Total Thrust Research Articles

Direct Method for Rapid Prototyping of Near-Optimal Aircraft Trajectories

Adirectmethod fora real-timegenerationofnear-optimal spatialtrajectoriesofshort-term maneuversonboard a e ying vehiclewith predetermined thrust history isintroduced. Thepaperstarts with a survey about the founders of the direct methods of calculus of variations and their followers in e ight mechanics, both in Russia and in the United States. It then describes a new direct method based on three cues: high-order polynomials from the virtual arc as a reference function for aircraft’ s coordinates, a preset history of one of the controls (thrust), and a few optimization parameters. The trajectory optimization problem is transformed into a nonlinear programming problem and then solved numerically using an appropriate algorithm in accelerated scale of time. A series of examples is presented. Calculated near-optimal trajectory is compared with real e ight data, and with the solution obtainedbyPontryagin’ smaximumprinciple.Fastconvergenceofthenumericalalgorithm,whichhasbeenalready implemented and tested onboard a real aircraft, is illustrated. Nomenclature aik = polynomial coefe cients g = acceleration due to gravity J = cost function j = quantity pertaining to the jth time node m = aircraft mass N = number of nodes n = polynomial order ¯ n = relative revolutions of engine’ s rotor nx, nz = tangential and normal projections of load factor, respectively Sh = penalty function T, ¯ T = total thrust and relative thrust (fraction of maximum thrust), respectively t = time t ¤

Analytical Predictions and Measurements of the Noise Radiated from Supersonic Coaxial Jets

The noise radiated from perfectly expanded coaxial jets was measured in an anechoic chamber for operating conditions with the same total mass flow and thrust and with the same temperature ratio. The shape of the measured noise spectrum at different angles to the jet axis was found to agree with spectral shapes for single, axisymmetric jets. Based on these spectra, the sound was characterized as being generated by large-scale turbulent structures or fine-scale turbulence. Modeling the large-scale structures as instability waves, a stability analysis was conducted for the coaxial jets to identify the growing and decaying instability waves in each shear layer and to predict their noise radiation pattern outside the jet. When compared to measured directivity, the analysis identified the region downstream of the outer potential core, where the two shear layers were merging, as the source of the peak radiated noise where instability waves, with their origin in the inner shear layer, reach their maximum amplitude. The changes in the measured noise directivity that occurred when the operating conditions were changed, holding mass flow and thrust constant, followed the trend predicted by the instability wave analysis.

Separation of propulsive and adhesive traction stresses in locomoting keratocytes.

Strong, actomyosin-dependent, pinching tractions in steadily locomoting (gliding) fish keratocytes revealed by traction imaging present a paradox, since only forces perpendicular to the direction of locomotion are apparent, leaving the actual propulsive forces unresolved. When keratocytes become transiently "stuck" by their trailing edge and adopt a fibroblast-like morphology, the tractions opposing locomotion are concentrated into the tail, leaving the active pinching and propulsive tractions clearly visible under the cell body. Stuck keratocytes can develop approximately 1 mdyn (10,000 pN) total propulsive thrust, originating in the wings of the cell. The leading lamella develops no detectable propulsive traction, even when the cell pulls on its transient tail anchorage. The separation of propulsive and adhesive tractions in the stuck phenotype leads to a mechanically consistent hypothesis that resolves the traction paradox for gliding keratocytes: the propulsive tractions driving locomotion are normally canceled by adhesive tractions resisting locomotion, leaving only the pinching tractions as a resultant. The resolution of the traction pattern into its components specifies conditions to be met for models of cytoskeletal force production, such as the dynamic network contraction model (Svitkina, T.M., A.B. Verkhovsky, K.M. McQuade, and G.G. Borisy. 1997. J. Cell Biol. 139:397-415). The traction pattern associated with cells undergoing sharp turns differs markedly from the normal pinching traction pattern, and can be accounted for by postulating an asymmetry in contractile activity of the opposed lateral wings of the cell.

Deriving the Generalized Rocket Kinetic Power Equations and Associated Propulsion Indexes.

In this study, firstly we endeavor to prescribe logic definitions and reasoning process for obtaining correct rocket power and relevant efficiency equations. With the Lagrangian Reynolds transport approach, we also rigorously derive these highly generalized equations for rocket total kinetic power, thrust power and related propulsive, thermal, and overall efficiencies. They involve a few more physical effects including rocket acceleration, relative flow velocity / steadiness, outlet pressure, and gravity, thus open an original route for improving rocket propulsion analysis / design. Incidentally, it is interesting to note that under some conditions, a rocket in flight may retain less kinetic energy due to ejecting more kinetic energy of burning propellant per second than the thrust power acquired. Also, the derived correct rocket total kinetic power equations are quite reasonable in that all the velocities involved are of relative nature, thus invariant with respect to different observers and shielding the possibility of violating energy conservation law.

Effect of Wall Roughness on the Flow Through Converging - Diverging Nozzles

An understanding of the effect of wall roughness on turbulent  ows is important in many engineering applications. The roughness can affect both skin-friction and pressure drag through such factors as the thrust ratios, discharge coefŽ cients, and static pressure distributions. The effect of roughness height on the performance of two-dimensional, converging – diverging nozzles is studied computationally. It is observed that while the total thrust decreases as the wall roughness increases, there is a tradeoff between the losses associated with the shock system and those associated with the skin-friction. However, the normalized skin-friction coefŽ cient is seen to be virtually independent of the Mach number variation. An empirical correlation is proposed to Ž t the observed variation of skin-friction coefŽ cient as a function of the roughness height.

NOISE FROM SUPERSONIC COAXIAL JETS, PART 2: NORMAL VELOCITY PROFILE

Instability waves have been established as noise generators in supersonic jets. Recent analysis of these slowly diverging jets has shown that these instability waves radiate noise to the far field when the waves have components with phase velocities that are supersonic relative to the ambient speed of sound. This instability wave noise generation model has been applied to supersonic jets with a single shear layer and is now applied to supersonic coaxial jets with two initial shear layers. In this paper the case of coaxial jets with normal velocity profiles is considered, where the inner jet stream velocity is higher than the outer jet stream velocity. To provide mean flow profiles at all axial locations, a numerical scheme is used to calculate the mean flow properties. Calculations are made for the stability characteristics in the coaxial jet shear layers and the noise radiated from the instability waves for different operating conditions with the same total thrust, mass flow and exit area as a single reference jet. The effects of changes in the velocity ratio, the density ratios and the area ratio are each considered independently.

NOISE FROM SUPERSONIC COAXIAL JETS, PART 3: INVERTED VELOCITY PROFILE

The instability wave noise generation model is used to study the instability waves in the two shear layers of an inverted velocity profile, supersonic, coaxial jet and the noise radiated from the dominant wave. The inverted velocity profile jet has a high speed outer stream surrounding a low speed inner stream and the outer shear layer is always larger than the inner shear layer. The jet mean flows are calculated numerically. The operating conditions are chosen to exemplify the effect of the coaxial jet outer shear layer initial spreading rates. Calculations are made for the stability characteristics in the coaxial jet shear layers and the noise radiated from the instability waves for different operating conditions with the same total thrust, mass flow and exit area as a single reference jet. Results for inverted velocity profile jets indicate that relative maximum instability wave amplitudes and far field peak noise levels can be reduced from that of the reference jet by having higher spreading rates for the outer shear layer, low velocity ratios and outer streams hotter than the inner stream.

Extremally accelerated observers in stationary axisymmetric spacetimes

Stationary observers with the extremal value of the total thrust, considered in stationary axisymmetric spacetimes, have interesting privileges: they Fermi-transport their 4-acceleration, and those with zero vertical acceleration measure that the particles on local radially non-accelerated circular orbits co- and counter-rotate with the same modulus of velocity.

Energetics of oscillating lifting surfaces by the use of integral conservation laws

The energetics of oscillating lifting surfaces in two and three dimensions is calculated by the use of integral conservation laws in inviscid incompressible flow for general and harmonic transverse oscillations. Wing deformations are prescribed as a function of time and total thrust is calculated from the momentum theorem, and energy loss rate due to vortex shedding in the wake is calculated from the principle of conservation of mechanical energy. Total power required to maintain the oscillations and hydro-dynamic efficiency are also determined. In two dimensions, the results are obtained in closed form. In three dimensions, the distribution of vorticity on the lifting surface is also required as input to the calculations. Therefore, unsteady lifting-surface theory must be used as well. The analysis is applicable to oscillating lifting surfaces of arbitrary planform, aspect ratio and reduced frequency and does not require calculation of the leading-edge thrust.

Mechanics of the startle response in the northern pike, Esox lucius

The thrust produced during an escape response (C-start) of a northern pike, Esox lucius (0.41 m total length, 0.398 kg), an acceleration specialist, is estimated using the Weihs model for fish fast-starts. High-speed cine film records (250 Hz) of pike C-starts were digitized and the angle of attack and displacement of all body sections determined. These parameters were incorporated into the model and thrust was calculated. A comparison of model predictions with values predicted from required forces found six of eight performance parameters to be within 22% for three fast-starts. A lack of significant difference between model estimates and required forces suggests that lift and acceleration forces are the major components of total thrust during C-type fast-starts. The caudal region, including the caudal, anal, and dorsal fins, contributes the most (>90%) to positive total thrust during the propulsive stage (stage 2). High velocities, large angles of attack, and large surface areas of these sections account for this. Approximately 77% of the positive total thrust during the propulsive stage is generated by the caudal fin and 28% by the anal and dorsal fins. Lift forces averaged over the fast-start are greater than average acceleration forces, but when positive acceleration forces of the propulsive stage only are considered, average lift and acceleration forces are similar (60 and 43% of total positive forces, respectively). Also, acceleration forces peak earlier than lift forces and contribute to an earlier escape response.

On Optimum Propulsion by Means of Small Periodic Motions of a Rigid Profile II. Optimization of the Period and Numerical Results

We present some numerically calculated optimum thrust generating small amplitude periodic motions of a rigid profile in an inviscid imcompressible fluid. The motions considered consist in general of both a heaving and a pitching part and have common period. Apart from the prescribed thrust, the motions have to satisfy the demand that the contribution to the total thrust of the suction at the leading edge not exceed a given number and are furthermore subjected to a constraint on their amplitude. Solutions of an analogous optimization problem for pure heaving motions are also discussed. Furthermore, the problem of optimizing the period of the motions is considered.

A New Method for Simulated Mass Casualty Evaluation: The Beilinson Hospital Exercise

AbstractA new method for evaluating the capabilities and performance of a general hospital in masscasualty exercises is described. This method is based on the use of simulation techniques which are realistic relative to the types and availability of the manpower required and to the time consumed by the assessments, interventions, and administrative duties and demands for each casualty encountered and the total workload thrust on the hospital by the cumulative requirements of all of the casualties. The simulation can be accomplished only after the time and equipment required for every possible diagnostic, therapeutic, and administrative procedure has been assessed for the specific hospital. Thereafter, it is possible to define the exact type and quantity of resources, in terms of time and manpower, consumed cumulatively by every simulated casualty assessed and treated during the exercise. The simulated victims are selected from a pool of young physicians who are briefed thoroughly by senior staff physicians prior to the exercise. Thus, the simulated subjects are provided lists of problems and the appropriate options for treatment. They also serve as controllers in the definition of time and manpower consumed for their specific injury set. Given this setting, it is possible to assess the functional performance of a hospital as a unit and for each of its components and also realistically estimate its capacity to manage disaster victims using a simulation of a disaster situation with mass casualties.

Existence of Optimum Propulsion by Means of Periodic Motions of a Rigid Profile

The optimum generation of thrust by means of a rigid profile which performs periodic motions in an inviscid incompressible fluid is discussed. For the description of the flow a linear theory is used. Apart from the demand that a certain mean value of thrust has to be generated, the motions considered have to satisfy an inequality constraint on the contribution of the mean suction force at the leading edge to the total thrust and are furthermore subject to a constraint on their amplitude. This leads to an infinite‐dimensional nonconvex optimization problem. It is proved that for most values of the parameters involved there exists at least one optimum motion.

Intermetallic Compounds for Strong High-Temperature Materials: Status and Potential

Materials of high strength have long been sought, but various needs - particularly those for aerospace applications - have added new dimensions: First, for use in aircraft and spacecraft parts of the least weight to do a given job are desired, i.e. materials of high specific strength (strength per unit density) or high specific stiffness (elastic modulus per unit density). Second, for inherently hot parts such as propulsion systems and their housings, strength and weight at elevated temperature are critical. The efficiency and total thrust of a jet engine increase with the peak temperature of the working fluid, and current limits are set by thermal constraints on materials. This paper reports that there are three features of the high- temperature intermetallics that give promise for better materials. First, many unexplored materials are available - about 400 binary compounds that melt above 1400{degrees}C. Second, the strong unlike-neighbor bonding that is responsible for ordering gives rise to high elastic moduli, and high moduli also imply high strength. Finally, some intermetallics have increasing strength with temperature (d{sigma}/dT {gt} 0) over a significant range. This behavior was first seen in Ni{sub 3}Al, later in other compounds of the same Ll{sub 2} structure, in B2more » and DO3 (cubic) compounds, and in tetragonal Be{sub 12}Nb(D2{sub b}), and TiAl (Ll{sub 0}). This property of d{sigma}/dT {gt} 0 is of obvious use in giving high strength at elevated temperature; it is equally important in not giving very high strength at low temperatures and thereby diminishing the chances of brittle failure at ambient temperatures.« less

Effect of air entrainment on airway pressure during endotracheal gas injection.

Turbulent jets in endotracheal tubes induce air entrainment and airway pressure changes. We attempted to understand the physical explanation for these effects, which open up to a wide range of applications in intubated patients. An in vitro study was performed on standard size endotracheal tubes with diameters of 8, 7, and 3 mm and several capillaries molded into the wall (less than 1 mm diam) allowing gas injection at approximately 1-2 cm from the tracheal end of the endotracheal tube. This produced a jet velocity-dependent gain in tracheal pressure (Ptr) during inspiration. Data have been interpreted with a theory, based on the classic momentum theorem, which indicates that the mechanisms involved resemble those of axisymmetrical confined jets: air entrainment by turbulent friction with a longitudinal increase in lateral pressure. The difference with axisymmetrical systems lies in the nonconservation of the total thrust in our system because, secondary to wall friction and to the nonaxial incidence of the jets, only a fraction of the jet momentum flux is transformed into pressure. This suggests faster mixing in the present lateral jet system, as shown by 1) the independence of Ptr on tracheal geometry and 2) the very rapid increase in lateral pressure. The present study supports the idea that pressure changes in the airways, which are potentially beneficial in intubated patients, can be satisfactorily generated by turbulent jets.

AN EXPERIMENTAL STUDY OF MULTI-CIRCULAR FACE SHIELD TUNNELLING

Using an ordinary circular shield for construction of double track railway tunnel, the cross section becomes larger than the net required section. As a result, the construction work takes not only more cost but also longer time. The multi-circular face (MF) shield tunnelling has been developed to mitigate these problems, and can build a tunnel with a special cross section comprising multi-circles partially overlapped.In this study, the experiment is executed to make clear the basic behaviors of double-circular face shields (one with two faces aligned horizontally and the other with faces aligned vertically). The results show that the cutter torque and total thrust force of the MF shield are smaller than those of a circular face shield to construct the same double track railway, and that the MF shield has good characteristics in the stability of a cutting face and in its maneuverability.

ＣＲ‐ＡＴＰの最適推進効率に関する基礎的考察

To clarify the effects of wake contraction, swirl velocity and mutual interactions on the cruising performances of a counter rotating propellers ATP, fundamental analyses based on the generalized momentum theory were carried out. Assuming a linear interaction scheme, the optimum propulsion efficiency and the wake geometry which minimize the total induced losses for a given thrust were established as solutions of a calculus of variations problem. The optimum combinations of operating parameters such as the thrust sharing ratio, the power sharing ratio and the disc area ratio between top and bottom propellers were also specified and their dependency upon the axial velocity, the total thrust level and the axial spacing were revealed. It was understood that, in addition to the counter rotating effect of propellers, upwash effect of the contracted top propeller wake on the outer part of the bottom propeller disc play a fundamental role for improving the propulsion efficiency of a CR ATP.

Surface and Subsurface Swimming of the Sea Snake Pelamis Platurus

ABSTRACT During anguilliform swimming at the surface, four half waves are present along the body of the yellow-bellied sea snake Pelamis platurus (Hydrophiidae). As in other anguilliform swimmers, wave amplitude increases towards the tail; however, the relative caudal amplitude of P. platurus is less than that of the aquatic snakes Natrix and Nerodia and the eel Anguilla. Kinematic analyses of near-surface swimming at 15 and 32cms−1 were made from high-speed ciné films, and Lighthill’s bulk momentum hydromechanical model was used to calculate swimming thrust power at these two velocities. The total thrust power generated by a 51 cm snake is 3·641 × 10−4 J s−1 at 15 cms−1 and 29·877× 10−4 J s−1 at 32 cm s−1, with respective Froude efficiencies of 79% and 81%. Subsurface swimming velocities are low (2–4 cm s−1), and snakes usually assume a posture in which the tail is elevated and the posterior part of the body assumes a nearly vertical orientation. Undulatory movements by snakes swimming in this posture involve torsional and rolling motions of the body which, through changes in the camber of the keel and body, may contribute to thrust.

The Electromagnetic Rocket Gun Impact Fusion Driver

An impact fusion driver is discussed which has the potential to accelerate a rocket-like small metallic projectile by a travelling magnetic wave to a few 100 km/sec over a reasonable distance. The propellant removes the heat produced in the projectile by resistive losses of the induced electric currents, and is thereby ejected from the projectile at a modest temperature. After having left the projectile, the propellant is shock-heated by the strong magnetic field of the travelling magnetic wave to high temperatures forming a high velocity jet. The total thrust on the projectile is the sum of the magnetic and recoil forces. In comparison to a rocket, the efficiency is much larger, with the momentum transferred to the gun barrel rather than to a tenuous jet. To reach impact fusion velocities the accelerator would be a few 100 m long.

Energetics and optimum motion of oscillating lifting surfaces of finite span

The energetics of an unswept wing of finite span oscillating harmonically in combined pitch and heave in in viscid incompressible flow are determined in closed form. The calculations are based on a recently developed low-frequency unsteady lifting-line theory. The energetic calculations for the wing consist of sectional and total values of thrust, leading-edge suction force, power required to maintain the wing oscillations, and energy-loss rate due to vortex shedding in the wake, where the latter quantity is only defined for the entire wing. These results are used to analyse the optimum motion of a wing oscillating harmonically: optimum motion minimizes the power input for fixed average total thrust. The optimum solution is found to be unique (at least for low reduced frequencies), in contrast to the two-dimensional optimum, which is non-unique. Numerical results are presented for the energetics and optimum motion of an elliptic wing.To understand better the structure of the known solution for the optimum motion of an oscillating two-dimensional airfoil, the solution is recast in terms of the normal modes of the energy-loss-rate matrix. It is found that one of the modes, termed here the ‘invisible mode’, plays a central role in the optimum solution and is responsible for its non-uniqueness. The three-dimensional optimum, which is unique, does not have an invisible mode.