Results of a landing gear loads test using a 0.0405-scale model (16-0) of the space shuttle orbiter in the Rockwell International NAAL wind tunnel (OA163B), volume 2
For abstract, see N77-33253.
Mennell, R. C.↗
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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
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Wind-tunnel Investigation at Low Speed of a Wing Swept Back 63 Degrees and Twisted and Cambered for Uniform Load at a Lift Coefficient of 0.5 and with a Thickened Tip Section
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Weiberg, James A↗
Novel Low Cost, High Reliability Wind Turbine Drivetrain
Clipper Windpower, in collaboration with United Technologies Research Center, the National Renewable Energy Laboratory, and Hamilton Sundstrand Corporation, developed a low-cost, deflection-compliant, reliable, and serviceable chain drive speed increaser. This chain and sprocket drivetrain design offers significant breakthroughs in the areas of cost and serviceability and addresses the key challenges of current geared and direct-drive systems. The use of gearboxes has proven to be challenging; the large torques and bending loads associated with use in large multi-MW wind applications have generally limited demonstrated lifetime to 8-10 years. The large cost of gearbox replacement and the required use of large, expensive cranes can result in gearbox replacement costs on the order of $\$$1M, representing a significant impact to overall cost of energy (COE). Direct-drive machines eliminate the gearbox, thereby targeting increased reliability and reduced life-cycle cost. However, the slow rotational speeds require very large and costly generators, which also typically have an undesirable dependence on expensive rare-earth magnet materials and large structural penalties for precise air gap control. The cost of rare-earth materials has increased 20X in the last 8 years representing a key risk to ever realizing the promised cost of energy reductions from direct-drive generators. A common challenge to both geared and direct drive architectures is a limited ability to manage input shaft deflections. The proposed Clipper drivetrain is deflection-compliant, insulating later drivetrain stages and generators from off-axis loads. The system is modular, allowing for all key parts to be removed and replaced without the use of a high capacity crane. Finally, the technology modularity allows for scalability and many possible drivetrain topologies. These benefits enable reductions in drivetrain capital cost by 10.0%, levelized replacement and O&M costs by 26.7%, and overall cost of energy by 10.2%. This design was achieved by: (1) performing an extensive optimization study that deter-mined the preliminary cost for all practical chain drive topologies to ensure the most competitive configuration; (2) conducting detailed analysis of chain dynamics, contact stresses, and wear and efficiency characteristics over the chain's life to ensure accurate physics-based predictions of chain performance; and (3) developing a final product design, including reliability analysis, chain replacement procedures, and bearing and sprocket analysis. Definition of this final product configuration was used to develop refined cost of energy estimates. Finally, key system risks for the chain drive were defined and a comprehensive risk reduction plan was created for execution in Phase 2.
17 WIND ENERGY↗
Open-Loop Control of Adjustable Tuned Mass Dampers for Floating Wind Turbine Platforms: Preprint
Floating offshore wind turbines have several advantages over their land-based counterparts, including access to stronger, more consistent winds and proximity to population centers. However, increased costs from the platform have been a challenge inhibiting their widespread adoption. New damping technologies with tunable target frequencies and damping ratios promise a greater degree of control over platform motions, allowing hulls to be designed smaller and reducing the overall cost of the turbines. In this work, a control strategy is proposed for these adjustable tuned mass dampers (TMDs). A frequency-domain model of the system is developed, from which response amplitude operators (RAOs) for the platform's rigid-body modes can be obtained for different natural frequencies and damping ratios of the dampers. Using these RAOs, and JONSWAP spectrums of operational and extreme sea states, the performance of the various damper settings are compared by evaluating the standard deviation of a rigid-body motion of interest (platform pitch or heave). By finding the optimal damper setting for a range of representative design load cases (DLCs), a lookup function is made to return the damper target frequency given the peak period of the sea state. To determine the current sea state, we propose a simple estimator that uses wave measurements (e.g., from a measurement buoy) to determine the peak period and significant wave height. The significant wave height is determined using the statistics of the past 100 seconds of wave elevation information and the peak period is computed using a frequency locked loop. Initial results show that we can use these estimated values to control the TMD natural frequency with an open loop controller. The controlled system is tested in a range of environmental conditions determined by the International Electrotechnical Commission design load cases (DLCs), which include normal and extreme wind and wave models. In these tests, we compare the performance of 4 cases: (1) no TMD, (2) a constant TMD based on the worst case DLC, (3) a controlled TMD based on known wind and wave environments, and (4) a real-time controlled TMD using estimated wind and wave environments. The effect of hull-based TMD control is also compared to changes in traditional wind turbine control via blade pitch.
control↗
Development of a 5-Component Balance for Water Tunnel Applications
The principal objective of this research/development effort was to develop a multi-component strain gage balance to measure both static and dynamic forces and moments on models tested in flow visualization water tunnels. A balance was designed that allows measuring normal and side forces, and pitching, yawing and rolling moments (no axial force). The balance mounts internally in the model and is used in a manner typical of wind tunnel balances. The key differences between a water tunnel balance and a wind tunnel balance are the requirement for very high sensitivity since the loads are very low (typical normal force is 90 grams or 0.2 lbs), the need for water proofing the gage elements, and the small size required to fit into typical water tunnel models. The five-component balance was calibrated and demonstrated linearity in the responses of the primary components to applied loads, very low interactions between the sections and no hysteresis. Static experiments were conducted in the Eidetics water tunnel with delta wings and F/A-18 models. The data were compared to forces and moments from wind tunnel tests of the same or similar configurations. The comparison showed very good agreement, providing confidence that loads can be measured accurately in the water tunnel with a relatively simple multi-component internal balance. The success of the static experiments encouraged the use of the balance for dynamic experiments. Among the advantages of conducting dynamic tests in a water tunnel are less demanding motion and data acquisition rates than in a wind tunnel test (because of the low-speed flow) and the capability of performing flow visualization and force/moment (F/M) measurements simultaneously with relative simplicity. This capability of simultaneous flow visualization and for F/M measurements proved extremely useful to explain the results obtained during these dynamic tests. In general, the development of this balance should encourage the use of water tunnels for a wider range of quantitative and qualitative experiments, especially during the preliminary phase of aircraft design.
Suarez, Carlos J.↗
Energy Imbalance Markets (Fact Sheet)
The anticipated increase in variable renewable generation, such as wind and solar power, over the next several years has raised concerns about how system operators will maintain balance between electricity production and demand in the Western Interconnection, especially in its smaller balancing authority areas (BAAs). Given renewable portfolio standards in the West, it is possible that more than50 gigawatts of wind capacity will be installed by 2020. Significant quantities of solar generation are likely to be added as well. Meanwhile, uncertainties about future load growth and challenges siting new transmission and generation resources may add additional stresses on the Western Interconnection of the future. One proposed method of addressing these challenges is an energy imbalancemarket (EIM). An EIM is a means of supplying and dispatching electricity to balance fluctuations in generation and load. It aggregates the variability of generation and load over multiple balancing areas (BAs).
14 SOLAR ENERGY↗
Coordination and Control of Flexible Building Loads for Renewable Integration; Demonstrations using VOLTTRON
Renewable energy resources such as wind and solar power have a high degree of uncertainty. Large-scale integration of these variable generation sources into the grid is a big challenge for power system operators. Buildings, in which we live and work, consume about 75% of the total electricity in the United States. They also have a large capacity of power flexibility due to their massive thermal capacitance. Therefore, they present a great opportunity to help the grid to manage power balance. In this report, we study coordination and control of flexible building loads for renewable integration. We first present the motivation and background, and conduct a literature review on building-to-grid integration. We also compile a catalog of flexible building loads that have great potential for renewable integration, and discuss their characteristics. We next collect solar generation data from a photovoltaic panel on Pacific Northwest National Laboratory campus, and conduct data analysis to study their characteristics. We find that solar generation output has a strong uncertainty, and the uncertainty occurs at almost all time scales. Additional data from other sources are also used to verify our study. We propose two transactive coordination strategies to manage flexible building loads for renewable integration. We prove the theories that support the two transactive coordination strategies and discuss their pros and cons. In this report, we select three types of flexible building loads—air-handling unit, rooftop unit, and a population of WHs—for which we demonstrate control of the flexible load to track a dispatch signal (e.g., renewable generation fluctuation) using experiment, simulation, or hardware-in-the-loop study. More specifically, we present the system description, model identification, controller design, test bed setup, and experiment results for each demonstration. We show that coordination and control of flexible loads has a great potential to integrate variable generation sources. The flexible loads can successfully track a power dispatch signal from the coordinator, while having little impact on the quality of service to the end-users.
32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
Buoyancy Stabilized Offshore Wind Turbine
Offshore wind resources are valued because they are close to load. However, the cost of energy is too high and detractors argue that they are unsightly. On the US East Coast and in the UK it would be beneficial to have turbines that could be installed in 50 to 150 meters as this would put turbines out of sight, in the strongest wind and close to infrastructure. Clear Path Energy’s (CPE) initial solution was a compliant, buoyancy stabilized design. However, the year one review revealed three major challenges with this approach: 1) Large waves caused large tilt angles requiring excessive support structure, 2) A large pile was needed to resist the 1,000 tons of upward force, and 3) Maintenance on the moving platform would be complicated. Following additional analysis, the design was modified to a compliant, tether stabilized design. Buoyancy was used, not for stability, but to reduce pressure on the articulated seabed connection. The seabed connection was simplified, mass was removed from the tower and the cost of the anchor system was substantially reduced.
17 WIND ENERGY↗
Coupled aero-hydro-geotech real-time hybrid simulation of offshore wind turbine monopile structures
Real-time hybrid simulation (RTHS) divides a structural system into an analytical and experimental substructure. The former is based on a well-established analytical model while the latter consists of a physical model in the laboratory, for which there is not a well-established analytical model. This paper extends real-time hybrid simulation to monopile-type Offshore Wind Turbines (OWTs) to enable the investigation of their behavior considering the response of pile foundations under operational and more severe conditions. The embedded foundation and surrounding soil of the OWT are modeled physically in a soil box in the laboratory while the remaining parts of the system and loading are modeled analytically. The program OpenFAST, developed by the National Renewable Energy Laboratory (NREL), is linked to the RTHS coordinator to determine the hydrodynamic and aerodynamic loads acting on the OWT, along with modeling the dynamics of the electric power generation equipment and associated controller for the OWT. The RTHS framework along with its initial implementation and validation are described in this paper. RTHSs of a 5 MW OWT subjected to operational and more severe conditions are performed to experimentally validate the framework. The framework offers a realistic approach to investigate the behavior of OWT structures supported on monopiles. Furthermore, this approach accounts for the coupled response of the OWT structure with its foundation, while experimentally capturing the nonlinearities of the soil-foundation interaction in real-time.
17 WIND ENERGY↗
A Method of Determining Aerodynamic-Influence Coefficients from Wind-Tunnel Data for Wings at Supersonic Speeds
A method is described for determining aerodynamic-influence coefficients from wind-tunnel data for calculating the steady-state load distribution on a wing with arbitrary angle-of-attack distribution at supersonic speeds. The method combines linearized theory with empirical adjustments in order to give accurate results over a wide range of angles of attack. The experimented data required are pressure distributions measured on a flat wing of the desired planform at the desired Mach number and over the desired range of angles of attack. The method has been tested by applying it to wind-tunnel data measured at Mach numbers of 1.61 and 2.01 on wings of the same planform but of different surface shapes. Influence coefficients adjusted to fit the flat wing gave good predictions of the spanwise and chord-wise distributions of loadings measured on twisted and cambered wings.
Gainer, Patrick A.↗
Aerodynamic characteristics of a wing with Fowler flaps including flap loads, downwash, and calculated effect on take-off
This report presents the results of wind tunnel tests of a wing in combination with each of three sizes of Fowler flap. The purpose of the investigation was to determine the aerodynamic characteristics as affected by flap chord and position, the air loads on the flaps, and the effect of flaps on the downwash.
Platt, Robert C↗
Heave Plate Hydrodynamic Coefficients for Floating Offshore Wind Turbines - A Compilation of Data
The National Renewable Energy Laboratory's OpenFAST software is utilized by academics and industry professionals alike to simulate offshore wind turbines. The software's modeling of hydrodynamic loads on heave plates attached to these structures relies on user-specified hydrodynamic coefficients. To guide the proper selection of these coefficients and potentially develop a new functionality within OpenFAST that automatically prescribes and/or adjusts the heave-plate hydrodynamic coefficients, we review past literature to examine the dependence of the added mass, damping, and drag coefficients on various relevant nondimensional parameters, including the Keulegan-Carpenter number, the frequency parameter, and the plate thickness ratio. Existing data in the literature show strong dependence of the hydrodynamic coefficients on the Keulegan-Carpenter number. We observe consistent trends across a range of different plate geometry, plate porosity, and flow conditions. Secondary dependence of the coefficients on the frequency parameter and plate thickness ratio is also present.
added mass↗
Heave-Plate Hydrodynamic Coefficients for Floating Offshore Wind Turbines - A Compilation of Data: Preprint
The National Renewable Energy Laboratory's OpenFAST software is utilized by academics and industry professionals alike to simulate offshore wind turbines. The software's modeling of hydrodynamic loads on heave plates attached to these structures relies on user specified hydrodynamic coefficients. To guide the proper selection of these coefficients and potentially develop a new functionality within OpenFAST that automatically prescribes and/or adjust the heave-plate hydrodynamic coefficients, this paper reviews past literature to examine the dependence of the added mass, damping, and drag coefficients on various relevant non-dimensional parameters, including the Keulegan-Carpenter number, the frequency parameter, and the plate thickness ratio. Existing data in the literature show strong dependence of the hydrodynamic coefficients on the Keulegan-Carpenter number. Consistent trends are observed across a range of different plate geometry, plate porosity, and flow conditions. Secondary dependence of the coefficients on the frequency parameter and plate thickness ratio is also present.
added mass↗
A nuclear wind/solar oil-shale system for variable electricity and liquid fuels production
The recoverable reserves of oil shale in the United States exceed the total quantity of oil produced to date worldwide. Oil shale contains no oil, rather it contains kerogen which when heated decomposes into oil, gases, and a carbon char. The energy required to heat the kerogen-containing rock to produce the oil is about a quarter of the energy value of the recovered products. If fossil fuels are burned to supply this energy, the greenhouse gas releases are large relative to producing gasoline and diesel from crude oil. The oil shale can be heated underground with steam from nuclear reactors leaving the carbon char underground - a form of carbon sequestration. Because the thermal conductivity of the oil shale is low, the heating process takes months to years. This process characteristic in a system where the reactor dominates the capital costs creates the option to operate the nuclear reactor at base load while providing variable electricity to meet peak electricity demand and heat for the shale oil at times of low electricity demand. This, in turn, may enable the large scale use of renewables such as wind and solar for electricity production because the base-load nuclear plants can provide lower-cost variable backup electricity. Nuclear shale oil may reduce the greenhouse gas releases from using gasoline and diesel in half relative to gasoline and diesel produced from conventional oil. The variable electricity replaces electricity that would have been produced by fossil plants. The carbon credits from replacing fossil fuels for variable electricity production, if assigned to shale oil production, results in a carbon footprint from burning gasoline or diesel from shale oil that may half that of conventional crude oil. The U.S. imports about 10 million barrels of oil per day at a cost of a billion dollars per day. It would require about 200 GW of high-temperature nuclear heat to recover this quantity of shale oil - about two-thirds the thermal output of existing nuclear reactors in the United States. With the added variable electricity production to enable renewables, additional nuclear capacity would be required. (authors)
29 ENERGY PLANNING, POLICY, AND ECONOMY↗
Augmented Adaptive Control of a Wind Turbine in the Presence of Structural Modes
Wind turbines operate in highly turbulent environments resulting in aerodynamic loads that can easily excite turbine structural modes, potentially causing component fatigue and failure. Two key technology drivers for turbine manufacturers are increasing turbine up time and reducing maintenance costs. Since the trend in wind turbine design is towards larger, more flexible turbines with lower frequency structural modes, manufacturers will want to develop methods to operate in the presence of these modes. Accurate models of the dynamic characteristics of new wind turbines are often not available due to the complexity and expense of the modeling task, making wind turbines ideally suited to adaptive control. In this paper, we develop theory for adaptive control with rejection of disturbances in the presence of modes that inhibit the controller. We use this method to design an adaptive collective pitch controller for a high-fidelity simulation of a utility-scale, variable-speed wind turbine operating in Region 3. The objective of the adaptive pitch controller is to regulate generator speed, accommodate wind gusts, and reduce the interference of certain structural modes in feedback. The control objective is accomplished by collectively pitching the turbine blades. The adaptive pitch controller for Region 3 is compared in simulations with a baseline classical Proportional Integrator (PI) collective pitch controller.
Frost, Susan A.↗
Distributed Wind Diffusion Model Overview (Presentation)
Distributed wind market demand is driven by current and future wind price and performance, along with several non-price market factors like financing terms, retail electricity rates and rate structures, future wind incentives, and others. We developed a new distributed wind technology diffusion model for the contiguous United States that combines hourly wind speed data at 200m resolution with high resolution electricity load data for various consumer segments (e.g., residential, commercial, industrial), electricity rates and rate structures for utility service territories, incentive data, and high resolution tree cover. The model first calculates the economics of distributed wind at high spatial resolution for each market segment, and then uses a Bass diffusion framework to estimate the evolution of market demand over time. The model provides a fundamental new tool for characterizing how distributed wind market potential could be impacted by a range of future conditions, such as electricity price escalations, improvements in wind generator performance and installed cost, and new financing structures. This paper describes model methodology and presents sample results for distributed wind market potential in the contiguous U.S. through 2050.
17 WIND ENERGY↗
Analysis of Unit-Level Changes in Operations with Increased SPP Wind from EPRI/LCG Balancing Study
Wind power development in the United States is outpacing previous estimates for many regions, particularly those with good wind resources. The pace of wind power deployment may soon outstrip regional capabilities to provide transmission and integration services to achieve the most economic power system operation. Conversely, regions such as the Southeastern United States do not have good wind resources and will have difficulty meeting proposed federal Renewable Portfolio Standards with local supply. There is a growing need to explore innovative solutions for collaborating between regions to achieve the least cost solution for meeting such a renewable energy mandate. The Department of Energy funded the project 'Integrating Midwest Wind Energy into Southeast Electricity Markets' to be led by EPRI in coordination with the main authorities for the regions: SPP, Entergy, TVA, Southern Company and OPC. EPRI utilized several subcontractors for the project including LCG, the developers of the model UPLAN. The study aims to evaluate the operating cost benefits of coordination of scheduling and balancing for Southwest Power Pool (SPP) wind transfers to Southeastern Electric Reliability Council (SERC) Balancing Authorities (BAs). The primary objective of this project is to analyze the benefits of regional cooperation for integrating mid-western wind energy into southeast electricity markets. Scenarios were defined, modeled and investigated to address production variability and uncertainty and the associated balancing of large quantities of wind power in SPP and delivery to energy markets in the southern regions of the SERC. DOE funded Oak Ridge National Laboratory to provide additional support to the project, including a review of results and any side analysis that may provide additional insight. This report is a unit-by-unit analysis of changes in operations due to the different scenarios used in the overall study. It focuses on the change in capacity factors and the number of start-ups required for each unit since those criteria summarize key aspects of plant operations, how often are they called upon and how much do they operate. The primary analysis of the overall project is based on security-constrained unit commitment (SCUC) and economic dispatch (SCED) simulations of the SPP-SERC regions as modeled for the year 2022. The SCUC/SCED models utilized for the project were developed through extensive consultation with the project utility partners, to ensure the various regions and operational practices are represented as best as possible in the model. SPP, Entergy, Oglethorpe Power Company (OPC), Southern Company, and the Tennessee Valley Authority (TVA) actively participated in the project providing input data for the models and review of simulation results and conclusions. While other SERC utility systems are modeled, the listed SERC utilities were explicitly included as active participants in the project due to the size of their load and relative proximity to SPP for importing wind energy.
17 WIND ENERGY↗
Challenges and Possible Solutions in Aeroelastic Modeling for the Distributed Wind Industry
Aeroelastic modeling (AM) is the primary methodology for structural and performance assessment of any wind turbine; it provides an understanding of the impact of design parameters on turbine loading and power response before witnessing it in the field. Despite these advantages, the use of AM in the distributed wind technology (DWT) sector is limited. This article represents a short summary of an in-depth assessment by the authors of the status of AM and its role within the distributed wind technology design standards. The research gathered input and feedback from a large number of U.S. and international stakeholders, reviewed technical strengths and weaknesses of the current edition of the design standards, analyzed the minutes from recent industry workshops and meetings, collected publicly available AM templates, and provided an evaluation of the existing AM codes. Several goals were achieved including providing strategies for the load assessment categorization of turbines based on rotor swept area and archetype, and guidance for AM verification and validation. Recommendations within this study will advance the value and the ease-of-use of AM, thereby allowing the industry to better capitalize this underutilized tool, resulting in a more efficient design process, an easier path to certification, and overall better and more reliable distributed wind technology products.
17 WIND ENERGY↗