Safe Operating Conditions Research Articles

A Timing-Based Framework for Designing Resilient Cyber-Physical Systems under Safety Constraint

Cyber-physical systems (CPS) are required to satisfy safety constraints in various application domains such as robotics, industrial manufacturing systems, and power systems. Faults and cyber attacks have been shown to cause safety violations, which can damage the system and endanger human lives. Resilient architectures have been proposed to ensure safety of CPS under such faults and attacks via methodologies including redundancy and restarting from safe operating conditions. The existing resilient architectures for CPS utilize different mechanisms to guarantee safety, and currently, there is no common framework to compare them. Moreover, the analysis and design undertaken for CPS employing one architecture is not readily extendable to another. In this article, we propose a timing-based framework for CPS employing various resilient architectures and develop a common methodology for safety analysis and computation of control policies and design parameters. Using the insight that the cyber subsystem operates in one out of a finite number of statuses, we first develop a hybrid system model that captures CPS adopting any of these architectures. Based on the hybrid system, we formulate the problem of joint computation of control policies and associated timing parameters for CPS to satisfy a given safety constraint and derive sufficient conditions for the solution. Utilizing the derived conditions, we provide an algorithm to compute control policies and timing parameters relevant to the employed architecture. We also note that our solution can be applied to a wide class of CPS with polynomial dynamics and also allows incorporation of new architectures. We verify our proposed framework by performing a case study on adaptive cruise control of vehicles.

Fluidelastic instability of a fuel rod bundle subjected to combined axial flow and jet cross-flow

Nuclear fuel bundles are subjected to axial coolant flow in addition to jet cross-flow in a specific design of pressurized water reactors (PWRs). The combined axial flow and jet cross-flow was found to induce fretting wear of the fuel rods at the spacer grid position. Investigating a reduced fuel rod bundle under jet in transverse flow (JITF) condition is necessary to determine safe vibration free operation conditions for these reactors.This paper presents an experimental and theoretical framework to understand the fluidelastic behavior of a rod bundle subjected to axial flow and localized jet cross-flow. A 6x5 axisymmetric flexible single-span rod bundle is used to simulate a part of a fuel assembly under combined flow. Two working flow conditions, pure axial flow, and JITF are studied on a mock-up PWR assembly. The experiments show that the arrays are stable under pure axial flow as expected. Then, the responses of the rod bundles under combined flows (i.e. JITF) are measured at three test axial flow velocities, VAxial= 1.0 m/s, 1.5 m/s, and 2.0 m/s. The results show that the critical jet cross-flow velocity increases linearly with the axial flow velocity with a velocity ratio (VR = VJet/VAxial) of 1.6.The second part of the work is the development of a fluidelastic instability model to predict the stability boundary for rod bundles under combined axial flow and jet cross-flow. The effect of axial flow on the jet cross-flow is introduced by implementing an incidence angle (θ) of jet flow with respect to the rods. The fluid-added damping terms in the developed model are shown to be functions of θ. The fluidelastic forces are expressed as functions of the projected rod area derivative to account for rod vibration. The stability analysis shows the capability of the model to predict the trend of critical jet cross-flow velocity with the axial flow velocity. The model validation shows the predicted critical velocities to be within an absolute error range from 7% to 12.5% when compared to experiments. The theoretical analysis highlights the importance of the cross-coupling fluidelastic forces in predicting the instability of the mock-up PWR assembly.

Design and thermodynamic analysis of a large-scale ammonia reactor for increased load flexibility

The prospect of large-scale production of green ammonia creates strong incentives for developing highly load-flexible Haber–Bosch loops to match hydrogen production by electrolysis and ammonia production, reducing the hydrogen buffer volume.In this work, we create a mechanistic model representing the ammonia synthesis reactor at full load and simplified models representing its periphery and its behavior at part load in UniSim® Design. We optimize the reactor using MATLAB, obtaining the minimum equipment size required to achieve a specified maximum load and operate safely at very low load.The reactor obtained by our novel approach allows to reduce the minimum feasible load by 41–48% over a reactor designed only for full load. We find a moderate pressure reduction combined with an adapted heat integration to be a promising way of maintaining safe operating conditions during part-load operation, while changing the gas composition in the synthesis loop cannot reduce the minimum load.

1200 GHz High Spectral Resolution Receiver Front-End of Submillimeter Wave Instrument for JUpiter ICy Moon Explorer: Part I - RF Performance Optimization for Cryogenic Operation

The Submillimeter Wave Instrument (SWI) is a spectrometer/radiometer instrument on board of Jupiter Icy Moons Explorer (JUICE) mission operating in two submillimeter heterodyne bands around 530 μm (530 – 625 GHz) and 255 μm (1080 – 1275 GHz). The paper presents the results of acceptance testing and performance optimization carried out on the flight and spare model of the 1200 GHz receiver front-end. The safe operation conditions at 120-150 K ambient temperature, such as maximum authorized input RF power, applied DC bias voltage are determined through the definition of the Schottky junctions dissipated power and current density ranges. A tuning procedure that optimizes the sensitivity of the front-end while keeping it within safe limits at 120-150K temperature operation is discussed. In part II, we present a detailed analysis of reliability and endurance testing.

Assessing the geomechanical state of the main working network state in the case of undermining in the conditions of weak rocks

Purpose. Geomechanical substantiation and determination of the parting state parameters for specific mining-geological and mining-technical conditions based on the analysis in order to substantiate the safe operating conditions of the undermined main working network. Methods. An algorithm for studying the state of the undermined main working network includes: analysis of the texture and mechanical properties of parting rocks; mine instrumental observations of the rock pressure manifestations in the main workings; modeling of the parting state using the finite element method (FEM); calculation and analysis of its stress-strain state (SSS) with prediction of the degree of stope operations influence on possible violations of the requirements to safety rules for the main working network operation. Findings. The texture peculiarities and mechanical properties of lithotypes around the network of main workings, the parting and the zone of future stope operations in the lower seam have been analyzed. The current state of the main workings has been studied and, together with the preliminary analysis, the rock pressure manifestations with an emphasis on the probable stope operations influence in the lower seam are predicted. For the final solution of this issue, the parameters have been substantiated and a geomechanical model of a parting behavior has been developed. Having calculated and analyzed the SSS of parting rocks, the conclusion can be drawn about the possibility of safe operation of the main working network. Originality. New knowledge has been gained about the peculiarities of distributing SSS components in the parting, which are distinguished by its large thickness (about 100 m), but by weak strength properties of all lithotypes without exception, which are further reduced by weakening factors of fracturing, stratification and moisture from a large number of coal seams occurring throughout the height of a parting. To study the state of a parting, for the first time, a spatial geomechanical model has been validated and constructed, taking into account all the elements reflecting mining-technical situation. Practical implications. Based on the analysis of parting SSS, the existence of its stable part with a thickness of about 37 m has been proven, which ensures the absence of the stope operations influence in the lower seam on the state of the main working network of the upper horizon, that is, the safe conditions for their operation have been substantiated. The conducted research is the basis for the development of recommendations for ensuring accident-free operation.

Loads Calculation and Strength Calculation of Landing String during Deepwater Drilling

As an important drilling tool, the landing string will be directly exposed to seawater during surface riserless drilling operations, and it will undergo complex deformation under the action of environmental loads such as ocean currents and waves and the displacement, heave and vibration of the drilling platform. At the same time, with the increase in water depth, the floating weight of drill pipe and casing also increases significantly, and the landing string will bear great tensile loads, which can easily cause accidents. Therefore, in this paper, based on ANSYS software, the finite element analysis models of three stages of the landing string lowering operation were established, and finite element simulations under different combinations of working conditions were carried out. Through theoretical analysis and numerical simulation, the ultimate load and stress distribution of the string under different operating sea conditions were obtained, and the external force requirements for restraining the lateral displacement of the string were proposed according to the existing standards of the industry. Thereby, the recommended safe operating time, safe operating conditions window and the required restraint reaction force of the support mechanism are given for landing string lowering operation throughout the year.

Modern approaches to strength design substantiation for critical elements of WWER NPP reactor internals

This study presents the theoretical and applied results on the development and application of refined models and methods for solving actual problems of mechanics related to the substantiation of strength and forecasting the service life of elements of the primary circuit equipment of WWER nuclear power plants (NPPs). The scientific and applied developments take into account current trends in global practice and contain new conceptual approaches to solving nonlinear boundary value problems in the mechanics of deformed structures. Refined mathematical models have been proposed and theoretically substantiated to describe non-isothermal inelastic deformation processes, taking into account the deformation history of thermal and power loading, radiation effects of hardening, swelling and creep of irradiated metal, and accumulated damage of brittle-ductile fracture. The obtained scientific results are the basis for the methodology of refined design strength analysis and residual life assessment of critical elements of the equipment of the first circuit of WWER reactor units to solve urgent problems of ensuring the conditions for safe operation of Ukrainian NPPs and justifying the terms of their service life extension

EXPANSION OIL WELL CEMENT BASED ON SUBSTANDARD RAW MATERIALS

Grouting cement is a type of Portland cement designed to insulate pipes of oil and gas wells and protect them from groundwater pressure, shifts of ground layers, and the negative effects of aggressive media. When solidified, the cement mortar forms a monolithic jacket, impermeable to liquids and gases. The material adheres firmly to the metal pipe and to the walls of the trunk drilled in the rock. The use of grouting cement creates conditions for safe operation of wells and prolongs their working period. In traditional construction, this type of Portland cement is not used. The exception is the foundation of drilling piles in difficult geological conditions. That's whay, the article presents the investigation of grouting cement with the basis of substandard raw materials.

Characterization of the secondary neutron field inside a cyclotron for production of radiopharmaceuticals

During production of radiopharmaceuticals, the radiation situation in cyclotron pit is an important parameter, which is being monitored to ensure fulfilment of the limits and conditions of safe operation. The neutron flux in the structural components of the accelerator is also an important parameter, because the secondary neutrons are responsible for activation of cyclotron structural components and may even affect structural changes in it. This paper aims to characterize the neutron field in inner positions of medical accelerator IBA 18/9 by activation detectors and by means of scintillation spectrometry. The backward angle measurement was realized also in special liquid water target (H218O) at U120M cyclotron to confirm the data obtained in IBA 18/9 cyclotron.

Analytical Investigation of Surface Temperatures for Different Sized CubeSats at Varying Low Earth Orbits

Abstract Thermal management is a challenging engineering problem for CubeSats due to the limited available volumes restricting the thermal control applications. Therefore, performing thermal modeling and analyses of these small satellites is very crucial for applying proper thermal control measures to maintain safe operating conditions in space. Despite the growing interest in this field, there are still a limited number of studies investigating the thermal behavior of CubeSats. In this paper, surface temperature profiles of 1U, 2U, 3U, 5U, 6U, and 12U sized CubeSats are simulated for varying low earth orbits. The effects of altitudes changing from 400 km to 2000 km and the beta angles changing from 0 to 75 deg are analytically investigated. Not only the coatings with different absorptance and emissivity values but also different amounts of internal heat dissipations are examined to reveal their impact on the thermal balance of satellites. Results demonstrate surface temperatures are highly dependent on those variables. The amount of heat absorbed by satellite panels is affected by the different sizes of CubeSats, different coating properties of panels, and different orbital configurations. The outcomes of this research may be beneficial especially in the early design phase for designing small satellites and selecting proper orbital configurations.

Experience of the examination of industrial safety of structuresof the open flyover of the slag yard of the open-hearth workshop of JSC TAGMET

Industrial safety expertise plays a huge role in preserving buildings and structures and preventing their destruction and undesirable consequences that are inevitable during the operation of damaged structures, especially in buildings with hazardous production or under heavy operating conditions of overhead cranes. Currently, due to the aging and wear of structures, the examination of industrial safety of buildings and structures is becoming increasingly important. Central Research Institute of Building Structures named after V.A. Koucherenko of JSC "SIC "Construction" since 1995 for almost 20 years conducted surveys of the workshops of JSC "Tagmet", giving conclusions on industrial safety and recommendations for repairing and strengthening damaged building structures in order to enable and conditions for further safe operation. The article provides an example of successfully carried out work on the inspection of shop structures, which can be extended to modern practice. The article analyzes the results of a survey of the technical condition of structures, classifies damages and gives recommendations for ensuring the safe operation of structures of an open crane overpass.

Pitting corrosion on highly alloyed stainless steels in dilute sulphuric acid containing sodium chloride

Stainless steels are widely used in industrial assets and equipment. Despite their good corrosion resistance under a wide range of operating conditions, there is the possibility of pitting corrosion in the presence of chlorides. However, very few studies have identified the safe operating conditions for various high-alloyed stainless steel grades by comparing their pitting susceptibility. In this research, the susceptibility to pitting attack of five stainless steels with austenitic and duplex microstructures was examined in dilute sulphuric acid solution with varying amounts of NaCl at the temperatures of 50, 90 and 130°C. Based on potentiodynamic polarization scans, none of the test materials underwent pitting corrosion at 50°C, but differences in susceptibility to pitting attack were clear between the test materials and NaCl concentrations at the temperature of 90°C, and further temperature increase facilitated uniform corrosion. 28-day immersion tests at 90°C confirmed the pitting susceptibility of duplex grades 1.4662 (PREN 33) and 1.4462 (PREN 35) in the presence of at least 2000 mg/L NaCl, but not the susceptibility of a corresponding austenitic grade 1.4539 (PREN 34). The grades 1.4547 (PREN 43) and 1.4410 (PREN 44) were not susceptible to pitting corrosion under any of the studied conditions. The results from materials microstructural and electrochemical characterization are presented and discussed in this paper.

Теория нагружения синтетических рыболовных материалов

An important task of mechanics of synthetic fishing twisted rope and string products and braided cords is to create a fundamental basis for describing their fracture processes during deformation in operation, i.e. to develop a framework for fracture mechanics (building models and algorithms for calculating structures and technological processes at large plastic deformations, taking into account fracture). There is considered the necessity of developing and introducing the simple and at the same time effective criteria of destruction, allowing to estimate reliably the conditions of safe operation of twisted rope and string products, threaded products and braided cords and especially the structures of industrial fishing gear. Determination of stress concentrations, is an obvious task in connection with the creation of new fishing trawls, purse seines and grips with complex shape-changing geometry. This problem is actual for many branches of industry, including transport and machine-building, where at the designing stage it is necessary to take into account possible emergency situations caused by intensive dynamic effects in twisted rope and string, threaded products and braided cords. Components and structures of twisted rope and string products, threaded products and braided cords should withstand the specified loads in a wide range of loading rates. In particular, the theory allows to solve nonlinear problems, taking into account changes in geometry of deformable twisted rope and string products, threaded products and braided cords, as well as to obtain analytical solutions of various problems.

Adaptive Complex Systems Applied in Electrical Submersible Pumps Control

Summary The oil and gas industry uses very expensive electrical submersible pumps (ESPs) to lift oil to the surface. It is common for the ESP to operate with a biphasic gas-liquid flow. However, large amounts of gas inside the pump generate instabilities, such as surges and gas locks. If operated for a long time under such instabilities, the performance of the ESP can decrease significantly, causing premature deterioration, which can lead to heavy losses and even a complete stoppage of production. To reduce the occurrence of this unstable operation, the research presented here proposes an adaptive controller based on the monitoring of the biphase condition. A nonlinear ESP model represents the pump behavior for a variable percentage of the two-phase flow, used by the controller learning complex adaptive technique, which is based on a genetic algorithm to generate a set of rules to keep the ESP in safe operating conditions. At the beginning of the training, the adaptive complex system generated erratic behavior; however, over time, it came to represent more precise rules, bringing performance to stable conditions. Furthermore, if the ESP eventually reaches a harmful condition, the adaptive controller takes action to return it to a safe condition. The result of the simulated tests shows that the complex adaptive controller can acquire enough knowledge after training to keep an ESP working in stable conditions, increasing the life of the production equipment and avoiding sudden stops during oil lifting.

Deep Learning-Based Transformer Moisture Diagnostics Using Long Short-Term Memory Networks

Power transformers play a crucial role in maintaining the stability and reliability of energy systems. Accurate moisture assessment of transformer oil-paper insulation is critical for ensuring safe operating conditions and power transformers’ longevity in large interconnected electrical grids. The moisture can be predicted and quantified by extracting moisture-sensitive dielectric feature parameters. This article suggests a deep learning technique for transformer moisture diagnostics based on long short-term memory (LSTM) networks. The proposed method was tested using a dataset of transformer oil moisture readings, and the analysis revealed that the LSTM network performed well in diagnosing oil insulation moisture. The method’s performance was assessed using various metrics, such as R-squared, mean absolute error, mean squared error, root mean squared error, and mean signed difference. The performance of the proposed model was also compared with linear regression and random forest (RF) models to evaluate its effectiveness. It was determined that the proposed method outperformed traditional methods in terms of accuracy and efficiency. This investigation demonstrates the potential of a deep learning approach for identifying transformer oil insulation moisture with a R2 value of 0.899, thus providing a valuable tool for power system operators to monitor and manage the integrity of their transformer fleet.

Effect of Culverts on the Thermal Regime of a Railway Embankment

A common issue for Canadian railway operators is the development of localized frost heave near railway culverts, which leads to nonuniform deformation of the track surface and degradation of the track geometry, damages the track component, and affects the quality of rides in railway operations. Frequent maintenance including placing wooden shims between rail and ties and often the reduction of train speeds are required to ensure safe operating conditions. Given the future expected climate patterns, freeze–thaw cycles are anticipated to become more frequent, and therefore, a greater understanding of their effect on the changing ground thermal regime under railway embankments is essential. This paper investigates the effects of culverts and insulation layers on changing the temperature regime of the ground during the winter–spring period through numerical modeling in TEMP/W (version 2019) two-dimensional (2D) and three-dimensional (3D) software. The model was calibrated using actual field measurements collected from an instrumented section of the track that has suffered from frost heaves at the proximity of a culvert. Using the results from 2D simulation, the effect of culverts on extending the frost zone, in both horizontal and vertical directions, was quantified. In addition, the effects of shape, installation depth, and the number of culverts on the frost penetration depth were discussed. Using TEMP/W 3D results, the most appropriate configuration to install the culverts was studied to minimize frost penetration.

Cooling performance of an active-passive hybrid composite phase change material (HcPCM) finned heat sink: Constant operating mode

The present study explores a hybrid thermal management technology based on air cooling and hybrid composite phase change material (HcPCM) filled finned heat sink for cooling performance of lower to medium heat flux dissipating electronic devices. Two-dimensional numerical simulations are conducted to study the conjugate heat transfer effects of three types of finned heat sink: air-cooled finned heat sink, HcPCM-cooled finned heat sink, and hybrid (air-HcPCM) cooled finned heat sink. A heat sink with a constant volume faction of plate-fins is designed in all cases and simultaneous effects of hybrid nanoparticles and air are investigated to keep the heat sink temperature at safe operating conditions between 40–60 ∘C. The effect of air is incorporated into the heat sink by applying the convective heat transfer coefficient of hc = 10–100 W/m2.K which tends to create the natural convection and forced convection heat transfer characteristics. The heat flux is varied from 25–40 kW/m2 in the current study. The hybrid nanoparticles of carbon additives (GO and MWCNTs) are dispersed into the RT-35HC, used as a PCM, with a volume fraction of 0% to 6%. Transient simulations are carried out using COMSOL Multiphysics to solve the governing equations for PCM based conjugate heat transfer model. The results showed that forced convection heat transfer improved the cooling performance of the hybrid heat sink compared to natural convection heat transfer. The addition of nanoparticles further enhanced thermal enhancement and uniform melting distribution of PCM inside the finned heat sink. The hc between 30 to 50 W/m2.K shows optimized values for forced convection heat transfer operating conditions. The volume fraction of 2% of GO+MWCNTs nanoparticles in recommended or optimum concentration for uniform melting of PCM inside the finned heat sink.

A Highly Efficient PFC Flyback Converter for Residential Lighting with Universal Input

This paper describes a power-factor-corrected-based flyback converter for low-power domestic lighting. The proposed flyback converter works in a discontinuous-conduction mode (DCM) and provides enhanced power-quality (PQ). In low-power residential lighting, the flyback converter is significantly preferred over non-isolated converters owing to its numerous advantages, such as its low component count, cost-effective solution, and safe operating conditions. The proposed DCM-based flyback converter has a simple circuit configuration and lower total harmonic distortions (THD) of input current by about 15% with an input power factor of around 0.97. A hardware prototype has been developed and examined at different AC source voltages to validate the feasibility and effectiveness of a proposed model. Experimental results show that the whole system efficiency satisfies Energy Star standards with 91.04 percent efficiency at a rated load of 24 Watts and 220 V AC mains and also fulfilled the stringent limits as per IEC61000-3-2 Class D standards.

Development of Deceleration-Based Friction Prediction Models and Methods on Semiprepared Runway Surfaces

Both civilian and military airfield managers require the safe operation of aircraft on runway surfaces. This includes the operation of ground traffic on airfield operating surfaces as well as connecting road infrastructure. Often times in austere environments, this road infrastructure is unpaved and consists mostly of either semiprepared or unbound soils. It has been shown in numerous research efforts that surface friction is an excellent indicator of safe operating conditions. Although a great deal of work has been done to quantify safe surface conditions for landing and takeoff operations on rigid and flexible pavement structures, limited research exists to extend such efforts to soil-based or semiprepared surfaces. The objective of this research was to develop deceleration-based surface friction prediction models on unpaved surfaces with varied moisture conditions and soil types. Surface friction, in this study, was quantified using the Findlay Irvine Mk2-D GripTester. Deceleration was measured using four smartphone inertial measurement units (IMUs), one Bowmonk IMU, and one Xsens IMU. Tests were conducted in three ground vehicles: a high-mobility multipurpose wheeled vehicle, a civilian ½-ton pickup truck, and a civilian full-size sport utility vehicle. The various deceleration-based devices tested here adequately correlated (coefficient of determination >0.6) with Mk2-D GripTester measurements collected on unpaved soil runways. The models and measurement methods detailed here are of considerable use to both semiprepared runway and ground vehicle operations managers around the world needing to measure safe surface conditions following inclement weather.

A New Compressor Failure Prognostic Method Using Nonlinear Observers and a Bayesian Algorithm for Heavy-Duty Gas Turbines

Failure prognostic predicts the remaining useful life (RUL) of machine/components, which will allow timely maintenance and repair leading to continuous reliable and safe operating conditions. In this article, a novel hybrid RUL prediction approach is proposed for heavy-duty gas turbines. Two common failures, namely the fouling in the gas turbine compressor and filter defect, are investigated. First, a discrete wavelet transform (DWT) is applied to real-time measurements to reduce the effect of noise. A parallel structure consisting of a Laguerre filter and neuro-fuzzy is then constructed to identify nonlinear failure dynamics and generate residuals. These residuals are then utilized to estimate the failure severity. Following that, Bayesian theory is employed to predict the RUL. A novel feature of the approach is that the Laguerre filter is designed by using orthogonal basis functions (OBFs), which deliver precise estimates. Another benefit is that the proposed parallel configuration accurately identifies failure dynamics and boosts the RUL prediction performance. Experimental test studies on heavy-duty gas turbines indicate the high efficiency of the proposed RUL estimation in comparison to other failure prognostic strategies.