bluuebunny/crossref_metadata_2025 huggingface dataset:
Unsteady Rotor-Stator Interaction of a Radial-Inflow Turbine With Variable Nozzle Vanes
Authors: Kawakubo Tomoki
Published: January 2011

For radial turbines used in automotive turbochargers, the importance of variable flow capacity by means of a variable geometry system is getting higher under the growing demands for improved engine performance and reduced engine emissions. To realize a high-performance and aeromechanically-reliable turbine stage, the unsteady flow phenomena caused by the rotor-stator interaction and their impact on the mechanical integrity must be understood deeply. In the present paper, the periodic disturbance generated by the rotor-stator interaction of a research turbine stage is investigated. The research purposes are (i) to extract the flow phenomenon which is responsible for the blade excitation, (ii) to identify the operating condition at which the influence of the extracted phenomenon becomes stronger, and (iii) to clarify how and where the disturbance energy is fed into the blades. Three dimensional unsteady stage CFD simulations are conducted to investigate the unsteady stage interaction. Two parameters are mainly focused: the nozzle vane angle and the stage pressure ratio. By changing the former, the effect of different degrees of reaction can be examined, while by changing the latter, the effect of different Mach number levels can be evaluated. The unsteady blade loading is extracted from the CFD result and coupled with the blade displacement obtained from the eigen vibratory mode analysis to examine the aeromechanical influence of the unsteady loading on the impeller blade excitation at various operating conditions. The nozzle shock wave and nozzle clearance flow are identified as the principal phenomena for the impeller blade excitation. At the mean section of the impeller blade the nozzle shock wave impinges on the S/S and diffracts on the P/S periodically, these two processes constitute high unsteady blade loading at the impeller L/E. At the shroud section the nozzle clearance flow generates high fluctuation in the relative flow direction to the impeller which results in high unsteadiness in the blade loading. These two phenomena are more important at vane closed conditions due to the higher nozzle loading. The higher the pressure ratio, the higher the normalized loading, though once the nozzle shock wave is established the normalized loading does not increase appreciably. Most of the excitation energy enters the blade at the impeller L/E at the closed condition, while it enters the blade both at the L/E and T/E at the open condition.
Internal Cooling Using Novel Swirl Enhancement Strategies in a Slot Shaped Single Pass Channel
Authors: Segura Del , Acharya Sumanta
Published: January 2011

Heat transfer results for a given slot shaped channel with a 3:1 aspect ratio are presented using various methods to enhance swirl in the channel including helical shaped-trip-strips and swirl-jets issuing from the side walls. Four different configurations of the swirl jets and one configuration of the helical trip strips were studied. The Reynolds numbers investigated range from 10,000 to 50,000 and are based on the mean velocity of the fluid at the channel inlet, or when swirl-jets are used, the equivalent mass flow rates at the exit of the main channel. Independently these heat transfer enhancement strategies have proven to be effective in either round channels, in the case of swirl jets and helical protrusions, or rectangular channels, in the case of trip strips. A transient technique combined with Duhamel’s superposition theorem was used to obtain the heat transfer coefficient distributions. Narrow-band liquid crystals were used to map the transient surface temperatures and were combined with thermocouples that measured the bulk-air temperatures along the flow path in the main channel. The results for the tests reported in this paper show mean heat transfer enhancement values (Nu/Nuo) greater than 4.5 and low normalized friction factors. Thermal performance factors ranged from 1.1–3.3 for the various configurations studied. These results show significant improvements over other types of heat transfer enhancement methods currently used in the mid-span section of turbine blades.
Predictions of Unsteady Interactions Between Closely Coupled HP and LP Turbines With Co- and Counter-Rotation
Authors: Praisner T. J. , Grover E. , Mocanu R. , Jurek R. , Gacek R.
Published: January 2011

Here we report on an analytical study of the unsteady aerodynamic interactions of a closely coupled, co-rotating, high- and low-pressure turbine configuration. The effort was focused on the prediction of unsteady surface pressures imparted on the first blade of the low-pressure turbine (LPT). As a first step, a baseline three-row time-accurate prediction was carried out for the first three rows of the low-pressure turbine (vane-blade-vane). In contrast to the three-row results, a four-row analysis, which included the blade of the high-pressure turbine, revealed that the temporally varying tangential load on the LPT blade was increased in amplitude by a factor of five compared to the three-row case with a shift in primary unsteady energy to unexpected frequencies. In the four-row analysis, a region of unusually high unsteadiness near the tip of the LPT blade was also characterized by an increase in the amplitude of the fluctuating surface pressure by a factor of nearly seven, again, with unexpected attendant frequencies. A model is presented which explains the unexpected frequencies realized in the four-row results and allows the redetermination of these frequencies without the use of CFD. In an effort to better understand the complex interactions between the high- and low-pressure turbines, the first vane of the low-pressure turbine was redesigned, and the remaining airfoils were reoriented, to establish a counter-rotating turbine configuration. While substantial reductions in unsteady surface-pressure amplitudes were realized near the tip of the LPT blade with the switch to counter rotation, the amplitude of the temporally varying tangential load on the blade remained notably higher than that from the three-low analysis. The precise physical cause for the high levels of local unsteadiness near the tip of the first LPT blade in the co-rotating configuration remains unclear.
Numerical Study of Flow and Heat Transfer of Impingement Cooling on Model of Turbine Blade Leading Edge
Authors: Liu Zhao , Feng Zhenping , Song Liming
Published: January 2011

In this paper a numerical simulation is performed to simulate the impingement cooling on internal leading edge region, which is stretched by the middle cross section of the first stage rotor blade of GE-E3 engine high pressure turbine, and in the condition that jets flow is ejected from a row of four different diameter circular nozzles. The relative performances of three versions of turbulence models including the RNG κ-ε model, the standard κ-ω model and the SST κ-ω model in the simulation of a row of circle jet impingement heat transfer are compared with available experimental data. The results show that SST κ-ω model is the best one based on simulation accuracy. Then the SST κ-ω model is adopted for the simulation. The grid independence study is also carried out by using the Richardson extrapolation method. A single array of circle jets is arranged to investigate the impingement cooling and its effectiveness. Four different jet nozzle diameters are studied and seven different inlet flow Mach numbers of each jet nozzle diameter are calculated. The influence of the ratio of the spacing of jet nozzle from the target surface to the jet nozzle diameter on impingement cooling is also studied, in case of a constant ratio of jet spacing to jet nozzle diameter in different jet nozzle diameters. The results indicate that the heat transfer coefficient on the turbine blade leading edge increases with the increase of jet Mach number and jet nozzle diameter, the spanwise area weight average Nusselt number decreases with the increase of the ratio of the spacing of jet nozzle from the target surface to jet nozzle diameter, and a lower ratio of spacing of jet nozzle from the target surface to the jet nozzle diameter is desirable to improve the performance of impingement cooling on turbine leading edge.
3D Modeling for Wet-Compression in a Single Stage Compressor Including Liquid Particle Erosion Analysis
Authors: Khan Jobaidur R. , Wang Ting
Published: January 2011

Gas turbine inlet fog / overspray cooling is considered as a simple and effective method to increase power output. To help understand the water mist transport in the compressor flow passage, this study conducts a 3-D computational simulation of wet compression in a single rotor-stator compressor stage using the commercial code, Fluent. A sliding mesh scheme is used to simulate the stator-rotor interaction in a rotating frame. Eulerian-Lagrangian method is used to calculate the continuous phase and track the discrete (droplet) phase respectively. Models to simulate droplet breakup and coalescence are incorporated to take into consideration the effect of local acceleration and deceleration on water droplet dynamics. Analysis on droplet history (trajectory and size) with stochastic tracking is employed to interpret the mechanism of droplet dynamics under the influence of local turbulence, acceleration, diffusion, and body forces. An liquid-droplet erosion model is included. The sensitivity of turbulence models on the results is conducted by employing 6 different turbulence models and 4 different time constants. The result shows that the local thermal equilibrium is not always achieved due to short residence time and high value of latent heat of water. Local pressure gradients in both the rotor and stator flow passages drive up the droplet slip velocity during compression. The erosion model predicts that the most eroded area occurs in leading edge and one spot of trailing edge of the rotor suction side.
Second Law Analysis of a Refrigeration System for a Novel Semi-Closed Gas Turbine-Absorption Combined Cycle
Authors: Ryu ChoonJae , Lear William E. , Sherif S. A.
Published: January 2011

The Power, Water Extraction, and Refrigeration (PoWER) engine has been investigated for several years as a distributed energy system, among other applications, for civilian or military use. Previous literature describing its modeling and experimental demonstration have indicated several benefits, especially when the underlying semi-closed cycle gas turbine is combined with a vapor absorption refrigeration system, the PoWER system described herein. The benefits include increased efficiency, high part-power efficiency, small lapse rate, compactness, less emission, air, and exhaust flows (which decrease filtration and duct size) and condensation of fresh water. The present paper describes the preliminary design and modeling of a modified version of this system as applied to distributed energy, especially useful in regions which are prone to major grid interruptions due to hurricanes, under - capacity, or terrorism. In such cases, the distributed energy system should support most or all services within an isolated service island, including ice production, so that the influence of the power outage is limited in scope. This paper describes the rather straightforward system modifications necessary for ice production. The primary focus of the paper is the use of this ice-making capacity to achieve significant load-leveling during the summer utility peak, hence reducing the electrical capacity requirements for the grid as well as load-leveling strategies.
Polynomials and Neural Networks for Gas Turbine Monitoring: A Comparative Study
Authors: Loboda Igor , Feldshteyn Yakov
Published: January 2011

Gas turbine health monitoring includes the common stages of problem detection, fault identification, and prognostics. To extract useful diagnostic information from raw recorded data, these stages require a preliminary operation of computing differences between measurements and an engine baseline, which is a function of engine operating conditions. These deviations of measured values from the baseline data can be good indicators of engine health. However, their quality and success of all diagnostic stages strongly depend on an adequacy of the baseline model employed and, in particular, on mathematical techniques applied to create it. To create the baseline model we have applied polynomials and the least square method for computing their coefficients over a long period of time. Some methods were proposed to enhance such a polynomial-based model. The resulting accuracy was sufficient for reliable monitoring gas turbine deterioration effects. The polynomials previously investigated enough are used in the present study as a standard for evaluating artificial neural networks, a very popular technique in gas turbine diagnostics. The focus of this comparative study is to verify whether the use of networks results in a better description of the engine baseline. Extensive field data of two different industrial gas turbines were used to compare these two techniques in various conditions. The deviations were computed for all available data and quality of the resulting deviations plots was compared visually. A mean error of the baseline model was an additional criterion for the comparing the techniques. To find the best network configurations many network variations were realized and compared with the polynomials. Although the neural networks were found to be close to the polynomials in accuracy, they could not exceed the polynomials in any variation. In this way, it seems that polynomials can be successfully used for engine monitoring, at least for the analyzed gas turbines.
Upgrading the Performance of a Centrifugal Barrel Compressor Family
Authors: Bygrave Jonathan , Villanueva Alfonso , Enos Ronald , Saladino Anthony , Serrino David , Prosser William
Published: January 2011

Rolls-Royce centrifugal barrel compressors have provided reliable service to many users in a wide variety of applications since their introduction in the mid-1950s. In 1968, a family of standard impellers was developed for use in each frame size, followed by additional families of other diameter impellers developed at various times to achieve more or less head per stage or lower flow capability. Various other upgrades have also taken place over the years, each leading to an improvement in performance and predictability. However, the performance levels that were being achieved consistently lagged behind those of the authors’ company’s pipeline compressor frame sizes. In 2006 it was decided to invest heavily in upgrading the company’s barrel compressor capabilities. This paper details some of the steps that were taken to develop a fully integrated upgrade of our most popular frame size, the RCB. The improvements in performance capabilities of the impellers in terms of efficiency and flow range are discussed together with the results of parametric studies to improve the inlet and discharge flow path configurations. A description of the validation testing of selected impellers at various relative Mach Numbers, undertaken in our single stage test rig, is also included.
Accuracy of Analytical Engine Weight Estimation During the Conceptual Design Phase
Authors: Donus Fabian , Schaber Reinhold , Schmidt Klaus-Juergen , Staudacher Stephan
Published: January 2011

This paper addresses the quality of weight estimation that can be achieved in the early design phase and illustrates the significance of the results for conceptual engine design. A study was undertaken to determine the accuracy of weight estimation during the conceptual design phase. To this end, different engines were modeled using the preliminary design tool MOPEDS. The estimation method used to generate the results is based on geometric models for the considered component parts that have been calibrated as closely as possible to the existing geometries. Furthermore, the modeled part weights provided by MOPEDS have been compared to the real part weights to assess the uncertainty of the estimation method. The deviations are discussed to identify where an improvement of the method could be profitable with regard to a better overall estimation. It has been shown that for some hardware the estimation method is already very accurate, whereas some parts have geometric models that require improvement to realize an overall high quality. One of the calibrated engine models was used additionally as the basis for a parameter study to determine the accuracy of the part weight estimation method using MOPEDS in automatic design mode. The results showed that the deviation in the overall component mass for each test case was nearly constant during this study.
Numerical Modelling of Fluid-Structure Interaction in a Turbine Stage for 3D Viscous Flow in Nominal and Off- Design Regimes
Authors: Rzadkowski Romuald , Gnesin Vitaly , Kolodyazhnaya Lubov
Published: January 2011

In recent years there have been major developments in turbomachinery aeroelasticity methods. There are now greater possibilities to predict blade vibrations arising from self-excitation or inlet flow distortion. This is not only important with regard to aircraft compressor and fan blade rows, but also in the case of the last stages of steam and gas turbines working in highly loaded off-design conditions. In order to predict the unsteady pressure loads and aeroelastic behaviour of blades (including the computation of shock waves, shock/boundary layer interaction and boundary layer separation), complete Reynolds-averaged Navier-Stokes (RANS) equations are used in modelling complex and off-design cases of turbomachinery flows. In this paper the 3D RANS solver, including a modified Baldwin and Lomax algebraic eddy viscous turbulence model, is presented to calculate unsteady viscous flow through the turbine stage, while taking into account the blade oscillations but without the separating of outer excitation and unsteady effects caused by blade motion. The numerical method uses the second order by time and coordinates an explicit finite-volume Godunov’s type difference scheme and a moving H-O structured grid. The structure analysis uses the modal approach and a 3D finite element model of blade. To validate the numerical viscous code, the numerical calculation results were compared with the 11th Standard Configuration measurements. Presented here are the numerical analysis results for the aeroelastic behaviour of a steam turbine last stage with 760 mm rotor blades in a nominal and an off-design regime.
Coating Methods to Increase Material Damping of Compressor Blades: Measurements and Modeling
Authors: Sun Jia , Kari Leif
Published: January 2011

Methods are developed to improve damping of compressor blades, where unconstrained and constrained damping techniques are applied to the blades to increase material damping, displaying both measurement and modeling results. Two specimens, titanium and stainless steel, are treated by aluminum oxide and epoxy coating material. Measurements of material damping of simple beam specimens without and with treatments are carried out and results show that both treatments give damping increase, where aluminum treatment is more effective for damping improvement than the corresponding epoxy treatment. The unconstrained damping layer model is used to predict the total material damping of the combined structure as well as the material damping of coating layer. Comparisons with measured results are made. The constrained-layer model is also used to optimize the damping configuration and parametric analyses are performed. Two compressor blades in titanium and stainless steel are tested in air and vacuum conditions to measure material damping and results show that difference between air and vacuum situations exists. One reason is being that the radiation loss factor produced in air condition increases damping comparing with the damping in vacuum condition. The calculation of the radiation loss factor is performed to match the measurement data and results demonstrate that the radiation loss factor is one factor and air friction is another strong factor in this case. Finally, increasing material damping gives a contribution to decrease peak stress values and therefore increase the life time of compressor blades.
Development of a Medium-Size Steam Reformer for CHP Applications Based on PEM Fuel Cells
Authors: Pisani Giovanni , Zerbinato Alberto , Tregambe Carlo , Benini Ernesto
Published: January 2011

This paper describes technological of a fuel processor for hydrogen production able to convert 10 cubic meters of methane per hour. This device has been developed to feed hydrogen CHP suitable for the most common residential applications. The measured conversion efficiencies are extremely high: after the steam reformer the results are 76%H2; 18%CO2; 0,5%CH4; 5%CO; but the carbon monoxide is totally reduced throughout the water gas shift and the partial oxidation which contemporarily increase the hydrogen to over 77%. According to these results, this fuel processor is one of the first middle sized reformer to achieve, at comparable costs per cubic meter, conversion performance that were normally obtained only by industrial reforming plants.
Experimental and Numerical Studies on Highly Loaded Supersonic Axial Turbine Cascades
Authors: Wolf T. , Kost F. , Janke E. , Haselbach F. , Willer L.
Published: January 2011

For the small to medium thrust range of modern aero engines, highly loaded single stage HP turbines facilitate an attractive alternative to a more conventional 2-stage HPT architecture. Whereas the potential benefits of reductions in component length and part count, hence, in weight and cost do motivate their application, the related risks are in maintaining associated losses of supersonic flows at low values as well as managing the interaction losses between HPT and the downstream sub-component to arrive at competitive levels of component efficiencies. This paper focuses on fundamental aerodynamic concept studies and related cascade experiments in support of a future highly loaded high-pressure turbine architecture. Starting with some general remarks on low-loss supersonic aerodynamic concepts for high-pressure turbines, results from development efforts towards 2D airfoil concepts viable for high-pressure turbine airfoils are shown. In particular, CFD based design approaches are compared against experimental data taken at DLR Go¨ttingen in un-cooled cascade tests and at engine representative levels of Mach and Reynolds numbers. For the airfoils investigated, it turns out that there is indeed a supersonic Mach number range were loss levels are comparable to high Mach number subsonic values, thereby enabling a competitive aerodynamic design concept for a 3D high-pressure turbine stage.
Sintering Behavior of Plasma-Sprayed Sm2Zr2O7 Coating
Authors: Yu Jianhua , Zhao Huayu , Tao Shunyan , Zhou Xiaming , Ding Chuanxian
Published: January 2011

Plasma-sprayed thermal barrier coating (TBC) systems are widely used in gas turbine blades to increase turbine entry temperature (TET) and better efficiency. Yttria stabilized zirconia (YSZ) has been the conventional thermal barrier coating material because of its low thermal conductivity, relative high thermal expansion coefficient and good corrosion resistance. However the YSZ coatings can hardly fulfill the harsh requirements in future for higher reliability and the lower thermal conductivity at higher temperatures. Among the interesting TBC candidates, materials with pyrochlore structure show promising thermo-physical properties for use at temperatures exceeding 1200 °C. Sm2Zr2O7 bulk material does not only have high temperature stability, sintering resistance but also lower thermal conductivity and higher thermal expansion coefficient. The sintering characteristics of ceramic thermal barrier coatings under high temperature conditions are complex phenomena. In this paper, samarium zirconate (Sm2Zr2O7, SZ) powder and coatings were prepared by solid state reaction and atmosphere plasma spraying process, respectively. The microstructure development of coatings derived from sintering after heat-treated at 1200–1500 °C for 50 h have been investigated. The microstructure was examined by scanning electron microscopy (SEM) and the grain growth was analyzed in this paper as well.
Model Based Shaft Crack Identification in Rotating Machinery
Authors: Sudhakar G. N. D. S. , Sekhar A. S.
Published: January 2011

Modern rotating machinery is prone to fatigue cracks due to the severe working and continuously varying loading conditions. To avoid failure of the rotating systems due to these cracks, the system needs to be continuously monitored. The reliability of the machinery can be enhanced with the fault identification at the early stages of their occurrence. Model based methods are used for crack identification in rotating systems successfully. Model based methods are of different types. One of the methods, the equivalent loads minimization method is studied here. It has a limitation that the error in identified crack depth increases with decrease in number of measured vibrations. In the present work, the theoretical fault model loads used in least squares minimization algorithm are transformed using modal expansion to reduce error in the identified fault parameters. The crack is identified accurately even in the case of less number of measured vibrations. The method is applied for crack identification in a centrifugal pump rotor using transverse vibrations. The results presented are obtained purely from FEM simulations.
Reliability Study of a North-Sea Jack-Up Under Action of Wave-in-Deck, SH- and SV-Seismic Waves Considering Spud-Can-Soil Interaction
Authors: Emami Azadi M. Reza
Published: January 2011

In the current study, the effect of spud-can-soil interaction modeling as well as wave load modeling and sea-state on the reliability index of a three-leg North-sea drilling type jack-up platform is studied. The platform has operated in depths of 95–105m and its three main legs modeled as pipe elements and the main deck is also modeled using general beam and also shell/plate elements. The spud-can foundation is modeled using elasto-plastic, hyper-elastic springs as well as spud-model of usfos using a general non-associative plasticity model. The wave-in-deck load is considered using API-RP2A [1], Shell and Statoil models. The SH and SV-seismic waves are considered separately at spud-can base as scaled. The preliminary results of this study showed that the annual probability of failure for the Jack-up platform is significantly affected by the random-sea and wave-in-deck modeling as well as spud-can-soil interaction modeling and soil parameters. Study of importance factors indicated that more refined spud-can-soil interaction modeling as well as wave-in-deck load modeling might improve the calculation models and hence reduce their associated uncertainty in reliability analysis of jack-up type platform.
Supporting New Insight in Pipeline Hydrodynamics Using Stochastic Approaches on External Corrosion Damage
Authors: Mustaffa Zahiraniza , van Gelder Pieter
Published: January 2011

Several recent discoveries in the fluid-structure interactions between the external flows and circular cylinders placed close to the wall have added new values to the hydrodynamics of unburied marine pipelines on a seabed. The hydrodynamics of waves and/or currents introduced vortex flows surrounding the pipeline. External corrosions formed in marine pipelines were assumed to be partly contributed by such fluid-structure interactions. The spatial consequences of such interactions were of interest of this study. This paper summarized some experimental and numerical works carried out by previous researchers on these new discoveries. Actual field data were utilized in this study to support this hypothesis. The characteristics of corrosion orientations in the pipelines were studied comprehensively using stochastic approaches and results were discussed. Results adopted from the field data acknowledged well to the hypothesis from the reported literature. The updated knowledge from this fluid-structure interaction is hoped to be given more attention by the industry and perhaps to be incorporated into the current subsea pipeline designs.
The Free Surface Flow Around a TLP
Authors: Yalpaniyan A. , Goodarzi M.
Published: January 2011

A TLP is a buoyant platform containing four cylindrical columns. The purpose of this study was to consider the effects of different model solvers in the numerical solution on the flow pattern around the TLP. The flow around the TLP was numerically simulated with inviscid, laminar, and turbulent solvers. Three Froude numbers were run for each case. There was a symmetry plane that allowed simulating just one half of the flow field. Therefore, two columns along the symmetry plane were considered in the results discussion. Beside the generated surface waves there was a pair of vortex behind each column none of them were actually symmetric. The vortex behind the first column significantly affected the flow pattern around the second one in the manner that the vortex behind the first column was larger than the next one. In all cases the outer vortex was larger than the inner one. The obtained results showed that the generated waves of the inviscid flow were smoother than the turbulent flow, and also those of the turbulent flow were smoother than the laminar ones. Compared to the mentioned results, the influence of the flow velocity on the wave heights was more significant.
Numerical Simulation of Hydroelastic Responses of Flat Stiffened Panels Under Slamming Loads
Authors: Luo Hanbing , Hu Jiajun , Guedes Soares C.
Published: January 2011

Explicit finite element code is adopted to simulate the dynamic response of flat stiffened panels under slamming loads. In order to validate the code, numerical simulation of pressure response is carried out and compared with experimental results published. One panel with ‘T’ stiffeners is proposed for water entry problem with 0° dead rise angle. Both rigid and flexible bodies are investigated. Pressure response on coupling surface is predicted and compared with each other. Hydroelastic response of stiffened panels is studied in details, with focus on stress response in panel and stiffener. Coupling effects between fluid and structures are discussed. Sensitivity analysis is carried out. Factors influencing the role of hydroelasticity are discussed, such as air cushion effects, impact velocity, and panel stiffness, etc.
Using Magnetic Measurement Technology in Marine Riser Stress Detection
Authors: Meng Fanshun , Deng Rui , Wang Dawei , Huang Yanming , Wang Liyan
Published: January 2011

The marine riser bears various power loads during operation. We designed the Quadrupole-type magnetic measurement probe based on the inverse magnetostrictive effect (the impact of stress on the magnetization) and performed finite element simulation and experimental analysis. The results of both the finite element analysis and magnetic measurement basically follow the same trend, so we conclude that this four-pole magnetic probe measurement can quantitatively evaluate the force state in a marine riser.
Application of a Viscoelastic Model for Polyester Mooring
Authors: Kim J. W. , Kyoung J. H. , Sablok A.
Published: January 2011

A new practical method to simulate time-dependent material properties of polyester mooring line is proposed. The time-dependent material properties of polyester rope are modeled with a standard linear solid (SLS) model, which is one of the simplest forms of a linear viscoelastic model. The viscoelastic model simulates most of the mechanical properties of polyester rope such as creep, strain-stress hysteresis and excitation period-dependent stiffness. The strain rate-stress relation of the SLS model has been re-formulated to a stretch-tension relation, which is more suitable for implementation into global performance and mooring analyses tools for floating platforms. The new model has been implemented to a time-domain global performance analysis software and applied to simulate motion of a spar platform with chain-polyester-chain mooring system. The new model provides accurate platform offset without any approximation on the mean environmental load and can simulate the transient effect due to the loss of a mooring line during storm conditions, which has not been possible to simulate using existing dual-stiffness models.
Extreme Structural Dynamic Response of a Spar Type Wind Turbine
Authors: Karimirad Madjid , Moan Torgeir
Published: January 2011

Proper performance of structures requires among other things that its failure probability is sufficiently small. This would imply design for survival in extreme conditions. The failure of a system can occur when the ultimate strength is exceeded (Ultimate Limit State) or fatigue limit (Fatigue Limit State) is passed. The focus in this paper is on the determination of extreme responses for ULS design checks. The present paper deals with coupled wave and wind induced motion and structural response in harsh condition up to 14.4 (m) significant wave height and 49 (m/sec) 10-min average wind speed (at top of tower, 90 m) for a parked floating wind turbine. In survival condition the wind induced resonant responses (mainly platform pitch resonance) are dominant. Due to platform resonant motion responses, the structural responses are close to Gaussian. The dynamic structural responses show that the process is wide banded. The critical structural responses are determined by coupled aero-hydro-elastic time domain simulation. Based on different simulations (20 1-hour, 20 2-hours, 20 3-hours and 20 5-hours) the mean up-crossing rate has been found in order to predict the extreme structural responses. The most probable maximum of the bending moment and the bending moment having up-crossing rate of 10−4 are found to be close in the present research. The minimum total simulation time in order to get accurate results is highly correlated to the needed up-crossing rate. The 1-hour and 2-hours original values cannot provide any information for 10−4 up-crossing rate. Comparison of different simulation periods shows that the 20 1-hour simulations can be used in order to investigate the 3-hours extreme bending moment if the proper extrapolation of up-crossing rate used.
Analysis of a Struck Ship With Damage Opening: Influence From Model and Material Properties Uncertainties
Authors: Hogstro¨m Per , Ringsberg Jonas W. , Johnson Erland
Published: January 2011

The conditions for damage stability and survivability of a ship struck in a collision in arbitrary sea-state are, from a structural point of view, determined by the size and shape of the damage opening in its side shell. In the current investigation, explicit finite element analyses (FEA) are presented of a ship-to-ship collision scenario in which the damage opening of a struck ship is calculated for a selection of damage degradation models and realistic material properties, here referred to as model and material properties uncertainties. The model uncertainty is considered as a possible (user-related) insecurity in the selection of the most appropriate damage criterion for the analysis; the shear failure and the forming limit diagram (FLD) criteria were compared in the current investigation. The uncertainty in material properties is accounted for in the constitutive material model description and the material parameters used in the two criteria. The size and shape of the damage openings predicted by the FEA are used in damage stability analyses in which the struck ship is subjected to wave motions in an arbitrary sea-state and flooding into the damage opening. The survivability of the struck ship is estimated for all of the damage opening cases. One of the main conclusions is that the high degree of accuracy that a researcher on structure analysis strives for has to be considered together with the natural variation of the sea-state that defines the characteristics in the following damage stability analysis. Consequently, by adoption of a holistic approach, in which structural integrity and damage stability research are combined using a systematic parameter (sensitivity) and collision-scenario-based analysis, simplified models and criteria can be developed more efficiently and with higher precision. It will also be clearer which variables are the most important to focus on when analyzing the survivability or risk for capsizing.
Soil Structure Interaction Through Two Parameter Foundation
Authors: Mullapudi T. Ravi S. , Ayoub Ashraf
Published: January 2011

Beams on foundations and piles resisting by surrounding soil are significantly complex due to the behavior of the surrounding semi-infinite soil media. Winkler’s model is the simplest element that account for the behavior of both the foundation and soil. The Winkler model is the one-parameter model which assumes the foundation reaction at a particular point is proportional to the soil displacement. Most of the existing elements assume the soil to be tensionless or even elastic. In reality, the soil cohesiveness plays an important role in the behavior of foundation elements. In this paper a new finite element formulation was developed in which the soil can be viewed as an inelastic element with a combination of cohesive behavior that transmits rotations due to bending, in addition to the well-known Winkler effect known as the two-parameter model. The non linear response of structures resting on this improved foundation model is analyzed following a Pasternak approach with improved soil parameters. The soil parameters are evaluated by an internal iteration which depends upon the loading and foundation parameters. Parametric analyses of a foundation element have been carried out and comparisons were made between different foundation parameters. The numerical performance of the element was further enhanced by adopting the newly developed mixed finite element formulation with fiber discretization. The presented solutions and applications show the superiority of the element in simulating the complex response of foundation structures.
Hydrodynamics of an Installation Barge With Bilge Keels and Stinger
Authors: Cueva Marcos , Hansen Alexandre S. , Silva Joa¯o Luis B. , Faria Fernando , Morato Andre
Published: January 2011

Multipurpose barges are used for accommodations, maintenance, equipment transport and installation and pipelay. For all these operations, the correct understanding of the motions of the vessel is essential for safety and to increase the uptime in the desired region. The motions of barges are well evaluated by the use of potential theory, but due to the presence of nonlinearities, asymmetries and devices such as bilge keels and stinger, the determination of the unit motions can be challenging, especially for roll motions. This work presents several results of motions, obtained from model tests and numerical calculations, for different configurations of a barge, with a focus on roll motion, but also considering heave and pitch, with and without the presence of bilge keels and stinger.
Axisymmetric Modeling of Constraint Effect on the Ductile Crack Growth Resistance of Circumferentially Cracked Pipes
Authors: Xu Jie , Zhang Zhiliang , O̸stby Erling , Nyhus Ba˚rd , Sun Dongbai
Published: January 2011

Ductile crack growth plays an important role in the analysis of the fracture behavior of structures. Crack-like defects in pipe systems often develop during fabrication or in-service operation. The standard single edge notched bending (SENB) specimen with crack depth of a/W = 0.5 has a significantly higher geometry constraint than actual pipes with circumferential surface cracks, which therefore introduces a high degree of conservatism in engineering critical assessment (ECA) of pipes. Moreover, it is difficult to know how conservative the results are, because the geometry constraint is highly material-dependent. For circumferential surface flaws in pipes, the single edge notched tension (SENT) specimen has frequently been used because it has a geometry constraint in front of the crack tip that is similar to the cracks in pipes. Much work has been carried out on tensile testing for the SENT specimen as an alternative fracture mechanics specimen of pipes. In studying fully circumferential cracks in pipes, the crack geometry, applied load and boundary conditions are symmetrical about the axis of revolution. A typical radial plane containing the axis of rotational symmetry can represent these axisymmetric bodies; therefore the three-dimensional analysis can be reduced to a two-dimensional problem. This work systemically applies 2D axisymmetric models to study the ductile crack growth behavior of pipes with fully internal and external circumferential cracks under large scale yielding conditions. The complete Gurson model (CGM) developed and implemented by Zhang was utilized to predict the ductile crack growth resistance curves. Pipes with various internal pressure, diameter-to-thickness ratios, crack depths and material properties, as denoted by hardening and initial void volume fraction, have been analyzed. The results have been compared with those of corresponding clamped-loaded SENT (with same crack depth) and standard SENB specimens. It clearly indicates that the SENT specimen is a good representation of circumferentially flawed pipes and an alternative to the conventional standard SENB specimen for the fracture mechanics testing in ECA of pipes.
Optimization Study of Pipeline Rock Armour Protection Design Based on Finite Element Analysis
Authors: Wang LeQin , Chia HongKiat
Published: January 2011

The design of pipeline protection with rock armour berms has been traditionally based on model testing because there has been no closed-form analytical solution available to resolve the complex interaction between the anchor, anchor chain, seabed soil and rock armour. Compared to the costly physical model test, a numerical procedure properly set up allows effective and extensive study on various rock berm configurations. It is expected that better optimized pipeline rock armour protection berm can be designed to offer appreciable savings on project cost. The authors have developed a Finite Element Analysis (FEA) based procedure which can predict the clearance between the anchor fluke tip and pipeline as well as the pushing force on the pipeline during anchor dragging. Both the clearance and pushing force can be used to assess the potential anchor damage to a pipeline with rock backfill protection. The FEA results have been successfully validated against results obtained from physical model tests. A series of numerical tests are performed considering the variations in the trench profile, the armour rock shape, rock particle size and grading properties etc. The protection mechanism of the rock armour berm, with regard to the above factors, is discussed to provide a better understanding for the significance of each parameter in the protection design. Guidelines in achieving an optimized rock berm protection design are also given.
Estimation of Sea State Parameters From Measured Ship Responses: The Bayesian Approach With Fixed Hyperparameters
Authors: Nielsen Ulrik D. , Iseki Toshio
Published: January 2011

The paper deals with estimation of sea state parameters on the basis of time histories of ship responses. The focus is on the Bayesian estimation concept, where the outcome is controlled by a set of hyperparameters, which theoretically must be optimised to provide the optimum solution in terms of sea state parameters. The paper looks into the possibility of fixing the hyperparameters since this will increase the computational efficiency of the method. Sensitivity studies with respect to the hyperparameters are made for both synthetic data and full-scale data.
A Technology of Electrical Energy Generated From Ocean Power Using Flexible Piezoelectric Device
Authors: Mutsuda Hidemi , Kawakami Kenta , Kurokawa Takayuki , Doi Yasuaki , Tanaka Yoshikazu
Published: January 2011

We have developed a way of harvesting electrical energy from the ocean power, e.g. tide, current, wave, breaking wave and vortex, using a flexible piezoelectric device consisting of piezo-electric polymer film (PVDF), silicon and natural rubber. The flexible piezoelectric device (FPED) is a hydro-electric ocean energy converter designed to convert renewable energy harnessed from ocean energy into usable electricity. The basic concept generating electric power using FPED is to utilize fluid structure interaction, e.g. flattering, flapping and periodic bending, caused by ocean energy. The FPED deformed by kinetic energy of the ocean power stores elastic energy and also converts it to the electric energy. We carried out some experiments using wave tank and the water tunnel with a bluff body. We have confirmed the electricity generated by wave, current and vortex using the FPED. The developed FPED could be a new technology of harvesting electrical energy from the ocean power. A floating platform attached FPED could be coupled with an offshore wind turbine as a hybrid energy system in ocean space.
Flow Field Distribution and Parameter Optimization Analysis of Spiral Tube Separators
Authors: Zhao Lixin , Zhang Miao , Li Feng , Hua Zhengrong
Published: January 2011

Focus on the spiral tube separator, model selection and basic parameters of numerical simulation are described. Flow field simulation analysis of spiral tube separators of both without holes and with holes are carried out respectively. Effects of gyration radius, inlet flowrate, number of spiral circles, and oil droplet diameter on flow field distribution and the separation performance of spiral tube separators are analyzed in detail. Simulation results also show that the gyration radius and inlet velocity are the two main factors affecting separation characteristics of spiral tube separators. In addition, the size of opening holes of spiral tube separator also affects separation result.
Application of Multidisciplinary Design Optimization in the Truss Spar Concept Design
Authors: Jiang Zhe , Cui Weicheng , Huang Xiaoping
Published: January 2011

In the traditional design of a Truss Spar, designers usually choose different discipline as major concentration in different design phases. The coupling effect among disciplines can hardly be accounted for. Multidisciplinary design optimization has been proved to be an effective tool for the design of complex engineering systems, which takes all disciplines into account at the same time and exploit coupling effect among disciplines, thereby achieving the optimal system solution. In this paper, a multidisciplinary optimization scheme for a Truss Spar is firstly developed and the Truss Spar is decomposed into four modules: weight module, hydrodynamic module, structure module and stability module. Response surface method is used to replace the high-fidelity analysis to perform the approximate mathematical models of the objective function/constraints as a function of design variables. In order to enhance the accuracy of the predicted optimum, the response surface models are continuously updated using the information obtained from the numerical simulation of latest iterative results. Finally, an optimal design solution, which satisfies all the constraints, is obtained using collaborative optimization. The characteristics of the optimized design solution including hull weight, heave response, stability performance and strength of the bottom deck, are much improved comparing with traditional design.
Numerical Simulation of Ship Turning in Level Ice
Authors: Su Biao , Riska Kaj , Moan Torgeir
Published: January 2011

The ice-worthy ship must have a verifiable turning ability in the specified ice conditions. At present, most studies on ship maneuverability in ice are conducted by field measurements. In this paper a numerical method which is introduced for predicting ship performance in level ice, is applied to simulate ship turning in level ice. A real icebreaker is modeled in the simulation program. The calculated results are analyzed and compared with the full-scale data measured during turning tests. A good agreement is achieved.