Dynamic Inflow Research Articles

Foreign direct investment as a stimulant in productivity convergence process between Visegrad Countries and UE-15

The explanation of reasons and degree of differentiation of wealth between countries remains an important issue in economics today. Theories of economic growth are focused principally on the identification of the long-term determinants of diversification of sources and economic growth, which in turn is associated with the notion of real convergence. Given the supply role of foreign capital that impacts on the economy, in the face of dynamic inflow of foreign direct investment (FDI) into developing countries’ economies, it seems reasonable to include it in convergence process modelling, especially in the modelling of the convergence of productivity. The productivity of the economy is in fact determined by the size of the capital accumulation (both domestic and foreign), savings rate and a number of other conditions. The author hypothesized that the presence of FDI contributes to the acceleration of pace of real convergence between Visegrad countries and EU-15. In this study we estimate interactions between FDI and productivity at both national and NACE level in the years 2000–2014. We concider, in panel data form, among others, productivity in terms of gross value added per employee, degree of penetration of FDI in the economy of the host country. Results suggest conditional β-convergence of productivity existence however they vary across countries, sectors and time. The analysis provides recommendations regarding the arguments for the sectoral policy aimed at encouraging foreign capital to increase its involvement, focusing on reducing productivity gap between the developing and developed countries belonging to European Union.

Effects of aerodynamic damping on the tower load of offshore horizontal axis wind turbines

Aerodynamic damping has an important effect on the dynamic response of offshore Horizontal Axis Wind Turbines (HAWTs). In this paper, an analysis of the loads on offshore HAWTs is presented. The analysis combines the aerodynamics, hydrodynamics and structural dynamics of the structure, and includes the effects of aerodynamic damping. The aim is to better understand the role of aerodynamic damping during the interaction of wind and wave and the structure, and to quantitatively evaluate the effects of aerodynamic damping on the lifetime fatigue load on offshore HAWT towers. The aerodynamic loads are estimated using the Blade Element-Momentum (BEM) theory, including the effects of dynamic inflow and dynamic stall. The wave dynamics is estimated assuming ‘random sea state’ described by the JONSWAP spectrum, with wave loads calculated using Morison’s equation and water kinematics modelled using linear wave theory. Two aerodynamic damping models are proposed: (1) a model based on the analysis of the rotor aerodynamics incorporating the tower-top motion of a constant-speed wind turbine, which is then modified for variable-speed wind turbines by introducing a correction factor; and (2) a model based on Salzmann and van der Tempel’s method (Salzmann and van der Tempel, 2005) to calculate the aerodynamic damping as the increase in the thrust per unit increase in the wind speed. The models are incorporated into a transient load analysis. The effects of aerodynamic damping on the lifetime fatigue loads of the tower are then investigated through load analysis of a 5MW offshore HAWT. In addition, the influence of different aerodynamic damping calculation methods on the prediction of fatigue loads is studied.

Tower Load Analysis of Offshore Wind Turbines and the Effects of Aerodynamic Damping

Abstract This study presents an analysis of the loads on offshore Horizontal Axis Wind Turbines (HAWTs). The aerodynamic loadsare estimatedusing the Blade Element-Momentum (BEM) theory, including the effects of dynamic inflow and dynamic stall. The wave loads are calculated using Morison's equation. Modelsare proposedto account for the effects of aerodynamic damping on the fatigue loading on the tower during its working lifetime. Load analysis of a 5 MW offshore HAWT is carried out and the influence of aerodynamic damping on the fatigue load is investigated.

Rotorcraft control response using linearised and non-linear flight dynamic models with different inflow models

ABSTRACTThe aim of the present study is to develop a relatively simple flight dynamic model which should have the ability to analyse trim, stability and response characteristics of a rotorcraft under various manoeuvring conditions. This study further addresses the influence of numerical aspects of perturbation step size in linearised model identification and integration timestep on non-linear model response. In addition, the effects of inflow models on the non-linear response are analysed. A new updated Drees inflow model is proposed in this study and the applicability of this model in rotorcraft flight dynamics is studied. It is noted that the updated Drees inflow model predicts the control response characteristics fairly close to control response characteristics obtained using dynamic inflow for a wide range of flight conditions such as hover, forward flight and recovery from steady level turn. A comparison is shown between flight test data, the control response obtained from the simple flight dynamic model, and the response obtained using a more detailed aeroelastic and flight dynamic model.

A fully coupled method for numerical modeling and dynamic analysis of floating vertical axis wind turbines

Offshore wind energy is one of the most promising renewable energy resources and an increasing interest arises to develop floating vertical axis wind turbines (VAWTs), which have the potential to reduce the cost of energy. Assessment of the performance of floating VAWTs requires sophisticated fully coupled aero-hydro-servo-elastic simulation tools, which are currently limited. This paper aims to develop a fully integrated simulation tool for floating VAWTs. Based on the actuator cylinder (AC) flow model, aerodynamic modeling of floating VAWTs is established with consideration of the effects of turbulence, dynamic inflow and dynamic stall. The developed aerodynamic code is then coupled with the code SIMO-RIFLEX to achieve a fully coupled tool, i.e. SIMO-RIFLEX-AC, which can account for the aerodynamic, hydrodynamics, structural dynamics and controller dynamics with high fidelity. A series of code-to-code comparisons with the codes HAWC2 and SIMO-RIFLEX-DMS are carried out using a landbased VAWT and a semi-submersible VAWT, and reveal that the present code can predict the aerodynamic loads and dynamic responses accurately. Moreover, the code SIMO-RIFLEX-AC can predict more accurate responses than the code SIMO-RIFLEX-DMS, such as the platform motions, tower base bending moments and tension in mooring lines.

Comparison of a coupled near- and far-wake model with a free-wake vortex code

Abstract. This paper presents the integration of a near-wake model for trailing vorticity, which is based on a prescribed-wake lifting-line model proposed by Beddoes(1987), with a blade element momentum (BEM)-based far-wake model and a 2-D shed vorticity model. The resulting coupled aerodynamics model is validated against lifting-surface computations performed using a free-wake panel code. The focus of the description of the aerodynamics model is on the numerical stability, the computation speed and the accuracy of unsteady simulations. To stabilize the near-wake model, it has to be iterated to convergence, using a relaxation factor that has to be updated during the computation. Further, the effect of simplifying the exponential function approximation of the near-wake model to increase the computation speed is investigated in this work. A modification of the dynamic inflow weighting factors of the far-wake model is presented that ensures good induction modeling at slow timescales. Finally, the unsteady airfoil aerodynamics model is extended to provide the unsteady bound circulation for the near-wake model and to improve the modeling of the unsteady behavior of cambered airfoils. The model comparison with results from a free-wake panel code and a BEM model is centered around the NREL 5 MW reference turbine. The response to pitch steps at different pitching speeds is compared. By means of prescribed vibration cases, the effect of the aerodynamic model on the predictions of the aerodynamic work is investigated. The validation shows that a BEM model can be improved by adding near-wake trailed vorticity computation. For all prescribed vibration cases with high aerodynamic damping, results similar to those obtained by the free-wake model can be achieved in a small fraction of computation time with the proposed model. In the cases with low aerodynamic damping, the addition of trailed vorticity modeling shifts the results closer to those obtained by using the free-wake code, but differences remain.

Space mapping techniques for the optimal inflow control of transmission lines

In this paper we present an efficient optimization approach for the dynamic inflow control of electric transmission lines. For the description of transmission lines several mathematical models are available. Here, we focus on the telegraph network equations which consist of a coupled system of hyperbolic differential equations. The optimization is then to find the best possible energy input in terms of boundary control to satisfy given demands. To solve this problem we introduce space mapping techniques based on a first discretize – then optimize approach. The idea of space mapping is the consideration of two model hierarchies (fine and coarse scale), where the coarse scale model is less accurate but easy to solve. We explain how this method works in the framework of inflow control, design the corresponding optimization algorithm and present various computational results to show the numerical efficiency.

Effects of low boundary walls under dynamic inflow on flow field and pollutant dispersion in an idealized street canyon

In this study, we examine the magnitude of the boundary layer inflow that gradually changes with time at the top of a building. A standard k-ε model was used to study how low boundary walls (LBWs) under dynamic wind field and dynamic vehicle flow affect the dispersion of pollutants in an idealized street canyon. The results show that the flow field under dynamic inflow inside the idealized street canyon within LBWs is composed of a major eddy and three corner eddies at the street level. When the external wind speed drops, the air is expanded, regarding which the canyon from air expansion is approximately 11 m high at time t = 25 min and 3 m at time t = 33 min. The air at the road corners is correspondingly expanded. The presence of LBWs increases the peak of pollutant concentrations in the canyon and alters the pollutant distribution at the canyon bottom under the dynamic flow at different time points. In the LBWs street canyon compared with the non-LBWs street canyon, the pollutant concentration peaks at time t = 25, 29, and 33 min increase by 12.74%, 30.90% and 22.80%, respectively. The presence of LBWs significantly decreases the maximum x-direction wind speeds at 1-m height in the bottom canyon at different time points but alters the wind directions at the corners and changes the value and distribution of turbulent kinetic energy in the canyon. The largest leeward and windward y-direction wind speeds under dynamic inflow are 27.41% and 32.75% compared with under steady inflow.

Modal analysis of finite-state dynamic inflow for rotary wing systems

In this paper, the finite-state helicopter rotor inflow modes have been studied based on eigenanalysis. The inflow velocity mode shapes with node lines have been displayed with various skew angles. The eigenvalues are highly coupled especially for higher skew angles, and the mode shapes change significantly for different angles. The changing of eigenvalues with different harmonic numbers is also exhibited in the tables for axial flow of both the Peters–He and Morillo dynamic inflow models. An easy way to estimate the eigenvalues of the Peters–He inflow model is also established.

Validation of engineering dynamic inflow models by experimental and numerical approaches

The state of the art engineering dynamic inflow models of Pitt-Peters, Øye and ECN have been used to correct Blade Element Momentum theory for unsteady load prediction of a wind turbine for two decades. However, their accuracy is unknown. This paper is to benchmark the performance of these engineering models by experimental and numerical methods. The experimental load and flow measurements of an unsteady actuator disc were performed in the Open Jet Facility at Delft University of Technology. The unsteady load was generated by a ramp-type variation of porosity of the disc. A Reynolds Averaged Navier-Stokes (RANS) model, a Free Wake Vortex Ring (FWVR) model and a Vortex Tube Model (VTM) simulate the same transient load changes. The velocity field obtained from the experimental and numerical methods are compared with the engineering dynamic inflow models. Velocity comparison aft the disc between the experimental and numerical methods shows the numerical models of RANS and FWVR model are capable to predict the velocity transient behaviour during transient disc loading. Velocity comparison at the disc between the engineering models and the numerical methods further shows that the engineering models predict much faster velocity decay, which implies the need for more advanced or better tuned dynamic inflow models.

Three-dimensional dynamic inflow below the rotor disk based on the finite-state method

This paper studies the problem of dynamic inflow below the rotor disk for skewed flow. With the information from the adjoint inflow equations plus the normal states, one can calculate the velocity in the hemisphere below the rotor disk plane without losing accuracy or convergence rate. The methodology enables one to calculate the velocity below the rotor disk with the finite-state method with the only cost of adding the uncoupled co-states. The three components of inflow are considered here and compared with the results from the convolution integrals. Numerical results in the frequency domain for simple harmonic motion show the effectiveness of the new method in three-dimensional inflow with big skew angle below the rotor disk.

Verifying the Blade Element Momentum Method in unsteady, radially varied, axisymmetric loading using a vortex ring model

AbstractAlthough the Blade Element Momentum method has been derived for the steady conditions, it is used for unsteady conditions by using corrections of engineering dynamic inflow models. Its applicability in these cases is not yet fully verified. In this paper, the validity of the assumptions of quasi‐steady state and annuli independence of the blade element momentum theory for unsteady, radially varied, axi‐symmetric load cases is investigated. Firstly, a free wake model that combines a vortex ring model with a semi‐infinite cylindrical vortex tube was developed and applied to an actuator disc in three load cases: (i) steady uniform and radially varied, (ii) two types of unsteady uniform load and (iii) unsteady radially varied load. Results from the three cases were compared with Momentum Theory and also with two widely used engineering dynamic inflow models—the Pitt‐Peters and the Øye for the unsteady load cases. For unsteady load, the free wake vortex ring model predicts different hysteresis loops of the velocity at the disc or local annuli, and different aerodynamic work from the engineering dynamic inflow models. Given that the free wake vortex ring model is more physically representative, the results indicate that the engineering dynamic inflow models should be improved for unsteady loaded rotor, especially for radially varied unsteady loads. © 2016 The Authors. Wind Energy Published by John Wiley & Sons, Ltd.

Influence of Dynamic Inflow States on Coupled Rotor Fuselage Modes

Influence of Dynamic Inflow States on Coupled Rotor Fuselage Modes

Free-Wake–Based Dynamic Inflow Model for Hover, Forward, and Maneuvering Flight

Free-Wake–Based Dynamic Inflow Model for Hover, Forward, and Maneuvering Flight

Calculation method of blade element aerodynamic loads based on small perturbation theory

A calculation method of blade element aerodynamic loads based on small perturbation theory is established for helicopter flight simulation application. The method synthesizes flap-lag-torsion elastic rotor blade mode,couples rotor dynamic inflow,unsteady aerodynamics model with dynamic stall and rotor trimming model. The entire model is developed in a standard state-space form. To verify this model,the UH-60 A helicopter is taken as an example,and the effects of yaw flow on rotor aerodynamic performance are studied at low speed flight and high speed flight. It is shown that yaw flow has a greater effect on rotor aerodynamic performance at high speed flight. Blade induced velocity fields and aerodynamic loads are simulated,and the results are compared with flight test data. It is shown by the results that the method can accurately predict the unsteady aerodynamic rotor loads in steady flight by capturing its variational characteristics along blade azimuthal locations,and it is still applicable for high speed flight.

Integrated Investigation of Dynamic Drainage Volume and Inflow Performance Relationship (Transient IPR) to Optimize Multistage Fractured Horizontal Wells in Tight/Shale Formations

This study presents an integrated approach to evaluate the efficiency of fracturing stimulation and predict well production performance. As the pressure disturbance propagates throughout the reservoir during long-time transient flow regimes, it will shape an expanding drainage volume. A macroscopic “compressible tank model (CTM)” using weak (integral) form of mass balance equation is derived to relate dynamic drainage volume (DDV) and average reservoir pressure to production history in extremely shale reservoirs. Fluids and rock compressibility, desorption parameters (for shale or coal gas), and production rates control the speed at which the boundaries advance. After the changes of average reservoir pressure within the expanding drainage volume are obtained, a new empirical inflow performance relationship (transient IPR) correlation is proposed to describe well performance during long transient flow periods in shale reservoirs. This new empirical correlation shows better match performance with field data than that of conventional Vogel-type IPR curves. The integrated approach of both CTM model and transient IPR correlation is used to determine and predict the optimal fracturing spacing and the size of horizontal section for few wells from one of shale oil plays in U.S. The results suggest the existence of optimal fracture spacing and horizontal well length for multistage fractured horizontal wells in shale oil reservoirs. In practice, this paper not only provides an insight in understanding the long transient flow production characteristics of shale reservoirs using concept of expanding drainage volume. Neither methods require comprehensive inputs for the strong form (differential) nor any prior knowledge about the sophisticated shale reservoir features (shape, size, etc.), the ultimate drainage volume, the ultimate recovery, optimal fracture spacing, and the length of horizontal section for each well can also be easily obtained by this new integrated analytical method.

Determining the effects of freshwater inflow on benthic macrofauna in the Caloosahatchee Estuary, Florida.

Florida legislation requires determining and implementing an appropriate range and frequency of freshwater inflows that will sustain a fully functional estuary. Changes in inflow dynamics to the Caloosahatchee Estuary, Florida have altered salinity regimes that, in turn, have altered the ecological integrity of the estuary. The purpose of this current project is to determine how changes in freshwater inflows affect water quality, and in turn, benthic macrofauna, spatially within the Caloosahatchee Estuary and between multiyear wet and dry periods. Thirty-four benthic species were identified as being indicator species for salinity zones, and the estuary was divided into 4 zones based on differences in community structure within the estuary. Community structure had the highest correlations with water quality parameters that were common indicators of freshwater conditions resulting from inflows. A significant relationship between salinity and diversity occurs both spatially and temporally because of increased numbers of marine species as salinities increase. A salinity-based model was used to estimate inflow during wet and dry periods for each of the macrofauna community zones. The approach used here (identifying bioindicators and community zones with corresponding inflow ranges) is generic and will be useful for developing targets for managing inflow in estuaries worldwide. Integr Environ Assess Manag 2016;12:529-539. © 2015 SETAC.

Superposition of vortex cylinders for steady and unsteady simulation of rotors of finite tip‐speed ratio

AbstractJoukowski introduced in 1912 a helical vortex model to represent the vorticity of a rotor and its wake. For an infinite number of blades but finite tip‐speed ratio, the model consists of a vortex cylinder of longitudinal and tangential vorticity, a root vortex and a bound vortex disk. A superposition of cylinders is used in this paper to model rotors of radially varying circulation. The relations required to form a consistent system of cylinders are derived. The model contains a term which is not accounted for in the standard blade element momentum (BEM) algorithm. This term is identified as the contribution from the pressure drop due to the wake rotation. The BEM algorithm can be corrected to account for this effect. Unlike previous work on the topic, the contribution is derived for a radially varying circulation. A high‐thrust correction is also presented to extend the model. The optimal power coefficient obtained with this model for the constant circulation rotor is assessed and compared with that of existing solutions. Results from prescribed thrust distributions are compared with that of actuator disk simulations. Steady simulations are performed to compare with the BEM algorithm. The model is also applied to compute the velocity field in the entire domain and perform unsteady simulations. Results for an unsteady simulation corresponding to a pitch change of the rotor is used to compare the model with measurements and a BEM code with a dynamic inflow model. Copyright © 2015 John Wiley & Sons, Ltd.

FAST, GH Bladed 및 CFD기법을 이용한 5MW 해상풍력터빈 시스템 설계하중조건 해석 및 비교

Design lifetime of a wind turbine is required to be at least 20 years. The most important step to ensure the deign is to evaluate the loads on the wind turbine as accurately as possible. In this study, extreme design load of a offshore wind turbine using Garrad Hassan (GH) Bladed and National Renewable Energy Laboratory (NREL) FAST codes are calculated considering structural dynamic loads. These wind turbine aeroelastic analysis codes are high efficiency for the rapid numerical analysis scheme. But, these codes are mainly based on the mathematical and semi-empirical theories such as unsteady blade element momentum (UBEM) theory, generalized dynamic wake (GDW), dynamic inflow model, dynamic stall model, and tower influence model. Thus, advanced CFD-dynamic coupling method is also applied to conduct cross verification with FAST and GH Bladed codes. If the unsteady characteristics of wind condition are strong, such as extreme design wind condition, it is possible to occur the error in analysis results. The NREL 5 MW offshore wind turbine model as a benchmark case is practically considered for the comparison of calculated designed loads. Computational analyses for typical design load conditions such as normal turbulence model (NTM), normal wind profile (NWP), extreme operation gust (EOG), and extreme direction change (EDC) have been conducted and those results are quantitatively compared with each other. It is importantly shown that there are somewhat differences as maximum amount of 18% among numerical tools depending on the design load cases.

Unsteady aerodynamic analysis for offshore floating wind turbines under different wind conditions.

A free-vortex wake (FVW) model is developed in this paper to analyse the unsteady aerodynamic performance of offshore floating wind turbines. A time-marching algorithm of third-order accuracy is applied in the FVW model. Owing to the complex floating platform motions, the blade inflow conditions and the positions of initial points of vortex filaments, which are different from the fixed wind turbine, are modified in the implemented model. A three-dimensional rotational effect model and a dynamic stall model are coupled into the FVW model to improve the aerodynamic performance prediction in the unsteady conditions. The effects of floating platform motions in the simulation model are validated by comparison between calculation and experiment for a small-scale rigid test wind turbine coupled with a floating tension leg platform (TLP). The dynamic inflow effect carried by the FVW method itself is confirmed and the results agree well with the experimental data of a pitching transient on another test turbine. Also, the flapping moment at the blade root in yaw on the same test turbine is calculated and compares well with the experimental data. Then, the aerodynamic performance is simulated in a yawed condition of steady wind and in an unyawed condition of turbulent wind, respectively, for a large-scale wind turbine coupled with the floating TLP motions, demonstrating obvious differences in rotor performance and blade loading from the fixed wind turbine. The non-dimensional magnitudes of loading changes due to the floating platform motions decrease from the blade root to the blade tip.