A Carrier Force for the Indian Navy

Which country added an aircraft carrier, a nuclear submarine, a squadron of long-range maritime patrol aircraft and two missile corvettes to its inventory in 1987-88? There are no prizes for the right answer, but many in the West are perplexed by India\u27s growing maritime power and are overcome by a sense of the preposterous that a third world country should begin to assume what has traditionally been the white man\u27s burden

Imaging of buried utilities by ultra wideband sensory systems

Third-party damage to the buried infrastructure like natural gas pipelines, water distribution pipelines and fiber optic cables are estimated at $10 billion annually across the US. Also, the needed investment in upgrading our water and wastewater infrastructure over the next 20 years is estimated by Environmental Protection Agency (EPA) at$400 billion, however, non-destructive condition assessment technologies capable of providing quantifiable data regarding the structural integrity of our buried assets in a cost-effective manner are lacking. Both of these areas were recently identified several U.S. federal agencies as \u27critical national need\u27. In this research ultra wideband (UWB) time-domain radar technology was adopted in the development of sensory systems for the imaging of buried utilities, with focus on two key applications. The first was the development of a sensory system for damage avoidance of buried pipes and conduits during excavations. A sensory system which can be accommodated within common excavator buckets was designed, fabricated and subjected to laboratory and full-scale testing. The sensor is located at the cutting edge (teeth), detecting the presence of buried utilities ahead of the cutting teeth. That information can be used to alert the operator in real-time, thus avoiding damage to the buried utility. The second application focused on a sensory system that is capable of detecting structural defects within the wall of buried structures as well as voids in the soil-envelope encasing the structure. This ultra wideband sensory system is designed to be mounted on the robotic transporter that travels within the pipeline while collecting data around the entire circumference. The proposed approach was validated via 3-D numerical simulation as well as full-scale experimental testing

High Power, Continuous-wave Supercontinuum Generation in Highly Nonlinear Fibers Pumped with High Order, Cascaded Raman Fiber Amplifiers

A novel method for efficient generation of high power, equalized continuous-wave supercontinuum source in an all conventional silica fiber architecture is demonstrated. Highly nonlinear fiber (HNLF) is pumped in its anomalous dispersion region using a novel, high power, L-band laser. The L-band laser encompasses a 6th order cascaded Raman amplifier which is pumped with a high power Ytterbium doped fiber laser and amplifies a low-power, tunable L-band seed source. The supercontinuum generated 35W of power with ~40% efficiency. The Supercontinuum spectrum was measured to have a high degree of flatness of better than 5 dB over 400 nm of bandwidth (1.3 - 1.7 micron, limited by spectrum analyzer range) and a power spectral density in this region of >50 mW/nm. The extent of the SC spectrum is estimated to be upto 2 micronComment: 6 pages, 5 figure

Multiscale computational framework for simulation of cellular solids

Natural and man-made cellular solids have been used in a variety of engineering applications. Despite their widespread use, the behavior of such materials is not well understood because of their high heterogeneity and complex microstructure. A multiscale computational framework is formulated to study the behavior of structures and components made from cellular solids over a wide range of spatial and temporal scales. The framework consists of two levels of models, a continuum level and a microstructural level. The continuum-level models utilize finite element (FE) and mesh-free (MF) methods in conjunction with spatial domain decomposition and temporal multitime-stepping to capture different local- and global-scale behavior. At the microstructural level, the framework relies on a realistic representation of the foam microstructure and homogenization techniques to couple it with the continuum-level models. This study focuses on addressing the issues related to the formulation and implementation of this multiscale framework. These issues include formulating a variationally consistent coupling of FE and MF methods in space and time at the continuum level, and formulating an efficient micromechanical constitutive model for cellular solids to simulate a wide range of material behavior. Numerical characteristics of the computational framework are studied using several benchmark problems

Accurate reduced-order models for structures and materials undergoing large 3D deformations and rotations

Structures and materials subject to extreme loads often exhibit large deformations and large rotations in 3D. Modeling of such phenomena is very challenging and has conventionally been done using detailed models of the structure or the material-system using continuum and/or structural finite elements. Using detailed continuum finite element models for large structures can be computationally infeasible and modeling of large deformations and rotations in 3D using structural finite elements (beam/plate/shell) requires complex numerical procedures to achieve good convergence. In this study, we present reduced-order models that utilize combinations of translational and rotational springs in 3D to model complex material and structural behavior. The kinematics of these models is described entirely using nodal coordinates as opposed to nodal rotational degrees of freedom so as to simplify the numerical implementation. The formulation enables us to express the response of every element in terms of not only its own coordinates, but also in terms of the coordinates of all its neighboring elements. The novel aspect of this study is that this approach, although being simple to implement, is able to account for all the dominant modes of response for a large class of problems involving large 3D deformations and rotations. We validate this approach using several benchmark tests and further use it to study two different types of problems. One set of problems involves the study of large frame structures subject to earthquakes and the modeling of their collapse. The other problem is the study of material-systems composed of cellular solids under extreme loads. Using several numerical examples, we show that, within certain limitations, this approach is able to capture the essential characteristics of the response of structures and materials undergoing large 3D deformations and rotations. We also compare its performance to that of conventional methods both in terms of accuracy and computational cost to show that these reduced-order models provide good results at minimal computational cost

Modeling of internal contact in cellular solids and reticulated structures for simulation of collapse, crushing and densification

Cellular solids, metal foams, and reticulated structures are used for a variety of applications, such as light-weight construction, impact absorption, acoustics, heat transfer, etc. Some of these applications involve very large deformations of the foam material that can cause the internal voids in the microstructure of these materials to collapse leading to contact and densification. Similar behavior is also observed in the collapse of light-weight reticulated structures. In order to study such processes, one needs a detailed model for capturing internal contact within the microstructure to evaluate its effect on global properties of the structure. In this study, we develop a simplified model for simulation of open-cell foams and reticulated structures using one-dimensional elasto-plastic elements to represent individual ligaments in the microstructure of the foam or elements in a reticulated structure. In order to model internal contact during collapse and crushing of cellular solids, the computational model was enhanced with the capability to detect and resolve contact between elements using an augmented Lagrangian method in an -energy-based approach. The formulation for capturing contact was modified to allow for smooth -transitions -between various contact pairs. Numerical issues with the detections, resolution and smoothing of contact to -facilitate convergence will be presented. This approach was used to study several benchmark problems and its -performance was evaluated by comparing the solutions with existing studies both in terms of errors and computational cost

On the convergence of dual-Schur partitioned time integrators

Partitioned time-integrators have often been used in computational science and engineering for solving coupled multidomain problems and even for single-domain problems with multiple spatial and/or temporal scales. Partitioning based on dual-Schur domain decomposition allows single-domain problems in solid and structural dynamics to be decomposed into nonoverlapping subdomains that can be solved independently using different time integration schemes and then coupled back together for greater computational efficiency. The coupling is achieved by using Lagrange multipliers to enforce continuity of the solution across the interface between the subdomains. It has been documented, through many numerical examples, that this coupling method preserves the accuracy and stability properties of the underlying time-integrators used within the individual subdomains. In this research, for the first time, we conduct a rigorous error analysis for such dual-Schur coupling methods and quantify the local and global truncation errors to show that partitioned time integrators preserve the theoretical rates of convergence within each individual subdomain and the global problem domain. We focus on a multitime-step method which allows one to couple subdomains that are solved with different time steps and time integrators from the Newmark family of schemes. We show that the second-order convergence rate enjoyed by the Newmark method for single domain problems is also preserved for partitioned systems with any time-step ratio between the two subdomains. Several numerical examples are shown to support this fact. This result lends a strong theoretical basis to the results observed only numerically heretofore in the literature and establishes an a priori error measure of error for dual-Schur partitioned numerical time integrators

Real-time-hybrid-simulation of Multi-degree-of-freedom Systems with Multiple Time Steps

Computational simulation and physical experiments are both widely used in testing the response of a structure under earthquake loadings, but physical experiments can be expensive for large problems and numerical may result in the loss of important structural behavior caused by a large amount of assumptions. Real-time hybrid simulation (RTHS) is a combination of these two approaches, which uses both a numerical and physical substructures that interact in real time to simulate structural behavior. The numerical and physical substructures are connected using a transfer system that enforces compatibility between them. The physical substructure needs to be run at a very high frequency (usually 1024 Hz) to ensure stability. This necessitates the numerical substructure be also computed at a correspondingly small time-step (1 millisecond). This research develops a method to speed up the numerical computation and enables the use of larger, more realistic numerical models within RTHS. The numerical substructure is split into multiple parts each solved at a different time-step, then coupled back together to obtain the global RTHS response. The portion closest to the experimental substructure is solved at a smaller time-step that meets the 1-millisecond limit, and the remaining portion is solved at a larger time-step. Multi-time-step RTHS is compared with single-time-step RTHS, in terms of the numerical error and computational time. This approach is shown to preserve accuracy of the computed result while meeting real-time constraint for RTHS computation. The current approach enhances our ability to study important structural dynamics with advanced numerical models