Side Moment Research Articles

Macro-micro interaction mechanism between FRPC pile and sand under horizontal bidirectional load

FRPC pile is a new type of composite pile formed by combining FRP material with traditional material. It has good physical and chemical erosion resistance, light weight, high strength and other advantages. Based on the particle image velocity measurement (PIV) technique, this paper studies the interaction between sand soil and FRPC pile by applying bidirectional horizontal load on the FRPC model pile embedded in sand soil. In the process of loading the FRPC model pile, a CCD high-speed industrial camera is used to take gray image of sand deformation around the test observation surface pile. DH3816 Strain Collecting Instrument was used to collect pile side strain, and image processing software PIVview2C was used to get displacement cloud picture. By analyzing the distribution of total displacement, horizontal displacement and vertical displacement of sandy soil under different loads, the micro mechanism of FRPC pile and sandy soil is clarified. The distribution of pile side moment was studied, and the macro mechanism of FRPC pile and sandy soil is clarified.

Numerical study on the aerodynamic coupling effects of spinning and coning motions for a finned vehicle

A numerical method was used to compute the flow over a four-finned vehicle under supersonic conditions to study the aerodynamic characteristics of a spinning finned vehicle in a coning motion. For each flow condition, the side force and side moment of a combined spinning and coning motion were computed at roll angles of 0°–90°. The results of the non-rolling, coning, and spinning motions were superposed by using a nonlinear aerodynamic model, and the superposed side force and side moment were compared with those of the combined motion. The results indicated significant aerodynamic coupling effects with the combined motion at low Mach numbers and high coning and spin rates. Flow analysis showed that the coupling effects were mainly produced by the shockwaves and expansion waves around fins.

Wind turbines ice distribution and load response under icing conditions

Wind turbines operating in cold climate are susceptible to icing events. Under icing conditions, in order to gain a better understanding of the ice distribution affected by different parameters, and the load response of different components, the NREL Phase VI was selected as the test case. Firstly, the ice distribution affected by different parameters with the multi-dispersed water droplets size was investigated. Results show that the ice mass and the ice thickness increase approximately linear from the blade root to the blade tip. Higher free stream wind speed, smaller pitch angle, higher liquid water content, larger water droplets median volumetric diameter and lower temperature have bigger effect on the blade icing. Secondly, the ice shapes on the blade tip region (r/R = 80%–100%) were simulated. Then the lift coefficients and the drag coefficients of the clean airfoils and the iced airfoils were calculated. Finally, the load response of the asymmetric icing (one blade is covered with ice, the other is free) and the symmetric icing (two blades are covered with ice) of the blade and the tower were analyzed. Results show that icing can decrease the rotor thrust force, the blade root edgewise moment and the blade root flatwise moment. For the low speed shaft, the asymmetric icing can induce additional imbalance shear force. For the tower base, the symmetric icing can decrease the fore after moment, whereas the asymmetric icing can increase the side to side moment. The asymmetric load can increase the blade and the tower fatigue damage up to 97.6% and 70.8%, respectively.

Complex Aerodynamics Behavior of High Spin APFSDS Projectile

The supersonic aerodynamics of a high spin armor-piercing fin-stabilized discarding sabot projectile (APFSDS) is numerically and experimentally investigated. Classically, using a 120 mm smooth bore gun, the value of the nondimensional steady spin rate of the inflight APFSDS projectile is about 0.01. In our case, a medium caliber APFSDS projectile is fired using a rifled barrel gun. The initial nondimensional spin rate, which is, with the Mach and the Reynolds numbers, the third similitude parameter governing the projectile aerodynamics, is significantly greater and about 0.09. Complex aerodynamics and flight dynamics were found and are detailed in the paper. In particular, the side force and moment evolutions with spin rate and angle of attack reflect a highly nonlinear behavior of the Magnus effect. The numerical predictions are mainly based on Reynolds-averaged Navier–Stokes (RANS) and URANS (Unsteady RANS) equations. Flight tests have been performed in an aeroballistics corridor. The exterior ballistics of the projectile was investigated using a yaw cards method, the experimental results are analyzed using a 6DOF flight dynamics model. The comparison between computational fluid dynamics (CFD) computations and flight tests results is satisfactory. CFD computations show, for the first time at our knowledge, that a roll-pitch coupling may appear.

Spin-Yaw Lock-In of a Rotationally Symmetric Missile

Spin―yaw lock-in has usually been associated with small aerodynamic asymmetries that produce a trim angle that rotates with the missile. Recent trajectory calculations using wind-tunnel measurements ofthe aerodynamic moment acting on a rotationally symmetric missile predicted spin―yaw lock-in. Thus, an asymmetry-induced trim moment is not necessary for lock-in. For a side moment that varies with the roll angle between the angle-of-attack plane and a fixed plane on the missile, this paper shows that lock-in of the coning motion and the rolling motion can occur. The conditions on the aerodynamic moments for occurrence of lock-in are derived and appropriate stability criteria are obtained. A simple case of a hypersonic finned missile is considered and the existence of lock-in is demonstrated.

초음속 노즐 출구에 비대칭적으로 설치한 램프 탭의 성능 연구

Thrust vector control(TVC) is the method which generates the side force and moment by controlling the exhausting gas directly from the supersonic nozzle to change the trajectory of a missile quickly. In this paper, performance study on the tapered ramp tabs asymmetrically installed in the supersonic nozzle exhaust for the thurst vector control has been carried out using the supersonic cold flow system. To study the shock wave structure and location of the oblique shock wave produced by the ramp tab, the flow field visualization using the schlieren system is conducted. This paper provides the thrust spoilage, three directional forces and moments and distribution of surface pressure on the region enclosed by the tapered ramp tabs.

Coning motion stability of wrap around fin rockets

Both the asymptotical stability criterion and the bounded stability criterion of the coning motion for wrap around fin (WAF) rockets are proposed through the analysis of coning motion equations, which can be easily used to determine the existence of the coning motion during the rocket design. The correctness of the criterions is verified by mathematical simulation examples of a WAF rocket with different setting angles. It is also found that the setting angle of WAF has great effects on the rolling moment and side moment of the rocket.

Influence of range extension on dynamic stability for artillery rockets with wrap around fins

This paper presents the effects of the range extension of an artillery rocket with wrap around fins on its dynamic stability. The increased total impulse of the rocket engine for 50% and flight through the atmosphere layers with low air density extend the range for more than 75% of the nominal range. However, the flight of the unguided rocket through the rarefied air produces difficulties related to the dynamic stability. The small changes in the side moment which is induced by the angle of attack and Magnus moment of the improved rocket can produce instabilities in flight and increasement the angle of attack. The tolerances of the side moment were determined for both basic and improved type of the rocket in order to prevent instable flight. The influence of the range extension on the probable errors in range and cross-range was analyzed as well.

Multigrid Computation of Incompressible Flows Using Two-Equation Turbulence Models: Part II—Applications

In this paper, computational results are presented for three-dimensional high-Reynolds number turbulent flows over a simplified submarine model. The simulation is based on the solution of Reynolds-Averaged Navier-Stokes equations and two-equation turbulence models by using a preconditioned time-stepping approach. A multiblock method, in which the block loop is placed in the inner cycle of a multi-grid algorithm, is used to obtain versatility and efficiency. It was found that the calculated body drag, lift, side force coefficients and moments at various angles of attack or angles of drift are in excellent agreement with experimental data. Fast convergence has been achieved for all the cases with large angles of attack and with modest drift angles.

Symptom of payload-induced flight instability

Abstract : Observations of instability caused by a moving payload--liquid or solid--have shown that large angular motions are always accompanied by a large spin-down moment. A simple general relation is derived between the side moment and the spin moment caused by the steady-state motion of any movable payload.

Low Reynolds number Navier-Stokes simulation for rotating liquid-filled containers

Three-dimensional, steady, laminar, incompressible Navier-Stokes equations are solved using an implicit finite-difference scheme based on successive over-relaxation. These low Reynolds number numerical simulations are used to predict the behavior of liquids undergoing steady spin and steady precession at a fixed precession angle. Low Reynolds number simulations are applicable to slowly spinning vehicles or highly viscous liquid payloads. The liquid is contained in a fully filled axisymmetric container; the particular geometry examined in this paper is a right-circular cylinder with flat or rounded endcaps. Numerical predictions of viscous and pressure moments due to the liquid fill at low Reynolds number are reported. These moments tend to increase the precession angle and reduce the spin rate of the container. Liquid-induced roll and side (yaw) moments are computed as functions of endcap height to cylinder radius (0 < e/a < 1), cylinder half-height to radius (0.5 < c/ a < 4), Reynolds number (20 < Re < 3 X 102), ratio of precession to spin rate (0.05 < r < 0.95), and precession angle (ac = 2 deg). For a given cylinder, rounded endcaps can decrease the resonant liquid-induced moment by about 20% and shift the resonance to a smaller Reynolds number (for fixed precessional frequency). Thus, rounded endcaps can produce flight stability for some projectiles with highly viscous liquid payloads.

Side moment exerted by a two-component liquid payload on a spinning projectile

Abstract : A linear boundary layer theory is derived for two liquids in a cylindrical cavity in a coning and spinning projectile. Predicted eigenfrequencies agree well with available experimental results. Side moment coefficients are computed for various cases. It is shown that significant increases in the single-liquid side moment can be caused by the addition of a small amount of heavier liquid and for certain locations of the liquid interface, pairs of eigenfrequencies can coalesce.

Subsonic and transonic aerodynamics of a wraparound fin configuration

Abstract : Subsonic and transonic aerodynamic data for a wraparound fin configuration are presented. Free-flight aeroballistic tests to obtain these data were conducted at atmospheric pressure and over a Mach number range of 0.6 to 1.35. The aerodynamic coefficients and derivatives presented in this paper were extracted from the position-attitude-time histories of the experimentally measured trajectories using nonlinear numerical integration data reduction routines. Results of this analysis indicate that a dynamic instability exists above Mach 1.0 and is related to an out-of-plane side moment which is dependent of the pitch angle. The stability boundaries associated with this side moment are mapped. Designers should consider this moment whenever wraparound fins are used. Keywords include: WAF(Wraparound Fins), Aerodynamic stability, Side moment, Pitch-roll resonance, Folding fins, and Submunitions.

Computations of projectile Magnus effect at transonic velocities

Abstract : The Magnus effect has long been the nemesis of shell designers. Although very small in magnitude, on the order of 1/10th the normal force, this spin-induced side moment has a significant destabilizing effect on projectiles. A combined computational and experimental research program has been ongoing at BRL in recent years to develop a predictive capability for the Magnus effect in particular and for projectile aerodynamics in general. This effort has been very successful in the supersonic regime. The research to be reported in this paper is an extension of this effort into the transonic regime. Utilizing the time marching, thin-layer Navier-Stokes computational technique developed at NASA ames Research Center, solutions have been obtained for a spinning, 6-caliber long, ogive-cylinder-boattail shape at Mach = 0.91 and angle of attack = 2degrees. The computed results predict the correct development of the Magnus force along the body, and comparisons between the computation and experiment are very favorable. Details of the flow field solution such as turbulent boundary- layer velocity profiles and surface pressure distributions are presented. The components which contribute to the Magnus effect are determined and presented as a function of axial position. A complete set of aerodynamic coefficients have been determined from the flow field solutions. Those to be presented here and compared with experimental data include the normal force and Magnus force coefficients. The computations for this research effort were obtained both on a CDC 7600 computer and Cray 1S. (etc.)

Moment induced by liquid payload during spin-up without a critical layer

Abstract : For a fully spun-up liquid payload, eigenfrequencies and liquid side moments induced by projectile coning motion have been computed by a linear boundary layer theory. For partially spun-up liquids, this theory can fail due to the presence of a critical layer in which the local angular velocity of the spinning motion is near the angular velocity of the projectile's coning motion. Late in the spin-up process, when more than 90% of the spin angular momentum has been acquired by the liquid, a critical layer usually does not exist. In this report, a linear-boundary-layer theory is developed to predict eigenfrequencies and the liquid moment during late spin-up times. The predicted eigenfrequencies agree well with those computed by the linearized Navier-Stokes technique of Gerber and Sedney. The side moments predicted by the linear-boundary-layer theory are available to projectile designers for flight stability analysis.

A relation between liquid roll moment and liquid side moment

Abstract : Spinning projectiles carrying liquid payloads and performing large coning motion have uniformly been observed to experience rapid despin. For linear fluid mechanics, it has been shown that the ratio of the magnitudes of the liquid roll moment to the liquid side moment is the tangent of the coning angle. The validity of this relationship is demonstrated by gyroscope data obtained by M. C. Miller and flight data for twelve projectiles analyzed by R. L. Pope.

Angular motion of a spinning projectile with a viscous liquid payload

Abstract : Liquid payload motion can have a significant effect on the stability of a spinning projectile. A general definition of the liquid moment is developed and expressions are obtained for the frequencies and damping rates of the projectile's angular motion. An expression for the liquid pressure moment is derived without the unnecessary mathematical approximations of the Stewartson- Wedemeyer theory, and wall shear effects are added to this improved SW pressure moment to obtain the total liquid moment. This moment expression applies to cavities that are fully filled, partially filled or fully filled with a central rod. The improved theory shows that as the Reynolds number decreases, (a) the eigenfrequency-related side moment peaks decrease steadily in size but that (b) the average side moment level first increases and then decreases. This latter predicted behavior is in good qualitative agreement with the D'Amico-Miller conjecture that relates the liquid spin-down moment to the liquid side moment. Good agreement is also obtained between the theory and all available published data from liquid- filled gyroscope experiments.

Flat spin of slender bodies at high angles of attack

Low-speed wind tunnel investigations are performed for the flat spin of slender bodies at high angles of attack at Reynolds numbers of (1.2-4.4) xlO5. Effects of the geometrical configuration of the model, freestream Reynolds number, and angle of attack on the flat spin motion are analyzed using spin rate measurements, in situ surface pressure distribution, and static aerodynamic characteristics. It is verified that the flat spin is caused by differences in flow patterns at the critical Reynolds number. The measured side moment can be used to predict the actual flat spin rate. The flat spin can be alleviated by causing early transition of the boundary layer with artificial surface roughness.

Instability of controlled projectiles in ascending or descending flight

Lloyd and Brown have shown that constant horizontal and vertical side forces and moments applied to a spinning projectile can result in dynamic instability. This instability arises from the nonlinear terms in the fixedplane coordinate system spin that appear in the equations of motion. By the use of the fixed-plane system (rather than Lloyd and Brown's nonrolling system) simpler relations can be developed, the full effects of gravity, drag and roll damping obtained, and the limitation to large gyroscopic stability factors removed. Very simple stability bounds are given for spinning finned missiles with spin rates well above resonance as well as for a gyroscopically stable shell. Exact solutions are given for finned missiles with zero spin but the motion of slowly spinning missiles should be numerically computed.

Ogive Cylinder Modified for Near-Minimum Side Moment

Abstract : Bodies of revolution develop side moments at large angles of attack due to asymmetric vortices. Consequently, a composite ogive cylinder model was designed in order to determine what modifications were necessary to suppress this moment. Low speed wind tunnel tests, in which the geometry of the model was systematically varied, revealed that a simple afterbody step down coupled with slight nose bluntness could reduce side moment by over 90% compared to the unmodified model. Conventional models were constructed in order to substantiate the results obtained with the composite model. Tests were conducted at three different velocities (85 mph, 120 mph, 140 mph). Large reduction in side moments (90% reductions) were obtained. (Author)