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The article is a personal recollection of the author's experiences with Jerry Ericksen, a renowned figure in the field of continuum mechanics. The author describes how they were advised to contact Ericksen and visit him at Johns Hopkins University, where they found him to be knowledgeable and open-minded. The author also mentions their later interactions with Ericksen and highlights the impact of his influential papers on their own research. Overall, the author expresses gratitude for Ericksen's mentorship and considers him a master of continuum mechanics. [Extracted from the article]

This paper addresses the prediction of spontaneous self-sustained transverse combustion instabilities in multi-injector engines using a multi-dimensional non-linear low-order Eulerian model. The approach utilizes a physically aware response function that directly links pressure oscillations to fuel mass flow rate, independent of external data. This enables accurate capture of the behavior of shear coaxial injectors that have been proven to show a peculiar dynamics of cyclic fuel accumulation and release in response to acoustic waves. A NASA test case is employed as a reference, and a comprehensive analysis is conducted to investigate the behavior of the model. Firstly, a preliminary analysis is performed within a quasi-one-dimensional framework for a reduced single-injector configuration. This analysis provides insights into the influence of key parameters on the instability onset. Subsequently, the full-scale geometry is considered in a multi-dimensional framework, and the low-order solver is employed to analyze the thermo-acoustic behavior of the engine. The model successfully captures the instability dynamics, including temporal evolution, dominant frequency, and mode shapes. Sensitivity analyses are conducted to examine the impact of the model free parameters on the unstable modes. Additionally, the effect of introducing baffles as damping devices within the combustion chamber is investigated. The results highlight the model predictive capabilities and its potential for guiding the design and optimization of liquid rocket engines. [ABSTRACT FROM AUTHOR]

Complex systems are difficult to manage, operate and maintain. This is why we see teams of highly specialised engineers in industries such as aerospace, nuclear and subsurface. Condition based monitoring is also employed to maximise the efficiency of extensive maintenance programmes instead of using periodic maintenance. A level of automation is often required in such complex engineering platforms in order to effectively and safely manage them. Advances in Artificial Intelligence related technologies have offered greater levels of automation but this potentially pivots the weight of decision making away from the operator to the machine. Implementing AI or complex algorithms into a platform can mean that the Operators' control over the system is diminished or removed altogether. For example, in the Boeing 737 Air Max Disaster, AI had been added to a platform and removed the operators' control of the system. This meant that the operator could not then move outside the extremely reserved, algorithm defined, "envelope" of operation. This paper analyses the challenges of AI driven condition based monitoring where there is a potential to see similar consequences to those seen in control engineering. As the future of society becomes more about algorithm driven technology, it is prudent to ask, not only whether we should implement AI into complex systems, but how this can be achieved ethically and safely in order to reduce risk to life. [ABSTRACT FROM AUTHOR]

Hollow fan blades made of titanium alloy are widely used in turbofan engines, and the residual stress (RS) inside the blades directly affects the performance of the blades and even the engine. Therefore, it is crucial to measure and study the RS distribution of titanium alloy hollow fan blades. This paper aims to investigate the RS distribution on the cross-section of a wide-chord hollow fan blade made of Ti-6Al-4 V titanium alloy. The multiple-cut contour method is utilized to determine the RS. A theoretical model of the multiple-cut contour method for fan blades is established, and the specimen was cut three times, followed by contour measurement of the cut planes, data processing and elastic finite element analysis. The RS map of the three cut planes is finally presented. The normal RS on three cross-sections of the fan blade is uniformly distributed, ranging from -50 MPa to 50 MPa. The normal RS distribution at different positions for the hollow fan blade can be obtained by the proposed multiple-cut contour method. The findings of this research provide a comprehensive insight into the distribution of RS in wide-chord hollow fan blades made of Ti-6Al-4 V titanium alloy. [ABSTRACT FROM AUTHOR]

The article provides general information related to the Journal of Optimization Theory and Application, as of August 1, 2003. The journal publishes carefully selected papers covering mathematical optimization techniques and their applications to science and engineering. Typical areas of application are, aerospace, mechanical engineering, mathematical biology, mathematical economics, and mathematical physics. The journal publishes survey papers, technical notes, book notices and other types of articles.

Lithography-based additive manufacturing methods emerged as a powerful method for manufacturing of complex-shaped ceramic parts with excellent functional and structural properties. This paper summarizes the current state of the art in this field by articulating technological challenges associated with printing of functional parts. In addition, the paper addresses process requirements towards further enhancing component quality. A key aspect for obtaining high-quality parts is related to controlling chemical composition and uniformity of the photopolymerizable slurries. The latter requires in-depth understanding of the underlying photochemical processes. Changes in the formulation of the resin as well as changes in the exposure strategy distinctly influence bond conversion and gelling, which, in turn, influence the properties of the green part during thermal processing. Properly optimized processes and material composition allow to target a variety of challenging applications including patient specific parts for digital dentistry, and 3D-printed ceramics which can operate in harsh environments, as may be required in aerospace or chemical engineering applications. The paper will also provide an outlook into novel opportunities for 3D-printed ceramics. [ABSTRACT FROM AUTHOR]

Operational modal analysis (OMA) methods are nowadays common in civil, mechanical and aerospace engineering to identify and monitor structural systems without any knowledge on the structural excitation provided that the latter is due to ambient vibrations. For this reason, OMA methods are embedded with stochastic concepts and then it is difficult for users that have no-knowledge in signal analysis and stochastic dynamics. In this paper an innovative method useful for structural health monitoring (SHM) is proposed. It is based on the signal filtering and on the Hilbert transform of the correlation function matrix. Specifically, the modal shapes are estimated from the correlation functions matrix of the filtered output process and then the frequencies and the damping ratios are estimated from the analytical signals of the mono-component correlation functions: a complex signals in which the real part represents the correlation function and the imaginary part is its Hilbert transform. This method is very simple to use since requires only few interactions with the users and thus it can be used also from users that are not experts in the aforementioned areas. In order to prove the reliability of the proposed method, numerical simulations and experimental tests are reported also considering comparisons with the most popular OMA methods. [ABSTRACT FROM AUTHOR]

Aerospace engineering is a relatively new topic in engineering. It deals with several aspects of activities related to space. It includes Astrodynamics, which is a field that studies the motion of spacecraft, like guidance and control, which studies different forms to guide the motion of a spacecraft, etc. All those fields started from the Celestial Mechanics, one of the first topics studied in Astronomy. The first studies had the goal to record and explain the motions of the stars, with special attention given to the motion of some "irregular" stars, which showed later to be planets. Considering the advances in the technology, those earlier studies generated the space activities that are well known nowadays. Different topics, like orbital and attitude maneuvers and determination of spacecrafts, mission design, etc. are covered. The present Focus Issue publishes several papers related to aerospace engineering in general and can be useful for further studies and planning of space missions. [ABSTRACT FROM AUTHOR]

Space debris poses a potentially catastrophic risk to large-scale LEO constellations due to its substantial cascading effects, thereby rendering efficient and timely debris removal a critical research area in contemporary aerospace engineering. This paper delves into the application of the three-dimensional traveling salesman problem with orbital transfer constraints for space debris removal task planning. To overcome the challenges of sparse optimal solutions and vulnerability to local optima in addressing large-scale space debris removal task planning problems, we introduce a new Hierarchical Exploration Artificial Bee Colony (HEABC) optimization algorithm. Initially, we present an innovative two-step search strategy that employs a short-and-long term hybrid approach to optimize search time utilization and enhance solution quality, thereby addressing the sparsity of optimal solutions in the HEABC algorithm. Subsequently, to mitigate the issue of converging to local optima in high-dimensional encoding-based search problems, we devise a dual population update strategy aimed at preserving the innate evolutionary driving force of the search population. This strategy ensures the continuous updating of the population, even in the absence of intrinsic driving forces. Ultimately, experimental results substantiate that our proposed HEABC algorithm attains superior task planning sequences in a reduced time span and exhibits heightened adaptability in comparison to various traditional search algorithms. This is corroborated by numerical experiments conducted on one publicly available and one STK-generated space debris datasets. [ABSTRACT FROM AUTHOR]

In model-based systems engineering projects, engineers from multiple domains collaborate by establishing a common system model. Multi-level modeling is a technique that can be used to model the development from abstract ideas to concrete implementations. However, current multi-level modeling approaches are not adequate for processes with multiple modeling phases that might have to be rearranged later. In this paper, we introduce multi-phase modeling that utilizes concepts of multi-level modeling by considering a description of the expected phase ordering per domain. Constraints aware of this context can express that certain elements are only valid in specific phases without having to determine a concrete phase ordering for a particular model. This enables using multi-phase modeling in flexible workflows, adapting to changing requirements and the definition of access rules in domain notation. We show feasibility of this multi-phase modeling by applying it to multiple real-life systems engineering projects of the aerospace domain. [ABSTRACT FROM AUTHOR]

In the process of continuous development, robot technology has been widely used in aerospace, medical, education, and service industries, and the relationship between robots and people is getting closer and closer. The improvement of robot intelligence is a process of continuous learning of external knowledge. Since the introduction of human-computer interaction technology, it has provided more and more technical support for human research robots. This paper firstly takes Tai Chi as an example, analyzes and deconstructs its standard Tai Chi putter movements, and obtains the corresponding movement parameter information. Then, the human body depth image and bone structure are obtained through the kinect sensor, and the human joint position data is recorded, and then the coordinate data is sent to the brain robot, thereby realizing the imitation learning of the robot's push movements in Tai Chi. The experimental results show that the proposed method can simulate the practice process of inversion of Tai Chi, can well analyze the shortcomings in the practice process, and can then promote the development of the sport. [ABSTRACT FROM AUTHOR]

The development of an intelligent artificial satellite health monitoring system is a key issue in aerospace engineering that determines satellite health status and failure using telemetry data. The modern design of data mining and machine learning technologies allows the use of satellite telemetry data and the mining of integrated information to produce an advanced health monitoring system. This paper reviews the current status and presents a framework of necessary processes on data mining to solving various problems in telemetry data such as error detection, prediction, summarization, and visualization of large quantities, and help them understand the health status of the satellite and detect the symptoms of anomalies. Machine learning technologies that include neural networks, fuzzy sets, rough sets, support vector machines, Naive Bayesian, swarm optimization, and deep learning are also presented. Also, this paper reviews a wide range of existing satellite health monitoring solutions and discusses them in the framework of remote data mining techniques. In addition, we are discussing the analysis of space debris flow analysis and the prediction of low earth orbit collision based on our orbital Petri nets model. Challenges to be addressed and future directions of research are identified and an extensive bibliography is also included. [ABSTRACT FROM AUTHOR]

Electromagnetic (EM) simulation tools have become indispensable in the design of contemporary antennas. Still, the major setback of EM-driven design is the associated computational overhead. This is because a single full-wave simulation may take from dozens of seconds up to several hours, thus, the cost of solving design tasks that involve multiple EM analyses may turn unmanageable. This is where faster system representations (surrogates) come into play. Replacing expensive EM-based evaluations by cheap yet accurate metamodels seems to be an attractive solution. Still, in antenna design, application of surrogate models is hindered by the curse of dimensionality. A practical workaround has been offered by the recently reported reference-design-free constrained modeling techniques that restrict the metamodel domain to the parameter space region encompassing high-quality designs. Therein, the domain is established using only a handful of EM-simulations. This paper proposes a novel modeling technique, which incorporates the response feature technology into the constrained modeling framework. Our methodology allows for rendering accurate surrogates using exceptionally small training data sets, at the expense of reducing the generality of the modeling procedure to antennas that exhibit consistent shape of input characteristics. The proposed technique can be employed in other fields that employ costly simulation models (e.g., mechanical or aerospace engineering). [ABSTRACT FROM AUTHOR]

The Swing-By maneuver is a technique used in many space mission to modify the trajectory of a spacecraft. The most usual goal is to increase the energy of the spacecraft, but it is also possible to reduce this energy. An important application is to break a spacecraft coming to the Earth using a Swing-By with the moon, which is the example used in the present paper. Other possibilities also exist, such as reducing the velocity of a spacecraft going to the planets Mercury or Venus. The goal is to help a possible capture by the planet, or at least to provide a passage with smaller velocities to allow better observations during the passage. Therefore, the goal of the present paper is to study the energy loss that a spacecraft may have during a powered Swing-By maneuver, which is a maneuver that combines a close approach by a celestial body with the application of an impulsive maneuver. The behavior of the energy variation is analyzed as a function of the parameters related to the pure gravity maneuver: periapsis radius, angle of approach and approach velocity; and the parameters related to the impulsive maneuver: the location of application of the impulse and its direction and magnitude. The maneuver is performed in a system composed by two bodies, such as the Earth-moon system, around the secondary body, and the energy is measured with respect to the primary body of the system. This problem is solved by developing a mathematical algorithm that guides larger efforts in terms of computer simulations. The results show maps of conditions made from the numerical simulations for different points of application and direction of the impulse, where the maneuver is advantageous and how much more energy can be removed from the spacecraft. [ABSTRACT FROM AUTHOR]

Aerospace thin-walled parts have a complex structure and high accuracy. Factors such as original residual stress, fixing, and machining may make low-rigidity parts deform easily, which is difficult for traditional craftwork to forecast and control. Especially in machining big aerospace parts, original residual stress has a great effect on machining deflection. In this paper finite element model of original residual stress is established to analyze the corresponding deflection by machining aerospace thin-walled parts. Simulation results are validated consistent with experimental results approximately. At last the paper puts forward the corresponding mend methods to control the deflection caused by original residual stress during the actual machining process. [ABSTRACT FROM AUTHOR]

Demands for higher flexibility in aerospace applications has led to increasing deployment of reconfiguarble modules. In several cases the industry is looking into Field Programmable Gate Arrays (FPGA) as a means of efficient adaption of existing components. This paper addresses the safety analysis issues for reconfigurable modules with an emphasis on FPGAs. FPGAs act as digital hardware but in the context of safety analysis they should be treated as software, i.e. with added demands on formal analysis. The contributions of this paper are twofold. First, we illustrate a development process using a language with formal semantics (Esterel) for design, formal verification of high-level design, and automatic code generation down to synthesizable VHDL. We argue that this process reduces the likelihood of systematic (permanent) faults in the design, and still produces VHDL code that may be of acceptable quality (size of FPGA, delay). Secondly, in a general approach that is equally applicable to other formal design languages, we illustrate how the effect of transient fault modes and faults in external modules can be formally studied. We modularly extended the component design model with fault models that represent specific or random faults (e.g. radiation leading to bit flips in the component under design), and transient or permanent faults in the rest of the environment. Some faults corrupt inputs to the component and others jeopardise the effect of output signals that control the environment. This process supports a formal version of Failure Modes and Effects Analysis (FMEA). The set-up is then used to formally determine which (single or multiple) fault modes cause violation of the top-level safety-related property, much in the spirit of fault-tree analyses (FTA). All of this is done with out building the fault tree and using a common model for design and for safety analyses. An aerospace hydraulic monitoring system is used to illustrate the analysis of fault tolerance . [ABSTRACT FROM AUTHOR]

Feature selection targets for selecting relevant and useful features, and is a vital challenge in turbulence modeling by machine learning methods. In this paper, a new posterior feature selection method based on validation dataset is proposed, which is an efficient and universal method for complex systems including turbulence. Different from the priori feature importance ranking of the filter method and the exhaustive search for feature subset of the wrapper method, the proposed method ranks the features according to the model performance on the validation dataset, and generates the feature subsets in the order of feature importance. Using the features from the proposed method, a black-box model is built by artificial neural network (ANN) to reproduce the behavior of Spalart-Allmaras (S-A) turbulence model for high Reynolds number (Re) airfoil flows in aeronautical engineering. The results show that compared with the model without feature selection, the generalization ability of the model after feature selection is significantly improved. To some extent, it is also demonstrated that although the feature importance can be reflected by the model parameters during the training process, artificial feature selection is still very necessary. [ABSTRACT FROM AUTHOR]

Curved displays have recently become very popular, with wide applications for both industry and consumers. However, built upon initially flat films, most flexible displays are often incompatible with general nondevelopable surfaces. In this paper, we report a method for producing curved displays of nondevelopable shapes by using a structure-mechanics-inspired functional optimization method to design tessellation patterns that fold into the desired shapes. Representative displays in spherical and saddle shapes are demonstrated. The microfabrication process is employed for manufacturing 2D flexible foldable circuit boards, pick-and-place technology is used for placing illuminant elements onto the boards, and mold guidance is used for folding 2-D sheets into curved 3D display prototypes. The proposed technology is feasible for mass production and advances the application of next-generation curved displays. [ABSTRACT FROM AUTHOR]

Constraints widely exist in the structural optimization problems, including not only expensive constraints but also inexpensive constraints with explicit or implicit analytical expressions. Simply omitting the infeasible sampling points generated by conventional design of experiments (DoE) techniques leads to fewer feasible points than desired and to the remaining points distributed sub-optimally. This paper presents a novel constrained space-filling and non-collapsing sequential sampling (CSFSS) method for the arbitrarily constrained design space. To this end, an improved local density is firstly proposed to measure the spatial distribution of the sampling points located in the feasible region. Then, a novel formulation based on the improved local density is proposed for the criterion of sequential sampling strategies, which can guarantee the space-filling and non-collapsing properties both preferably optimal. Afterwards, several methods are proposed to tackle the challenging multimodal optimization problem posed by sequential sampling strategies. Finally, a replacement-based strategy is proposed to further elevate the quality of the design. Extensive numerical results, including an application for the lightweight design of cylindrical stiffened shells in aerospace engineering, highlight the satisfying performance of the proposed method not only in obtaining a high quality of constrained experimental designs but also in competitive contributions to constrained optimization gains. [ABSTRACT FROM AUTHOR]

Introduction: Because the fluid-conveying piping system has a wide range of engineering applications such as mechanical, civil, astronautical and aeronautical engineering and so on, the vibration control is very necessary due to possible damage to the pipe system caused by vibration. This paper presents a vibration reduction scheme of pipeline conveying fluid which can reduce vibration effectively. Objectives: By coupling the Bragg scattering bandgap mechanism with the inertia amplification mechanism, a strategy to enhance the bandgap properties of the periodic non-uniform pipes conveying fluid is proposed. Methods: The band structures for flexural waves in the fluid-conveying periodic non-uniform pipes with periodically distributed inertial amplification mechanisms are determined using the transfer matrix method, and the frequency ranges of the bandgaps and vibration reduction are analyzed. Results: The vibration attenuation capacity of the periodic non-uniform pipes under different fluid velocities, amplification masses and amplification angles is investigated. The bandgaps of the non-uniform pipe conveying fluid with periodic inertial amplification mechanisms obtained by the numerical method are compared with the vibration experiments. The results show that the piping systems with the design of the periodic pipe structures can be effective in reducing vibration. Conclusion: The fluid velocity has slight effect on the band-gap properties of the non-uniform fluid-conveying pipes with periodic inertial amplification mechanisms. The band-gap properties and vibration attenuation performance of the non-uniform fluid-conveying pipes with periodic inertial amplification mechanisms can be enhanced more efficiently by a larger amplification angle and amplification mass. [ABSTRACT FROM AUTHOR]

In additive manufacturing (3D printing) of products for aerospace, medical, or other critical applications, the quality of the manufactured part must be 'certified' before it can be used. New methods are needed to certify the quality during the fabrication process. The digital 3D quality certificate (3DQC) assures that process monitor values were within specification during the entire fabrication process. This paper proposes an approach for using high resolution infrared thermal imaging to monitor the temperature of individual layers before, during, and after laser scanning. Temperature data is indexed to the part geometry using a binary template created from the sliced 3D model. This data provides a record of the process conditions during the creation of each volume element of the part. Two temperatures are discussed in this paper: the peak temperature achieved during laser scanning and the residual temperature in the layer just before adding the next powder layer. Both of these monitors show a relationship to the geometry of the part, the layer cross-sectional area, and the presence or absence of an underlying solid layer. While both of these temperatures likely relate to part quality, this relationship is not yet understood. Ultimately, this monitor data can be used to control the process, e.g., modify the laser scan or the wait time before recoating, in order to provide more uniform sintering of each volume element of the part. [ABSTRACT FROM AUTHOR]

Graph: Roger L. Fosdick This publication is dedicated to Roger L. Fosdick who celebrated his 85th birthday on November 18, 2021. Roger is Professor Emeritus of the Aerospace Engineering and Mechanics department at the University of Minnesota, Twin Cities. Accordingly, we were granted complete autonomy as guest editors and Roger has not been involved with the editing or oversight of publication of the articles in the collection, all of which were refereed. [Extracted from the article]

It has previously been shown in the literature that the generalized Euler sequences (also known as Davenport sequences) provide a universal set of attitude representations. However, while these works assert the existence of generalized Euler angles for a given attitude, they do not provide explicit ranges that those angles must lie within. In addition, they do not generally provide physical insight into what a generalized Euler sequence is. This paper addresses these two points. As such, this paper contains a comprehensive self-contained treatment of generalized Euler sequences. In particular, a constructive approach is taken to proving that the generalized Euler sequences provide a universal set of attitude representations. In doing so, specific ranges that contain the generalized Euler angles are obtained, and physical insight is provided into the generalized Euler sequences. The singularity of the generalized Euler sequences is characterized, and it is shown that the generalized Euler angles are uniquely specified within their restricted ranges when away from the singularity condition. [ABSTRACT FROM AUTHOR]

Thin-walled shell structures are widely used in aeronautical and aerospace engineering. This paper develops an effective B-spline parameterization method for stiffener layout optimization of shell structures. Height variables are defined by B-spline control parameters to characterize the stiffener layout reinforcing the shell structure. A continuous height field is subsequently generated via B-spline and basis functions. In view of possible curvatures of shell structures, the height field is projected from parametric space onto the shell structure by means of the parametric mapping. In this work, the finite element method is adopted with the solid-shell coupling method used for structural analysis. Pseudo-densities associated with solid elements are determined based on the B-spline parameterization and Heaviside function. Several numerical examples are dealt with to demonstrate the proposed method. Compared with the standard density-based method, the proposed method produces checkerboard-free design results with a clear layout and naturally avoids overhang stiffeners. [ABSTRACT FROM AUTHOR]

This paper reviews the potential of polymer and ceramic matrix composites for aerospace/space vehicle applications. Special, unique and multifunctional properties arising due to the dispersion of nanoparticles in ceramic and metal matrix are briefly discussed followed by a classification of resulting aerospace applications. The paper presents polymer matrix composites comprising majority of aerospace applications in structures, coating, tribology, structural health monitoring, electromagnetic shielding and shape memory applications. The capabilities of the ceramic matrix nanocomposites to providing the electromagnetic shielding for aircrafts and better tribological properties to suit space environments are discussed. Structural health monitoring capability of ceramic matrix nanocomposite is also discussed. The properties of resulting nanocomposite material with its disadvantages like cost and processing difficulties are discussed. The paper concludes after the discussion of the possible future perspectives and challenges in implementation and further development of polymer and ceramic nanocomposite materials. [ABSTRACT FROM AUTHOR]

With the foundation of the Division of Plasma Physics of the American Physical Society in April 1959, plasma physics was presented as the general study of ionized gases. This paper investigates the degree to which plasma physics, during its first decade, established a community of interrelated specialties, one that brought together work in gaseous electronics, astrophysics, controlled thermonuclear fusion, space science, and aerospace engineering. It finds that, in some regards, the plasma community was indeed greater than the sum of its parts and that its larger identity was sometimes glimpsed in inter-specialty work and studies of fundamental plasma behaviors. Nevertheless, the plasma specialties usually worked separately for two inter-related reasons: prejudices about what constituted 'basic physics,' both in the general physics community and within the plasma community itself; and a compartmentalized funding structure, in which each funding agency served different missions. [ABSTRACT FROM AUTHOR]

Engineering companies are currently shifting their focus from selling products to providing services, hence the products' designers must increasingly consider life-cycle requirements, in addition to conventional design parameters. To identify possible areas of concern, engineers must consider knowledge throughout the life cycle of similar or related products. However, because of the size and distributed nature of a company's operation, engineers often do not have access to front-line maintenance data. In addition, the large number of documents generated during the design and operation of a product makes it impractical to manually review all documents thoroughly during a task. As a case study, this paper discusses the concept and development of a large hypermedia based Knowledge Desktop that has been developed to support the maintenance and future design of aircraft engines. As part of the development cycle, the performance of the software and its acceptance by the user community has been fully evaluated. The evaluation method considered in this paper focuses on the subjective opinion of the users and measures the ease with which users could retrieve the information required to perform specific tasks. [ABSTRACT FROM AUTHOR]

Alloy 718 (UNS N07718) was developed for use in aircraft gas turbine engines, but its unique combination of room-temperature strength and aqueous corrosion resistance made it a candidate for oilfield fasteners, valves, drill tools, and completion equipment. As well environments became more severe, stress corrosion and hydrogen embrittlement failures in production equipment drove the evolution of the composition and microstructure that distinguish today's oilfield-grade 718 from aerospace grades. This paper reviews the development of the grade and its applications and describes some of its unique characteristics, testing, and manufacturing methods as well as newer alloys designed for high-pressure high-temperature (HPHT) conditions. [ABSTRACT FROM AUTHOR]

This paper describes some research stimulated by a fundamental shift that is occurring in the manufacture and marketing of aero engines for commercial and defence purposes, away from the selling of products to the provision of services. The collaborating aerospace company offers contracts under which it remains responsible for the maintenance of engines which have been purchased by airlines through these contracts based on payment for usage. This has triggered a major re-assessment of the design of aero engines to reduce their overall life cycle costs, while maintaining performance efficiency. In this context, the use of in-service experience of existing engines is important in the design of components and systems of a new engine, to tackle in-service issues through design and thus to reduce maintenance costs and increase reliability. This paper aims at identifying designers' requirements regarding in-service information. Semi-structured interviews with designers from an aerospace company were conducted; after these interviews, the designers were requested to comment on a set of questions regarding in-service information, indicating how frequently they might ask each of them when designing a new component or system. In addition, some documents containing the in-service information considered by the designers in designing components and systems of a new engine were analysed. The results indicate what in-service information is required by designers for this new task. [ABSTRACT FROM AUTHOR]

Information on the 3rd Institute of Electrical and Electronics Engineers (IEEE) Multi-Conference on Systems and Control (MSC) held at Park Inn Pulkovskaya Hotel in St. Petersburg, Russia on July 8-10, 2009 is presented. Topics focus on the modern problems of control theory and applications and scientific programs on agrotechnical, aerospace, and automobile control systems were presented. The conference featured several scientists including M. Sugeno, R. Horowitz, and F. Bullo.

Additive manufacturing (AM) technologies such as fused deposition modeling (FDM) have been widely used in various fields of today's manufacturing industries such as transportation, aerospace, and medical because of its ability to produce parts of complex designs with less manufacturing time and cost. However, a proper selection of input process parameters is a vital aspect in order to obtain the best quality of the printed part. This paper presents several approaches, namely response surface methodology, particle swarm optimization, and symbiotic organism search, to find the optimal parameter settings for better surface quality, i.e., surface roughness of the FDM printed part. Layer height, print speed, print temperature, and outer shell speed were considered as the input parameters and surface roughness as the output response. The experimental design was carried out using response surface methodology (RSM) method. Then, the relationship between the input parameters and the surface roughness was established using regression model. Once the accuracy of the model had been validated, the model was then coupled with particle swarm optimization (PSO) and symbiotic organism search (SOS) to optimize the input parameters that would lead to minimum surface roughness. Experimental results showed that the surface roughness obtained using PSO and SOS have improved about 8.5% and 8.8%, respectively, compared with the conventional method, i.e., RSM. A good agreement between the predicted surface roughness and the experimental values was also observed. [ABSTRACT FROM AUTHOR]

Risk management is a well-known method to face technological challenges through a win–win combination of protective and proactive approaches, fostering the collaboration of operators, researchers, regulators, and industries for the exploitation of new markets. In the field of autonomous and unmanned aerial systems, or UAS, a considerable amount of work has been devoted to risk analysis, the generation of ground risk maps, and ground risk assessment by estimating the fatality rate. The paper aims to expand this approach with a tool for managing data protection risks raised by drones through the design of flight maps. The tool should allow UAS operators choosing the best air corridor for their drones based on the so-called privacy by design principle pursuant to Article 25 of the EU data protection regulation, the GDPR. Among the manifold applications of this approach, the design of fly zones for drones can be tailored for public authorities in the phase of authorization of new operations, much as for national Data Protection authorities that have to control the lawfulness of personal data processing by UAS operations. The overall aim is to present the first win–win approach to data protection issues, aerospace engineering challenges, and risk management methods for the threats posed by this technology. [ABSTRACT FROM AUTHOR]

Frame structures are extensively used in mechanical, civil, and aerospace engineering. Besides generating reasonable designs of frame structures themselves, frame topology optimization may serve as a tool providing us with conceptual designs of diverse engineering structures. Due to its nonconvexity, however, most of existing approaches to frame topology optimization are local optimization methods based on nonlinear programming with continuous design variables or (meta)heuristics allowing some discrete design variables. Presented in this paper is a new global optimization approach to the frame topology optimization with discrete design variables. It is shown that the compliance minimization problem with predetermined candidate cross-sections can be formulated as a mixed-integer second-order cone programming problem. The global optimal solution is then computed with an existing solver based on a branch-and-cut algorithm. Numerical experiments are performed to examine computational efficiency of the proposed approach. [ABSTRACT FROM AUTHOR]

With the development of aerospace engineering, the space on-orbit servicing has been brought more attention to many scholars. Obstacle avoidance planning of space manipulator end-effector also attracts increasing attention. This problem is complex due to the existence of obstacles. Therefore, it is essential to avoid obstacles in order to improve planning of space manipulator end-effector. In this paper, we proposed an improved ant colony algorithm to solve this problem, which is effective and simple. Firstly, the models were established respectively, including the kinematic model of space manipulator and expression of valid path in space environment. Secondly, we described an improved ant colony algorithm in detail, which can avoid trapping into local optimum. The search strategy, transfer rules, and pheromone update methods were all adjusted. Finally, the improved ant colony algorithm was compared with the classic ant colony algorithm through the experiments. The simulation results verify the correctness and effectiveness of the proposed algorithm. [ABSTRACT FROM AUTHOR]

There has been an intensive international effort to develop high-order Computational Fluid Dynamics (CFD) methods into design tools in aerospace engineering during the last one and half decades. These methods offer the potential to significantly improve solution accuracy and efficiency for vortex dominated turbulent flows. Enough progresses have been made in algorithm development, mesh generation and parallel computing that these methods are on the verge of being applied in a production design environment. Since many review papers have been written on the subject, I decide to offer a personal perspective on the state-of-the-art in high-order CFD methods and the challenges that must be overcome. [ABSTRACT FROM AUTHOR]

The immense design freedom offered by additive manufacturing yields tremendous benefits, but it also raises the question of how to best go about designing components to exploit this design freedom. In early design phases, design tools need to utilize this freedom, but do so with low computational cost and with a good estimate of the final weight to correctly assess the part's influence on the overall product design. This is especially important for aerospace designs. In this paper, a design methodology is devised for cellular structures to be manufactured using additive manufacturing techniques, specifically for such early design phases. This design methodology uses adaptive meshing techniques to design the topology of the cellular structure, after which the struts of that cellular structure are optimized separately to reduce the dimensionality of the problem. The method is demonstrated for a small generic bracket and an aircraft bracket design from the literature. For these problems, our method is fast enough to evaluate many thousands of design options. This results in identifying promising candidate designs for further detailed design work. [ABSTRACT FROM AUTHOR]

SLAU2 and AUSMPW + , both categorized as AUSM-type Riemann solvers, have been extensively developed in gasdynamics. They are based on a splitting of the numerical flux into advected and pressure parts. In this paper, these two Riemann solvers have been extended to magnetohydrodynamics (MHD). The SLAU2 Riemann solver has the favorable attribute that its dissipation for low-speed flows scales as O (M 2) , where M is the Mach number. This is the physical scaling required for low-speed flows, and the dissipation in SLAU2 for MHD is engineered to have this low Mach number scaling. The AUSMPW + , when its pressure flux is replaced with that of SLAU2, has the same low Mach number scaling. At higher Mach numbers, however, the pressure-split Riemann solvers were found not to function well for some MHD Riemann problems, despite the fact that they were engineered to have a dissipation that scales as O (| M |) for high Mach number flows. The HLLI Riemann solver (Dumbser and Balsara in J Comput Phys 304:275–319, 2016) has a dissipation that scales as O (| M |) , which makes it unsuitable for low Mach number flows. However, it has very favorable performance for higher Mach number MHD flows. Since the two families of Riemann solvers perform very well over a range of intermediate Mach numbers, the best way to benefit from the mutually complementary strengths of both these Riemann solvers is to hybridize between them. The result is an all-speed Riemann solver for MHD. We, therefore, document hybridized SLAU2–HLLI and AUSMPW + –HLLI Riemann solvers. The hybrid Riemann solvers suppress the oscillations that appeared in single-solver solutions, and they also preserve contact discontinuities, as well as Alfvén waves, very well. Furthermore, their better resolution at low speeds has been demonstrated. We also present several stringent one-dimensional test problems. [ABSTRACT FROM AUTHOR]

The dynamic behavior of a structure can be formulated in terms of the waves propagating through its members. This approach is commonly known as the Travelling Wave Method (TWM). The propagation of an external excitation within structural members, and the behavior of waves at a discontinuity are defined by the amplitude of displacement waves, and the wave reflection and transmission coefficients. The assemblage of these properties provides a concise method to formulate the dynamic response of structures. Although it has been used for the analysis of aerospace structures, the TWM has rarely been used for the analysis of civil engineering structures. This paper presents the theoretical basis and the formulation of the wave-propagation approach to analyze the dynamic response of civil-engineering-type structures, and discusses its advantages over the commonly used Finite Element Method (FEM). It is shown by examples that TWM requires less computational time than FEM, can incorporate the frequency-dependent soil-structure interaction effects in the analysis directly, and gives more accurate results at high frequencies. The last one is particularly important for detecting small and invisible damages in structures, since most of such damage is hidden in high frequencies. [ABSTRACT FROM AUTHOR]

Titanium alloys display low density, high mechanical strength and good corrosion resistance, being ideal structural materials for aerospace engineering. In this paper, the effects of nitrogen on the anelastic properties of the bcc alloy Ti-13V-11Cr-3Al were investigated. The results show an asymmetric thermally activated relaxation structure in the high-temperature region. This relaxation structure was decomposed, and relaxation processes due to stress-induced ordering of nitrogen atoms around the metallic matrix and substitutional solutes were identified. [ABSTRACT FROM AUTHOR]

Wrinkling is one of the major defects in tube-compression process. As a new method, the pressure distribution of viscous medium can be controlled when wrinkles occur in tube-compression process by viscous pressure forming (VPF) and then wrinkles can be eliminated under certain condition. So the tube-compression limit is greatly improved by expanding the deformation area in this new developed process. However, the limit of tube-compression by VPF is hard to be predicted according to existing forming limit theory. In this paper, process window diagrams considering some parameters of tube-compression length, tube-blank diameter, and limit diameter reduction were predicted by finite element method, and were verified by experiments. The results show that the diagrams can predict the limit diameter reduction of tube-blank, and also can reflect the states of wrinkles and the possibility of its elimination during tube-compression by VPF, which can provide guidance for the application of this forming technology. [ABSTRACT FROM AUTHOR]

This paper presents test results and analyses of safety lock wire and cotter pins with castellated nuts used as locking features in threaded fasteners. These mechanical components are used to secure hardware in aerospace and other applications as well as to assess whether a fastener has been tampered with. Tests are performed on aerospace threaded fasteners. Locking moments up to safety lock wire and cotter pin failure are measured. Calculations of locking moment to failure are provided and compared to measured results. For fasteners with safety lock wire, the angle of turn with applied moment is measured and computed. For fasteners with cotter pins and castellated nuts, the angles of turn from clearances and applied moment are computed. Since both safety lock wire and cotter pin with castellated nut applications result in some angle of turn, analysis for loss of preload with angle of turn is developed. Calculations show modest loss in preload for typical angles of turn for long bolts, but a significant loss of preload is found for short bolts. [ABSTRACT FROM AUTHOR]

Over the last 10 years, Shanghai Institute of Technical Physics, Chinese Academy of Sciences, has developed very high-efficiency pulse tube cryocoolers (PTCs) for aerospace applications. These PTCs can provide cooling power from milliwatt scale to tens of watts over a range of temperatures from 30 to 170 K and can be used to cool a variety of detectors in space applications (such as quantum interference devices, radiometers and ocean color sensors) that must operate at a specific cryogenic temperature to increase the signal-to-noise ratio, sensitivity and optical resolution. This paper reviews the development of single-stage PTCs over a range of weights from 1.6 to 12 kg that offer cooling powers at the cold temperature range from 40 to 170 K. In addition, a two-stage 30 K-PTC is under development. [ABSTRACT FROM AUTHOR]

This paper presents a two-level approximation method for multi-objective optimization of a composite stiffened panel. The purpose is to seek the minimum structural mass and maximum fundamental frequency subject to given displacement constraints and manufacturing limitations. The design variables are the stiffener layout, and laminate stacking sequences for stiffeners and the panel skin. By introducing the concept of ground structure in both stiffener layout and laminate stacking sequence, the design problem is formulated with mixed discrete and continuous variables. Two types of discrete variables represent the existence of each stiffener and the existence of each ply in the laminate, respectively, with continuous ones for ply thicknesses. Considering the objectives are of different dimensions, a weighted min-max objective function is defined and minimized. The problem is firstly made explicit with branched multipoint approximate functions. Genetic algorithm (GA) is then adopted to optimize two types of discrete variables, determining which stiffeners/layers are deleted or retained. For fitness calculation in GA, a second-level approximation is built to optimize continuous ply thicknesses of the necessary layers that are retained. By giving different initial designs of stiffener layout and laminate stacking sequences, reasonable optimization results, which are tradeoffs between the considered two objectives, are obtained as design options. From the number of required structural analysis, it shows that the proposed method has a good efficiency in seeking rational solutions, which are tradeoffs between conflicting objectives and also feasible designs satisfying all considered constraints. [ABSTRACT FROM AUTHOR]

Titanium alloy profiles are excellent candidates for lots of applications, especially in aerospace field. High temperature is needed in the hot stretch-forming process because of the low plasticity of titanium alloy at room temperature. Resistance heating, with the benefit of device simplification and energy saving, is one of the most commonly used heating methods. In this paper, temperature variation model was developed for titanium alloy profile during resistance heating. The results show that the equilibrium temperature rises as the heating power increases. The temperature variation curves show that the temperature increases rapidly firstly, then keep nearly constant. Shorter heating time is needed to achieve the equilibrium temperature when higher heating power is applied. The thermal variation shows promising agreement with the experimental data, which confirms the feasibility of the developed models. [ABSTRACT FROM AUTHOR]

The use of active vibration isolation devices (AVIDs) in aerospace engineering is subject to the following restrictions. First, the volume for installing additional devices is always limited in instrument racks and compartments. Secondly, in many cases, it is impossible to add supports for servo actuators for fundamental or design considerations. In the paper, it has been shown that this problem can be solved if the inertial servo actuators are used in AVIDs instead of reference actuators. A transfer function has been theoretically calculated for an AVID controlled by inertial actuators. It has been shown that the volume of a six-mode single-housing AVID with inertial actuators can be 2-2.5 times smaller than that of devices with support actuators. [ABSTRACT FROM AUTHOR]

Some structures require keeping a specific safety level even if part of their elements have collapsed. The aim of this paper is to obtain the optimum design of these structures when uncertainty in some parameters that affects to the structural response is also considered. A Reliability-Based Design Optimization (RBDO) problem is formulated in order to minimize the mass of the structure fulfilling probabilistic constraints in both intact and damaged configurations. The proposed methodology combines the formulation of multi-model optimization with RBDO techniques programmed in a Matlab code. Two application examples are presented consisting of a two-dimensional truss structure with stress constraints as well as a curved stiffened panel of an aircraft fuselage subjected to buckling constraints. [ABSTRACT FROM AUTHOR]

Aircraft landing gear assemblies comprise of various subsystems working in unison to enable functionalities such as taxiing, take-off and landing. As development cycles and prototyping iterations begin to shorten, it is important to develop and improve practical methodologies to meet certain design metrics. This paper presents an efficient methodology that applies high-fidelity multi-disciplinary design optimization techniques to commercial landing gear assemblies, for weight, cost, and structural performance by considering both structural and dynamic behaviours. First, a simplified landing gear assembly model was created to complement with an accurate slave link subassembly, generated based of drawings supplied from the industrial partner, Safran Landing Systems. Second, a Multi-Body Dynamic (MBD) analysis was performed using realistic input motion signals to replicate the dynamic behaviour of the physical system. The third stage involved performing topology optimization with results from the MBD analysis; this can be achieved through the utilization of the Equivalent Static Load Method (ESLM). Lastly, topology results were generated and design interpretation was performed to generate two designs of different approaches. The first design involved trying to closely match the topology results and resulted in a design with an overall weight savings of 67%, peak stress increase of 74%, and no apparent cost savings due to complex features. The second design focused on manufacturability and achieved overall weight saving of 36%, peak stress increase of 6%, and an estimated 60% in cost savings. [ABSTRACT FROM AUTHOR]

Fiber-reinforced ceramic-matrix composites are advanced, temperature resistant materials with applications in aerospace engineering. Their analysis involves the detection and separation of fibers, embedded in a fiber bed, from an imaged sample. Currently, this is mostly done using semi-supervised techniques. Here, we present an open, automated computational pipeline to detect fibers from a tomographically reconstructed X-ray volume. We apply our pipeline to a non-trivial dataset by Larson et al. To separate the fibers in these samples, we tested four different architectures of convolutional neural networks. When comparing our neural network approach to a semi-supervised one, we obtained Dice and Matthews coefficients reaching up to 98%, showing that these automated approaches can match human-supervised methods, in some cases separating fibers that human-curated algorithms could not find. The software written for this project is open source, released under a permissive license, and can be freely adapted and re-used in other domains. [ABSTRACT FROM AUTHOR]

Complex systems are increasingly being developed as part of portfolios or sets of related complex systems. This enables synergies such as commonality between portfolio systems that can significantly reduce portfolio life-cycle cost and risk. While offering these benefits, commonality usually also incurs up-front as well as life-cycle penalties in cost and risk due to increased design complexity. The resulting trade-off needs to be carried out during the architecting stage of the portfolio life cycle when there is maximum leverage to improve life-cycle properties due to degrees of freedom available in architectural and design decisions. This paper outlines a 4-step methodology for the identification and assessment of commonality opportunities in complex systems portfolios during the architecting stage of the portfolio life cycle. The methodology transforms a solution-neutral description of a portfolio of aerospace systems based on system functionality, requirements, and metrics into a set of preferred portfolio design solutions with commonality. The methodology is based on a 2-stage approach that identifies preferred architectures for each system in the portfolio individually prior to heuristic commonality analysis between systems based on a pairwise assessment of system overlap in functionality, technologies, operational environments, and scale. Application of the methodology is demonstrated with a retrospective analysis of NASA's Saturn launch vehicle portfolio. [ABSTRACT FROM AUTHOR]

There are many applications in aeronautical/aerospace engineering where some values of the design parameters/states cannot be provided or determined accurately. These values can be related to the geometry (wingspan, length, angles) and or to operational flight conditions that vary due to the presence of uncertainty parameters (Mach, angle of attack, air density and temperature, etc.). These uncertainty design parameters cannot be ignored in engineering design and must be taken into the optimisation task to produce more realistic and reliable solutions. In this paper, a robust/uncertainty design method with statistical constraints is introduced to produce a set of reliable solutions which have high performance and low sensitivity. Robust design concept coupled with Multi-Objective Evolutionary Algorithms (MOEAs) is defined by applying two statistical sampling formulas; mean and variance/standard deviation associated with the optimisation fitness/objective functions. The methodology is based on a canonical evolution strategy and incorporates the concepts of hierarchical topology, parallel computing and asynchronous evaluation. It is implemented for two practical Unmanned Aerial System (UAS) design problems; the first case considers robust multi-objective (single-disciplinary: aerodynamics) design optimisation and the second considers a robust multidisciplinary (aero-structures) design optimisation. Numerical results show that the solutions obtained by the robust design method with statistical constraints have a more reliable performance and sensitivity in both aerodynamics and structures when compared to the baseline design. [ABSTRACT FROM AUTHOR]