bluuebunny/crossref_metadata_2025 huggingface dataset:
Acoustic Perturbation Effects on the Fluid Dynamics and Swirling Flame Response in a Non-Premixed Co-Flow Burner
Authors: Idahosa Uyi , Saha Abhishek , Khatami Navid , Xu Chengying , Basu Saptarshi
Published: January 2011

An investigation into the response of non-premixed swirling flames to acoustic perturbations at various frequencies (fp = 0–315 Hz) and swirl intensities (S = 0.09 and 0.34) is carried out. Perturbations are generated using a loudspeaker at the base of an atmospheric co-flow burner with resulting velocity oscillation amplitudes |u′/Uavg| in the 0.03–0.30 range. The dependence of flame dynamics on the relative richness of the flame is investigated by studying various constant fuel flow rate flame configurations. Flame heat release is quantitatively measured and simultaneously imaged using a photomultiplier (PMT) and a phase-locked CCD camera. Both of which are fitted with 430nm bandpass filters for observing CH*chemiluminescence. The flame response is observed to exhibit a low-pass filter characteristic with minimal flame response beyond pulsing frequencies of 200Hz. Flames at lower fuel flow rates are observed to remain attached to the central fuel pipe at all acoustic pulsing frequencies. PIV imaging of the associated isothermal fields show the amplification in flame aspect ratio is caused by the narrowing of the inner recirculation zone (IRZ). The Rayleigh criterion (R) is used to assess the potential for instability of specific perturbation configurations and is found to be a good predictor of unstable modes. Phase conditioned analysis of the flame dynamics yield additional criteria in highly responsive modes to include the effective amplitude of velocity oscillations induced by the acoustic pulsing. Highly amplified responses were observed in pulsed flame configurations with Strouhal numbers (St = fpUavg/dm) in the 1–3.5 range. Heat release to velocity perturbation time delays on the order of the acoustic pulsing period also characterized the highly responsive flames. Finally, wavelet analyses of heat release perturbations indicate sustained low frequency oscillations that become more prominent for low acoustic pulsing frequencies in lean flame configurations.
Active Control of Combustion Instabilities in a Matrix Burner Using Primary and Pilot Fuel and Acoustic Forcing
Authors: Bohn Dieter , Ohlendorf Nils , Weidner Frank , Willie James F.
Published: January 2011

Lean premixed flames applied in modern gas turbines leads to reduce NOx emissions, but at the same time they are more susceptible to combustion instabilities than diffusion flames. These oscillations cause pressure fluctuations with high amplitudes and unacceptable noise as well as the risk of component or even engine failure. They can lead to pockets of fuel being formed in the mixing chamber and to bad mixing, which leads to increase in emissions. This paper reports the successful decoupling of the pressure and heat release inside the combustion chamber of a matrix burner using two actuation techniques. This led to the successful attenuation of the dominant instability modes occurring inside the combustor of the matrix burner. In the first case, acoustic forcing was used to decouple the pressure and the heat release inside the combustor. This was achieved by using a loudspeaker to modulate the primary air mass flow. This was followed by using acoustic forcing in CFD to decouple the pressure and heat release inside the combustor. For the action of the loudspeaker, sinusoidal forcing was used to mimic the modulation action of the diaphragm of the loudspeaker. In the second case, a fast gaseous “on-off” injector was used to modulate the primary fuel mass flow. After this, pilot fuel modulation was used to stabilize the flame. The control law governing the primary and pilot fuel modulation is discussed in details. The effect of open loop control on NOx emissions in the burner is also reported and discussed.
Channel Height and Jet Spacing Effect on Heat Transfer and Uniformity Coefficient on an Inline Row Impingement Channel
Authors: Ricklick Mark , Claretti Roberto , Kapat J. S.
Published: January 2011

Future high performance turbine airfoils will likely be cooled in a near wall configuration, potentially employing a combination of narrow, distributed internal cooling channels and impingement. In such applications, the jets impinge against a target surface, and then exit along the channel formed by the jet plate, target plate, and side walls. Local convection coefficients are the result of both the jet impact, as well as the channel flow produced from the exiting jets and the complex interaction between the jet and the cross flow. Numerous studies have explored the effects of jet array and channel configurations on both target and jet plate heat transfer coefficients, yet with little consideration of thermal stress related effects. A detailed study on the uniformity coefficient that these jets and cross flow generate on the surface is carried out. It is important to maintain a high uniformity coefficient while still having a high heat transfer coefficients to reduce thermal stresses. It is also important to use as little flow as possible while maintaining a high heat transfer coefficient. The study presented experimentally investigates the effects of wall height, jet Reynolds number, and jet spacing on the Nusselt number and uniformity of a narrow inline row impingement channel. The channel height was set at 1, 3, and 5 diameters, jet spacing was 5 and 15 diameters, and the channel width was kept constant at 4 diameters. Although heat transfer coefficients are highly sensitive to the jet Reynolds number and channel height, the uniformity of the distribution is mainly governed by the channel height and jet spacing. A channel height of 3 jet diameters tended to produce the best uniformity coefficients, regardless of the jet to jet spacing; with side walls out performing target surfaces.
Two Schemes of Multi-Objective Aerodynamic Optimization for Centrifugal Impeller Using Response Surface Model and Genetic Algorithm
Authors: Liu Xiaomin , Zhang Wenbin
Published: January 2011

This paper presents two schemes of multi-objective aerodynamic optimization design for centrifugal impeller blade. One is genetic algorithm(GA) combined with a commercial computational fluid dynamics(CFD) software, and the other is GA combined with the surrogate model. The two schemes are respectively applied to multi-objective optimization for the same centrifugal impeller blade. For multi-objective genetic algorithm(MOGA), non-uniform mutation and Pareto ranking and fitness-sharing technique are used to obtain fast convergence speed and good capability to search the Pareto front of GA. For the surrogate model based on radial basis function(RBF), design of experiments(DOE) technology is adopted to select samples. The parameters and weight coefficients in the surrogate model are solved by GA instead of traditional least square method. According to the geometrical feature of centrifugal impeller, a three-dimensional reconstruction method for the blade shape based on non-uniform rational B-spline(NURBS) is introduced. The numerical simulation is used to evaluate the aerodynamic performance of the optimal and initial impeller. The computational results show that the aerodynamic performance of impellers designed by both optimization schemes is improved to some extent. At the same time, the main reasons for the improvement in aerodynamic performance of the optimal impeller are revealed. For the optimal impellers, the isentropic efficiency and total pressure ratio are increased by about 1.0% and 3.0% respectively. Through comparison of two schemes applied to the centrifugal impeller optimization design, it is found that the computational performance of the second optimization scheme is superior to that of the first optimization scheme.
Forced Response Analysis of Mistuned Turbine Bladings
Authors: Siewert Christian , Stu¨er Heinrich
Published: January 2011

It is well-known that the vibrational behavior of a mistuned bladed disk differs strongly from that of a tuned bladed disk. A large number of publications dealing with the dynamics of a mis-tuned bladed disk is available in the literature. Nearly all published mechanical models for a mistuned bladed disk consider the mistuning in terms of a perturbation of the mass and/or the stiffness matrix or in terms of a perturbation of the tuned system natural frequencies. Therefore, the possible effect of a damping mistuning is neglected in these models. In this paper, a model of a mistuned bladed disk with a combined damping and natural frequency mistuning is presented. This model is based on the well-known Fundamental Model of Mistuning with a novel extension to include the damping mistuning in a straight-forward way.
Acoustic Analysis of the NREL Phase VI Wind Turbine
Authors: Ranft Kirsten , Ameri Ali A. , Alexander J. Iwan D. , Envia Edmane
Published: January 2011

The aim of this work is to predict the aerodynamic noise emitted from the NREL Phase VI Wind Turbine [1]. Specifically rotational noise and broadband noise of the blade have been investigated. The approach to predict aeroacoustic noise is based on the acoustic analogy [2]. In acoustic analogy, the sources of aerodynamic noise are derived from the flow equations and the resulting radiated noise is calculated using the Ffowcs Williams and Hawkings equation [3]. Thus, the prediction of aerodynamic noise requires an accurate solution of the flow field. In this work the flow field around the blade has been modeled using FLUENT’s k-ω SST turbulence model. A hybrid grid containing approximately 1.5 × 106 tetrahedral and prismatic elements has been created. The near field around the blade is a structured O-grid with 100 cells along the chord and 50 cells normal to the blade surface. To obtain the resolution of the viscous sublayer, a y+ of approximately unity has been chosen. For the flow computation a simple scheme is used with a second order upwind method and wind speeds of 7m/s, 10m/s and 25 m/s, respectively and a rotor rotation speed of 72 rpm.
Littoral Combat Ship (LCS), Gas Turbine Reliability Engineering Implementation
Authors: Dundics Marton , Finley Brian , Krooner Ken , Roche Thomas , Rodgers Robert
Published: January 2011

The development of the Littoral Combat Ship (LCS) and its life cycle support design objectives were driven by three key objectives: 1) High level of ship mission availability while performing any one of the three mission capabilities; 2) Minimal Total Ownership Cost (TOC); 3) Manning compliment lower than the similar predecessor class of ships. To achieve these concurrent goals, the ship design provides functionality including advanced automation for machinery control, as well as mission function reconfiguration and execution. Unfortunately, information-based automated machinery reliability management decision support was not part of the ship design. This type of decision support is vital in enabling a significantly reduced crew and the advance planning required for executing the scheduled short maintenance availabilities. Leveraging existing equipment monitoring technologies deployed throughout the legacy fleet with the reliability engineering approach on LCS will improve the operational availability of gas turbine propulsion systems and allow executing the ship’s Concept of Operations (CONOPS). To address the reliability and TOC risks with the initially defined sustainment approach, a Reliability Engineering derived Condition Based Maintenance (CBM) strategy was developed, such that it could be implemented using a proven remote monitoring infrastructure. This paper will describe the Reliability Engineering based CBM approach and how it will be implemented on the LCS-1 and LCS-2 propulsion gas turbine engines and other critical systems to achieve system level operational reliability, the LCS life cycle support design objectives, and defined sustainment strategies.
Numerical Simulation of Combustion Processes and Analysis of Temperature Field Non-Uniformity in GTE-65 Gas Turbine Combustor
Authors: Tarasov Dmitry , Lebedev Alexander , Simin Nikolay , Grinevich Viktor
Published: January 2011

Our company has tested annular combustion chamber, being one of main components of hot gas path for GTE-65 gas turbine in mid power class. In order to arrange gaseous fuel oxidation process a method of lean homogenized air-fuel mixture burning is realized in the combustor. The same type two-contour burner modules are installed on the combustor cap in two rows by 60 burners in a row (120 burners in all). To optimize control algorithm and confirm main performances a model compartment, representing 1/12 part (segment) of actual combustion chamber, was produced. The tests have been conducted with using GP “Ivchenko-Progress” and OJSC “Power Machines” test rigs on modes from ignition to full load. Stable firing mode and pollutant emissions have been determined and the liner temperature condition and temperature field unevenness have been checked. The combustor control algorithm was optimized. As a result of the conducted tests there were confirmed environmental requirements to the combustor NOx emissions (less than 25 ppm). Mathematical simulating machine was being used to predict the combustor operation performances at the gas turbine operating in field conditions. 3D numerical analysis was carried out to predict the temperature and NOx fields before the experiment preparation. In order to meet the numerical model with the test conditions after the experiment the boundary conditions were specified (fuel / air temperature and mass flow rate). Full and partial load calculations were performed for simulation and field operation conditions. The calculation results were compared with experimental data obtained in the course of bench test. Errors obtained by comparison with numerical and experimental data were as follows: • full model pressure drop: ∼ 3–4%; • ratio of peripheral and radial non-uniformities of temperature fields: ∼ 2%; • nitrogen oxides at various operation modes: maximum 25 ppm. The obtained results make it possible to go on the combustor testing in field conditions.
Experimental Study of Surface Roughness Effects on a Turbine Airfoil in a Linear Cascade: Part I—External Heat Transfer
Authors: Lorenz M. , Schulz A. , Bauer H.-J.
Published: January 2011

The present experimental study is part of a comprehensive heat transfer analysis on a highly loaded low pressure turbine blade and endwall with varying surface roughness. Whereas a former paper [1] focused on full span heat transfer of a smooth airfoil and surface roughness effects on the endwall, in this work further measurements at the airfoil midspan with different deterministic surface roughness are considered. Part I investigates the external heat transfer enhancement due to rough surfaces whereas part II focuses on surface roughness effects on aerodynamic losses. A set of different arrays of deterministic roughness is investigated in these experiments, varying the height and eccentricity of the roughness elements, showing the combined influence of roughness height and anisotropy of the rough surfaces on laminar to turbulent transition and the turbulent boundary layer as well as boundary layer separation on the pressure and suction side. It is shown that — besides the known effect of roughness height — eccentricity of roughness plays a major role in the onset of transition and the turbulent heat transfer. The experiments are conducted at several free-stream turbulence levels (Tu1 = 1.4% to 10.1%) and different Reynolds numbers.
Hybrid LES Approach for Practical Turbomachinery Flows: Part 2—Further Applications
Authors: Tucker Paul , Eastwood Simon , Klostermeier Christian , Xia Hao , Ray Prasun , Tyacke James , Dawes William
Published: January 2011

A hybrid Large Eddy Simulation (LES) related technique is used to explore some key turbomachinery relevant flows. Near wall RANS modeling is used to cover over especially small scales, the LES resolution of which is generally intractable with current computational power. Away from walls, large eddy type simulation is used but with no LES model (NLES). Linking of the two model zones through a Hamilton-Jacobi equation is explored. The hybrid strategy is used to predict turbine and compressor endwall flows, flow around a fan blade section, jet flows and a cutback trailing edge. Also, application of NLES to the flow in an idealized high pressure compressor drum cavity is considered. Generally, encouraging results are found. However, challenges remain, especially for flows where transition modeling is important.
Aerodynamics and Heat Transfer for a Cooled One and One-Half Stage High-Pressure Turbine: Part III—Impact of Hot Streak Characteristics on Blade Row Heat Flux
Authors: Mathison R. M. , Haldeman C. W. , Dunn M. G.
Published: January 2011

The influence of hot streak magnitude and alignment relative to the vane leading edge on blade row heat flux are investigated for a one and one-half stage high-pressure turbine with a film-cooled vane, purge cooling, and un-cooled blades. The full-stage turbine is operated at design-corrected conditions. In addition to investigating the impact of different hot-streak characteristics, this study also looks at the interaction of cooling flow with the hot streaks. This paper builds on the investigation of profile migration utilizing temperature measurements presented in Part I and the heat transfer measurements presented in Part II. Hot streaks aligned with the vane mid-pitch have a greater impact on blade temperatures and heat-flux values than hot streaks aligned with the vane leading edge. The leading edge hot streaks tend to be mixed out over the surface of the vane. The magnitude of the hot streak is observed to have the largest influence on the temperature and heat flux for the downstream blade. Time-accurate measurements confirm these conclusions and indicate that further analysis of the time-accurate data is warranted. Film cooling is found to impact a hot streak profile in a way similar to that observed for a radial profile. Differences in core to coolant temperature ratio cause the uniform profile to show different coolant effects, but the overall spread of the cooling appears similar.
Application, Calculation and Experimental Evaluation of SCF for Aluminum Drill Pipe With Steel Connector
Authors: Tikhonov Vadim , Kultsep Alexander , Alikin Rudolf , Gelfgat Mikhail , Basovich Vladimir , Kostarev Viktor
Published: January 2011

Aluminum alloys are among the most promising materials for manufacture of drill pipes for deepwater and ultra-deepwater drilling in corrosive environment. Aluminum drill pipes are made with steel tool-joints to increase the number of connection makings-and-breakings. One of the major concerns of aluminum drill pipe operation in deepwater complex profile wells is the fatigue of their connection. This paper presents the results of study of fatigue properties of aluminum alloy 1953T1 Light Alloy Drill Pipes of Improved Dependability (LAIDP) 147×13 mm that are most extensively used in Russia. During assembly, the pin and box of steel tool-joint are heated and screwed on the tubular ends. After cooling, this assembly provides a reliable permanent connection. The study includes experimental determination of the S-N curve of small-scale specimens of aluminum tubular, FEA of the connection with the SCF determined and fatigue testing of the full-scale LAIDP connection. FEA is based on 3D model. The material properties of tubular are modeled as elastic-plastic. The distribution of hot-assembly stresses is considered in detail. Alternating bending load is applied by several semi-cycles. The results of analysis of Stress Concentration Factor (SCF) at various axial loads, bending moment ranges, friction factors of contact surfaces and interference of connection are given. Full-scale fatigue testing of connection specimen is carried out to verify the results of analysis.
Intermediate Ocean Wave Termination Using a Cycloidal Wave Energy Converter
Authors: Siegel Stefan G. , Jeans Tiger , McLaughlin Thomas
Published: January 2011

We investigate a lift based wave energy converter (WEC), namely, a cycloidal turbine, as a wave termination device. A cycloidal turbine employs the same geometry as the well established Cycloidal or Voith-Schneider Propeller. The interaction of intermediate water waves with the Cycloidal WEC is presented in this paper. The cycloidal WEC consists of a shaft and one or more hydrofoils that are attached eccentrically to the main shaft and can be adjusted in pitch angle as the Cycloidal WEC rotates. The main shaft is aligned parallel to the wave crests and fully submerged at a fixed depth. We show that the geometry of the Cycloidal WEC is suitable for wave termination of straight crested waves. Two-dimensional potential flow simulations are presented where the hydrofoils are modeled as point vortices. The operation of the Cycloidal WEC both as a wave generator as well as a wave energy converter interacting with a linear Airy wave is demonstrated. The influence that the design parameters radius and submergence depth on the performance of the WEC have is shown. For optimal parameter choices, we demonstrate inviscid energy conversion efficiencies of up to 95% of the incoming wave energy to shaft energy. This is achieved by using feedback control to synchronize the rotational rate and phase of the Cycloidal WEC to the incoming wave. While we show complete termination of the incoming wave, the remainder of the energy is lost to harmonic waves travelling in the upwave and downwave direction.
Extreme Response Analysis of Floating Structures Using Coupled Frequency Domain Analysis
Authors: Low Ying Min , Grime Andrew J.
Published: January 2011

In the dynamic analysis of a floating structure, coupled analysis refers to a procedure in which the vessel, moorings and risers are modeled as a whole system, thus allowing for the interactions between the various system components. Because coupled analysis in the time domain is impractical owing to prohibitive computational costs, a highly efficient frequency domain approach was developed in a previous work, wherein the drag forces are linearized. The study showed that provided the geometric nonlinearity of the moorings/risers is insignificant, which often holds for ultra-deepwater systems, the mean-squared responses yielded by the time and frequency domain methods are in close agreement. Practical design is concerned with the extreme response, for which the mean upcrossing rate is a key parameter. Crossing rate analysis based on statistical techniques is complicated as the total response occurs at two timescales, with the low frequency contribution being notably non-Gaussian. Many studies have been devoted to this problem, mainly relying on a technique originating from Kac and Siegert; however, these studies have mostly been confined to a single-degree-of-freedom system. The aim of this work is to apply statistical techniques in conjunction with frequency domain analysis to predict the extreme responses of the coupled system, in particular the modes with a prominent low frequency component. It is found that the crossing rates for surge, sway and yaw thus obtained agree well with those extracted from time domain simulation, whereas the result for roll is less favorable, and the reasons are discussed.
Tension-Based Tension Leg Platform: Technologies for Ultra Deepwater Applications
Authors: Srinivasan Nagan
Published: January 2011

This paper is about technology of the Tension Leg Platform (TLP) for use in ultra deepwater to support dry-tree in oil and gas production. New TLP concept for ultra deepwater development is introduced in this paper. A technically feasible and cost-effective artificial sea-bed is used to ease the tendon design practical at such deep water in harsh environment. The truss-pontoon is utilized to reduce the vertical and horizontal wave loadings. A simple and slim hull easy to design, fabricate, transport and install is obtained. Installation method is illustrated. Optional riser-support tower is proposed to make production risers feasible in 8000 ft of water depth with no riser pre-tension to the hull and with no vortex induced vibration problems. The paper enhances the TLP capability in deepwater.
Investigating the Transient Flooding and Sloshing in Internal Compartments of an ITTC Damaged Ro-Ro Passenger Ferry: Part I—Experimental Setup
Authors: Khaddaj-Mallat Chadi , Toularastel Jean-Luc , 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 intermediate flooding stages that might be more severe than the final condition, and the ship could actually sink in these early stages. The intermediate flooding stages depend upon hosts of factors pertaining to the vessel itself, the accident that caused the damage, as well as the environment. These factors are interdependent, and some of them 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 by quantifying these interactions using a novel-to-ocean-engineering methodology, the so-called DOE method, and try to find and then optimize a model for the transient flooding phase of Passenger Ro-Ro ferries. The present paper presents the physical background of the problem, as well as the innovative experimental set up that have been conceived to attain the objectives and hopefully lead to sound conclusions.
Simulation of Jack-Up Overturning Using the Monte Carlo Method With Artificially Increased Significant Wave Height
Authors: Jensen Jo̸rgen Juncher
Published: January 2011

It is well known from linear analyses in stochastic seaway that the mean out-crossing rate of a level r is given through the reliability index, defined as r divided by the standard deviation. Hence, the reliability index becomes inversely proportional to the significant wave height. For non-linear processes the mean out-crossing rate depends non-linearly on the response level r and a good estimate can be found using the First Order Reliability Method (FORM), see e.g. Jensen and Capul (2006). The FORM analysis also shows that the reliability index is strictly inversely proportional to the significant wave height irrespectively of the non-linearity in the system. However, the FORM analysis only gives an approximation to the mean out-crossing rate. A more exact result can be obtained by Monte Carlo simulations, but the necessary length of the time domain simulations for very low out-crossing rates might be prohibitive long. In such cases the property mentioned above for the FORM reliability index can be assumed valid in the Monte Carlo simulations making it possible to increase the out-crossing rates and thus reduced the necessary length of the time domain simulations by applying a larger significant wave height than relevant from a design point-of-view. The mean out-crossing rate thus obtained can then afterwards be scaled down to the actual significant wave height. Some previous results using this property have been presented by Tonguc and So¨ding (1986), albeit in a more empirical way. In the present paper the usefulness of this property to estimate extreme wave loads will be evaluated considering the overturning of a jack-up rig.
On the Mechanics of a Subsea Gas Pipeline Vibration
Authors: Osheku Charles A. , Olunloyo Vincent O. S. , Olayiwola Patrick S.
Published: January 2011

A well-posed boundary value problem of mathematical physics, governing the vibration characteristics of a deep offshore gas transmission pipeline, as influenced by the mechanics of fluid-structure-mud flow interaction is formulated. For this problem, a segment of a gas transmission pipeline is partially buried in the muddy soil under the ocean-floor, which is idealized as an elastic beam on an elastic foundation, is investigated analytically. By employing integral transforms, closed form analytical results, for the dynamic interaction response and the two natural frequencies associated with each mode of vibration are derived. In particular, the effect of operating variables such as the internal fluid transmission velocity, temperature and pressure variations, compressibility factor, geotechnical properties, debris and mud flow velocities are demonstrated for design analysis and field applications.
Residual Stress Effects on the Crack-Front Constraints for Surface Cracks in Pipes
Authors: Qian Xudong , Li Tieping
Published: January 2011

This paper investigates the effect of residual stresses on the linear-elastic KI-T fields along the front of circumferential surface cracks in pipelines. The numerical procedure simulates three typical patterns of residual stresses through a modified eigenstrain approach, which combines a thermal loading with a mechanical traction imposed on the heat-affected zone. The three residual stress profiles considered correspond to the high-heat input, the medium-heat input and the low heat input welding processes for circumferential butt welds in pipes outlined in BS 7910. The linear-elastic KI-T stresses, computed from the interaction-integral approach, characterize the constraints along the front of the circumferential flaw. The numerical investigation, covering a comprehensive matrix of geometric parameters, shows that different residual stress fields impose substantial effects on the KI-T stresses along the front of the surface crack in the wall of a pipeline. The deepest point along the crack-front often experiences low crack-front constraints characterized by the computed negative T-stresses for all three residual stress fields considered. The magnitudes of the KI-values and T-stresses show pronounced variations with the change in the ratio of the crack depth over the wall thickness of the pipe (a/t). The variation in the crack aspect ratio (the crack depth over the crack length, a/c) introduces marginal variation in the computed T stresses. The ratio of the outer diameter to the wall thickness of pipe imposes very little effect on the linear-elastic crack-front constraints for the geometric parameters considered.
Stochastic Models for Long-Term Prediction of Extreme Waves: A Literature Survey
Authors: Vanem Erik
Published: January 2011

This paper presents a literature survey on time-dependent statistical modelling of extreme waves. The focus is twofold: on statistical modelling of extreme waves and time-dependent statistical modelling. The first part will consist of a thorough literature review of statistical modelling of extreme waves and wave parameters. The second part will focus on statistical modelling of time- and space-dependent variables in a more general sense, and will focus on the methodology and models used also in other relevant application areas. It was found that limited effort has been put on developing statistical models for waves incorporating spatial and long-term temporal variability and it is suggested that model improvements could be achieved by adopting approaches from other application areas. Finally, a review of projections of future extreme wave climate is presented.
The Response of an Elastically Mounted Rigid Cylinder Subjected to Vortex Shedding and Support Motion
Authors: Soares Luiz F. N. , Wanderley Juan B. V. , Vitola Marcelo , Sphaier Sergio H. , Levi Carlos
Published: January 2011

The vortex induced vibration (VIV) on a circular cylinder is investigated by the numerical solution of the two-dimensional Reynolds average Navier-Stokes equations. An upwind and Total Variation Diminishing (TVD) conservative scheme is used to solve the governing equations written in curvilinear coordinates and the k–ε turbulence model is used to simulate the turbulent flow in the wake of the body. The cylinder is supported by a spring and a damper and free to vibrate in the transverse direction. Results are obtained for the phase angle, amplitude, and frequency for an elastically mounted rigid cylinder subjected to vortex shedding and support motion. The numerical results showed the strong influence of the support motion on the response amplitude. This kind of scenario is found in the attachment between platform and riser. The motion of platforms on the ocean free surface can cause this kind of excitation and amplify the vortex induced vibration response amplitude of risers.
Time Domain VIV Prediction for Top Tensioned Risers
Authors: Cheng Yongming , Lambrakos Kostas F. , Burke Roger , Stanton Paul
Published: January 2011

Top Tensioned Risers (TTRs) have been widely used with floating production systems such as Spars and TLPs in deepwater field developments. A TTR system provides direct access to subsea wells from a floating platform for drilling, workover, and completion operations. It is often subjected to Vortex-Induced Vibration (VIV) caused by ambient ocean currents or vessel motions. This paper investigates time domain VIV prediction for TTRs used in a typical Spar floating production system. A typical TTR has strong nonlinear and time-varying dynamic characteristics. The existing gaps between the riser and keel guide and between riser top centralizers and the supporting conductor result in intermittent VIV behaviors of the riser. In addition, hydraulic tensioners are widely used to provide tension to a TTR. The tension from tensioners varies with the riser’s dynamic response especially in the vertical direction. The time domain approach, which has been benchmarked and published in about ten technical papers, is thus more appropriate to predict TTRs’ VIV performance than a frequency domain method. This paper first introduces a typical TTR structure and then presents the analysis methodology and features of the time domain VIV prediction program ABAVIV. An example TTR is used to illustrate intermittent VIV behaviors such as top tension, interaction load at the keel guide, and VIV response at the location of top centralizers. This paper further studies the sensitivity of the VIV response to different current profiles. It finally uses the time domain approach to analyze the VIV response of the riser with its boundary conditions fixed and compares the results with those from a frequency domain program. A conclusion is finally drawn about the use of time domain VIV prediction for Spar TTRs.
Analysis Methodology of Vortex-Induced Motions (VIM) on a Monocolumn Platform Applying the Hilbert-Huang Transform Method
Authors: Gonc¸alves Rodolfo T. , Franzini Guilherme R. , Rosetti Guilherme F. , Fujarra Andre´ L. C. , Nishimoto Kazuo
Published: January 2011

Vortex-Induced Motion (VIM) is a highly non-linear dynamic phenomenon. Usual spectral analysis methods, using the Fourier transform, rely on the hypotheses of linear and stationary dynamics. A method to treat non-stationary signals that emerge from non-linear systems is denoted Hilbert-Huang transform method (HHT). The development of an analysis methodology to study the VIM of a MPSO (Monocolumn Production, Storage and Offloading System) using HHT was presented. The purposes of the analysis methodology are to improve the statistics characteristics of VIM. The results showed to be comparable to results obtained from the traditional analysis (mean of the 10% highest peaks) principally for the motions in the transverse direction, although the difference between the results from the traditional analysis for the motions in the in-line direction showed a difference of around 25%. The results from the HHT analysis are more reliable than the traditional ones, owing to the larger number of points to calculate the statistics characteristics. These results should be used to design the risers and mooring lines, as well as to obtain parameters of the VIM to calibrate numerical predictions.
An Approximate Method for Stochastic Linearization of Viscous Roll Damping
Authors: Drobyshevski Y. , Whelan J. R.
Published: January 2011

Accurate prediction of roll motions is important for the design of vessels of various types, especially ship-shaped floating production, storage and offloading (FPSO) systems for the oil and gas industry. For frequency domain analysis with sea spectrum, the viscous roll damping is usually linearised following a known procedure of stochastic linearization. This involves replacing damping terms that are non-linear with roll velocity with an equivalent linear term such that the error between certain statistical properties of the non-linear and linearised roll responses is minimized. An iterative procedure is used for this calculation where repetitive computations of Response Amplitude Operators (RAO) are undertaken by solving equations of motions until convergence is obtained. If the sea state changes the analysis must be repeated. For motions analysis in multidirectional seas or with fully directional (carpet) spectrum such computations must be carried out for several wave directions, and the numerical burden becomes an issue. This is especially the case for vessel operability or response based analyses, when the number of sea states considered is measured in thousands. The paper presents a method for an approximate stochastic linearization, which is intended to adjust the viscous roll damping without re-computing complete motion RAOs. On the basis of a single degree of freedom roll model, a pair of correction functions are introduced, which describe the effect of change in the viscous damping on the roll amplitude and phase via a single parameter. Assuming that the effect of viscous roll damping is qualitatively similar for any wave direction, the problem is reduced to solving a single non-linear equation about the unknown parameter. The procedure is numerically efficient; it requires the knowledge of some “reference” RAO and phase functions, but does not involve solving equations of motions and the knowledge of all hydrodynamic coefficients of the vessel. Comparison between the proposed method and the exact stochastic linearization demonstrates that the method is sufficiently accurate in predicting stochastic roll amplitudes, as well as in generating both the RAO and the phase functions of roll motion. It is also demonstrated that the impact of changing the equivalent roll damping on other vessel motions, which are weakly coupled with roll, is small and may be ignored.
Parametric Rainflow Fatigue Damage for Some Power Spectra of Common Use
Authors: Olagnon Michel , Gue´de´ Zakoua
Published: January 2011

Rainflow counting is widely accepted as the method that is most suited to analysis of fatigue damage of materials submitted to irregular loading. Formulas such as the Wirsching-Light and the Dirlik one allow to take into account spectral shape and bandwidth in an empirical or semi-empirical manner to obtain a best estimate damage reduction of the rainflow counting with respect to the narrow-band approximation. However, if one considers parametric shape families of common use for the spectra, a more straightforward way is to make damage depend on the shape parameter of the family rather than on the spectral moments. We provide here such semi-empirical parametric formulas for the Jonswap, Wallops, Triangle and Power-tail families. In addition, the ICA formula allows us to extend the above formulas to the well-known bimodal spectral shape proposed by Ochi-Hubble.
Model Test on Drag of Cylinders With Helical Grooves at High Reynolds Numbers
Authors: Huang Shan , Kitney Neil
Published: January 2011

Towing tank model tests at high Reynolds numbers, up to 1.1×106, were carried out in order to investigate the effects of the triple-starting helical grooves on drag reduction of smooth and rough circular cylinders in uniform cross flow. In total, four cylinders were tested including smooth and rough cylinders with and without helical grooves.
Approximation of Crossing Intensities for Non Linear Responses Subjected to Non Gaussian Loadings
Authors: Galtier Thomas , Gupta Sayan , Rychlik Igor
Published: January 2011

Crossing intensity constitute an important response characteristic for randomly vibrating structures, especially if one is interested in estimating the risk against failures. This paper focusses on developing approximations by which estimates of the crossing intensities for response of marine structures can be obtained in a computationally efficient manner, when the loads are modeled as a special class of non-Gaussian processes, namely as LMA processes. Ocean waves exhibit considerable non-Gaussianity as marked by their skewed marginal distributions and heavy tails. Here, a new class of processes-the Laplace driven Moving Average (LMA) processes are used to model the ocean waves. LMA processes are non-Gaussian, strictly stationary, can model in principle any spectrum and have the additional flexibility to model the skewness and the kurtosis of the marginal distribution. The structure behavior assumed is limited to quadratic systems characterized by second order kernels, which is common for marine structures. Thus, an estimation of the crossing intensities of the response involves studying the crossing characteristics of a LMA process passing through a second order filter. A new computationally efficient hybrid method, which uses the saddle point approximations along with limited Monte Carlo simulations, is developed to compute crossing intensity of the response. The proposed method is illustrated through numerical examples.
Added Resistance of a VLCC in Short Waves
Authors: Guo Bingjie , Steen Sverre
Published: January 2011

In quantifying speed loss due to waves, added resistance in short waves plays an important role, because most of the time a ship travels in small sea states. It is known that added resistance in small sea states is difficult to predict accurately. In order to study improved prediction methods, numerical calculations and experiments on added resistance of a VLCC in head waves have been carried out. This paper explores a radiated energy method, an asymptotic method (Faltinsen 1980) and their combination. In addition, experimental determination of added resistance in short waves is challenging. The paper discusses the sensitivity of the results to the quality of the waves, and it is also discussed how different approaches for measuring and analyzing waves might influence the results. A novel procedure for carrying out and analyzing added resistance test results is described, and the table for the precision error of the experiment is given. Finally the results from experiments and numerical calculations are compared. The results show that the added resistances predicted by th e combined numerical calculation are a bit smaller than the experimental results at lower Froude number, while they are in good agreement at higher Froude number.
Problems and Solutions in the Course of Deballasting
Authors: Yang Yong , Ma Jie
Published: January 2011

In the course of vessel deballasting, the deballasting time and residual water in ballast tanks are requested specifically and strictly. The problems which occurred during deballasting are analyzed and a great deal of experiences and test datum are obtained with a case in the paper. It redounds to the design of the ballast system in the future.
Research and Design of Technologies for Reducing Vibration and Noises in a Science Icebreaker
Authors: Yong Yang , Jie Ma
Published: January 2011

In accordance with the development of green shipbuilding technologies in the world, a science icebreaker is dealt with vibration isolation system in main generator station on the basis of the characteristics of complex vibration isolation system. The pumps in engine room are adopted with raft isolation system to reduce vibration. Damping materials are utilized to reduce cabin noises in order to improve the inhabited conditions onboard.
Estimation of Wave Loading Induced Fatigue Accumulation and Extreme Response of a Container Ship in Severe Seas
Authors: Mao Wengang , Li Zhiyuan , Galtier Thomas , Ringsberg Jonas W. , Rychlik Igor
Published: January 2011

The hydrodynamic analysis of a 4400 TEU container ship with constant forward speed is carried out by the nonlinear numerical code WASIM in the time domain under severe sea states. Straightforward fatigue estimation is performed using the rainflow counting approach based on simulated time series of stresses. The narrow-band approximation, which has been validated in previous work with good accuracy by full-scale measurement of a 2800 TEU container ship, is implemented to estimate the fatigue damage based on the same responses. It is concluded that a slight deviation from the Gaussian process does not influence the fatigue estimation by narrow-band approximation. In addition, extreme response is defined by the level up-crossing approach. The Gaussian crossing model using Rice’s formula is employed to predict the extreme response based on the responses from above numerical analysis. It shows that the Gaussian model is not suitable for this prediction. A more complicated level crossing model is proposed which is based on the Laplace Moving Average method. Its accuracy in prediction of extreme responses is analyzed and presented with good agreement by means of numerical simulations.
Calculation and Analysis of Dynamic Load’s Cushioning of the Fixed Pile-Leg in Marine Structure
Authors: Yang Qi , Tang Jing
Published: January 2011

In this paper, we establish a mechanical model of the structural dynamic analysis for the legs of fixed pile leg marine structures, where the hull doesn’t float out of the water. We make a calculation and analysis of the dynamic model by using the finite element analysis software “ABAQUS”. Also the cushioning mechanism of different materials is analyzed. Accordingly we establish a dynamic analysis model of a cushioning system. An elastic modulus linear model is used to simulate rubber materials, in order to carry out a qualitative analysis of the cushioning effect of a cushioning device in a reinforcing area. Taking rubber materials’ different elastic modulus and different load impact frequencies as variables, a series of calculation results and analysis are presented. Through a comparative analysis of the different structural dynamic response between the buffered and the non-buffered, we draw the conclusion that the dynamic load of the legs has been effectively alleviated with a cushioning device which is helpful in leg-protection.