Bow Wave Effect Research Articles

Vibration suppression of flexible hose for autonomous aerial refueling based on adaptive boundary compound controller

The suppression of vibrations in flexible hoses during autonomous aerial refueling (AAR) is crucial for enhancing mission success rates and safety, advancing AAR technology. In this paper, an adaptive boundary compound control (ABCC) strategy is proposed to address the vibration suppression problem of the flexible hose of a tanker subject to the bow wave effect (BWE) of the receiver, state output constraint, and partial actuator failure. Unlike previous studies, this research takes into account the impact of the receiver's BWE on these vibrations. The flexible hose is modeled as a three-dimensional Euler-Bernoulli beam (TDEBB), utilizing partial differential equations (PDEs) to provide a more accurate description of its dynamic characteristics. Furthermore, the proposed ABCC strategy accurately detects all disturbances, ensures that the system state output remains within specified limits, and maintains stability even in the face of actuator failures. Last but not least, numerical comparisons and simulations demonstrate that the ABCC method significantly suppresses hose vibrations and maintains end displacement within a narrow range.

Modeling and Simulation of Bow Wave in Aerial Refueling

In a probe-and-drogue aerial refueling system, the tanker docking system consists of a hose and a drogue. When the receiver approaches the drogue, the dynamics of the drogue may be seriously disturbed by the aerodynamic effect from the receiver which is commonly known as the bow wave effect. In this paper, a numerical simulation method based on potential flow theory is proposed to investigate the bow wave effect. The proposed method is efficient and can be conveniently used in the modelling and simulation of autonomous aerial refuelling system. The results of this method are highly consistent with the CFD results, which demonstrates the effectiveness of the proposed method.

Deep learning based trajectory optimization for UAV aerial refueling docking under bow wave

In the autonomous aerial refueling (AAR) docking process, the bow wave generated by the receiver has a strong effect on the drogue, which affects the docking success rate greatly. Thus, a deep learning based trajectory optimization method which aims to decrease the bow wave effect on the drogue is proposed in this paper. There are mainly three parts in the proposed trajectory optimization method. Firstly, a precise bow wave model based on deep learning is presented to estimate the bow wave effect on the drogue. Furthermore, due to the dynamic characteristic of the drogue, a simple and practical drogue motion prediction model under multiple disturbances is carried out to provide a precise prediction of the drogue position at the next time. Moreover, considering the strict attitude constraints requirements in the AAR docking process, a novel reference observer is designed to estimate the receiver attitude from the optimized trajectory under wind perturbations. Then, the proposed trajectory optimization method could not only diminish the bow wave effect on the drogue largely but also satisfy the attitude constraints of the receiver. Finally, the effectiveness of the proposed method is demonstrated by the simulations.

Influence of the receiver aircraft’s bow wave on the motion characteristics of the drogue in hose-drogue refueling system

In the docking process of hose-drogue aerial refueling system, the bow wave effect of an approaching receiver aircraft will produce a strong aerodynamic effect on the drogue which intensify the deviation of drogue and increase the difficulty of the docking. This paper presents a receiver aircraft’s bow wave effect modeling method based on potential flow theory and considers the major shape characteristics of the receiver aircraft. This method is used in a probe-drogue aerial refueling dynamic simulation system, which combined with the hose-drogue dynamic model and tanker wake dynamic model. The motion characteristics of the drogue under different flight altitude, flight velocity and docking velocity are calculated and analyzed. The results show that when the other conditions are certain, when the flight altitude increases, the bow wave effect decreases the vertical and longitudinal influence on the drogue, increases the lateral influence. When the flight velocity increases, the bow wave effect increases the vertical and longitudinal influence on the drogue, decreases the lateral influence. When the docking velocity increases, the drogue’s swing displacement and the swing velocity are all increased.

Study on the affecting factors of bow wave effect modeling in hose-drogue refueling system

In the docking process of aerial refueling hose-drogue system, the bow wave effect of an approaching receiver aircraft will produce a strong aerodynamic effect on the drogue which intensify the deviation of drogue and increase the difficulty of the coupling. This paper presents a receiver aircraft’s bow wave effect modeling method previously developed by the authors is continued to study, which based on potential flow theory and considers the major shape characteristics of the receiver aircraft. This method is used in a simulation system, which combined with the hose-drogue dynamic model and tanker downwash model. The model of the receiver aircraft, which includes the fuselage, cockpit, main wing and other structural factors, is simulated respectively. The motion law of drogue under different bow wave model is analyzed. The results show that the fuselage, cockpit and main wing structure have significant influence on the bow wave effect.

Drogue dynamic model under bow wave in probe-and-drogue refueling

Probe-and-drogue refueling (PDR) is widely adopted owing to its simple requirement of equipment and flexibility, but it has an apparent drawback that the drogue position is susceptible to disturbances. There are three types of disturbances: atmospheric turbulence, trailing vortex of the tanker, and bow wave effect caused by the receiver. The former two disturbances are independent of the receiver, whereas the bow wave effect, which depends on the state of the receiver, greatly influences the docking within a close distance. As far as the authors know, little attention has been paid to the bow wave effect on docking control in existing literature. The existing literature related to the bow wave focuses on either qualitative static results obtained from experiments, or lookup tables based on computational fluid dynamics (CFD) analysis. These are inapplicable to the PDR docking controller design directly. This paper proposes a lower order dynamic model to describe drogue dynamics under the bow wave effect. The model consists of two components: one is a second-order transfer function matrix to describe the drogue dynamics, and the other is a nonlinear function vector to describe the bow wave effect model. A closed-loop simulation including the two components shows that the generated drogue dynamics are similar to those of a real experiment reported in an existing literature.

Maneuverability of Large Receiver of Different Size and Weight in Aerial Refueling

This work evaluates the ability of a large receiver aircraft with two different sizes and three different mass configurations to maneuver and maintain contact position behind a KC-135 tanker in the presence of prevailing wind and atmospheric turbulence. A linear quadratic regulator controller is designed for trajectory tracking of the receiver aircraft relative to the tanker. The flight tracks followed in simulation by each aircraft are taken from 2004 testing of a Learjet behind a KC-135 that was part of the U.S. Air Force Research Laboratory Automated Aerial Refueling program and includes significant winds at altitude. The simulation also includes the aerodynamic coupling between the aircraft through the trailing and bound vortices of each aircraft as well as their volumes (bow wave effect for the tanker).

Bow Wave Effect in Aerial Refueling: Computational Analysis and Modeling

Mechanisms contributing to the “bow wave” effect of a receiver on a tanker are investigated, and a modeling method for dynamic simulation is developed. Vortex lattice and Cart3D codes are used to calculate the aerodynamic forces and moments for a C-141B behind a KC-135. The vortex lattice code significantly underpredicts the bow wave effect, whereas the Cart3D code shows good agreement with available flight data. The modeling method uses stream functions for inviscid flow around solid bodies. The flowfield induced by the presence of aircraft bodies is superimposed on the flowfield generated by horseshoe vortices. The resultant flowfield is approximated by the effective uniform translational and rotational velocity components, which are used in the buildup equations for the aerodynamic force and moment coefficients of both tanker and receiver aircraft. This method applied to a flying wing behind a KC135 shows good agreement with Cart3D results. It is concluded that the major contribution to the “bow wave” effect is the effect of the displacement of air due to the volume of the receiver and not upwash from the bound vortex due to the lift of the receiver. This disagrees with earlier studies that did not have the benefit of flight data to use as a benchmark.

Sampling epifauna, a necessity for a better assessment of benthic ecosystem functioning: An example of the epibenthic aggregated species Ophiothrix fragilis from the Bay of Seine

Sampling the sea bottom surface remains difficult because of the surface hydraulic shock due to water flowing through the gear (i.e., the bow wave effect) and the loss of epifauna organisms due to the gear’s closing mechanism. Slow-moving mobile epifauna, such as the ophiuroid Ophiothrix fragilis, form high-density patches in the English Channel, not only on pebbles like in the Dover Strait or offshore Brittany but also on gravel in the Bay of Seine (>5000indm−2). Such populations form high biomasses and control the water transfer from the water column to the sediment. Estimating their real density and biomass is essential for the assessment of benthic ecosystem functioning using trophic web modelling. In this paper, we present and discuss the patch patterns and sampling efficiency of the different methods for collecting in the dense beds of O. fragilis in the Bay of Seine. The large Hamon grab (0.25m−2) highly under-estimated the ophiuroid density, while the Smith McIntyre appeared adequate among the tested sampling grabs. Nowadays, diving sampling, underwater photography and videos with remote operated vehicle appear to be the recommended alternatives to estimate the real density of such dense slow-moving mobile epifauna.

Resilient Modulus of Soft Soil Beneath High-Speed Rail Lines

Modern high-speed rail lines are being built increasingly on marginal land, to reach city centers while avoiding housing areas. Often this land is composed of soft alluvial soils, which exhibit a low resilient modulus. The measurement, prediction, modeling, and implications of resilient modulus values for such subgrades are discussed. Measurement considers the use of repeated-load triaxial testing, resonant column, and in situ methods, illustrating these with sample data. Prediction draws on both analytical and finite-element techniques to illustrate the critical speed (the bow-wave effect) and how it is influenced by resilient modulus. Modeling reveals the available relationships—and their limitations—for deriving subgrade stiffness in this dynamic situation. Implication then uses these to define the relevant effects of resilient modulus values on design problems.