Moment Coefficients Research Articles

Parametric Investigation of Canards on a Flying Wing UAV Using the Taguchi Method

The current work investigates the effect of canard geometric characteristics on the performance of a lightweight flying wing Unmanned Aerial Vehicle (UAV), capable of both conventional and Vertical Take-Off and Landing (VTOL) flight. The canards are sized as horizontal stabilizers to enhance the UAV’s longitudinal stability and minimize trimming requirements during cruise. Using a Design of Experiments (DOE) approach and, specifically, the Taguchi method, six canards’ design parameters are investigated on three different levels. These parameters are the sweep angle (Λ), aspect ratio (AR), taper ratio (λ), vertical position in relation to the main wing (vpos), incidence angle (ic), and dihedral angle (Γ). An L27 orthogonal array (OA) is used to investigate the influence of these key design parameters using two performance criteria, namely the Lift-to-Drag ratio (L/D) and the pitching moment coefficient (Cm), at cruise conditions (designated as L/Dcruise and |Cm|cruise). The investigation is conducted by using high-fidelity Computational Fluid Dynamics (CFD) methods for each of the 27 configurations defined by the L27 OA, over a range of angles of attack. Based on the CFD results, two distinct combinations are derived for maximum L/Dcruise and minimum |Cm|cruise using the Signal-to-Noise ratio (SNR) analysis. The optimal design parameter combinations for the two performance criteria are A2B1C1D1E1F1 and A2B2C1D2E2F3, respectively. Finally, the Pareto Analysis of Variance (ANOVA) technique is conducted to define the contribution of each of the six design parameters on the L/Dcruise and the |Cm|cruise. More specifically, ic seems to have the most significant effect on L/Dcruise, whereas Λ is the most important parameter for |Cm|cruise.

Influence of Low Speed and High Angle of Attack on Sting Support Interference

In order to improve the quality of low-speed and high angle of attack test data and master the law of support interference, a numerical simulation study of support interference was carried out for a wind tunnel tensioning tail brace system. The results show that the impact of the beam of wire-assistant sting support on longitudinal aerodynamics characteristics of aircraft is small, and the “E” sting greatly affects longitudinal aerodynamics characteristics at a high angle of attack. The yawing moment coefficients decrease, and rolling moment coefficients increase at the angle of attack from 0°to 20° with the existence of wire-assistant sting support. With the increase of side slip angle, the interference becomes bigger, then becomes smaller, and 30°is the biggest.

Analysis of Aircraft Parking Stability Based on Atmosphere Boundary Theory

Based on numerical simulation technology, the aerodynamic load research of civil aircraft parked on the ground is conducted. The CRM model parked on the ground is established by CFD software. Based on the atmospheric boundary layer theory, the seven incoming flow conditions for numerical calculation are designed. And the aerodynamic loads’ change of the aircraft model is calculated when the -90° sideslip angle. The result shows that the mooring load on the nose landing gear mainly comes from the longitudinal load caused by the upwards pitching moment on the flat tail and the lateral load caused by the yaw moment; since the rolling moment coefficient is less than the pitching moment coefficient by two orders of magnitude, which hardly affects the mooring load. The study provides a reference for reducing the mooring load of civil aircraft under heavy wind conditions.

Determination of the critical velocity of a straight wing with a high aspect ratio

An aerodynamic problem on an air flow around a large aspect ratio rectangular wing is investigated in this study. According to the theory of Vlasov, the wing is considered to be a thin rod. External loads are assumed to be proportional to the airfoil angle of attack related to the dimensionless coefficient of the lift and the pitching moment coefficient. These coefficients depend on the airfoil parameters and the Mach number M and are determined by experimental measurements for subsonic and supersonic velocities. In this case, to define the unstable cases of the wing, one bases on the Lyapunov stability theory. Equations of bending and torsional free vibrations have resulted. Based on the analysis of natural frequencies (eigenfrequencies), it is possible to determine the changing positions of the real part and the imaginary part of the characteristic equation solution. These positions can cause instabilities for the wing such as torsional divergence and flutter.

Pengaruh Net Generation Terhadap Interaksi Sosial Pada Pelajar Sma Negeri I Kota Sukabumi

Indication of the problem from this research is social interaction that cannot be separated from the communication process. Social interaction in the real world is reduced due to the presence of advanced technology, informational society and the Internet generation or the Net Generation. This generation tends to interact in cyberspace, so social interaction in real life is increasingly limited. From this background, the research aims to determine Net Generation among students of SMAN I Sukabumi City, social interaction of Net Generation, and how much influence Net Generation has on social interaction. This study uses an associative descriptive method with Rating Scale measurements and analysis using a continuum line. Meanwhile, to find out how big the correlation between the two variables, the researcher used the product moment correlation formula, the coefficient of determination and hypothesis testing. Meanwhile, for processing the data results, the application of Statistical Product and System Solution (SPSS) Statistics Version 14.0 is used. The sample in this study was 115 people from a total population of 1,720 people. The sampling technique used was random sampling. Based on the results of the analysis, the Net Generation of SMAN I students in Sukabumi City obtained an average value of 3.8 and was in the agree category. Social interaction in SMAN I Sukabumi students obtained an average score of 3.7 and entered the agree category. There is a positive and significant influence between Net Generation and Social Interaction. This is based on the results of the calculation of the Pearson product moment coefficient, the correlation value (837) is 0.837, which means that there is a very strong correlation. The coefficient of determination is 70% while the remaining 30% is the influence of other variables that are not included in the research title. Then to test the hypothesis, because t count > t table which is 16.47 > 1.981 then Hₒ is rejected. In conclusion, there is a positive and significant influence between Net Generation on Social Interaction in Students of SMAN I Sukabumi City.

Analysis of Von Kármán Swirling Flows Due to a Porous Rotating Disk Electrode

The study of Von Kármán swirling flow is a subject of active interest due to its applications in a wide range of fields, including biofuel manufacturing, rotating heat exchangers, rotating disc reactors, liquid metal pumping engines, food processing, electric power generating systems, designs of multi-pore distributors, and many others. This paper focusses on investigating Von Kármán swirling flows of viscous incompressible fluid due to a rotating disk electrode. The model is based on a system of four coupled second-order non-linear differential equations. The purpose of the present communication is to derive analytical expressions of velocity components by solving the non-linear equations using the homotopy analysis method. Combined effects of the slip λ and porosity γ parameters are studied in detail. If either parameter is increased, all velocity components are reduced, as both have the same effect on the mean velocity profiles. The porosity parameter γ increases the moment coefficient at the disk surface, which monotonically decreases with the slip parameter λ. The analytical results are also compared with numerical solutions, which are in satisfactory agreement. Furthermore, the effects of porosity and slip parameters on velocity profiles are discussed.

Aerodynamic Coefficients of a Microspoiler for Spin-Stabilized Projectiles

In this paper, the aerodynamic coefficients of a microspoiler for a spin-stabilized projectile are studied using a computational fluid dynamics (CFD) simulation. To guarantee an effective study, the CFD simulation methodology is validated by the current literature and a wind-tunnel test. As a result, the additional axial force coefficient, additional normal force coefficient, and normal moment coefficient are obtained and varied with a wide range of Mach numbers (from 0.6 to 2.0), angles of attack (from 0 to 30°), and aerodynamic roll angles (from 0 to 180°). The numerical simulation results show that, in addition to the freestream Mach number and the angle of attack, the effect of the aerodynamic roll angle on the additional axial force and normal force coefficients cannot be negligible. By observing and analyzing a series of pressure field plots around the uncontrolled and controlled projectiles, some important phenomena are reasonably discussed. It was found that the complicated variation in the aerodynamic coefficients of the microspoiler is induced by flow modifications, such as the pressure distribution around the projectile. The results of this research are expected to be supplementary to those concerning the aerodynamic characteristics of spin-stabilized projectiles with microspoilers, as concluded in the current literature.

The effect of loading conditions and ship speed on the wind and air resistance of a containership

Although air resistance is relatively low in comparison to the total resistance of a ship, in the case of containerships, it can vary depending on the loading conditions and the layout of the stored containers. Over the years, containerships have increased in size and thus the air resistance has increased due to the increased windage area. The present study aims to assess the effect of different container configurations and trim on wind and air resistance as well as the influence of ship speed on air resistance. Numerical simulations based on viscous flow around a post Panamax 6750-TEU containership were conducted for open sea conditions. The verification studies for the grid size and time step were conducted and a validation study was performed using the available experimental results. The numerical results are reported with the non-dimensionalized wind load coefficients using the ITTC recommendations for the determination of the representative wind velocity. It is shown that the trim angle has the greatest influence on the moment coefficient, while the largest air resistance is obtained for the empty containership. The results also show that trim by bow causes lower values of air resistance, while trim by stern leads to higher values in comparison to an even keel condition. Finally, the portion of air resistance in the total resistance varies from 3.5% up to 5.8% for container configurations 9 and 2, respectively.

The effect of wind characteristics on tall buildings with porous double-skin façades

Wind loads on tall buildings with porous double-skin façade (PDSF) systems were studied for various wind characteristics. Experiments were performed on a small-scale building model in a boundary layer wind tunnel. A single-skin building model was used as a reference case alongside three PDSF systems of 25%, 50% and 65% porosity. Two atmospheric boundary layer (ABL) simulations were created corresponding to category I (rural) and category III (suburban) ABLs of the EN-1991-1-4:2005 standard. Wind loads on the building model were studied based on high-frequency force balance measurements of integral moments, while pressure distribution on the building model surfaces was analyzed based on pressure measurements. Experiments were performed for ten flow incidence angles 0° < α < 45° with a 5° increment. The obtained results are considered highly relevant both for research purposes and engineering applications, especially considering the lack of similar studies currently available. In particular, the rural ABL simulation yields larger mean pressure coefficients. The effect of the ABL characteristics on the pressure coefficient standard deviation depends substantially on α, while the most notable difference is observed on the windward building model surface at α = 0°, where the suburban ABL causes a substantially higher standard deviation. The mean across-wind moment coefficient of the suburban ABL simulation is lower at all α points, while its standard deviation is lower for α > 0°. The along-wind moment coefficient in the suburban ABL simulation is ∼20% lower than in the rural ABL simulation, a trend which is observed for all α points. In contrast, the along-wind moment standard deviation is ∼25% larger in the suburban ABL simulation. The power spectral density of the along-wind moment is considerably lower in the suburban ABL simulation.

Insight on the dynamics of hydromagnetic stagnation‐point flow of magnetite‐water nanofluid due to a rotating stretchable disk: A two‐phase modified Buongiorno modeling and simulation

AbstractThe hydromagnetic stagnation‐point flow of magnetite‐water nanofluid due to a rotating stretchable disk has been numerically accessed. The nanofluid flow has been modeled by employing the two‐phase modified Buongiorno model that incorporates the volume fraction dependent effective nanofluid properties, Brownian motion, and thermophoresis effects. Von Kármán's similarity transformations are utilized in transmuting the mathematically modeled equations into a system of first‐order ODEs which are then resolved numerically using the bvp4c numerical scheme. The consequence of influential parameters on the flow profiles and the physical quantities has been presented through graphs and tables. Engineering quantities like moment coefficient and pumping efficiency of the disk are also elucidated in this research work. Results show that an augmentation in the Hartmann number descends the velocity profiles and ascends the nanofluid temperature profile. Further, a drop in the drag coefficient and a rise in the heat transfer rate are noted with an increment in the velocity ratio parameter. The tidings of this numerical simulation have applications in spin coating, rotating heat exchangers, and rotating disk reactors.

Experimental Study on Dynamic Stall of Airfoil in Rotor Reverse Flow Region

The large reverse flow region of the rotor with a high advance ratio is an important factor that affects the performance improvement of helicopters. This paper examines the dynamic stall of the airfoil in the reverse flow region of the rotor to develop a set of dynamic pressure measurement systems for the airfoil in the reverse low region. The pitch oscillation experiment of the NACA0018 airfoil in and out of the rotor reverse flow region has been carried out, and the influence of the airfoil motion parameters on dynamic stalls has been studied. The results show that the airfoil is more likely to stall in the reverse flow region under static conditions and that stall is invariant to the Reynolds number. After a stall occurs, the lift coefficient decreases more slowly with the increase of the angle of attack (about 10% of that in the forward flow state). Under the dynamic environment, in a pitching cycle, the quarter chord moment coefficient of the airfoil alternates between positive and negative frequently during reverse-blowing. The pitching oscillation in the reverse flow region is more sensitive to the changes in airfoil parameters than that under normal flow, and there is a marked difference. The alternating moment of the airfoil in the reverse flow region is significant: the greater the pitching amplitude, the greater the alternating moment. In the reverse-blowing state, with the increase in reduced frequency, the dynamic stall angle of attack increases more significantly.

Effects of flexible films on the aerodynamics of a 5:1 rectangular cylinder

The present study demonstrates the aerodynamics of a 5:1 rectangular cylinder with flexible films perpendicularly mounted on its upper surface at both the upstream and downstream ends in wind angle of attack (AOA) up to 20°. Flow and pressure fields around the cylinder are examined by smoke-wire visualizations and pressure measurements in a wind tunnel, respectively. Experimental results show that periodic flapping-induced vortices (FIVs) chiefly caused by the leading-edge flapping film play important roles in the cylinder flow and pressure field properties. The FIVs have a positive effect on the reattachment of the cylinder leading-edge shear layer. For the leading-edge film, the tip of the flapping film would touch down on the cylinder upper surface due to the large amplitude flapping of the film at fD/U∞ ≈ 0.811 (f is the film flapping frequency, D is the model characterized length, and U∞ is the free oncoming flow velocity). Meanwhile, the periodic FIVs dominate the cylinder flow and aerodynamic properties in the range of AoA = [0°, 8°), thus defined as the wall-flapped mode. With an increase in AoA = [8°, 20°], the tip of the flapping leading-edge film would not touch down owing to the small amplitude flapping of the film. Simultaneously, the periodic FIVs have limited effects on the cylinder flow and aerodynamic properties, thus named as the free-flapping mode. Compared to the without flexible films case, the scale of the FIVs is smaller than that of the impinging leading-edge vortices but in a higher frequency, resulting in a quick dissipation of the cylinder impinging shear layer instability, rapid recovery of the pressure on the cylinder upper surface, and reductions in the cylinder drag coefficient, lift coefficient, moment coefficient, and spanwise correlation. For the trailing-edge film, it flaps at fD/U∞ ≈ 0.650 and has a limited effect on the cylinder flow and aerodynamic properties. Finally, the flexible films can significantly mitigate the static stall of the rectangular cylinder, which may stabilize the elongated bluff bodies.

NUMERICAL SIMULATION OF THE VISCOUS FLOW AROUND SHIPS TURNING IN SHALLOW WATER

Due to the effect of water depth, hydrodynamic characteristics of ships manoeuvring in shallow waters are quite different from those in deep water. In the present study, the CFD method is used to investigate the hydrodynamic behaviour of the ESSO OSAKA model in model-fixed condition in deep and shallow waters by solving RANS equations, which performs steady turning motion with the effect of free surface considered. The governing equations are discretized by the finite volume method (FVM) and the free surface is captured by applying the volume of fluid (VOF) method. Viscous hydrodynamic characteristics and flow fields in a series of cases at different water depths and speeds are investigated respectively. By comparing the numerical results in shallow water with those in deep water, it was found that effects of water depth and free surface are significant on ship’s hydrodynamic forces. The coefficients of drag, lateral force and yaw moment all increase with the decrease of water depth. The drag coefficient in shallow water is about 45% larger than that in deep water. However, effect of water depth on the lateral force coefficient is small, it is about 15% larger in shallow water than that in deep water. While, it has significant effect on the yaw moment coefficient, which is about 25% larger in shallow water than in deep water. And as the water depth increases, the effect of the free surface gradually becomes smaller. Both coefficient of pressure component of drag force and drag coefficient in the present simulation are about 7% smaller than the case without considering the free surface at h/d ≥ 3.0, while that of frictional component is almost the same. When h/d ≥ 3.0, the lateral force and yaw moment coefficients are almost the same as when the free surface is not considered. The error between the present numerical result and the measurements is within 10%, which indicates that RANS method has promising capability to predict the hydrodynamic forces on ships manoeuvring in shallow water.

Fast Nonlinear Static Aeroelasticity Method for High-Aspect-Ratio Wings at Different Mach Regimes

A low-computational-cost method is proposed in this paper to predict steady-state nonlinear aeroelastic response for high-aspect-ratio wings. This fast nonlinear static aeroelasticity method relies on a simple but robust mathematical approach. The work presented in this paper evaluates the accuracy of a nonlinear aerodynamic method on a large range of Mach numbers for a geometry representative of a typical industrial high-aspect-ratio-wing aircraft. The robustness of the method relies on the accurate estimation of the local pressure field based on an aerodynamic database using a local incidence estimated with a vortex lattice method. The database can be filled with flight test, wind tunnel test, or high-fidelity numerical simulation. The structural deformation is provided by a coupled aeroelastic high-fidelity numerical simulation, and so this paper focuses mainly on the development and validation of the aerodynamic model. Then, the flexible coefficients of the wing are compared to the high-fidelity aeroelastic numerical simulations for a set of Mach numbers ranging from subsonic to transonic conditions. The results presented in this paper show that the present method is very accurate for low-Mach-number regimes (error is lower than 1% on lift), and it is also adapted to transonic flow regimes because the error on lift is lower than 5%. For high Mach numbers, the current solution commits larger errors on drag and pitching moment coefficients.

Bearing performance degradation assessment and remaining useful life prediction based on data-driven and physical model

Intelligent health maintenance of bearings usually consists of two stages: constructing effective health assessment indicators and accurate remaining useful life prediction models. However, many prediction models are available only when many constraints are met, and the health assessment indicators may not be able to accurately track the performance degradation process of bearings. This study proposes a bearing performance degradation assessment and remaining life prediction method. First, the health evaluation index family (referred to as the generalized high-order moment coefficient) was constructed based on the generalized power mean and high-order origin moments for health assessment. Subsequently, an improved Paris–Erdogan model is proposed, which uses the optimal health evaluation index as input to predict the remaining life of the bearing after the initial failure. The experimental results show that the proposed method has a higher performance degradation tracking accuracy and a smaller prediction error than the combination of traditional statistical indicators and prediction models.

Fast Prediction of Multiple Parameters Related to Iced Airfoil Based on POD and Kriging Methods

Ice accretion threatens aircraft safety. With the wide application of unmanned aerial vehicles (UAVs), the design of ice-tolerant UAVs has become a problem that must be solved. Forty conditions for the continuous/intermittent maximum icing conditions were sampled in Appendix C of Federal Aviation Regulations Part 25. Herein, numerical simulations of icing were performed on an NACA 0009 airfoil for 5, 15, and 30 min, and the ice mass and ice shapes were obtained at different times. Numerical simulations of the aerodynamic characteristics of the iced configuration at 5, 15, and 30 min were conducted, and the coefficients of lift, drag, and pitch moment were obtained. Surrogate models of the ice shape, mass of the ice accretion, lift coefficient, drag coefficient, and pitch moment coefficient at different moments were built based on proper orthogonal decomposition and kriging interpolation. The results demonstrate that the surrogate models accurately predicted the ice shape, ice mass, lift coefficient, drag coefficient, and pitch moment coefficient at different moments. Compared with the numerical simulation results, the maximum relative errors of the ice mass, lift coefficient, drag, and pitch moment predicted by the surrogate models were 7.8%, 3.4%, 3.9%, and 7.6%, respectively. This method can help in designing the ice-tolerant UAVs and envelope determination under icing conditions.

Experimental study of static wind force on typical substation post disconnect switchgear three-post structure under different wind angles

As a wind load-sensitive structure, the wind characteristics of typical post-disconnect switchgear in substations are of great significance to the design of the wind resistance of the structure. To study the static wind characteristics of the three-post structure of post-disconnect switchgear, this paper conducts high-frequency force balance (HFFB) wind tunnel tests on the three-post model of post-disconnect switchgear and obtains information on the variation law of the static wind force coefficient of the model with the wind angle and the most unfavorable wind angle. The results show that the model drag coefficient, combined force coefficient, and skewed wind load factor are M-shaped and symmetric at about 90° under different wind angles, and the most unfavorable wind angles are 60° and 120°; the lift coefficient and torsional moment coefficient are antisymmetric about 0°, and the overall values are small. In general, the model is mainly subjected to along-wind static wind force, and the static wind force distribution is influenced by the skewed wind and changes uniformly. The model mainly produces a bending effect under the action of static wind force, and the torsion effect is not obvious.

Robust image hashing based on quaternion polar complex exponential transform and image energy

To apply the quaternion moments to the image feature extraction process and improve the performance of the image hashing algorithm, we propose a hashing algorithm based on quaternion polar complex exponential transform and image energy. First, the input color image is preprocessed to form a secondary image. The secondary image is subjected to fast quaternion generic polar complex exponential transform to obtain the mixed low-order moment coefficients as the global features of the image. Second, the algorithm extracts energy change features on the edges of the secondary image and energy point features in the center of the image as energy features of the image under the YCbCr color space. Finally, the image’s mixed low-order moment and energy features are combined and scrambled to form the final hash sequence. The experimental results show that the proposed algorithm balances robustness and differentiation well. Moreover, the hash sequence is the shortest, and the algorithm has better check-all and check-accuracy rates compared with other algorithms in the copy detection experiments.

Experimental Assessment of Aero-Propulsive Effects on a Large Turboprop Aircraft with Rear-Engine Installation

This paper deals with the estimation of propulsive effects for a three-lifting surface turboprop aircraft concept, with rear engine installation at the horizontal tail tips, conceived to carry up to 130 passengers. This work is focused on how the propulsive system affects the horizontal tailplane aerodynamics and, consequently, the aircraft’s static stability characteristics using wind tunnel tests. Both direct and indirect propulsive effects have been estimated. The former produces moments whose values depend on the distance from the aircraft’s centre of gravity to the thrust lines and propeller disks. The latter entails a change in the angle of attack and an increment of dynamic pressure on the tailplane. Several tests were also performed on the body-empennage configuration to investigate the propulsive effects on the aircraft’s static stability without the appearance of any aerodynamic interference phenomena, especially from the canard. The output of the experimental campaign reveals a beneficial effect of the propulsive effects on the aircraft’s longitudinal stability, with an increase in the stability margin of about 2.5% and a reduction in the directional stability derivative of about 4%, attributed to the different induced drag contributions of the two horizontal tail semi-planes. Moreover, the rolling moment coefficient experiences a greater variation due to the propulsion depending on the propeller rotation direction. The outcomes of this paper allow the enhancement of the technical readiness level for the considered aircraft, giving clear indications about the feasibility of the aircraft configuration.

Assessment of Model Validation, Calibration, and Prediction Approaches in the Presence of Uncertainty

Abstract Model validation is the process of determining the degree to which a model is an accurate representation of the true value in the real world. The results of a model validation study can be used to either quantify the model form uncertainty or to improve/calibrate the model. The model validation process becomes complex when there is uncertainty in the simulation and/or experimental outcomes. These uncertainties can be in the form of aleatory uncertainties due to randomness or epistemic uncertainties due to lack of knowledge. Five different approaches are used for addressing model validation and predictive capability: (1) the area validation metric (AVM), (2) a modified area validation metric (MAVM) with confidence intervals, (3) the validation uncertainty procedure from ASME V&amp;V 20, (4) a calibration procedure interpreted from ASME V&amp;V 20, and (5) identification of the model discrepancy term using Bayesian estimation. To provide an unambiguous assessment of these different approaches, synthetic experimental data is generated from computational fluid dynamics simulations of an airfoil with a flap. A simplified model is then developed using thin airfoil theory. The accuracy of the simplified model is assessed using the synthetic experimental data. The quantities examined include the two-dimensional lift and moment coefficients for the airfoil with varying angles of attack and flap deflection angles. Each of these approaches is assessed for the ability to tightly encapsulate the true value at conditions both where experimental results are provided and prediction locations where no experimental data are available. Generally, it was seen that the MAVM performed the best in cases where there is a sparse amount of data and/or large extrapolations. Furthermore, it was found that Bayesian estimation outperformed the others where there is an extensive amount of experimental data that covers the application domain.