Journal of Aerospace Engineering

To achieve a high thrust-to-weight ratio engine design, topology optimization design of the turbine disk structure is carried out. Considering centrifugal load and thermal load, a topology optimization algorithm program with minimum average compliance is presented. The rational approximation of material properties model is combined for the material interpolation scheme and the thermal effect of the material is considered by a linear fitting function. A dynamic evolution rate based on a sigmoidal function is proposed to accelerate the iteration convergence. Based on the alternative material interpolation scheme and the dynamic evolution rate model, the bidirectional evolutionary structural optimization (BESO) method is extended. A three-dimensional finite element model of the turbine disk is established for topology optimization. The effects of filter radius and penalty factor on the optimization results are discussed. The results show that the BESO algorithm combined with the dynamic evolution rate improves the optimization efficiency. Compared with the original structure, the total weight of the optimized turbine disk is reduced by 35.0% and the structural stiffness is improved by 32.1%.

This study presents an innovative approach to attitude control in microsatellites by utilizing a spherical magnetohydrodynamic attitude control device (MHD-SACD) for three-axis attitude adjustments. A novel method is developed to quantify the output torque generated by this device, analyzing the relationship between torque, voltage, and average fluid velocity. Utilizing the energy conservation principle, an equivalent coupling circuit for the MHD-SACD is derived to assess its power dynamics. This leads to the formulation of the electromagnetic torque equation. Additionally, simulations are conducted to calculate friction torque and resultant output torque. The findings provide a qualitative assessment of the device’s torque characteristics, serving as a reference for future design optimization and setting the stage for subsequent experimental investigations. This study introduces a groundbreaking perspective to the domain of microsatellite attitude control.

Rapid launching is a crucial technology for the digitalization and regularization of space transportation systems. This paper focuses on the fast trajectory prediction of the launch-vehicle boost phase. A high-precision and high-efficiency analytical solution of the whole boost phase dynamics model of the rocket is obtained by adopting one of the regular perturbation methods called the state-space perturbation method in the launch rotated coordinate system. An analytical framework known as the perturbation expansion framework is proposed by first figuring out the correlation with the state variables/independent variables and then performing the approximate expansion. This framework can successfully address the issue of analytically solving the transfer matrix and integral term caused by the coupling and time-varying properties among state variables of the affine equations of the boost phase. The analytical solution developed in this paper has great fidelity and takes into account the combined effects of various factors, including thrust, aerodynamic force, Earth’s gravity, oblateness, and rotation. It can serve as a theoretical guide for the rapid launch requirements and iterative design processes for early rocket demonstrations in engineering.

Abstract

This study investigates the potential of an optimized combination of active nose droop and active Gurney flap (CADAG) in a new flow control strategy to manage dynamic stall over a pitching blade section under variable Mach number flow. The optimization method employs the genetic algorithm coupled with a computational fluid dynamic (CFD) solver and artificial neural network. The base blade section belongs to a section positioned at $\mathrm{r}/\mathrm{R}=0.865$ of the rotor blade of the UH-60A helicopter in forward flight condition. A high relative angle of attack on the retreating side makes the flow susceptible to dynamic stall. A nose droop is employed to control the dynamic stall of the blade section, and a Gurney flap is used to maintain the balance of the generated lift of the blade during 360° of rotation. A comprehensive investigation is performed to determine the most significant parameters affecting the performance of the present combined active flow control. The ratio of the total generated lift to the drag is chosen as the objective function of the optimization. Results show that this ratio and the total generated lift in one rotation cycle increase by 193% and 13%, respectively, at the optimum condition of the present combined active flow control, while the ratio of the generated lift over the advancing side to the retreating side is equal to that of the base blade section. In addition, the dynamic stall hysteresis loop reduces significantly, and the maximum value of the drag coefficient and the negative aerodynamic damping decrease up to 87% and 83% compared to the base blade section, respectively. In general, the proposed innovative combined active flow control is an adjustable method to alleviate dynamic stall and improve the aerodynamic performance of rotary wings in different operation conditions.

Practical Applications

The rotary blades are extensively used in rotorcraft, turbo engines, and wind turbines. Despite their massive use, they suffer from some essential issues, of which the most important one is the so-called dynamic stall. Dynamic stall is a complex phenomenon that limits the performance of the rotary blades. Due to the physics governing a rotary wing, such as a helicopter rotor blade, dynamic stall and flow separation are very common. Understanding dynamic stall physics and providing solutions to prevent it is still one of the main challenges of aerodynamic scientists. The present study introduces a novel adjustable method for practically alleviating the dynamic stall on helicopter blade section in forward flight conditions to improve its aerodynamic performance in different operational conditions. A comprehensive investigation is carried out to determine the key parameters affecting the proposed method. These findings can serve as a valuable tool for other researchers to develop various active flow control strategies. This article applies an optimization process using artificial neural networks, genetic algorithms, and CFD tools, which forms a comprehensive framework that can be easily extended to other applications.

The secondary air system of a gas turbine engine is a complex fluid network that is sensitive to geometric variations in the flow elements caused by manufacturing, assembly, and operating conditions. Geometric uncertainty of the flow elements is a major cause of secondary air system failure. To reduce the performance uncertainty due to geometric uncertainty, this paper constructs a probabilistic analysis method that couples the primary air system and the secondary air system and proposes a robust optimization mathematical model for the rotor axial bearing loads of the secondary air system, using the control of the rotor axial bearing loads as an example. A case study is presented to demonstrate the application of the proposed robust optimization method in controlling the scatter of axial bearing loads. Probabilistic analysis and sensitivity analysis are performed for the original design scheme and the robust optimization design scheme of the secondary air system. The results show that the standard deviation of the high-pressure axial bearing loads in the robust optimization design scheme is 72.9% lower than that in the original design scheme under the same uncertainty distribution of the labyrinth clearance. In addition, the sensitivity of the axial bearing loads to the labyrinth clearance is reduced. Thus, it is demonstrated that the proposed robust optimization method can effectively reduce the functional scatter and the sensitivity to geometric variations in the gas turbine secondary air system.

Abstract

Near-ground flight is an important state of microducted fan aircraft. To explore the ground effects on the aerodynamic performance of microducted fan systems in near-ground hovering, a full three-dimensional (3D) numerical simulation methodology, which was validated by current experiments, is established in this paper. First, the hovering performance of ducted fan systems without ground effects was studied. Taking the system without ground effects as the reference, the ground effects due to altitude and slope were calculated and analyzed. The simulation results revealed that compared with the results of the current experiments, the maximum prediction error of 6% is reached when the induced power is 30 W. This indicates that the simulation methodology can work effectively. Moreover, a comparison of the performance of the system without ground effects revealed that ground effects can be ignored when the system altitude is greater than the duct length. In contrast, when the system altitude is within the duct length, the mass flow rate can greatly decrease with decreasing system altitude. This is because the blocking effect from the ground becomes significant. Additionally, the ground slope makes the flow field of the ducted fan system asymmetric. Globally, the system is not as sensitive to ground slopes within 18° because the ground effects for both sides of the ducted system are balanced to a certain extent. A side away from the ground can enhance the aerodynamic performance of the system. However, the other side close to the ground weakens the system performance. The mass flow and thrust performance can increase slightly when the slope is less than 12°, and the system behavior tends to stabilize when the slope is greater than 12°.

Practical Applications

When microducted aircrafts are used to perform tasks, such as taking photos and ground detection, they are usually flown close to the ground, and alternate hovering with and without ground effects is frequently conducted. Thus, problems related to the aerodynamic interference between the terrain and the fuselage and between the fuselage and the rotor can occur. As shown in this study, the aerodynamic performance of ducted fan systems is affected by ground effects when ducted systems operate at an altitude of one times the duct length. In addition, at an altitude of 0.5 times the duct length, the thrust of the duct system increases with increasing slope within 18°. When the slope is greater than 12°, the influence of the slope from the left and right sides at the duct outlet is almost balanced. In general, the system altitude, ground slope and their effects on system performance need to be considered during the design process. The results can provide a design benchmark and optimization directions for designers, thereby reducing environmental constraints on ducted aircrafts and cost and improving the reliability.

The coaxial compound helicopter has been offered as an idea for a high-performance rotorcraft that possesses high-speed qualities that conventional helicopters do not. This work seeks to create a flight dynamics model of a coaxial compound helicopter and investigate its trim, stability, and controllability. Regarding this, this study builds aerodynamic models for each component of a coaxial compound helicopter (coaxial rotor, fuselage, horizontal stabilizer, vertical stabilizer, and propeller). For coaxial rotor configuration, an equivalent flapping model, a reflected model, an inflow model taking the upper and lower rotor’s impact into account, and a phased cyclic pitch model are done. A nonlinear coaxial compound helicopter mathematical model is constructed, and the trim across the entire flight envelope is carried out. The nonlinear model is linearized in order to evaluate stability and control derivatives. The trim results exhibit a high degree of concordance with the reference, thereby validating the flight dynamics model.

A novel safety-guaranteed rendezvous control (SGRC) method is proposed for obstacles avoidance during the rendezvous with a noncooperative target in this paper. An artificial potential field with the addition of a velocity safety corridor is used to describe the motion of space and achieve the constraint on the global velocity of the service spacecraft during the rendezvous. Furthermore, the velocity error term of the system is constrained by combining the prescribed performance control (PPC) method, thereby improving the steady- and transient-state performance of the system while reducing fuel consumption. On this basis, a newly constructed virtual auxiliary state containing both artificial potential fields and self-bounded system state error is developed, and a safety-guaranteed control method capable of achieving rendezvous with the noncooperative target for obstacle avoidance is designed. Two sets of numerical simulation results verify the effectiveness as well as the adaptability of the proposed control method.

Aeroengine models are widely used to identify aerodynamic parameters of components and play an important role in many applications. Due to differences in gas path characteristics, traditional physics-based models do not typically match actual engines. This paper proposes a new hybrid modeling framework that combines data-driven modules. The proposed method adds a steady-state correction module and a dynamic compensation module on the basis of the physics-based model, reducing the differences in gas path characteristics through two stages of modeling, and obtaining the final hybrid model. The steady-state correction module uses a particle swarm optimization (PSO) algorithm, and the dynamic compensation module uses a long short-term memory (LSTM) neural network. The modeling method is validated using actual data from different engine individuals, and the proposed method demonstrates better performance than traditional methods.

Developing constitutive models that can be used to model composite structural systems subjected to impact loads where modeling damage, failure, and delamination are critical is a challenging task. Often processing experimental data to develop the composite material model and, especially, the delamination model can be tedious, subjective, and error prone. In this paper, procedures for characterizing the behavior of laminated unidirectional composites (UDCs) are explained. First, laboratory tests are conducted to obtain the orthotropic material properties of a commonly used composite, IM7-8552. The obtained data are used in the MAT_213 model in LS-DYNA. Second, fracture-related tests, i.e., double-cantilever beam (DCB) and end-notched flexure (ENF) tests, are conducted to obtain the load-displacement responses. Finally, an inverse analysis approach is used by combining response surface methodology (RSM) and gradient-based numerical optimization to find the optimal values of the traction-separation law (TSL) parameters to build the constitutive model for modeling delamination. The developed cohesive zone element (CZE) model is then validated using the experimental results of a quasi-isotropic tension test. It is shown that the overall process of analyzing the experimental data and building a finite-element model is simpler, and the results from the validation test indicate that the developed methodology can yield accurate predictions.

Abstract

Lunar bases for long-term human habitation are a topic of growing interest to engineers. Structures to be built on the surface of the Moon must be designed to resist extreme environmental hazards such as hard vacuum/no atmosphere, low gravity, ionizing radiation, large temperature variations, moonquakes, and meteoroid impacts. Protective regolith covers may provide adequate shielding from some of these hazards. This paper presents a methodology that utilizes established physics-based models to determine the immediate effects of hypervelocity impacts (HVI), including crater geometry and shock pressure, for engineering design of lunar structures. First, empirical equations and nondimensional scaling laws for computing geometric features of HVI craters are discussed. These damage estimation tools are adopted from the fields of spacecraft design and planetary impact cratering. Next, the planar impact approximation model is discussed, which utilizes one-dimensional shock wave physics and impedance matching conditions to estimate the peak initial pressures generated in HVI. Comprehensive parametric analyses, encompassing a wide range of impact velocities and impactor masses as well as a variety of impactor and target materials, are performed to demonstrate applications of the models to both regolith-shielded and unshielded structures. Crater geometry descriptors and peak shock pressures in HVI scenarios involving various impactor-target combinations are computed with in-house programs and compared with computational results reported in the literature. The analyses indicate that for a given target, the main factors determining cratering damage are impactor mass, impactor density, and impact velocity, while the initial shock pressure is influenced mainly by impact velocity and impactor density. A comparison of impact pressures experienced by monolithic unshielded targets and granular dry sand layers highlights the potential importance of providing regolith-like shielding to attenuate HVI effects. Practical implications of the study are discussed from an engineering design perspective, underscoring the considerable value of such models to practitioners.

Practical Applications

A practical methodology for determining cratering and peak shock pressure due to hypervelocity meteoroid impacts on unshielded and regolith-shielded lunar structures is proposed in this work. The methodology utilizes well-established physics-based models of hypervelocity impact effects. These models have several advantages that make them suitable for inclusion in lunar structural design guidelines: (1) the models presented are relatively simple yet realistic, empirical, and analytical models; (2) the models do not rely on computationally expensive numerical methods and have been successfully implemented using a commonly available scientific computing platform; and (3) the models consider several essential aspects of the complex physics of hypervelocity meteoroid impacts, which is essential to ensure accurate prediction of the immediate effects of such impacts for lunar structure design. Additionally, this work also includes a wide-ranging parametric analysis that explores and compares the predictions of the physics-based models from an engineering design perspective, encompassing a variety of impact scenarios and impactor-target combinations. The results highlight the practical importance of providing a protective shield, composed of a regolith-like granular material, to mitigate the peak shock pressure sustained by lunar structures in hypervelocity meteoroid impacts. The models, applications, and results presented herein are of immediate relevance to practicing engineers.

Abstract

Inspired by buckle-induced structural deformation, a new type of tensegrity robot using bending bars is proposed. First, a combination of numerical calculation and the finite-element simulation method was adopted to determine the influence of geometric parameters on equivalent stiffness, and the basic configuration parameters were determined. Then, the tensegrity dynamical model and the ground contact model were established using a nonlinear finite-element method, and four rolling gaits of the robot were realized by driving diagonal cables. Finally, an experimental prototype of the bending bar tensegrity robot was built for rolling gait experiments. The results show that the experimental rolling motion is in good agreement with the theoretical model. Through continuous curve path rolling, the minimum turning radius of the robot was determined, and the motion mode of the prismatic tensegrity robot was enriched.

Practical Applications

Tensegrity structure is a self-balancing system composed of compression bars and tension cables, which has aroused numerous scholars’ research interest in civil architecture, mechanical engineering, aerospace, biomedical, and other fields. The results cover model design, form-finding analysis, static equilibrium stability analysis, optimization design, dynamic response analysis, and so on. In fact, when the tensegrity mechanism is applied to a mobile robot, a change in shape can be achieved by shortening some cables with the actuator, so the system’s stiffness contradicts the ability to deform. The focus of this work is to propose a new type of bending bar design that can replace the spring to meet the needs of large deformation and avoid weakening the structure’s overall stiffness. This design realizes the rolling motion mode of the robot and can be applied to the motion mode of other prismatic tensegrity robots.

The elliptic shock wave has potential applications in the design of hypersonic inlets and waveriders. In this study, an optimization design process and a mathematical model for an elliptic shock wave are proposed. An elliptic cone flow field is employed to generate an elliptic shock wave whose shape is predetermined using the value of aspect ratio. The design of the shock wave is transformed into an optimization problem, and an optimization design process with the gas viscosity considered is developed. The elliptic cone is parameterized, and the parameters are adjusted by an optimization algorithm to meet the requirements. The results show that the optimization process can realize the accurate design of an elliptic shock wave. Based on the analysis of the elliptic cone flow field, the shock wave can be well approximated as an elliptic cone, and the aspect ratio of the shock wave is positively correlated with three factors: the aspect ratio and slenderness ratio of the elliptic cone and the incoming Mach number. The relationship between the aspect ratio of the shock wave and these three factors is modeled by a feed-forward neural network with accuracy verified, which is beneficial for the rapid design of elliptic shock waves.