Thrust Curve Research Articles

Modeling and dynamic characteristics analysis on solid attitude control motor using pintle thrusters

In this paper, a model of the opening and closing processes of attitude control motor (ACM) with dual pintle thrusters is presented. The critical part of the model of ACM could be seen as a valve which is actually analyzed. Electromagnetic subsystem, pintle moving subsystem, throttle subsystem, chamber pressure filling subsystem and thrust subsystem are investigated detailed, their interactions considered too. Model validation is performed by comparing the simulated and measured thrust curves, which shows different characteristics with single pintle motor due to the coupling effect of two thrusters. The ACM response is split into the starting delay, pintle motion and thrust delay time. Some key controlling and structural factors concerning with the three stage time are discussed in detail, and the effects illustrate opposite trends between opening and closing process. Consequently, the parameters should be designed properly to reduce total response time.

Optimal Design of Elastic Circular Plane Arches

Even if arches represent an old structural system adopted in construction practice since two thousand years ago, they are still adopted just if large spans have to be covered. The structural efficiency of arches principally depends on optimal material exploitation, due to the minimization of the thrust curve eccentricity, which reduces structural material volume and weight. Although the millenarian use and a very abundant literature dealing with arches, there is still scope for design optimization, so this study is framed within this context, investigating plane circular arches under uniformly distributed vertical load and self-weight. The arches are simply supported with bending springs at end sections. In a first step an analytical solution of the arch static is derived in dimensionless form. Next, the volume of the arch is minimized. Finally the results are charted to allow their use in a design process.

A generalized method to extend airfoil polars over the full range of angles of attack

The accurate prediction of airfoil polars over the whole range of angles of attack and for different Reynolds numbers is pivotal to ensure an accurate prediction of wind turbine aerodynamic performance. In particular, modeling correctly the deep-stall and post-stall airfoil behavior is essential to reproduce reliable power and thrust curves for high wind conditions, especially as far as stall-controlled wind turbines are concerned. This need is even more urgent in vertical-axis wind turbines, in which the airfoils do experience a continuous variation of the angle of attack, exceeding the stall limit even in normal operating points.This paper presents a new method for extending an existing database of airfoil aerodynamic coefficients, e.g. in the common ranges of aeronautical references, over the ±180° range of angles of attack for an arbitrary airfoil shape. Moving from a few basic geometric data, as maximum thickness, camber and leading-edge radius, the whole curves of lift and drag coefficients are reconstructed starting from deep-stall conditions. The proposed correlation is compared to different models for the post-stall extrapolation of the airfoil behavior and experimental data, showing a good agreement with experimental polars for both symmetrical and cambered airfoils.

Performance of Mixture-Ratio-Controlled Hybrid Rockets for Nominal Fuel Regression

This paper discusses the impacts of oxidizer-to-fuel mass ratio () shifts on the flight performance of single-stage sounding rockets using the flight simulations of three scales of -controlled and -uncontrolled hybrid rockets under a nominal fuel regression behavior without uncertainty. The flight simulation code includes three factors dependent on the : thermodynamic states of the burned gas (theoretical ), shifts in efficiency, and nozzle throat erosion. In the flight simulations, a thrust control law was applied to increase the apogee and evaluate the effects of shifts in the thrust curve including throttling. For the best cases in each scale, -controlled hybrid rockets slightly improved the performance by 2.03–2.42% in the averaged specific impulse. However, the performance of the -controlled sounding rockets is essentially the same as the -uncontrolled type under the median regression behavior: especially when considering the slight increases in the mass and complexity of the oxidizer feed system needed for control. Considerable scale effects on the throat erosion and theoretical were observed, but that of the efficiency was negligible. The improvement of the theoretical was the primary contributor to flight performance, which was responsible for a larger than 70% share in the total increase. The second largest contribution was the improvement of the efficiency with a share of 21.8–24.3%. The control gave an improvement of throat erosion corresponding to 5.75% in the total increase for the smallest scale; but, with increasing of the scale, the throat area increase ratio became small so that the throat erosion improvement contribution was reduced to 1.21%.

Optimal relationship between power and design-driving loads for wind turbine rotors using 1-D models

Abstract. We investigate the optimal relationship between the aerodynamic power, thrust loading and size of a wind turbine rotor when its design is constrained by a static aerodynamic load. Based on 1-D axial momentum theory, the captured power P̃ for a uniformly loaded rotor can be expressed in terms of the rotor radius R and the rotor thrust coefficient CT. Common types of static design-driving load constraints (DDLCs), e.g., limits on the permissible root-bending moment or tip deflection, may be generalized into a form that also depends on CT and R. The developed model is based on simple relations and makes explorations of overall parameters possible in the early stage of the rotor design process. Using these relationships to maximize P̃ subject to a DDLC shows that operating the rotor at the Betz limit (maximum CP) does not lead to the highest power capture. Rather, it is possible to improve performance with a larger rotor radius and lower CT without violating the DDLC. As an example, a rotor design driven by a tip-deflection constraint may achieve 1.9 % extra power capture P̃ compared to the baseline (Betz limit) rotor. This method is extended to the optimization of rotors with respect to annual energy production (AEP), in which the thrust characteristics CT(V) need to be determined together with R. This results in a much higher relative potential for improvement since the constraint limit can be met over a larger range of wind speeds. For example, a relative gain in AEP of +5.7 % is possible for a rotor design constrained by tip deflections, compared to a rotor designed for optimal CP. The optimal solution for AEP leads to a thrust curve with three distinct operational regimes and so-called thrust clipping.

Structural optimization of elastic circular arches and design criteria

Even if arches represent an old structural system adopted in construction practice since two thousand years ago, they are still adopted just if large spans have to be covered. The structural efficiency of arches principally depends on optimal material exploitation, due to the minimization of the thrust curve eccentricity, which reduces structural material volume and weight. Although the millenarian use and a very abundant literature dealing with arches, there is still scope for design optimization, so this study is framed within this context, investigating plane circular arches under uniformly distributed vertical load and self-weight. The arches are simply supported with bending springs at end sections. In a first step an analytical solution of the arch static is derived in dimensionless form. Next, the volume of the arch is minimized. Finally, the results are charted to allow their use in a design process.

Optimize Energy Efficiency of Quadrotors Via Arm Rotation

Quadrotors have been used in many areas such as cargo transportation, agriculture, and search and rescue. The low energy density of power sources and the low energy efficiency of quadrotors have prevented quadrotors from a wider range of applications where a large payload has to be carried or long flight time is required. This paper optimizes the energy efficiency of a quadrotor via rotating its arms to proper positions calculated based on the dynamics model of the quadrotor and the power–thrust curve of rotors. The conditions that a quadrotor in steady-state can achieve the optimal energy efficiency are mathematically derived and the energy efficiency of a quadrotor in various scenarios is analyzed. Based on the analysis, an arm-rotation approach is proposed to optimize the energy efficiency of a quadrotor with a center-of-gravity offset in steady hovering. It is shown with simulation that an example quadrotor with rotatable arms can save up to 13% of energy. Experiments show that the same example quadrotor can save even more energy in practice, owing to the byproduct of the arm-rotation approach.

A new numerical approach for determining optimal thrust curves of masonry arches

In this paper a new numerical approach for determining admissible thrust curves for masonry arches is proposed. Arbitrary loading conditions, including distributed loads applied to the extrados and to the intrados of the arch, but also horizontal inertial forces simulating the effects of seismic actions are considered for arches of any geometry. The admissible solutions, corresponding to equilibrium thrust curves entirely contained in the thickness of the arch, are consistent with the lower bound theorem of Limit Analysis and, thus, are “safe” solutions from a structural point of view. The well-established Milankovitch's theory for the equilibrium of masonry arches is reviewed and generalized. Then, a specific formulation of the theory is presented, allowing the construction of an effective and efficient numerical procedure based on the Point Collocation Method and enriched by a constrained optimization routine. The latter is aimed at determining, among all the admissible equilibrium solutions, the optimal solution matching specific requirements of interest for applications, as the solution corresponding to the maximum or minimum thrust. The proposed procedure is discussed and validated with reference to the cases of circular, parabolic and pointed arches. In particular, maximum and minimum thrust solutions have been determined for all the examined cases.

A Fully Coupled Computational Fluid Dynamics Method for Analysis of Semi-Submersible Floating Offshore Wind Turbines Under Wind-Wave Excitation Conditions Based on OC5 Data

Accurate prediction of the time-dependent system dynamic responses of floating offshore wind turbines (FOWTs) under aero-hydro-coupled conditions is a challenge. This paper presents a numerical modeling tool using commercial computational fluid dynamics software, STAR-CCM+(V12.02.010), to perform a fully coupled dynamic analysis of the DeepCwind semi-submersible floating platform with the National Renewable Engineering Lab (NREL) 5-MW baseline wind turbine model under combined wind–wave excitation environment conditions. Free-decay tests for rigid-body degrees of freedom (DOF) in still water and hydrodynamic tests for a regular wave are performed to validate the numerical model by inputting gross system parameters supported in the Offshore Code Comparison, Collaboration, Continued, with Correlations (OC5) project. A full-configuration FOWT simulation, with the simultaneous motion of the rotating blade due to 6-DOF platform dynamics, was performed. A relatively heavy load on the hub and blade was observed for the FOWT compared with the onshore wind turbine, leading to a 7.8% increase in the thrust curve; a 10% decrease in the power curve was also observed for the floating-type turbines, which could be attributed to the smaller project area and relative wind speed required for the rotor to receive wind power when the platform pitches. Finally, the tower-blade interference effects, blade-tip vortices, turbulent wakes, and shedding vortices in the fluid domain with relatively complex unsteady flow conditions were observed and investigated in detail.

Prediction of Noise and Acoustical Spectrum of Counter-Rotating Propellers

The acoustical performance of a counter-rotating marine propeller system is computed using the Ffowcs, Williams and Hawkings (FWH) algorithm. The solution procedures, where finite volume computational fluid dynamics calculations were exploited, was validated with a conventional propeller having experimental results (namely David Taylor Model Basin [DTMB] 4119). The large eddy simulation formulation and the sliding mesh technique are employed to build thrust and torque curves. Mesh dependency, turbulence model, and discretization schemes were all assessed to have repeatable and accurate results. Because the application under consideration involved inhomogeneous flow and blade interactions, DTMB 3684 and 3685 counterrotating propeller (CRP) models were used for comparisons. In terms of validation of numerical acoustics, the acoustical model evaluation study was first performed on a flow over a cylinder and a rain gutter model. The FWH approach produced good results for the spectrum at near-field and far-field locations. The performance of an inclined propeller, namely VP1304, in a noncavitating condition was investigated and the results were compared with the experiments conducted at the Potsdam Model Basin. Pressure pulses of this propeller in the cavitation tunnel were also attained and compared with experimental results. The amplitudes of the pressure fluctuations were in good agreement with the experimental data except for the weak third harmonics. Last, the generic form of the CRP system attached to an underwater vehicle body was considered to investigate the acoustic spectrum in terms of blade passing frequencies, interacted harmonics and radiated noise. 1. Introduction Propellers are used to drive marine systems including underwater vehicles. To boost their performance and fuel efficiency, they were designed mainly by experimentations. Recent studies (Denny 1968; Liu & Hong 2011), however, show that useful information about the characteristics of different conventional propellers can be extracted with the computational fluid dynamics (CFD) methodology which generally produces results supporting the experimental findings. As, for example, Subhas et al. (2012) succeeded to reproduce the blade characteristics of the INSEAN E779a propeller-designed and manufactured by Marine Technology Research Institute in the field of naval architecture and marine engineering in Italy-using the CFD. Similar finite volume calculations (Güngör & Özdemir 2015b) of the performance of propeller P4382 agreed well with the available experimental data. Embedding a model (Xia et al. 2012) for cavitation occurring on blade surfaces has been shown to improve the numerical performance in comparison with the calculations that neglect the cavitation effects. In the present analyses, we take into account the single-phase nature of the flow, and the cavitation effects are neglected with the emphasis placed in the noncavitating regions where reliable test results are available. Thus, to produce meaningful results, propeller hydrodynamics needs be considered especially under inhomogeneous flow conditions. Experiments (Potsdam Experimental Team 2015) on propellers subjected to the inhomogeneous flow reveal a variable wake in front of the propeller, which can be conveniently modeled numerically although unsteady interactions make the convergence difficult. On the other hand, the counter-rotating propeller (CRP) tests might be necessary to understand the interactions between the blades and hubs. To observe the axial distance effect, the CRP tests were handled in a cavitation tunnel (Hecker & McDonald 1960) where thrust and torque comparison assists in validations of numerical computing for each propeller's performance.

Modeling of horizontal axis wind turbine wakes in Horns Rev offshore wind farm using an improved actuator disc model coupled with computational fluid dynamic

In order to increase the accuracy and ability to predict the total energy gained in wind farms, it is necessary to use accurate wake models. In the present study, an improved methodology is applied on actuator disc in order to take all the operational and geometrical characteristics into account such as airfoil type, angular velocity, twist, and chord distribution. In wind farms, turbines are affected by upstream ones resulting in a non-uniform upstream velocity for each turbine. However, in literature, for all the wind turbines in a wind farm, thrust coefficient curve at undisturbed wind speed is used in order to estimate the upstream speed resulting in some errors. This weakness of actuator disc is resolved by a hybrid methodology based on blade element momentum theory and mass conservation coupled with computational fluid dynamics to be independent of thrust coefficient curve and calculate more accurate incoming velocity according to operational condition. It has been observed that by using the developed model and considering the details of wind turbines and more accurate incoming wind speed, in spite of steady state simulation and low computational cost, the interaction between different turbines is well-described. For turbulence modeling, standard k-∊ turbulence model is used and it is shown that the error of power estimation in second row of turbines especially in 270° wind angle is decreased significantly. In large wind sectors, such as 270±10°, ±15°,222±10°, ±15° and 312±5°, ±10° the proposed model performs as well as LES simulation. The developed methodology is practical for designing and optimization of new wind farms even if the technical specifications such as thrust curve would not be available from manufacturer.

Downstream effects from contemporary wind turbine deployments

High-resolution regional simulations of the downstream effects of wind turbine arrays are presented. The simulations are conducted with the Weather Research and Forecasting (WRF) model using two different wind turbine parameterizations for a domain centered on the highest density of current wind turbine deployments in the contiguous US. The simulations use actual wind turbine geolocations and turbine specifications (e.g. power and thrust curves). Resulting analyses indicate that for both WT parameterizations impacts on temperature, specific humidity, precipitation, sensible and latent heat fluxes from current wind turbine deployments are statistically significant only in summer, are of very small magnitude, and are highly localized. It is also shown that use of the relatively recently developed new explicit wake parameterization (EWP) results in faster recovery of full array wakes. This in turn leads to smaller climate impacts and reduced array-array interactions, which at a system-wide scale lead to higher summertime capacity factors (2-6% higher) than those from the more commonly applied ‘Fitch’ parameterization. Our research implies that further expansion of wind turbine deployments can likely be realized without causing substantial downstream impacts on weather and climate, or array-array interactions of a magnitude that would yield substantial decreases in capacity factors.

On use of hybrid rocket propulsion for suborbital vehicles

While the majority of operating suborbital rockets use solid rocket propulsion, recent advancements in the field of hybrid rocket motors lead to renewed interest in their use in sounding rockets. This paper presents results of optimisation of sounding rockets using hybrid propulsion. An overview of vehicles under development during the last decade, as well as heritage systems is provided. Different propellant combinations are discussed and their performance assessment is given. While Liquid Oxygen, Nitrous Oxide and Nitric Acid have been widely tested with various solid fuels in flight, Hydrogen Peroxide remains an oxidiser with very limited sounding rocket applications. The benefits of hybrid propulsion for sounding rockets are given. In case of hybrid rocket motors the thrust curve can be optimised for each flight, using a flow regulator, depending on the payload and mission. Results of studies concerning the optimal burn duration and nozzle selection are given. Specific considerations are provided for the Polish ILR-33 “Amber” sounding rocket. Low regression rates, which up to date were viewed as a drawback of hybrid propulsion may be used to the benefit of maximising rocket performance if small solid rocket boosters are used during the initial flight period. While increased interest in hybrid propulsion is present, no up-to-date reference concerning use of hybrid rocket propulsion for sounding rockets is available. The ultimate goal of the paper is to provide insight into the sensitivity of different design parameters on performance of hybrid sounding rockets and delve into the potential and challenges of using hybrid rocket technology for expendable suborbital applications.

High powered rocketry: design, construction, and launching experience and analysis

In this study, the nuts and bolts of designing and building a high powered rocket have been presented. A computer simulation program called RockSim was used to design the rocket. Simulation results are consistent with time variations of altitude, velocity, and acceleration obtained in the actual flight. The actual drag coefficient was determined by using altitude back-tracking method and found to be 0.825. Speed of the exhaust determined to be 2.5 km s−1 by analyzing the thrust curve of the rocket. Acceleration in the coasting phase of the flight, represented by the second-degree polynomial of a small leading coefficient, have been found to approach ‘-g’ asymptotically.

Influences of surge motion on the power and thrust characteristics of an offshore floating wind turbine

Abstract The power and thrust characteristics of an offshore floating wind turbine (OFWT) not only depend on the tip speed ratio λ and the blade pitch angle θ, but also closely relate to the platform motions. In this paper, the influences of the platform surge motion on the behaviors of the power output and rotor thrust of a typical Spar-type OFWT are investigated using Free Vortex Method (FVM). The influences of the surge frequency and amplitude are analyzed separately at first. Afterwards, a reduced frequency k is proposed to combine the influences of surge frequency and amplitude. The power and thrust curves are derived as functions of the tip speed ratio λ and reduced frequency k with blade pitch angle θ constant at zero. Results show that when the reduced frequency increases, mean power output decreases at low tip speed ratios but increases at high tip speed ratios; mean thrust decreases slightly for all tip speed ratios except λ = 12. Power and thrust variations increase as tip speed ratio or reduced frequency increases. Power and thrust coefficients decline with an increasing reduced frequency.

Moment-Curvature-Thrust Relationships for Beam-Columns

Moment–curvature–thrust relationships (M–κ–N) are a useful resource for the solution of a variety of inelastic and geometrically non-linear structural problems involving elements under combined axial load and bending. A numerical discretised cross-section method is used in this research to generate such relationships for I-sections, rectangular box-sections and circular or elliptical hollow sections. The method is strain driven, with the maximum strain limited by an a priori defined local buckling strain, which can occur above or below the yield strain depending on the local slenderness of the cross-section. The relationship between the limiting strain and the local slenderness has been given for aluminium, mild steel and stainless steel cross-sections through the base curve of the Continuous Strength Method. Moment-curvature-thrust curves are derived from axial force and bending moment interaction curves by pairing the curvatures and moments for a given axial load level. These moment–curvature–thrust curves can be transformed into various formats to solve a variety of structural problems. The gradient of the curves is used to find the materially and geometrically non-linear solution of an example beam-column, by solving numerically the moment–curvature ordinary differential equations. The results capture the importance of the second order effects, particularly with regard to the plastic hinge formation at mid-height and the post-peak unloading response.

Solid-Rocket-Motor Performance-Matching Design Framework

An effective performance-matching design framework for solid rocket motor tailored toward satisfying various thrust-performance requirements is presented in this research paper through an innovative and specialized general-design approach developed to evaluate the general-design parameters. During the general-design stage, a combination of grain web and area ratio is selected as the design variables to be adjusted to obtain the general parameters. Based on the general parameters obtained, a grain-design stage incorporates the level-set method and simulates solid-propellant evolution and internal ballistic analysis, thereby obtaining the thrust performance. Grain-design effectiveness is determined by how closely the designed solid-rocket-motor performance matches and compares to a prespecified thrust curve. An efficient sequential-field-approximate-optimization algorithm is proposed and used to minimize the average rms error between the desired and designed thrusts. Validation of the proposed design framework is carried out by evaluating motor cases possessing different thrust requirements, and results obtained highlight the proposed framework as a practical and efficient strategy for solid-rocket-motor designs.

Description of an 8 MW reference wind turbine

An 8 MW wind turbine is described in terms of mass distribution, dimensions, power curve, thrust curve, maximum design load and tower configuration. This turbine has been described as part of the EU FP7 project LEANWIND in order to facilitate research into logistics and naval architecture efficiencies for future offshore wind installations. The design of this 8 MW reference wind turbine has been checked and validated by the design consultancy DNV-GL.This turbine description is intended to bridge the gap between the NREL 5 MW and DTU 10 reference turbines and thus contribute to the standardisation of research and development activities in the offshore wind energy industry.

Experimental and numerical study of a 10MW TLP wind turbine in waves and wind

This paper presents tests on a 1:60 version of the DTU 10MW wind turbine mounted on a tension leg platform and their numerical reproduction. Both the experimental setup and the numerical model are Froude-scaled, and the dynamic response of the floating wind turbine to wind and waves is compared in terms of motion in the six degrees of freedom, nacelle acceleration and mooring line tension. The numerical model is implemented in the aero-elastic code Flex5, featuring the unsteady BEM method and the Morison equation for the modelling of aerodynamics and hydrodynamics, respectively. It was calibrated with the tests by matching key system features, namely the steady thrust curve and the decay tests in water. The calibrated model is used to reproduce the wind-wave climates in the laboratory, including regular and irregular waves, with and without wind. The model predictions are compared to the measured data, and a good agreement is found for surge and heave, while some discrepancies are observed for pitch, nacelle acceleration and line tension. The addition of wind generally improves the agreement with test results. The aerodynamic damping is identified in both tests and simulations. Finally, the sources of the discrepancies are discussed and some improvements in the numerical model are suggested in order to obtain a better agreement with the experiments.

핀틀 구동속도에 따른 핀틀 추력기의 비정상상태 특성에 대한 실험적 연구

본 논문에서는 핀틀 추력기의 비정상상태 특성을 파악하기 위하여 구동기의 속도를 측정하였으며, 정상상태 실험을 통해 비정상상태 실험 시스템을 구성하였다. 비정상상태 실험은 총 3 가지의 구동 속도(3.01 mm/s, 5.65 mm/s, 10.83 mm/s)를 이용하여 진행하였다. 그 결과 핀틀이 후진하는 경우가 전진하는 경우보다 더 빨리 명령 압력 값에 수렴하였으며, 이는 핀틀이 후진하는 경우가 연소실의 압력이 높은 상태로 형성되어 있기 때문이다. 핀틀이 전 후진하는 경우에 추력 곡선에 특이점들이 나타났으며, 이는 연소실 압력과 노즐 목 면적 변화에 기인하여 나타난 질유량 변화로 인한 것이다. 구동 속도가 빠를수록 이러한 현상이 뚜렷하게 나타났다. The purpose of this study is to investigate unsteady-state characteristics of a pintle thruster with various pintle speed. Based on steady state experimental results, non-linear pintle stroke equation is obtained and applied to the unsteady state experimental system. For the unsteady state experiments, three different pintle speeds are used: 3.10 mm/s, 5.65 mm/s, 10.83 mm/s, respectively. Results show that backward pintle stroke results in faster convergence time because of high chamber pressure during backward pintle stroke sequence. During the forward and backward process, thrust curve shows singular points. These phenomenons is caused by variation of mass flow rate, which is mainly due to changes of both chamber pressures and nozzle throat area. This behavior becomes distinctive for a faster pintle speed case.