<div>Execution comparison techniques compare multiple executions from the same program or highly similar programs to identify state differences including control flow differences and variable value differences. Execution comparison has been used to debug sequential, concurrent, and regression failures, by reasoning about the causality between execution differences and input differences, thread scheduling differences, and syntactic differences among program versions, respectively. However, execution comparison techniques have several limitations. First, executions may have benign differences, which are not related to the behavior differences that the user can observe. Second, huge storage spaces are required to record two independent executions. Third, the techniques can only compare executions from the same or similar programs.</div><div><br></div><div>In this dissertation, we present an execution comparison technique that (1) removes benign differences, (2) requires less space, and (3) can compare two different programs implementing similar algorithms. Also, we present that the execution comparison technique can be used in identifying and extracting a functional component out of a binary. First, we present a dual execution engine that executes multiple executions at the same time and only introduces the desired differences. Also, the engine compares the executions on-the-fly and stores the differences only. Second, we present a technique to compare two programs written by two different programmers. Especially we will show that this technique can compare the buggy program from a student and the correct from the instructor and can reason about the errors.</div><div><br></div>

<p> A general formulation of the analysis of plane coupled shear walls is presented. The "continuous method" of analysis of coupled shear walls is reformulated in terms of deflection variables. The assumption that midpoints of the connecting beams are points of contraflexure is relaxed so that the resulting theory is applicable to the general case where the lateral loading on the piers can be arbitrarily distributed. The governing equation of the structural system under static loading with the appropriate boundary conditions are given. The effect of asymmetry of the structure is discussed. As an application of the derived theory, the problem of shear walls subjected to differential foundation settlement and rotation is studied. Solutions to deflections and internal stresses, under such conditions, are given. Evaluation of the internal stresses was performed on a practical shear wall structure and the results analysed. Through the use of deflection variables, the formulation is extended into the regime of dynamics. The governing equation of motion with appropriate boundary conditions are given. The free vibration of coupled shear walls is studied and design curves for the fundamental natural frequency are presented. The use of substitutive symmetric systems and its effects on the fundamental frequency of asymmetric systems are examined. Theoretical natural frequencies were verified by dynamic testing on two models to show that the proposed theory is sufficiently accurate to provide information for dynamic analysis in seismic design. / Thesis / Master of Engineering (ME)

<p> An oblique four bar structural model with fixed member ends, being the most general building for space frames, is analysed under free and steady-state vibrations, using discrete mass method. </p> <p> Experimental techniques for measurement of free and steadystate vibrations are described. </p> <p> Experimental results have been compared against analytical ones. </p> / Thesis / Master of Engineering (MEngr)

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This thesis investigates the torsional performance of steel structures with and without rigid diaphragm constraints through numerical simulations and evaluates the appropriateness of relevant design provisions in current seismic design codes. In the first part of the work, six theme structures with different (1) in-plane stiffness of diaphragm, and (2) horizontal configurations of vertical braced frames were designed and their performance evaluated through both nonlinear static and dynamic analyses. Comparisons of the analytical results between the structures with and without rigid diaphragm constraints indicate that the in-plane rigidity of the diaphragms affects the efficiency of in-plane force transfer mechanisms, resulting in different global ductility and strength demands. Rigid diaphragm structures exhibit higher global strengths as well as higher torsional rotation capacity because of the infinite in-plane stiffness of the diaphragm. Semi-rigid diaphragm structures have higher ductility demands due to the finite in-plane diaphragm stiffness. The inclusion of bi-axial forces in the analyses reduces the structural strength and increases the ductility demands on the peripheral frames. The axial forces in the collectors and chords that make up the diaphragm depend on (1) the sequence of brace buckling and (2) vertical configuration of the braced frames. The results show higher axial forces in collectors in the roof diaphragms, and higher chord axial forces in the third floor diaphragms. The shear connections in the beams that make up both the collectors and chords are susceptible to failure due to the significant increment of axial forces in those members. The conventional beam analogy used in design can severely underestimate the axial forces in chords and collectors when the structures step into the inelastic stage. / Ph. D.

There has always been a challenge for designing structures against extreme dynamic loads. Blast loading falls under these loads category and blast resistant design has been gaining more interest during the past decade. Among different types of structures, Reinforced Concrete (RC) structures are usually recommended to be used for blast resistant design. However, the nonlinearities associated with these structures make their accurate analysis complicated. Therefore, simplified techniques have been introduced for nonlinear dynamic analysis of these structures. This study focuses on developing simplified computational strategies for the dynamic analysis of blast loaded RC elements including beams, panels/slabs and columns. For RC beams, the basis for commonly used Single-Degree-of-Freedom (SDOF) models has been outlined. A Multi-Degrees-of-Freedom (MDOF) model which takes into account the concrete nonlinear properties has been developed and the effect of varying the number of degrees-of-freedom (DOF) on response has been studied. Results showed that increasing the number of DOF affects the pressure-impulse (P-I) diagrams, especially in the impulsive regime, as the extent of damage increased. In addition, the model was compared with the experimental data and showed good agreement. For RC panels, a SDOF technique, based on the US Army Technical Manual TMS-1300 instructions, was constructed and results were compared with the ones obtained from explicit Finite Element (FE) analysis. Compared to the FE results, SDOF model yielded conservative predictions for deflection but it usually underestimated the dynamic reactions. A modification for reaction calculation was proposed which resulted in significantly better prediction of the reaction for the impulsive range of loading. Finally, considering the important role of columns in providing the overall stability of the structure, a MDOF model was developed for RC columns and the load carrying capacity of the columns was investigated for different levels of axial load, strain rate and damage. Increasing the strain rate enhanced the column's cross section properties whereas increasing the levels of axial load reduced the cross section curvature and the column deflection capacities. Results also showed that good detailing at the supports can significantly improve the load carrying capacity of RC columns. / Thesis / Master of Applied Science (MASc)

The Explicit Finite Element Method is a powerful tool in nonlinear dynamic finite element analysis. Recent major developments in computational devices, in particular, General Purpose Graphical Processing Units (GPGPU's) now make it possible to increase the performance of the explicit FEM. This dissertation investigates existing explicit finite element method algorithms which are then redesigned for GPU's and implemented. The performance of these algorithms is assessed and a new asynchronous variational integrator spatial decomposition (AVISD) algorithm is developed which is flexible and encompasses all other methods and can be tuned based for a user-defined problem and the performance of the user's computer. The mesh-aware performance of the proposed explicit finite element algorithm is studied and verified by implementation. The current research also introduces the use of a Particle Swarm Optimization method to tune the performance of the proposed algorithm automatically given a finite element mesh and the performance characteristics of a user's computer. For this purpose, a time performance model is developed which depends on the finite element mesh and the machine performance. This time performance model is then used as an objective function to minimize the run-time cost. Also, based on the performance model provided in this research and predictions about the changes in GPU's in the near future, the performance of the AVISD method is predicted for future machines. Finally, suggestions and insights based on these results are proposed to help facilitate future explicit FEM development.

Many challenges in software quality can be tackled with dynamic analysis. However, these techniques are often limited in their efficiency or scalability as they are often applied uniformly to an entire program. In this thesis, we show that dynamic program analysis can be made significantly more efficient and scalable by first performing a static data flow analysis so that the dynamic analysis can be selectively applied only to important parts of the program. We apply this general principle to the design and implementation of two different systems, one for runtime security policy enforcement and the other for software test input generation. For runtime security policy enforcement, we enforce user-defined policies using a dynamic data flow analysis that is more general and flexible than previous systems. Our system uses the user-defined policy to drive a static data flow analysis that identifies and instruments only the statements that may be involved in a security vulnerability, often eliminating the need to track most objects and greatly reducing the overhead. For taint analysis on a set of five server programs, the slowdown is only 0.65%, two orders of magnitude lower than previous taint tracking systems. Our system also has negligible overhead on file disclosure vulnerabilities, a problem that taint tracking cannot handle. For software test case generation, we introduce the idea of targeted testing, which focuses testing effort on select parts of the program instead of treating all program paths equally. Our “Bullseye” system uses a static analysis performed with respect to user-defined “interesting points” to steer the search down certain paths, thereby finding bugs faster. We also introduce a compiler transformation that allows symbolic execution to automatically perform boundary condition testing, revealing bugs that could be missed even if the correct path is tested. For our set of 9 benchmarks, Bullseye finds bugs an average of 2.5× faster than a conventional depth-first search and finds numerous bugs that DFS could not. In addition, our automated boundary condition testing transformation allows both Bullseye and depth-first search to find numerous bugs that they could not find before, even when all paths were explored. / text

Points-to analysis is a static program analysis that computes reference informationfor a given input program. It serves as input to many client applicationsin optimizing compilers and software engineering tools. Unfortunately, the Gold Standard – i.e., the exact reference information for a given program– is impossible to compute automatically for all but trivial cases, and thus, little can been said about the accuracy of points-to analysis. This thesis aims at paving the way towards a Gold Standard for points-to analysis. For this, we discuss theoretical implications and practical challenges that occur when comparing results obtained by different points-to analyses. We also show ways to improve points-to analysis by different means, e.g., combining different analysis implementations, and a novel approach to path sensitivity. We support our theories with a number of experiments.

In recent years, power demands around the world and particularly in North America increased rapidly due to increase in customer’s demand, while the development in transmission system is rather slow. This stresses the present transmission system and voltage stability becomes an important issue in this regard. Pattern recognition in conjunction with voltage stability analysis could be an effective tool to solve this problem In this thesis, a methodology to detect the voltage stability ahead of time is presented. Dynamic simulation software PSS/E is used to simulate voltage stable and unstable cases, these cases are used to train and test the pattern recognition algorithms. Statistical and algorithmic pattern recognition methods are used. The proposed method is tested on IEEE 39 bus system. Finally, the pattern recognition models to predict the voltage stability of the system are developed.