Accepted Manuscripts

Todd M. Hetrick, Suzanne A. Smyth, Russell A. Ogle and Juan Ramirez
ASME J. Risk Uncertainty Part B   doi: 10.1115/1.4037866
This paper explores an infrequently encountered hazard associated with liquid fuel tanks on gasoline-powered equipment using unvented fuel tanks. Depending on the location of fuel reserve tanks, waste heat from the engine or other vehicle systems can warm the fuel during operation. In the event that the fuel tank is not vented and if the fuel is sufficiently heated, the liquid fuel may become superheated and pose a splash hazard if the fuel cap is suddenly removed. Accident reports often describe the ejection of liquid as a geyser. This geyser is a transient, two-phase flow of flashing liquid. This could create a fire hazard and result in splashing flammable liquid onto any bystanders. Many existing fuel tank systems are vented to ambient through a vented tank cap. It has been empirically determined that the hazard can be prevented by limiting fuel tank pressure to 1.5 psig. However, if the cap does not vent at an adequate rate, pressure in the tank can rise and the fuel can become superheated. This phenomenon is explored here to facilitate a better understanding of how the hazard is created. The nature of the hazard is explained using thermodynamic concepts. The differences in behavior between a closed system and an open system are discussed and illustrated through experimental results obtained from two sources: experiments with externally heated fuel containers and operation of a gasoline-powered riding lawn mower. The role of the vented fuel cap in preventing the geyser phenomenon is demonstrated.
TOPICS: Engines, Fuel storage, Gasoline, Risk, Fuels, Hazards, Pressure, Superheating, Vents, Waste heat, Containers, Transients (Dynamics), Flammable liquids, Flashing, Accidents, Fire, Two-phase flow, Vehicles
Hidemasa Yamano, Hiroyuki Nishino, Kenichi Kurisaka and Takahiro Yamamoto
ASME J. Risk Uncertainty Part B   doi: 10.1115/1.4037877
The objective of this paper is to develop a probabilistic risk assessment (PRA) methodology against volcanic eruption for decay heat removal function of sodium-cooled fast reactors. In the volcanic PRA methodology development, only the effect of volcanic tephra (pulverized magma) is taken into account because there is a great distance between a plant site assumed in this study and volcanoes. The volcanic tephra (ash) could potentially clog air filters of air-intakes that are essential for the decay heat removal. The degree of filter clogging can be calculated by atmospheric concentration of ash and tephra fallout duration and also suction flow rate of each component. This study evaluated a volcanic hazard using a combination of tephra fragment size, layer thickness and duration. In this paper, functional failure probability of each component is defined as a failure probability of filter replacement obtained by using a grace period to filter failure. Finally, based on an event tree, a core damage frequency has been estimated by multiplying discrete hazard frequencies by conditional decay heat removal failure probabilities. A dominant sequence has been identified as well. In addition, sensitivity analyses have investigated the effects of a tephra arrival reduction factor and pre-filter covering.
TOPICS: Sodium fast reactors, Probabilistic risk assessment, Risk, Failure, Filters, Probability, Heat, Hazards, Damage, Sensitivity analysis, Suction, Air filters, Flow (Dynamics)
Christophe Journeau, Viviane Bouyer, Nathalie Cassiaut-Louis, Pascal Fouquart, Pascal Piluso, Gérard Ducros, Stéphane Gossé, Christine Guéneau, Andrea Quaini, Beatrix Fluhrer, Alexei Miassoedov, Juri Stuckert, Martin Steinbrueck, S Bechta, Pavel Kudinov, Wei Min Ma, Bal Raj Sehgal, Zoltan Hozer, Attila Guba, Dario Manara, David P. Bottomley, Manfred Fischer, Gert Langrock, Holger Schmidt, Monika Kiselova and Jiri Zdarek
ASME J. Risk Uncertainty Part B   doi: 10.1115/1.4037878
SAFEST (Severe Accident Facilities for European Safety Targets) is a European project networking the European experimental laboratories focused on the investigation of a nuclear power plant (NPP) severe accident (SA) with reactor core melting and formation of hazardous material system known as corium. The main objective of the project is to establish coordinated activities, enabling the development of a common vision and severe accident research roadmaps for the next years, and of the management structure to achieve these goals. In this frame, a European roadmap on severe accident experimental research has been developed to define research challenges to contribute to further reinforcement of Gen II and III NPP safety. The roadmap takes into account different SA phenomena and issues identified and prioritized in the analyses of severe accidents at commercial NPPs and in the results of the recentEuropean stress tests carried out after the Fukushima accident. Nineteen relevant issues related to reactor core meltdown accidents have been selected during these efforts. These issues have been compared to a survey of the European SA research experimental facilities and corium analysis laboratories. Finally, the coherence between European infrastructures and R&D needs has been assessed and a table linking issues and infrastructures has been derived. The comparison shows certain important lacks in SA research infrastructures in Europe, especially in the domains of core late reflooding impact on source term, reactor pressure vessel failure and molten core release modes, spent fuel pool accidents, as well as the need for a large scale experimental facility operating with up to 500 kg of chemically prototypic corium melt.
TOPICS: Safety, Hazardous substances, Stress, Melting, Accidents, Failure, Nuclear power stations, Spent nuclear fuels, Reactor vessels, Risk, Fukushima nuclear disaster, Japan, 2011
Niki Lymperea, Andreas Nikoglou and Evangelos Hinis
ASME J. Risk Uncertainty Part B   doi: 10.1115/1.4037879
This study presents an assessment of the RELAP5/MOD3.3 using the experimental work upon the rewetting mechanism of bottom flooding of a vertical annular water flow inside a channel enclosing concentrically a heated rod. The experiments have been carried out in the experimental rig 1 of the Nuclear Engineering Department of National Technical University of Athens (NTUA-NED-ER1) inside which the dry out and the rewetting process of a hot vertical rod can be simulated. Experiments have been conducted at atmospheric conditions with liquid coolant flow-rate within the range of 0.008 and 0.050 kg·s-1 and two levels of subcooling 25 and 50 K. The initial average surface temperature of the rod for each experiment was set at approximately 823 K. The predicted rod surface temperatures during rewetting of the RELAP5/MOD3.3 calculations were compared against the experimental values. The results presented in this study show that RELAP5/MOD3.3 provides temperature estimations of the reflooding mechanism within acceptable marginal error. However, larger deviations between predicted and experimental values have been observed when subcooled water was used instead of saturated one.
TOPICS: Flow (Dynamics), Temperature, Nuclear engineering, Coolants, Errors, Floods, Subcooling, Water, Risk
Keith Friedman, Khanh Bui and John Hutchinson
ASME J. Risk Uncertainty Part B   doi: 10.1115/1.4037725
Vehicle door latch performance testing presently utilizes uniaxial quasi-static loading conditions. Current technology enables sophisticated virtual testing of a broad range of systems. Door latch failures have been observed in vehicles under a variety of conditions. Typically these conditions involve multi-axis loading conditions. The loading conditions presented during rollovers on passenger vehicle side door latches have not been published. Rollover crash test results, rollover crashes, and physical FMVSS 206 latch testing results are reviewed. The creation and validation of a passenger vehicle door latch model is described. The multi-axis loading conditions observed in virtual rollover testing at the latch location are characterized and applied to the virtual testing of a latch in the secondary latch position. The results are then compared with crash test and real world rollover results for the same latch. The results indicate that a door latch which meets the secondary latch position requirements may fail at loads substantially below the FMVSS 206 uniaxial failure loads. In the side impact mode, risks associated with door handle designs and the potential for inertial release can be considered prior to manufacturing with virtual testing. An example case showing the effects of material and spring selection illustrate the potential issues that can be detected in advance of manufacturing. The findings suggest the need for reexamining the relevance of existing door latch testing practices in light of the prevalence of rollover impacts and other impact conditions in today's vehicle fleet environment.
TOPICS: Doors, Testing, Failure, Risk, Vehicles, Manufacturing, Stress, Springs, Testing performance
Timothy G Zhang, Kimberly Thompson and Sikhanda Satapathy
ASME J. Risk Uncertainty Part B   doi: 10.1115/1.4037647
This study focuses on the effect of skull fracture on the load transfer to the head for low-velocity frontal impact of the head against a rigid wall or being impacted by a heavy projectile. The skull was modeled as a cortical-trabecular-cortical layered structure in order to better capture the skull deformation and consequent failure. The skull components were modeled with an elastoplastic with failure material model. Different methods were explored to model the material response after failure, such as eroding element technique, conversion to fluid, and conversion to SPH (smoothed particle hydrodynamics) particles. The load transfer to the head was observed to decrease with skull fracture.
TOPICS: Stress, Skull fractures, Risk, Failure, Particulate matter, Projectiles, Hydrodynamics, Deformation, Fluids
Michael Todinov
ASME J. Risk Uncertainty Part B   doi: 10.1115/1.4037519
The paper treats the important problem related to risk controlled by the simultaneous presence of critical events, randomly appearing on a time interval and shows that the expected time fraction of simultaneously present events is insensitive to the distribution of events durations. In addition the paper shows that the probability of simultaneous presence of critical events is practically insensitive to the distribution of the events durations. These counter-intuitive results provides the powerful opportunity to evaluate the risk of overlapping of random events through the mean duration times of the events only, without requiring the distributions of the events durations, their variance or the mixing proportions of the individual distributions, in the case of duration times represented by distribution mixtures. A closed-form expression for the expected fraction of unsatisfied demand for random events following a homogeneous Poisson process in a time interval is introduced for the first time. In addition, a closed-form expression related to the expected time fraction of unsatisfied demand, for a fixed number of consumers initiating random demands with a specified probability, is also introduced for the first time. The concepts stochastic separation of random events based on the probability of overlapping and the average overlapped fraction are also introduced. Methods for providing stochastic separation and optimal stochastic separation achieving balance between risk and cost of risk reduction are presented.
TOPICS: Reliability, Risk, Probability, Separation (Technology), Risk reduction
Stefan Erschen, Fabian Duddeck, Matthias Gerdts and Markus Zimmermann
ASME J. Risk Uncertainty Part B   doi: 10.1115/1.4037485
In the early development phase of complex technical systems, uncertainties caused by unknown design restrictions must be considered. In order to avoid premature design decisions, sets of good designs are sought rather than one (possibly optimal) design that may later turn out to be infeasible. A set of good designs is called a solution space and serves as target region for design variables, including those that quantify properties of components or subsystems. Algorithms that approximate solution spaces as high-dimensional boxes are available, in which edges represent permissible intervals for single design variables. The box size is maximized to provide large target regions and facilitate design work. As a result of geometrical mismatch, however, boxes typically capture only a small portion of the complete solution space. To reduce this loss of solution space, this paper presents a new approach that optimizes a set of permissible two-dimensional regions for pairs of design variables, so- called 2D-spaces. Each 2D-space is confined by polygons. The Cartesian product of all 2D-spaces forms the solution space for all design variables, wherein all designs are good. An optimization problem is formulated that maximizes the size of the solution space, and is solved using an interior-point algorithm. The approach is applicable to arbitrary systems with performance measures that can be expressed or approximated as linear function of their design variables. Its effectiveness is demonstrated in a design problem of vehicle chassis development.
TOPICS: Space, Complex systems, Risk, Design, Algorithms, Optimization, Vehicles, Uncertainty
Arvind Keprate and R.M. Chandima Ratnayake
ASME J. Risk Uncertainty Part B   doi: 10.1115/1.4037353
Vibration induced fatigue (VIF) failure of topside piping is one of the most common causes of the hydrocarbon release on offshore oil and gas platforms operating in the North Sea region. An effective inspection plan for the identification of fatigue critical piping locations has the potential to minimize the hydrocarbon release. One of the primary challenges in preparation of inspection program for offshore piping is to identify the fatigue critical piping locations. At present, the three-staged risk assessment process (RAP) given in the EI guidelines is used by inspection engineers to determine the likelihood of failure (LoF) of process piping due to VIF. Since the RAP is afflicted by certain drawbacks, this manuscript presents an alternative risk assessment approach (RAA), to RAP for identification and prioritization of fatigue critical piping locations. The proposed RAA consists of two stages. The first stage involves a qualitative risk assessment using Fuzzy-AHP methodology to identify fatigue critical systems (and the most dominant excitation mechanism) and is briefly discussed in the manuscript. The fatigue critical system identified during stage 1 of RAA undergoes further assessment in the second stage of the RAA. This stage employs a fuzzy-logic method to determine the LoF of the mainline piping. The outcome of the proposed RAA is the categorization of mainline piping, into high, medium or low risk grouping. The mainline piping in the high-risk category is thereby prioritized for inspection. An illustrative case study demonstrating the usability of the proposed RAA is presented.
TOPICS: Underwater pipelines, Fatigue, Vibration, Risk assessment, Risk, Pipes, Inspection, Failure, Engineers, Fuzzy logic, Ocean engineering, Performance, Excitation, North Sea, Process piping
Dengji Zhou, Tingting Wei, Huisheng Zhang, Shixi Ma and Fang Wei
ASME J. Risk Uncertainty Part B   doi: 10.1115/1.4037328
An abnormal operating effect can be caused by different faults, and a fault can cause different abnormal effects. An information fusion model, with hybrid-type fusion frame, is built in this paper, so as to solve this problem. This model consists of data layer, feature layer and decision layer, based on an improved D-S evidence algorithm. After the data preprocessing based on event reasoning in data layer and feature layer, the information will be fused based on the new algorithm in decision layer. Application of this information fusion model in fault diagnosis is beneficial in two aspects, diagnostic applicability and diagnostic accuracy. Additionally, this model can overcome the uncertainty of information and equipment to increase diagnostic accuracy. Two case studies are implemented by this information fusion model to evaluate it. In the first case, fault probabilities calculated by different methods are adopted as inputs to diagnose a fault, which is quite different to be detected based on the information from a single analytical system. The second case is about sensor fault diagnosis. Fault signals are planted into the measured parameters for the diagnostic system, to test the ability to consider the uncertainty of measured parameters. The case study result shows that the model can identify the fault more effectively and accurately. Meanwhile, it has good expansibility, which may be used in more fields.
TOPICS: Sensors, Algorithms, Fault diagnosis, Probability, Signals, Uncertainty, Risk
Hossein Salimi, Saeed Kiad and Mohammad Pourgol-Mohammad
ASME J. Risk Uncertainty Part B   doi: 10.1115/1.4037219
In this study, stochastic analysis is aimed for space structures (satellite in LEO, made of aluminum 2024-T3), with the focus on fatigue failure. Primarily, the deterministic fatigue simulation is conducted using Walker and Forman models with constant amplitude loading. Deterministic crack growth was numerically simulated by the authors developed algorithm and is compared with commercial software for accuracy verification as well as validation with the experimental data. For the stochastic fatigue analysis of this study, uncertainty is estimated by using the Monte Carlo simulation. It is observed that by increasing the crack length, the standard deviation (the measure of uncertainty) increases. Also, it is noted that the reduction in stress ratio has the similar effect. Then stochastic crack growth model, proposed by Yang and Manning, is employed for the reliability analysis. This model converts the existing deterministic fatigue models to stochastic one by adding a random coefficient. Applicability of this stochastic model completely depends on accuracy of base deterministic function. In this study, existing deterministic functions (power and second polynomial) are reviewed and three new function I) fractional, II) global and III) exponential are proposed. It is shown that the proposed functions are potentially used in the Yang and Manning model for better results.
TOPICS: Fatigue, Aluminum, Reliability, Simulation, Stress, Event history analysis, Space frame structures, Fracture (Materials), Algorithms, Computer software, Fatigue analysis, Fatigue cracks, Polynomials, Satellites, Fatigue failure, Uncertainty, Risk
Javad Sovizi, Rahul Rai and Venkat Krovi
ASME J. Risk Uncertainty Part B   doi: 10.1115/1.4037122
Loosely-interconnected cooperative systems such as cable robots are particularly susceptible to uncertainty. Such uncertainty is exacerbated by addition of the base mobility to realize reconfigurability within the system. However, it also sets the ground for predictive base reconfiguration in order to reduce the uncertainty level in system response. To this end, in this paper we systematically quantify the output wrench uncertainty based on which a base reconfiguration scheme is proposed to reduce the uncertainty level for a given task (uncertainty manipulation). Variations in tension and orientation of the cables are considered as the primary sources of the uncertainty responsible for non-deterministic wrench output on the platform. For non-optimal designs/configurations, this may require complex control structures or lead to system instability. The force vector corresponding to each agent (e.g., pulley and cable) is modeled as random vector whose magnitude and orientation are modeled as random variables with Gaussian and von Mises distributions, respectively. In a probabilistic framework, we develop the closed-form expressions of the mean and variances of the output force and moment given the current state (tension and orientation of the cables) of the system. This is intended to enable the designer to efficiently characterize an optimal configuration (location) of the bases in order to reduce the overall wrench fluctuations for a specific task. Numerical simulations as well as real experiments with multiple iRobots are performed to demonstrate the effectiveness of the proposed approach.
TOPICS: Computer simulation, Robots, Cables, Fluctuations (Physics), Pulleys, Tension, Uncertainty, Mechanical admittance, Risk, Uncertainty quantification
Kasmet T. Niyongabo and Scott B. Nokleby
ASME J. Risk Uncertainty Part B   doi: 10.1115/1.4032634
A proof-of-concept detector prototype capable of collecting and storing radiometric data in the Jet Boring System (JBS) during pilot hole drilling at the Cigar Lake uranium mine is presented. Cigar Lake is the world’s second highest known grade uranium mine and is located in northern Saskatchewan, Canada. Variant design is used to design, develop, test and implement the detector’s firmware, software and hardware. The battery powered detector is attached inside a JBS drill rod to collect radiometric data through the drilling cycle. A readout box is used to initiate the detector, recharge the battery and download radiometric data afterthe pilot hole drilling cycle is complete.Functional testing results are presented and comparative test results between the JBS gamma probe and the AlphaNUCLEAR Hi-Flux probe are evaluated. Field data collected from a pilot hole is plotted against the pilot hole’s driving layout and jetting recipe to show the accuracy of the readings collected.

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