This study provides a comprehensive analysis of the impact of helideck surface conditions on the safe operation of helicopter landing and take-off platforms on offshore drilling vessels. Over time, the deterioration of helideck surface coatings necessitates periodic friction coefficient testing every two years in compliance with international standards. Surface coatings that fail to meet the required thresholds are replaced, and the performance of the renewed surface is reassessed using the Helideck Micro GripTester (HMGT), in accordance with U.K. Safety Regulation Group CAP 437 (2023) standards for offshore helicopter landing areas. The findings indicate that the renewed helideck surface coatings lead to a significant increase in the coefficient of friction, thereby enhancing the stability of helicopters upon landing and while on deck. Independent sample t-test and correlation analyses confirmed statistically significant differences between the old and new surface conditions, demonstrating the positive impact of surface improvements on coefficient of friction and, therefore, operational safety. Furthermore, machine learning techniques were employed to model and analyse the non-linear relationships between surface conditions and flow number. The model results demonstrate that variations in helideck surface coatings directly influence helicopter performance and operational safety. These findings underscore the critical importance of regular resurfacing and friction testing in ensuring the safety and reliability of offshore helicopter operations.

The frequency responses of circulation control and separation control using mini-spoilers for loads attenuation on plunging swept and unswept wings were compared in a water tunnel study. At the pre-stall angle-of-attack, the effectiveness of the spoilers significantly diminishes with increasing reduced frequency of the plunging motion. For the leading-edge spoiler, this happens because the roll-up of the vorticity promotes flow reattachment and reduces the effectiveness of loads attenuation. For the trailing-edge spoiler, the effectiveness of lift attenuation also decreases with increasing reduced frequency, due to the shedding of leading-edge vortices and immersion of the trailing-edge spoiler in the separated flow. The decay of the frequency response for both types of spoilers is similar, implying that it is dictated by the flow separation near the leading edge of the wing in both cases. With increasing sweep angle of the wings, the spoilers’ effectiveness decreases significantly in comparison to the unswept wing. Strong spanwise flow develops for the leading-edge spoiler, which sheds a streamwise vortex, with the same direction of rotation as the wing-tip trailing vortex. This causes partial reattachment of the flow and reduction of the separation area behind the spoiler. With increasing reduced frequency, strong leading-edge vortices dominate the flow over the wing. The leading-edge vortices generate additional vortex lift and also cause the trailing-edge spoiler to be immersed in the massively separated flows. Both factors reduce the effectiveness of the spoilers.

The impact of the self-sealing band on interior ballistics is investigated during the gun launching, and a high-precision interior ballistics coupling algorithm that takes leakage into account is proposed. This study focuses on a 65 mm short-barrel, equal-caliber balanced cannon, integrating Abaqus finite element software with an interior ballistics calculation programme. It uses a User-defined AMPlication Load (VUAMP) subroutine to achieve real-time coupling calculations of the chamber pressure and self-sealing band deformation, correcting variations in the chamber pressure. Experimental results show that the coupling algorithm offers the higher precision compared to traditional interior ballistics models and can effectively capture the impact of leakage on the interior ballistics performance. Further research reveals that changes in the charge amount and assembly gap significantly affect the sealing performance of the self-sealing band and the leakage of propellant gases, which in turn influence the chamber pressure and projectile velocity. The high-precision coupling algorithm proposed in this paper provides the effective theoretical support for the design of the self-sealing band and the analysis of cannon performance.

Membrane aerofoils are used for the design of small unmanned air vehicles which have gained interest in the past few years. This paper deals with the nonlinear uncertain aeroelastic analysis of an elastically supported membrane aerofoil. The uncertainties in the aerofoil aerodynamic coefficients are estimated due to five uncertain input parameters, which are the initial tension coefficient, the membrane elastic modulus, the stiffness coefficients of the two supporting springs at the trailing edge and the leading edge, and the fifth parameter is the free stream angle-of-attack. Both static uncertain aeroelasticity and dynamic aeroelasticity for a sinusoidal gust loading are considered. A detailed novel parametric analysis is performed to assess the effect of each parameter. The analysis is carried out using a nonlinear aeroelastic finite element method, which is based on the Theodorsen’s unsteady aerodynamics theory. The polynomial chaos expansion method is used for the uncertainty quantification process and for the sensitivity analysis. Also, the Karhunen-Loéve expansion is used to model the random field of the elastic modulus. The interesting results of the analysis show that the effect of each uncertain input depends on the values of the other parameters and that the initial tension is the key parameter. The type of the probability density functions (or histograms) of the aerodynamic coefficients can vary from a Gaussian distribution to an exponential-like distribution.

Bio-inspiration can be used to improve the aerodynamic performance of commercial multirotor propellers. In the present study, insect wings are used as a source of inspiration, and the effects of inspiration from insect’s wing shape on the propeller performance–, especially this effect on parameters like thrust, torque, and propeller efficiency, are investigated. Six insect species have been selected as inspiration: Hemiptera, Orthoptera, Neuroptera, Mantodea, Odonata and Hymenoptera. The analyses have been done using the numerical simulation of flow and the moving reference frame (MRF) method alongside the SST k-ω turbulence model. The simulations were carried out over a range of rotational speeds, varying from 4,000 to 8,000 rpm, for propellers with a diameter of 0.24 m. All propellers utilised the Eppler E63 airfoil. To ensure the accuracy of the present numerical simulation results, validation was done by comparing them with experimental data from the DJI Phantom-3 propeller. The results of validation showed significant agreement with the experimental data. The results indicated that the insect-inspired propellers generate higher thrust compared to conventional propellers. Additionally, for a constant thrust force, the inspired propellers exhibit lower rotational speeds. Moreover, in terms of thrust, the Hemiptera insect-inspired propeller outperforms the DJI Phantom-3 propeller, achieving a notable average improvement of 34.182%.

A path being planned for an unmanned aerial vehicle (UAV) or its armed conformation called the unmanned combat aerial vehicle (UCAV) has a critical importance on the flight safety and success of the task including reconnaissance, surveillance, monitoring or destroying. The Back-and-Forth (BaF) algorithm is one of the most recent greedy techniques that executes a heuristic approach for generating two backbone candidates and a combination procedure for bringing advantageous segments of them in order to solve the geometric description of the path planning problem. This study was devoted to a thread-based parallel implementation of the BaF algorithm, also named the multi-threaded BaF (tBaF for short). The threads of the tBaF algorithm increase their search bounds gradually according to the assigned thread indexes and execute the heuristic approach and combination procedure of the BaF for calculating paths. A set of detailed experiments was carried out with the aim of evaluating the performance of the tBaF, and its results were compared with the BaF and 14 other meta-heuristic-based path planners over three battlefield scenarios and their 12 test cases containing the preidentified enemy threats. Comparative studies showed that the different local and global search capabilities of the threads gained with the newly introduced thread-based organisation give a significant contribution to the path planning performance and allow the tBaF to be ranked among the top three planners even though it requires at least from four to eight times less function calls than the tested meta-heuristics.

The multi-UAV task allocation problem can be divided into two components: optimising UAV resource allocation and developing an optimal execution plan. Existing single-population algorithms often get trapped in local optima and require improved accuracy. Although multi-population algorithms perform better, they introduce higher complexity, significantly increasing running time. This paper proposes a Two-Stage Multi-Population Wolf Pack Algorithm (2SMPWPA) to address these issues. This algorithm innovatively splits the task allocation problem into two stages: the initial stage focuses on optimising UAV resource utilisation. In contrast, the subsequent stage focuses on optimising the execution plans for the existing UAV resources. Furthermore, the algorithm categorises the population into a leader group and two normal groups, where the leader group consists of elite individuals from the ordinary groups. To ensure the outstanding individuals in the normal groups have adequate computational resources, a population competition mechanism is introduced to dynamically adjust the size of each sub-population based on their average contribution to the optimal solution. To prevent the ‘big eats small’ scenario, the algorithm incorporates population protection and migration mechanisms to maintain diversity. Additionally, a population communication mechanism is implemented to preserve ‘vitality’ during the later iterations, preventing the algorithm from converging to local optima. Comparative experiments demonstrate that the 2SMPWPA significantly outperforms recent algorithms regarding solution accuracy, effectively addressing the trade-off between solution precision and running time.

This study outlines design principles for a generic thermal management system (TMS) using a multi-design point approach. Four TMS configurations were analysed for a regional turboprop and short-haul type aircraft, focusing on total system gross power as an indicator of cost and environmental impact. Mechanisms were introduced to prevent coolant freezing. Results highlight the puller fan configuration as the most beneficial, leveraging temperature differentials and using the Meredith effect for increased operating capability. The ram-air configuration is slightly more efficient than the puller fan configuration for regional aircraft, but only for high system efficiencies and with operational constraints (taxiing in hot day conditions). Dual fan configurations offer significant thrust but also increased mass. The dual fan configuration shows comparable total system gross power to the puller fan for short-haul aircraft in cruise conditions, but not for regional aircraft. The pusher fan is not optimal for both aircraft types since the radiator significantly increases the heat exchanger inlet temperature, which results in higher drawbacks in terms of mass and total system gross power. In conclusion, the study emphasises the necessity to consider all relevant effects in the TMS design, such as drag, mass and efficiency, to allow the design of an optimal overall system.

This paper presents experimental studies on a novel active high-frequency coaxial injector system designed for enhanced flow mixing and control at extreme flow velocity conditions. The flow dynamics and mixing characteristics of the system operating at 15kHz were captured using planar laser-induced fluorescence (PLIF) and particle image velocimetry (PIV) techniques and compared against its steady and baseline modes. In pulsed mode, this active injection system delivers a pulsed supersonic actuation air jet at the inner core of the coaxial nozzle that provides large mean and fluctuating velocity profiles in the shear layers of an acetone-seeded fluid stream injected surrounding the core through an annular nozzle. The instantaneous velocity, vorticity and acetone concentration fields of the injector are discussed. The high-frequency streamwise vortices and shockwaves tailored to the mean flow significantly enhanced supersonic flow mixing between the fluids compared to a classical steady coaxial configuration operating at the same input pressure. The paper analyses the dynamic and diffusion characteristics of this active coaxial injection system, which may have potential for supersonic mixing applications.

Wall cooling is a promising method in controlling compressible flows, including hypersonic shock wave turbulent boundary layer interaction (STBLI). Based on the verified DNS method, a 30-degree compression ramp is used to generate STBLI for Ma of 5 and wall to recovery temperature ratio ranging from 0.2 to 1.0. The results indicate that the separation zone decreases for cold wall conditions and quantitatively validate the wall-temperature-corrected interaction scaling theory in recent literature. The heat transfer results show that the wall cooling greatly influences the heat flux distribution and peak values in STBLI. The two-stage heat flux increase disappears for the cold wall, which corresponds to the reduced separation bubble. The local decrease of the recovery temperature is observed after the shock, which causes the negative heat flux minimum for near ‘adiabatic’ wall conditions and can be attributed to the acceleration of the near-wall supersonic fluid in the turning process. On the whole, the decrease of the wall temperature leads to the 24.3% decrease of the peak heat flux enhancement, and the underlying mechanism is the decrease of the near-wall turbulent aerodynamic heat dissipation enhancement for the wall cooling.

Interpretability and explainability are at the core of applications developed for control of safety-critical systems, requiring low-complexity models, with physically meaningful insights, and maximum prediction accuracy. This can lead to two very distinct representations of non-linear systems: models purely based on first-principles, highly explainable but extremely difficult to use in practice, or data-intensive, with almost no interpretability but tailored to each specific application. To harness the advantages of both approaches, this paper introduces a novel polynomial linear-parameter-varying framework with stability guarantees to model gas turbine engines, with interpretable dynamical states. The identification problem is split into three stages: (i) identification of the scheduling variable mapping via least squares; (ii) identification of the state dynamics via constrained least squares optimisation involving linear matrix inequalities; (iii) identification of the output equation via least squares. The modelling framework inherits interpretability through the selection of physical variables as dynamical states, while model smoothness is enforced by the use of polynomial functions, which are amenable for control design and optimisation. A unique model for the gas turbine engine is obtained at sea level static, and then extended to wider operating conditions through transformations to referred variables. The effectiveness of the modelling framework is demonstrated on two scenarios, using an engine from the literature, in which low prediction errors were observed, including avoidance of instabilities. Potential applications range from digital-twins and Monte-Carlo simulations, to gain-scheduled and model predictive control, or even economic optimisation, among others.

Harmonic drives, commonly utilised in space manipulators for high transmission ratios and efficient energy transfer, introduce joint flexibility that leads to issues such as hysteresis, vibration and nonlinear coupling. An adaptive control approach with friction compensation is proposed for flexible joint space manipulators to mitigate joint flexibility and address nonlinear friction issues. According to singular perturbation decoupling, the dynamic system of space manipulators is decomposed into two second-order subsystems with distinct time scales. By introducing the concept of an integral manifold, the two subsystems of fast and slow are refactored into two distinct tracking systems. For the slow subsystem, an adaptive control scheme with friction compensator is designed, employing an enhanced linear parameterisation expression. The friction compensator is designed with a decomposition-based compensation control scheme. Meanwhile, a proportional-derivative (PD) controller is provided for the refactored fast subsystem, which avoids incorporating second-order derivative terms of elastic torques into the proposed controller, thereby enhancing computational efficiency and engineering practicability. Approximate differential filters are utilised to estimate the joint velocities of the links and the differential terms of joint elastic torques, which reduces noise disturbances and improves the robustness of the control system. Notably, a modified compensation scheme is proposed to solve the problem that the conventional singular perturbation method is limited to be utilised in space manipulators with weak joint flexibility. Furthermore, the stability proof of the entire system is conducted according to the Lyapunov stability theorem. Ultimately, simulations and analyses demonstrate that the provided strategy is effective.

Micromix combustion technology emerges as a promising solution to address challenges in achieving clean combustion, particularly for hydrogen utilisation. This review provides a critical analysis for the potential of micromixing by delving into its core principles, diverse applications and the factors influencing its performance. The paper focuses on injector design, flame stabilisation and NOx mitigation strategies within the micromixing framework. Key findings include innovative burner designs, optimised air distribution techniques and the crucial role of fuel properties, especially for hydrogen combustion. The review highlights significant reductions in NOx emissions achieved through micromix combustion technology. For instance, NOx emissions were lowered to 2.2 ppm at φ = 0.4, representing a 45% improvement compared to conventional design configurations. Furthermore, a reduction of 40% in NOx emissions compared to standard configurations was observed at an equivalence ratio of 0.65. The study also compares NOx emissions between hydrogen and its blended fuels, showing lower emissions for methane. By highlighting the importance of optimising fuel mixture formation and flame stability for various operating conditions, this review underscores the significance of micromix combustion for advancing sustainable combustion technologies with low NOx emissions and reduced chance of flashback in hydrogen combustion.

The hypersonic vehicle surfaces are subjected to intense thermal loads during atmospheric re-entry. Such conditions induce material ablation and structural deformation, potentially causing changes to aerodynamic configuration that critically endanger mission integrity. In this paper, a mathematical model of thermochemical non-equilibrium magnetohydrodynamics (MHD) at low magnetic Reynolds number is introduced to investigate the effects of MHD on the flow field. Variation of the magnetic pole angle (θ), the flow field profiles are quantitatively analysed, including gas component distributions and aerodynamic heating characteristics. Results indicate that the heat flux at the stagnation point initially decreases and then increases with θ increasing, reaching a minimum at θ = 60°. A portion of the heat flux from the blunt position is transferred to the shoulder (α between 30° and 60°). Notably, the shock standoff distance also shows a non-monotonic trend with θ increasing, peaking at θ = 30°, mirroring the effect of θ on the stagnation point heat flux. As θ increases, the component of the Lorentz force along the X-direction gradually increases, with its peak position corresponding to the shock standoff distance. The electrons and nitrogen atoms are primarily concentrated at the blunt nose, while nitric oxide and oxygen atoms are predominantly distributed along the vehicle wall. The dissociation region of the gas is influenced by the shock standoff distance, which increases as the shock standoff distance increases. At θ = 30°, the concentration of oxygen atoms, nitrogen atoms, nitric oxide molecules and electrons on the stagnation point line reaches its maximum. The present study provides a theoretical foundation for the application of MHD thermal protection methods on hypersonic vehicles.