Tower Mass Research Articles

A sensitivity-based estimation method for investigating control co-design relevance

Abstract. Control co-design is a promising approach for wind turbine design due to the importance of the controller in power production, stability, load alleviation, and the resulting coupled effects on the sizing of the turbine components. However, the high computational effort required to solve optimization problems with added control design variables is a major obstacle to quantifying the benefit of this approach. In this work, we propose a methodology to identify if a design problem can benefit from control co-design. The estimation method, based on post-optimum sensitivity analysis, quantifies how the optimal objective value varies with a change in control tuning. The performance of the method is evaluated on a tower design optimization problem, where fatigue load constraints are a major driver, and using a linear quadratic regulator targeting fatigue load alleviation. We use the gradient-based multi-disciplinary optimization framework Cp-max. Fatigue damage is evaluated with time-domain simulations corresponding to the certification standards. The estimation method applied to the optimal tower mass and optimal cost of energy show good agreement with the results of the control co-design optimization while using only a fraction of the computational effort. Our results additionally show that there may be little benefit to using control co-design in the presence of an active frequency constraint. However, for a soft–soft tower configuration where the resonance can be avoided with active control, using control co-design results in a taller tower with reduced mass.

A Review on the Heat-Source Tower Heat Pump Systems in China

Based on air-, water-, and ground-source heat pump systems, a novel type of heat pump system, named the heat-source tower heat pump system (HSTHPS), has recently been developed in the southern area of China. The HSTHPS overcomes the evaporator frosting problems of the air-source heat pump system (ASHPS) when the ambient temperature is lower, and it avoids the geological condition constraints of the water- and ground-source heat pump systems. However, studies on the HSTHPS are insufficient, thereby limiting its development and applications. Thus, the present review provides a detailed literature review on the advancements of HSTHPSs in China, including the HSTHPS operation principle, heat-source tower (HST) structure, heat and mass transfer characteristics, HSTHPS performance, antifreeze solution use, and antifreeze solution regeneration. Studies on the heat and mass transfer characteristics of HSTs are sufficient for guiding the application. Regarding open systems, the solution drifting to the air needs to resolved, and future studies need to focus on structure optimization for heat exchangers in closed systems. Moreover, advanced defrosting technology should be applied to closed-type HSTs, and a suitable operation strategy for HSTHPSs should be developed. Future priorities should involve integrating HSTHPSs with additional renewable energy in order to achieve continuous, stable, and efficient heating in winter based on the characteristics of local climate and renewable energy.

Bounds on tower mass scales in the presence of throats of different warping

In Type IIB flux compactification realizing the metastable de Sitter (dS) vacuum, the uplift potential can be generated by D3‾-branes at the tip of Klebanov-Strassler throat. Then the uplift potential obeys the scaling law with respect to the tower mass scale msc, which can be the Kaluza-Klein (KK) mass scale associated with the throat containing D3‾-branes or the bulk tower mass scales, depending on the warping of the throat. On the other hand, in the presence of another throat of stronger warping, the KK mass scale associated with this throat is lower than msc. Nevertheless, the Higuchi bound and the condition that the tower mass scale is higher than the gravitino mass provide the upper bound on msc determined by the lowest tower mass scale (or gravitino mass). This bound also can be interpreted as the lower bound on the lowest tower mass scale determined by msc. We investigate this bound in detail when the throat containing D3‾-branes is strongly and weakly warped, respectively.

Revisiting the refined Distance Conjecture

The Distance Conjecture of Ooguri and Vafa holds that any infinite-distance limit in the moduli space of a quantum gravity theory must be accompanied by a tower of exponentially light particles, which places tight constraints on the low-energy effective field theories in these limits. One attempt to extend these constraints to the interior of moduli space is the refined Distance Conjecture, which holds that the towers of light particles predicted by the Distance Conjecture must appear any time a modulus makes a super-Planckian excursion in moduli space. In this note, however, we point out that a tower which satisfies the Distance Conjecture in an infinite-distance limit of moduli space may be parametrically heavier than the Planck scale for an arbitrarily long geodesic distance. This means that the refined Distance Conjecture, in its most naive form, does not place meaningful constraints on low-energy effective field theory. This motivates alternative refinements of the Distance Conjecture, which place an absolute upper bound on the tower mass scale in the interior of moduli space. We explore two possibilities, providing evidence for them and briefly discussing their implications.

Uplift and towers of states in warped throat

We investigate the connection between the distance conjecture and the uplift potential. For this purpose, we consider the concrete model, the warped deformed conifold embedded into Type IIB flux compactifications, with the uplift potential produced by overline{textrm{D}3} -branes at the tip of the throat. Whereas the various mass scales associated with towers of states can be found, it turns out that the lightest tower mass scale satisfies the scaling behavior with respect to the uplift potential, which is meaningful provided the number of overline{textrm{D}3} -branes is nonzero. This indicates that the effective theory becomes invalid in the vanishing limit of the uplift potential by the descent of an infinite tower of states from UV, as predicted in the distance conjecture. Since too large uplift potential is also problematic due to the runaway behavior of the moduli potential as well as the sizeable backreaction of overline{textrm{D}3} -branes, the uplift potential is bounded from both above and below. In the simple model like the KKLT or the large volume scenario in which non-perturbative effect is dominatd by the single term, this bound can be rewritten as the bound on the size of the superpotential.

Design optimisation of wind turbine towers with reliability-based calibration of partial safety factors

Having an optimal design of the wind turbine tower, with a minimum mass (cost) while fulfilling multiple design constraints, plays an important role in ensuring an economic and safe design of the wind turbine. During the design of wind turbine towers, partial safety factors (PSFs) are currently commonly used to account for the uncertainties in the loads and material properties due to its easy implementation. The values of PSFs given in design standard are generic and are not derived for a specific design. For a site-specific design of wind turbine towers, the details of the load parameters, such as the type of distributions and the coefficient of variation, can be obtained through the condition monitoring system. With these information, the PSFs can be calibrated based on the reliability method, meeting the target reliability index and avoiding over or under engineering of wind turbine tower structures. In this work, a parametric finite element analysis model is integrated with a genetic algorithm to develop a structural optimisation model of wind turbine towers. The optimisation framework minimises the tower mass under multiple design constraints. The optimisation model has been applied to a representative 2.0 MW onshore wind turbine tower. PSFs are calibrated on the basis of reliability. The optimal tower design with calibrated PSFs is compared against the design with un-calibrated PSFs. Results indicate that the tower design with calibrated PSFs achieves a mass reduction of 2.9% in comparison to the design with un-calibrated PSFs.

Impact of the ground clearance on the annual energy production and tower cost of an offshore wind turbine

This article analyzes the impact of the ground clearance on the Annual Energy Production (AEP) and tower cost of a 20 MW offshore wind turbine. In addition, the influence of the rated wind speed on the analysis result will be considered. The AEP is computed by considering wind speed variation over the swept area of the rotor blades. The tapered tubular steel tower is considered for mass and cost calculation. The tower is considered as a fixed-free cantilever beam with concentrated mass at the free end. The analysis shows that the ground clearance only has a minor impact on the AEP but it has a remarkable impact on the tower mass. Specifically, when the ground clearance reaches 50 meters, the AEP only increases by roughly 3% while tower mass is nearly doubled compared to the case with no ground clearance. The results also reveal the significant impact of the rated speed on both the AEP and tower mass.

STUDY ON THE ISOLATION EFFECT OF SUBWAY COVER STRUCTURES

In order to study the seismic isolation effect of the subway superstructure comprehensively, a simplified two-degree-of-freedom model of the large base with multiple towers was presented, and the influences of mass ratio and period ratio on dynamic characteristics and seismic response of structures were investigated. In addition, a precise model of the subway superstructure was established by ETABS to study the effect of tower height, tower number, isolation floor stiffness, and viscous dampers on the structural dynamic characteristics, seismic isolation coefficient. The analysis results of the simplified two-degree-of-freedom model show that in the general period ratio range, the shear-weight ratio of the tower has almost no change with its mass variation, while the shear-weight ratio of the large base decreases when the tower mass increases. The analysis results of the precise model of the large base with multi-tower show that the seismic inertial force is evenly distributed along the height of the tower, and the building height has little effect on the earthquake action, and the seismic effect of the large base increases slightly as the height of the tower increases. As the number of towers increases, the seismic isolation effect of the tower decreases slightly, the seismic effect of the large base is less than that of non-seismic isolation structures. As the stiffness of the seismic isolation floor increases, the seismic effect of the tower increases and the seismic effect of the large base decreases. After viscous dampers are installed, the distribution of seismic force along the height of the tower changes significantly, the seismic action decreases at the bottom of the tower and the seismic action is significantly amplified at the top. Setting viscous dampers can effectively reduce the seismic action of the large base.

The web of swampland conjectures and the TCC bound

We consider the swampland distance and de Sitter conjectures, of respective order one parameters λ and c. Inspired by the recent Trans-Planckian Censorship conjecture (TCC), we propose a generalization of the distance conjecture, which bounds λ to be a half of the TCC bound for c, i.e. lambda ge frac{1}{2}sqrt{frac{2}{3}} in 4d. In addition, we propose a correspondence between the two conjectures, relating the tower mass m on the one side to the scalar 1 potential V on the other side schematically as msim {left|Vright|}^{frac{1}{2}} , in the large distance limit. These proposals suggest a generalization of the scalar weak gravity conjecture, and are supported by a variety of examples. The lower bound on λ is verified explicitly in many cases in the literature. The TCC bound on c is checked as well on ten different no-go theorems, which are worked-out in detail, and V is analysed in the asymptotic limit. In particular, new results on 4d scalar potentials from type II compactifications are obtained.

A simplified structural model for monopile-supported offshore wind turbines with tapered towers

When estimating the natural frequency of wind turbine structures using the single-degree-of-freedom modeling, usually part of the tower mass is concentrated to the tower top. However, the ratio of concentration is usually specified without considering that tapered towers are common in practice, which may cause certain errors. Additionally, the behavior of wind turbine structures may also be considerably influenced by the foundation flexibility and the substructure of offshore wind turbines. In this paper, a rigid-base single-degree-of-freedom structural model was proposed for wind turbines with tapered towers based on Rayleigh’s method. Then, for structural modeling of monopile-supported offshore wind turbines, the concentrated spring model was introduced to simulate the flexibility of the monopile foundation as well as the transition piece, and inertial and flexural effects of the substructure were also included. Accordingly, the closed-form solution of the natural frequency of wind turbine structures was derived and was verified to be satisfactory compared to existing numerical and experimental studies. This simplified structural model was also shown to approximate the seismic response of wind turbine structures. It was further used to demonstrate the influence the foundation scour on the natural frequency of offshore wind turbine structures, exhibiting its applicability to scour monitoring.

Calculational model for first-mode eigenfrequency of a semi-guy-wired vertical-axis wind turbine tower

A simple model for accounting for tower mass when estimating the first-mode eigenfrequency of a semi-guy-wired tower has been derived. This extends previous work where an analytical model of the semi-guy-wired tower of a 200-kW vertical-axis wind turbine was developed. The model was primarily used to estimate the eigenfrequencies as a result of adding guy wires to a free-standing tower (thus creating a semi-guy-wired setup). However, a weakness with the model was that the tower mass was accounted for in a rough way that essentially ignored the guy wires, which gave a larger-than-necessary error. In this work, an effective top mass, that takes into account the tower mass and the constraints from the guy wires, is derived to achieve a higher accuracy when estimating the first-mode eigenfrequency. This, together with the earlier models, gives a more complete method to estimate the eigenfrequencies for a semi-guy-wired wind turbine.

COMPUTATION AND EXPERIMENTAL STUDIES OF THE DYNAMIC CHARACTERISTICS OF THE ARMOUR HULL MODEL

The paper presents a computational experimental comparison of the dynamic characteristics of a fragment of a model body of an armored personnelcarrier. The method of experimental research was to determine the dynamic response from the action of a shock load by a rubberized drummer. Theresults were recorded with a 795M vibration spectrum analyzer using an acceleration sensor DN-3-M1. Numerical studies are performed in the moduleof transient dynamic analysis. For the obtained dependencies, the Fourier transform is constructed. A separate stage of computational and experimentalstudies was performed varying the mass of the combat module. It is determined that the results obtained by the experimental method are in goodagreement with the similar results obtained by calculation methods. The comparison was performed for accelerations, velocities and displacements atcontrol points and for Fourier transform also. The influence of tower mass on the natural oscillations spectrum was also analyzed in the work. Studieshave shown that increasing of tower mass reduces the system's natural frequency

Development of Modified Incompressible Ideal Gas Model for Natural Draft Cooling Tower Flow Simulation

The article deals with the development of incompressible ideal gas like model, which can be used as a part of mathematical model describing natural draft wet-cooling tower flow, heat and mass transfer. It is shown, based on the results of a complex mathematical model of natural draft wet-cooling tower flow, that behaviour of pressure, temperature and density is very similar to the case of hydrostatics of moist air, where heat and mass transfer in the fill zone must be taken into account. The behaviour inside the cooling tower is documented using density, pressure and temperature distributions. The proposed equation for the density is based on the same idea like the incompressible ideal gas model, which is only dependent on temperature, specific humidity and in this case on elevation. It is shown that normalized density difference of the density based on proposed model and density based on the nonsimplified model is in the order of 10-4. The classical incompressible ideal gas model, Boussinesq model and generalised Boussinesq model are also tested. These models show deviation in percentages.

Comparative LCA of technology improvement opportunities for a 1.5-MW wind turbine in the context of an onshore wind farm

This paper presents life cycle assessment (LCA) results of design variations for a 1.5-MW wind turbine due to the potential for advances in technology to improve their performance. Five LCAs have been conducted for design variants of a 1.5-MW wind turbine. The objective is to evaluate potential environmental impacts per kilowatt hour of electricity generated for a 114-MW onshore wind farm. Results for the baseline turbine show that higher contributions to impacts were obtained in the categories of ozone depletion potential, marine aquatic eco-toxicity potential, human toxicity potential and terrestrial eco-toxicity potential compared to technology improvement opportunities (TIOs) 1–4. Compared to the baseline turbine, TIO 1 with advanced rotors and reduced tower mass showed increased impact contributions to abiotic depletion potential, acidification potential, eutrophication potential, global warming potential and photochemical ozone creation potential, and TIO 2 with a new tower concept involving improved tower height showed an increase in contributions to abiotic depletion potential, acidification potential and global warming potential. Additionally, lower contributions to all the environmental categories were observed for TIO 3 with drivetrain improvements using permanent magnet generators while increased contributions towards abiotic depletion potential and global warming potential were noted for TIO 4 which combines TIO 1, TIO 2 and TIO 3. A comparative LCA study of wind turbine design variations for a particular power rating has not been explored in the literature. This study presents new insight into the environmental implications related with projected wind turbine design advancements.

Sensitivity and Uncertainty Analysis of Counter-Flow Mechanical Draft Cooling Towers—I: Adjoint Sensitivity Analysis

For counter-flow mechanical draft cooling towers, the air in the fill can reach the point of saturation before leaving the fill section. The heat and mass transfer to the saturated air by evaporative cooling inside the fill are modeled with some assumptions and with over 50 parameters for boundary conditions, cooling tower geometries, heat and mass transfer correlations, water and air thermal properties, etc. Because of the parameter uncertainties and modeling assumptions, the accuracy and reliability of the cooling tower model need to be evaluated by quantifying the uncertainties associated with the model output. First, sensitivities of the model output with respect to all the model parameters need to be analyzed. Based on the cooling tower model, this work developed adjoint sensitivity models for the saturated case to compute efficiently and exactly the sensitivities of the model responses to all model parameters by applying the general adjoint sensitivity analysis methodology for nonlinear systems. The solution of the adjoint sensitivity models are independently verified. With the sensitivities known, the model parameters can be ranked in their importance for contributing to response uncertainties. The propagation of the uncertainties in the model parameters to the uncertainties in the model outputs can be evaluated. By further applying the predictive modeling for coupled multiphysics systems methodology, the cooling tower model for the saturated case can be improved by reducing the model prediction uncertainties through assimilation of experimental measurements and calibration of model parameters.

Methodology for optimizing composite towers for use on floating wind turbines

A methodology for the design and optimization of a composite wind turbine tower for use on a floating offshore platform is presented. A composite turbine tower on a floating offshore platform not only has the potential to reduce maintenance and upkeep costs associated with the use of steel offshore but also has potential to reduce the tower mass and subsequently the support platform mass. The optimization problem is formulated to obtain a turbine tower that meets all strength and serviceability criteria and minimizes the tower mass. The optimization and design process link a number of dynamic analyses and finite element routines using a genetic algorithm. This work documents the optimization and design software and illustrates its use in various case studies for a 6 MW floating wind turbine system. Case studies include the optimization of a steel tower as a comparison to a composite material tower and the use of a cored, sandwich panel composite tower versus a solid composite tower. The results demonstrate that significant reductions in the tower mass are likely when comparing a steel tower with a composite tower. Also demonstrated for the platform and turbine configuration considered in this work is that the minimum mass tower design is driven towards a solid shell composite configuration, rather than a sandwich panel tower shell, in the face of reasonable design constraints.

Hydraulic-electric hybrid wind turbines: Tower mass saving and energy storage capacity

This study investigates concept of introduction of a hydraulic motor in the nacelle to convert rotor shaft work into hydraulic power that is transmitted to the electric generator at ground/sea level. This combination of hydraulic and electric power generation can help simplify or even eliminate the gearbox, and significantly reduce the head weight mass that the tower needs to support. Also, this hybrid concept allows energy storage in the tower which can reduce electric generator size. The analytical technique for tower mass savings employed herein was validated and used to show that 33%–50% of the tower mass may be saved through decreased tower thickness. In addition, the hydraulic-electric generator concept is compatible with employing isothermal CAES in the tower. Analysis based on cross-over pressure for the design limit indicates that this energy storage concept provides more than 24 h of energy storage if one considers S-glass towers of 10 MW or more. To accompany the above engineering analysis, a CAPEX cost model was developed based on recent production wind turbines and system designs. The hydraulic-electric hybrid system with CAES was estimated to yield a total CAPEX savings of 17% due to a substantial decrease in generator and electrical infrastructure costs.

Integrated design of downwind land‐based wind turbines using analytic gradients

AbstractWind turbines are complex systems where component‐level changes can have significant system‐level effects. Effective wind turbine optimization generally requires an integrated analysis approach with a large number of design variables. Optimizing across large variable sets is orders of magnitude more efficient with gradient‐based methods as compared with gradient‐free method, particularly when using exact gradients. We have developed a wind turbine analysis set of over 100 components where 90% of the models provide numerically exact gradients through symbolic differentiation, automatic differentiation, and adjoint methods. This framework is applied to a specific design study focused on downwind land‐based wind turbines.Downwind machines are of potential interest for large wind turbines where the blades are often constrained by the stiffness required to prevent a tower strike. The mass of these rotor blades may be reduced by utilizing a downwind configuration where the constraints on tower strike are less restrictive. The large turbines of this study range in power rating from 5–7MW and in diameter from 105m to 175m. The changes in blade mass and power production have important effects on the rest of the system, and thus the nacelle and tower systems are also optimized. For high‐speed wind sites, downwind configurations do not appear advantageous. The decrease in blade mass (10%) is offset by increases in tower mass caused by the bending moment from the rotor‐nacelle‐assembly. For low‐wind speed sites, the decrease in blade mass is more significant (25–30%) and shows potential for modest decreases in overall cost of energy (around 1–2%). Copyright © 2016 John Wiley & Sons, Ltd.

Mathematical Model of Two Phase Flow in Natural Draft Wet-Cooling Tower Including Flue Gas Injection

The previously developed model of natural draft wet-cooling tower flow, heat and mass transfer is extended to be able to take into account the flow of supersaturated moist air. The two phase flow model is based on void fraction of gas phase which is included in the governing equations. Homogeneous equilibrium model, where the two phases are well mixed and have the same velocity, is used. The effect of flue gas injection is included into the developed mathematical model by using source terms in governing equations and by using momentum flux coefficient and kinetic energy flux coefficient. Heat and mass transfer in the fill zone is described by the system of ordinary differential equations, where the mass transfer is represented by measured fill Merkel number and heat transfer is calculated using prescribed Lewis factor.

Quasi One-Dimensional Model of Natural Draft Wet-Cooling Tower Flow, Heat and Mass Transfer

The article deals with the development of CFD (Computational Fluid Dynamics) model of natural draft wet-cooling tower flow, heat and mass transfer. The moist air flow is described by the system of conservation laws along with additional equations. Moist air is assumed to be homogeneous mixture of dry air and water vapour. Liquid phase in the fill zone is described by the system of ordinary differential equations. Boundary value problem for the system of conservation laws is discretized in space using Kurganov-Tadmor central scheme and in time using strong stability preserving Runge-Kutta scheme. Initial value problems in the fill zone is solved by using standard fourth order Runge-Kutta scheme. The interaction between liquid water and moist air is done by source terms in governing equations.