Spar Concept Research Articles

Performance and Emissions Benefits of Cooled Ceramic Matrix Composite Vanes for High-Pressure Turbines

Abstract Ceramic matrix composites (CMCs) offer great potential for developing lighter and more efficient aero-engines. Due to their high-temperature capability, CMCs are mainly used in the hot gas section in order to replace cooled metallic components and thus save cooling air. Especially CMC vanes for high-pressure turbines (HPTs) have been researched and tested in the past. A realistic design approach for cooled CMC vanes is the so-called shell and spar concept. The application of such vanes in HPTs as inlet guide vanes (IGVs) at constant rotor inlet temperature (T41) enables performance and emissions benefits which are assessed by means of a reference engine in this paper. Compared to metallic IGVs, more temperature-resistant CMC IGVs require significantly less cooling air and generate lower cooling losses. A quantitative comparison will be presented. Consequently, the redesign of the reference engine to the setting of a hybrid HPT leads to a reduction in thrust specific fuel consumption (TSFC) by 0.23% at cruise conditions. Additionally, there is potential to extract the IGV cooling air at a lower pressure level, increasing the cruise TSFC gain to 0.41%. In the course of the redesign process, the turbine inlet temperature (T4) is reduced by 50 K in order to reach the same T41 with a lower IGV coolant mass flow. Regarding emissions, this leads to a decreased production of nitrogen oxides (NOx). Hence, several NOx emissions parameters can be reduced by more than 4%.

BP’s Argos FPU Offers Fresh Lessons for the Future of Deepwater GOM Projects

Tipping the scales at well over 60,000 tons, BP’s Argos platform is a giant among giants in the deepwater US Gulf of Mexico (GOM). Standing 27 stories tall, the platform has a deck the length and width of an American football field and is one of BP’s largest in the region. One-time KBR subsidiary GVA designed the semisubmersible, the centerpiece of the supermajor’s $9 billion Mad Dog II project built to unlock additional production potential of the Miocene-aged reservoirs estimated to hold more than 5 billion bbl of oil in place. But that wasn’t always the plan. Over a decade ago, BP’s Mad Dog II looked quite different. On paper, the producer was looking at an all-subsea development tied back to another large spar platform—dubbed Big Dog—to host the additional reserves. The development plan envisioned a massive truss spar. Its topsides would need to be installed via three separate offshore lifts then fully integrated at the field site. Any offshore heavy lift is an execution risk. In 1998, an accident while lifting the south module onto Texaco’s Petronius compliant tower in the GOM resulted in the loss of that section of the topsides and delayed the project for a year and a half. That module weighed 3,600 tons. Another hesitation for BP? The price tag. All-in, the spar-based Mad Dog II solution was estimated to cost around $19 billion. That included 30-plus wells. Ultimately, the spar concept was scrapped, and BP moved back to square one and a blank sheet of paper. “The reserves were there,” said Chris Ruthven, project general manager, Mad Dog II. “We knew the reserves were there. In fact, ironically, the team developed the field with the smallest of the four big platforms that BP did back at that point in time: Thunder Horse, Holstein, Atlantis, and Mad Dog. It was the smallest, but ultimately, it was the second-biggest field. It turned out to be huge. All that appraisal showed we’ve got a lot of reserves. So, we went back and went with an analog to Atlantis. Atlantis was seen as a good fit requiring much less offshore integration work. Operations loved the asset, and it was a very safe design. We landed on that concept, and we tried to keep it almost pretty much the same in terms of the overall layout of the facility, but it’s a little bit bigger footprint.” Mad Dog proper was discovered in 1998 via an exploration well in over 6,100 ft of water located in Green Canyon Block 826. The well was drilled to a measured depth of 22,410 ft and encountered around 215 ft of hydrocarbon-bearing Miocene reservoirs. The discovery was followed by a 1999 well drilled to a total depth of 22,410 ft and a further successful appraisal well in February 2000. Mad Dog, covering Green Canyon blocks 825, 826, and 782, was sanctioned as a spar-based development in 2002. The project came online in early 2005.

Aerodynamic characterization of barge and spar type floating offshore wind turbines at different sea states

AbstractThe wake dynamics behind a compliant floating offshore wind turbine (FOWT) with two alternative supporting platforms of spar buoy and barge platform are studied numerically. The computational model is based on the large eddy simulation and the use of the actuator disk model of the FOWT rotor in which the circular actuator disk is discretized with an unstructured two‐dimensional triangular mesh in a structured three‐dimensional Cartesian grid of the fluid domain. The wake dynamics and platform motions are calculated for laminar and turbulent inflow conditions. The flow solver is verified through a series of experimental wake measurements done behind a porous disk model and is also cross‐validated against previously published results. The dynamics of the floating spar and barge structures are calculated from wave–structure interaction for three distinctive sea states. The time history of power extraction and wind force for the floating offshore wind turbine are recorded and compared against a fixed horizontal axis wind turbine. The motion of the barge platform is found to induce low‐frequency modulation of the wake, whereas the spar buoy primarily displays similar wake dynamics to the fixed turbine. It is discussed how a single turbine utilizing the spar concept can be more energy efficient under the wave‐induced motion. Moreover, for both laminar and turbulent inflow conditions, due to the large axial oscillation experienced by the barge concept, the turbine wake recovers more rapidly. This suggests that for a tighter spacing of the turbines in a farm, the barge platform concept can be leveraged to obtain higher energy‐capturing efficiency over a fixed area.

Spar-Type Vertical-Axis Wind Turbines in Moderate Water Depth: A Feasibility Study

The applications of floating vertical-axis wind turbines (VAWTs) in deep water have been proposed and studied by several researchers recently. However, the feasibility of deploying a floating VAWT at a moderate water depth has not yet been studied. In this paper, this feasibility is thoroughly addressed by comparing the dynamic responses of spar-type VAWTs in deep water and moderate water depth. A short spar VAWT supporting a 5 MW Darrieus rotor at moderate water depth is proposed by following the deep spar concept in deep water. A fully coupled simulation tool, SIMO-RIFLEX-DMS code, is utilized to carry out time domain simulations under turbulent wind and irregular waves. Dynamic responses of the short spar and deep spar VAWTs are analyzed and compared, including the natural periods, wind turbine performance, platform motions, tower base bending moments, and tension of mooring lines. The statistical characteristics of the thrust and power production for both spars are similar. The comparison of platform motions and tower base bending moments demonstrate a good agreement for both spars, but the short spar has better performance in surge/sway motions and side–side bending moments. The 2P response dominates the bending moment spectra for both spars. A significant variation in tension of Mooring Line 1 and a larger corresponding spectrum value are found in the short spar concept. The results indicate that the application of short spar VAWTs is feasible and could become an alternative concept at moderate water depth.

A 3D FEM model for floating wind turbines support structures

The relevance of the interaction between the structural stiffness and the wind turbine dynamics are well known by the industry from decades of expertise. However, the novel floating concepts are commonly designed by tools that disregard the individual structural stiffness of the elements which compose the floating platform. Usually, these elements are treated as rigid body elements in the design process. However, their flexibility can be relevant in the long time structural life assessment, particularly for the fatigue assessment. Then, a structural analysis that includes the dynamic effects over the deformation of the structure is required. The paper proposes a model that integrates the instantaneous deformation of the structure by a nonlinear dynamic Finite Element Analysis (FEA) computation in a fully coupled Offshore Wind Turbine (WT) model in the time domain.A 3D hydro-aero-servo-elastic coupled numerical model in time domain for structural analysis of floating or bottom fixed structures has been developed at the UPC-BarcelonaTech. The code integrates the forces exerted by the waves and currents as well as the aerodynamic loads, including the wind turbine, and the mooring system. For the hydrodynamic loads the Morison’s equation is used to compute waves and current forces. Both Airy (regular and irregular) and Stokes 5th order wave theories are implemented. The mooring system can be computed in a quasi-static way or considering their fully dynamics. The aerodynamic loads are computed with AeroDyn standalone module from NREL, which is coupled to the FE model. The structure is discretized with one-dimensional beam finite elements, in which the formulation considers small strains as well as large motions under the implementations of the Euler beams theory. With this approach, the dynamic interaction between the wind turbine and the structure, as well as the effects on the internal forces are implicitly coupled in the formulation.A comparison of the Windcrete concrete SPAR concept experimental Response Amplitude Operators (RAO) against the numerical results are presented, as well as some results from simulations under normal operation conditions.

開断面と閉断面を組み合わせた二重筒によるTwist型モーフィング翼桁構造

A new concept of twistable morphing spar is proposed to achieve an objective distribution of the twist angle more arbitrary and validity of the proposed design method is confirmed through experiments and numerical simulations using finite element analyses. A key aspect of the proposed twistable morphing spar concept is a double cylinder consisting of two cylinders, which is employed as a spar of twistable morphing wing. The ends of these cylinders are connected to each other at the tip side. One cylinder (Inner-cylinder) is a thick closed-section member. It carries torsion moments and connected to motor that provides moment to the member at the root side. The other cylinder (Outer-cylinder) is a variable-shape member composed of open and closed-sections. It is designed to achieve an objective distribution of twist angles, and is connected to the aircraft fuselage at the root side. The objective distribution of the twist angle can be achieved by designing the parameter we selected appropriate. In accordance with the design method, we manufactured an experimental model using a 3D printer and twist experiment was carried out. From comparison of the experimental results and the numerical simulation, feasibility of the twistable morphing spar and the validity of the design method were confirmed.

Analysis of Structural Second Order Effects on a Floating Concrete Platform for FOWT's

The irruption of the floating wind energy in the offshore engineering is changing the paradigm of the structural analysis for those new structures, which are significantly smaller and more slender than those previously existing from the O&G industry and in which the most important load is applied around 100m above the mean sea level. Those characteristics require the structural analysis to include the dynamic effects over the deformation of the structure, integrating the instantaneous deformation of the structure into the nonlinear dynamic finite element analysis (FEA) computation.A numerical model which couples the hydrodynamic and aerodynamic effects in a time domain structural analysis, has been developed at the UPC. The code integrates the forces exerted by the waves and currents as well as the aerodynamic loads, including the wind turbine, and the mooring system. For the hydrodynamic loads, Morison's equation in combination with the Stoke's 5th order nonlinear wave theory are used to compute the resulting forces. The mooring system is treated in a quasi-static way and the aerodynamic loads are computed with FAST. The structure is discretized with one-dimensional beam elements, in which the formulation considers small strains as well as large motions.The model computes a dynamic time domain nonlinear FEA for FOWT's, integrating all the effects of the external forces and the structural stiffness to obtain the displacements at each point of the structure at each time step. With this approach, the dynamic interaction between the wind turbine and the structure, as well as the effects on the internal forces are implicitly considered in the formulation. A comparison of the structure motions and internal forces for a concrete spar concept is presented assuming a nonlinear rigid body approach and a nonlinear dynamic time-domain FEA.

Twist Morphing Using the Variable Cross Section Spar: Feasibility Study

This paper presents the variable cross section spar (VCSpar) concept that facilitates varying the shear center position relative to the aerodynamic center, allowing the external aerodynamic loads to twist the structure and maintain its deformed shape. The VCSpar is considered in this paper as integrated within the wing of a representative unmanned aerial vehicle (UAV) to enhance its flight performance and control authority. A preliminary design study was conducted to assess the potential benefits of the concept using a low-fidelity design tool. Then, aeroelastic modeling of the concept was performed where the VCSpar was modeled as a two-dimensional equivalent aerofoil using bending and torsion shape functions to express the equations of motion in terms of the twist angle and plunge displacement at the wingtip. The aerodynamic lift and moment acting on the equivalent aerofoil were modeled using Theodorsen’s unsteady aerodynamic theory. A low-dimensional state-space representation of an empirical Theodorsen’s transfer function was adopted to allow time-domain analyses.

Span Morphing Using the Compliant Spar

This paper develops and models the Compliant Spar concept that allows the wing span to be varied to provide roll control and enhance the operational performance for a medium altitude long endurance (MALE) UAV. The wing semi-span is split into morphing partitions and the concept maybe incorporated in each partition; however only the tip partition is considered here. The Compliant Spar is made of compliant joints arrange in series to allow the partition to be flexible under axial (spanwise) loads but at the same time stiff enough to resist bending loads. Each compliant joint consists of two concentric overlapping AL 2024-T3 tubes joined together using elastomeric material. Under axial (spanwise) loading, the elastomeric material deforms in shear allowing the overlapping distance between the tubes to vary and hence the length (in the spanwise direction) of the joint/spar to vary. High fidelity modelling of the concept is performed. Then, structural optimisation studies are performed to minimise the axial stiffness and the structural mass of the concept for various design constraints. The flexible skin and actuation system to be used are also addressed.

Hydroelastic code-to-code comparison for a tension leg spar-type floating wind turbine

The development of robust design tools for offshore wind turbines requires knowledge of both wave and wind load models and response analysis. Verification of the numerical codes is required by the use of experiments and code-to-code comparisons. This paper presents a hydroelastic code-to-code comparison between the HAWC2 and USFOS/vpOne codes for a tension leg spar (TLS) wind turbine with a single tether. This concept is hence based on the TLP and Spar concepts. The comparison is performed using coupled hydroelastic time domain simulations. Several aspects of modelling, such as wave simulation, hydrodynamic and structural modelling, are addressed for the TLS. Wave-induced motions of the support structure affect the power performance of a wind turbine. Furthermore, overload of the tension leg should be avoided. In this paper, the motion and tension responses are compared. The tension leg introduces nonlinear effects on the spar motion. These nonlinear effects include combined-frequency effect such as double, difference and sum of wave, as well as natural pitch and surge frequencies. Hydrodynamic loads are based on a combination of the Morison formula and the pressure integration method. A comparison indicates that the motion and tension responses obtained in the two codes are in good agreement.

Numerical investigation on the hydrodynamic performances of a new spar concept

Recently, the spar platform concept develops quickly in the offshore oil and gas exploitations, especially in deep and ultra-deep water, owing to its benign motion performance, excellent stability and adaptation to wide range of water depth. Many new spar concepts have been put forward with the purpose of reducing fabrication difficulty and cost, while meeting the requirements of exploitation in the meantime. Based on the aims mentioned above, a new spar concept was presented in this article and its hydrodynamics both in operating and survival conditions was studied by means of numerical simulation. Basic model tests were also conducted to calibrate the numerical approach. Following aspects are highlighted: (1) new spar concept, (2) global performance of the spar concept and (3) mooring line analysis.

Reliable Riser Systems for Spars

The Spar concept as a floating vessel is now recognized as a reliable and economic option for developing deepwater offshore hydrocarbon reservoirs. Many of the advantages of the Spar concept are attributed to the variety of riser systems that can be accommodated. This paper presents a discussion of design considerations for the top tensioned and steel catenary risers deployed from a Spar offshore production vessel. Results from extreme event strength analysis, Spar motion and current-induced fatigue analysis, and a riser-to-riser wake interference analysis are presented. Steel catenary risers are presented, including a comparison of results for risers supported by a Spar and a Semi. These analyses demonstrate that simple and reliable riser systems can be designed for use with the Spar platform concept.