Failure Of Elements Research Articles

NEW PIDHID UP TO THE MOVEMENT OF FIRE SAFETY WATER SYSTEMS

When obtaining estimates that characterize the level of fire safety of the hydrogen storage and supply system, there is an error due to the subjective nature of its occurrence. It is noted that it is possible to weaken the influence of the subjective nature on these estimates by using the probabilistic characteristics of failure of the main elements of the hydrogen storage and supply system. Such basic elements include a gas generator. It is shown that the diffusion processes between the hydroreactive sample and the liquid - water are accompanied by the appearance of gas bubbles located on the reacting surface. This process - chemical boiling is characterized by internal characteristics. Internal characteristics were obtained experimentally for hydroreactive samples based on sodium aluminum hydride, which are approximated by polynomials of the fourth order and represent the dependence of the diameter of gas bubbles and the generation frequency on the diameter of the reacting surface. It is noted that the characteristics of the gas generator depend on the orientation of the reacting surfaces of the hydroreactive sample. The growth rate of basic bubbles practically does not depend on the diameter of the reacting surface, and the size of this surface for the vertical arrangement of the reacting surface is several percent larger than for its horizontal arrangement. The most unfavorable mode of gas generation is the case when the reactive surface of the hydro-reactive sample is oriented downwards. It is shown that increasing the reliability of the gas generator of the hydrogen storage and supply system is possible due to the implementation of a hydroreactive sample with a polylike one - a passive method and due to the formation of hydrodynamic forces acting on gas bubbles - an active method. These recommendations are embodied on the example of a hydrogen storage and supply system with vibrational movement of a hydroreactive sample, which is made in the form of a set of identical long cylinders assembled in a mesh cassette. Keywords: water saving and supply system, gas generator, fire safety, reliability.

Influence analysis of the connective elements failures on the road bridges steel reinforced superstructures service reliability

The paper considers the influence issues of connective elements failures, in particular flexible pin stops, on the road bridges steel reinforced superstructures service reliability. The authors have formulated possible criteria for the superstructure failure both for the first and the second groups of limit states, and also developed scenarios of connective elements exclusion from the structures operation, that are modeling the failure of individual connective elements in the operation process. For five finite element models of road bridges steel reinforced superstructures a numerical experiment on modeling of the connective elements exclusion from the operation of the structure was carried out. The calculation results for each scenario and for the partial scenario realization levels were analyzed in terms of possible superstructures failures as a whole. Numerical experiment results have shown that at the exclusion of a separate small group of connective elements increases the maximum stresses in the over-supported beams sections by up to 3 %, and further development of the connective elements disconnection scenario can lead to an increase in stresses by 20 %. It is concluded that for existing steel reinforced superstructures the risk of superstructures failure under normal operating conditions due to disconnection of connective elements is low, even in the case of almost unlikely complete disconnection of all connective elements. Nevertheless, the exclusion from operation of connective elements may be more critical in cases of abnormal bridge structure operation or in cases of significantly lower engineering reserves of the structure in terms of strength and stiffness.

Preventing failure propagation in steel truss bridges

AbstractMetal and steel truss bridges are essential for transportation networks worldwide but are vulnerable to collapse due to deterioration and increasing traffic loads, particularly for ageing structures. Several bridge collapses, such as the Seongsu bridge (South Korea, 1994), I‐35 bridge (USA, 2007), and Chauras bridge (India, 2012), have highlighted the need to develop accurate robustness assessment strategies and efficient mitigation of collapse risks. This paper summarizes results of experimental and computational studies for a steel riveted bridge with a truss‐type structure. The experimental component presented involves unique tests to be performed on a 21 m full‐scale bridge span subjected to the failure of different elements under laboratory conditions. The paper then presents a first approach to explore different damage and failure scenarios for steel truss bridges, which will assist in defining data collection strategies for optimised monitoring and developing data analysis methods for real‐time diagnosis of ageing bridges. With this, the paper contributes to avoiding progressive collapses and presents a framework, developed as part of an ongoing project, to identify vulnerable zones for prioritising monitoring systems that anticipate failure propagation and prevent collapse. The framework is based on a systematic analysis of past bridge failures and simulations of carefully designed generic cases.

Метод синтеза антенной решетки со сниженным уровнем боковых лепестков при наличии отказов каналов и модулей

A method of matrix amplitude-phase synthesis of a flat antenna array with module failures according to the requirements for the envelope of the side lobes is proposed. The problem is reduced to finding the extremum of the Rayleigh ratio of two Hermitian forms, one of which takes into account the requirements for the envelope of the side lobes and is positively determined. The proposed method differs from the known ones by an iterative procedure for searching for a weight function for the formation of integral coefficients of a positive-definite Hermitian matrix of the Rayleigh relation. In the proposed method, failure accounting is carried out using two identical diagonal matrices, single values of these matrices correspond to serviceable elements, and zero – faulty ones. The condition of positive definiteness of the quadratic form, taking into account the requirements for the envelope of the side lobes, is achieved by weighing the diagonal coefficients of the matrix. As a result, when changing the structure of failures of elements and modules of the antenna array, it is not necessary to adjust the dimension of the problem. It is shown that in the presence of module failures, the level of the side lobes of the volumetric directional pattern increases significantly. At the same time, the use of conventional weight signal processing of antenna array channels with a reduced level of side lobes leads to a loss of power of the signal component at the output of the antenna array with a slight decrease in the level of side lobes. It has been found that the application of the proposed method makes it possible to achieve a noticeable decrease in the level of side lobes with controllable losses of the signal-to-noise ratio at the output of the antenna array.

Element Failure Risk Assessment of Soil Slope

Element Failure Risk Assessment of Soil Slope

Robust Interval Prediction of Intermittent Demand for Spare Parts Based on Tensor Optimization.

Demand for spare parts, which is triggered by element failure, project schedule and reliability demand, etc., is a kind of sensing data to the aftermarket service of large manufacturing enterprises. Prediction of the demand for spare parts plays a crucial role in inventory management and lifecycle quality management for the aftermarket service of large-scale manufacturing enterprises. In real-life applications, however, demand for spare parts occurs randomly and fluctuates greatly, and the demand sequence shows obvious intermittent distribution characteristics. Additionally, due to factors such as reporting mistakes made by personnel or environmental changes, the actual data of the demand for spare parts are prone to abnormal variations. It is thus hard to capture the evolutional pattern of the demand for spare parts by traditional time series forecasting methods. The reliability of prediction results is also reduced. To address these concerns, this paper proposes a tensor optimization-based robust interval prediction method of intermittent time series for the aftersales demand for spare parts. First, using the advantages of tensor decomposition to effectively mine intrinsic information from raw data, a sequence-smoothing network based on tensor decomposition and a stacked autoencoder is proposed. Tucker decomposition is applied to the hidden features of the encoder, and the obtained core tensor is reconstructed through the decoder, thus allowing us to smooth outliers in the original demand sequence. An alternating optimization algorithm is further designed to find the optimal sequence feature representation and tensor decomposition factors for the extraction of the evolutionary trend of the intermittent series. Second, an adaptive interval prediction algorithm with a dynamic update mechanism is designed to obtain point prediction values and prediction intervals for the demand sequence, thereby improving the reliability of the forecast. The proposed method is validated using the actual aftersales data from a large engineering manufacturing enterprise in China. The experimental results demonstrate that, compared with typical time series prediction methods, the proposed method can effectively grab the evolutionary trend of various intermittent series and improve the accuracy of predictions made with small-sample intermittent series. Moreover, the proposed method provides a reliable elastic prediction interval when distortion occurs in the prediction results, offering a new solution for intelligent planning decisions related to spare parts in practical maintenance.

Analiza awarii podczas eksploatacji podmorskich złóż ropy i gazu

Failures caused by offshore oil and gas structures operations are investigated. This work is based on the description and analysis of real case studies of accidents on offshore stationary and floating platforms; it combines foundational knowledge and current research on the latest developments in the field. It was shown that strength characteristics of offshore reinforced concrete and steel elements change during operation and cause the accumulation of defects and damages. It was established that corrosive wear, corrosion-mechanical processes, and crack-like defects are the decisive causes of element failure. It was shown that up to 60–75% of all damages to and failures of offshore engineering facilities' steel structures occur due to the corrosion-mechanical influence of an aggressive environment and force loads. This means that issues of corrosion-mechanical failure of such structures have become an industrial-scale problem. It thus allows us to draw the following conclusions: improvement of steel offshore drilling platforms (ODPs) maintenance system involves the development of new models and methods of managing the operational reliability of these structures, aimed at making decisions that take into account the crack resistance and fatigue-corrosion strength of steel ODPs in contact with the corrosive-active environment. Only on the basis of such scientifically and economically grounded models can rational strategies be shaped for carrying out revisions of the ODPs technical condition, ensuring the necessary level of their reliability during the operation period. This investigation can be very helpful to improve the design and construction of more reliable and durable offshore stationary and floating platforms.

Numerical Analysis of Cyclic Impact Damage Evolution of Rock Materials under Confining Pressure

To study the effect of cyclic impacts and confining pressure on the damage evolution of rock materials, numerical simulations of cyclic impact tests on rock materials under confining pressure were carried out by LS-DYNA using dynamic relaxation and full restart analysis. The static confining pressure was applied by dynamic relaxation, and cyclic impacts were realized by full restart analysis. As the crack generation and propagation result in the failure of elements in the finite element model, the damage variable defined by the crack density method was characterized by volume reduction. Numerical simulation indicates that both the confining pressure and amplitude of incident stress waves significantly affect the damage evolution of rock materials. High incident stress waves lead to severe damage, while large confining pressure results in minor damage. Under confining pressure, the damage to rock materials is alleviated due to the constraint effect on crack propagation. The number of cyclic impacts before macroscopic fracture increases as the confining pressure increases and decreases when the amplitude of the incident stress waves increases. The cumulative damage of rock materials under confining pressure progressively increases with the number of cyclic impacts, and the damage evolution exhibits three distinct stages: rapid rising, steady development, and sharp rising.

Simulation of blast propagation and structural effects of accidental hydrogen-air-mixture explosion in a two-stage light-gas gun laboratory for hypervelocity impact experiments

Two-stage light-gas guns allow to accelerate projectiles up to velocities of several kilometers per second to conduct impact experiments. The projectile acceleration is obtained through a mechanism that relies on the expansion of a light gas, such as helium or hydrogen. Hydrogen allows to employ higher projectile velocities and masses than helium, together with lower wear of the launch tube. However, its use requires a thorough assessment of potential risks of explosion. In this work, we present a combined blast and structural numerical analysis to evaluate the effects of hydrogen deflagration as a consequence of accidental leakage scenarios during the operation of a two-stage light-gas gun. As a test case, we study the Large Gun operated at Fraunhofer EMI in Freiburg, Germany. The possible failure of non-structural elements, such as doors and windows, and the subsequent blast propagation into areas adjacent to the room hosting the facility are also accounted for. The simulation procedure presented in this work is scalable to similar and larger facilities for impact research as well as to other contexts involving analogous risks of gas explosions.

Strategies for improving resilience of regional integrated energy systems in the prevention–resistance phase of integration

The construction of integrated energy systems can help improve energy efficiency and promote global energy transition. However, in recent years, the occurrence of extreme natural disasters has brought certain threats to the safe and stable operation of the integrated energy system. Thus, it is necessary to improve the ability of the integrated energy system to resist disasters, reduce disaster losses, and restore energy supply as soon as possible, i.e., improve its resilience. Considering the influence of pre-disaster prevention measures and disaster-time operational measures on system disaster resilience and the correlation between the two, this paper proposes a system hardening strategy based on three-layer robust optimization. The upper layer formulates the optimal hardening strategy of the system before the disaster event occurs, the middle layer identifies the failed elements in the worst disaster situation, while the lower layer realizes the system operational optimization by coordinating the energy storage charging and discharging plan of each subsystem. The strategy can reduce the total supply shortage of the integrated energy system and improve the flexibility of the system in the pre-disaster prevention and disaster resistance integration stages.

Complex System Reliability Analysis using a Model‐Based Shared Systems Simulation

AbstractThe continued growth of system complexity is challenging traditional qualitative, heuristics‐based approaches to architecting system emergence. As these emergent attributes are products of the architecture and established early in the system development lifecycle, where ambiguity is most pronounced, a shift to a model‐based approach is viewed as essential to understanding system interdependencies and the impacts of tradeoff decisions. This paper discusses how model‐based systems engineering methods and a coupled architecture‐simulation can be used to model system reliability. Employing a probabilistic model of system element failure, the coupled simulation is shown to predict system reliability for various architecture configurations early in the system design process. The advantages this quantitative system performance assessment provide to stakeholder decision‐making are reviewed, and the simulation model is extended to demonstrate how the complexity‐resilience tradeoff can impact system reliability.

Research of frogs point wear resistance in various conditions for transportation systems: main-line railway and subway

The experience of operating switches shows that load-bearing elements fail for two main reasons: defects and wear. The percentage failure of elements due to one reason or another depends on the operating conditions in which they operate. In this case, the most worn elements of switches are pointers and point frogs and their service life is determined by the amount of tonnage passed through them before reaching the standard values of wear or the appearance defects. The article is devoted to the study of wear resistance of switches operated in various transport systems, namely, mainline transport and subways. The article considers the issues of predicting the standard service life cross elements of typical angles using operational studies for subway conditions and a new theoretical methodology based on the analysis of switches withdrawn from operation after they reach the standard wear values for mainline transport. For analytical calculations, the method of modeling the interaction process and graph-analytical methods were used. As a result of the study, the analytical equations predictive curves for the formation vertical wear as a function of the passed tonnage for the switches point frogs operated on lines of mainline railway transport and the Kyiv subway were established.

Wear and Subsurface Stress Evolution in a Half-Space under Cyclic Flat-Punch Indentation

Wear is a tremendously important phenomenon, which takes place on the surfaces of two solids in contact under cyclic loads and constitutes one of the most-significant ways of failure for mechanical elements. However, it is not the only source of failure in contacting solids. The subsurface stresses should also be considered, due to the fatigue and crack initiation problems. Nevertheless, these stresses (i.e., their maximum values and distributions) evolve with the solids’ surface wear (i.e., with the load cycles) and also depend on the friction intensity. Therefore, their evolution should be properly computed to predict failures in mechanical elements under wear conditions. This work focused on the study of the evolution of the surface wear and the subsurface stress distributions generated—in an elastic half-space—by a cylindrical flat-ended punch, under cyclic indentation loading (i.e., radial fretting wear conditions). Based on a numerical scheme recently presented by the authors, this is the first time that, for this contact problem, the surface wear and subsurface stress distribution (i.e., maximum value and its location)—and its evolution—were simultaneously analyzed when orthotropic friction and fretting wear conditions were considered. The studies presented in this work were developed for purely elastic contact assumptions.

Joint Optimization of Condition-Based Maintenance and Performance Control for Linear Multi-State Consecutively Connected Systems

Industrial systems such as signal relay stations and oil pipeline systems can be modeled as linear multi-state consecutively connected systems, which comprise sequentially ordered elements and fail if the first and the final elements are not connected. The performance level of each element is controllable, which determines how many elements an element can connect and affects its degradation rate. Accumulated degradation can cause element failure, which may lead to costly system failure. This paper aims to minimize long-term maintenance-related costs, including system failure costs. We provide optimal maintenance planning and performance control for every system degradation state through Markov decision process modeling and a dynamic programming algorithm. Load-sharing, restricted maintenance capacity, maintenance setup costs, and the structural characteristics of the system are considered in the model, all of which influence the optimal maintenance and performance control policy. Regarding degradation management, reducing the difference in degradation levels between elements, e.g., replacing more-degraded elements first, can be cost-effective. However, increasing the difference in degradation by maintenance or performance control can also lower maintenance-related costs in specific situations, which is discussed in numerical experiments. We also illustrate structural insights regarding the proposed model, including sensitivity analyses of maintenance capacity, setup costs, and the difference between preventive and corrective replacement costs.

Assessment of efficiency improvement reserves of maintenance and repair systems of high-voltage electrical equipment of industrial enterprises

The problems of choosing a strategy for the maintenance of the equipment of the power supply system of an industrial enterprise, taking into account the risk its failure and the problem of distributing the volume of the repair program in order to reduce maintenance costs and, accordingly, the cost of production, are considered. A method for assessing the magnitude of risk for the technological process of an industrial enterprise of the metallurgical industry, taking into account the power supply scheme of the electric receiver, is proposed. Special attention is paid to taking into account the influence of the power supply system of an industrial enterprise on the operation of final electrical receivers directly involved in the technological process. An example of using the proposed technique in a real power supply system with available statistical data on its failures is considered. The article formulates an approach to assessing the risk of failure of elements of the power supply network of an industrial enterprise, taking into account the operational scheme of power supply, and also shows the insufficiency of assessing the risk of power supply failures only from the failure of circuit elements through which electric power is directly transmitted to the electric receiver in question.

An approach to detecting anomalies in a self-similar network traffic

Aim. The effects of cyber attacks cause failures of network elements, theft of information and other unlawful actions. Cyber attacks are often accompanied by untypical traffic activity and anomalies. The paper aims to develop an approach to detecting anomalies in network traffic by identifying the degree of self-similarity of the traffic using fractal analysis and statistical methods. Methods. The paper uses methods of mathematical statistics, mathematical analysis, fractal analysis. Results. The paper suggests an approach to identifying anomalies in network traffic by evaluating self-similarity and using statistical methods for improving the accuracy of cyber attack detection. At the first stage, the Hurst exponent is calculated for the reference traffic. At the second stage, actual traffic is divided into optimal time intervals; for each interval, the Hurst exponent is calculated. If the identified value of the Hurst exponent differs from the one obtained for the reference traffic, it is decided that there is an anomaly. At the final stage, statistical analysis is used in order to precisely localise the anomaly. The authors analysed fractal and statistical methods that resulted in the identification of more efficient methods to be used as part of the proposed approach. For fractal analysis, the DFA method was proposed, while for statistical analysis, the ARFIMA method was proposed. Conclusion. The suggested approach allows identifying cyber attacks in real time or near-real time.

On a problem of calculating a set of spare parts that have two types of failures

Aim. The paper, that continues [24], aims to develop an algorithm that would allow finding the required number of spare items (SPTA) for a complex system, whose elements may or may not be maintainable. Unlike in [24], as a generalisation, the paper introduces additional inoperable states. Those states are characterised by system downtime associated with the replacement of a failed element with an element from the SPTA. If the time of replacement of a failed element is not a negligibly small value as compared to other time indices of the serviced system, it becomes necessary, as suggested, to account for additional inoperable states. Methods. Markov models are used for describing the technical system under consideration. The final probabilities were obtained using a developed system of Kolmogorov equations. A stationary solution was obtained for the system of Kolmogorov equations. Classical methods of the probability theory and mathematical theory of dependability, some special functions were used. Conclusions. The paper formalizes the problem of determining the required number of SPTAs for a system with items that may fail at a random moment in time. The failures may be of two types. The first type of failures leaves an item in an inoperable repairable state. In this case, the item can be repaired in the maintenance unit of the company that operates such item. The second type of failures, a more catastrophic one, leaves the item in an inoperable non-repairable state, and it can be repaired only by the manufacturer or a specialized maintenance company. A Markov graph was built for the respective birth and death process. Equations were formalised for typical states of the Markov graph. A stationary solution was obtained for the system of Kolmogorov equations using induction. The theorem of general solution was proven for all the states of the Markov graph. In case of unlimited repair, the solution is significantly simplified. It was shown that, on an assumption of unlimited repair and momentary replacements, the solution matches the one earlier obtained in a simplified form in [24]. The limit values of the probabilities of inoperable critical and non-critical states were found. They allow concluding that, in case of unlimited repair, the growth of the size of SPTA causes the probability of a critical state of insufficient SPTA to tend to and become zero. Additionally, the probability of an inoperable state associated with the replacement of a failed item with an equivalent from the SPTA that takes a certain time is defined by a stationary unavailability of the alternating repair process. The general solution of the problem allows formalising the SPTA sufficiency coefficient. The required number of SPTAs is identified by progressively increasing the number of SPTAs until the probability of inoperable critical states is below the defined probability of SPTA shortage. An example of finding the required number of SPTAs is given

Behaviour of masonry walls reinforced by fiber reinforced polymers

Masonry structures revealed their vulnerability to seismic loads through the damage sustained during the earthquake. Consequently, a problem with load transmission has arisen due to the failure of structural elements. To address this issue, various studies have been conducted to explore reinforcement or repair solutions aimed at enhancing the stability of damaged elements by increasing their resistance. Reinforcing a structure consists in improving the mechanical characteristics of the different elements that compose it. Choosing the accurate fiber reinforced polymers (FRPs) configuration to reinforce masonry walls increase the adhesion between the fiber reinforced polymer (FRP) and the wall subjected to the diagonal compression. The reinforcement system performance is mainly related to the quality of the adhesion between the masonry base and the material used for reinforcement. The assessment of the bonding quality is important and allows measurement of the tensile adhesion of FRP composites.

Experimental and numerical investigation of the damage characteristics of a ship side plate laterally punched by a scaled raked bow indenter

Experimental and numerical simulation studies are conducted on a scaled ship side-shell quasi-statically punched at the mid-span by a raked bow indenter to investigate its damage characteristics from deformation to a large opening. A scaled stiffened panel and a raked bow indenter are designed in model tests. Numerical simulation is performed to simulate the indentation responses. The experimental and numerical results are compared well in terms of resistance-penetration curves, final damage shapes and especially the three failure models, i.e., initial fracture, model “I” crack and model “III” crack. In addition, the whole damage process, the energy dissipation characteristics of the specimen and failure related parameters in three specific failed elements corresponding to the three failure models are analyzed through numerical simulation. The results demonstrate that the energy dissipated by the stiffener and frictional effect is substantial during the crack propagation process. In addition, shell elements involved with three failure models prior to fracture are mainly subjected to tension and bending effects, as shell elements cannot satisfactorily simulate the transverse shear effect. Finally, the influences of collision parameters, the failure sequence of integration points, modeling of weld seams, mesh resolution and failure criteria on the numerical simulation results are discussed.

Effect of stress triaxiality cut-off value in the fracture criterion on predicting the ballistic behavior of Al2024-T351 plate impacted by blunt- hemisphere- and ogival-nosed projectiles

Finite element analysis has been carried out to study the effect of stress triaxiality cut-off value in the fracture criterion on the ballistic behavior of 9.94 mm thick Al2024-T351 plates impacted by rigid blunt-, hemisphere- and ogival-nosed projectiles. The plastic and fracture behavior of plates are described by a modified Johnson-Cook (MJC) model and our recently proposed DF2021 criterion, which are implemented into ABAQUS/Explicit finite element code with VUMAT subroutine. The stress triaxiality cut-off parameter in the DF2021 criterion is varied as 0.0, 0.1, 0.2, 0.3, 0.4, and 0.5 with a larger stress triaxiality cut-off parameter corresponding to a lower stress triaxiality cut-off value. The effect of stress triaxiality cut-off values on the ballistic behavior of the targets against three different nose-shaped projectiles is evaluated and compared in terms of ballistic limit velocities, residual velocities, and failure patterns in the impact process. It is observed that the ballistic limit velocity increases with the stress triaxiality cut-off value under the impact of blunt-nosed projectiles while it first decreases and then increases with the stress triaxiality cut-off value under the impact of the hemisphere- and ogival-nosed projectiles. The formed shear plug or fragments exhibit different profiles with variations of the stress triaxiality cut-off value under the impact of hemisphere- and ogival-nosed projectiles, but uniformly exhibit a cylinder shape under the impact of blunt-nosed projectiles. The numerical results are compared with available experiments. It is found that the predictions from the DF2021 criterion with a cut-off parameter of 0.1 have the best agreement with the experiments. The reason causing the difference in the ballistic behavior due to the change of stress triaxiality cut-off value is discussed by analyzing the stress states of failed elements and the energy dissipation. The objective of the study is to evaluate the necessity of considering the stress triaxiality cut-off value in a fracture criterion in predicting ballistic behavior through finite element simulations.