Steady Lifting Research Articles

Development of a Lizard-Inspired Robot for Mars Surface Exploration

Exploring Mars is beneficial to increasing our knowledge, understanding the possibility of ancient microbial life there, and discovering new resources beyond the Earth to prepare for future human missions to Mars. To assist ambitious uncrewed missions to Mars, specific types of planetary rovers have been developed for performing tasks on Mars' surface. Due to the fact that the surface is composed of granular soils and rocks of various sizes, contemporary rovers can have difficulties in moving on soft soils and climbing over rocks. To overcome such difficulties, this research develops a quadruped creeping robot inspired by the locomotion characteristics of the desert lizard. This biomimetic robot features a flexible spine, which allows swinging movements during locomotion. The leg structure utilizes a four-linkage mechanism, which ensures a steady lifting motion. The foot consists of an active ankle and a round pad with four flexible toes that are effective in grasping soils and rocks. To determine robot motions, kinematic models relating to foot, leg, and spine are established. Moreover, the coordinated motions between the trunk spine and leg are numerically verified. In addition, the mobility on granular soils and rocky surface are experimentally demonstrated, which can imply that this biomimetic robot is suitable for Mars surface terrains.

A velocity decomposition formulation for 2D steady incompressible lifting problems

The principle of velocity decomposition is used to efficiently and accurately solve the Navier–Stokes boundary-value problem for lifting flows. The velocity vector is decomposed as the sum of irrotational and vortical components. The irrotational component is represented using a velocity potential which satisfies the Laplace equation with a modified boundary condition that is written in terms of the Navier–Stokes solution. A viscous potential can be found which satisfies the Navier–Stokes problem directly outside of the rotational regions of the fluid such that the fluid domain over which the Navier–Stokes equations must be solved numerically can be greatly reduced. The viscous potential is used as a Dirichlet boundary condition for the total velocity on the boundaries of the reduced fluid domain. The velocity decomposition approach is used to solve for the flow over a 2D NACA0012 foil in both laminar and turbulent regimes.

Application of a 2D harmonic polynomial cell (HPC) method to singular flows and lifting problems

Further developments and applications of the 2D harmonic polynomial cell (HPC) method proposed by Shao and Faltinsen [22] are presented. First, a local potential flow solution coupled with the HPC method and based on the domain decomposition strategy is proposed to cope with singular potential flow characteristics at sharp corners fully submerged in a fluid. The results are verified by comparing them with the analytical added mass of a double-wedge in infinite fluid. The effect of the singular potential flow is not dominant for added mass and damping, but the error is non-negligible when calculating mean wave loads using direct pressure integration. Then, the double-layer nodes technique is used to simulate a thin free shear layer shed from lifting bodies, across which the velocity potential is discontinuous. The results are verified by comparing them with analytical results for steady and unsteady lifting problems of a flat plate in infinite fluid. The latter includes the Wagner problem and the Theodorsen functions. Satisfactory agreement with other numerical results is documented for steady linear flow past a foil and beneath the free surface.

Lifting regimes of thermal plumes in vertical layer

Theoretical investigation of the dynamics of free thermal plumes in a thin vertical layer has been performed for the case of a cavity heated from below by means of a dotted thermoelement. Three-dimensional numerical modeling has been carried out with the help of package OpenFOAM. This integrable platform is meant for calculations in the area of continuous media mechanics. Four basic plume growth types (viscous-diffusive, inviscid-diffusive, viscous-nondiffusive and inviscid-nondiffusive regimes) are found. Animated images for various lifting regimes are obtained to observe the time-dependent behavior of thermal plumes. The stages of plume formation in a relatively thin layer, its steady lifting and deceleration by the top boundary have been analyzed for different profiles of the plume front. The interaction of two synchronous plumes is studied numerically, and the formation of a common thermal front is demonstrated.

Identification of local upwelling zones in the Bering Sea using hydrochemical parameters

Based on the data for the oxygen in the surface layer of the Bering Sea, the areas of pronounced undersaturation (down to 75–80% and below) were distinguished in the surface layer of the Bering Sea. The low percentage values as such of the oxygen saturation might be sustained at the sites of quasi-stationary upwellings. However, in this case, the surface layer should be characterized by decreased temperature and increased salinity as related to the surrounding waters, as well as by increased concentrations of nutrients (phosphates, nitrates, and silicon). The corresponding tests showed that most of the distinguished “patches” of oxygen undersaturation were verified by the oceanological parameters; i.e., these were local upwellings. Some of them were studied quite thoroughly (even with the mechanisms proposed for the formation of steady water lifting), particularly in the area of the Aleutian Islands. However, there are some poorly studied areas (so-called questionable ones) at which the low oxygen content is not confirmed by the hydrochemical parameters (plainly, they are not available); this requires more profound and detailed study.

New Hybrid Method for Predicting the Flowfields of Helicopter Rotors

Based on a Navier-Stokes/full potential/free wake solver, a new hybrid method was developed for efficient predictions of the three-dimensional viscous flowfield of a helicopter rotor under both hover and forward flight conditions. The developed flow solver was composed of three modules: 1) a compressible Navier-Stokes analysis to model the viscous flow and near wake about the blade, 2) a compressible potential flow analysis to model the inviscid isentropic potential flow region far away from the rotor, and 3) a free wake model to account for tip vortex effects once the tip vortex leaves the viscous flow region and enters the potential flow region. In this hybrid method, a moving embedded grid methodology was adopted that accounts for rigid blade motions in rotation, flapping, and pitching. A dual-time method was employed to fulfill the calculation of the unsteady flowfields of helicopter rotors, and a third-order upwind scheme (MUSCL) and flux-difference splitting scheme without introducing artificial viscosity were used to calculate the flux. To search suitable donor elements in embedded grids to pass information between the viscous flow and potential flow zones, a new searching scheme was implemented. The sectional pressure distributions of a UH-60A helicopter rotor and an AH-1G model rotor in hover and forward flight, with and without the wake model, were calculated, and the developed hybrid model was validated by comparing with available experimental data. The simulated steady and unsteady lifting results of a model rotor with three different blade-tip planforms demonstrate the benefits of the curvilinear swept tip and constant swept tip in suppressing supercritical flows.

Numerical Computations and Integrations of the Wave Resistance Green's Function

In order to develop an efficient method, using Kelvin--Havelock singularities, to compute the steady lifting flow around a ship with forward speed, the accuracy of computations of Green's function and boundary integrations have been investigated. The computations have been done using interpolation from tables for the nonoscillatory term of Green's function and using series for the oscillatory one; it has been shown that a region exists, close to the free-surface, where this last term must be computed by complete integration to ensure a prescribed error. Three schemes of boundary integrations have been studied; first boundary integrations have been performed using a Gauss method. Then, to improve accuracy, Fourier and boundary integrations have been interchanged either only for the oscillatory term or for both terms. Numerical results are compared and discussed taking into account both precision and computational time, for a submerged ellipsoid and for a lifting surface-piercing body.

Design system for optimum contra-rotating propellers

A new type of contrarotating propeller (CRP) system has been developed through the cooperative research work of five shipbuilding companies in Japan (Hitachi Zosen Corporation; Kawasaki Heavy Industries, Ltd.; Mitsui Engineering and Shipbuilding Co., Ltd.; NKK Corporation; and Sumitomo Heavy Industries, Ltd.). This paper describes a design system for an optimum CRP, which is one of the numerous outcomes of this work. The optimum design system is composed of three theoretical programs: (1) the design program of the optimum CRP; (2) the steady lifting surface program of the CRP; (3) the unsteady lifting surface program of the CRP. These theoretical programs will be discussed in the first part of the paper, and the design system supported by these theoretical programs will then be verified by comparing calculated and experimental results.

The potential impact of soot particles from aircraft exhaust on cirrus clouds

Homogeneous freezing of sulfate aerosols may dominate ice nucleation in cirrus, implying that large supersaturations are required for cirrus cloud initiation at low temperatures. However, insoluble particles from the surface or soot particles injected directly into the upper troposphere by jet aircraft may act as heterogeneous ice nuclei. If the soot particles are sufficiently effective ice nuclei, then they will allow ice nucleation at lower supersaturations than those required for homogeneous freezing, resulting in an increase in the areal coverage of cirrus clouds. Simulations using a detailed ice cloud model indicate that cirrus driven by slow, steady lifting (a few cm‐s−1) will be transient, precipitating clouds if only pure sulfate haze aerosols are present. However, if effective heterogeneous nuclei are present, then extensive, persistent, diffuse cirrus should form. In addition, heterogeneous ice nucleation on insoluble particles may modify the number of ice crystals nucleated in cirrus, resulting in alterations of the cloud evolution and radiative properties. Heterogeneous freezing on relatively few insoluble particles (Ninv <0.1 cm−3) should result in fewer ice crystals nucleating than if homogeneous freezing were to occur. However, if large numbers of insoluble particles are present, the ice crystal number density may be increased.

The Lifting Line Equation for a Curved Wing in Oscillatory Motion

AbstractAn unsteady linear lifting line method for the determination of the circulation and lift distribution along the span of a curved wing subject to harmonic small amplitude oscillations is presented. The method relies on the Pistolesi‐Weissinger 3/4‐chord steady lifting line theory and couples it to the unsteady theory developed by Possio for the motion of lifting surfaces. It leads to an integro‐differential equation of a modified Prandtl's type, where the unknown is the circulation. This equation has been carefully analysed in order to evidence all the singularities and to treat them in the most convenient way. The numerical procedure consists of a gaussian quadrature technique based on Chebyshev's polynomial approximation of the unknown function. The method has been appraised through the comparison of a number of solutions, pertaining to different wing configurations, with existing solutions based on lifting surface theory.

A Numerical Analysis of Steady Lifting Surface Problems by Proposal of Green Function Considering Wave Generation Caused by Vortex System (2 nd Report)

A Numerical Analysis of Steady Lifting Surface Problems by Proposal of Green Function Considering Wave Generation Caused by Vortex System (2 nd Report)

Accurate finite element method for steady and quasisteady lifting aerofoil

A finite element formulation based on superposition is proposed for a lifting aerofoil in incompressible potential flow. An accuracy improvement technique for the singularity at the aerofoil trailing edge is discussed. It is shown that the quarter-node quadrilateral element can be readily employed to simulate this singularity. It is also demonstrated that the circulation in the flow field can be easily represented by a single constraint equation rather than introducing an artificial cut line in the mesh. The influence of finite-element mesh size on solution accuracy and the correct form of the boundary condition have been investigated as well. Numerical examples are given for both steady and quasisteady Joukowski aerofoils of various thicknesses and at a range of incidences. In all test cases, good agreement is observed between the analytical solution and the numerical result.

A Numerical Analysis of Steady Lifting Surface Problems by Proposal of Green Function Considering Wave Generation Caused by Vortex System

In this paper, Green function considering wave generation caused by vortex system is proposed. The Green functions of an isolated point vortex for the various image systems present an appearance of different wave-making properties. However, composed Green function of vortex ring has uniqueness for the different image system. Accordingly, Green function with image system satisfying rigid wall conditions is applied to numerical analysis of steady lifting surface problems. Then, waves are created only by transverse component of vortex system but longitudinal one doesn't create wave system.The lift forces acting on hydrofoils, for example, some rectangular wings and delta wings are calculated considering the free surface effects by means of present method. Numerical results present the free surface effects remarkably for the rectangular wings rather than delta wings. And the effects appear strongly as aspect ratio increases. Present analysis method is practically useful because the ordinary computational program for the Green function of a point doublet with x-directional axis can be applied to the present case by slight modification.

Numerical study of steady supersonic separated flow past spatial lifting systems

At the present, spatial lifting systems are usually calculated numerically using linear approximation. However, the practical application of such systems at moderate and large angles of incidence requires new approaches that allow for various nonlinear effects such as large disturbances, flow separation, and jumps in entropy across shock waves. The existing investigations [3, 4] generally cover only simple systems (bodies of revolution, wings, and so on). Here, a numerical method is proposed for investigating supersonic flows past complicated spatial systems. The method extends and continues the well-known methods widely used to solve analogous problems in subsonic aerodynamics [5, 6]. Some examples of the computation of the aerodynamic parameters for flows past wings and spatial lifting systems are also given.

Unsteady Hydrodynamic Forces on a Lifting Body

A simplified method described in the previous report, has been extended to calculate steady and unsteady lift of arbitrary three-dimensional body and wing configurations, in which the velocity potential is expressed by the doublet distribution over body, wing and the wake. The velocity potential on a thick body is simply obtained by subtracting the interior velocity potential defined inside the body from the solution of the doublet distribution for the translating oscillation. This method is applied to study hydrodynamic interactions between body and wing configurations in steady and unsteady lifting problems.Experiments for a body of revolution with and without a pair of low aspect ratio wing are carried out for steady lift with angle of attack and unsteady lift in heaving oscillation. Those results are compared graphically with the present theory, together with approximated calculations by equivalent wings.

Analytical flutter investigation of a composite propfan model

A theoretical model and an associated computer program for predicting subsonic bending-torsion flutter in propfans are presented. The model is based on two-dimensional unsteady cascade strip theory and three-dimensional steady and unsteady lifting surface aerodynamic theory in conjunction with a finite element structural model for the blade. The analytical results compare well with published experimental data. Additional parametric studies are also presented illustrating the effects on flutter speed of steady aeroelastic deformations, blade setting angle, rotational speed, number of blades, structural damping, and number of modes.

Unsteady lifting-line theory by the method of matched asymptotic expansions

An unsteady lifting-line theory is presented for a general motion of a wing of high aspect ratio. Our matched-asymptotic-expansions analysis parallels that of Van Dyke (1964) in his solution for the steady lifting line, but is complicated by the shedding of transverse vortices associated with variation of circulation with time. The principal result is an expression for the downwash due to three-dimensional effects. Numerical calculations are presented for a wing of elliptic planform following a curved path.

The induced downwash and lift on a wing of high aspect ratio in unsteady motion

SummaryAn unsteady lifting line theory for a general motion of a wing of high aspect ratio is presented. Our analysis parallels that of Van Dyke (1964) in his solution for the steady lifting line by the method of matched asymptotic expansions but is complicated by the shedding of transverse vortices associated with variation of circulation with time. We find expressions for the downwash due to three-dimensional (finite span) effects and the lift on the wing. Calculations are presented for a wing of elliptic planform following a curved path.

A vortex-lattice method for general, unsteady aerodynamics

A general method of calculating unsteady, incompressible, inviscid, three-dimensional flows around arbitrary planforms has been developed. The method is an extension of the vortex-lattice technique. It is not limited by aspect ratio, camber, or angle of attack, as long as vortex breakdown does not occur above the surface of the wing and separation occurs only along sharp edges. As the wing performs arbitrary maneuvers, the position of the wake and the distribution of circulation on the wing and in the wake are obtained as functions of time. One desirable feature of the present method is its ability to treat steady lifting flows very efficiently. Several examples of steady and unsteady flows are presented. These include rectangular wings, with and without flaps, delta, and cropped delta wings.

Transonic integral equation formulation for lifting profiles and wings

Introduction T are at present three different integral equation formulations for studying the direct problem of steady inviscid isentropic transonic flow past thin lifting profiles, where the freestream Mach number M^ (< 1) and the body shape are prescribed. Two of these formulations are by Ndrstrud,' and the third is by Nixon and Hancock. The formulation in Ref. 2 has been extended to the threedimensional case of lifting wings by N^rstrud. The basic integral equation governed by the perturbation potential of a lifting wing was given earlier by Heaslet and Spreiter and Klunker. About two years ago, a controversy started from a criticism by Nixon regarding the correctness of the formulation of N^rstrud which, according to Nixon, leads to nonunique solution. Ntfrstrud, on the other hand, pointed out some mistakes in the Nixon critique, creating further confusion. Recently, Chakraborty and Niyogi showed that the formulations of Nefrstrud and Nixon and Hancock are equivalent. The purpose of the present Note is to point out a sign error in the second formulation of Ntfrstrud and to indicate an alternative way of obtaining the appropriate formulation for this case.