-strength shock wave converging at the structure corner. In order to avoid that the crevasse occurs at the corner firstly, three strengthening structure forms were designed for the cabin corner: thickening connection, circular connection and inclined plate connection. Failure process of the joint in the two-cabin structure under the explosive loading was simulated by the nonlinear dynamic software DYTRAN. Comparing the response of the corner strengthening structure to that of the conventional structure, it was concluded that three strengthening structure forms changed failure mode of the cabin structure effectively and the crevasse initiated at the explosion pressure release hole on the transverse bulkhead, which reduced the tearing of the cabin corner. To seek more reasonable corner strengthening structure, the pressure and the stress on the bulkhead under the explosive loading of the three corner strengthening structures were compared. The results showed the inclined plate connection can prevent the shock wave from concentrating at the corner, decrease the stress on the longitudinal bulkhead, and resist the shock wave spreading into the inner cabins most effectively in the three strengthening forms.
Fault Isolation and Quality Assessment for Shipboard Monitoring
Authors: Lajic Zoran , Nielsen Ulrik Dam , Blanke Mogens
Published: January 2011

In this paper a new approach for increasing the overall reliability of a monitoring and decision support system will be explained. The focus is on systems used for ship operator guidance with respect to, say, speed and heading. The basic idea is to convert the given system into a fault tolerant system and to improve multi-sensor data fusion for the particular system. Fault isolation is an important part of the fault tolerant design for in-service monitoring and decision support systems for ships. In the paper, a virtual example of fault isolation will be presented. Several possible faults will be simulated and isolated using residuals and the generalized likelihood ratio (GLR) algorithm. It will be demonstrated that the approach can be used to increase accuracy of sea state estimations employing sensor fusion quality test.
A Finite Macro-Element for Cylindrical Layer Modeling
Authors: Provasi Rodrigo , Martins Clo´vis de Arruda
Published: January 2011

The offshore industry is in constant evolution due to the need of reach increasing water depths for new oil fields exploitation. In this scenario, not only new types of platforms are being designed, but also new types of risers, including flexible pipes and new umbilical cable configurations. The greatest difficulty to generate a new concept for a riser is to determine if it is viable or not. Flexible pipes and umbilical cables are complicated to model, due to the interactions between their layers and the large number of possible arrangements. To predict the behavior of flexible pipes and umbilical cables, adequate models are necessary. One can rely on finite element models, which show a great difficulty in mesh generation and convergence (specially due to the contact pairs). One can also rely on analytical models, which have many limitations due to simplifications (even though they are necessary). Another possible approach is to define macro elements, which represent a component, instead of classical finite elements (such as tetrahedric elements). Related to that approach, this paper presents a tubular element, which describes a cylinder with isotropic properties and can accept various sorts of loads. This element has its displacements and loads described using Fourier series and, for each term of the series, a solution is obtained. The effect is then superposed and the complete solution is obtained. This formulation is implemented and their results compared to those obtained by a classical finite element modeling tool, with good agreement.
Variation of Heave Added Mass and Damping Near Seabed
Authors: Wadhwa Hemlata , Krishnamoorthy Balaji , Thiagarajan Krish P.
Published: January 2011

During installation of subsea structures such as mud mats, the tension in crane wires can experience spikes when the structure is near the seabed. It is hypothesized that such spikes may be caused by the structure undergoing resonant oscillations, which in turn may be due to changes in added mass and damping near the seabed. Such motions can cause hardship for operators as they interfere with precise positioning during installation. With increasing exploration and production in deep and remote fields, the size and weight of subsea equipments are continuously increasing. Installation operations such as lifting and lowering, positioning of the object require good knowledge of the hydrodynamic coefficients. Following on ideas used in Norwegian offshore, the mud mat is modeled as a circular disk. Experiments are conducted on an oscillating solid disk of diameter and thickness 200 mm and 2 mm respectively. The heave oscillations are forced by a programmable actuator, at amplitudes varying from 1–56 mm and frequencies from 1.0–1.8 Hz. The elevation ‘h’ of the disk from the mean seabed is varied from 0.2–2 times the disk radius. The forces on the disk are measured using a submersible high-sensitivity load cell. The motions of the disk are restricted to axial (heave) direction, and are measured with a displacement transducer. The measured forces and displacement are analyzed using a Fourier Transform algorithm to separate the added mass and damping effects. The authors have found similar trends in the hydrodynamic behavior of a disk approaching the seabed to what was found when the disk approached the free surface in Wadhwa & Thiagarajan [1]. The added mass and damping coefficients were found to increase with increasing KC, as well as with increasing proximity to the seabed. Another noticeable feature of the experiments was the cavity formation underneath the oscillating structure. The width of the cavity was about 3–4 times the radius of the disk and depth was about one third/fourth of the radius of the disk. The size of the cavity and the increase in hydrodynamic forces near the seabed suggest the importance of knowledge of hydrodynamic behavior near the seabed.
Emerging Trends in Umbilical Technology: Limitations and Recommendations
Authors: Dobson Alan , Fogg Dave
Published: January 2011

The impact of increasingly diverse functional requirements and extreme service conditions is having a significant effect upon the evolution of accepted umbilical technology. The current trend in deep water developments in the Gulf of Mexico, Brazil and West Africa coupled with a more diverse range of functional requirements such as medium voltage power supply to subsea equipment, high pressure and high temperature fluid injection, and integrated service functionality has lead to the development of a number of niche solutions being developed. These generally fall outside of the traditional umbilical design scope and as such are not effectively governed by existing industry design standards. The paper will discuss the current trends in umbilical technology; describing the limitations of existing accepted technologies with respect to functionality and extreme service requirements and highlight emerging technologies which are being developed by industry to address current limitations. The current legislative deficiencies related to emerging technologies will be discussed and will be focused upon medium voltage power umbilicals, high pressure high temperature umbilicals, and integrated service umbilicals.
Hydrodynamic Verification on the Motion Characteristics of FPSO Based on the Full Scale Measurement Data Features of Current and Wind
Authors: Zhao Wenhua , Yang Jianmin , Hu Zhiqiang , Wei Yuefeng
Published: January 2011

FPSO is subjected to complex sea loads during its service life. Series of coupled hydrodynamic analysis in time domain for FPSO and its mooring system have been conducted within the recent ten years. Among these analyses, the coefficients of wind force and current force for FPSO hull were calculated by the empirical formulae mostly. It is known that these coefficients are of great importance in the motion predictions of the FPSO in the analysis. The verification of the feasibility of these formulae is necessary. In this paper, the feasibility and the accuracy of these empirical formulae are verified through the comparison between the results of hydrodynamic analysis and those of full scale measurement data. A full scale measurement project sponsored by CNOOC for Nanhai Fenjin, an FPSO operating in South China Sea, has been carrying out by Shanghai Jiao Tong University since Oct 2007. Large amount of valuable data of the six-degree motions for the FPSO has been obtained. To do the comparison, a typical serious sea state is selected out to be the objective course. In the course, the response spectrums for heave, roll and pitch motions are calculated based on the measurement data. Besides, a series of coupled hydrodynamic analysis for the FPSO are conducted, using the code DeepC. The response spectrums of the motions for heave, roll and pitch in the same sea state are also obtained through the spectrum analysis. Using these motion spectrums, comparisons between the results of hydrodynamic analysis and those of full scale measurement are fulfilled. With the comparisons, the feasibility of the empirical formulae of the coefficients for wind force and current force are verified. The correction coefficients are added to the empirical formulae and new hydrodynamic analysis based on the new formulae are conducted. It is shown that the new analysis results are in good agreement with those of the full scale measurement, which validated the practicability and feasibility of the modified formulae on the motion prediction of FPSO.
High Resolution Wave Tank Testing of Scaled Wave Energy Devices
Authors: Rhinefrank Ken , Schacher Al , Prudell Joe , Stillinger Chad , Naviaux David , Brekken Ted , von Jouanne Annette , Newborn David , Yim Solomon , Cox Dan
Published: January 2011

In many industries, such as the wave energy industry, the importance of accurate physical model testing in the development process to full scale devices cannot be overemphasized. This paper presents a new, high-precision wave tank testing system and process designed and implemented by Columbia Power Technologies (CPT) and Oregon State University (OSU). The system’s high level of functionality was demonstrated during characterization of CPT’s wave energy converter (WEC) and is now established at OSU’s O.H. Hinsdale Wave Research Laboratory (HWRL), in collaboration with the Northwest National Marine Renewable Energy Center (NNMREC) headquartered at OSU. The critical instrumentation, optical motion tracking system, data acquisition and related components developed for wave tank testing are fully characterized herein, and the paper concludes with example testing of a scaled wave energy device including experimental results.
Estimation of the Long Term Correlation Coefficients by Simulation
Authors: Petricic Martin , Mansour Alaa E.
Published: January 2011

This paper proposes a simulation method for obtaining the estimate of the long term correlation coefficients between different low-frequency wave-induced loads acting on a ship hull. They are essential part of the load combination procedures in design and strength evaluations. Existing theory is limited to linear time-invariant systems with weakly stationary stochastic inputs such as waves during a single sea state (short-term). The simulation treats the non-stationary wave elevations during the ship’s entire life (long-term) as a sequence of different stationary Gaussian stochastic processes. Different sea states (HS, T0, Wave Direction) are sampled, using rejection sampling, from the joint probability density functions fitted to every Marsden zone on the ship’s route. The time series of the loads are simulated from the load spectra for each sea state, including the effects of loading condition, heading, speed, seasonality and voluntary as well as involuntary speed reduction. The estimates of the correlation coefficients are then calculated from these time series. The simulation time can be significantly reduced (to the order of seconds rather than hours and days) by introducing the seasonal variations into a single voyage. It is proven that the estimate of the correlation coefficient, obtained by simulating only a single voyage, approaches the true correlation coefficient in probability as the number of simulated load values increases. The simulation method can also be used for finding the long-term exceedance probabilities of the peak values of individual loads as well as for analyzing various load combinations (linear and nonlinear). Related concepts and limitations of this method are demonstrated by an example of a containership operating between Boston, MA and Southampton, UK.
An Experimental Study on Rigid-Object Water-Entry Impact and Contact Dynamics
Authors: Challa Ravi , Idichandy V. G. , Vendhan C. P. , Yim Solomon
Published: January 2011

The dynamics of a generic rigid water-landing object (WLO) during water impact is presented in this paper. Tests from a range of drop heights were performed in a wave basin using a 1/6th-Froude scale model of a practical prototype using different drop mechanisms to determine the water impact and contact effects. The first experimental case involved dropping the WLO by using a rope and pulley arrangement, while the second case employed an electromagnetic release to drop the object. Hydrodynamic parameters including peak acceleration, touchdown pressure and maximum impact/contact force were measured using the two different drop mechanisms. The WLO was assumed as rigid, so the experimental results could be correlated with von Karman and Wagner closed form solutions and the maximum accelerations predicted are bounded by these classical analytical solutions. The major purpose of this study are to use the experiments to determine trends that occur when the object is dropped from successive heights using different drop mechanisms by varying the entry speed, angle of impact and the weight of the object. The predictions from the experimental results were used for subsequent numerical studies. Results from the drop tests show that the impact acceleration and touchdown pressure increases practically linearly with the increase in the height of the drop and the data provides conditions of drop mechanism that keep impact accelerations under specified limits for the WLO prototype.
Finite-Element and Smoothed Particle Hydrodynamics Modeling of Rigid-Object Water-Entry Impact Dynamics and Validation With Experimental Results
Authors: Challa Ravi , Yim Solomon , Idichandy V. G. , Vendhan C. P.
Published: January 2011

A numerical study on the dynamic response of a generic rigid water-landing object (WLO) during water impact is presented in this paper. The effect of this impact is often prominent in the design phase of the re-entry project, to determine the maximum force it is subjected to, for material strength determination to ensure structural and equipment integrity, human safety and comfort. The predictive capability of the explicit finite-element arbitrary Lagrangian-Eulerian (ALE) and smoothed particle hydrodynamics (SPH) methods of a state-of-the-art nonlinear dynamic finite-element code for simulation of coupled dynamic fluid structure interaction (FSI) responses of the splashdown event of a WLO were evaluated. The numerical predictions are first validated with experimental data for the maximum impact accelerations and then used to supplement experimental drop tests to establish trends over a wide range of conditions including variations in vertical velocity, entry angle and object weight. The results show that the fully coupled FSI models can capture the water-impact response accurately for all range of drop tests considered and the impact accelerations are practically linearly with the increase in the height of the drop. The reliability of the maximum impact accelerations was calibrated with approximate classical von Karman and Wagner closed-form solutions.
Lattice Boltzmann Simulation of Hydro-Turbine Blade Hydrofoil in the Exploitation of Tidal Current Energy
Authors: Wang Shujie , Wang Yingying , Yuan Peng , Xu Chao
Published: January 2011

As tidal current regarded as a sustainable resource to be exploited for future generation of electrical power, the hydrodynamics of hydro-turbine has become a focus in research for the extraction of energy from marine currents. The lift and drag characteristics of hydro-turbine’s blade hydrofoil are the key factors affecting efficiency and cavitation and vortex are considered as the important influences on life span of blade hydrofoil. Lattice Boltzmann Method (LBM), a new numerical method of computational fluid dynamics, is adopted to simulate and analyze the performance of blade hydrofoil. NACA0012, NACA63-215, NACA2412, NACA4411 and NACA4424 are simulated at different angles of attack using D2Q9 model and boundary condition of nonequilibrium bounce-back scheme to obtain pressure coefficient, lift coefficient, drag coefficient and streamline in each regime. Suitable hydrofoil and angle of attack can be chosen and utilized based on the results obtained which compared well with the results published in the technical literature, and accuracy and feasibility of LB method for engineering application are verified simultaneously.
Modeling and Analysis of a Free Spanning Pipeline With Randomly Distributed Corrosion
Authors: Li Lei , Lin Mian
Published: January 2011

Some corrosion defects will appear outside the aged submarine pipelines due to the corrosive sea environment. These defects can depress the strength and integration of the pipeline systems. This paper establishes a novel model using finite element method to describe the corroded pipelines with randomly distributed corrosion defects according to the probability function. Several free spanning pipelines models with random corrosion of different distributed parameters (averaged value and variance) are presented. Then the displacement and stress distribution of the pipelines are calculated subject to external fluid forces. The wet modes are calculated subsequently. At last the effects of the characteristic parameters of corrosion defects are discussed by analyzing the present results. Some conclusion may be useful for perceiving the randomly distributed corrosion how to affect the pipelines operation status.
Behavior of Installation for Suction Anchor in Soft Clay
Authors: Li Ling-ling , Dai Heng-jun , Wang Li-zhong
Published: January 2011

Suction anchor foundations are being increasingly used for a variety of offshore application. In designing a suction anchor geotechnical engineering must consider the installation process as well as the in-place performance. The main objective of the present study was to investigate the penetration behavior of the suction anchor in normally consolidated and sensitive clay. Numerical analyses are preformed to study the installation by suction in soft clay. The effects of the penetration depth, the shear strength ratio along the interface between the anchor and the clay on the installation process on the failure mechanism and the pattern of soil flow at the anchor tip during installation are discussed in detail. The shear strength reduction factor is the key factor of the installation procedure, and it has a strong effect on the limited installable aspect ratio. The displacement vectors show that the clay beneath the anchor tip will move up inside the anchor when the anchor moves down while soils beneath the tip as well as soils outside the skirt wall also flow inward at the reverse bearing capacity failure. Finally, some conclusions are made, which can be useful in practice.
Fatigue Analysis of Multi-Spanning Subsea Pipeline
Authors: Rezazadeh Kosar , Zhu Liyun , Bai Yong , Zhang Liang
Published: January 2011

Free-span occurs normally in pipeline at uneven seabed, dynamic seabed or pipeline crossing. The analysis of free-span, including static analysis and dynamic analysis, is an important subject in the study of pipeline integrity management. Static analysis of free span for subsea pipeline is to evaluate the stress distribution of spanning pipeline in the ultimate conditions, and qualify the stress with design codes in the engineering analysis. However, dynamic analysis of subsea spanning pipeline is much complicated due to VIV fatigue. In 2006 DNV-RP-F105 suggested a methodology of dynamic analysis for long spanning pipeline with multi-mode responses, but the fatigue analysis method for multi-modes is not detailed. In addition, the fatigue analysis of multi-spanning pipeline is not clear. The gap between the continuous two spans, and the pipe-soil interaction control the fatigue damage of the multi-spanning pipeline. In this paper, a VIV fatigue analysis method for multi-spanning pipeline is suggested based on VIV analysis. In this method, Abaqus FE model is developed first to obtain the stress distribution and the natural frequency of each vibration mode for spanning pipeline on seabed in different configurations with three multi-spans, and then the fatigue analysis of VIV is carried out for the spanning pipeline based on DNV-RP-F105. An example of fatigue analysis for a multi-spanning pipeline is presented; finally, several sensitivity analyses demonstrate the effects of key parameters on the VIV fatigue.
Measurement of Soil Suction and Soil-Water Characteristics of Bentonite-Sand Mixtures
Authors: Hu Pan , Yang Qing , Luan Maotian
Published: January 2011

The soil-water characteristic curve (SWCC) is a widely used experimental means for assessing fundamental properties of unsaturated soils for a wide range of soil suction values. The study of SWCC is helpful because some properties of unsaturated soils can be predicted from it. Nowadays, much attention has been paid to the behaviours of highly compacted bentonite-sand mixtures used in engineering barriers for high level radioactive nuclear waste disposal. It is very important to study the various performances of bentonite-sand mixtures in order to insure the safety of high-level radioactive waste (HLW) repository. After an introduction to vapor phase method and osmotic technique, a laboratory study has been carried out on compacted bentonite-sand mixtures. The SWCC of bentonite-sand mixtures has been obtained and analyzed. The results show that the vapor phase method and osmotic technique is suitable to the unsaturated soils with high and low suction.
Re-Evaluation of VIV Riser Fatigue Damage
Authors: Modarres-Sadeghi Yahya , Bourguet Re´mi , Triantafyllou Michael S. , Tognarelli Michael , Beynet Pierre
Published: January 2011

The paper describes a new characterization of the properties of the vortex-induced vibrations (VIV) of marine risers, which emerges from processing field and experimental data. We show that two currently employed assumptions: (a) that VIV is a statistically steady-state response containing one or several frequencies, and (b) that VIV consists of alternating dominant modes (mode-sharing), are inadequate. Instead, we find that the response either contains strong traveling wave components accompanied by high force harmonics; or consists of a chaotic wandering among several traveling and standing waves, associated with a wide-band spectrum; both types of response require careful consideration for correct fatigue evaluation.