Reentry trajectory optimization for reusable launch vehicles (RLVs) is a class of optimal control problems with multiple highly nonlinear constraints. Nature-inspired algorithms (NIAs), which can somehow reduce the reliance on initial points, function differentiability, and convexity, with gradient-free nature and ease of implementation, have been actively applied in RLV reentry trajectory optimization problems. As NIAs are primarily designed for unconstrained optimization, constraint-handling techniques (CHTs), which play a crucial role in addressing RLV trajectory optimization issues and significantly impact the overall quality of the solutions, are necessary to guide the search towards feasible regions. However, the existing literature has not yet, or at least not systematically, investigated how well the current CHTs perform. Additionally, an in-depth analysis of parametric approaches and a performance evaluation framework is not yet available. To bridge this gap, this research constructs a benchmark model based on Space Shuttle reentry scenarios, investigates the effects of collocation type and interpolation method, and compares the performance of eight CHTs. An improved marine predator whale optimization algorithm is developed as a direct search engine, with results analyzed using the Wilcoxon signed rank and the Friedman tests. The results show that the epsilon-constrained technique and multi-objective-based CHTs with the algorithm, are somewhat superior in overall performance, and can produce relatively high-quality solutions over other competitors, while the optimization framework facilitates algorithm integration and CHTs for RLV reentry trajectory optimization problems.

Onboard generation of reentry trajectory optimization for a reusable launch vehicle (RLV) is challenging as it must meet strict requirements for real-time performance. Machine learning has brought this field fresh insights due to its great extraction of data performance and predictive accuracy. In this work, the extreme learning machine (ELM), which is often favored in real-time applications, is employed to make onboard trajectory predictions by exploiting the underlying functional relationship obtained from offline data of statecontrol variable pairs. To boost the generalization performance of the ELM, a regularization term is added, and the marine predator whale optimization algorithm (MPWOA) is utilized to optimize the input weights as well as hidden layer biases of the networks. Afterward, four-hidden layer feedforward neural networks (FLFNNs), a single-hidden layer hybrid MPWOA-BPNN (backpropagation neural networks), an ELM model, and three ELM-based particle swarm optimization, whale optimization algorithm and marine predators algorithm models, were developed for comparison. The results revealed that the MPWOA-ELM model outperformed the other models in the testing phase performance indices of the mean absolute error, mean absolute percentage error, root mean squared error, and determination coefficient. Meanwhile, Monte Carlo simulations showed that the model performed remarkably well in real-time, with a trajectory being generated in about 3.405 s. Specifying the current flight state of the RLV, the proposed model can directly generate guidance instructions and then achieve an onboard generation of reentry trajectory with high computational efficiency and reliability. (c) 2024 Published by Elsevier B.V. on behalf of COSPAR.

Trajectory optimization is essentially an optimal control problem (OCP) with highly nonlinear dynamic properties and complex constraints, and a critical part of spacecraft design. In this paper, a hybrid algorithm is proposed for automatic reentry trajectory optimization of reusable launch vehicle (RLV) without providing user-specified initial guesses and a priori knowledge about the optimal trajectory. The method combines the strong robustness and global optimization properties of hyper-heuristic whale optimization algorithm (HHWOA) with the efficient and accurate features of the Gauss pseudospectral method (GPM). HHWOA works as the first-stage optimizer aims to obtain an approximate solution to provide a high-quality initial guess for the GPM, while the GPM works as the second-stage optimizer aims to accelerate the search of the optimum neighborhood to obtain an accurate optimal solution. Additionally, to enhance the progress during the evolutionary process, HHWOA is equipped with opposition-based learning, differential evolution operators, chaotic map sequences and smoothing technique strategies. The utilization of such strategies can potentially smooth the flight trajectory and improve the global convergence of the algorithm, while the three OCPs have shown their superiority in HHWOA. In order to evaluate the performance of the hybrid algorithm, complex constrained RLV maximum cross-range reentry problems with three different path constraint scenarios are investigated. Furthermore, more discussion and experiments are likewise conducted to investigate the impact of the parameters on the performance of the algorithm. The results show that the proposed hybrid algorithm can be very effective in addressing RLV reentry trajectory optimization problems.

The nonlinear thermal flutter behavior of variable stiffness composite laminates (VSCL) with curvilinear fibers in high supersonic flow is investigated. The first order shear deformation theory (FSDT) combining von Karman large-deflection strain-displacement relations, quasi-steady first-order piston theory aerodynamics and quasi-steady thermal stress theory are used to formulate the nonlinear panel flutter finite element equations of motion. The fiber orientation within a layer is assumed to vary linearly from [Formula: see text] at the center to [Formula: see text] at the vertical edges of the rectangular lamina. The flutter characteristics of variable stiffness composite laminates with different temperature distributions are then studied. The results show that the critical dynamic pressure decreases as [Formula: see text] or [Formula: see text] increases, whereas the limit cycle amplitude increases as [Formula: see text] or [Formula: see text] increases for the same dynamic pressure. The critical dynamic pressure and limit cycle amplitude both increase when the temperature gradient along panel thickness increases. Simple harmonic motions, unharmonic but periodic motions, and chaotic motions can be observed on VSCL under different temperatures. It also turns out that temperature distribution has similar influence on both the critical dynamic pressure and limit cycle amplitude of VSCL.

This paper presents three-dimensional solutions for the buckling of variable angle tow (VAT) composite laminated plates. Thep-version finite element with hierarchical basis functions is adopted to determine the buckling of VAT composite laminates with different parameters. Inter-element compatibility is achieved by matching the generalized displacements at the vertices, edges, and faces shared by neighboring elements. The buckling loads of symmetrical and anti-symmetrical laminates with various boundary conditions are obtained. A convergence study is performed and the accuracy of the method is confirmed by comparing the numerical results with those in the literatures. The verified results indicate that the present 3Dp-FEM method is accurate for the buckling analysis of VAT composite laminated plates, and that these three-dimensional results may serve as a benchmark for future studies.

为了在产品设计中系统、全面、准确地反映用户需求,提高维修性要求与产品设计特征之间的关联性,提出维修需求到维修性要求再到产品设计特征的规范化映射方法.通过对用户需求陈述的处理和基于启发式问题的分析,进行用户需求识别;基于系统工程方法,展开维修性设计分析;运用质量功能展开法,进行用户需求向设计要素的转换.将该方法用于某无人机通用操控席位的操作台维修性设计,为生成符合用户需求的系统布置方案提供了权衡依据,在减少设计差错的同时提升了需求转换的精度与效率,验证了方法的可行性.

A three-dimensional finite element model for scarf-repaired composite laminate was established on continuum damage model to predict the load capacity under tensile loading. The mixed-mode cohesive zone model was adopted to the debonding behavior analysis of adhesive. Damage condition and failure of laminates and adhesive were subsequently addressed. A three-dimensional bilinear constitutive model was developed for composite materials based on damage mechanics and applied to damage evolution and loading capacity analyses by quantifying damage level through damage state variables. The numerical analyses were implemented with ABAQUS finite element analysis by coding the constitutive model into material subroutine VUMAT. Good agreement between the numerical and experimental results shows the accuracy and adaptability of the model.

An analytical solution for the buckling and postbuckling behavior of stiffened arbitrary laminat-ed composite panels is presented.The stiffened composite panels are modeled as panels with elastic re-strains.The analytical formulations for the buckling and the postbuckling behavior subjected to com-pression,shear as well as combined compression and shear loads are derived by constructing the deflec-tion function and using Galerkin method.Nondimensional parameters are introduced to express the solu-tion in a simple formulation.The initial imperfections and prebuckling deflection are considered to pre-dict the postbuckling behavior more exactly.Comparisons of the finite element method(FEM)are con-ducted to evaluate the effect of the geometric parameters,spring stiffness,etc.Considering the web of stiffener reinforced to the panels,the averaged stiffness method is applied to the buckling and postbuck-ling analysis of composite panels with T-shaped stiffener.Compared with analytical simplified models and FEM results for the stiffened composite panels with T-shaped stiffeners,the good accuracy of the averaged stiffness methods in predicting the buckling and postbuckling behavior is demonstrated.

Panel flutter behaviour of variable stiffness laminates in high supersonic flow is of great interest in design.The nonlinear flutter behaviour of variable stiffness composite laminates with curvilinear fibers in high supersonic flow is investigated,and effects of boundary condition and ply orientation are studied.The classical lamination theory along with the von-Karman large deflection strain-displacement relationship is used for structural modeling,and the linear piston theory is used for aerodynamic modeling.The aeroelastic model of panel flutter is established based on the principle of virtual work and the finite element method,which is then solved by Newmark method.The flutter behavior under different boundary conditions and ply orientation are obtained.The results show that the critical dynamic pressure decreases as the path orientations in the center and vertical edges of a plate (T0 or T1) increases,and the limit cycle amplitude increases as T0 or T1 increases under the same dynamic pressure.It also turns out that the designability of composite laminates can be improved by using curvilinear fibers,the flutter behaviour of variable stiffness composite laminates can be changed by varying the fiber orientation.

Based on the Hamilton principle, the dynamics and the flutter characteristics of three-dimensional variable-stiffness composite laminates under supersonic flow were investigated. The von-Karman large deflection strain-displacement relationship and the piston theory were employed to account for the structural and aerodynamic nonlinearities, respectively. The natural frequency and the flutter of composite laminates were computed by finite element method, and the impacts of temperature, boundary conditions and ply orientations of curvilinear fibers on flutter were discussed. The results indicate that thermal load and boundary condition have a significant effect on the flutter boundary. It also turned out that the dynamics and flutter of variable-stiffness composite panels can be modified by varying the fiber orientation angle.

A maintenance time prediction method based on virtual reality technology is presented to improve the accuracy of underlying maintenance motion time prediction. First, the maintenance time prediction process based on virtual reality is established considering maintenance simulation and macroscopical maintenance time predic-tion. Then, a maintenance motion classification is proposed for maintenance simulation and motion time predic-tion, and according to the characteristics of each classification, the procedure is set up for predicting ideal main-tenance motion time based on simulation results, motion experiments and predetermined time system theories. Finally, the qualitative indicators such as accessibility, visibility, and labor intensity of the actual maintenance are transformed to quantitative values to fix the ideal maintenance motion time and compute the realistic motion time of the actual maintenance. The method was applied to the time prediction of civil aircraft maintenance task for supporting decision making of the product structure design and system layout. The feasibility of this method is verified.

This paper studies a closed-form solution for the nonlinear postbuckling behavior of long unsymmetrical rotationally-restrained laminated composite plates subjected to shear load. The analysis method described can be applied to the postbuckling behavior of stiffened plates under limitations of the local buckling mode, in which the portion of panel with two stiffeners is modeled as a thin plate with two edges restrained with torsion springs. Nondimensional parameters are introduced in order to cover a wide class of material properties and laminate configurations. An appropriate mode shape function is proposed for the postbuckling process, under the assumption that the buckling mode remains unchanged as the deflection increases. Substituting the shape function into the governing equations, an precise closed-form solution for the load–deflection relationship is derived using the Galerkin method. To conclude, stiffened composite plates with representative unsymmetrical laminate configurations are used as analytical models for a comparison of the closed-form solution. The finite element simulation demonstrates the closed-form solution’s ability to predict postbuckling behavior with high computational efficiency.

An optimization method combining improved genetic algorithm with sequential quadratic programming was proposed for the design of reusable launch vehicle reentry trajectory.The advantages of being insensitive to initial values and global convergence of genetic algorithm(GA),and rapid convergence and high precision of sequential quadratic programming(SQP)were developed.The weakness including solution vibration of GA and small convergence radius,being sensitive to initial values and easy to fall into a local extremum of SQP was overcome.The improved genetic algorithm with simulated annealing penalty function was employed to globally search design space and sequential quadratic programming for local optimization,while the direct collocation method was used to discretize optimal control problem into nonlinear programming problem.A global high-precision solution can be obtained without initial guess.Results show the correctness,effectiveness,insensitive to initial values and good robustness of the algorithm.

Based on the two dynamic grid methods ( spring smooth approximation method and local remeshing method ) and the function/shape function method , according to the facts that the program and the parameters change frequently at the phase of aircraft conceptual design , a dynamic grid method is proposed for the shape of the 2D airfoil.The method passes the changed boundary information to the grid , so that the grid is changed accordingly.Compared with the commonly used dynamic grid method , this method has better strength and resilience of the parameters performance , so the grid is generated fast.NACA 2415 airfoil , which adopts the " class function " and " shape function " translation technique ( CST ), is simulated in the case of low-speed turbulent flow under different angles of attack.The results show that the proposed dynamic grid technique can better simulate the flow characteristics of the airfoil and draw airfoil aerodynamic coefficients more accurately.The technique has good application value for parameter determination at the phase of aircraft conceptual design.

A geometric class function/shape function transformation technique is introduced,and it meets requirements of dimension and shape driven parametric geometry modeling of aircraft.The modeling method can give a brief representation of various shapes or configurations with fewer variables compared with traditional CAD and modeling method based on conic curves.Variation of dimensions or class function/shape function variables can get a family of parametric surfaces,and more shapes or configurations are obtained conveniently.The liftingbody and waverider configurations demonstrate that the method is simple,effective and versatile,and can be used in external shape optimization of conceptual design.

e-维修不只是一种单纯的维修策略、维修计划或维修方式,而是维修领域的一场革命。e-维修可大幅提升商用飞机维修的技术与管理水平,提高商用飞机的可用性和运营可靠性,缩短维修时间,降低维修成本,必将对商用飞机的维修产生长期而深远的影响。

A process modeling method was raised based on the cooperative pattern in airplane design,aiming at the difficulty of complexity and enormous magnitude of airplane design process.Investigating design steps,tools and organization of airplane design experienced,3 cooperative patterns were summarized.Characteristics of each pattern were revealed in its application scene.Modeling method separates knowledge requirement of airplane and modeling with cooperative connection net.The net was built by linking design objects and cooperative activities of some patterns.Petri net analysis was introduced to find iterating portions in the net.Simplifying the net with folding iterating portions,leads to a skeleton of design process.Process model was built by adding incidental information to the skeleton.With a use case,the method was proven to be more objective and convenient.

To tackle the problems not having explicit semantics and powerful analysis ability of the traditional task decomposition and process modeling methods for airplane design in the cooperative development mode, an airplane general arrangement process modeling method based on task-related WBS and Petri nets is presented. On the basis of airplane system WBS, the TR-WBS model is built by using five constraint relations including optional, mandatory, choice, precedence, and feedback. By mapping the airplane general arrangement process model into a Petri net based model, the static structure description and dynamic analysis of airplane general arrangement design tasks is obtained, and the integration of the task decomposition and the process modeling is realized. The correctness, effectiveness and applicability of the method are verified through the established airplane general arrangement and coordination system.

A process modeling method was raised based on cooperation pattern in airplane design, aiming at the difficulty of complexity and enormous magnitude of airplane design process. By investigating design steps, tools and organization of airplane design experienced, 3 cooperation patterns were summarized. Detailed modeling method based on cooperation pattern and Petri net was described, proven to be less specialized knowledge dependent and convenient.

The structures of undercarriages in Boeing 737 planes are briefly introduced. Based on the service bulletins of Boeing 737 during the last three decades, the malfunctions about the undercarriages of the plane are generalized. Further, the reasons for the malfunctions, as well as the measurements to deal with the malfunctions, are listed. The present work is very helpful for designing big airliner of our country.