Pitching Moment Research Articles

Roll and Pitch Motion Analysis of a Biologically Inspired Quadruped Water Runner Robot

In this paper, the roll and pitch dynamics of a biologically inspired quadruped water runner robot are analyzed, and a stable robot design is proposed and tested. The robot’s foot—water interaction force is derived using drag equations. Roll direction instability is attributed to a small roll moment of inertia and large instantaneous roll moments generated by the foot—water interaction forces. Roll dynamics are modeled by approximating the water as a linear spring. Using this model, estimates on the roll moment of inertia that can endure moments generated by water interactions are derived. Instability in the pitch direction is caused by the thrust force the four feet exert on the water. To correct this, a circular tail which can negate the pitch moment around the center of mass is proposed. Both passive and active tail designs which can cope with disturbances are introduced. Based on these analyses, a stable water runner is designed, and built. Experimental high-speed video footage demonstrates the stable roll and pitch motion of the robot. Simulations are used to estimate robustness against disturbances, waves, and leg running frequency variations. It is found that roll motion is more sensitive to disturbances when compared with the pitch direction.

Robust oscillation control of wheeled mobile robots

In cases where a wheeled mobile robot runs fast on a rough surface, the sensors mounted on the robot’s body may be destroyed due to the body acceleration and oscillation. In this article, we propose a new scheme to reduce the body acceleration at any specified location for mobile robots with the actuators set on the wheel axes. To achieve this, a combined ideal robot model is designed. In the combined ideal robot model, the location where the acceleration performance is at its best can easily be moved by setting only two design parameters. Next, a robust model tracking controller is developed so that the behavior of an actual mobile robot can track the combined ideal robot model. The developed controller has the following useful properties. (1) The body acceleration at any specified location can easily be improved. (2) The developed controller has good robustness for uncertainties in robot mass, pitch and roll moment of inertia of the robot’s body, and the position of the center of gravity.

Lateral Stability and Control of a Tailless Aircraft Configuration

The aerodynamics of a generic aircraft configuration known as Swing was investigated. The configuration used had two trailing-edge flaps on each wing used for control around all three stability axes included pitch, roll, and yaw. Tests are done in the low-speed wind tunnel L2000 at a freestream velocity of 30 m/s corresponding to a Reynolds number of 6.9 · 105 was applied. A NACA-66009 airfoil was used for the wing, and the outer wing section was twisted up 5° around the leading-edge point of the wing. Asymmetric deflections with the same amplitude for both flaps on each wing were applied for roll control. The deflection of the flaps was recorded with a motion capture system. The infrared light was emitted from four cameras and the light was reflected back to the cameras with a scan rate of 100 Hz and the system computed the distance to the markers. The results revealed that a sudden increase in pitch moment were observed at angles of attack above 10° and the flaps deflected with the same amplitude.

Aerodynamic Modification of NACA 0012 Airfoil by Trailing-Edge Plasma Gurney Flap

The effect of a novel plasma Gurney flap on the aerodynamic characteristics of a NACA 0012 airfoil is studied by solving the Reynolds-averaged Navier–Stokes equations. The plasma actuator is simulatedwith a phenomenological model. The results indicate that the plasma Gurney flap can increase the lift and nose-down pitching moment of the airfoil, and the mechanism is the same as that of the conventional Gurney flap. The flowfield presents that the vonKarman vortex street disappears near the trailing edge of the airfoil with a plasmaGurney flap, which decreases the airfoil’s drag and thus increases the lift-to-drag ratio before stall. By comparing the lift and nose-down pitching moment increments with the conventional Gurney flap and the jet Gurney flap, the equivalent height or jet blowing momentum coefficient of the plasma Gurney flap are estimated.

Motion of meteor form bodies at an arbitrary angle of attack

Drag, lifting force, and pitch moment coefficients are obtained as functions of the attack angle during supersonic flow around using a numerical experiment for cube and plate-shaped meteorite bodies. It is shown that during motion in the atmosphere, the body orientations with respect to the approach flow at which its front part corresponds to the edge with the maximum area are statically stable.

Application of circulation control for three-axis control of a tailless flight vehicle

The application of circulation control (CC) manoeuvre effectors to a tailless flight vehicle enables the possibility of providing control moments about three axes without the use of conventional control surfaces. Strong similarities exist between the use of split flap elevons and CC units used as trailing edge devices for the provision of three-axis control. Both control types can produce independent roll and pitching moments by lateral symmetric operation. Yawing moments can also be produced by simultaneous blowing from upper and lower CC slots increasing the local section axial force. An existing datasheet method for predicting the lift and pitching moment increments for plain flaps is modified to support some aspects of sizing CC devices; however, there are some significant gaps such as high fidelity models for the prediction of Coanda jet separation from the curved trailing edge, which require further research. A case study is presented in which the provision of three-axis control moments using CC is evaluated for a tailless 20 kg class gas-turbine-powered model aircraft. Wind tunnel experiments are used to demonstrate the validity of the aerodynamic design of the vehicle and the ability to produce control moments from CC sufficient to meet basic trim and manoeuvre requirements. The peak values of CC control gains achieved for δ CL/ δ Cμ is 20 and the control gain for δ CD/ δ Cμ for use as part of a ‘thrust’-based yaw control scheme from blowing from both upper and lower slots is low (∼0.5); however this is sufficient to trim the case study aircraft at 8° of sideslip at cruise conditions with 10 per cent mass flow bleed from the engine. For lateral symmetric operation of CC controls, the change in pitching moment with control lift increment has been shown to be similar for both CC and flaperon devices

Flight Dynamics and Simulation of Laser Propelled Lightcraft

A seven degree-of-freedom (7DOF) dynamic model was developed to provide insight into the flight behavior of Type 200 and other related lightcraft, and to serve as a research tool for developing future engine-vehicle configurations for laser launching of nanosatellites (1–10+kg). Accurate engine, beam, and aerodynamics models are included to improve the predictive capability of the 7DOF code. The aerodynamic forces of lift, drag, and aerodynamic pitching moment were derived from FLUENT® computational fluid dynamics predictions, and calibrated against limited existing wind tunnel data. To facilitate 7DOF model validation, simulation results are compared with video analysis of actual flights under comparable conditions. Despite current limitations of the 7DOF model, the results compared well with experimental flight trajectory data.

Unsteady Aerodynamic Coefficients Obtained by a Compressible Vortex Lattice Method

Unsteady solutions for the aerodynamic coefficients of a thin airfoil in compressible subsonic or supersonic flows were studied. The lift, the pitch moment, and pressure coefficients were obtained numerically for the following motions: the indicial response (unit step function) of the profile, i.e., a sudden change in the angle of attack; a thin profile penetrating into a sharp edge gust (for several gust velocity ratios); a thin profile penetrating into a one-minus-cosine gust and sinusoidal gust, i.e., a typical gust used in commercial aircraft design; oscillating airfoil; and also the interaction of the profile with a convected (from convection phenomenon) vortex passing under the profile, a phenomenon known in literature as BVI (Blade Vortex Interaction) or for a profile case AVI (Airfoil Vortex Interaction). The present work uses a numerical approach based on vortex singularity. The numerical model was created through the profile discretization in uniform segments and the compressible flow vortex singularity was used. The results available in the literature are based on approximated exponential equations, or computed via Computational Fluid Dynamics (CFD). Thus, the purpose of this method is to obtain a more accurate computation compared to those of approximated equations, and quite faster than those done via CFD. The results yielded by the present methodology were also compared with solutions available in the literature. The results were obtained for subsonic and supersonic flow in compressible environment.

Experimental Study of Liquid Slosh Dynamics in a Partially-Filled Tank

This article reports on an experimental study conducted to investigate slosh forces and moments caused by fluid slosh within a partly-filled tank subjected to lateral and longitudinal excitations applied independently. The experiments were performed on a scale model cleanbore and a baffled tank with laterally placed single- and multiple-orifice baffles. The experiments were conducted for three different fill volumes and different types of excitations: continuous harmonic and single-cycle sinusoidal excitations of different amplitudes and discrete frequencies. The dynamic forces and moments caused by fluid slosh with the baffled and cleanbore tank configurations were measured for different fill volumes and excitations using three-axis dynamometers. It is shown that the resulting forces and moments comprise many spectral components that can be associated with the excitation, resonance, and vibration and beat frequencies. Modulation of excitation frequency with the resonant frequency was also evident for all fill conditions and tank configurations when the two were in close proximity. The results also showed that the peak amplifications of forces and moments occur in the vicinity of the resonant frequency. At higher frequencies, the peak magnitudes of the forces, however, reduced significantly to values lower than the inertial forces developed by an equivalent rigid mass. At a given excitation condition, the slosh force amplitude increased with a decrease in the fill volume. It was also observed that the presence of baffles has negligible effect on the lateral slosh force and the corresponding resonant frequency. However, it caused a significant increase in the longitudinal mode resonant frequency. The baffles greatly reduced the amplifications in longitudinal force and pitch moment under longitudinal acceleration excitations.

Macro-fiber composite actuators for a swept wing unmanned aircraft

AbstractThe purpose of the research presented here is to exploit actuation via smart materials to perform shape control of an aerofoil on a small aircraft and to determine the feasibility and advantages of smooth control surface deformations. A type of piezoceramic composite actuator known as Macro-Fiber Composite (MFC) is used for changing the camber of the wings. The MFC actuators were implemented on a 30° swept wing, 0·76m wingspan aircraft. The experimental vehicle was flown using two MFC patches in an elevator/aileron (elevon) configuration. Preliminary flight and wind-tunnel testing has demonstrated the stability and control of the concept. Flight tests were performed to quantify roll control using the MFC actuators. Lift and drag coefficients along with pitch and roll moment coefficients were measured in a low-speed, open-section wind tunnel. A vortex-lattice analysis complemented the database of aerodynamic derivatives used to analyse control response. The research, for the first time, successfully demonstrated that piezoceramic devices requiring high voltages can be effectively employed in small air vehicles without compromising the weight of the overall system.

Unsteady Airfoil with Dynamic Leading- and Trailing-Edge Flaps

Unsteady Airfoil with Dynamic Leading- and Trailing-Edge Flaps

Computational Modeling of Variable-Droop Leading Edge in Forward Flight

In recent years, there has been significant interest in on-blade concepts that expand the operating envelope of helicopters without compromising the performance characteristics of the baseline rotor. The variable-droop leading-edge concept is explored in a modified version of the Navier-Stokes solver OVERFLOW. Modifications were made to the solver to allow deforming-grid capability. This concept was explored in dynamic stall tests of the VR-12 and SC1095 helicopter airfoils. The variable-droop leading-edge airfoils have dramatically reduced drag and moment rises associated with dynamic stall. Using the results of these tests, a modified UH-60A rotor incorporating variable-droop leading-edge airfoils was analyzed using loosely coupled computational fluid dynamics and comprehensive structural dynamics with OVERFLOW and DYMORE and compared with the standard UH-60A rotor for high-thrust-case flight 9017. Results show a reduction in the peak negative pitching moment. The rotor efficiency was shown to improve by 2.9% and the 4/rev component of vertical force reduced by 8%. These performance improvements can be improved with an improved droop schedule and by incorporating improved transonic airfoils.

CALCULATION OF THE UNSTEADY AIRLOADS ON WIND TURBINE BLADES UNDER YAWED FLOW

A dynamic stall model is coupled with the blade element momentum theory to calculate the cyclic variation of the aerodynamic characteristics of the wind turbine in yawed flow. In the dynamic stall model, unsteady effects under attached flow conditions are simulated by the superposition of indicial aerodynamic responses. The movement of the unsteady flow separation point is related to the static separation based on the Kirchhoff flow model via a deficiency function, in which the unsteady boundary layer response and the leading edge pressure response are taken into consideration. The induced vortex force and the associated pitching moment are represented empirically in a time-dependent manner during dynamic stall. The required input of the inflow velocity and incidence to the dynamic stall model is calculated using the improved blade element momentum theory. The calculated results are compared well with the NREL UAE Phase VI experimental data. For completeness, possible factors causing the difference between calculated and experimental results are analyzed and discussed in detail in this paper.

Analysis of Parameter Sensitivity Using Robust Design Techniques for a Flatfish Type Autonomous Underwater Vehicle

Hydrodynamic parameters play a major role in the dynamics and control of Autonomous Underwater Vehicles (AUVs). The performance of an AUV is dependent on the parameter variations and a proper understanding of these parametric influences is essential for the design, modeling, and control of high-performance AUVs. In this paper, the sensitivity of hydrodynamic parameters on the control of a flatfish type AUV is analyzed using robust design techniques such as Taguchi's design method and statistical analysis tools such as Pareto-ANOVA. Since the pitch angle of an AUV is one of the crucial variables in the control applications, the sensitivity analysis of pitch angle variation is studied here. Eight prominent hydrodynamic coefficients are considered in the analysis. The results show that there are two critical hydrodynamic parameters, that is, hydrodynamic force and hydrodynamic pitching moment in the heave direction that influence the performance of a flatfish type AUV. A near-optimal combination of the parameters was identified and the simulation results have shown the effectiveness of the method in reducing the pitch error. These findings are significant for the design modifications as well as controller design of AUVs.

Gain scheduling PID control with pitch moment rejection for reducing vehicle dive and squat

This paper presents a derivation of a full vehicle model to study vehicle dynamics behaviour in longitudinal direction. The full vehicle model is then validated using an instrumented experimental vehicle based on the driver input from brake and throttle pedals. Two tests are performed for the purpose of model validation, namely, sudden braking and sudden acceleration test. The results of the validation show that the behaviours of the model closely follow the behaviour of a real vehicle. An active suspension control system is then developed on the validated full vehicle model to reduce unwanted vehicle motions during braking and throttling manoeuvres. The proposed controller structure for the active suspension system is gain scheduling PID control with pitch moment rejection loop. The results show that the proposed control structure is able to significantly improve the dynamic performance of the vehicle during sudden braking and sudden acceleration under various conditions.

Active Control of Flapping Wings Using Wing Deformation

A new method for the attitude control of a flapping-wing aircraft is proposed. In this method, the variations in wing deformation, that is, the feathering angle and the camber, are controlled by pulling the wing at a certain point with a thread connected to a servomotor. The experimental setup for verifying the practicability of this method was developed, and aerodynamic forces and wing deformation were measured. It was concluded that thread control caused effective wing deformation, and the variation in the deformation generated the pitching moment that controls the attitude of a flapping-wing aircraft.

작동기수가 부족한 자율무인잠수정 그룹의 편대제어기법

This paper presents an asymptotic formation control scheme for a group of underactuated autonomous underwater vehicles (AUVs) where only three control inputs - surge force, yaw moment and pitch moment are available for each vehicle's six degree of freedom (DOF) underwater motion. Usually, the dynamics agents applied in most of the formation algorithms presented so far have been modeled as particle systems, which is a simple double-integrator system. Therefore, these algorithms cannot be directly applicable to the practical systems, especially to the underwater vehicles whose dynamics are highly nonlinear. Moreover, the vehicles considered in this paper are underactuated. The formation control is derived using general potential function method, and the corresponding potential function consists of two parts: interactions between vehicles and virtual-leader following. Proposed formation scheme guarantees asymptotic local stability of closed-loop system. Numerical simulations are carried out to illustrate the effectiveness of proposed formation scheme.

Thin-ship theory and influence of rake and flare

The basic computational task of the thin-ship theory of free-surface potential flow about a ship that advances at constant speed along a straight path in calm water, of large depth and lateral extent, is considered. Specifically, a straightforward method for evaluating the pressure and the wave profile at a ship hull (the wave drag, hydrodynamic lift and pitch moment, and sinkage and trim are also considered) in accordance with Michell’s thin-ship theory is given. A main ingredient of this method is a simple analytical approximation to the local-flow component in the expression for the Green function (associated with the classical Michell–Kelvin linearized free-surface boundary condition) of thin-ship theory. This practical Green function is used to evaluate and analyze steady flow about a four-parameter family of ship bows with rake and flare. In particular, the variations of the bow-wave height and location with respect to the draft-based Froude number, the entrance angles at the top and bottom waterlines, and the rake angle are explored via a systematic parametric study. This parametric study provides estimates—immediately useful for design—of the influence of rake and flare on the height and the location of a ship bow wave, and shows that rake and flare effects can be significant, especially at low Froude numbers.

Active Flow Control at Low Angles of Attack: Stingray Unmanned Aerial Vehicle

Active flow control using fluidic actuators, via arrays of synthetic jet actuators, was used to provide control power for the Stingray unmanned aerial vehicle in the longitudinal (pitch) and lateral (roll) directions at low angles of attack. Using this technique, the pitch and roll moments were altered such that the effect is similar to that of a deflection of conventional control effectors. The control effectiveness of the synthetic jets on the aerodynamic performance of the Stingray unmanned aerial vehicle was investigated experimentally in a wind tunnel. Global flow measurements were conducted, where the moments and forces on the vehicle were measured using a six-component sting balance. The effect of the actuation was also examined on the surface static pressure at two spanwise locations. In addition, a particle image velocimetry technique was used to quantify the flowfield over the model, both the global flowfield as well as the localized interaction domain near the synthetic jet orifice. The synthetic jets were able to alter the local streamlines and displace the boundary layer through the formation of a small quasi-steady interaction region on the suction surface of the Stingray unmanned aerial vehicle's wing. Phase-locked particle image velocimetry data were acquired to provide insight into the growth, propagation, and decay of the synthetic jets impulse and their interaction with the crossflow. Furthermore, the changes induced on the moments and forces can be proportionally controlled by either changing the momentum coefficient or by driving the synthetic jets with a pulse modulation waveform. This can lead the way for future development of closed-loop control models.

Pitching stabilizationviacaudal fin-wave propagation in a forward-sinking parrot cichlid (Cichlasoma citrinellum×Cichlasoma synspilum)

Caudal fin-wave propagation (CFP) is a commonly observed behavior in a fish but has been little investigated. Our objective is to understand the function of a CFP for a forward-sinking parrot cichlid that adopts a tilted-down swimming posture. We utilized stereoscopic digital particle-image velocimetry to measure the velocity fields in the wake of both the caudal fin and the pectoral fins and to evaluate the corresponding hydrodynamic forces. The tilted-down posture of this fish is inherently unstable because of the presence of the head-down pitching moment induced from the buoyant force of the body. The down-stroke of the pectoral fins results also in a head-down pitching moment that destabilizes the fish. Our results indicate that a CFP facilitates the pitching stabilization of a fish. In a forward-sinking parrot cichlid, a CFP produces periodic jets (CFP jets) that are oriented laterally and posterodorsally, which result in both thrust and negative lift that induce a head-up pitching moment. The CFP jets are initially trapped by the ventral part of the caudal fin, strengthened and reoriented by the dorsally propagating fin wave, and expelled near the dorsal part of the caudal fin.