Forward Thrust Research Articles

Measurement of Impulsive Thrust from a Closed Radio-Frequency Cavity in Vacuum

A vacuum test campaign evaluating the impulsive thrust performance of a tapered radio-frequency test article excited in the transverse magnitude 212 mode at 1937 MHz has been completed. The test campaign consisted of a forward thrust phase and reverse thrust phase at less than vacuum with power scans at 40, 60, and 80 W. The test campaign included a null thrust test effort to identify any mundane sources of impulsive thrust; however, none were identified. Thrust data from forward, reverse, and null suggested that the system was consistently performing with a thrust-to-power ratio of .

Some Details of Jet Engine Thrust

This article throws light on details of jet engine thrust. The momentum flux of the engine exiting flow is greater than that which entered, brought about by the addition of the energy input from combusted fuel, and giving rise to engine thrust. Thrust arises from pressure and frictional forces on these surfaces, e.g., blades, vanes, endwalls, ducts, etc. This interior force view of thrust is easy to visualize but quite another thing to actually measure. In doing research on secondary flow in gas turbine passages, researchers have measured both steady-state momentum changes and surface forces, in the much simpler case of a turbine blade cascade. The thrust values for each component in the Rolls-Royce single spool engine have been shown in this paper. It has been noted that from the compressor, gas path flow enters the engine case diffuser, where a pressure gain produces another component of forward thrust of 2,186 lbt. Newton’s second law of motion allows us to examine engine component behavior that exhibits both forward and rearward propelling forces, which results in the net thrust our airline passengers have purchased.

Lift forces induced by phase lag between the vortex sheddings from two tandem bluff bodies

Flow-induced forces on two tandem circular cylinders of identical diameter are numerically studied at a Reynolds number of 200. The cylinder center-to-center spacing ratio is varied from 2 to 9. We focus on fluctuating (rms) lift coefficient of the upstream cylinder, vortex dynamics in the gap between cylinders, and phase lag between vortex shedding from the two cylinders. The phase lag was a linear function of the spacing ratio as known in the literature; but it is, as proved here, indeed a nonlinear function of the spacing ratio, Strouhal number and convection velocity of vortices in the gap between the cylinders. The shedding from the two cylinders turns out to be inphase and antiphase alternately as the spacing ratio increases. We unearth that both phase lag and spacing ratio influence the fluctuating lift of the upstream cylinder. With an increase in the spacing ratio, while the influence of the spacing ratio on fluctuating lift diminishes rapidly in an overdamped manner, that of the phase lag makes the fluctuating lift variation underdamped sinusoidal. The inphase and antiphase flows correspond to a local maximum and a local minimum, respectively, in the fluctuating lift variation. An equation is deduced, showing the relationship between the fluctuating lift, spacing ratio, and phase lag. The physics behind the damped-sinusoidal variation in the fluctuating lift is discussed. The investigation directs that the streamwise separation between two tandem wings of airplanes/submarines should be taken into account or optimized. It would also be interesting to see whether fish exploits phase-lag-induced lift to enhance its forward thrust.

Adverse Events During Apheresis Procedures: Audit at a Tertiary Hospital.

Apheretic platelets are better quality blood components which reduce donor exposure and chances of TTIs to transfusion recipients when compared to the whole blood derived components. Though safe, these apheretic donations are associated with donor adverse events. We evaluated the incidence of such adverse events associated with the modern apheresis procedures that would provide an insight as well as help formulating preventive steps to avoid frequent occurrences of such events. This prospective audit-based observational study was conducted over 1year. Donors for plateletpheresis were selected as per the standard operating procedure of the Apheresis Lab. The apheresis procedures were done on the MCS+(Haemonetics Corp.), Trima Accel (Terumo BCT) and COM.TEC (Fresenius Kabi AG). 1740 apheresis procedures were performed, out of which 1708 were plateletpheresis and 32 therapeutic plasma exchange (TPE) procedures for 7 patients. A total of 102 adverse events were noted; of which, 80 (78.43%) events were associated with donors, 15 (14.71%) were owed to equipment related problems and 7 (6.86%) were technical aberrations. All the events associated with donors were mild. No adverse events were reported with any of the 32 TPEs. Apheresis procedures are associated with adverse events which can be reduced by meticulous donor-vigilance, superior training modules for the technical personnel and continued supervision of experienced transfusion medicine specialists. Continued efforts towards making the donor's experience with apheresis more pleasant give a forward thrust to the noble vision of preparing a voluntary apheresis donor pool in India.

Benchmarking numerical models of brittle thrust wedges

We report quantitative results from three brittle thrust wedge experiments, comparing numerical results directly with each other and with corresponding analogue results. We first test whether the participating codes reproduce predictions from analytical critical taper theory. Eleven codes pass the stable wedge test, showing negligible internal deformation and maintaining the initial surface slope upon horizontal translation over a frictional interface. Eight codes participated in the unstable wedge test that examines the evolution of a wedge by thrust formation from a subcritical state to the critical taper geometry. The critical taper is recovered, but the models show two deformation modes characterised by either mainly forward dipping thrusts or a series of thrust pop-ups. We speculate that the two modes are caused by differences in effective basal boundary friction related to different algorithms for modelling boundary friction. The third experiment examines stacking of forward thrusts that are translated upward along a backward thrust. The results of the seven codes that run this experiment show variability in deformation style, number of thrusts, thrust dip angles and surface slope. Overall, our experiments show that numerical models run with different numerical techniques can successfully simulate laboratory brittle thrust wedge models at the cm-scale. In more detail, however, we find that it is challenging to reproduce sandbox-type setups numerically, because of frictional boundary conditions and velocity discontinuities. We recommend that future numerical-analogue comparisons use simple boundary conditions and that the numerical Earth Science community defines a plasticity test to resolve the variability in model shear zones.

Milton Now: Alternative Approaches and Contexts. Edited by Catharine Gray and Erin Murphy. New York: Palgrave Macmillan, 2014. Pp. ix+284.

<i>Milton Now: Alternative Approaches and Contexts</i>. Edited by Catharine Gray and Erin Murphy. New York: Palgrave Macmillan, 2014. Pp. ix+284.

Resistance and Seakeeping Investigation for Optimization of the Floating Hull of Wave Glider

Wave glider is the first unmanned autonomous marine robot to use only the ocean’s endless supply of wave energy for propulsion. Wave glider comprises fin system, tether and float which harvest all of its energy from waves and sun to produce forward thrust. As a consequence of the lack of design information and data for the wave glider, the main aim of the study is using computational fluid dynamics (CFD) to present a method to predict calm water resistance for the floating hull through calculations of 3 different hull forms using the same mesh generation under the same conditions. Calculations are carried out using 3 different mesh sizes for Froude number in the range of 0.10 to 0.40 and compared for accuracy of the solution parameters. Wigley parabolic hull, high speed round bilge form (NPL) and Series 60 have been comparatively investigated in order to estimate the hydrodynamics performance of the hull. The linear seakeeping analysis, coupled heave and pitch motions, roll motion, in irregular waves, with one parameter Bretschneider and JONSWAP spectra. Numerical computations have been performed for motion response predictions of the three hulls which cover wave angles from 0? to 180? at 45? intervals for six different forward speeds from 0 to 4.304 knots using Maxsurf Motion software. The close agreement between the numerical predictions shows the importance of CFD applications in estimating the hydrodynamics performance to design the floating hull and the numerical method is useful in glider design. The fine grid is fit to the calculation and shows the most appropriate results because convergent results are obtained as the mesh size decrease so the fine grid is the one which will be applied for the other hulls. Also it can be observed that the added resistance and the RAOs for NPL hull are less than the other hulls. Therefore from the comparisons, the NPL hull is the optimum hull compared to the other hulls from the resistance and seakeeping point of view.

Bio-harmonized control experiments of a carangiform robotic fish underwater vehicle

This paper presents experimental implementation and comparison of three different control schemes of a bio-inspired robotic fish underwater vehicle. The dynamics model is obtained by unifying conventional rigid body dynamics and bio-fluid dynamics of a carangiform fish swimming given by Lighthill’s(LH) slender body theory. It proposes an inclusive mathematical design for better control and energy efficient path travel for the robotic fish. The system is modeled as an two-link robot manipulator (caudal tail) with a mobile base (head). This forward thrust drives the robotic fish head represented by a combined non-linear equation of motion in earth fixed frame. We develop and compare the dynamic motion closed loop control strategy of the bio-harmonized robotic fish based on three different non-linear control schemes using CTM (Computed Torque Method), FF (Feed-Forward) controllers both with dynamic PD compensation and finally a proposed combination of CTM with FF. An inverse dynamic control method based on non-linear state function model including hydrodynamics is proposed to improve tracking performance. CTM control generates a feedback loop for linearization and decoupling robot dynamic model with a shorter response time, while a dynamic PD compensation in the FF path is employed by FF scheme through the desired trajectories. FF model-based strategy results in an improved tracking and shorter route to travel between two points. Overall results indicate that performances of the proposed control schemes based on the inverse dynamic model are comparable and useful for robotic fish motion tracking in fluid environment.

Characterization of a Dipeptidyl Peptidase and its Role in Motility of Rat Epididymal Maturing Spermatozoa

Dipeptidyl peptidase is a highly glycosylated serine protease with a broad tissue distribution. In the present study, we investigated the alteration of the activity of dipeptidyl peptidase of spermatozoa at different maturational levels in rat epididymis and the apparent correlation of enzyme activity with sperm forward motility. The maximum activity of the enzyme was observed in spermatozoa from the corpus or middle part of the epididymis. This glycyl-proline ρ-nitroanilide hydrolyzing enzyme of epididymal spermatozoa showed significant similarities with biochemical properties of dipeptidyl peptidase (DPP) type IV. Sitagliptin, a specific inhibitor of DPPIV, leads to a more effective and complete inhibition of the peptidase in spermatozoa collected from different parts of epididymis. The complete inhibition by Hg2+ and partial insensitivity toward Cd2+ also confirmed the similarities with ion sensitivity of DPPIV. Treatment of mature cauda spermatozoa with sitagliptin (1 mM) showed a significant inhibition in forward thrust in motility. This result suggests that sperm forward motility may be regulated by DPPIV-like enzyme of maturing epididymal spermatozoa.

CFD Study of an Annular-Ducted Fan Lift System for VTOL Aircraft

The present study aimed at assessing a novel annular-ducted fan lift system for VTOL aircraft through computational fluid dynamics (CFD) simulations. The power and lift efficiency of the lift fan system in hover mode, the lift and drag in transition mode, the drag and flight speed of the aircraft in cruise mode and the pneumatic coupling of the tip turbine and jet exhaust were studied. The results show that the annular-ducted fan lift system can have higher lift efficiency compared to the rotor of the Apache helicopter; the smooth transition from vertical takeoff to cruise flight needs some extra forward thrust to overcome a low peak of drag; the aircraft with the lift fan system enclosed during cruise flight theoretically may fly faster than helicopters and tiltrotors based on aerodynamic drag prediction, due to the elimination of rotor drag and compressibility effects on the rotor blade tips; and pneumatic coupling of the tip turbine and jet exhaust of a 300 m/s velocity can provide enough moment to spin the lift fan. The CFD results provide insight for future experimental study of the annular-ducted lift fan VTOL aircraft.

Multi-jet propulsion organized by clonal development in a colonial siphonophore

Physonect siphonophores are colonial cnidarians that are pervasive predators in many neritic and oceanic ecosystems. Physonects employ multiple, clonal medusan individuals, termed nectophores, to propel an aggregate colony. Here we show that developmental differences between clonal nectophores of the physonect Nanomia bijuga produce a division of labour in thrust and torque production that controls direction and magnitude of whole-colony swimming. Although smaller and less powerful, the position of young nectophores near the apex of the nectosome allows them to dominate torque production for turning, whereas older, larger and more powerful individuals near the base of the nectosome contribute predominantly to forward thrust production. The patterns we describe offer insight into the biomechanical success of an ecologically important and widespread colonial animal group, but, more broadly, provide basic physical understanding of a natural solution to multi-engine organization that may contribute to the expanding field of underwater-distributed propulsion vehicle design.

Reflections: Neurology And The Humanities. Silvia's blessing.

The first thing I noticed was Silvia's rocking. Back and forth, back and forth, the faux leather of the chair squeaking with each forward thrust of her diminutive, skinny frame. Then her huge sunglasses, much too big for her face, framing long black hair. And her teeth—white and protruding, but too large for her slender face and small mouth. She looked to be 12 or 13, but I wasn't sure.

Bat flight

Bat flight

Comparative Investigation of an Automated Oceanic Wave Surface Glider Robot Influence on Resistance Prediction Using CFD Method

The wave glider is composed of two parts: the float is roughly the size and shape of a surfboard that contains all the instrumentation needed for scientific experiments; the sub has wings and hangs 6 meters below on an umbilical tether. This difference allows wave energy to be harvested to produce forward thrust. According to the lake of design information and data for the wave glider, the main aim of the study is using computational fluid dynamics (CFD) to present a method to predict calm water resistance for the floating part of the wave glider (the hull). Wigley parabolic hull and high speed round bilge form (NPL) have been investigated in order to estimate the hydrodynamic performances of the hull using CFD software fluent. Wave glider is designed with slender hull shapes in order to decrease the wave making resistance of the ship.In this paper a method is evaluated by comparing the numerical predictions for wigley and NPL forms (2m) using the same mesh generation method under the same conditions to design the hull. Calculations for total calm water resistance are carried out using three different mesh sizes for Froude numbers in the range of 0.10 to 0.40 and compared for accuracy of the solution parameters. The close agreement between the numerical predictions shows the importance of CFD applications in estimating the hydrodynamics performance to design the floating hull and the numerical method is useful in glider design. This means that the method discussed in this paper can be used for the resistance calculation of some hulls like the float of the glider.

Separability of drag and thrust in undulatory animals and machines.

For nearly a century, researchers have tried to understand the swimming of aquatic animals in terms of a balance between the forward thrust from swimming movements and drag on the body. Prior approaches have failed to provide a separation of these two forces for undulatory swimmers such as lamprey and eels, where most parts of the body are simultaneously generating drag and thrust. We nonetheless show that this separation is possible, and delineate its fundamental basis in undulatory swimmers. Our approach unifies a vast diversity of undulatory aquatic animals (anguilliform, sub-carangiform, gymnotiform, bal-istiform, rajiform) and provides design principles for highly agile bioinspired underwater vehicles. This approach has practical utility within biology as well as engineering. It is a predictive tool for use in understanding the role of the mechanics of movement in the evolutionary emergence of morphological features relating to locomotion. For example, we demonstrate that the drag-thrust separation framework helps to predict the observed height of the ribbon fin of electric knifefish, a diverse group of neotropical fish which are an important model system in sensory neurobiology. We also show how drag-thrust separation leads to models that can predict the swimming velocity of an organism or a robotic vehicle.

Experiments with actively pitch-controlled and spring-loaded oscillating foils

Experiments with a horizontal foil undergoing harmonic heave motion while traveling at a steady forward speed were performed. The objective was to study different pitch strategies for maximizing the forward thrust. An oscillating foil can replace the rotating propeller as ship propulsor, or the foil can be mounted to the ship in order to create auxiliary thrust in waves. The latter was the motivation behind the experiments presented in this paper. An actively pitch-controlled foil was tested, where two vanes measured the inflow angle to the foil and a motor pitched the foil based on a specified control algorithm. The effect of varying the parameters in the pitch-control algorithm was tested in practice and is discussed here. A spring-loaded foil was also tested. The pitch motion of the spring-loaded foil is shown to produce higher thrust than that of the actively pitch-controlled foil tested. It was also found that the efficiency with spring-loaded pitch motion was higher than the efficiency with forced harmonic pitch motion leading the heave motion with a 90° phase angle.

Kinematics of swimming and thrust production during powerstroking bouts of the swim frenzy in green turtle hatchlings.

ABSTRACTHatchling sea turtles emerge from nests, crawl down the beach and enter the sea where they typically enter a stereotypical hyperactive swimming frenzy. During this swim the front flippers are moved up and down in a flapping motion and are the primary source of thrust production. I used high-speed video linked with simultaneous measurement of thrust production in tethered hatchlings, along with high-speed video of free swimming hatchlings swimming at different water speeds in a swim flume to investigate the links between kinematics of front flipper movement, thrust production and swimming speed. In particular I tested the hypotheses that (1) increased swimming speed is achieved through an increased stroke rate; (2) force produced per stroke is proportional to stroke amplitude, (3) that forward thrust is produced during both the down and up phases of stroking; and (4) that peak thrust is produced towards the end of the downstroke cycle. Front flipper stroke rate was independent of water speed refuting the hypothesis that swimming speed is increased by increasing stroke rate. Instead differences in swimming speed were caused by a combination of varying flipper amplitude and the proportion of time spent powerstroking. Peak thrust produced per stroke varied within and between bouts of powerstroking, and these peaks in thrust were correlated with both flipper amplitude and flipper angular momentum during the downstroke supporting the hypothesis that stroke force is a function of stroke amplitude. Two distinct thrust production patterns were identified, monophasic in which a single peak in thrust was recorded during the later stages of the downstroke, and biphasic in which a small peak in thrust was recorded at the very end of the upstroke and this followed by a large peak in thrust during the later stages of the downstroke. The biphasic cycle occurs in ∼20% of hatchlings when they first started swimming, but disappeared after one to two hours of swimming. The hypothesis that forward thrust is produced during both the up and down stroke was only supported relatively rarely in hatchlings that exhibited the diphasic cycle, the majority of time forward thrust was only produced during the downstroke phase. The hypothesis that peak forward thrust is produced during the end of the downstroke was supported in both the monophasic and biphasic thrust producing stroke cycles.

Optic Flow Regulation in Unsteady Environments: A Tethered MAV Achieves Terrain Following and Targeted Landing Over a Moving Platform

The present study deals with the risky and daunting tasks of flying and landing in non-stationary environments. Using a two Degree-Of-Freedom (DOF) tethered micro-air vehicle (MAV), we show the benefits of an autopilot dealing with a variable - the flow - which depends directly on two relative variables, the groundspeed and the groundheight. The micro-helicopter was shown to follow the ups and downs of a rotating platform that was also oscillated vertically. At no time did the MAV know in terms of ground height whether it was approaching the moving ground or whether the ground itself was rising to it dangerously. Nor did it know whether its current groundspeed was caused only by its forward thrust or whether it was partly due to the ground moving backwards or forwards. Furthermore, the MAV was shown to land safely on a platform set into motion along two directions, vertical and horizontal. This paper extends to non-stationary environments a former approach that introduced the principle of optic flow regulation for altitude control. Whereas in the former approach no requirement was set on the robot's landing target, the target's elevation angle was used here in a second feedback loop that gradually altered the robot's pitch and therefore its airspeed, leading to smooth landing in the vicinity of the target. Whether dealing with terrain following or landing, the MAV followed followed appropriately the unpredictable changes in the environment although it had no explicit knowledge of groundheight and groundspeed. The MAV did not make use of any rangefinders or velocimeters and was simply equipped with a 2-gram vision-based autopilot.

English

This paper presents the simulation of flapping-wing unmanned aerial vehicle model using X-plane and Matlab/ Simulink. The flapping-wing ornithopter model (i.e. an aircraft that flies by flapping its wings) has been developed in plane maker software and executed in the X-plane environment. The key idea of flapping-wing mechanism in X-plane software is by varying its dihedral angle sinusoidally. This sinusoidally varying dihedral angle of wing creates upward and downward stroke moments inturn this creates a lift and a forward thrust for flying the flapping-wing model. Here pitch, roll, yaw and throttle (flapping rate) is fed as reference input through the user datagram protocol (UDP) port. The difference between the reference inputs, the simulated outputs are again fed back to simulator through UDP port and the gains are observed for the responses of flapping-wing unmanned aerial vehicle in Matlab/Simulink environment. Here various gains are used to monitor the optimized flying of flapping-wing model. Defence Science Journal, Vol. 64, No. 4, July 2014, pp.327-331, DOI:http://dx.doi.org/10.14429/dsj.64.4933

Research on Cotton Stalk Harvester Based on Double Roller Type

This paper studies the development status of domestic and foreign cotton stalk harvester. On this basis, a double roller cotton stalk Harvester is designed, which is suitable for small plots. It can pull out the entire cotton stalk through two pairs of reverse rotation of the roller and the forward thrust of tractor. In order to increase the friction force between the roller and the cotton stalk, the two pairs of roller axes are designed with a certain angle and the surface is designed into a rugged, spiral into distribution, which can adapt to the different diameters of cotton stalk harvesting.