Thrust Variation Research Articles

Evaluation of an Uncoupled Method for Analyzing the Seismic Response of Wind Turbines Excited by Wind and Earthquake Loads

There is a significant interaction between wind and earthquakes for large-scaled wind turbines due to an aeroelastic effect. This study evaluates the accuracy of an uncoupled method extensively utilized to analyze the seismic response of wind turbines at the operational state. Initially, the oscillation of the blade for the National Renewable Energy Laboratory (NREL) 5 MW wind turbine excited by wind and wind-earthquake combination, respectively, is compared using the fully coupled method to verify the assumption in this uncoupled method. Subsequently, the influence of ground motions on the aerodynamic loadings of the rotor is discussed to evaluate the interaction between wind and earthquake loads. In addition, the accuracy of the uncoupled method is assessed by comparing the analysis results of the coupled and uncoupled methods, where different mean wind speed and equivalent aerodynamic damping ratio are considered. The results indicate that the oscillation velocity of blades and thrust on the rotor are significantly influenced by ground motions. Moreover, the amplitude of thrust variations caused by earthquakes increases monotonously with the oscillation velocity amplitude of blade-root. The errors between the two models are beyond the engineering margins for some earthquakes, such that it is difficult to optimize a consistent aerodynamic damping in the uncoupled model to accurately predict the seismic response of wind turbines.

Experimentally validated study of the impact of operating strategies on power efficiency of a turbine array in a bi-directional tidal channel

Flexible operation across a wide range of operating conditions is required to maximise the contribution of tidal turbine arrays to the future energy mix. This study establishes a basin efficiency range of a small array of horizontal axis turbines between 0.45 and 0.79, with dependency on turbine operating point and flow direction. This range is largely due to variation of array thrust as array power varies by less than 15% for all operating points.Analysis of array thrust, power and wakes was conducted using a RANS actuator disc model and assessed against new experimental measurements using porous discs. RANS array thrust predictions are within 10% of the experimental study. Turbine thrust differs within each array, varying by −60% to +30% compared to isolated turbines. Row-specific operating points reduce this range by a factor of two whilst also increasing the basin efficiency slightly for a given flow speed.Accounting for time variation of basin efficiency reduces the energy yield by almost 5% relative to arrays modelled with a constant net array thrust coefficient. Arrays with row-specific local thrust coefficients generate similar net power to arrays with velocity-specific array operating points but reduce the occurrences of large rates of change of power.

Performance characteristics of a solid oxide fuel cell hybrid jet engine under different operating modes

Solid oxide fuel cell (SOFC) technology is promising. Jet engines can be integrated with SOFCs (SOFC hybrid jet engine) for aircraft. The specific thrust of the engine is greatly improved by replacing turbines with SOFC systems. Four operating modes are designed for the engine to achieve about 50% ∼ 100% thrust variation. Mode 1: Regulating the fuel flow in the reformer under the constant air flow for the SOFC system. Mode 2: Regulating the fuel flow in the afterburner with zero fresh air for afterburners. Mode 3: Regulating the fuel and air flow for the SOFC. Mode 4: Regulating the fuel flow in the afterburner with constant air flow for afterburners. The performance and thermodynamic parameters of the engine under different operating modes are examined and compared according to the built mathematical models. The simulation results show that the effects of operating modes on the engine are remarkably different from that on the traditional SOFC gas turbine hybrid systems for electricity generation. All of the parameters of components change sharply in modes 1 and 3, and the thermal efficiency of the engine increases respectively from 0.577 to 0.687 and 0.491 to 0.687 with the increase of load. The component parameters of the engine are slightly changed in modes 2 and 4 except the parameters related to the afterburner. In mode 2, the thermal efficiency decreases from 0.577 to 0.454. It decreases from 0.491 to 0.434 in mode 4. In a nutshell, the performance of the engine can be varied in a wide range under the operating model 4 with increasing the afterburner temperature from 832 K to 2261 K. The operating mode 4 is the best.

Ship hull wake effect on the hydrodynamic performance of a heave–pitch combined oscillating fin

ABSTRACT The hydrodynamic analysis of flapping foil inspired by the thunniform fish propulsion is carried out numerically. The hydrodynamic performances of 2D and 3D rigid oscillating foils are analysed for a range of Strouhal numbers (St). The performance parameters such as thrust coefficient, power coefficient and hydrodynamic efficiency are obtained in both open water and behind ship conditions, where the wake effect of the ship influences the hydrodynamic performance parameters of the foil. Thrust and efficiency variations with Strouhal number are estimated and it is found that the efficiency reaches maximum at St = 0.3.

The helix approach: Using dynamic individual pitch control to enhance wake mixing in wind farms

AbstractWind farm control using dynamic concepts is a research topic that is receiving an increasing amount of interest. The main concept of this approach is that dynamic variations of the wind turbine control settings lead to higher wake turbulence, and subsequently faster wake recovery due to increased mixing. As a result, downstream turbines experience higher wind speeds, thus increasing their energy capture. In dynamic induction control (DIC), the magnitude of the thrust force of an upstream turbine is varied. Although very effective, this approach also leads to increased power and thrust variations, negatively impacting energy quality and fatigue loading. In this paper, a novel approach for the dynamic control of wind turbines in a wind farm is proposed: using individual pitch control, the fixed‐frame tilt and yaw moments on the turbine are varied, thus dynamically manipulating the wake. This strategy is named the helix approach because the resulting wake has a helical shape. Large eddy simulations of a two‐turbine wind farm show that this approach leads to enhanced wake mixing with minimal power and thrust variations.

Performance enhancement of twisted-bladed Savonius vertical axis wind turbines

It is important to determine the most optimal configuration of a Savonius vertical axis wind turbine that attains the best performance with a high self-starting ability. Thus, the effects of several design parameters including twist angle, overlap ratio, and endplates size ratio, along with the wind velocity on the performance of the Savonius wind turbine are investigated. Novel assessment methods based on flow field characteristics such as streamlines and pressure fields around the Savonius wind turbine are carried out. This is the first contribution to understand how geometrical variables influence the aerodynamic performance of the twisted Savonius rotor. Moreover, the variation of torque, power, thrust, and static torque coefficients are estimated. Thus, a three-dimensional, incompressible unsteady Reynolds-averaged Navier-Stokes model in conjunction with k-ω shear-stress transport turbulence model is developed. The model is numerically simulated and validated using the experimental and numerical data available in literature. Results indicate that the Savonius rotor with a twist angle of 45°, an overlapping ratio of zero, and endplates size ratio of 1.1 attains the highest net output power compared to other designs. It is found that at a wind velocity of 6 m/s, the Savonius rotor achieves a maximum power coefficient of 0.223, and with further increase of the wind velocity to 10 m/s, the power coefficient reaches 0.231. In addition, the current developed design has a positive static torque coefficient at all rotor angles, and consequently, it achieves a high self-starting ability. However, for the conventional (untwisted) design, the maximum attainable power coefficient was found to be 0.174 at an overlapping ratio of 0.15, and equal endplate size ratio. In addition, negative values of the static torque coefficient were observed at a specific range of rotor angles that prevent the self-starting ability. Accordingly, the new twisted rotor design not only enhances the power coefficient but the self-starting ability as well. The findings of the current results provide another direction for researchers and designers to utilize the twisted Savonius wind turbine.

Advanced prediction of tunnel boring machine performance based on big data

Predicting the performance of a tunneling boring machine is vitally important to avoid any possible accidents during tunneling boring. The prediction is not straightforward due to the uncertain geological conditions and the complex rock-machine interactions. Based on the big data obtained from the 72.1 ​km long tunnel in the Yin-Song Diversion Project in China, this study developed a machine learning model to predict the TBM performance in a real-time manner. The total thrust and the cutterhead torque during a stable period in a boring cycle was predicted in advance by using the machine-returned parameters in the rising period. A long short-term memory model was developed and its accuracy was evaluated. The results show that the variation in the total thrust and cutterhead torque with various geological conditions can be well reflected by the proposed model. This real-time predication shows superior performance than the classical theoretical model in which only a single value can be obtained based on the single measurement of the rock properties. To improve the accuracy of the model a filtering process was proposed. Results indicate that filtering the unnecessary parameters can enhance both the accuracy and the computational efficiency. Finally, the data deficiency was discussed by assuming a parameter was missing. It is found that the missing of a key parameter can significantly reduce the accuracy of the model, while the supplement of a parameter that highly-correlated with the missing one can improve the prediction.

Indirect Rotational Energy Harvesting System to Enhance the Power Supply of the Quadcopter

This paper presents a simple energy harvesting system using unpowered freewheeling propellers mounted on the quadcopter without changing its actual design. Different layout configurations have been analysed and its thrust variation also tested to place the harvesting system in a suitable place in the quadcopter. The same and different size freewheeling propellers running coordination and its speed ratio are examined at various speed. To know the flow performance the freewheeling propellers Reynolds number is calculated. The freewheeling propellers rotational energy which creates an electrical power by means of micro BLDC generator. The harvested energy from the BLDC generator is maximized using three-phase MOSFET enabled controlled rectifier with hysteresis comparator. To meet the requirement of powering the quadcopter the output voltage from the generator is boosted and regulated using single DC-DC SEPIC boost converter with high voltage and current range. This energy can be directly charge secondary battery or power the other electronic payloads. The freewheeling propeller energy harvesting system has been implemented and tested in the laboratory at static condition which gives 51 per cent of harvested current.

Facility pressure effects on a Hall thruster with an external cathode, II: theoretical model of the thrust and the significance of azimuthal asymmetries in the cathode plasma

A theoretical model of the thrust produced by a Hall thruster has been developed to provide insight into the longstanding problem of performance dependence on facility pressure. Inputs to the model have been provided by 2D (r–z) axisymmetric simulations that were guided by measurements of the ion velocity field from laser induced fluorescence diagnostics. The combined analyses yield very good agreement with thrust measurements from ground tests of the SPT-140, a Hall thruster operating with an external cathode, and suggest two new findings. First, at intermediate pressures (∼9–15 μTorr) the rise of the thrust with increasing pressure is largely due to fast atoms produced by charge exchange collisions with beam ions. The acceleration region remains spatially invariant and the thrust rise is linear with pressure. As the pressure increases further, displacements of the acceleration region towards the anode become sizeable and reduce the rate of increase in thrust. Second, the thrust increase from vacuum to the lower values of pressure (≲9 μTorr) is driven largely by transport of electrons along magnetic lines, from the cathode to the near-plume of the thruster, which explains why the rise is nonlinear with pressure. It is argued based on first-principles that this higher rate of thrust variation observed at the lowest pressures may be strongly linked to the highly asymmetric distribution of the external-cathode electrons around the discharge. This would explain the insensitivity of performance in thrusters with centrally-mounted cathodes as well as the longstanding challenges 2D axisymmetric simulations have had in uncovering the source of the thrust dependence on facility pressure.

RETRACTED ARTICLE: Preserving learnability and intelligibility at the point of care with assimilation of different speech recognition techniques

The neoteric introduction of 5G technology in mobile internet is transforming Internet of mobile Things (IoMT) massively by addressing low latency, support for a large number of IoMT devices, and less power consumption, thereby delivering cost-effective solutions to low-end devices. This transformational technology enables a ubiquitous connected critical communication network between the healthcare system and IoT, as they largely depend on low-end devices for gathering data at the point of care. Gathering and interpolation of data from things are moved over to the cloud, making the extraction of knowledge and decision-making capabilities more robust. Vocal signals form the basis of communication between human beings with the transfer of complex data with variations in thrust, pitch, and tones. The representation and recognition of these analog signals by digital systems prove to be quite exciting and challenging. The spoken language models are converted to digital signals to be identifiable based on different cues like phonetic, prosodic, phonotactic, and lexical features. Voice patterns tend to be specific for every individual with a slight orientation towards the language spoken by the individual of a particular region. While speech patterns tend to alter the meaning of words with tones, high and low pitches in the utterance of the words, NLP tends to learn specific associations of words through vectors. The focus on learned networks in solving the problem of speech synthesis to text with minimal loss and high predictability of syllable of word, sentence, and paraphrase is needed. The creation of a knowledge base corpus of learned variable prosody of features helps in the learnability of interestingness directly without any perturbations. The learning algorithms to realize the degree of understandability of speech with the word, sentence identified, and transcription with substantial noise interference. The transfer of the acoustic features learned by algorithms proves to be quiet challenging as they are distorted by sudden environmental changes. Syllable extracted from the speech translation may or may not represent the Sentiment of the word, with different phonetical modulation. Utilization of the MobileNets and DistillBERT to transfer the language extraction and the edge reducing the time of processing and reducing the corpus of the size, reducing the adversial learning of the voice features and the patterns, reducing the Transfer of learned corpus and patterns.

Effects of Heaving Motion on the Aerodynamic Performance of a Double-Element Wing in Ground Effect

The broad implication of the paper is to elucidate the significance of the dynamic heaving motion in the aerodynamic performance of multi-element wings, currently considered as a promising aspect for the improvement of the aerodynamic correlation between CFD, wind tunnel and track testing in race car applications. The relationship between the varying aerodynamic forces, the vortex shedding, and the unsteady pressure field of a heaving double-element wing is investigated for a range of mean ride heights, frequencies, and amplitudes, using a two-dimensional (2D) unsteady Reynolds-averaged Navier-Stokes (URANS) approach and an overset mesh method for modelling the moving wing. The analysis of the results shows that at high frequencies, i.e., k ≥ 5:94 and amplitudes a/c ≥ 0:05 the interaction of the shear vorticity between the two elements results in the generation of cohering leading and trailing edge vortices on the flap, associated to the rapid variation of thrust and downforce enhancement. Both the occurrence and intensity of these vortices are dependent upon the frequency, amplitude, and mean ride height of the heaving wing. The addition of the flap significantly alters the frequency of the shed vortices in the wake and maintains the generation of downforce for longer time in ground proximity. The comparison with the static wing provides evidence that the dynamic motion of a race car wing can be beneficial in terms of performance, or detrimental in terms of aerodynamic correlation.

Development of a prediction model of transient thrust variation for spacecraft liquid propulsion systems

Development of a prediction model of transient thrust variation for spacecraft liquid propulsion systems

프로펠러 가진에 의한 저속 디젤엔진을 갖는 추진축계의 종진동

The axial vibration of propeller-induced excitation can be mostly seen in warships that have high-speed rotation propulsion shafting systems equipped with reduction gears. Coupled torsional and axial vibration is mainly focused on the excitation force that is induced by the cylinder’s gas pressure and the piston’s reciprocating mass in low-speed two-stroke diesel engines with seven or fewer cylinders; more complex vibration modes with one or more nodes can be seen in engines with eight or more cylinders. This thrust variation force caused by the axial vibration is the excitation force of the ship’s deckhouse in the longitudinal direction and has been researched extensively in the past. Recently, super-size containerships have been built that have more than 20 000 TEU. These ships have adopted low-speed diesel engines with 10 or more cylinders as their prime mover and the distance between the propeller and the main engine has increased significantly due to the streamlining of their hulls. As a result, there is the probability of resonance between the propeller’s axial excitation and the second node vibration. While this vibration frequency is rare, the possibility of resonance with the ship’s superstructure can create vibrations in the pipes and various accessories surrounding the main engine and stern tube. In addition, severe vibrations can occur if the natural frequency of these parts and that of the axial vibration are similar, which necessitates installing an additional damper on the intermediate shaft that resembles an axial vibration damper that is attached to the crankshaft free end. This paper intends to research the characteristics of axial vibration through theoretical analysis and measurement data with a focus on the 2nd order axial excitation of the propeller blade number in a propulsion shafting system with a 11G90ME engine as the research model.

Numerical performance investigation of a thrust-optimized nozzle at different altitudes

One of the major design aspects of jet propulsion engines is the nozzle design. The value of thrust generated by the nozzle is dependent on both the nozzle design and the flight altitude. The present paper is intended to shed more light on the jet flow structure and its evolution with flight altitude. In addition, the variation of thrust generated by the nozzle with flight altitude is addressed. A well-defined nozzle profile is adopted as a case study and numerical simulation using a commercial CFD tool is conducted. The solution method is validated by reproducing the experiments conducted on the case study nozzle.

Out-of-plane relative control of an ion beam shepherd satellite using yaw attitude deviations

According to the concept of active debris removal, named “ion beam shepherd”, a shepherd satellite must be controlled to move at a certain small distance in front of a space debris object during the de-orbiting phase. Due to the considerable duration of this phase, the propellant consumption is a key driver for the control system design. As shown in recent studies, the in-plane relative motion of such a formation can be controlled using a thrust variation of only one compensation thruster of the shepherd. This control strategy allows designers to significantly reduce the propellant mass needed to fulfill a de-orbiting mission but does not ensure the controllability of the formation in the out-of-plane direction. To fill this gap this paper proposes to deviate the yaw attitude of the shepherd for applying control actions in the out-of-plane direction. The laws of the yaw angle variation are designed to effectively damp out the out-of-plane oscillations. Computer simulations demonstrate that a required relative spatial position of the formation can be maintained by varying only two values: the yaw angle of the shepherd and thrust of the compensation thruster. The analysis shows that the de-orbiting rate deteriorates insignificantly due to the attitude deviation of the ion beam.

Combined Chemical–Electric Propulsion for a Stand-Alone Mars CubeSat

Stand-alone interplanetary CubeSats require primary propulsion systems for orbit maneuvering and precise trajectory control. The current work focuses on the design and performance characterization of the combined chemical–electric propulsion systems that shall enable a stand-alone 16U CubeSat mission on a hybrid high-thrust–low-thrust trajectory from a supersynchronous geostationary transfer orbit to a circular orbit about Mars. The high-thrust chemical propulsion is used to escape Earth and to initiate stabilization at Mars. The low-thrust electric propulsion is used in heliocentric transfer, ballistic capture, and circularization. For chemical propulsion, design and performance characteristics of a monopropellant thruster and feed system using ADN-based FLP-106 propellant are presented. For electric propulsion, a performance model of an iodine-propelled inductively coupled miniature radiofrequency ion thruster is implemented to calculate the variation of thrust, specific impulse, and efficiency with input power. A power-constrained low-thrust trajectory optimization using the thruster performance model is pursued to calculate the transfer time, , and the required propellant mass for fuel-optimal and time-optimal transfers. Overall, the combined chemical–electric systems yield a feasible propulsion solution for stand-alone CubeSat missions to Mars that balances propellant mass and transfer time.

Investigation on the Performance of a Ducted Propeller in Oblique Flow

In this study, the ducted propeller has been numerically investigated under oblique flow, which is crucial and challenging for the design and safe operation of the thruster driven vessel and dynamic positioning (DP) system. A Reynolds-averaged Navier–Stokes (RANS) model has been first evaluated in the quasi-steady investigation on a single ducted propeller operating in open water condition, and then a hybrid RANS/LES model is adapted for the transient sliding mesh computations. A representative test geometry considered here is a marine model thruster, which is discretized with structured hexahedral cells, and the gap between the blade tip and nozzle is carefully meshed to capture the flow dynamics. The computational results are assessed by a systematic grid convergence study and compared with the available experimental data. As a part of the novel contribution, multiple incidence angles from 15 deg to 60 deg have been analyzed with different advance coefficients. The main emphasis has been placed on the hydrodynamic loads that act on the propeller blades and nozzle as well as their variation with different configurations. The results reveal that while the nozzle absorbs much effort from the oblique flow, the imbalance between blades at different positions is still noticeable. Such unbalance flow dynamics on the blades, and the nozzle has a direct implication on the variation of thrust and torque of a marine thruster.

Lateral variation of the Main Himalayan Thrust controls the rupture length of the 2015 Gorkha earthquake in Nepal.

The Himalaya orogenic belt produces frequent large earthquakes that affect population centers along a length of over 2500 km. The 2015 Gorkha, Nepal earthquake (M w 7.8) ruptured the Main Himalayan Thrust (MHT) and allows direct measurements of the behavior of the continental collision zone. We study the MHT using seismic waveforms recorded by local stations that completely cover the aftershock zone. The MHT exhibits clear lateral variation along geologic strike, with the Lesser Himalayan ramp having moderate dip on the MHT beneath the mainshock area and a flatter and deeper MHT beneath the eastern end of the aftershock zone. East of the aftershock zone, seismic wave speed increases at MHT depths, perhaps due to subduction of an Indian basement ridge. A similar magnitude wave speed change occurs at the western end of the aftershock zone. These gross morphological structures of the MHT controlled the rupture length of the Gorkha earthquake.

Neural Partial Differentiation Based Nonlinear Parameter Estimation from Noisy Flight Data

This paper focuses on the application of neural partial differentiation (NPD) approach to estimate the longitudinal parameters of an aircraft HFB 320 from noisy flight data. By exciting both short period and phugoid modes of an aircraft with thrust variation, the aircraft system dynamics becomes highly nonlinear and aerodynamic parameters appears nonlinear to the state trajectories of velocity, AOA, pitch rate and pitch angle. This paper highlights the application of NPD for such a class of nonlinear dynamics; previously it was used only for the estimation of parameter appearing linear to the states. The extracted the nonlinear longitudinal parameters of HFB 320 aircraft are compared with the parameters estimated by using adaptive Unscented Kalman Filter (UKF) approach. Finally, the estimation results are validated by comparing with flight data and the responses obtained from the estimates by adaptive UKF.

Improving Tidal Turbine Performance Through Multi-Rotor Fence Configurations

Constructive interference between tidal stream turbines in multi-rotor fence configurations arrayed normally to the flow has been shown analytically, computationally, and experimentally to enhance turbine performance. The increased resistance to bypass flow due to the presence of neighbouring turbines allows a static pressure difference to develop in the channel and entrains a greater flow rate through the rotor swept area. Exploiting the potential improvement in turbine performance requires that turbines either be operated at higher tip speed ratios or that turbines are redesigned in order to increase thrust. Recent studies have demonstrated that multi-scale flow dynamics, in which a distinction is made between device-scale and fence-scale flow events, have an important role in the physics of flow past tidal turbine fences partially spanning larger channels. Although the reduction in flow rate through the fence as the turbine thrust level increases has been previously demonstrated, the within-fence variation in turbine performance, and the consequences for overall farm performance, is less well understood. The impact of turbine design and operating conditions, on the performance of a multi-rotor tidal fence is investigated using Reynolds-Averaged Navier-Stokes embedded blade element actuator disk simulations. Fences consisting of four, six, and eight turbines are simulated, and it is demonstrated that the combination of device- and fence-scale flow effects gives rise to cross-fence thrust and power variation. These cross-fence variations are also a function of turbine thrust, and hence design conditions, although it is shown simple turbine control strategies can be adopted in order to reduce the cross-fence variations and improve overall fence performance. As the number of turbines in the fence, and hence fence length, increases, it is shown that the turbines may be designed or operated to achieve higher thrust levels than if the turbines were not deployed in a fence configuration.