Multilevel Design Optimization Under Uncertainty with Application to Product-Material Systems

The main objective of this research is to develop a computational design tool for multilevel optimization of product-material systems under uncertainty. To accomplish this goal, an exponential penalty function (EPF) formulation based on method of multipliers is developed for solving multilevel optimization problems within the framework of Analytical Target Cascading (ATC). The original all-at-once constrained optimization problem is decomposed into a hierarchical system with consistency constraints enforcing the target-response coupling in the connected elements. The objective function is combined with the consistency constraints in each element to formulate an augmented Lagrangian with EPF. The EPF formulation is implemented using double-loop (EPF I) and single-loop (EPF II) coordination strategies and two penalty-parameter-updating schemes. The computational characteristics of the proposed approaches are investigated using different nonlinear convex and non-convex optimization problems. An efficient reliability-based design optimization method, Single Loop Single Vector (SLSV), is integrated with Augmented Lagrangian (AL) formulation of ATC for solution of hierarchical multilevel optimization problems under uncertainty. In the proposed SLSV+AL approach, the uncertainties are propagated by matching the required moments of connecting responses/targets and linking variables present in the decomposed system. The accuracy and computational efficiency of SLSV+AL are demonstrated through the solution of different benchmark problems and comparison of results with those from other optimization methods. Finally, the developed computational design optimization tool is used for design optimization of hybrid multiscale composite sandwich plates with/without uncertainty. Both carbon nanofiber (CNF) waviness and CNF-matrix interphase properties are included in the model. By decomposing the sandwich plate, structural and material designs are combined and treated as a multilevel optimization problem. The application problem considers the minimum-weight design of an in-plane loaded sandwich plate with a honeycomb core and laminated composite face sheets that are reinforced by both conventional continuous fibers and CNF-enhanced polymer matrix. Besides global buckling, shear crimping, intracell buckling, and face sheet wrinkling are also treated as design constraints

Multilevel Design Optimization Under Uncertainty with Application to Product-Material Systems

The main objective of this research is to develop a computational design tool for multilevel optimization of product-material systems under uncertainty. To accomplish this goal, an exponential penalty function (EPF) formulation based on method of multipliers is developed for solving multilevel optimization problems within the framework of Analytical Target Cascading (ATC). The original all-at-once constrained optimization problem is decomposed into a hierarchical system with consistency constraints enforcing the target-response coupling in the connected elements. The objective function is combined with the consistency constraints in each element to formulate an augmented Lagrangian with EPF. The EPF formulation is implemented using double-loop (EPF I) and single-loop (EPF II) coordination strategies and two penalty-parameter-updating schemes. The computational characteristics of the proposed approaches are investigated using different nonlinear convex and non-convex optimization problems. An efficient reliability-based design optimization method, Single Loop Single Vector (SLSV), is integrated with Augmented Lagrangian (AL) formulation of ATC for solution of hierarchical multilevel optimization problems under uncertainty. In the proposed SLSV+AL approach, the uncertainties are propagated by matching the required moments of connecting responses/targets and linking variables present in the decomposed system. The accuracy and computational efficiency of SLSV+AL are demonstrated through the solution of different benchmark problems and comparison of results with those from other optimization methods. Finally, the developed computational design optimization tool is used for design optimization of hybrid multiscale composite sandwich plates with/without uncertainty. Both carbon nanofiber (CNF) waviness and CNF-matrix interphase properties are included in the model. By decomposing the sandwich plate, structural and material designs are combined and treated as a multilevel optimization problem. The application problem considers the minimum-weight design of an in-plane loaded sandwich plate with a honeycomb core and laminated composite face sheets that are reinforced by both conventional continuous fibers and CNF-enhanced polymer matrix. Besides global buckling, shear crimping, intracell buckling, and face sheet wrinkling are also treated as design constraints

Investigation of Iron Passivity and Chloride-induced Depassivation in Alkaline Electrolytes using Reactive Force Field Molecular Dynamics (ReaxFF-MD)

The corrosion and passivity of iron (and carbon steel) in media with different alkalinity as well as iron depassivation have been studied extensively using electrochemical methods and nano-scale surface characterization studies. The electrochemical techniques provide valuable information about the average electrochemical behavior of relatively large metal surfaces, typically in centimeter-square scale or larger. However, electrochemical processes on these surfaces typically occur in nanometer scale. Although nano-scale surface characterizations provide valuable information about passive films that form on carbon steel and iron in alkaline electrolytes, and their chloride-induced depassivation, they cannot explain the dynamic processes that lead to their formation as they can only provide data at particular instants. Atomistic modeling techniques such as Reactive Force Field Molecular Dynamics (ReaxFF-MD) have the potential to fill this gap. This research used ReaxFF-MD simulations to answer fundamental questions on iron corrosion, passivation and chloride-induced depassivation in four interrelated thrusts: Thrust 1: ReaxFF-MD was used to study the initial stages of iron corrosion in pure water. The simulations were performed on iron under various applied external electric fields and temperatures. Oxide film formation was accompanied by iron dissolution in water, indicating active corrosion and supporting the expected thermodynamic behavior of iron in pure water. Oxide film thickness and iron dissolution increased with increasing applied external electric field. Corrosion rates increased slightly with increasing temperature within the temperature range of this investigation (300–350 K). Critical stages of the iron corrosion process during the simulations were identified as dissociation of water to OH- and H+, adsorption of OH- on the iron surface, penetration of oxygen into iron to form iron oxides, and dissolution of iron into solution. Comparisons of the simulated charge distributions and pair distribution functions to those of reference oxides showed the formed oxide compositions were not pure phases, but rather a mixture of oxides. Thrust 2: The applicability of the classical EDL models was investigated to study corrosion and passivity of iron in neutral and alkaline media using ReaxFF-MD. The performance of the classical EDL models were studied in the ReaxFF-MD simulations of iron exposed to neutral (pH = 7) and highly alkaline (pH = 13.5) electrolytes under applied electric fields. Although the Helmholtz model was able to produce iron corrosion in the neutral electrolyte, it did not result in passive film formation in the highly alkaline solution system. The Gouy-Chapman model was not capable of simulating passivity for iron in the highly alkaline solution system or active corrosion in the neutral electrolyte. The Stern model was the only model that could simulate passivity and corrosion of iron for highly alkaline and neutral electrolytes, respectively. This study showed that ReaxFF-MD simulations of iron in neutral and alkaline electrolytes should use the Stern model for representing the EDL. Thrust 3: The passivity of Fe(110) in a 0.316 M NaOH solution (pH = 13.5) was investigated using ReaxFF-MD. The simulations were carried out under an applied electric field of 30 MeV/cm. The electrical double layer was modeled using the Stern model. Under these conditions, following the expected thermodynamic behavior, a protective passive film formed during 500 ps simulation time. The initial stages of passivation differed from simulations that had been carried out in neutral electrolytes such that the highly alkaline environment allowed the stabilization of the metal through the formation of an Fe(OH)2 layer on the metal surface. This created conditions for oxygen diffusion into metal without dissolution of iron atoms into the electrolyte. The passive film had a multiple oxide structure such that outer layers were in the form of Fe2O3, middle layers were in the form of Fe3O4, and the inner layer was in the form of FeO. This multi-layer structure is in agreement with theoretical passivity models that are based on an inner barrier layer that forms directly on the metal substrate (FeO), and outer layers (Fe3O4 and Fe2O3) that precipitates through the further oxidation of the iron ejected from the inner layer. A parallel XPS investigation confirmed the findings of ReaxFF-MD simulations. Thrust 4: Chloride-induced depasivation of iron in pH 13.5 NaOH solution was studied using ReaxFF-MD, electrochemical tests and x-ray photoelectron spectroscopy (XPS). The breakdown of the passive film by chlorides initiates with iron dissolution from the first layer of the passive film into the electrolyte. Iron dissolution and corresponding iron vacancy formation in the first layer of the passive film take place in four stages that involves local acidification of the electrolyte adjacent to the metal surface, followed by iron dissolution into the electrolyte in the form of Fe(OH)Cl2 and FeCl3. Chloride in the electrolyte mainly acts as a catalyst and do not penetrate into the passive film. The four-step process for the initiation of the passive film breakdown was used to explain the concept of a critical chloride threshold and the well-documented electrochemical observation that critical chloride thresholds are higher in solution with solution with higher pH. The ReaxFF-MD simulations support the depassivation hypothesis that is described by the point defect model. Both ReaxFF-MD simulations and XPS analysis showed that chlorides increase the Fe+3/Fe+2 of the passive film, and this increase is more evident in the inner and middle layers of the film. It is expected that these fundamental findings of this research will facilitate the development of new corrosion mitigation strategies such as customized corrosion inhibitors and inexpensive corrosion-resistant steels

Assessment of the prevalence of occupational accidents and their influential actors in an electricity distribution company during a five-year period

BACKGROUND: Occupational accidents have been considered as one of the most important crippling factors contributing to disabilities and life-threatening situations in many countries. This study was conducted to survey the prevalence of occupational accidents and the factors of that lead to injuries in an Electricity Distribution Company during a five-year period. METHODS: In this descriptive study, the accident report form included items asking about the season of the year when the accident occurred, the ages and the average age of those injured, the type of employment, work experience, nature of the injuries that occurred, parts of the body affected, treatments that were applied, average number of days lost per accident, the levels of education of those involved, and their marital status. Data was analyzed using SPSS. RESULTS: A total of 66 Electricity Distribution Company workers were determined to be suffering from injuries due to accidents. The accidents mostly occurred in the summer (33). Most of the injured workers (16.7) belonged to the age groups of 25 to 29 and 40 to 44; there were no accidents reported for workers who were less than 20. About 48 of the accident victims had to be hospitalized. Furthermore, 35 of the accident victims were treated in outpatient clinics, and 7.4 of the accident victims died. We demonstrated that there were significant relationships between: 1) marital status and accidental injuries (P0.05) or work experience and the distribution of the accidents (P>0.05). CONCLUSION: This study indicated that most of the injuries in these accidents were related to the nature of employment, marital status, and level of education. The results showed the necessity for providing appropriate safety training for the workers

Influence Of Overlay Thickness On Interface Bonding

Overlaying is an efficient and proven pavement preservation approach for flexible pavements. The overlay thickness varies from 1 in. to 4 in. depending on the conditions of the existing pavement, financial resources, etc. In the recent decade, financial constraints in conjunction with the push for pavement preservation, the overlay thickness is being reduced to less than an in. The ultra-thin overlay is a new cost-effective method that can be used to preserve functional pavement problems and provide satisfactory ride quality. Although studies have been conducted to evaluate pavement systems using numerical simulation, the research in the area of evaluating existing layer and overlay layer as a composite layer is limited. With the advent of Ultra-thin layers, the durability of pavement system will be significantly influenced if both layers separate from each other. The several experimental studies have focused on the interface bonding between the overlay and existing asphalt layer. They evaluated how different criteria like tack coat type, dust, or moisture can affect the interface bonding strength between layers. But the impact of different interface bonding strength on pavement structure and durability of overlay itself has not been extensively evaluated. Overlay thickness impact on pavement structural characteristics is another aspect of the subject that still needs a lot of research. The main purpose of this study was to perform numerical simulation of several pavements systems with different overlay thicknesses and to evaluate the effect of overlay thickness and overlay-existing asphalt layer interface bonding on pavement performance. Three-dimensional finite element models have been used to simulate different pavement systems using ABAQUS software. Different interface bonding strength has also been implemented for each of the pavement systems to evaluate the effect of interface bonding strength. Models with linear elastic-perfectly plastic behavior for the base and subgrade was selected for the base and subgrade layer. Viscoelastic behavior of the asphalt material has been modeled using dynamic modulus test results and Prony series. Finite and semi-infinite elements have been developed to model the pavement systems. Passing (moving) vehicle\u27s load used to see the impact of overlaying in highways or other places that vehicles drive at nearly constant speed. The pavements performance under braking conditions was also necessary to see how overlay works under stop and go traffic conditions or near intersections. Rather than uniform distributed load, the load was non-uniformly distributed in the tire footprint are to simulate actual field conditions. Frictional and cohesive contact approach was followed to define interface layer and bonding between the two layers. Frictional contact has been used to simulate the interface characteristics between existing asphalt and base layer. The cohesive contact was used to define the tack coat layer properties. Maximum deflection at the top surface of the pavement and the maximum tensile strength at the bottom of the existing asphalt layer has been observed as the two most important criteria determining pavement performance. To evaluate the durability of the overlay itself, contact opening between the overlay and existing asphalt layer has been observed. The evaluation results identified that overlay thickness of less than 2 in. doesn\u27t add structural strength to the pavement system. The overlays with the thickness of less than 1 in. significantly influences stress levels at the interface; therefore, bonding between the two layers is important. The moving load versus braking loads should be considered for evaluating the composite pavement design system

What Do Patients Expect from Their Physicians?

Background: To identify the most important expectations that patients have from their physicians. Methods: We collected data from 199 hospitalized and 201 ambulatory patients (response rates 88% and 93% respectively). We used random sampling for selection of hospitalized patients and systematic sampling for the ambulatory ones. The questionnaire consisted of 18 different expectation items categorized in 5 domains. The participants scored each item from 1 to 9 using a VAS scale and ranked domains based on their importance. We analyzed the data using univariate and regression analyses. Results: Among the ambulatory patients, the mean±standard error of the most important expectations was as follows: com­petency (8.9±0.01), courteousness (8.8±0.04), consultation in case of need (8.8±0.4), clear explanation of the disease (8.8± 0.05) and attentiveness (8.8±0.04). In hospitalized patients, the following items were the most important: competency (8.4± 0.08), courteousness (8.4±0.09), availability of physician (8.4±0.09), consultation in case of need (8.2±0.11), setting follow­ing appointments (8.2±0.1), and disease follow-up (8.2±0.09). In both groups, the most important domain of expecta­tions was "competency and quality of care" followed by "availability" in hospitalized and "giving information and patient auton­omy" among ambulatory patients. Conclusions: Our findings are similar to what reported in the literature from other countries and cultures. In addition to physician expertise and knowledge, patients value giving information and efficient doctor-patient relationship

Presentation of a method for consequence modeling and quantitative risk assessment of fire and explosion in process industry (Case study: Hydrogen Production Process)

Introduction: Process industries, often work with hazardous and operational chemical units with high temperature and pressure conditions, such as reactors and storage tanks. Thus, probabilities of incidence such as explosions, and fire are extremely high, The purpose of this study was to present a comprehensive and efficient method for the quantitative risk assessment of fire and explosion in the process units. .Material and Method: The proposed method in this study is known as the QRA and includes seven steps. After determination of study objectives and perfect identification of study process, first, qualitative methods are used to screen and identify hazard points and the possible scenarios appropriate are identified and prioritized. Then, estimation of frequency rate are done using past records and statistics or Fault Tree Analysis along whit Event Tree. PAHST professional software and probit equations are used in order to consequence modeling and consequence evaluation, respectively. In the last step by combination of consequence and frequency of each scenario, individual and social risk and overall risk of process or under study unit was calculated.  .Result: Applying the proposed method showed that the jet fire, flash fire and explosion are most dangerous consequence of hydrogen generation unit. Results showed that social risk of the both fire and explosion caused by full bore rupture in Desulphrizing reactor (Scenari3), Reformer (scenario 9) and Hydrogen purification absorbers are unacceptable. All of the hydrogen generation unit fall in ARARP zone of fire individual risk (FIR) and FIR up to 160 m of boundary limit unit is unacceptable. This distance is not only beyond of hydrogen generation unit boundary limit, but also beyond of complex boundary limit. Desulphurization Reactor (75%) and Reformer (34%) had the highest role in explosion individual risk in the control room and their risks are unacceptable.  .Conclusion: Since the proposed method is applicable in all phases of process or system design, and estimates the risk of fire and explosion by a quantitative, comprehensive and mathematical-based equations approach. It can be used as an alternative method instead of qualitative and semi quantitative methods

The role of modeling and consequence evaluation in improving safety level of industrial hazardous installations: A case study: Hydrogen production unit

Background and aims: One of the most essential and important steps for improving safety level in existing or designing units is consequence evaluation of hazards such as fire, explosion and dispersion of hazardous chemical substances. Due to severe operational conditions, high explosive and flammable gases such as methane and hydrogen, hydrogen production process is causing major industrial accidents of the view life and financial losses. Therefore safety is main concern of hydrogen producers. Methods: First, all hazards and potential scenarios of hydrogen production were identified by applying HAZID Technique, and after collecting the required data, consequence modeling was done by means of professional software PHAST6.54. Death probability of people by means of valid equations of probit was calculated and ultimately, the severity of the consequences was estimated using conventional criteria. Results: The results revealed that, jet fire caused by a full bore rupture in Desulphurization reactor has the highest fatality (26person). The harm effect distance, maximum radiations of this incident were 250 m, 370 kW/m2 respectively. A full bore rupture in Reformer can lead to the most dangerous flash fire. So that people at distance up 130 m from placing leakage and affected area 1505m 2 were exposed to concentration of 61120 ppm and all people would be killed. The most dangerous vapor cloud explosion caused by hydrogen purification absorbers, so that distances up to 60m from absorbers location all people would be killed and all process equipments and buildings will be completely destroyed. The safe distance of hydrogen production unit equals to 746 m from its boundary limit. Conclusion: Consequence evaluation is a quantitative and comprehensive method for estimation and evaluation of potential incidents severity of industrial hazardous units. The occurrence of incidents such as fires and explosions has the great life and financial losses in the hydrogen production process, Thus safety of industries nearby hydrogen production and consume must be specifically considered

Optimal Operation of Active Distribution Grids: A System of Systems Framework

Active distribution grid is composed of autonomous systems which should collaborate with each other in order to operate the entire distribution grid in a secure and economic manner. This paper presents a system of systems (SoS) framework for optimally operating active distribution grids. The proposed SoS framework defines both distribution company (DISCO) and microgrids (MGs) as independent systems, and identifies the process of information exchange among them. As the DISCO and MGs are physically connected together, the operating condition of one might impact the operating point of other systems. The proposed mathematical model uses a decentralized optimization problem aimed at maximizing the benefit of each independent system. A hierarchical optimization algorithm is presented to coordinate the independent systems and to find the optimal operating point of the SoS-based active distribution grid. The numerical results show the effectiveness of the proposed SoS framework and solution methodology. © 2010-2012 IEEE

Assessment of the prevalence of occupational accidents and their influential actors in an electricity distribution company during a five-year period

BACKGROUND: Occupational accidents have been considered as one of the most important crippling factors contributing to disabilities and life-threatening situations in many countries. This study was conducted to survey the prevalence of occupational accidents and the factors of that lead to injuries in an Electricity Distribution Company during a five-year period. METHODS: In this descriptive study, the accident report form included items asking about the season of the year when the accident occurred, the ages and the average age of those injured, the type of employment, work experience, nature of the injuries that occurred, parts of the body affected, treatments that were applied, average number of days lost per accident, the levels of education of those involved, and their marital status. Data was analyzed using SPSS. RESULTS: A total of 66 Electricity Distribution Company workers were determined to be suffering from injuries due to accidents. The accidents mostly occurred in the summer (33). Most of the injured workers (16.7) belonged to the age groups of 25 to 29 and 40 to 44; there were no accidents reported for workers who were less than 20. About 48 of the accident victims had to be hospitalized. Furthermore, 35 of the accident victims were treated in outpatient clinics, and 7.4 of the accident victims died. We demonstrated that there were significant relationships between: 1) marital status and accidental injuries (P0.05) or work experience and the distribution of the accidents (P>0.05). CONCLUSION: This study indicated that most of the injuries in these accidents were related to the nature of employment, marital status, and level of education. The results showed the necessity for providing appropriate safety training for the workers