The research projects in this area are sponsored by:. The main objective of the research is to attain agile and stable control of distributed tactical operations with unmanned airborne, land-borne, and ocean-borne vehicles.
The operating environment is uncertain and rapidly changing…The goal is to develop: i theoretical techniques and tools to provide decision support for Command, Control, and Communications C3 operations; ii a flexible modeling framework to support management of the dynamics in a C3 environment; iii new concepts and architectures to spawn revolution in C3 technologies for both military and commercial applications; and iv a versatile testbed and prototype components for validation of C3 concepts and architectures.
This research project is sponsored by:. The main objective of the research is to achieve high performance of operating machinery with increased reliability, availability, component durability, and maintainability. The goal of Life Extending Control is to ensure structural integrity of mechanical components by minimizing the material damage e. This requires interdisciplinary efforts involving Systems Sciences and Mechanics of Materials for augmentation of the current system-theoretic and artificial intelligence AI techniques for synthesis of decision and control laws with governing equations and inequality constraints that would model the properties of the materials for the purpose of damage representation and failure prognosis.
The major challenge in these research projects is to characterize the damage generation process in a continuous-time setting, and then utilize this information for synthesizing algorithms of robust control, diagnostics, and risk assessment. Slosh can also cause fluid to be vented instead of the gas, which is not only wasteful, but dangerous; venting fluid can impart unexpected thrust to the vehicle and even cause the vents to freeze closed, potentially resulting in catastrophic tank over-pressurization.
Slosh during transfer can affect the thermal state of the propellant and ullage, which may cause performance issues during tanking and detanking operations.
In addition to the thermodynamic effects, slosh may have fluid dynamic effects on transfer and vice versa. Thanks to recent advances in computational capabilities, accurate numerical modeling of slosh is now possible. Computational Fluid Dynamics CFD tools are critical to predicting slosh dynamics and finding ways to mitigate the above and other concerns. CFD programs are very complex and require extensive experimental validation before the results can be trusted.
These CFD programs have been validated by experiments on the ground using water and oil and found to be quite accurate. However, in the absence of gravity, the physics change drastically and liquids behave differently.
These programs have not been validated for cryogenic fluids in microgravity. I am proposing to modify various slosh experimental platforms for use with cryogenic liquid nitrogen LN2 to gather data relevant to benchmarking and expanding CFD simulation tools to characterize slosh dynamics of cryogenic propellants in 1g, micro- and zero-gravity storage, transfer, and management applications.
The slosh experimental platforms that I will modify for use with LN2 include ground-based, sounding rocket-based, and zero-g aircraft-based test apparatuses. Slosh-management devices and fluid transfer research will be conducted along with the pure slosh experiments. These apparatuses, once modified for cryogenic LN2, will then inherently or with slight further modifications be able to study boil-off, stratification, ullage collapse, and those phenomenas interactions with slosh.
Avenues for unconstrained, 6 DOF, zero-g on-orbit slosh tests will also be explored. Include more reviewers who have a diverse knowledge of the systems involved. In addition to looking at the project from different angles, the diversity of background will result in a keener awareness of the impact of changes to all organizations. Documentation is also very important to use this analysis technique. So, when reviewing documents, use many and different types of resources systems and software engineers, hardware engineers, system operations personnel, etc.
The obvious benefit is a better product as a result of critique from numerous angles. SFMEA's should be used in all of the following areas, though you should focus on the safety-critical aspects. Figure 1 shows a subsystem, indicating how each piece interacts with the others. Logic and and ors is not included in this introductory diagram. The end items are the pressure sensor and temperature sensor.
The diagram shows how the failures propagate up through the system, leading to a hazardous event. There are no right or wrong rules, but you need to know ahead of time what will be considered a failure, what kinds of failures will be included levels of fault-tolerance, and other information.
Some sample ground rules are: Some words bold for emphasis. You may not have sufficient information in some areas, such as the speed at which data is expected at an interface port of the system. If the assumption is incorrect, when it is examined it will be found to be false and the correct information will be supplied sometimes loudly.
This examination will occur when you describe what you believe to be the normal operation of the system or how the system handles faults to the other project members. Each one is important. Once written, it serves as a focus to be further explored and exploded.
Look at the interactions between components, look for assumptions, limitations, and inconsistencies. Figure 2 shows the process of recognizing your assumptions, documenting them, finding out what the reality is, and clarifying them for future reference.
A narrow perspective can prevent you from seeing interactions between components, particularly between software and hardware. Communicate with those of differing backgrounds and expertise. In performing an FMEA, defining whatever is being worked on is the first order of business. Depending on where the project is in the development life-cycle requirements, design, implementation , documents will exist as resources for performing the SFMEA.
If the documentation is lacking, you will have to do some detective work. Often there is a collection of semi-formal paperwork on the requirements or design produced by the software team but not written into a formal requirement or design document. If little is on paper, you will have to interview the developers and project management, hardware engineers, systems people, etc.
Break a project down into its subsystems. Break a subsystem down into its components. This process begins with a high-level project diagram which consists of blocks of systems, functions, or objects. Each block in the system will then have its own diagram, showing the components that make up the block subsystem. Not every subsystem will need to be detailed to its lowest level. Deciding what subsystems need further breakdown comes with experience. If in doubt, speak with the project members most familiar with the subsystem or component.
During the requirements phase, the lowest-level components may be functions or problem domains. CSCIs, units, objects, instances, etc. You need to understand the system, how it works, and how the pieces relate to each other. Producing this diagram helps you, the analyst, put the information together. They can provide feedback on the validity of your understanding of the system.
There will probably be hardware items on this list. It is important to identify functions that need protection. A failure may be the compromise of one of these functions by a lower-level software unit. There are also interfaces to be dealt with. There are more problems identified with interfaces, according to some researchers than any other aspect of software development. Interfaces are software-to-software function calls, interprocess communication, etc. These are included in the system FMEA.
Interfaces also loosely include transitions between states or modes of operation. As you look at the system, you will find that you need to make more assumptions. Write them down. When all else fails, and there is no place to get useful information, sometimes a guess is in order. Again, write it down and go discuss it with others. If you are a software person, go talk with safety and systems. If you are a safety specialist, talk with systems, software, and reliability experts.
The normal operations of the system include it performing as designed, being able to handle known problem areas, and its fault tolerance and failure response if designed into the system.
Hopefully, the system was designed to correctly and safely handle all anticipated problems. This step identifies how the software responds to the failures. In order to understand the operation of a system, it may be necessary to work and communicate with systems engineering if you are a software engineer. Systems engineering must also communicate with software engineering, and both must talk with safety and Software Assurance SA.
The normal operation of the software as part of the system or function is described in this part of the SFMEA. Go back to the block diagrams you created earlier. Starting at the lowest level, look at a component and determine the effect of that component failing, in one of its failure modes, on the components in the level above it.
However, with the information of the surrounding microstructure from DCT, these heavily misoriented regions were often linked to grain boundaries. The regions of high misorientation near grain boundaries indicate deformation processes such as lattice rotation and dislocation pile up. The NF-HEDM reconstruction used in the simulation without the twin instantiated was not seeded with the orientation of the twin.
The CP-FFT model enforced the macroscopic strain rate along the loading direction defined during sample cyclic loading, no other boundary conditions were prescribed. The model was run for a single cycle where it was determined that the computation time of further cycling was not necessary as a good match was found between the micromechanical fields from DFXM and CP-FFT, which were not expected to evolve qualitatively due to the form of the constitutive equations used Due to the Fourier transform formulation of the model, the volume had to have periodic boundary conditions.
To ensure continuity to transmit load, the microstructure was mirrored along the loading direction; the artificial mirrored boundary did not affect the results of this study, as multiple grains lay between the artificial boundary and our GOI Along the other directions, a gas phase of zero stiffness was added to simulate the free surfaces.
The governing equations Supplementary Note 6 and simulation routine are described further by Lebensohn et al. The Voce hardening and crystal plasticity parameters were fit by calibrating the macroscopic stress-strain curve of the model to the experimentally captured curve. The necessary values of the stiffness tensor were taken from Cerrone et al. The datasets generated and then analyzed during the current study are available upon reasonable request to the corresponding author. Boettner, R.
On the formation of fatigue cracks at twin boundaries. Thompson, A. The influence of grain and twin boundaries in fatigue cracking. Acta Met. Miao, J. Acta Mater. Sangid, M. The role of grain boundaries on fatigue crack initiation—an energy approach. James, E. The fracture of metals under repeated alternations of stress. A, Contain. A Math. Character , — ADS Google Scholar. Mughrabi, H. Li, L. Higher fatigue cracking resistance of twin boundaries than grain boundaries in Cu bicrystals.
Abuzaid, W. Slip transfer and plastic strain accumulation across grain boundaries in Hastelloy X. Solids 60 , — Energetics of residual dislocations associated with slip—twin and slip—GBs interactions. A , 21—30 Stinville, J. High resolution mapping of strain localization near twin boundaries in a nickel-based superalloy. Llanes, L. The role of annealing twin boundaries in the cyclic deformation of f. A , 21—27 Article Google Scholar.
A physically based fatigue model for prediction of crack initiation from persistent slip bands in polycrystals. Kacher, J. Dislocation interactions with grain boundaries.
Solid State Mater. Wilkinson, A. High-resolution electron backscatter diffraction: An emerging tool for studying local deformation. Strain Anal. The role of slip transfer at grain boundaries in the propagation of microstructurally short fatigue cracks in Ni-based superalloys.
Naragani, D. Investigation of fatigue crack initiation from a non-metallic inclusion via high energy x-ray diffraction microscopy. Poulsen, H. X-ray diffraction microscopy based on refractive optics. Simons, H. Dark-field X-ray microscopy for multiscale structural characterization. Ahl, S. Ultra-low-angle boundary networks within recrystallizing grains. Mavrikakis, N.
Bucsek, A. Sub-surface measurements of the austenite microstructure in response to martensitic phase transformation. Levine, L. Disordered long-range internal stresses in deformed copper and the mechanisms underlying plastic deformation.
Li, R. Unraveling submicron-scale mechanical heterogeneity by three-dimensional X-ray microdiffraction. Natl Acad. Hektor, J. Long term evolution of microstructure and stress around tin whiskers investigated using scanning Laue microdiffraction. Gabb, T. Shade, P. Fiducial marker application method for position alignment of in situ multimodal X-ray experiments and reconstructions.
Kiener, D. FIB damage of Cu and possible consequences for miniaturized mechanical tests. A , — Ludwig, W. New opportunities for 3D materials science of polycrystalline materials at the micrometre lengthscale by combined use of X-ray diffraction and X-ray imaging.
A , 69—76 Moulinec, H.
0コメント