Cyclic exchange neighborhood search technique for the K-means clustering problem

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2004.Includes bibliographical references (p. 151-152).Cyclic Exchange is an application of the cyclic transfers neighborhood search technique for the k-means clustering problem. Neighbors of a feasible solution are obtained by moving points between clusters in a cycle. This method attempts to improve local minima obtained by the well-known Lloyd's algorithm. Although the results did not establish usefulness of Cyclic Exchange, our experiments reveal some insights on the k-means clustering and Lloyd's algorithm. While Lloyd's algorithm finds the best local optimum within a thousand iterations for most datasets, it repeatedly finds better local minima after several thousand iterations for some other datasets. For the latter case, Cyclic Exchange also finds better solutions than Lloyd's algorihtm. Although we are unable to identify the features that lead Cyclic Exchange to perform better, our results verify the robustness of Lloyd's algorithm in most datasets.by Nattavude Thirathon.M.Eng

Roll damping prediction of a free floating barge

PhD ThesisTraditionally the problem of calculating the motion responses of a ship in a seaway has been formulated in frequency domain in terms of linear potential theory. By using the potential flow method in roll calculation, the fluid is assumed to be ideal, irrotational and viscous effects are neglected. Experiments have shown that the roll amplitude responses of rectangular bodies floating in beam waves are overestimated when calculated by potential flow method. This is largely attributable viscous effects [1]. For this reason seakeeping calculation methods introduce empirical factors to account for viscous effects. On the other hand, much of the nonlinear forces and moments experienced by ship in a seaway may be due to the viscous effects leading to flow separation and generation of vortices [2]. One approach to modelling flow separation and vortex shedding is to solve the Navier-Stokes equations. However, for moving bodies in the presence of a free surface at high Reynolds numbers (which implies the use of fine computational meshes) the software and hardware resources required, supposing the problem is even viable, are often so large as to be prohibitive. Another approach is to use methods based on vortex dynamics for modelling separated flows about bluff bodies. These methods were developed as a means of modelling high Reynolds number flows in which the vorticity is confined to small sub-domains of otherwise irrotational flows [2]. This work concerns development of a purely theoretical model for estimating the roll response of vessels that takes these effects into account. The objective of this thesis is to develop a model including viscous effects that can be used in seakeeping and survivability calculations. The idea being proposed is to match a local discrete vortex based method to a global model of a body floating with six degrees of freedom. A software is developed that can be bolted on to conventional seakeeping software so that the motions of sharp edged bodies floating in waves can be calculated without recourse to empirical methods. The theoretical approach to predict roll damping for a three-dimensional barge shaped floating vessel in the frequency domain is described here. The approach consists of matching a simple discrete vortex method (DVM) describing local separated flow, to an inviscid three-dimensional seakeeping code. Model tests have been carried out to validate the theoretical model and the associated add-on software. As demonstrated in this report, there is a good agreement between the model test RAO and the damped RAO indicating the theoretical method provides a good estimate of the viscous damping of the vessel due to vortex shedding from its edges. Although viscous damping in sway and heave motions is not as significant as for the roll for a barge the same methodology can be used to calculate viscous damping for both sway and heave as well. As tangential relative fluid velocities are used in this method the same final relative velocities can be used to calculate skin friction damping component. In this study skin friction damping is considered to be negligible and is ignored in the final calculated damped RAO

Ultra-lightweight nanorelief networks : photopatterned microframes

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2007.Includes bibliographical references.Lightweight nano-network structures in polymers have been fabricated and investigated for their mechanical properties. Fabrication techniques via holographic interference lithography and phase mask lithography were implemented for periodic and quasiperiodic bicontinuous polymer-air structures on the submicrometer length scale. For 3D quasiperiodically nanostructured materials, quasicrystalline phase mask lithography utilizing 2D quasiperiodic phase mask was successfully employed. 2D hexagonal arrays of air cylinders in SU8 polymer films and 3D four-beam connected (3- R3m ) and octagonal quasicrystalline SU8 films were fabricated and analyzed in this thesis. For investigating the mechanical properties of various nano-network structures, three different methods of mechanical characterization were applied. Atomic force microscopy with its nanometer scale resolution was adopted to conduct force measurements to probe local elastic properties of the sample. Templated by the light intensity distribution from three-beam interference, the spatial distribution of elastic modulus was observed in the pattern of 2D hexagonal air-cylinder and a uniform SU8 polymer film by AFM nanoindentation. A second method for mechanical characterization, the microtensile tester enabled us to evaluate a symmetry effect on the elastic and plastic properties of the polymer fibers and thin films. Large plastic deformation of 200nm-diameter struts comprising the 3D periodic and quasiperiodic microframes of the normal brittle bulk polymer was discovered and is an example of length-scale dependent mechanical behavior. Crack propagation and energy absorption were guided along the symmetry directions in the periodic structures. However, there was found no preferred direction of crack propagation in quasicrystalline nanostructures due to the absence of translational symmetry.(cont.) The third method, Brillouin light scattering (BLS) allowed estimation of the phonon properties in the structured films and the associated mechanical properties. The BLS measurements also confirmed the isotropy of modulus with the symmetry of the structures. The length scale dependence, the effect of structural symmetry and the processing dependence of the mechanical behavior of the various nanostructures in SU8 polymer films were observed. The hundred-nanometer length scale of 3D nanostructures induces plastic deformation of struts under an applied force, which makes the film tougher and energy absorbing. The symmetry of the structured films determines the preferred direction of crack propagation and following fracture behavior. Octagonal-patterned (8mm) quasicrystalline films via quasicrystalline phase mask lithography (QCPML) exhibit higher specific toughness and fracture strength with the unit mass than uniform solid films.by Taeyi Choi.Ph.D

Data-driven fault detection using trending analysis

The objective of this research is to develop data-driven fault detection methods which do not rely on mathematical models yet are capable of detecting process malfunctions. Instead of using mathematical models for comparing performances, the methods developed rely on extensive collection of data to establish classification schemes that detect faults in new data. The research develops two different trending approaches. One uses the normal data to define a one-class classifier. The second approach uses a data mining technique, e.g. support vector machine (SVM) to define multi class classifiers. Each classifier is trained on a set of example objects. The one-class classification assumes that only information of one of the classes, namely the normal class, is available. The boundary between the two classes, normal and faulty, is estimated from data of the normal class only. The research assumes that the convex hull of the normal data can be used to define a boundary separating normal and faulty data. The multi class classifier is implemented through several binary classifiers. It is assumed that data from two classes are available and the decision boundary is supported from both sides by example objects. In order to detect significant trends in the data the research implements a non-uniform quantization technique, based on Lloyd’s algorithm and defines a special subsequence-based kernel. The effect of the subsequence length is examined through computer simulations and theoretical analysis. The test bed used to collect data and implement the fault detection is a six degrees of freedom, rigid body model of a B747 100/200 and only faults in the actuators are considered. In order to thoroughly test the efficiency of the approach, the test use only sensor data that does not include manipulated variables. Even with this handicap the approach is effective with the average of 79.5% correct detection and 16.7% missed alarm and 3.9% false alarms for six different faults

Breaking symmetries in ordered materials : spin polarized light transport in magnetized noncentrosymmetric 1D photonic crystals, and photonic gaps and fabrication of quasiperiodic structured materials from interference lithography

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2006."February 2006."Includes bibliographical references.Effects of breaking various symmetries on optical properties in ordered materials have been studied. Photonic crystals lacking space-inversion and time-reversal symmetries were shown to display nonreciprocal dispersion relations, and to exhibit a remarkable set of symmetry-related properties. Even in 1D, these materials are found to display indirect photonic band gaps, backward wave propagating modes (antiparallel phase and group velocities) which enable negative refraction at the air-crystal interface, ability to allow bending light with perpendicular magnetic fields, unidirectional superprism effects, etc. By calculating the complex photonic band structure, we show that the gap modes differ fundamentally from the commonly assumed evanescent modes with purely imaginary wave vectors - solely due to symmetry, we show that the gaps of nonreciprocal photonic crystals have complex wave vectors with both imaginary components and non-zero, frequency dependent real components. This basic finding is further studied in the context of tunneling dynamics, by considering the problem of tunneling time for nonreciprocal photonic band gap barriers (the tunneling wave packet has an energy in the middle of the gap).(cont.) It was found that the classical Hartman effect (independence of tunneling time on barrier length, beyond a certain length), previously implied as universal, is forbidden solely due to symmetry. Instead of a classical zero group delay, we find that tunneling wave packets with opposite spins display non-zero group delays, with opposite signs. Due to analogies based on symmetry, these results directly impact the problem of spin-polarized electronic tunneling in magnetized noncentrosymmetric semiconductors, such as GaMnAs or carbon nanotubes with applied axial magnetic fields. An interference lithography based fabrication process was developed to produce 2D and 3D quasiperiodically structured materials, which have long-range order but break translational symmetry. Multiple exposure interference lithography was used to fabricate 2D quasicrystals with feature sizes as small as 100nm. Replica molding was used to fabricate transparent and conformable 2D quasiperiodic phase masks, which subsequently allowed the fabrication of 3D structured materials with quasiperiodicity by coherent diffraction lithography. The effect of the higher point group symmetries of 2D quasicrystals on photonic band gap formation (TM polarized only) was studied by finite difference time domain calculations, and it was found that increasing the rotational symmetry does not always lead to wider gaps.by Ion Bita.Ph.D

Design of robust slow-speed ships for sustainable operation

Phd ThesisMulti-objective optimisation that considers the energy efficiency and economic success is an important aspect of ship design and operation. Both the hydrodynamic and economic performance characteristics need to be addressed in the early stages of the design, and secured during the life span of a ship. Because of the conflicting nature of these two objectives, there are various trade-offs at stake in the goal for making ships more efficient and greener to comply with IMO regulations while reducing the building and operating costs and increasing the profitability at the same time for all stakeholders especially owners and operators. In attempt to reduce the amount of greenhouse gas emissions from ships, and hence to achieve a lower EEDI value, this research approaches the problem of improving the energy efficiency of ships. That is achieved by optimising the hull design over a speed range through parametric modification to reduce resistance and required power, and also through adopting slow steaming concept. Moreover, the research aims to determine the best practice to reduce the annual cost of running a ship and to increase the annual revenue as well as to make the ship a more profitable investment over her life span. The profit per tonne.mile and the net present value NPV are estimated in the economic analysis to be used as indicators to compare alternative designs for different routes and market conditions scenarios. To achieve this aim, the main operational and economic aspects such as the fluctuations in the fright rates and fuel prices in the shipping market are covered in the economic analysis. In addition, the acquiring price and salvage value are included in order to obtain solid comparisons. An optimisation framework using a VBA macro code has been developed based on the concept of Pareto optimality to assess decision making, and to determine robust designs as well as operational profiles based on results from the hydrodynamic model, environmental impact model, and the economic model. The optimisation process is carried out for a Panamax tanker case study using 5 parameters and a set of constraints for the hull parameters and speed. The outcome from the optimisation framework is a set of Pareto optimal solutions where weight factors are appointed to give the flexibility when addressing the importance of each individual function. The solutions are presented graphically to form what is known as Pareto front which determines the design space and the trade-offs between the different competing objective ii functions. This optimisation framework could assist decision making where it is possible to choose a robust design or designs that offer a near-optimum performance regardless any fluctuations in the market and or the operation profile, and eliminate any significant sub-optimal design

Interaction of stress and magnetic properties in patterned copper-nickel-copper thin films

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2007.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Includes bibliographical references (p. 135-137).In recent years, the epitaxial Cu/Ni/Cu thin film system has been extensively studied, due to its wide range of perpendicular magnetization. It has proved to be a model system to explore the interactions of strain, surface energies and magnetic properties. For that reason, is also an ideal system to explore the effects of patterning. It is expected that the miniaturization of patterned magnetic devices will be accompanied by a transition from polycrystalline to epitaxial films. This transition will require a detailed theoretical understanding of the interaction of strain and magnetic properties in patterned epitaxial magnetic thin films. The Cu/Ni/Cu film system is used in this work to explore a triaxial model for an orthorhombic symmetry of strain. By patterning the Cu/Ni into nanolines and measuring the resulting magnetic anisotropy, the validity of the model has been tested. It has been shown that upon patterning certain thicknesses of nickel into nanolines, the easy axis of magnetization shifts from out of the film plane to in-plane, transverse to the line direction, an observation at odds with the direction of magnetization predicted by shape considerations alone. This transition is explained by the dominant magnetoelastic energy for the Cu/Ni/Cu nanoline system.(cont.) The resulting anisotropy values are consistent with strain relief values predicted by finite element modeling. In addition, the low temperature properties of the Cu/Ni/Cu epitaxial film system have been explored. The variation of the overall magnetic anisotropy as a function of temperature is found to be proportional to the cube of the reduced magnetization. In addition, the easy axis of magnetization for certain thicknesses of nickel has been found to shift from in-plane to perpendicular with the reduction of temperature.by Elizabeth Friend.Ph.D

The assessment of mooring line damping for offshore structures

With increasing water depth of oil and gas exploration, greater importance has been attached to the damping force from mooring systems. The effect is significantly important to slow drift motion of the floating structure, and it is also coupled with its motions. Coupled analysis is thus preferred to be applied to estimate the floating structure motions and to calculate the mooring system response, especially for offshore structures in deep-water.;In this study, the aim is to achieve a better understanding of mooring line induced damping estimation. Drag forces normal to the mooring line due to the motion of the mooring line through the water, are the main source of hydrodynamic damping of the mooring line. A method of energy dissipation based on the mooring line dynamic response obtained by Orcaflex is developed. The validation is established through two types of mooring lines in shallow water and deep water.;The present approach shows a good agreement with the published results, but with two exceptions. One is for the mooring line oscillated by a very slow LF motion in shallow water, when the hydrodynamic damping is very small. Another one is for the wire mooring line oscillated by WF motion in deep water, the result shows significant discrepancy with that from the quasi-static method.;Then a non-dimensional analysis is completed, due to the strong complexity of the mooring line induced damping. The effects of the factors can be divided into three groups: first, the effects from pretension and scope are related to the geometry changes of the mooring line; second, the oscillation, current velocity and drag coefficient make contributions to the drag forces of mooring line directly; and the last, the effects of stiffness and seabed friction which, it was found, can be neglected.;In order to experimentally investigate the chain behaviour moving in water, a series model tests for the damping characteristics of a single chain line is implemented through oscillation tests of various parameters. The drag coefficient ( C D ) variations with different Reynold ( Rn ) and KC numbers are investigated. The drag coefficients in this study range from 1.5 to 4.0, which is case-dependent, because both Reynold ( Rn ) and KC number affect them.;With the increase of KC number, the drag coefficient shows a decrease with exceptions occurring in low KC cases. In addition, it is shown that the chain segments near the fairlead and touch down area are most sensitive to the drag coefficient, which is consistent with the velocity distribution along the mooring line.;Finally, the validation is established by comparing the results of experimental tests and numerical simulations. Based on the assessment of drag coefficient from the scaled experimental investigation, numerical simulations of estimated drag coefficient are carried out within Orcaflex. A good agreement is achieved between the numerical calculations and experimental measurements, which illustrates that the present method can be applied for mooring line damping estimation. Meanwhile, the effects of the amplitude and frequency of the oscillation are studied.With increasing water depth of oil and gas exploration, greater importance has been attached to the damping force from mooring systems. The effect is significantly important to slow drift motion of the floating structure, and it is also coupled with its motions. Coupled analysis is thus preferred to be applied to estimate the floating structure motions and to calculate the mooring system response, especially for offshore structures in deep-water.;In this study, the aim is to achieve a better understanding of mooring line induced damping estimation. Drag forces normal to the mooring line due to the motion of the mooring line through the water, are the main source of hydrodynamic damping of the mooring line. A method of energy dissipation based on the mooring line dynamic response obtained by Orcaflex is developed. The validation is established through two types of mooring lines in shallow water and deep water.;The present approach shows a good agreement with the published results, but with two exceptions. One is for the mooring line oscillated by a very slow LF motion in shallow water, when the hydrodynamic damping is very small. Another one is for the wire mooring line oscillated by WF motion in deep water, the result shows significant discrepancy with that from the quasi-static method.;Then a non-dimensional analysis is completed, due to the strong complexity of the mooring line induced damping. The effects of the factors can be divided into three groups: first, the effects from pretension and scope are related to the geometry changes of the mooring line; second, the oscillation, current velocity and drag coefficient make contributions to the drag forces of mooring line directly; and the last, the effects of stiffness and seabed friction which, it was found, can be neglected.;In order to experimentally investigate the chain behaviour moving in water, a series model tests for the damping characteristics of a single chain line is implemented through oscillation tests of various parameters. The drag coefficient ( C D ) variations with different Reynold ( Rn ) and KC numbers are investigated. The drag coefficients in this study range from 1.5 to 4.0, which is case-dependent, because both Reynold ( Rn ) and KC number affect them.;With the increase of KC number, the drag coefficient shows a decrease with exceptions occurring in low KC cases. In addition, it is shown that the chain segments near the fairlead and touch down area are most sensitive to the drag coefficient, which is consistent with the velocity distribution along the mooring line.;Finally, the validation is established by comparing the results of experimental tests and numerical simulations. Based on the assessment of drag coefficient from the scaled experimental investigation, numerical simulations of estimated drag coefficient are carried out within Orcaflex. A good agreement is achieved between the numerical calculations and experimental measurements, which illustrates that the present method can be applied for mooring line damping estimation. Meanwhile, the effects of the amplitude and frequency of the oscillation are studied

A New Measure For Clustering Model Selection

A new method for determining the number of k-means clusters in a given data set is presented. The algorithm is developed from a theoretical perspective and then its implementation is examined and compared to existing solutions