Sensitivity analysis of reliability for structure-based software via simulation

Computer simulation is an appealing approach for the reliability analysis of structure-based software systems as it can accommodate complexities present in realistic systems. When the system is complex, a screening experiment to quickly identify important factors (components) can significantly improve efficiency of the analysis. The challenge is to guarantee the correctness of the screening results with stochastic simulation responses. Control Sequential Bifurcation (CSB) is a new method for factors screening using simulation experiments, when only main effects models are considered. By grouping factors, CSB can identify the importance of factors while reducing the simulation effort. With appropriate hypothesis testing procedures embedded, CSB procedure can simultaneously control the Type I error probability and the power. The existing work has focused on normally distributed output responses. This thesis extends the existing CSB procedure by embedding Meeker\u27s conditional sequential test to deal with binary responses and guarantee the desired error control for factor screening results. The effectiveness of the extended factor screening procedure is demonstrated with the application on a software system

Cross-layer system reliability assessment framework for hardware faults

System reliability estimation during early design phases facilitates informed decisions for the integration of effective protection mechanisms against different classes of hardware faults. When not all system abstraction layers (technology, circuit, microarchitecture, software) are factored in such an estimation model, the delivered reliability reports must be excessively pessimistic and thus lead to unacceptably expensive, over-designed systems. We propose a scalable, cross-layer methodology and supporting suite of tools for accurate but fast estimations of computing systems reliability. The backbone of the methodology is a component-based Bayesian model, which effectively calculates system reliability based on the masking probabilities of individual hardware and software components considering their complex interactions. Our detailed experimental evaluation for different technologies, microarchitectures, and benchmarks demonstrates that the proposed model delivers very accurate reliability estimations (FIT rates) compared to statistically significant but slow fault injection campaigns at the microarchitecture level.Peer ReviewedPostprint (author's final draft

Model-based dependability analysis : state-of-the-art, challenges and future outlook

Abstract: Over the past two decades, the study of model-based dependability analysis has gathered significant research interest. Different approaches have been developed to automate and address various limitations of classical dependability techniques to contend with the increasing complexity and challenges of modern safety-critical system. Two leading paradigms have emerged, one which constructs predictive system failure models from component failure models compositionally using the topology of the system. The other utilizes design models - typically state automata - to explore system behaviour through fault injection. This paper reviews a number of prominent techniques under these two paradigms, and provides an insight into their working mechanism, applicability, strengths and challenges, as well as recent developments within these fields. We also discuss the emerging trends on integrated approaches and advanced analysis capabilities. Lastly, we outline the future outlook for model-based dependability analysis

Durability Analysis of Concrete Bridge Deck Exposed to the Chloride Ions Using Direct Optimized Probabilistic Calculation

Durability of reinforced concrete structures is a deeply discussed problem recently. Concrete structures in the external environment are very often affected by chloride ions from de-icing salt or sea water. Chloride ions penetrate through the concrete cover layer of the reinforcement and can cause eventually the corrosion of the steel. However, when estimating the durability of the structure, it is not sometimes possible to express the parameters by constant values; therefore, the probabilistic methods come in handy. Then, the variability of inputs and outputs can be expressed by histograms. Two probabilistic approaches were applied in this task – Monte Carlo simulation with Simulation-Based Reliability Assessment method, which is widely used for such type of problems, and the Direct Optimized Probabilistic Calculation, which is still relatively new type of approach. The result is a comparison of mentioned methods in terms of accuracy on the model of one-dimensional chloride penetration with time independent diffusion coefficient by using the Fick’s Second Law of Diffusion

Fault Tolerant Adaptive Parallel and Distributed Simulation through Functional Replication

This paper presents FT-GAIA, a software-based fault-tolerant parallel and distributed simulation middleware. FT-GAIA has being designed to reliably handle Parallel And Distributed Simulation (PADS) models, which are needed to properly simulate and analyze complex systems arising in any kind of scientific or engineering field. PADS takes advantage of multiple execution units run in multicore processors, cluster of workstations or HPC systems. However, large computing systems, such as HPC systems that include hundreds of thousands of computing nodes, have to handle frequent failures of some components. To cope with this issue, FT-GAIA transparently replicates simulation entities and distributes them on multiple execution nodes. This allows the simulation to tolerate crash-failures of computing nodes. Moreover, FT-GAIA offers some protection against Byzantine failures, since interaction messages among the simulated entities are replicated as well, so that the receiving entity can identify and discard corrupted messages. Results from an analytical model and from an experimental evaluation show that FT-GAIA provides a high degree of fault tolerance, at the cost of a moderate increase in the computational load of the execution units.Comment: arXiv admin note: substantial text overlap with arXiv:1606.0731

Application of numerical modelling to the comprehensive analysis of slope stability

Paper deals with the comprehensive methodology for the numerical simulation of potentially unstable slopes combining engineering geological, hydrological, hydrogeological and geotechnical computational model for the assessment of slope stability. Engineering geological model based on available survey data characterizes the rock environment using individual quasi-homogenous units. Model is defined on the basis of documented lithostratigraphic units in exploration probes and field relief documented by advanced methods, including satellite radar interferometry and laser surface scanning. On the basis of engineering geological model, the hydrological model using MIKE SHE software (Finite Difference Method) was performed. Hydrological model includes simulation of surface runoff, evapotranspiration and flow in unsaturated near-surface zone. The model was calibrated on the basis of available field data. Outputs from this model were used as input initial conditions of the following hydrogeological model. Software FEFLOW based on the Finite Element Method was subsequently used to the creation of hydrogeological model focused on the water flow and distribution of pore pressures of groundwater in individual quasi-homogeneous units in saturated zone. The infiltration condition determined by the hydrological model is considered and a flow model with variable saturation is applied. Finally, the geotechnical stability model of slope following the engineering geological, hydrological and hydrogeological models was performed. The occurrence of plastic and failure zones (assuming elastic-perfectly plastic Mohr-Coulomb constitutive model) inside the slope was simulated by using software MIDAS GTS NX based on the Finite Element Method. Stability factor SSRF (Shear Strength Reduction Factor) is evaluated based on the Shear Strength Reduction Method) as the ratio of actual shear strength and minimum shear strength required to maintain stability. Paper deals also with the comparison of stability factor of natural slope obtained from 3D and 2D numerical model. Generally, in the case of natural slope the condition of plane strain is not fulfil, 2D model is not realistic and 3D model is needed, especially in case of concave morphology of slope

Towards Identifying and closing Gaps in Assurance of autonomous Road vehicleS - a collection of Technical Notes Part 1

This report provides an introduction and overview of the Technical Topic Notes (TTNs) produced in the Towards Identifying and closing Gaps in Assurance of autonomous Road vehicleS (Tigars) project. These notes aim to support the development and evaluation of autonomous vehicles. Part 1 addresses: Assurance-overview and issues, Resilience and Safety Requirements, Open Systems Perspective and Formal Verification and Static Analysis of ML Systems. Part 2: Simulation and Dynamic Testing, Defence in Depth and Diversity, Security-Informed Safety Analysis, Standards and Guidelines