Transition Piece Research Articles

A review of fatigue performance of bolted connections in offshore wind turbines

Flanged bolted connections are used in offshore wind turbines to connect the monopile to the transition piece, and the transition piece to the tower. Forces and moments generated by the effects of winds, waves and currents subject these connections to variable amplitude cyclic loads. In the harsh marine offshore environment areas such as bolt threads are vulnerable to fatigue cracking and failure. Their structural integrity and life are influenced by coatings, lubricants, bolt size, design and tension, manufacturing tolerances and flange contact.This paper presents a review of the main challenges for fatigue life assessment of M72 bolted connections used in offshore wind turbines to connect the monopile to the transition piece, and the factors affecting the fatigue performance. Existing standards and guidelines along with different fatigue assessment methods presented in the literature are discussed in terms of their suitability for fatigue life assessment of M72 bolted connections for offshore wind turbines. One of the key challenges in fatigue life assessment of large scale bolts (e.g. M72) is the lack of experimental data points from which fatigue design curves can be derived. Recommendations are made for how to improve the current best practice for fatigue assessment of large scale bolted connections in the offshore wind industry and potential areas for further investigation are proposed for future research.

O geometriji prelaznih komada u odnosu na plosnato-ovalne cevi

O geometriji prelaznih komada u odnosu na plosnato-ovalne cevi

Materials Solutions to Address High Temperature Fretting Wear in Gas Turbine Combustor Components

Structural parts like combustor and its components plays an important role in the overall performance of a land based heavy duty gas turbines. Due to system dynamics and poor material combinations, these parts undergo severe wear leading to durability issues and even part failures. Parts like liners, burners, transition piece and seals are free to undergo small amplitude motion and lead to fretting and related wear. In many situations, these component surfaces are un-coated or not protected from the severe degradation. The objective of this work is to develop a robust coating system to mitigate fretting and related wear under elevated temperature. A molybdenum rich-cobalt based tribaloy-800 is used to address the wear issues and studied in greater details. Tribaloy-800 multilayer coating is deposited on Nickel base alloy by HVOF coating process to achieve maximum distribution of laves hard phase. Further, coating is heat treated under vacuum furnace to optimize the microstructure which is desirable to work on these harsh operating conditions. A custom built fretting wear setup was used to perform gross-slip wear test, as standard laboratory experiments may not simulate the field wear mechanisms better. Both uncoated and coating materials were studied at elevated temperature (550 °C) under constant stress up to 3 million cycles to produce steady state wear rate. Fretting wear data reveals severe galling type of wear mechanisms in uncoated materials lead to fast removal material from the surface. Both as-coated and heat-treated coatings produced better wear resistance under same test conditions compared to uncoated nickel alloy. Heat treated tribaloy-800 coating shows crystalline rich laves phase distribution lead to superior wear performance.

Probability of wave slamming and the magnitude of slamming loads on offshore wind turbine foundations

Physical model tests were analyzed with the objective to establish a formulae for the probability of wave slamming on offshore wind turbine foundations and the associated slamming force. Furthermore, the effect of wave slamming is analyzed for a monopile wind turbine foundation using a state-of-the-art aeroelastic model. The laboratory measurements were carried out in Deltares’ Atlantic Basin as part of the joint industry project “wave impacts on fixed turbines”, in short JIP-WiFi. Long crested and irregular waves typical for the North Sea were applied and more than 130 design storms and 500 slamming impacts were analyzed. A simple closed form expression for the probability of wave slamming is presented and a reasonable agreement with the laboratory measurements shown. A criterion for when wave slamming should be included in design computations is formulated based on the sea state steepness. It is observed that wave slamming occurs during tests with a flat seabed, and that seabed features, such as sand waves, significantly increase the probability of wave slamming. Furthermore, a simplified slamming load formulation is proposed based on observations from a subset of the laboratory tests. The magnitude of the slamming load is validated against the remaining part of the laboratory measurements and compared with existing slamming load formulations. The new formulation is in better agreement with the underlying measurements than existing formulations and is of a simpler form which makes it easier to apply. The new slamming load formulation is applied in design computations for a realistic wind turbine with the offshore wind farm Gemini as base case. The computations show that wave slamming, at this specific location, is not governing the structural design. However, wave slamming may introduce high accelerations in the transition piece located in the free surface zone where waves are impacting the structure.

Construction possibilities for monolithic concrete spar buoy serial production

The monolithic nature of Windcrete, that sees floater, transition piece and tower as a single concrete structure, has direct impact on its potential construction process. The large-draft spar-buoy, to be fully completed in a coastal facility, requires horizontal transport that prompts construction also to be done horizontally. Then, the constraints to produce Windcrete structures are: large concrete structure built in horizontal position, preferably in a single monolithic pour with high quality standards, and this within reasonable production time if the project is considered at commercial deployment stage. In search for an appropriate solution, proposals will seek inspiration from a variety of engineering fields: mechanized tunnelling practices, far-reaching adaptations of slip-forming, reinforced centrifugal concrete pipe production and even trenchless technologies such as pipe jacking will all serve as a basis to elaborate a series of tailored solutions compatible with the specific requirements of Windcrete.

Experimental study on ultimate bending performance of grouted connections in offshore wind turbine support structures

This paper investigated six grouted connection specimens under ultimate four point bending test. The different eccentricity values of pile tube, overlap length and thickness of transition piece (TP) tube has been studied. It was found that all the specimens failed in a similar ductile mode. The eccentricity values had little effect on bending capacity, stiffness and ductility. However, the increased eccentricity values would aggravate the radial and inner cracks in grout material. Meanwhile, the overlap length and the thickness of the TP tube had apparent effect on bending behavior. Moreover, the effects of the eccentricity were studied and discussed by theories of composite beams in material mechanics.

Closed form solution for the first natural frequency of offshore wind turbine jackets supported on multiple foundations incorporating soil-structure interaction

Offshore Wind Turbines (OWTs) are dynamically sensitive structures and as a result estimating the natural frequency of the whole system taking into effect the flexibility of the foundation is one of the major design considerations. The natural frequency is necessary to predict the long-term performance as well as the fatigue life. Currently, jackets supported on multiple foundations (such as piles or suction caissons) are being considered to support WTG (Wind Turbine Generators) for deeper water developments. This paper presents a practical method to compute the natural frequency of a jacket supporting WTG by incorporating Soil-Structure-Interaction (SSI) based on closed form solutions. The formulation presented can be easily programmed in a spreadsheet type program and can serve as a convenient way to obtain the natural frequency with the least amount of input. The basis of this method is the Euler-Bernoulli beam theory where foundations are idealized with a set of linear springs. In this method, a 3-Dimensional jacket is first converted into a 2-Dimensional problem along the orthogonal planes of vibration which are essentially the principal axes of the foundation geometry. Subsequently, the jacket is converted into an equivalent beam representing it's stiffness and a formulation is presented to find an equivalent beam for the entire tower-jacket system. Using energy methods, an equivalent mass of the RNA (Rotor Nacelle Assembly)-tower-jacket system is also calculated and the fixed base frequency of the jacket is estimated. To consider the flexibility effects of the foundation, a formulation for an equivalent rotational spring of the foundation is developed. A method to incorporate the mass of the transition piece is also presented. Finally, a step-by-step application of the methodology is presented by taking example problems from literature which also serves the purpose of validation and verification.

Methodology for assessment of operational limits including uncertainties in wave spectral energy distribution for safe execution of marine operations

Marine operations need to be executed in a cost-effective and safe manner. Safety depends on safety margins that are included in the operational limits. These operational limits are normally given in terms of sea state parameters, i.e. significant wave height (Hs) and peak period (Tp), here denoted as Hs(Tp). Safety margins on Hs(Tp) should account for various sources of uncertainties in weather forecasts, wave spectral shape, numerical models, etc. Wave spectra at an offshore site may be multi-modal and not necessarily resemble analytical spectra, such as Joint North Sea Wave Project (JONSWAP) or Pierson-Moskowitz (PM) models. Since floating vessels are sensitive to wave spectral energy distribution, Hs(Tp) operational limits should account for this source of uncertainty. This paper provides a general methodology to assess the uncertainty in Hs(Tp) limits due to variability in wave spectral energy distribution. This is important for safe execution of marine operations. The methodology uses response-based operational limits, directional (2D) hindcast wave spectra and dynamic coupled models of marine operation activities. A case study of an offshore wind turbine transition piece installation is shown to illustrate the proposed methodology.

Transition piece design for an onshore hybrid wind turbine with multiaxial fatigue life estimation

Steel tubular structures are somewhat entrenched for the wind turbine towers. Recently, steel hybrid lattice/tubular towers are being investigated as a conceivable answer for taller onshore wind turbines for which convectional steel tubular towers are less competitive. Hybrid lattice/tubular towers require a transition piece which serves as a connection between lattice and tubular part. As the transition piece is supposed to transfer all the dynamic and self-weight loads to the lattice and foundation, these structural elements present unique features and are critical components to design and ought to resist strong cyclic bending moments, shear forces, and axial loads. Well-designed transition pieces with optimized ultimate state and fatigue capacities for manufacturing contribute to the structural soundness, reliability, and practicability of new onshore wind turbines hybrid towers. This research focuses on the investigation of the transition piece for an onshore wind turbine hybrid tower. The 5-MW reference wind turbine and a hybrid lattice/tubular tower were simulated in the servo-hydro aero-elastic analysis tool (by ASHES software) from which the loads and dynamic response of the supporting structure were obtained. Cross-sectional forces at the transition piece elevation were calculated and the connection with the lattice structure is designed. The transition piece was designed by finite element model considering ultimate limit load and fatigue load, using nonlinear analysis and multiaxial fatigue for life-time prediction, respectively. Multiaxial fatigue life was calculated based on Brown–Miller and Smith–Watson–Topper methods. In comparison, Smith–Watson–Topper method comes out to be more conservative. Potential of using high-strength steel S690 was investigated.

Pipeline Valves Technology, Material Selection, Welding, and Stress Analysis (A Case Study of a 30 in Class 1500 Pipeline Ball Valve)

Pipeline valves are the largest, heaviest, and most important valves on an offshore platform with long delivery time. A pipeline valve is either a ball type or through conduit gate valve type with a top entry design. The top entry design provides advantages such as a lower risk of leakage, greater mechanical strength against pipeline loads, and ease of maintenance (online maintenance) compared to the side entry design. A 30 in pipeline ball valve in class 1500 and carbon steel body material was chosen for stress analysis in this paper. The valve was connected to the pipeline through pup pieces from both sides. The pup pieces were connected to the body of the valve through transition pieces. The large 30 in valve has an emergency shut down safety function and is equipped with a hydraulic actuator. The valve is designed based on the American Petroleum Institute (API) 6D Specification for Pipeline and Piping valves. The proposed formula of wall thickness calculation in this paper is based on the American Society of Mechanical Engineers (ASME) Section VIII, Division 2, Boiler and Pressure Vessel Code (BPVC) instead of the ASME B16.34 standard. The wall thickness values given in the ASME B16.34 standard of “Valves Flanged, Threaded and Welding End” are very conservative and thick, which makes pipeline valves heavier and more expensive. Noticeably, ASME B16.34 requires an even higher thickness due to assembly loads, actuation (opening and closing) loads, and shapers other than circular that are applicable for pipeline valves. These valves should withstand loads from pipeline systems such as axial, torsion, and bending moments. ASME B16.34 does not specify the body wall thickness of the pipeline valves under the pipeline loads and moments. This paper aims to create a model to prove that the 30 in Class1500 pipeline valve will withstand the loads and moments with the thickness of the valve calculated using ASME Section VIII, Division 2 methods. The criteria and the model used to prove the suitability of the valve against the loads and moments are based on ASME Section VIII, Division 2.

Heat Transfer Designed for Bionic Surfaces with Rib Turbulators Inspired by Alopias Branchial Arch in a Simplified Gas Turbine Transition Piece

The energy needed for highly efficient heat transfer has shown a continuous growth, as the energy reduction. For highly efficient power convection, gas turbine is an important device at present. But, the design of highly efficient gas turbine is limited by the temperature and the material’s temperature resistance around the inlet. One part of the inlet need to be protected from burning out is transition piece. A bionic thermal surface with rib turbulators is designed according to the turbulence function of alopias’ branchial arches and is evaluated for thermo-protection enhancement in a simplified gas turbine transition piece using computational fluid dynamics (CFD) simulation. With the given diameter (Φ = 10.26 mm) of the impinging hole, three different horizontal distances (S) from impinging holes to the front of first-row rib were solved, which were S1 = 20 mm, S2 = 40 mm, and S3 = 60 mm, respectively, in case 1. But, the results revealed that S is not a significant influence factor on heat transfer efficiency. The cooling coefficient increases from 0.194 to 0.198 when the distance varies from S1 to S3. In case 2, rib turbulator width (W) and height (H) have been studied in ranges from 0.5 × Φ to 1.5 × Φ. All of the numerical results indicated that the best size of the rib turbulators could improve the heat transfer efficiency to 32.5%, when comparing with the smooth surface. All of the comparisons will benefit the structural design of heat transfer, which could be used for solving more severe problems in thermo-protection.

International Experience in Developing Low-Emission Combustors for Land-Based, Large Gas-Turbine Units: Mitsubishi Heavy Industries’ Equipment

This is the second paper in a series of publications summarizing the international experience in the development of low-emission combustors (LEC) for land-based, large (above 250 MW) gas-turbine units (GTU). The purpose of this series is to generalize and analyze the approaches used by various manufacturers in designing flowpaths for fuel and air in LECs, managing fuel combustion, and controlling the fuel flow. The efficiency of advanced GTUs can be as high as 43% (with an output of 350–500 MW) while the efficiency of 600–800 MW combined-cycle units with these GTUs can attain 63.5%. These high efficiencies require a compression ratio of 20–24 and a temperature as high as 1600°С at the combustor outlet. Accordingly, the temperature in the combustion zone also rises. All the requirements for the control of harmful emissions from these GTUs are met. All the manufacturers and designers of LECs for modern GTUs encounter similar problems, such as emissions control, combustion instability, and reliable cooling of hot path parts. Methods of their elimination are different and interesting from the standpoint of science and practice. One more essential requirement is that the efficiency and environmental performance indices must be maintained irrespective of the fuel composition or heating value and also in operation at part loads below 40% of rated. This paper deals with Mitsubishi Series M701 GTUs, F, G, or J class, which have gained a good reputation in the power equipment market. A design of a burner for LECs and a control method providing stable low-emission fuel combustion are presented. The advantages and disadvantages of the use of air bypass valves installed in each liner to maintain a nearly constant air to fuel ratio within a wide range of GTU loads are described. Methods for controlling low- and high-frequency combustion instabilities are outlined. Upgrading of the cooling system for the wall of a liner and a transition piece is of great interest. Change over from effusion (or film) cooling to convective steam cooling and convective air cooling has considerably increased the GTU efficiency.

Wear characteristics of a combustion liner for power generation gas turbine

Wear is the main degradation of the combustor components in gas turbine power generation. One of the most vital components in a gas turbine is the combustion liner which is often observed with severe wear damage. In this study, the combustion liner was made from Hastelloy X (a nickel-based superalloy material). The degradation generally occurred at the mating surfaces of the combustion liner which consisted of the fuel nozzle and a transition piece. The purpose of this study was to determine and characterise the dominant wear mechanisms at two different contact surfaces (connected to stainless steel and Nimonic 263) after being exposed to 8,000 hours of run time at high temperature and vibration. The worn surfaces were analysed and the wear mechanism was discussed.

Совершенствование технологии изготовления длинномерных композиционных переходников сталь 20 - сталь 08Х18Н10Т методом горячей винтовой прокатки в вакууме

Совершенствование технологии изготовления длинномерных композиционных переходников сталь 20 - сталь 08Х18Н10Т методом горячей винтовой прокатки в вакууме

Application of explosion welding for manufacture of trimetallic transition pieces of cryomodules of linear collider

Application of explosion welding for manufacture of trimetallic transition pieces of cryomodules of linear collider

Применение сварки взрывом для создания триметаллических переходников криомодулей линейного коллайдера

Применение сварки взрывом для создания триметаллических переходников криомодулей линейного коллайдера

Improvement of the technology of producing extended composite transition pieces of steel 20 — steel 08Kh18N10T made by the method of hot screw rolling in vacuum

Improvement of the technology of producing extended composite transition pieces of steel 20 — steel 08Kh18N10T made by the method of hot screw rolling in vacuum

Analytical and numerical investigation of bolted steel ring flange connection for offshore wind monopile foundations

The monopile foundation is the dominant solution for support of wind turbines in offshore wind farms. It is normally grouted to the transition piece which connects the foundation to the turbine. Currently, the bolted steel ring flange connection is investigated as an alternative. The monopile--transition piece connection has specific problems, such as out-of-verticality and installation damage from driving the MP into the seabed and it is not fully known how to design for these. This paper presents the status of the ongoing development work and an estimate of what still needs to be covered in order to use the connection in practice. This involves presentation of an analytical and non-linear FE analysis procedure for the monopile-transition piece connection composed of two L flanges connected with preloaded bolts. The connection is verified for ultimate and fatigue limit states based on an integrated load simulation carried out by the turbine manufacturer.

Measurement correction method for force sensor used in dynamic pressure calibration based on artificial neural network optimized by genetic algorithm

We present an optimization algorithm to obtain low-uncertainty dynamic pressure measurements from a force-transducer-based device. In this paper, the advantages and disadvantages of the methods that are commonly used to measure the propellant powder gas pressure, the applicable scope of dynamic pressure calibration devices, and the shortcomings of the traditional comparison calibration method based on the drop-weight device are firstly analysed in detail. Then, a dynamic calibration method for measuring pressure using a force sensor based on a drop-weight device is introduced. This method can effectively save time when many pressure sensors are calibrated simultaneously and extend the life of expensive reference sensors. However, the force sensor is installed between the drop-weight and the hammerhead by transition pieces through the connection mode of bolt fastening, which causes adverse effects such as additional pretightening and inertia forces. To solve these effects, the influence mechanisms of the pretightening force, the inertia force and other influence factors on the force measurement are theoretically analysed. Then a measurement correction method for the force measurement is proposed based on an artificial neural network optimized by a genetic algorithm. The training and testing data sets are obtained from calibration tests, and the selection criteria for the key parameters of the correction model is discussed. The evaluation results for the test data show that the correction model can effectively improve the force measurement accuracy of the force sensor. Compared with the traditional high-accuracy comparison calibration method, the percentage difference of the impact-force-based measurement is less than 0.6% and the relative uncertainty of the corrected force value is 1.95%, which can meet the requirements of engineering applications.

Mass Housing Neighbourhoods in Medium-Sized Andalusian Cities. Between Historic City Centres and New Peripheral Developments

This paper aims to analyse the evolution experienced by the neighbourhoods that comprise the so-called first periphery. Most of them have been thoroughly studied, has led to recognize theirs values and to be included in the catalogues of heritage protection of their respective cities. However, this research shows that is pending an in-depth analysis in cities of intermediate scale. Its significance lies not only in the fact that they are the most significant operations of architecture of the modern movement in their respective cities, but are especially noteworthy the values derived from its strategic location within the urban structure of these intermediate scale cities. Being near to city centre, they have been constituted as transition pieces between historic sites, new peripheral developments, and even, their nearest territory. As method, this research proposes a comparative analysis of traceability among different study cases, from medium-sized cities of the Andalusian Coast (Spain). In this context, it means recording the evolution that these promotions have been experienced since their first designs until their current situation. It attempts to find the characteristics that have resulted in the urban configuration of this periphery and to recognize the sum of all the cultural, economic, social and technological aspects that conditions the ways of life that today are detected in them. Definitely, the knowledge generated by this research allows extracting architectural and urban values of these examples, which justify its necessary dissemination as part of our legacy.