Large-scale multidisciplinary design optimization of a NASA air taxi concept using a comprehensive physics-based system model

A large-scale finite element model-based design optimization algorithm is developed for improving the drive-cycle efficiency of permanent magnet (PM) synchronous machines with wide operating ranges such as those used in traction propulsion motors. The load operating cycle is efficiently modeled by using a systematic k -means clustering method to identify the operating points representing the high-energy-throughput zones in the torque–speed plane. The machine performance is evaluated over these cyclic representative points using a recently introduced computationally efficient finite element analysis, which is upgraded to include both constant torque and field-weakening operations in the evaluation of the machine performance metrics. In contrast with the common practice, which aims at enhancing the rated performance, the entire range of operation is considered in the present design optimization method. Practical operational constraints imposed by the voltage and current limits of the motor-drive system, excessive PM demagnetization, and torque ripple are accounted for during the optimization process. The convergence to the optimal design solutions is expedited by utilizing a new stochastic optimizer. The developed design algorithm is applicable to any configuration of sinewave-drive PM and synchronous reluctance motors over any conceivable load profile. Its effectiveness is demonstrated by optimizing the well-established benchmark design represented by the Toyota Prius Gen. 2 interior PM motor configuration over a compound operating cycle consisting of common U.S. driving schedules. Multiphysics electromagnetic, thermal, and mechanical performance of the optimized design solutions is discussed in a postdesign optimization stage.

This paper describes the development of a geographic independent virtual design environment for large-scale Multidisciplinary Design Optimization (MDO) problems. The environment described provides a designer with the ability to see and interact with a 3-D Virtual Reality (VR) representation of the design or a representation of a subset of the design space. The designer can make graphical alterations to the design and see the effects in real-time. The environment supports multiple users to be logged on at the same time and to see the desired design changes and effects hi real time or near real time made by other designers. The designers have several means of communication available involving words, pictures, and text to communicate their ideas and concepts.

An emergency care system is an important aspect for healthcare organisations in low- and middle-income countries (LMICs) with a growing burden from emergency disease conditions. Evaluations of emergency care systems in LMICs in broader contexts are lacking. Thus, this study aimed to develop a comprehensive emergency medical system model appropriate for resource-constrained settings, based on expert opinions. We used the Delphi method, in which questionnaire surveys were administered three times to an expert panel (both emergency medical care providers and healthcare service researchers), from which opinions on the model's components were compiled. The panel members were mostly from Asian countries. In the first round, the questionnaire drew a list of model components developed through a literature review; the panel members then proposed new components to create a more comprehensive list. In the second and third rounds, the panel members rated the listed components to achieve consensus, as well as to remove components with low ratings. Finally, we rearranged the list to improve its usability. In total, 32 experts from 12 countries participated. The final model totalled 177 components, categorised into 8 domains (leadership, community-based actions, emergency medical services, upward referral, definitive care, rehabilitation, downward referral, and evaluation and research). No components needed removal. We developed a comprehensive emergency care system model, which could provide a basis to evaluate emergency care systems in resource-constrained LMICs; however, field-testing and validation of this system model remain to be done.

Electromechanical product is an important part of mechanical and electrical control system, and its quality plays a key role in the normal operation process. In this paper, a comprehensive fault diagnosis system and quality evaluation model for electromechanical products is analyzed. Firstly, the feature extraction of different faults is carried out, and the fault features of electromechanical products are simplified by using the approximation set information system properties of rough set theory. Secondly, the subjective weight index model is determined based on the rough information system properties of rough set theory. Then, the evaluation weight of each index of quality evaluation model for electromechanical products is obtained by the importance measurement of information system properties. Finally, this paper illustrates that the results of fault diagnosis and quality evaluation of ball valves as well as the availability of scientific.

Aircraft conceptual design is a high-dimensional, multidisciplinary design optimization (MDO) problem. It involves a large number of design variables (~10-1000s), multiple disciplines, and diverse operating conditions, including nominal on-design and off-design scenarios such as structural sizing and system failure modes. Recent advancements in modeling and adjoint-based sensitivity analysis have facilitated the use of low- to mid-fidelity physics-based models to achieve computationally efficient solutions for this complex, large-scale MDO problem. However, employing higher-fidelity simulations, such as CFD-based aerodynamic analysis, for large-scale MDO of aircraft concepts remains challenging. This is largely due to the high computational cost and the complex mesh movement requirements associated with significant design geometry changes, particularly at the conceptual design stage. In this paper, we propose initial steps toward a mesh movement algorithm designed to bridge the gap between high-fidelity aerodynamic analysis and large-scale MDO of aircraft concepts using mixed-fidelity system models. The algorithm minimizes the projection error volume between the mesh and the central geometry while incorporating a non-uniformity penalty to maintain mesh quality. Additionally, it computes intersection curves between intersecting geometries, ensuring that the mesh conforms to the outer hull of the geometry. We demonstrate the proposed algorithm on a simple test case involving a wing and fuselage configuration.

Next-generation additive manufacturing technologies will enable novel, low-weight, highperformance aircraft structures. Topology optimization techniques can be used to obtain unconventional internal aircraft wing structures that can be manufactured using additive methods which depart significantly from conventional rib-spar wing constructions. However, there are significant issues that must be overcome when applying traditional topology optimization techniques to the design of aerospace structures. These challenges include efficiently solving large-scale design problems, and applying buckling criteria within a topology optimization design formulation. In this paper, we seek to address these issues by applying a scalable topology optimization method to the undeformed Common Research Model (uCRM) wing with buckling constraints applied to the skins of the wingbox. The proposed approach uses a multigrid-preconditioned Krylov method to solve the large-scale finite element analysis problem, coupled with a parallel interior-point optimizer to solve the largescale constrained design optimization problem. This proposed method is applied to two different optimization problems: mass-constrained compliance minimization, and mass-constrained bucklingload maximization. In addition, we apply a segment-wise topology optimization design strategy to the uCRM wingbox.

The process of constructing computationally benign approximations of expensive computer simulation codes, or metamodeling, is a critical component of several large-scale Multidisciplinary Design Optimization approaches. Such applications typically involve complex models, such as finite elements, computational fluid dynamics, or chemical processes. The decision regarding the most appropriate metamodeling approach usually depends on the type of application. However, several newly-proposed kernel-based metamodeling approaches can provide consistently accurate performance for a wide variety of applications. The authors recently proposed one such novel and effective metamodeling approach — the Extended Radial Basis Function approach — and reported encouraging results. To further understand the advantages and limitations of this new approach, we compare its performance to that of the typical radial basis function approach, and another closely related method — kriging. Several test functions with varying problem dimensions and degrees of nonlinearity are used to compare the accuracies of the metamodels using these metamodeling approaches. We consider several performance criteria, such as metamodel accuracy. effect of sampling technique, effect of problem dimension, and computational complexity. The results suggest that the E-RBF approach is a potentially powerful metamodeling approach for MDO-based applications.

Automatic generation of global shell-element meshes for large-scale structural design optimization

Large-scale system design optimization is a numerical tool used in solving system design problems that involve a large number of design variables. These systems are often multidisciplinary with many disciplines interacting with each other. The scale of these problems demands a gradient-based approach for efficient solutions, and it is often implemented by coupling an engineering model with an optimizer. The optimizer reads the outputs of the model and generates design variable values at which the model is evaluated in the next iteration. This iterative process continues until the optimizer converges to a specific design. A recently developed theory on multidisciplinary derivative computation and its implementation in a modular framework have made it feasible to solve large-scale system design optimization problems in only hundreds of model evaluations. This has led to an increase in the number of applications for large-scale system design optimization with new applications still emerging. This paper presents a new optimization formulation that can further reduce the required number of model evaluations by unifying two widely used optimization architectures, namely, multidisciplinary feasible and simultaneous analysis and design. Complex engineering systems that require solution of large nonlinear systems can potentially benefit from this new formulation, and the optimized solutions can be reached in just tens of model evaluations. We demonstrate this order of magnitude improvement through the application of our new algorithm on a cantilever beam design problem. The paper also provides details on practical implementation of this new formulation in an equality-constrained optimization setting.

Through a systematic optimization study using high-fidelity finite-element (FE) models, torque capability of three common synchronous machine technologies, namely a permanent magnet (PM) synchronous machine (PMSM) with V-shaped rare-earth (RE) rotor magnets, a PMSM with deep V-shaped ferrite rotor magnets, and a synchronous reluctance machine (SynRM) with four layers of conforming flux barriers are compared for an application in a 48-V mild hybrid electric car. The optimization of the deep V-shaped ferrite PMSM automatically resulted in a spoke-type PM layout for maximum torque production. Yet, an optimized SynRM with conforming flux barriers was achieved that could produce a higher torque than ferrite PMSM. One machine technology is selected and is subsequently subjected to a large-scale FE model-based drive-cycle design optimization. Various pole-slot combinations are methodically compared in terms of drive-cycle losses, active material cost, torque ripple, and PM demagnetization level. More than 20,000 designs were analyzed over ten energy-centric torque-speed points to identify an optimal design solution. The results of multi-physics analysis incorporating electromagnetics, computational fluid dynamics (CFD), and structural analyses are provided, including a study on two different water jacket concepts. A final design is prototyped and initial experimental results are provided.

Actuator saturation is a common nonlinearity. In wave energy conversion, force saturation conveniently limits drivetrain size and cost with minimal impact on energy generation. However, such nonlinear dynamics typically demand numerical simulation, which increases computational cost and diminishes intuition. This paper instead uses describing functions to approximate a force saturation nonlinearity as a linear impedance mismatch. In the frequency domain, the impact of controller impedance mismatch (such as force limit, finite bandwidth, or parameter error) on electrical power production is shown analytically and graphically for a generic nondimensionalized single degree of freedom wave energy converter in regular waves. Results are visualized with Smith charts. Notably, systems with a specific ratio of reactive to real mechanical impedance are least sensitive to force limits, a criteria which conflicts with resonance and bandwidth considerations. The describing function method shows promise to enable future studies such as large-scale design optimization and co-design.

Despite intense efforts, current generation comprehensive Earth system models have, to our knowledge, not been able to simulate the full extent of the atmospheric pCO2 drawdown (as recorded in ice cores) during the Last Glacial Maximum (LGM). Yet, the intermediate complexity model CLIMBER-2 has successfully been used to simulate not only the LGM drawdown but also the transient evolution of CO2 concentrations during entire glacial–interglacial cycles. To better understand why this is the case, we compare the CLIMBER-2 results to pre-industrial and LGM simulations using two related models with increasing complexity, namely, the recently developed intermediate complexity model CLIMBER-X and the state-of-the-art comprehensive Earth system model MPI-ESM as used in the PalMod project, focusing on ocean carbon cycle changes.

Over the past few million years, the Earth descended from the relatively warm and stable climate of the Pliocene into the increasingly dramatic ice age cycles of the Pleistocene. The influences of orbital forcing and atmospheric CO2 on land-based ice sheets have long been considered as the key drivers of the ice ages, but less attention has been paid to their direct influences on the circulation of the deep ocean. Here we provide a broad view on the influences of CO2, orbital forcing and ice sheet size according to a comprehensive Earth system model, by integrating the model to equilibrium under 40 different combinations of the three external forcings. We find that the volume contribution of Antarctic (AABW) vs. North Atlantic (NADW) waters to the deep ocean varies widely among the simulations, and can be predicted from the difference between the surface densities at AABW and NADW deep water formation sites. Minima of both the AABW-NADW density difference and the AABW volume occur near interglacial CO2 (270–400 ppm). At low CO2, abundant formation and northward export of sea ice in the Southern Ocean contributes to very salty and dense Antarctic waters that dominate the global deep ocean. Furthermore, when the Earth is cold, low obliquity (i.e. a reduced tilt of Earth’s rotational axis) enhances the Antarctic water volume by expanding sea ice further. At high CO2, AABW dominance is favoured due to relatively warm subpolar North Atlantic waters, with more dependence on precession. Meanwhile, a large Laurentide ice sheet steers atmospheric circulation as to strengthen the Atlantic Meridional Overturning Circulation, but cools the Southern Ocean remotely, enhancing Antarctic sea ice export and leading to very salty and expanded AABW. Together, these results suggest that a ‘sweet spot’ of low CO2, low obliquity and relatively small ice sheets would have poised the AMOC for interruption, promoting Dansgaard–Oeschger-type abrupt change. The deep ocean temperature and salinity simulated under the most representative ‘glacial’ state agree very well with reconstructions from the Last Glacial Maximum (LGM), which lends confidence in the ability of the model to estimate large-scale changes in water-mass geometry. The model also simulates a circulation-driven increase of preformed radiocarbon reservoir age, which could explain most of the reconstructed LGM-preindustrial ocean radiocarbon change. However, the radiocarbon content of the simulated glacial ocean is still higher than reconstructed for the LGM, and the model does not reproduce reconstructed LGM deep ocean oxygen depletions. These ventilation-related disagreements probably reflect unresolved physical aspects of ventilation and ecosystem processes, but also raise the possibility that the LGM ocean circulation was not in equilibrium. Finally, the simulations display an increased sensitivity of both surface air temperature and AABW volume to orbital forcing under low CO2. We suggest that this enhanced orbital sensitivity contributed to the development of the ice age cycles by amplifying the responses of climate and the carbon cycle to orbital forcing, following a gradual downward trend of CO2.

A twin-lift system offers an efficient and economically attractive solution to the heavy lift problem. A three-dimensional model including the rigid-body dynamics of the two helicopters, the spreader bar, and the load is developed. The mathematical model for helicopter aerodynamics consists of generic, nonlinear, force, and moment models for each helicopter component: main rotor, tail rotor, fuselage, and empennage. The spreader bar and load aerodynamics are also included in the system model. Using the comprehensive system model, a nonlinear controller based on approximate input-output feedback linearization is synthesized. The nonlinear feedback law forms an outer loop for the twin-lift flight control system and is used in conjunction with the existing stability augmentation systems of the helicopters, which constitute the inner loop for the flight control system. The controller performance is illustrated by a closed-loop simulation of a typical twin-lift mission.

Electrification of vessel power and propulsion system has been widely utilized in the shipbuilding industry in recent years. It is expected to be adopted in all marine vessel segments as the increasingly strict marine greenhouse gas (GHG) emissions regulations push the maritime fleet to decrease its reliance on conventional fuels such as marine diesel oil (MDO). With the development of sustainable energy sources and energy storage technologies, such as fuel cells, batteries, and super-capacitors, these renewable energy sources are integrated into the marine electric power system to reduce or even achieve zero-emission operation. A comprehensive shipboard power system model is the crucial foundation for the further research. In this paper, a hybrid shipboard power configuration will be studied and modeled using Matlab/Simulink. The detailed model using average converters’ models for the ship power system will be described. Besides, the simulation results shall be shown and analyzed considering a typical harbor tugboat load profile.