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They originate during the propagation of radiation in space.

PHASE II: Based on Phase I effort the small business will continue to address and develop the PFM modeling capability in a systematic way to move from a qualitative visualization to a quantitative assessment. Show how the PFM model can predict 3D crack nucleation, propagation, branching and interaction under complex load spectrum. Test and validate the model by closely following crack propagation test data set for complex loading.

Pecularities of stevia () pro­pagation by seed.

DESCRIPTION: Sonar performance models are used to assess the use of a particular sonar system for specific tasks including submarine detection, mine hunting, or swimmer detection. Feeding the performance models are acoustic models which are numerical solutions to a wave equation based on knowledge of the underlying physics and physical conditions in the prevailing environment. For active sonar systems, Transmission Loss (TL) and Reverberation Level (RL) are key sonar equation parameters derived from the acoustic fields predicted by models and used in the sonar equation to assess performance. For the majority of the existing propagation codes used in the Navy, whether based on ray theory, normal modes, wavenumber integration, or the parabolic equation, the starting point is the assumption of a horizontally stratified waveguide. Likewise, excepting volumetric contributions which are primarily biologic scattering, reverberation models are predominantly based on acoustic scattering from rough horizontal surfaces such as the seabed or sea surface. Consequently, most existing acoustic propagation models are concerned with predicting forward propagating and scattered acoustic energy. While three-dimensional acoustic models exist, or are being developed, they are based on refraction of acoustic energy owing to bathymetric changes and or internal waves or fronts that do not scatter energy strongly in the back-propagating direction. The existing models are adequate for applications in the deep ocean or open littorals, but sonar operators are increasingly being asked to perform tasks including navigation or detection in more confined waterways such as rivers or ports. However, models are generally not available for predicting the acoustic field in such highly geometrically constrained and dynamic environments. These environments can be characterized by vertical or near vertical boundaries such as piers and breakwaters and have large tidally driven depth variations over short time periods. They also may be populated with large scattering objects such as deep draft vessels and mooring dolphins that impact the acoustic field.

Arama sonuçarı "Self-Propagating Combustion Synthesis"

Theyare variants of qualitative matter and energy that propagate in space with thevelocity of light without mixing.

The challenge is to determine how multiple sources of uncertainties are propagated in a model developed specifically for an AM process, such as in reference [2], and then how to quantify the uncertainty of the resulting material properties and microstructure to predict desired performance in probabilistic terms. Keeping this challenge in mind, the topic requires: a comprehensive approach [3] to quantify the uncertainties of material and process model parameters; recommendations on minimizing both material and process uncertainties in production; and suggestions for acceptance metrics/criteria and tolerances for decision making.

DESCRIPTION: Additive manufacturing (AM) has the potential to revolutionize part design and acquisition for the Navy. Further development is needed before AM is accepted for the production of structural components and current efforts to advance AM often overlook its foundation: the material. For many Navy applications, this material is typically a metallic powder used in a powder bed AM system. Current state-of-the-art metal powders, in particular stainless steel powders, have been found to be incapable of producing parts that meet the performance requirements for Naval applications without extensive post processing. Research has shown that powder characteristics like particle size, shape, and distribution; packing density; conductivity; and chemical composition have significant impact on a part’s microstructure which contributes to producing unsatisfactory parts. These properties have also been found to vary widely from supplier to supplier due to different powder processing techniques and self-established specifications. As such, many AM machine manufacturers impose limits on the powders they allow to be used in their machines forcing their consumers to purchase only the manufacturer’s specified powder or risk voiding their warranty.

Full text of "NEW" - Internet Archive

KEYWORDS: underwater acoustics, propagation, scattering, communications, sonar, 3D acoustic modeling, sonar simulation, performance estimation

OBJECTIVE: Produce a 3D Acoustic model for predicting three-dimensional acoustic field parameters in environments characterized by complex geometries with variable boundary and propagation conditions. Assess the new model for use in existing, or newly developed, sonar performance estimation tools to address the optimal placement of sensors in constrained environments.

A modular and scalable cooling system technology that will largely replace the legacy water-to-air cooling systems and forced air-cooling systems is needed so thermal loading can be handled at the source versus in a centralized location that requires complex, expensive, non-reconfigurable distribution systems. Reductions in piping and ducting distribution systems reduces acquisition cost and system weight. Modular cooling will also allow for additional sensors, tactical displays, and consoles to be incorporated into the AEGIS Integrated Combat System because advanced thermal management technology enables a smaller footprint for. An approach that is localized on or near the heat generation source without significant direct shipboard support systems is desired. This system must pass military standards for shock and vibration (Ref 3 and 4). The advanced cooling system should be self-contained and scalable for the anticipated heat loads. Utilization of shipboard support systems such as water should be minimized or eliminated. Scalability to accommodate larger, currently customized, processing cabinets greater than the 5 kW heat load associated with the MCEs is preferred. This would be an attractive enabler to a flexible infrastructure where larger, standardized mission processing packages may be needed for larger and more powerful shipboard radar systems. Legacy radar rooms currently generate as much as 25 kW of heat and the new radar system will be increasing the heat load to these radar rooms to approximately 100 kW or more. Since combat systems in general account for approximately 80% of the total space-cooling load, an advanced thermal management technology could potentially provide space that is more available for the MCEs. The computer room would not require extensive ventilation ducting. The shipboard HVAC systems and associated fan rooms near combat system spaces can be significantly downsized. The shipboard chilled water system could similarly be downsized and would be used for condenser water supply and HVAC cooling coils to accommodate the Hull, Mechanical, & Electrical (HM&E) services within the combat system spaces.

partition of unity based cohesive zone formulation for propagating cracks in porous ..
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Electronic Journals Alert (user copro, News) - Google …

PHASE III DUAL USE APPLICATIONS: Integrate the developed fatigue crack initiation and propagation analysis package into processes at the FRC’s, and potentially work in conjunction with the original equipment manufacturers for analysis of repairs and new designs. Methods and techniques developed can be folded into commercial software package for broad use in a wide variety of industrial applications in estimating the life of a variety of safety critical structures.

self-assembled, closely packed silicon ..

Phase field model development will be required in order to link spatial and temporal evolution of complex crack patterns to the external applied load by utilizing finite element and iso-geometric analysis (IGA) discretization methods. Starting with an initial 2D analysis, the PFM model has to describe the complex phenomena of 3D crack evolution at a microscale as well as the final fracture at the macroscale. The proposed PFM model may include an appropriate plasticity model to study load interactions occurring in complicated loading situations such as variable amplitude loading. Finite element based numerical implementations of the PFM crack propagation under dynamic loading is desirable. Furthermore, the application of PFM to dynamic ductile fracture needs to be further explored, addressing the limitations and assumptions and enhancements as needed.

Synthesis and thermoelectric ..

As such, computational models are desired for fatigue crack nucleation and propagation that alleviates the complexity of re-meshing and can track the crack tip in complex microstructures, while at the same time can be efficiently implemented in an efficient computational framework. The phase field model technique in conjunction with isogeometric analysis that utilizes the geometric model, can provide the solution which does not require any criteria for crack initiation and propagation under random spectrum loading including environmental effects.

Method and structure for fabricating solar cells ..

We seek a capability to model the three-dimensional acoustic field, including propagation, scattering, and reverberation in complex environments. Approaches should include, but are not limited to, predicting complex pressure from a point source, with a minimum frequency of 1 kHz, placed arbitrarily within a representative harbor environment, e.g. Mayport Basin, Florida. Solutions should provide ¼ wavelength resolution for area dimensions greater than six million square feet for a typical depth of 50 feet. The environment may be open to the sea, but must include at least one vertical boundary representative of a quay wall, a breakwater, and a blockage representing a deep draft vessel with draft of 60%-90% of the channel depth. A broadband model is preferred, but a narrowband solution is acceptable if accompanied by a conceptual plan for development into a full broadband solution. Computational efficiency and speed is not a priority, but will be given consideration. Amongst other things, it is expected this capability will form the basis for existing or new sonar performance estimation tools. In particular, the model combined with an appropriate decision aid could address the optimal placement of sensors in complicated environments for tasks including establishing underwater communication links or harbor surveillance.

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