Thrust Fluctuation Research Articles

Thrust noise cause analysis and suppression of a cusped field thruster

The drag-free control technology is a critical technology to guarantee the ultra-low disturbance satellite platform. Thrust noise is the primary disturbance of the drag-free control system because the thruster acts as the actuator of this system, so it would seriously affect the performance of the control system. To study and suppress thrust noise, a cusped field thruster, which has the feasibility of being applied to the drag-free control tasks, is used in this research. According to the experimental results of thrust noise, it can be seen that the thrust noise spectrum under different working conditions is different slightly, but the trend is similar. The amplitude spectrum densities of thrust in the high-frequency region present white noise characteristics, while the amplitude spectrum densities increase with the decrease of frequency in the low-frequency region. Based on the input-output thrust model and the experimental data of the anode voltage and flow rate, the effects of the anode voltage fluctuation and flow rate fluctuation on the thrust noise are analyzed. The high-frequency part (above 0.05Hz) of thrust noise is mainly caused by the flow rate noise, while the drift of thruster operation states leads to low-frequency (10−3Hz–0.05Hz) fluctuation of thrust. Finally, based on the feedback control theory, a noise suppression method is designed by controlling the anode voltage. Closed-loop simulation results of the thruster verify that the method is effective.

Modeling and mode transition simulation of over-under turbine based combined cycle (TBCC) propulsion system based on inlet/engine matching

Abstract The over-under turbine based combined cycle (TBCC) propulsion system dynamic model is established, including the engine model and inlet model. A dual-channel inlet is designed to match the engine and the inlet performance parameters are obtained by computational fluid dynamics (CFD) calculation, which provides original data for the integrated Inlet/Engine matching model. Control plan is designed to ensure that the engine is not over-temperature, over-rotation or surging based on correlation analysis. The simulation results show that the designed control plan can keep the TBCC propulsion system continuous in thrust during the mode transition, and the thrust fluctuation is about 10%.

Dynamic loads and thrust hysteresis of near-surface open propeller in regular head waves-an experimental study in a circulating water channel

This paper investigates the dynamic load characteristics of a near-surface open propeller in regular head waves based on a model experiment in a circulating water channel, with the aid of captured free-surface profiles. The influences of periodical variation of submergence depth and inflow velocity on the dynamic load characteristics are systematically investigated, and the thrust hysteresis in periodical emergence condition is quantitatively evaluated. As conclusions, a critical instantaneous submergence depth is identified for this propeller in regular waves at a certain advance ratio; above this value, the dynamic load characteristics are not dominated by the propeller-surface interactions. For a periodically emerged propeller, the influence of the periodical variation of inflow velocity on the dynamic load characteristics is more significant as either submergence depth or wave height increases. With increasing wave period, the wave-caused load fluctuation amplitude increases in a more obvious manner in periodical emergence condition, but decreases less obviously in full submergence condition. Regarding the thrust hysteresis, it takes approximately 5 revolutions for this propeller in full submergence to regain full thrust. Lastly, the thrust fluctuation and loss due to slipstream inclination is considered responsible for thrust hysteresis, which happens as the previously emerged propeller heads into full submergence.

New optimization design method for a double secondary linear motor based on R-DNN modeling method and MCS optimization algorithm

Traditional linear motor optimization methods typically use analytical models combined with intelligent optimization algorithms. However, this approach has disadvantages, e.g., the analytical model might not be accurate enough, and the intelligent optimization algorithm can easily fall into local optimization. A new linear motor optimization strategy combining an R-deep neural network (R-DNN) and modified cuckoo search (MCS) is proposed; additionally, the thrust lifting and thrust fluctuation reductions are regarded as optimization objectives. The R-DNN is a deep neural network modeling method using the rectified linear unit (RELU) activation function, and the MCS provides a faster convergence speed and stronger data search capability as compared with genetic algorithms, particle swarm optimization, and standard CS algorithms. Finally, the validity and accuracy of this work are proven based on prototype experiments.

Ship Airwakes in Waves and Motions and Effects on Helicopter Operation

Insight into the effects of motions and waves on a ship airwake can be used to provide information regarding safe conditions for at sea flight operations and pilot training. We present a study on the effects of waves and motions on a ship's airwake and a helicopter operating above the flight deck using full scale computational fluid dynamics simulations. The ONR Tumblehome Ship (ONRT) geometry is analyzed in wind and regular head waves corresponding to nominal sea states 3 and 6. In order to separate the effects of waves and motions, simulations are conducted for both sea states with combinations of: waves and motions, waves and no motions, no waves with motions, and no motions or waves. A triple velocity decomposition is conducted in order to quantify changes in the airwake due to motions and waves. The aerodynamic loads on a helicopter hovering in the airwake are studied with one-way and two-way coupling approaches. The one-way coupled analysis uses the velocity field data from the full scale airwake simulations along with disk actuator theory to calculate thrust fluctuations for three different rotor sizes operating above the flight deck. In the two-way coupled study a helicopter loosely based on the Sikorsky SH-60 Seahawk hovering above the flight deck of the ONRT is simulated, including dynamic overset grids of the main rotor, tail rotor and fuselage. This approach captures the interaction between the rotor downwash and the ONRT airwake. The study shows that for the lower sea state 3 the motions and waves have little effect on the airwake behavior, exhibiting little change with respect to the baseline case without motions and waves. At sea state 6 the flow field is modified significantly, which also affects the forces on the helicopter. Force fluctuations show main peaks at the wave encounter frequency and the blade passage frequency, as well as higher harmonics. The one-way coupling approach shows that larger rotors effectively filter out small scale fluctuations while smaller diameter rotors are affected by smaller flow structures.

Comparative analysis of bilateral permanent magnet linear synchronous motors with different structures

Permanent magnet linear synchronous motor (PMLSM) has the advantages of high thrust density and good control accuracy, which can be applied in high-power and high-speed occasions. In this paper, the analytical models are established to obtain the electromagnetic performance for the PMLSMs with dual secondaries and dual primaries. The air-gap flux density and the electromagnetic thrust are also obtained by the finite element model to verify theoretical analysis. Besides, an improved structure is also put forward in order to suppress the thrust fluctuation of the PMLSM. Finally, the advantages and disadvantages of two PMLSMs topologies are listed. These analyses would provide a guide for the design of PMLSMs applied in high-power and high-speed occasions.

Vortex Model and Blade Span Influence on Orthogonal Blade-Vortex Interaction Noise

The influence of the vortex impingement location on the aerodynamic and acoustic response of a rotating blade during an orthogonal interaction is studied by means of computational fluid dynamics. The objective is to identify and quantify precisely the noise reduction achieved by reducing the blade span. The Batchelor vortex model is primarily considered as it accounts for the axial velocity deficit observed in the core of realistic tip vortices. Separated simulations were also carried out for a Lamb–Oseen vortex and a purely axial velocity deficit to highlight and quantify the influence of the vortex velocity components on the interaction as well as to balance design optimizations performed relying on methods not able to model viscous effects. The analysis of the blade aerodynamic and acoustic responses shows that the magnitude of the thrust fluctuation and radiated noise are always higher for a Batchelor vortex than for a Lamb–Oseen vortex when the vortex core impinges below the blade tip. For both vortex models, the thrust fluctuation and radiated noise reach their peak for an interaction close to the blade tip. They decrease slowly as the vortex impingement moves inward the blade and decrease strongly as the vortex passes above the tip. Finally, the noise directivity pattern is dipolar for the interaction close to or above the blade tip and becomes more and more quadrupolar as the radius of the interaction moves toward the blade root.

Numerical simulation of the transient flow in a pump-turbine during load rejection process with special emphasis on hydraulic acoustic effect

In this study, a load rejection process of a pump-turbine was simulated using the large eddy simulation method with and without considering the hydraulic acoustic effect. In the simulation, the hydraulic acoustic effect was considered via a revised density function which is called weak water compressibility model. Analysis showed that numerical results considering water compressibility and without the consideration both agree well with the experimental data except some local regions. Compared with the experiments, the simulation deviations of the rotational speed were less than 5%, and the local maximum deviations of the fluctuating pressure were no more than 30% during the whole load rejection process. However, the simulation considering the water compressibility has a better behavior than that without the consideration in the predictions of pressure fluctuation. And the performance characteristics with the consideration are systematically lower than those without the consideration. In some operating conditions, the performance characteristics with the consideration are even 30%–50% lower than those obtained without the consideration. Additionally, it is noted that the fluctuation of the axial hydraulic thrust on the runner with consideration is more severe than that without the consideration. Hence, the water compressibility has an obvious influence on the simulation of the load rejection of pump-turbines.

Research on torque fluctuation suppression method of linear motor based on magnetic field orientation control

AbstractIn order to solve the problem of torque fluctuation caused by uneven magnetic field of AC servo linear motor, a novel torque fluctuation suppression method based on magnetic field‐oriented control was proposed for a U‐type three‐phase permanent magnet synchronous linear motor (PMSLM) without iron core. Considering the nonideal magnetic field and the thrust fluctuation of winding, the d‐q coordinate model of PMSLM is established by coordinate transformation. Based on Matlab, PMSLM vector closed‐loop control system model is designed, and the compensation coefficient of torque fluctuation is determined. The prototype platform of PMSLM was built, and the driver with current loop, velocity loop, and position loop is designed. Then the influence of thrust fluctuation before and after suppression on the tracking error of velocity and position is studied. The experimental results show that the suppression of thrust fluctuation can greatly improve the speed fluctuation and position tracking accuracy.

Performance and Effect of Load Mitigation of a Trailing-Edge Flap in a Large-Scale Offshore Wind Turbine

As a result of the large-scale trend of offshore wind turbines, wind shear and turbulent wind conditions cause significant fluctuations of the wind turbine’s torque and thrust, which significantly affect the service life of the wind turbine gearbox and the power output stability. The use of a trailing-edge flap is proposed as a supplement to the pitch control to mitigate the load fluctuations of large-scale offshore wind turbines. A wind turbine rotor model with a trailing-edge flap is established by using the free vortex wake (FVW) model. The effects of the deflection angle of the trailing-edge flap on the load distribution of the blades and wake flow field of the offshore wind turbine are analyzed. The wind turbine load response under the control of the trailing-edge flap is obtained by simulating shear wind and turbulent wind conditions. The results show that a better control effect can be achieved in the high wind speed condition because the average angle of attack of the blade profile is small. The trailing-edge flap significantly changes the load distribution of the blade and the wake field and mitigates the low-frequency torque and thrust fluctuations of the turbine rotor under the action of wind shear and turbulent wind.

Numerical Analysis of Full-Scale Ship Self-Propulsion Performance with Direct Comparison to Statistical Sea Trail Results

Accurate prediction of the self-propulsion performance is one of the most important factors for the energy-efficient design of a ship. In general, the hydrodynamic performance of a full-scale ship could be achieved by model-scale simulation or towing tank tests with extrapolations. With the development of CFD methods and computing power, directly predict ship performance with full-scale CFD is an important approach. In this article, a numerical study on the full-scale self-propulsion performance with propeller operating behind ship at model- and full-scale is presented. The study includes numerical simulations using the RANS method with a double-model and VOF (Volume-of-Fluid) model respectively and scale effect analysis based on overall performance, local flow fields and detailed vortex identification. The verification study on grid convergence is also performed for full-scale simulation with global and local mesh refinements. A series of sea trail tests were performed to collect reliable data for the validation of CFD predictions. The analysis of scale effect on hull-propeller interaction shows that the difference of hull boundary layer and flow separation is the main source of scale effect on ship wake. The results of the fluctuations of propeller thrust and torque along with circulation distribution and local flow field show that the propeller’s loading is significantly higher for model-scale ship. It is suggested that the difference of vortex evolution and interaction is more pronounced and has larger effects on the ship’s powering performance at model-scale than full-scale according to the simulation results. From the study on self-propulsion prediction, it could be concluded that the simplification on free surface treatment does not only affect the wave-making resistance for bare hull but also the propeller performance and propeller induced ship resistance which can be produced up to 5% uncertainty to the power prediction. Roughness is another important factor in full-scale simulation because it has up to an approximately 7% effect on the delivery power. As a result of the validation study, the numerical simulations of full-scale ship self-propulsion shows good agreement with the sea trail data especially for cases that have considered both roughness and free surface effects. This result will largely enhance our confidence to apply full-scale simulation in the prediction of ship’s self-propulsion performance in the future ship designs.

Research on the Method of Suppressing the End Detent Force of Permanent Magnet Linear Synchronous Motor Based on Stepped Double Auxiliary Pole

Permanent magnet linear synchronous motors have the advantages of high thrust density, high acceleration, high speed, and high efficiency, which are widely used in CNC lathes, lithography machines, rail transportation, etc. In high-speed, high-precision servo control systems, detent force fluctuation caused by end effect can easily cause problems such as speed fluctuation, mechanical vibration and electromagnetic noise, which affect the servo performance of permanent magnet linear synchronous motors. Aiming at the detent force fluctuation caused by the end effect of permanent magnet linear synchronous motor, this paper proposes a stepped double auxiliary pole method. The method has a good suppression effect on the end normal force fluctuation and the end thrust fluctuation, which improves the servo performance of the permanent magnet linear synchronous motor in the high-precision servo system. In the traditional methods of suppressing the fluctuation of end detent force, two common methods are using a magnetic isolation aluminum plate and optimizing the auxiliary pole size. The former needs a magnetic isolation aluminum plate to connect the auxiliary pole and the primary mover. Therefore, it needs to add the connection device to connect those three parts. The connection device complicates the auxiliary pole part and increases manufacturing difficulty. The latter does not change the manufacturing process, but in the early design process, the optimum size of the auxiliary needs to be considered. Compared with these two methods, the one proposed in this paper avoids the complex structure of magnetic isolation aluminum plate, the stepped double auxiliary pole is integrated with the primary mover. Moreover, it has a fixed structure with optimum size. Therefore, the method in the paper does not change the manufacturing process, improves the strength of the initial pole structure, and reduces design period. Finally, the finite element analysis by ANSYS was performed to illustrate the correctness and effectiveness of the method.

Pole Optimization and Thrust Ripple Suppression of New Halbach Consequent-Pole PMLSM for Ropeless Elevator Propulsion

Permanent magnet linear synchronous motors (PMLSM) has the advantages of high speed, high thrust density, high power density, high power factor and high reliability. In order to save permanent magnet (PM) materials and reduce magnetic leakage, a new type of PMLSM with Halbach consequent-pole (HCP) structure is presented, which has great potential for application to the ropeless elevator system. By using extensive finite element analysis (FEA), the electromagnetic properties of the proposed HCP-PMLSM, including magnetic field, back electromagnetic force (back-EMF), thrust force and cogging force are simulated and compared with the consequent pole PMLSM (CP-PMLSM) and surface-mounted pole PMLSM (SP-PMLSM). The comparison results show that the proposed HCP configuration can reduce substantial PM material and increase the air-gap magnetic field effectively. Then, the influence trend of HCP parameters such as pole thickness, pole width ratio, auxiliary PM width and magnetism angle, are studied and analyzed for evaluating the output performance in HCP-PMLSM. On this basis, Response surface method (RSM) is employed to optimize the HCP parameters with the target of maximum average thrust, minimum thrust ripple, and highest PM utilization. Furthermore, a double-sided pole shift method was proposed to significantly suppress the thrust fluctuation of HCP-PMLSM. Lastly, experimental results are provided to verify the investigation.

Multi-Objective Optimization of Double Primary Tubular Permanent Magnet Synchronous Linear Motor in Wide Temperature Range Environment Based on Pareto Front Method

In order to improve the thrust density of the electric actuator in aircraft, a double primary tubular permanent magnet synchronous linear motor is designed. By establishing the magnetic circuit model, the air gap magnetic density and thrust characteristics of outer and inner primary motors are analyzed. Considering that it works in the wide temperature range environment, a multi-objective optimization of motor is carried out. The surrogate model established by neural network is used to simplify the mathematical model of the motor. In order to improve the average thrust, restrain the thrust fluctuation and reduce the difference of output thrust under different environment temperatures, the Pareto front method is used to determine the target range of the optimal parameters, and gradually strengthen conditions, so as to obtain the optimal scheme of motor design.

Joint Computational-Experimental Investigation of Harmonically Pitching Airfoil Aerodynamics in Uniform-Shear Approach Flow

This work explores the aerodynamics of an airfoil oscillating in a uniform-shear flow at chord Reynolds number of approximately using complementary two-dimensional Navier–Stokes computations and direct force measurements. A NACA-0012 airfoil is pitched harmonically about its quarter-chord, with 2° amplitude and reduced frequency up to 12, in positive-shear approach flow for nondimensional shear rates in the range 0.0–1.0. The results show that the wake of the airfoil exhibits symmetry breaking that leads to a deflected wake toward the high-speed side as the reduced frequency increases beyond the reduced frequency for an aligned vortex street. The frequency at which the vortex alignment takes place is nearly independent of nondimensional shear rate. Interestingly, the presence of shear seems to have little or no effect on the average drag/thrust and root mean square (rms) of the lift and thrust fluctuation, whereas a prominent influence is seen on the average lift. The latter switches sign from negative to positive at a reduced frequency of approximately 3, and it increases in magnitude with both increasing nondimensional shear rate and reduced frequency.

Coupled Fluid-Structure Interaction Modelling of Loads Variation and Fatigue Life of a Full-Scale Tidal Turbine under the Effect of Velocity Profile

Velocity profiles in tidal channels cause cyclic oscillations in hydrodynamic loads due to the dependence of relative velocity on angular position, which can lead to fatigue damage. Therefore, the effect of velocity profile on the load variation and fatigue life of large-scale tidal turbines is quantified here. This is accomplished using Fluid Structure Interaction (FSI) simulations created using the ANSYS Workbench software, which couples the fluid solver ANSYS CFX to the structural solver ANSYS transient structural. While these load oscillations only minimally impact power and thrust fluctuation for rotors, they can significantly impact the load variations on individual rotor blades. To evaluate these loadings, a tidal turbine within a channel with a representative flow that follows a 1/7th power velocity profile and an onset turbulence intensity of 5% is simulated. This velocity profile increases the thrust coefficient variation from mean cycle value of an individual blade from 2.8% to 9% and the variation in flap wise bending moment coefficient is increased from 4.9% to 19%. Similarly, the variation from the mean cycle value for blade deformation and stress of 2.5% and 2.8% increased to 9.8% and 10.3%, respectively. Due to the effect of velocity profile, the mean stress is decreased, whereas, the range and variation of stress are considerably increased.

Thrust Control of a Double-Sided Linear Induction Motor With Segmented Power Supply

Due to the dynamic longitudinal end effect, the motor flux is lagging and the thrust is fluctuated in a long-primary double-sided linear induction motor (DSLIM). In this paper, a thrust fluctuation reduction method is proposed for the DSLIM with segmented power supply. The mathematical model of the DSLIM module considering the dynamic longitudinal end effect is established first, and a new field orientation is presented by solving variation of the motor flux when the secondary enters or leaves a motor module. Then, the thrust expression is deduced based on the new field orientation, and a coefficient is proposed to present the thrust bias in a single module. The restraint of the thrust bias is implemented by increasing or changing the slip frequency according to the orientation in the movement. The proposed coefficient and the thrust control method are validated by simulation and experiment results.

Research on the Thrust Characteristics and Temperature Rise of Slot-less Tubular Linear Motor for Active Vehicle Suspension

This paper presents a Slot-less Tubular Permanent Magnet Linear Motor (ST-PMLM), which does not have the cogging structure in the stator. Meanwhile, its lateral stator core doesn’t split, so the motor only has longitudinal edge effect. Since the ST-PMLM is supposed to be used as the active damper for vehicle suspension system, this paper focus on two aspects: increasing the output thrust and restraining the thrust fluctuation of the motor. Firstly, the equivalent magnetic circuit model of the ST-PMLM is established. The influences of structural parameters, including the thickness of the magnetic pole, the length of the air gap, the thickness of primary iron core and the thickness of primary winding, on the air gap flux density and the output thrust are analyzed. Then, the distribution of the magnetic field at the end of the primary iron core is observed. Length compensation in the end of primary iron core is adopted in order to reduce the thrust fluctuation. Finally, the prototype of ST-PMLM is developed and the experiment test bench is built. Based on the no-load test of the prototype, the effectiveness of the primary core length compensation in suppressing end effects and inhibiting fluctuations are verified.

Computational Investigation on Unsteady Loads of High-Speed Rigid Coaxial Rotor with High-Efficient Trim Model

A computational fluid dynamics method is built to study the unsteady aerodynamic loads of a high-speed rigid coaxial rotor model, taking account of lift offset (LOS). The flowfield is simulated by solving Reynolds Averaged Navier–Stokes equations, and moving overset mesh is adopted to include blade motions. A high-efficient trim model for coaxial rotor is developed, where the “delta method” is implemented. Performance of Harrington rotor-1 is calculated for validation. Forward flight cases in three advance ratios are conducted. Results indicate that the temporal thrusts of coaxial rotor at low advance ratio share some fluctuations similar to hover state. In forward flight, the impulsive thrust fluctuations caused by blade-meeting are obviously exhibited around 270° for upper blades, and the strengths increase with the increase of LOS and advance ratio. At higher advance ratios, the blade thrusts of the upper and lower rotors tend to be the same. At the advance ratio of 0.6, two new kinds of Blade–vortex interaction (BVI) are captured. One is the parallel BVI caused by the root vortex and the other is the complex interaction among the tip vortex, root vortex and the rear blade.

Electron spins coupling of coconut shell activated nanocarbons in solid propellant on improving to the thrust stability and specific impulses

The role of activated coconut carbon in the combustion of solid propellant composed by ammonium perchlorate, aluminum, and hydroxyl terminated polybutadiene on improving to the thrust stability and specific impulses have been studied experimentally. Nanocarbons derived from coconut shells produces carbon compounds which dictates electron spin coupling sp2-sp3 when there is an increase in temperature until combustion occurs. Strong nanocarbon bonds require high temperatures and pressures to release bonds and bind oxygen. The results show that activated carbon plays a role in controlling the propellant combustion reaction and reduces thrust fluctuations. But the particle size plays a very decisive role. In micro size the activated carbon becomes a thermal load so thrust power decrease. At nano size the very wide contact area of the activated carbon accelerates the decomposition process to absorb large amounts of energy. While carbon nano as capacitors active side control the combustion reaction so that the exothermic process takes place more gradual and smoother that prolong burning time. As a result, there is an increase in heat flow that amplifies thrust stability and specific impulses.