Numerical and experimental analysis of initial water impact of an air-dropped REMUS AUV

Submitted in partial fulfillment of the requirements of the degree of Master of Science at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 2005The initial water impact of a free-falling object is primarily related to the fluid forces on the wetted surface of the object. The shape-dependent added-mass coefficients express the fluid forces integrated over the body, and thus physically represent the additional inertia of water accelerated with fie body. The field of hydrodynamic impact has been primarily concerned with estimating the added-mass coefficients of various types of bodies for different water impact types, such as seaplane landings, torpedo drops, and ship slamming. In this study, a numerical model has been constructed to estimate the hydrodynamic impact loads of a REMUS dropped in free-fall from a helicopter in a low hover. Developed by von Alt and associates at Woods Hole Oceanographic Institution, the REMUS (Remote Environmental Monitoring Units) is a small, man-portable, torpedo shaped Autonomous Underwater Vehicle (AUV) that is normally operated from small boats for a variety of scientific, industrial, and military applications. Finite-element method software and computer aided drafting tools were used to create a simplified model of REMUS without fins, propeller, or transducers. This axisyrnmetric REMUS model was cut by a flat free surface at various pitch angles and submergence values, and a panel mesh of the wetted surface of the vehicle was created using an automatic mesh generator. Surface boundary conditions are enforced for the free surface by reflecting the body panels using the method of images. Each panel mesh was evaluated for its added-mass characteristics using a source collocation panel method developed by Dr. Yonghwan Kim, formerly of the Vortical Flow Research Laboratory (VFRL) at the Massachusetts Institute of Technology Experimental impact tests were conducted with a specially-instrumented test vehicle to verify the initial impact accelerations

Development of a hardware-in-the-loop analysis framework for advanced ITS applications

As Intelligent Transportation Systems (ITS) become more prevalent, there is a need for a system capable of the rigorous evaluation of new ITS strategies for a wide variety of applications. Pre-deployment testing and fine-tuning of the system, performance evaluation, and alternatives analysis are all potential benefits that could be gained through the evaluation of ITS. Simulation, an increasingly popular tool for transportation analysis, would seem an ideal solution to this problem as it allows for the consideration of many scenarios that may be improbable or impossible to observe in the field. Also, simulation provides a framework that allows for the application of rigorous analysis techniques to the output data, providing an accurate and statistically significant conclusion. The difficulty is that many ITS strategies are difficult or impossible to implement in a simulated environment. The rapid nature of technology development and the complicated nature of many ITS solutions are difficult to emulate in simulation models. Furthermore, the emulation of a particular ITS solution is not guaranteed to provide the same result that the physical system would, were it subject to the same inputs. This study seeks to establish a framework for the analysis of advanced ITS applications through the use of Hardware-in-the-Loop Simulation (HILS), which provides a procedure for interfacing simulation models with real-world hardware to conduct analysis. This solution provides the benefits of both advanced ITS evaluation and simulation for powerful and accurate analysis. A framework is established that includes all the steps of the modeling process including construction, validation, calibration, and output analysis. This ensures that the process surrounding the HILS implementation is valid so that the results of the evaluation are accurate and defendable. Finally, a case study of the application of the developed framework to the evaluation, a real-world implementation of an advanced ITS application (SCATS in this case) is considered. The effectiveness of the framework in creating and evaluating a corridor using a simulation model wed to real-world hardware is shown. The results of the analysis show the power of this method when correctly applied and demonstrate where further analysis could expand upon the proposed procedure.M.S.Committee Chair: Dr. Michael Hunter; Committee Member: Dr. Jiawen Yang; Committee Member: Dr. Jorge Laval; Committee Member: Dr. Michael Rodger

Structural studies of main group metal carboxylates and dithiocarbamates

The work contained in this thesis describes the crystal structures of a number of tin(IV) and tellurium(IV) carboxylates and dithiocarbamates. The results show the regularity at which these types of compounds form secondary bonds (weak interactions), and the effect of the lone pair of tellurium(IV) on the geometries formed. The area has been studied through the determination of the following crystal structures: i) monocarboxylates: Ph3SnOCOCH2Cl, Ph3SnOCOCHCh, Ph3SnOCOCCh.MeOH. Ph3SnOCOCCh and Ph3TeOCOCCh. ii) dicarboxulates : Ph2Sn(OCOCH3)2, Ph2Sn(OCOCH2CI)2 and Ph2Te(OCOCCI3)2 iii) dithiocarbamates : Ph2Te(S2CNEt2)2, Ph2Te(S2CN(Et)(Ph))2 and Ph2Te(S2CNPh2)2 In addition to these, six hydrolysis products of Ph3SnOCOCCh are reponed. These com- pounds show the varied results that are obtained from the facile dearylation of the organotin com- pound by a strong organic acid in the presence of water. The following structures are reported: Ph2 Sn(OH)(OCOCCh), {[Pb2Sn(OCOCCh)hOh (two isomers), [(PbSn))(Oh(OCOCCh)sh, [PhSn(O)(OCOCCh)]6 and [(Ph 2 Sn)2(OH)(OCOCCh)3h

Restructuring Failed Financial Firms in Bankruptcy: Selling Lehman\u27s Derivatives Portfolio

Lehman Brothers\u27 failure and bankruptcy deepened the 2008 financial crisis whose negative effect on the United States\u27 economy lasted for several years. Yet, while Congress reformed financial regulation in hopes of avoiding another crisis, bankruptcy rules such as those that governed Lehman\u27s failure, have persisted unchanged. When Lehman failed, it lost considerable further value when its contracting counterparties terminated their financial contracts with Lehman. These broad terminations degraded Lehman\u27s overall value to its creditors beyond the immediate losses that caused its downfall. Lehman\u27s financial portfolio was thought to be running a paper profit of over $20 billion when it filed, and is said to have lost up to$75 billion as a result of the post-filing liquidation by Lehman\u27s counterparties of their deals with Lehman. How such a vast value loss can occur and how bankruptcy can ameliorate the problem are the subjects of this Article

Large-effect flowering time mutations reveal conditionally adaptive paths through fitness landscapes in Arabidopsis thaliana.

Contrary to previous assumptions that most mutations are deleterious, there is increasing evidence for persistence of large-effect mutations in natural populations. A possible explanation for these observations is that mutant phenotypes and fitness may depend upon the specific environmental conditions to which a mutant is exposed. Here, we tested this hypothesis by growing large-effect flowering time mutants of Arabidopsis thaliana in multiple field sites and seasons to quantify their fitness effects in realistic natural conditions. By constructing environment-specific fitness landscapes based on flowering time and branching architecture, we observed that a subset of mutations increased fitness, but only in specific environments. These mutations increased fitness via different paths: through shifting flowering time, branching, or both. Branching was under stronger selection, but flowering time was more genetically variable, pointing to the importance of indirect selection on mutations through their pleiotropic effects on multiple phenotypes. Finally, mutations in hub genes with greater connectedness in their regulatory networks had greater effects on both phenotypes and fitness. Together, these findings indicate that large-effect mutations may persist in populations because they influence traits that are adaptive only under specific environmental conditions. Understanding their evolutionary dynamics therefore requires measuring their effects in multiple natural environments

Final Vermont Greenhouse Gas Inventory and Reference Case Projections, 1990-2030

This report estimates the anthropogenic greenhouse gas emissions and carbon sinks for Vermont from 1990-2030