Large Safety Factors Research Articles

Management information platform based on Internet of Things

In order to study the financial management mode and innovation of electric power enterprises under the current situation, a research method of electric power financial management innovation in the era of Internet of Things is proposed. According to the network topology of the system and the analysis of the Android system, the client of the financial management system, the main functional modules of the system and the data warehouse are designed. The client of the financial management system will divide the client into an information interaction unit and a data calculation unit according to the actual needs of the client; the main functional modules of the system are divided into account management unit, salary management unit, project management unit, system management unit, and fixed asset management unit. Unit, revenue and expenditure management unit and report management unit, the sub-units of each unit are divided into brief analysis, and the outpatient registration fee management module and inpatient fee management module of the revenue and expenditure management unit are introduced in detail; in the hospital financial data warehouse, in the application layer An interactive platform is built between it and the data warehouse, and the module is integrated into the existing data warehouse to realize the processing, storage and operation of massive data. The proposed system has a large operating safety factor, high user satisfaction, and an average system flexibility factor of 0.94. The power financial management information platform based on the Internet of Things has a very good performance in the application. Therefore, the method in this paper can enhance the work efficiency of electric power enterprises and enhance the core competitiveness of electric power enterprises.

Reversal of the Parallel Drift Frequency in Anomalous Transport of Impurity Ions.

It is found that, in the studies of heavy ion transport with gyrokinetic simulations, the ion parallel drift frequency can reverse sign in velocity space when the amplitude variation of the electrostatic potential fluctuation is strong along the magnetic field line. As a result, the particle transport related to the parallel dynamics is strongly enhanced. It is noted that, while parallel gradient of the fluctuation amplitude can be instigated by a large magnetic shear or safety factor in a tokamak, the generic mechanism is independent of its cause, which suggests broader applications to kinetic plasma problems. Some relevant topics are briefly addressed in the end.

Investigation of alternative RF power limit control methods for 0.5T, 1.5T, and 3T parallel transmission cardiac imaging: A simulation study.

To investigate safety and performance aspects of parallel-transmit (pTx) RF control-modes for a body coil at . Electromagnetic simulations of 11 human voxel models in cardiac imaging position were conducted for , and and a body coil with a configurable number of transmit channels (1, 2, 4, 8, 16). Three safety modes were considered: the 'SAR-controlled mode' (SCM), where specific absorption rate (SAR) is limited directly, a 'phase agnostic SAR-controlled mode' (PASCM), where phase information is neglected, and a 'power-controlled mode' (PCM), where the voltage amplitude for each channel is limited. For either mode, safety limits were established based on a set of 'anchor' simulations and then evaluated in 'target' simulations on previously unseen models. The comparison allowed to derive safety factors accounting for varying patient anatomies. All control modes were compared in terms of the amplitude and homogeneity they permit under their respective safety requirements. Large safety factors (approximately five) are needed if only one or two anchor models are investigated but they shrink with increasing number of anchors. The achievable is highest for SCM but this advantage is reduced when the safety factor is included. PCM appears to be more robust against variations of subjects. PASCM performance is mostly in between SCM and PCM. Compared to standard circularly polarized (CP) excitation, pTx offers minor improvements if local SAR limits are always enforced. PTx body coils can safely be used at . Uncertainties in patient anatomy must be accounted for, however, by simulating many models.

Achieving High Energy Efficiency: Recent Advances in Zn‐Air‐Based Hybrid Battery Systems

Rechargeable Zn‐air batteries (ZABs) are regarded as an attractive green energy storage technology, featured with large theoretical energy densities and intrinsic high safety factors. However, hindered by the sluggish kinetics of both oxygen reduction reaction and oxygen evolution reaction, rechargeable ZABs are confronted with some critical challenges such as low operating voltage, poor energy efficiency, and limited cycle life. Zn‐air‐based hybrid batteries (ZAHBs), integrating the advantages of a conventional ZAB with supplementary redox reactions, have emerged as a promising solution to address those challenges. Based on working principles, the hybrid batteries can be categorized into two groups: Zn‐M/air hybrid batteries (M = Ni, Co, Ag, Cu, and Mn) and Zn‐X/air hybrid batteries (X = KI, ethanol, and urea), which can achieve improved energy efficiency and density by optimizing charge–discharge voltage. Herein, a comprehensive overview of ZAHBs is provided, including the classification, latest progress, and electrochemical properties, as well as detailed discussion of relevant mechanisms. Moreover, the perspectives and opportunities for future research in the field of hybrid battery systems are also outlined. This review shall give helpful guidance on the design and application of ZAHBs, and provide important insights into the development of new electrochemical energy storage systems.

Autonomous healing of fatigue cracks via cold welding.

Fatigue in metals involves gradual failure through incremental propagation of cracks under repetitive mechanical load. In structural applications, fatigue accounts for up to 90% of in-service failure1,2. Prevention of fatiguerelies on implementation of large safety factors and inefficient overdesign3. In traditional metallurgical design for fatigue resistance, microstructures are developed to either arrest or slow the progression of cracks. Crack growth is assumed to be irreversible. By contrast, in other material classes, there is a compelling alternative based on latent healing mechanisms and damage reversal4-9. Here, we report that fatigue cracks in pure metals can undergo intrinsic self-healing. We directly observe the early progression of nanoscale fatigue cracks, and as expected, the cracks advance, deflect and arrest at local microstructural barriers. However, unexpectedly, cracks were also observed to heal by a process that can be described as crack flank cold welding induced by a combination of local stress state and grain boundary migration. The premise that fatigue cracks can autonomously heal in metals through local interaction with microstructural features challenges the most fundamental theories on how engineers design and evaluate fatigue life in structural materials. We discuss the implications for fatigue in a variety of service environments.

ANALISIS DEFORMASI DAN STABILITAS LERENG DENGAN VARIASI GEOMETRI DAN PERKUATAN GEOTEKSTIL PADA PROYEK GEDUNG FAKULTAS HUKUM UII

Indonesian Islamic University (UII) is a private university located in Sleman, Special Region of Yogyakarta. As an educational institution, UII must be able to fulfill the infrastructure to carry out the teaching and learning process for its students, namely the lecture building. At present UII has campuses spread across Kaliurang (integrated campus), Condongcatur (Faculty of Economics), and student parks (Faculty of Law). The process of building a law faculty building UII is on the road Kaliurang km14.5 which is just below the foot of Mount Merapi and has contours of mountainous land. The contours of mountainous land have different levels of land up and down. In mountainous areas can cause problems, namely landslides. In the construction of the UII law faculties building, a suitable slope design is needed, so to solve the problem, slope stability analysis is used. This method is carried out by analyzing the deformation and slope stability by strengthening the geotextiles using the Plaxis 8.2 program. Slope modeling is designed with variations in geometry and variations in water level. Geometry variations used are geometry 70 °, 60 °, and 50 ° while variations in water level with dry water conditions, depth of water conditions 3.8 m, and saturated water conditions. In carrying out the analysis using structural loads and earthquake loads. Deformation analysis is seen from horizontal point X deformation, vertical point X deformation and horizontal deformation of Y-Y pieces. The results of this study are that slope with geotextile reinforcement have large safety factor and small deformations. A more slope geometry variation (50°) result in a larger safety factor and has a small deformation than steep geometry (70°). Groundwater variation have an influence on the results of the safety factor and deformation. The face of saturated ground water has a low safe value and large deformation due to having more water content.

Axial cyclic loading of piles in low-to-medium-density chalk

Comprehensive field investigations into the axial cyclic loading behaviour of open steel pipe piles driven and aged in low-to-medium-density chalk identify the conditions under which behaviour is stable, unstable or metastable. Post-cycling monotonic tests confirmed that stable cycling enhanced pile capacity marginally, while unstable cases suffered potentially large losses of shaft capacity. Metastable conditions led to intermediate outcomes. The patterns by which axial deflections grew under cyclic loading varied systematically with the normalised loading parameters and could be captured by simple fitting expressions. Cyclic stiffnesses also varied with loading conditions, with the highest operational shear stiffnesses falling far below the in situ seismic test values. The monotonic and cyclic axial responses of the test piles were controlled by the behaviour of, and conditions within, the reconsolidated, de-structured, chalk putty annuli formed around pile shafts during driving. Fibre-optic strain gauges identified progressive failure from the pile tip upwards. Large factors of safety were required for piles to survive repetitive loading under high-level, two-way conditions involving low mean loads, while low-amplitude one-way cycling had little impact. A simple ‘global’ prediction procedure employing interface shear and cyclic triaxial tests is shown to provide broadly representative predictions for field behaviour.

Analysis of the Mechanical Performance and Durability of Adhesively Bonded Joints Used in the Milling Tool Industry

Epoxy adhesives, widely used in multiple structural applications, are used in the milling tool industry to replace brazing and mechanical fastening when joining the cutting bits to the tool body; though their durability is still a concern. This work aims to evaluate and characterise the effect of environmental factors associated with a tool’s life cycle on the performance of these bonded joints. A gravimetric analysis was conducted on bulk adhesive plates for water, cutting emulsion and dielectric fluid to obtain diffusion and relaxation rates. Novel real joint shear specimens were developed to enable strength testing on joints which are comparable with the final application. These specimens were immersed in fluids and subjected to thermal cycles or a corrosive finishing surface treatment to simulate the tool’s life cycle. The joint’s resistance was then benchmarked. Lastly, a dimensional variation test was carried out on tool prototypes before and after ageing, showing no significant dimensional variation which could compromise the cutting performance of the tool. Overall, though it was possible to identify a decrease in strength of around 20% in most tests, joint strength was still within the values necessary for safe operation, with a large safety factor still being retained.

Numerical Analysis of Seepage Failure Modes of Sandy Soils within a Cylindrical Cofferdam

Soil seepage failure within cofferdams is a dangerous phenomenon that always poses difficulties for designers and builders of excavations in zones with high water levels. When the hydraulic head difference H between the upstream and downstream sides reaches a critical height, the downstream soil seepage failure occurs. Depending on soil properties, soil-wall interface characteristics, and cofferdam design, different seepage failure modes can be observed: heaving, boiling, liquefaction, or failure by reduction of the passive earth pressure. In the literature, there are differences, sometimes very large, in the critical value of the hydraulic head loss Hc/D inducing seepage failure given by several methods proposed for stability verification. Then, complex cases are generally approached using simplifying assumptions and adopting large safety factors to take account of uncertainties. In practice, geotechnical engineers deal with many kinds of excavations and different shapes of cofferdams, such as rectangular, square, or circular, which generate three-dimensional (3D) flow conditions. Axisymmetric seepage flow through the soil in a circular cofferdam is often used to model such 3D seepage flow. In this paper, using the numerical code FLAC, several numerical simulations are carried out in axisymmetric groundwater flow conditions to analyze the seepage failure modes of cohesionless sandy soils within a cylindrical cofferdam. The effects of the cofferdam radius, internal soil friction, soil dilatancy, and interface friction on the Hc/D value and failure mode are studied. The numerically obtained seepage failure modes are presented and discussed in various scenarios. The present results, illustrated in both tables and graphs, show a significant decrease in the value of Hc/Dinducing seepage failure, with a decrease in the cofferdam radius. They also indicate the sensitivity of the seepage failure mode to internal soil friction, soil dilatancy, interface friction, and cofferdam radius. As well, new terms are proposed for the seepage failure mode designations based on the 3D view of the downstream soil deformation. Doi: 10.28991/CEJ-2022-08-07-06 Full Text: PDF

Mining Stress Evolution Law of Inclined Backfilled Stopes Considering the Brittle-Ductile Transition in Deep Mining

To study the mining stress evolution law of inclined backfilled stope in deep mining, this paper first proposes a method for determining the parameters of the brittle-ductile transition model corresponding to the Hoek–Brown criterion and Mohr-Coulomb criterion under high geostress. Then, a model composed of inclined backfilled stopes with different depths is established to simulate the sequential mining process of ore bodies with varying depths from shallow to deep. The numerical model’s stratum displacement, rock mass stress distribution, and risk factors show that the mining-induced stress will move to the upper stopes and the stratum below the deepest stope. The transfer range and influence degree of mining-induced stress will increase with the increase of the deep mining, resulting in the most dangerous backfilled stope occurring one to two layers above the deepest stope and the apparent stress concentration area occurring below the deepest stope. To prevent disasters caused by mining stress, pillars in inclined deep stopes should have large safety factors. Replacing low-strength backfills with high-strength backfills can reduce the stress concentration in the stratum below the deepest stope.

Numerical optimisation of bonded joints for the manufacture of edge milling tools

Edge milling tools for processing wood are currently assembled using brazing or fastening, joining the cutting insert to the tool body. However, the demand for lighter tools has led to a growing interest on changing this process to adhesive bonding.To determine the performance of the joint a cohesive zone model (CZM) was implemented, recurring to ANSYS® MechanicalTM. To optimise its geometry, a parametric simulation was performed using a simplified single insert model of the full milling tool. Due to the large number of design points, a two-step approach was adopted, focusing on optimising certain parameters in each stage. For the loading condition, a rotational velocity test under overspeed condition, required by the relevant safety standard, was performed. Finally, in terms of output, the stresses generated, as well as differences in cost or manufacturing processes compared to the already commercialised tool configuration were analysed.The developed model highlighted the large safety factor present in the original, base-line design, demonstrating that adhesive bonding can lead to a highly durable and resistant milling tool. The developed model also allowed to optimise some of the key design parameters, while providing paths for minimising the tool’s manufacturing cost and ensuring maximum performance.

Risk Assessment of Contaminants in Sewage Sludge Applied on Norwegian Soils

Risk Assessment of Contaminants in Sewage Sludge Applied on Norwegian Soils

Static hazards of container filling

AbstractThe maximum filling rates recommended by IEC and NFPA for conductive intermediate bulk containers (IBC) conflict with each other and take no account of the filling pipe diameter. A model previously developed to predict maximum liquid surface potentials in medium tanks was re‐derived using analytical approximation rather than curve fitting techniques and modified for application to conductive containers. Physically consistent flow rate limits are given for all sizes of container. Relative to the 25 kV hazardous potential threshold, IEC's flow velocity limit of 2 m/s theoretically provides a large safety factor for IBC filling that increases linearly from 2 to 5 as the inside diameter of the filling pipe decreases from 78 to 27 mm. However, because potential varies with the inverse cube of pipe diameter, the safety factor provided by NFPA's flow rate limit of 225 L/min diminishes from 8 to 1/2 over the same range and surface potentials exceed 25 kV for filling pipe diameters below about 35 mm. The model is extended to address elevated dielectric constants and practical guidance is provided for different filling pipe options. We also warn of specific practices that could increase the likelihood of a fire or explosion.

Perfluorinated alkyl substances: Sewage treatment and implications for receiving waters

This study comprises a detailed analysis of data for perfluorooctanesulfonic acid (PFOS), and perfluorooctanoic acid (PFOA) for over 600 wastewater treatment works effluents (WwTW) as well as samples upstream and downstream of each discharge of effluent into its receiving water. This has allowed an investigation of not only the effectiveness of removal of the perfluoroalkyl substances (PFAS) compounds during wastewater treatment but also implications for compliance with the environmental quality standard (EQS) set for PFOS under the Water Framework Directive. It is shown that effluents contain concentrations of PFOS that exceed the annual average EQS by a factor between 1.1-fold and 40-fold. The corresponding factors for PFOA are between 2-fold and 22-fold. The presence of high concentrations upstream, means that between a quarter and a third of individual effluents are found to reduce the concentration of fluorocarbons in the river downstream of the discharge point. The elevated concentrations upstream of the studied wastewater treatment works suggest inputs of these perfluoro compounds into the aquatic environment are ubiquitous and therefore difficult to address from simply setting permit conditions for individual WwTW. The freshwater EQS set for PFOS is based on several worst-case accumulation coefficients and large safety factors, which, when combined, result in a sub ng/L EQS. Consequently, the use of the biota derived quality standard may be a more realistic measure of environmental risk. It may be prudent, to assess the effectiveness of controls implemented in the last few years before considering widespread end-of-pipe treatment.

Study on the Reduction of the Resonant Stress of Turbine Blades Caused by the Stage Interaction Force (Simultaneous Optimization of Blade Resonant Stress and Amount of Unbalance)

Abstract Although the bladed disks of turbomachinery are nominally designed to be cyclically symmetric (tuned system), the vibration characteristics of individual blades on a disk vary slightly owing to manufacturing tolerances, deviations in material properties, wear during operation, etc. These small variations break the cyclic symmetry and split eigenvalue pairs. Actual bladed disks with small variations are called mistuned systems. The resonant stress on a mistuned bladed disk may become large and cause a blade failure due to high cycle fatigue. Especially for a bladed disk with a free-standing blade structure, it is essential to use a sufficiently large safety factor at the design stage, considering the mistuning effect. Traditionally, blade designers have adopted various countermeasures to reduce the resonant stress at the design stage. Besides the countermeasures adopted in blade design, for a variable speed engine, which cannot avoid resonance, it is thought that a practical optimization method for a mistuned system (bladed disk with a free-standing blade structure) is to sort the blades so that the resonant stress is minimized. In this study, a simultaneous method for optimizing the blade resonant stress and the amount of unbalance causing rotor vibration is proposed. In this method, first, the natural frequencies and weights of all blades on a disk are measured. Then, a mistuned system is assembled and the analysis model is generated. Next, the resonant stress and the amount of unbalance in the mistuned system are analyzed. To reduce the computation time, the reduced-order model known as fundamental mistuning model (FMM) is used to calculate the resonant stress in the mistuned system. The analyses of the resonant stress and the amount of unbalance are carried out repeatedly, sorting the blades on the disk, and the optimal solution is explored using Monte Carlo simulations (MCS) or discrete differential evolution (DDE). As an example, a mistuned bladed disk of an aero-engine was analyzed, and the validity of the proposed method was verified.

Early Detection of Fatigue Crack Damage in Ductile Materials: A Projection-Based Probabilistic Finite State Automata Approach

Abstract Fatigue failure occurs ubiquitously in mechanical structures when they are subjected to cyclic loading well below the material’s yield stress. The tell-tale sign of a fatigue failure is the emergence of cracks at the internal or surface defects. In general, a machinery component has a finite fatigue life based on the number of cycles, it can sustain before a fracture occurs. However, the estimated life is generally conservative and often a large factor of safety is applied to make the component fail-safe. From the perspective of better utilization of a machinery component, it is, however, desirable to have maximum usage of the component without a catastrophic failure. It is, therefore, conducive to have a measure that can capture precursors to failure to facilitate active diagnosis of the machinery health. In this study, a precursor detection method is developed upon modifications of probabilistic finite state automata (PFSA). The efficacy of the proposed method is demonstrated on cold-rolled AL7075-T6 notched specimens in a computer-instrumented and computer-controlled fatigue testing apparatus. The results show that the proposed method is capable of detecting the emergence of cracks (at ∼95% accuracy) and also can capture precursors with good fidelity.

Effects of extensible modelling on composite riser mechanical responses

The change from steel risers to composites comes with uncertainties that led to large safety factors. One area of uncertainty is the predicted response and stresses derived from commercial packages that are based on formulations that assume in-extensible riser. However, composite pipes exhibit a lower axial stiffness and therefore the velocity of the axial waves will change with a corresponding change in dynamic response. To determine the effect of this assumption, this paper assesses the effect of extensibility on the time-domain response. It is found that the in-extensible model predicts 3 times the number of high frequency tension cycles in the 20 kN tension range. To determine the impact of this change on the stress, the accuracy of available composite pipe models is benchmarked using shell, continuum-shell and solid elements. The quadratic and continuum-shell elements provide a maximum percentage difference of 4% compared to solid elements but the continuum-shell is selected as it has a lower computational cost. The response from the extensible and in-extensible models are input into the pipe model, they provide similar Tsai-Wu failure factors, alleviating concerns when modelling the strength. However, the change in dynamics remains a concern for other applications such as machine-learning or digital-twins.

Condition Monitoring Technologies for Steel Wire Ropes – A Review

In this research, we review condition-monitoring technologies for offshore steel wire ropes (SWR). Such ropes are used within several offshore applications including cranes for load handling such as subsea construction at depths up to 3-4000 meters, drilling lines, marine riser tensioner lines and anchor lines. For mooring, there is a clear tendency for using fiber ropes. Especially for heavy-lift cranes and subsea deployment, winches with strong ropes of up to 180 mm in diameter may be required, which has a considerable cost per rope, especially for large water depths. Today’s practice is to discard the rope after a predetermined number of uses due to fatigue from bending over sheaves with a large safety factor, especially for systems regulated by active heave compensation (AHC). Other sources of degradation are abrasion, fretting, corrosion and extreme forces, and are typically accelerated due to undersized or poorly maintained sheaves, groove type, lack of lubrication and excessive load.Non-destructive testing techniques for SWR have been developed over a period of 100 years. Most notably are the magnetic leakage techniques (electromagnetic methods), which are widely used within several industries such as mining and construction.The content reviewed in this research is primarily the developments the last five years within the topics of electromagnetic method, acoustic emissions (AE), ultrasound, X- and γ-rays, fiber optics, optical and thermal vision and current signature analysis. Each technique is thoroughly presented and discussed for the application of subsea construction. Assessments include ability to detect localized flaws (i.e. broken wire) both internally and externally, estimated loss of metallic cross sectional area, robustness with respect to the rough offshore environment, ability to evaluate both rope and end fittings, and ability to work during operation.

Multivariate statistical modelling of the drivers of compound flood events in south Florida

Abstract. Miami-Dade County (south-east Florida) is among the most vulnerable regions to sea level rise in the United States, due to a variety of natural and human factors. The co-occurrence of multiple, often statistically dependent flooding drivers – termed compound events – typically exacerbates impacts compared with their isolated occurrence. Ignoring dependencies between the drivers will potentially lead to underestimation of flood risk and under-design of flood defence structures. In Miami-Dade County water control structures were designed assuming full dependence between rainfall and Ocean-side Water Level (O-sWL), a conservative assumption inducing large safety factors. Here, an analysis of the dependence between the principal flooding drivers over a range of lags at three locations across the county is carried out. A two-dimensional analysis of rainfall and O-sWL showed that the magnitude of the conservative assumption in the original design is highly sensitive to the regional sea level rise projection considered. Finally, the vine copula and Heffernan and Tawn (2004) models are shown to outperform five standard higher-dimensional copulas in capturing the dependence between the principal drivers of compound flooding: rainfall, O-sWL, and groundwater level. The work represents a first step towards the development of a new framework capable of capturing dependencies between different flood drivers that could potentially be incorporated into future Flood Protection Level of Service (FPLOS) assessments for coastal water control structures.

Design of a New XY Flexure Micropositioning Stage With a Large Hollow Platform

This paper presents the design of a new flexure-based xy micropositioning stage with a large hollow platform, which is suitable for practical use with a microscope. The designed mechanism has a parallel-kinematic structure and is actuated by two voice coil motors. By employing multistage compound parallelogram flexures, the stage is designed as a four-layer structure, which produces a motion output platform with a large hollow space and large range of motion. Analytical modeling was carried out for parametric design of the stage. Evaluation results show that the designed xy stage exhibits a large safety factor and high natural frequency. Moreover, the large hollow platform is well-suited for practical applications with a microscope.