A hybrid linear actuator based on screw clamp operation principle: Design and experimental verification

This paper presents a hybrid linear actuator using screw clamp operation principle. The actuator mainly consists of a hollow electromagnetic torque motor located between two clamping nuts, two hollow cylindrical shaped piezoelectric stacks symmetrically configured at two ends of the actuator and a feed-screw (also considered as the mover of the actuator) assembled throughout all the parts. The torque motor is symmetrically connected to two clamping nuts via two torsion coupling springs located at either end of the motor spindle. Two piezoelectric stacks can work independently to propel the opposing loads, which effectively take advantage of the anti-compression and non-tensile characteristics of piezoelectric element. The special feature of the actuator is the screw clamp mechanism, the operation of which involves intermittent rotation of two nuts (driven by the torque motor) on a feed-screw to achieve the bi-direction piezoelectric motion accumulation. Furthermore, the application of feed-screw could decrease the actuator’s sensitivity to wear, in order to realize a rigid self-locking and thus ensure the actuator’s holding capacity. A prototype was fabricated and the experimental results show that the no-load speed, maximum thrust, and peak power of the actuator were 20 mm/s, 280 N, and 1.54 W, respectively.

Numerical Analysis of the Effect of Flexibility on the Propulsive Performance of a Heaving Hydrofoil Undergoing Sinusoidal and Non-Sinusoidal Motions

Numerical simulations of fluid-structure interaction (FSI) on an elastic foil heaving with constant amplitude in freestream flow are carried out at a low Reynolds number of 20,000. The commercial software STAR-CCM+ is employed to solve the flow field and the large-scale passive deformation of the structure. The results show that introducing a certain degree of flexibility significantly improves the thrust and efficiency of the foil. For each Strouhal number St considered, an optimal flexibility exists for thrust; however, the propulsive efficiency keeps increasing with the increase in flexibility. The visualisation of the vorticity fields elucidates the improvement of the propulsive characteristics by flexibility. Furthermore, the mechanism of thrust generation is discussed by comparing the time-varying thrust coefficient and vortex structure in the wake for both rigid and elastic foils. Finally, in addition to sinusoidal motions, we also consider the effect of non-sinusoidal trajectories defined by flattening parameter S on the propulsive characteristics for both rigid and elastic foils. The non-sinusoidal trajectories defined by S=2 are associated with the maximum thrust, and the highest values of propulsive efficiency are obtained with S=0.5 among the cases considered in this work.

Mid-fidelity simulations and comparisons of five techniques for axial induction control of a wind turbine

As wind turbines are more frequently placed in arrays, the need to understand and mitigate problems arising from their wakes has increased. When downstream turbines are in the wakes of upstream ones, the downstream turbines produce less power, require more maintenance, and have shorter lifetimes. One wake mitigation technique is known as axial induction control (AIC) and it involves derating (operating suboptimally) upstream turbines such that more energy remains in their wakes for downstream turbines to harvest. While there has been considerable research on this technique, much of it has suffered from a misunderstanding of the most important parameters in optimizing AIC. As such, the research has been largely inconclusive. Herein, we seek to rectify several perceived shortcomings of previous work by using mid-fidelity simulations to compare five different techniques for AIC at three different derate percentages against a baseline case and examining the recovery of the wake. We find that only the case with the lowest derate, 10 %, and using maximum thrust exceeds the baseline when estimating the combined power of the simulated turbine and a virtual turbine five diameters downstream and that it produced 10 % more power. Furthermore, these results help to validate previous work that concluded that the excess energy that is in the wake of a derated turbine will be at the edges of the wake unless the wake can sufficiently recover before the next downstream turbine. Finally, all together this suggests that the precise combination of derate percentage and the method used to derate turbines (i.e., the precise combination of pitch and torque controls), as well as the spacing and arrangement of turbines, must all be considered when optimizing AIC, and that substantial power gains may be possible.

A New 3D Shaping Method for Low-Thrust Trajectories between Non-Intersect Orbits

This paper proposes a new shape-based method in spherical coordinates to solve three-dimensional rendezvous problems. Compared with the existing shape-based methods, the proposed method does not need parameter optimization. Moreover, it improves the flexibility of orbit fitting, greatly reduces the velocity increment and maximum thrust acceleration, and ensures the orbit safety to a certain extent. The shaping function can provide the initial estimate for numerical trajectory optimization and improve the convergence rate in a certain range when combined with the normalization method. The superiority of the proposed method over the existing methods is demonstrated by two numerical examples. Its effectiveness at initial estimation generation in the indirect optimization of a low-thrust trajectory is demonstrated by the third example.

Integrated study on the comprehensive magnetic-field configuration performance in the 150 kW superconducting magnetoplasmadynamic thruster

Higher magnetic fields are always favoured in the magnetoplasmadynamic thruster (MPDT) due to its superior control of the plasma profile and acceleration process. This paper introduces the world's first integrated study on the 150 kW level AF-MPDT equipped with a superconductive coil. A completely new way of using superconducting magnet technology to confine plasma with high energy and extremely high temperatures is proposed. Using the PIC method of microscopic particle simulation, the plasma magnetic nozzle effect and performance of the MPDT under different magnetic-field conditions were studied. The integrated experiment used demonstrated that, in conjunction with the superconducting coil, greater homogeneity and a stronger magnetic field not only caused more even cathode ablation and improved its lifespan but also improved the performance of the MPDT (maximum thrust was 4 N at 150 kW, 0.56 T). Maximum thrust efficiency reached 76.6% and the specific impulse reached 5714 s.

Формування областей основних параметрів модифікацій транспортного літака за умовами його базування

Along with the unique flight performance indicators and economic indicators that characterize heavy transport aircraft, the priority is also to ensure the basing for their heavier modifications at the airfields declared for the base aircraft. This problem arises at the very early stage of the modification creation, when its main parameters such as the gross mass at takeoff and thrust-to-weight ratio are formed. This is due to the very essence of creating a modification ‑ increasing its carrying capacity (which leads to increase in the gross mass at takeoff and flight range ) with an increased payload by increasing the mass of fuel on board. Ensuring growth of flight and hour , performance underlies the creation of all modifications of transport category aircraft. For heavier modifications than their base aircraft, it is further complicated by the fact that the base models are based on the runways of the second and first class airfields, which creates an insurmountable limitation on the available runway length. The second limitation is the value of the decision-making speed during takeoff, in case of failure of the critical engine during the takeoff run, which predetermines the required length of the runway. Since the takeoff masses of aircraft modifications of this type continue to increase, the problem of their basing on the runways of existing airfields arises by forming the takeoff weight relationship – decision-making speed in case of a critical engine failure ‑ thrust-to-weight ratio, providing the basing of a heavier modification at the airfield declared for the base aircraft . To implement this condition, a model for determining the speed , in which a safe termination of the takeoff run is possible in the event of a critical engine failure. The resulting model allows to take into account a number of restrictions due to the properties of heavy aircraft, such as the minimum and maximum thrust of the cruise engines, which makes it possible to make reasonable recommendations in the operating rules for aircraft of this type. Taking into account the expressions obtained to determine , a model has been formed to determine and assess the required thrust-to-weight ratio of a heavier modification by condition for modifications with a takeoff weight of more than 300 tons. It has been established that the required relative thrust-to-weight ratio should be within . Defining parameters such as , and is the basis for the implementation of other modification changes in the heavy transport aircraft.

PENGARUH KEMIRINGAN POROS BALING-BALING TERHADAP KECEPATAN PERAHU KETINTING

Ketinting boat in operation using propeller with engine located on deck. This position resulted in the propeller dipping by making a certain angle, in addition the depth of the propeller also overlapped the speed of the ship.This phenomenon is something very important to be examined with the aim of obtaining maximum speed in relation to the angle of tilt of the propeller and the amount of maximum thrust required.The method used is an experimental method in which the model of the ship and propeller are made according to the desired scale, and so conduct testing on the towing tank.The test result obtained is a slope that creates the optimal speed of the ketinting boat is at a slope of 18° with a speed of V = 5.05 knots and a maximum thrust of PT = 13.15 kW.

A Compact Linear Ultrasonic Motor Composed by Double Flexural Vibrator

A minimized linear ultrasonic motor was proposed, and two flexural bimorph vibrators were utilized to form its stator. The construction of the linear ultrasonic motor and its operation principle was introduced. Two working modes with the same local deformation distribution were chosen on the basis of Finite Element Analysis (FEA). To obtain its optimized structural parameters, sensitivities on frequency difference were calculated, and a way of decreasing the frequency difference of two working modes was introduced. A prototype of the optimized model was made. The modal testing of the stator and its performance evaluation was conducted. The modal testing results were in good agreement with that of the simulation. The maximum speed of the prototype is 245 mm/s, and its maximum thrust is 1.6 N.

Effect of Twist Drill Geometry and Drilling Parameters on Hole Quality in Single-Shot Drilling of CFRP/Al7075-T6 Composite Stack

Drilling two different materials in a layer, or stack-up, is being practiced widely in the aerospace industry to minimize critical dimension mismatch and error in the subsequent assembly process, but the compatibility of the drill to compensate the widely differing properties of composite is still a major challenge to the industry. In this paper, the effect of customized twist drill geometry and drilling parameters are being investigated based on the thrust force signature generated during the drilling of CFRP/Al7075-T6. Based on ANOVA, it is found that the maximum thrust force for both CFRP and Al7075-T6 are highly dependent on the feed rate. Through the analysis of maximum thrust force, supported by hole diameter error, hole surface roughness, and chip formation, it is found that the optimum tool parameters selection includes a helix angle of 30°, primary clearance angle of 6°, point angle of 130°, chisel edge angle of 30°, speed of 2600 rev/min and feed rate of 0.05 mm/rev. The optimum parameters obtained in this study are benchmarked against existing industry practice of the capability to produce higher hole quality and efficiency, which is set at 2600 rev/min for speed and 0.1 mm/rev for feed rate.