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"Ground-effect machines Design"
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Lift System Design of Air Cushion Vehicle
Lift system plays key role to Air Cushion Vehcile overall performance, whose design includes cushion flow demanding analysis, lift fan design, airflow distribution and pressure control. The method to calculate cushion flow exit velocity variation with craft speed was firstly presented based on cushion induced wave. Through application development in CATIA, a full solution was presented to check if craft keeps in safety flight boundary at maximum calm water speed. Through analysis, current cushion flow demanding method based on statistic former ACVs seems conservative for particular ACV with super high cushion density, which was adviced to decrease by 10%∼15%. New double discharge lift fan for polar hovercraft was developed through CFD simulation, model test, full-scale utilizing. To reach designed bag-cushion pressure ratio, polar ACV model skirt feed holes was added by 1/3 more than simple geometrical scale. Larger bag feed holes and lower bag-cushion pressure ratio are effective means to lower lift power.
Journal Article
Investigation of resistance performance of anti-icing wave-plate separators for marine gas turbines intake system
Due to their high power and efficiency, gas turbines are commonly used propulsion systems in hovercraft propulsion systems. In polar and cold marine environments, when a hovercraft rises, a significant number of droplets are generated on the water surface and are drawn into the gas turbine’s air intake with the cold air. This paper takes the structure of the original wave-plate separator as a reference and designs two structures: the rhombic anti-icing wave-plate separator (RAWS) and the streamlined anti-icing wave-plate separator (SAWS). Experimental and numerical simulation methods are employed to calculate the air intake resistance of the two structures at speeds ranging from 1 to 10 m/s. The results show that the K-ε standard enhanced wall function turbulent model is the closest to experimental measurements, with all calculated results having an error below 5%, demonstrating reliability. Compared to RAWS, the calculated total pressure loss for the SAWS structure decreases by 200 Pa under a designed air intake velocity of 7 m/s, representing a relative reduction of 40.8%. This provides a valuable reference for the design and resistance optimization of ship air intake anti-icing devices.
Journal Article
Investigating the Effect of Geometric Shape on Air Cushion Lift Force
One of the crucial and challenging issues for researchers is presenting an appropriate approach to evaluate the aerodynamic characteristics of air cushion vehicles (ACVs) in terms of system design parameters. One of these issues includes introducing a suitable approach to analyze the effect of geometric shapes on the aerodynamic characteristics of ACVs. The main novelty of this paper lies in presenting an innovative method to study the geometric shape effect on air cushion lift force, which has not been investigated thus far. Moreover, this paper introduces a new approximate mathematical formula for calculating the air cushion lift force in terms of parameters, including the air gap, lateral gaps, air inlet velocity, and scaling factor for the first time. Thus, we calculate the aerodynamic lift force applied to nine different shapes of the air cushions used in the ACVs in the present paper through the ANSYS Fluent software. The geometrical shapes studied in this paper are rectangular, square, equilateral triangle, circular, elliptic shapes, and four other combined shapes, including circle-rectangle, circle-square, hexagonal, and fillet square. Results showed that the cushion with a circular pattern produces the highest lift force among other geometric shapes with the same conditions. The increase in the cushion lift force can be attributed to the fillet with a square shape and its increasing radius compared with the square shape.
Journal Article
A Reformulated-Vortex-Particle-Method-Based Aerodynamic Multi-Objective Design Optimization Strategy for Proprotor in Hover and High-Altitude Cruise
An improved multi-objective design optimization framework is proposed for the efficient design of proprotor blades tailored to specific high-altitude mission requirements. This framework builds upon existing methods by leveraging a reformulated Vortex Particle Method (rVPM) and incorporates three key stages: (1) rapid determination of overall proprotor parameters using a semi-empirical model, (2) optimized blade chord and twist distribution bounds based on minimum energy loss theory, and (3) global optimization with a high-fidelity rVPM-based aerodynamic solver coupled with a multi-objective hybrid optimization algorithm. Applied to a small high-altitude tiltrotor, the framework produced Pareto-optimal proprotor designs with a figure of merit of 0.814 and cruise efficiency of 0.896, exceeding mission targets by over 15%. Key findings indicate that large taper ratios and low twist improve hover performance, while elliptical blade planforms with high twist enhance cruise efficiency, and a tip anhedral further boosts overall performance. This framework streamlines the industrial customization of proprotor blades, significantly reducing the design space for advanced optimization while improving performance in demanding high-altitude environments.
Journal Article
Numerical prediction of noise reduction solution on hovercraft propellers using LES and FW–H methods
Hovercrafts are known to produce excessive noise during operation, and the experimentally measured overall sound pressure level (OASPL) noise of the propeller is as high as 115 dB, which causes significant disturbances to surrounding residents and the environment. To address the research gap concerning noise issues associated with air-ducted propellers used in hovercrafts and other related fields, this article aims to investigate the impact of the clearance between the blade tips and the ducted on the aerodynamic and acoustic characteristics of the air propeller in the hovercraft. The aerodynamic and acoustic performance of the air propeller is evaluated using large eddy simulation (LES) and the Ffowcs Williams–Hawkings (FW–H) acoustic model, and the difference between numerical calculations and experiments is less than 3 dB. Results suggest that smaller tip clearance effectively reduces propeller noise without sacrificing aerodynamic performance. The maximum overall sound pressure level is reduced by 9.7 dB, while a reduction of 4.84 dB is observed at the blade passing frequency (BPF). However, increasing the tip clearance amplifies the downstream evolution of propeller wake vortices, resulting in a deterioration of the aerodynamic and acoustic performance of the propeller. This finding explains the mechanism by which tip clearance affects propeller noise and offers significant guidance for the future design and optimization of air propellers.
Journal Article
Adaptive sliding mode-based full-state stabilization control of an underactuated hovercraft
Hovercraft is commonly used for military operations, transportation, and scientific research. Therefore, considering the use of hovercraft, it is very important to design a controller that ensures its stabilization to enhance its performance. Since a hovercraft has only two control inputs with three degrees of freedom, designing a stabilization controller is a very difficult task. The hovercraft model is derived from a simple ship equation that is nonlinear and underactuated. In this work, the controller design is conducted for the full-state stabilization problem to stabilize the underactuated hovercraft. Using the inputs and state transformations, the dynamic model of the hovercraft is transformed into an equivalent system consisting of two cascaded connected subsystems. Dynamic input terms are introduced due to the modified dynamic cascaded system, and an adaptive sliding mode control (SMC) scheme is employed to handle these terms and to clutch the stabilization problem. To eliminate the high-frequency switching effect in SMC and enhance the speed of reaching phase, an atan-based strong exponential reaching law is employed. To construct the stabilizing controller, an appropriate Hurwitz sliding surface and a Lyapunov function are selected, and the adaptive laws are derived such that the derivative of the Lyapunov function is strictly negative, so as to guarantee the stability of the closed-loop system. To demonstrate the efficacy of the proposed control, numerical simulations are run to stabilize the planar position and orientation, revealing that all states and control inputs are asymptotically convergent to the origin since a quantitative comparison is also made between the classical switching law and the suggested switching law for energy consumption.
Journal Article
Rotorcraft Aeromechanics
A rotorcraft is a class of aircraft that uses large-diameter rotating wings to accomplish efficient vertical take-off and landing. The class encompasses helicopters of numerous configurations (single main rotor and tail rotor, tandem rotors, coaxial rotors), tilting proprotor aircraft, compound helicopters, and many other innovative configuration concepts. Aeromechanics covers much of what the rotorcraft engineer needs: performance, loads, vibration, stability, flight dynamics, and noise. These topics include many of the key performance attributes and the often-encountered problems in rotorcraft designs. This comprehensive book presents, in depth, what engineers need to know about modelling rotorcraft aeromechanics. The focus is on analysis, and calculated results are presented to illustrate analysis characteristics and rotor behaviour. The first third of the book is an introduction to rotorcraft aerodynamics, blade motion, and performance. The remainder of the book covers advanced topics in rotary wing aerodynamics and dynamics.
eBook
Control scheme for waypoint navigation of an underactuated hovercraft
This article presents a control scheme for navigation by waypoints given in the X-Y plane for an underactuated hovercraft, which has three Degrees of Freedom and two control inputs. The control scheme is made up of three feedforward Backstepping Controllers (BC); two act directly on the actuated coordinates, while the third corresponds to an auxiliary control that is responsible for manipulating the orientation angle (actuated coordinate) based on the error of the Y axis (underactuated coordinate), allowing the tracking of desired reference points in the X-Y plane. The proposed scheme is numerically validated for different cases that involve trajectory tracking through different waypoints. Additionally, the displacement from one reference point to another is carried out by tracking a Bezier polynomial trajectory, which guarantees a smooth transition from one waypoint to another; therefore, to controlling the time in which the vehicle reaches the reference value. Finally, a comparison of the proposed scheme with respect to the use of Feedforward PID Controllers (FFPC) is presented.
Journal Article
Design conception and evaluation of an unmanned amphibious aerial vehicle using systematic approach
This article’s incitement interprets Unmanned Amphibious Aerial Vehicle (UAAV)’s conceptual design process in a systematic approach. The UAAV is conceptualised to be an ideal tool for limnologists in water quality assessment. Integration of hovercraft with the multi-rotor system helps collect water samples from remote and inaccessible water bodies. The UAAV flies in multi-rotor mode, subsequently land and glide along the water surface in hovercraft mode. The new and unconventional vehicle configuration makes the conceptual stage a challenging one in the design process. To overcome the challenges and strapped configuration of vehicle design, the Authors used a systematic approach of scenario-based design, morphological matrix, and Pugh’s method in the design process of the “Pahl & Beitz” model to retrieve the best possible UAAV design. The conglomerate design of UAAV is evaluated for its design requirements, and the computational analysis is performed to examine the mechanical strength and flow characteristics of UAAV. The experimental prototype of UAAV demonstrates the competence of flying in the air and hovering in water through field trials.
Journal Article