Journal of Aerospace Engineering

Research on the movement of lunar-based equipment is an essential subject in lunar exploration. The uncertainties of the complex lunar surface environment affect the steady movement of lunar-based equipment. In this paper, a novel robust control strategy, namely model-based $p$-sectionalized control strategy (MPS control), is proposed for the mechanical legs of lunar-based equipment to maintain stability. The novel robust controller is designed based on the dynamic model of the mechanical leg and the controller is proven theoretically based on Lyapunov stability theory. A numerical simulation and the real-time experiment were carried out, and traditional controllers are introduced in the comparison. The results of both the simulation and the experiment verify the effectiveness of the proposed controller.

Abstract

Separated flow inside a compressor cascade is a challenging and complicated issue in aero-engines. Severe flow separation is an important cause of rotational stall in compressors. It is well known that humpback whales have excellent underwater maneuverability owing to the presence of unique raised structures, called tubercles, in front of their flippers. Inspired by the foregoing, we introduced the leading-edge tubercles of humpback whales in the stator of a compressor. The effects of this approach on flow separation were investigated, particularly in the corner region. First, a suitable tubercle amplitude and wavelength were selected for the stator. The flow losses and flow characteristics of the baseline and bioinspired airfoil were numerically determined using the steady Reynolds-averaged Navier–Stokes (RANS) method. The feasibility of the numerical model was verified by comparison with available experimental results. The working conditions were then divided into three regions according to the flow characteristics. Typical working conditions representative of different loss characteristics were studied. Finally, the influence mechanism of the tubercle on flow separation at the corner region under three-dimensional flow-separation conditions was investigated. The results revealed that the leading-edge tubercles induced the formation of a pair of counter-rotating streamwise vortices, substantially reducing the flow separation at the front of the pressure side. This delayed the stall at high negative incidence angles by driving the low-momentum flow in the separation area to interact with the high-momentum main flow. The relative loss reduction improved by 9.65% at $i=-20°$. At high positive incidence angles, owing to blockage in the middle of the linear cascade, the induced vortices formed by each leading-edge tubercle converged into a larger vortex structure with a scale opposite to that of the passage vortex. They interacted with the passage vortex and corner vortex and suppress their development. Therefore, the tubercles effectively reduced corner separation and widened the stall boundary. The relative loss reduction improved by 9.35% at $i=+9°$.

Practical Applications

In this study, we evaluated the vortex and flow field structure of a secondary flow with the introduction of tubercles. The physical mechanism was numerically revealed using a linear cascade. The performance of the tubercles illustrated that the introduction of tubercles caused minimal additional losses in the region of low incidence angles. At high incidence angles, the tubercles induced a pair of counter-rotating streamwise vortices, effectively controlling corner separation and improving the aerodynamic performance. The relative loss reduction improved by 9.65% at $i=-20°$ and by 9.35% at $i=+9°$. Thus, this paper presents a novel concept for the application of tubercles along the leading edge of a stator in a compressor. The tubercles were found to perform well, particularly under conditions with large flow separations. We can consider this as a new passive flow control method, similar to a vortex generator. This method may also be applied to control the flow separation in rotor or turbine blades and has potential applications in the fields of drag and noise reduction, stall suppression, and heat transfer.

Analysis of the effect of pressure on the unsymmetrical plan-shaped buildings due to impact of wind forces is more complicated than the symmetrical plan-shaped buildings. Toward this, the present paper is focuses on the study of the wind effects on the inner face of C-shaped unconventional buildings by considering the surface mean pressure coefficient $(\overline{C_p})$ as the major influencing parameter. Experimental investigation was carried out to obtain the pressure coefficient ($C_p$) over the surfaces of the C-shaped building models by considering some important configurations like the side ratio, frontal ratio, height ratio, and angle of incidence in a subsonic wind tunnel. In the present study, model equations to predict the $\overline{C_p}$ are developed by applying various artificial intelligence (AI) approaches such as the model tree (MT) and group method of data handling (GMDH) with neural network (GMDH-NN) as well as combinatorial (GMDH-C) algorithm to the experimental results. In the AI approach, the side width ratio $(D/d)$, frontal ratio $(B/d)$, depth ratio $(H/d)$, relative width ratio $(B/b)$, angle of incidence ($\theta$), and face angle ($\varphi$) are considered as input to the algorithm to develop the model equation for predicting $\overline{C_p}$. The performances of the model equations are tested through various statistical error analyses. The importance of input parameters is also analyzed through the sensitivity analysis technique. The results clearly indicate that the proposed GMDH-NN model is the best alternative approach to predict the surface mean pressure coefficient on C-shaped buildings with coefficient of determination $(R^2)$ of 0.96 and 0.92 during the training and testing phases respectively. To verify the model equation more accurately, the predicted results are also tested through uncertainty analysis which gave satisfactory results for GMDH-NN as compared to MT and GMDH-C, approaches.

The mechanical behavior of Martian regolith–structure interfaces is of great significance for the design of Mars rover and excavation tools, as well as for infrastructure construction for Mars exploration. This paper aims to understand the basic interface response of MGS-1 and JEZ-1 Martian simulants. The characteristics of simulant–simulant and simulant–steel interface are investigated by a direct shear apparatus in the laboratory. The compression properties of the two Martian regolith simulants are also investigated by one-dimensional oedometer tests, finding that both MGS-1 and JEZ-1 are less compressible and lower swelling soils. The direct shear results indicate that the peak and residual cohesion of MGS-1 and JEZ-1 are less than 8 kPa. The peak internal friction angles (38.8°–40.6°) of MGS-1 and JEZ-1 are lower than two previously tested typical simulants (i.e., JSC Mars-1 and MMS-1) with values ranging between 5.4° and 10.0°, while the residual friction angles (38.2°–39.7°) are similar to those of JSC Mars-1 and MMS-1. All the adhesion values of the smooth and rough interfaces are lower than 5 kPa. For the tests employing a smooth steel plate, resulted in peak interface friction angles of MGS-1 and JEZ-1 are 17.6° and 18.9°, and the residual interface friction angles are of 14.5° and 16.7°, respectively. For the tests employing a rough steel plate, the peak interface friction angles of MGS-1 and JEZ-1 are 38.3° and 36.2°, and the residual interface friction angle values of 33.4° and 33.2°, respectively. The interface friction angles of MGS-1 and JEZ-1 are lower than the corresponding internal friction angles. The properties of simulant–steel interface obtained from this paper provide information for the design and construction of humans’ settlement infrastructure, and are also of interest for spacecraft hardware development for future Mars exploration.

The counterrotating compressor of Rotor-Rotor-Stator (R/R/S) layout is considered to be a crucial technical path for engine thrust-to-weight improvement because it can achieve a high-pressure rise level with low weight and a short axial length. To guide the selection of key aerodynamic parameters in counterrotating compressor design schemes, a zero-dimensional physics–based model is proposed, which can calculate kinetic energy variation across the compressor rotor passages based on enthalpy rise and velocity triangles. Numerical investigations on two counterrotating compressors with different pressure ratios have been conducted employing the Reynolds-averaged Navier-Stokes (RANS) method to validate and support the physics-based model. It was found that the model prediction results and CFD numerical results of two counterrotating compressors showed a global agreement, with the deviations in relative kinetic energy variation coefficient less than 3%, implying the accuracy of the proposed model. This model can be used for the loop iteration between the one-dimensional (1D) and two-dimensional (2D) preliminary design schemes of a counterrotating compressor.

Dynamic stall is a nonlinear fluid phenomenon. It is caused by the vortex generation and motion of the leading edge of the wing. When the angle of attack (AOA) changes rapidly, it causes the vortex to delay and shed. Dielectric barrier discharge (DBD) plasma actuators have been demonstrated for active flow control, which can delay stall and increase the lift–drag ratio. In this study, the prediction–correction direct-forcing immersed boundary (DFIB) method was used to simulate the interaction between fluid and the NACA 0012 flapping wing. This method is capable of simulating complex fluid–structure interaction problems without additional mesh regeneration. Meanwhile, the Smagorinsky model was used in the large eddy simulation to simulate turbulence on the NACA 0012 wing. In this study, the first part verified that the lift and drag data through the fixed wing at a Reynolds number of ${10}^5$ were consistent with published experimental data. The second part verified that the velocity profile of the DBD plasma actuator on the flat plate was consistent with published numerical results. Finally, the feasibility of linear and serrated DBD plasma actuators for applying flow through a wing with different AOAs was verified. In addition, we investigated whether a DBD plasma actuator installed 10% of the chord length from the leading edge could effectively improve the lift–drag ratio across the stroke. The serrated DBD plasma actuator significantly delayed the separation point on the upper surface of the wing and generated a suitable leading-edge vortex (LEV) scale at the beginning of the downstroke. The results showed that the Saw 30° DBD plasma actuator configuration can improve the lift–drag ratio by more than 20% over the linear DBD plasma actuator. When configuring the Saw 30° DBD plasma actuator on the wing, it was found that proper LEV scale and vorticity magnitude can improve the lift–drag ratio.

A design strategy to provide suitable baseline prop-rotors for sophisticated applications is presented. Unlike those approaches aimed at improving the aerodynamic performance of an already refined blade by high-fidelity methods, the new strategy can efficiently work out proper configurations with no baseline. It is introduced through the design process of the initial blades for a small uncrewed tilt-rotor aircraft. Moreover, the strategy consists of four main parts, including identifying ideal boundaries for chord and twist distributions under the theory of minimum energy loss, building surrogate models based on a low-fidelity aerodynamic method, conducting a multi-objective optimization within the ideal boundaries, and finally, selecting feasible configurations on the resulting Pareto front through a high-fidelity aerodynamic method. Under the given design requirements, a representative configuration can achieve a figure of merit around 0.7 and a cruise efficiency of more than 0.6, acceptable for its size. This strategy is beneficial for customizing prop-rotors in industrial applications and effectively shrinking design spaces for more advanced optimizations. The design process revealed that a highly twisted root could help boost the cruise efficiency at the design point by evening the span-wise loading and mitigating the induced vortex near the root. Narrowing the loading gap between the two design states might help obtain a higher cruise efficiency from the design planning level. Moreover, solely using the infilling scheme of expected improvement could impair surrogate models’ global accuracy and further impact the selection of optimal configurations in a multi-objective optimization problem; thus, a mixture of multiple infilling criteria may be worth trying.

Solving the reliability problem of primary ice detection systems is of great significance to support the design of anti-icing systems. In this paper, an efficient method employing a feature-enhanced neural network (FENN)–transfer learning (TL) surrogate model was developed to process two types of features (flight and aircraft parameters). A FENN was established with an autoencoder, and TL was implemented with 15 new points. A new loss function was designed and combined with FENN to control the direction of prediction error. The determination coefficient was 0.993 in the holding state and 0.997 in the local area near the dangerous state. Based on 1 million predicted results of Common Research Model (CRM) airfoil, the primary ice detection system is most likely to have reliability problems at a low angle of attack and low-speed flight state, and angle of attack has the greatest influence. FENN-TL proved a flexible and efficient method for reliability analysis of primary ice detection systems. This method and the obtained CRM results can be further used to support the design and airworthiness certification of large aircraft.

The establishment of lunar habitats is significant for humans to explore the Moon and carry out scientific work. Constructing lunar habitats through additive manufacturing using lunar in situ resource is a promising solution. This study proposed a parametric design and multiobjective optimization approach based on genetic algorithms for the structure of lunar habitats. Structural shape was translated into design parameters, which were optimized during the design phase. The optimization objectives were determined considering the material mass consumption, space efficiency, and resistance ability for extreme extraterrestrial environment of the structure. Three kinds of genetic algorithm–based multiobjective optimization methods were used and compared to optimize the structural parameters. The optimized Pareto solution set containing multiple solutions based on the hypervolume index are obtained. Finite-model analysis was performed on the structures of the Pareto solution set and the optimal structure was determined based on the results of maximum stress and displacement. Finally, partially scaled-down physical models were produced through additive manufacturing to demonstrate the optimized double-shell habitat structure.

To study the far-field aerodynamic noise of the leading-edge slat of a high-lift airfoil configuration, an experimental investigation of the BANC-II/30P30N airfoil model was carried out in the D5 areo-acoustic wind tunnel at Beihang University. A novel Kevlar-walled closed test section design was applied, as a way of upgrading the capabilities of a conventional aerodynamic wind tunnel to include far-field acoustic measurements for larger models at real Reynolds numbers. After the flap was retracted and the slat was deployed to isolate slat noise from other possible sources, the surface pressure distribution and the far-field sound pressure signals under different operating conditions were obtained by varying flow speed and angle of attack. The slat noise spectrum characteristics and the dependence of far-field noise on free stream velocity and airfoil incidence angle were acquired by the fast Fourier transform. The joint time-frequency analysis methods (short-time Fourier transform and continuous Morlet wavelet transform) were employed to process the far-field unsteady acoustic signal to identify the inherent physical mechanisms involved in the generation of multiple low-frequency tonal peaks emerging from the broadband component of the slat noise spectra. Results of the short-time Fourier transform (STFT) and wavelet analysis clearly showed that the dominant acoustic energy of these tonal noise was shared between the primary modes through rapid switching in time. Furthermore, the analysis results also indicated that an amplitude-modulation phenomenon exists in the dominant modes. The joint probability density function method was introduced to quantify the mode-switching phenomenon, and the results provided strong evidence that mode-switching occurs between the dominant modes of these low-frequency tones.

Designing thermal barrier coatings (TBCs) with varied thicknesses on surface of a turbine vane has practical significance. The present study focused on reducing the residual stress levels through optimally designing the interface morphology in TBC at the junction between zones with different coating thicknesses. The two-dimensional FEM was employed to estimate the interface stress level. The combined influences of the internal interface morphology parameters and the external geometrical parameters of TBCs on the interface stress behaviors were discussed deeply. The TBC with unchanged thickness was chosen as the reference. The comparisons revealed that the maximum increment in harmful tensile stress level due to the variation of thickness can reach 60%. Relative to the other phases, the interface morphology featuring zero phase can acquire a higher harmful stress level and larger high-stress region. The proposed interface with nonuniform morphologies can reduce the harmful stress by about 60%. The criteria in the amplitude variations and the location of each period with the external geometrical parameters were acquired. The thickened thermally grown oxide can reduce properly the benefits of the modifications of interface morphology on the reduction of stress; however, the maximum decrement can be controlled below 15%.

We propose an adjustable digital image correlation (DIC) system for the wind tunnel testing of small and large-scale aerospace and civil structures. A novel mounting rig with azimuth and pitch rotation fixtures was designed and developed for the DIC setup that can be installed from outside of the wind tunnel test section. The independent mounting rig makes the DIC system adjustable as per the shape and size of the test structure, which can reduce the installation and calibration efforts in wind tunnel testing. Telecentric lenses optimize the far-field optics of the DIC system. It allows the user to implement a rigorous calibration procedure to study magnification effects. We calibrated the DIC system at various fields of view and depths of field to ensure its suitability for wind tunnel experiments in which accuracy is a prime concern. The DIC measurements can be verified with the Euler transformation algorithm with a suitable combination of azimuth, pitch, and camera optical parameters. Case studies included a large-scale parachute model and a bioinspired flexible flapping wing to ensure the applicability of proposed system for both large- and small-scale structures. The inflated parachute diameter and the wing deformation fields were comparable to those predicted by the Euler transformation relationship. The DIC system can be coupled and synchronized with other measurement systems such as sting balances and particle image velocimetry for the real-time study of structural deformation, aerodynamic forces, and flow characteristics in the vicinity of structures.

Abstract

Multilobed hybrid airships are being considered the next paradigm for reinvigorated utilization of lighter-than-air systems toward the realization of a green aviation future. However, increased epistemic understanding pertaining to their underlying complex aerodynamics in comparison to their conventional single-lobed counterparts is essential to augment the global implementation of these airships. This paper presents a comprehensive numerical investigation carried out at low subsonic speeds and a Reynolds number ($Re$) of $3.9\times {10}^5$ to capture the aerodynamics related to a trilobed airship hull in comparison to a single-lobed (conventional) airship hull based on the LOTTE profile. Postsolver validation, the study deliberates key aerodynamic aspects that need consideration while replacing a single-lobed airship with a trilobed airship. It is established that a trilobed hull with the same hull volume leads to significantly higher aerodynamic efficiency (109%) due to the increased lift coefficient in comparison to the conventional hull. However, reduced longitudinal stability and increased drag coefficient values (83.9%) with the difference being higher at higher angles are its biggest shortcomings. The paper makes use of the pressure coefficient as well as the flow-field description plots to decipher the alleviation of three-dimensional relieving, and the flow intermixing effects at the nose and stern portions, respectively in the case of trilobed hull leading to these aerodynamic deviations. Furthermore, the paper makes use of a webbed trilobed variant, to alleviate the aforementioned drag penalties by virtue of reduced flow separation in the stern portion. Notwithstanding, this benefit, a webbed trilobed variant leads to reduced lift coefficient values compared to the baseline trilobed hull variant. Hence, this paper underscores key aerodynamic differences between the conventional and trilobed hull variants and makes use of this understanding to mitigate drag penalty related to the latter by closing the gap between its three lobes.

Practical Applications

This paper explores the aerodynamic aspects that need to be considered while making use of multilobed hybrid airships in place of conventional single-lobed hulls. Understanding these results can be helpful for modifying the preexisting multilobed hull models so that their utility can be enhanced within the air mobility sector leading to the realization of a sustainable aviation future. This aerodynamic comparison has been accomplished through a sequence of computational simulations carried out in low subsonic and highly turbulent flow conditions. The results show that the trilobed hull with the same volume as the conventional hull achieves a significantly higher lift-to-drag ratio (109%) due to its increased lift coefficient. However, the trilobed hull also exhibits reduced longitudinal stability and increased drag coefficient values (83.9%), particularly at higher angles. Various post-processing tools like pressure coefficient and flow-field description plots were used to underscore the flow physics related to these aerodynamic variations. Following this comprehensive comparison, the paper further presents a new trilobed hull variant called the webbed trilobed hull. Due to the inherent structure, flow associated with these modified hulls was modified leading to drag mitigation at the expense of reduced lift coefficient. Overall, this research sheds light on some key aerodynamic differences between the conventional and trilobed hull variants paving the way for design modification for improved efficiency and performance of the multilobed hulls.

The unstable movement of the shock train in a hypersonic inlet–isolator always brings difficulty to its closed-loop control, and some methods should be taken to stabilize the shock. The flow control method, for example a ramp, developed for a design condition cannot adapt to a wide range of flight conditions. Therefore, a control method of the shock oscillation based on the multistability is proposed and investigated numerically. Successive ramps with different configurations are involved to achieve the local stable regions within the shockwave–boundary layer interaction region. First, the uncontrolled case is studied. With a specified backpressure ratio, the first separation shock exhibits a limit cycle oscillation within the shockwave–boundary layer interaction region, and the downstream flow also fluctuates violently. Then, the controlled case demonstrates that the shock oscillation can be effectively suppressed by the multiple favorable pressure gradient regions induced by the ramps. In addition, with an enhancement in the number and height of the ramps, both the separation shock and the downstream flow are stabilized.

This study proposes a Gaussian-discretization control vector parametrization (CVP) algorithm to improve the reentry trajectory optimization accuracy of a hypersonic vehicle (HV) with a complex path and terminal state constraints. First, the reentry trajectory optimization problem (TOP) of the HV is established by analyzing the equations of motion and constraints. Second, a Gaussian distribution strategy is derived to obtain a suitable control parametrization time grid for improving control quality. By combining the handling strategies for path and terminal constraints, an efficient, non-uniform control parametrization trajectory optimization method is established, and the HV trajectory optimization algorithm framework is provided in detail. Lastly, the proposed algorithms are implemented on a widely studied common aero vehicle model. Numerical simulation tests are conducted on terminal-time-free and terminal-time-fixed TOPs to optimize the reentry downrange. Test results show that the proposed method has a stable solving ability with high satisfaction of terminal constraints. Simulation results reveal that the proposed method efficiently increases the downrange compared with other CVP methods under the tested scenario, thus showing the effectiveness of the proposed distribution strategy.

To collect solar energy in outer space, Tethered Collecting Solar Power Satellite Systems have been proposed by several authors in the last years. A geostationary orbit would be the best location for a space-based solar power. However, a geostationary satellite occupies a single ring in the equatorial plane of the Earth. For this reason, out-of-plane configurations for solar panel systems have been studied by various authors to increase the number of slots over a particular longitude. In this paper, we assume a two-body tethered satellite system, where the microwave transmitting satellite is placed on a geostationary orbit and the tethered solar panel is deployed from the microwave transmitter. A tension control law is derived in conjunction with thruster forces by linearization of the dynamics of the tethered satellite system around an out-of-plane configuration. The stability analysis carried out in this paper shows that the linear motion is asymptotically stable. Results of numerical simulation show that the linear control strategy performs well for the nonlinear system, so that the solar panel achieves a nonplanar configuration.

In this paper, an attempt has been made to implement the classical second order SMC for a nonlinear model of the Quadrotor with varied trajectories in a closed loop in simulation for the available model along with the model identified for Hexsoon Edu 450 Quadrotor. The controller is developed using an equivalent control technique that was realized using MATLAB. Because the quadrotor system is complex, the dynamic modeling has to be done by considering six degrees of freedom prior to the controller design. Primarily the attitude controllers of the quadrotor should be settled at the desired values. Then, the position controllers must be stabilized using effective tuning of the parameters of the controller. This paper presents a three-dimensional trajectory tracking of the quadrotor using a sliding mode controller (SMC) which is stable and accurate as per the comparison because the maneuvering of the quadrotor is a quick process. The results of the designed (SMC) are compared with a nonlinear PID controller in the literature. The result proved the robustness of the SMC against the uncertainties of the system compared with NPID.

This study investigated the time-optimal low-thrust interplanetary transfer problem, and proposes a fast estimation method for guessing the initial costate and optimal transfer time based on a surrogate model, and applied it to the problem of the 11th Global Trajectory Optimization Competition (GTOC 11). Two core methods are proposed in this paper: (1) a fast generation method called the neighbor point iteration algorithm (NPIA) is presented for rapidly generating low-thrust databases with high efficiency and accuracy; and (2) deep neural networks (DNNs) are adopted to learn the state–costate pairs of low-thrust databases, and the surrogate network can quickly estimate the initial costate and optimal transfer time of the low-thrust interplanetary problem. Experiments verified the proposed method and investigated the influence of network structure, learning rate, and loss function on the accuracy of network estimation. The effects of database generation and network estimation were compared based on three transfer scenarios: coplanar, non-coplanar, and arbitrary orbital transfer. In addition, the application case study showed that the proposed method can quickly obtain the time-optimal low-thrust solution to GTOC 11’s interplanetary transfer, which achieves high precision and meets the terminal constraints.

Development of the fast model of phase transformations in the Pyrowear 53 steel was the objective of the paper. An upgrade of the JMAK (Johnson–Mehl–Avrami–Kolmogorov) was proposed. Coefficients in the model were introduced as modified Gauss functions of the temperature. Changes in the carbon and molybdenum concentrations due to precipitation were accounted for. Dilatometric tests were carried out across a wide range of cooling rates. Identification of the model was performed using inverse analysis for the results of these tests. Three austenitization cycles prior to transformations were applied and an influence of the grain size on the nucleation and kinetics of phase transformations was accounted for in the model. All the tests were carried out on the core samples with the nominal chemical composition and on the carburized samples. Numerical tests confirmed the good accuracy of the model for both compositions in the whole investigated range of the grain size.

A robust controller for an octocopter is essential for flight stability. The presence of matched and unmatched disturbances can deteriorate a stable performance. This work proposes a robust controller for an octocopter to reject the matched and unmatched disturbances. The effects of fast varying external disturbances and parametric uncertainty on octocopter are considered matched disturbances and sensor measurement noise is modeled as unmatched disturbances. To alleviate the effects of disturbances an alpha uncertainty and disturbance estimator based integral sliding mode (ISMC-Alpha UDE) control law is proposed. The Lyapunov theory is used for stability analysis of the proposed ISMC-Alpha UDE control law. Comparative numerical simulations along with root mean square error (RMSE) analysis are presented to show the better performance of the proposed controller. The proposed controller offers reduced and smooth control efforts to achieve robust state tracking performance by mitigating the effects of matched and unmatched disturbances. The Monte Carlo simulations are performed to validate the efficacy of the proposed design.

A novel time domain method is proposed to estimate the time-varying statistics of nonstationary random pressure load from structural strain response samples. Orthogonal polynomials and Karhunen–Loève expansion are adopted to represent the spatial distribution of the stochastic pressure load and the random structural strain data, respectively, which transform the random pressure load identification problem to a problem of estimating a few deterministic time-varying coefficients. Numerical simulation on a plate structure subjected to nonstationary random fluctuating load is conducted to validate the proposed method, and the influence of the load’s correlation length on the identification accuracy is also discussed. To show the application perspective of the proposed method, the nonstationary gust-induced random pressure load on a wing structure is reconstructed from structural strain data. Some practical aspects, such as the number of response samples, the level of noise in the strain response, the order of orthogonal polynomial used, and the regularization method used, on the performance of the load identification method are also discussed.

Aimed at solving the problem of automatic pipe routing in complex space, a novel method based on the sine cosine algorithm (SCA) is proposed. First, a three-dimensional environment of pipe routing is built. Then, the geometric interference degree and the total length of the path are taken as the optimization objectives, instead of considering geometric feasibility as a constraint. Afterward, a mutation mechanism is added to the original SCA to enhance the optimization performance of the algorithm. The experimental results of two separate case studies show that the improved SCA (ISCA) performs better than the genetic algorithm (GA) and ant colony optimization (ACO), and achieves a good solution at a fast speed at an early stage of the evolution. Finally, the proposed method is used to solve pipe-routing problem for a fuel tank in aircraft production. The results show that the ISCA has excellent optimization capability in solving the pipe-routing problem.

Abstract

The dynamic stall of the airfoil can adversely affect the performance of helicopter rotor blades, jet engine compressor blades, wind turbine blades, and so on. Therefore, the flow control on the dynamic stall is necessary. This paper conducted an experimental study on the multiobjective flow control effect of the dynamic stall on a NACA0012 airfoil using a passive vortex generator (VG). The control effect of the VG on the dynamic stall is discussed, and the control mechanism is explained. Within the scope of this paper, the VG could significantly increase the maximum normal force coefficient ($Cn$) by 0.223, reduce the peak negative moment coefficient ($Cm$) by 0.049, and delay the stall angle of attack of $Cn$ and $Cm$ by $\mathrm{\Delta }\alpha =1.8°$ and 2.9°, respectively. These multiobjective control effects were attributed to the control of the complex vortices on the suction surface. The VG delays stall by suppressing the formation of the shear layer vortex, and enhances the aerodynamic performance during dynamic stall by energizing the dynamic stall vortex (DSV). The effects of the VG on the convection speed and strength of the DSV are additionally investigated from a space-time perspective. Within the reduced-frequency range studied in this paper, the DSV convection speed controlled by VG was smaller than that of the baseline airfoil, and the VG could significantly enhance the strength of the DSV.

Practical Applications

Dynamic stall phenomena are widely found in nature (wings of flying birds, fins of swimming fish, and so on) and in engineering (bionic flutter wings, helicopter rotors, wind turbine blades, and so on). It is widely believed that the DSV is the main flow structure dominating the dynamic stall. For helicopter rotor blades and large wind turbine blades, dynamic stall is prone to occur in the blade tip under complex realistic conditions. The vortex lift during dynamic stall will significantly raise the blade load, and the motion of the DSV will cause a sharp change in the blade moment, which may damage the blade structure and control system. Therefore, the dynamic stall needs to be controlled. In this paper, passive VGs were used to control the dynamic stall on an airfoil, and ideal multiobjective control effects were obtained: reducing the negative peak moment, increasing the maximum lift coefficient, delaying the stall, and reducing the hysteresis effect. This work is a guideline for the dynamic stall control of helicopter rotor and wind turbine blades.

Abstract

Human lunar and planetary exploration can be simplified by the exploitation of in situ resources. High priorities are placed on propellant and life support consumables, such as oxygen and water. The latter can be considered a biproduct of propellant production, and is essential for sustained human presence. Its existence was detected on the Moon and on Mars. However, its endemic occurrence as ice can make storage and transportation difficult, so a conversion to its liquid state often is preferable. The disadvantage of this is that energy-intensive active heating systems are required to prevent freezing. Recently, a method was presented that potentially can eliminate this disadvantage by maintaining the liquid state down to $-120°\mathrm{C}$, even at pressures as low as 0.1 mbar. This is achieved by mixing the water with a commercially available lipid, thereby forming a lipidic mesophase. Transportation of the mesophase in cryogenic hydraulic networks is achieved easily by pumping, and this can be exploited to design a centralized closed-loop liquid water storage system for a lunar base. The distinguishing feature is that the tanks can be placed outside the human habitats. Key system components are potentially manufacturable in situ. In this work, an architecture for the life support part of such a system is proposed, and the key chemical processes are demonstrated experimentally. The first of these is the scale-up of the water–lipid enrichment process by a factor of 5 from typical laboratory scales. The second is the extraction of water from the mesophase by distillation. It is shown that 79% by weight of the water is extractable for reuse, and the remainder presumably forms an azeotrope with the lipid. The power required to circulate the mixture between human habitats and external tanks is estimated to be $<41\mathrm{kW}$ for a crew of 10.

Practical Applications

Water can be mixed with a commercially available lipid using a simple thermal process. A surprising attribute of this mixture is that it remains liquid, i.e., it does not freeze, at temperatures as low as $-120°\mathrm{C}$. As a result, pumps can be used to transport the liquid through hydraulic networks. This can be exploited to construct water supply and storage networks in cold environments without the need for an active heating system. Potential applications of this technology are in extraterrestrial and terrestrial environments. The former includes the development of lunar and planetary installations for life support and exploration as part of the ongoing effort to extend human presence beyond Earth. The latter include water storage and supply systems for cold terrestrial environments in which access to clean liquid water is required but such water scarce. Examples are regions above the Arctic circle, Antarctica, high-altitude environments, or, generally, regions with extended freezing periods.

To reduce the influence of flight-propulsion coupling of a wide-speed vehicle on itself, this study investigated the integrated control considering the flight-propulsion coupling constraints. First, a control-oriented mathematical model of flight-propulsion integration for a wide-speed vehicle was established. On this basis, the nonlinear dynamic inversion (NDI) and incremental nonlinear dynamic inverse (INDI) control methods were adopted to design the attitude control algorithms of the slow outer loop and fast angular rate inner loop, respectively. The necessary modules, such as reference model, error control, and online estimation, were introduced into the NDI controller to ensure flight quality and robustness of the wide-speed vehicle. Then, based on the online model that involves the flight-propulsion coupling characteristics (FPCCs) of the wide-speed vehicle, a coupling control scheme for the wide-speed vehicle that considers its attitude and engine was designed by manipulated cross-linking. Simulation results indicate that the proposed NDI flight-propulsion control scheme can effectively address the flight-propulsion coupling of the wide-speed vehicle and guarantee the expected control performance.