Computational model for prediction of particle degradation during dilute-phase pneumatic conveying: modeling of dilute-phase pneumatic conveying

A complete model of particle impact degradation during dilute-phase pneumatic conveying is developed, which combines a degradation model, based on the experimental determination of breakage matrices, and a physical model of solids and gas flow in the pipeline. The solids flow in a straight pipe element is represented by a model consisting of two zones: a strand-type flow zone immediately downstream of a bend, followed by a fully suspended flow region after dispersion of the strand. The breakage matrices constructed from data on 90° angle single-impact tests are shown to give a good representation of the degradation occurring in a pipe bend of 90° angle. Numerical results are presented for degradation of granulated sugar in a large scale pneumatic conveyor.     

Research on strength degradation of oil transmission pipeline by third-party damages

The integral strength of the pipeline is badly hurt by drilled holes. Whether the pipeline can work normally after being repaired is in concern. While it is hard to determine the strength degradation of the pipeline by field experiments, that is to say, what is the ultimate pressure that the damaged pipeline can bear after being repaired? Three segments of pipeline will be experimented in this paper; they were directly cut from pipelines. The first was cut from a pipeline which had been in service for about 30 years and the drilled holes had been repaired by welding hats; the second was cut from the same pipeline while the drilled holes had been repaired by welding sheet; the third was cut from a brand new pipeline. Hydraulic pressure tests were performed for these three segments respectively. The test method, test procedure and test results will be fully discussed. Furthermore, FEM analysis was performed for the first and the second segment and results were analyzed in this paper.     

Ensemble learning for predicting degradation under time-varying environment

Product lifetime prediction is challenging when the product is subject to a time-varying operational environment. Most of the existing studies use some functions to explicitly specify the relationship between degradation parameters and environmental conditions so as to reveal how the degradation process evolves over time. However, in many applications, the assumptions needed for establishing these functions cannot be validated in engineering practice or they cannot accurately model the entire underlying degradation mechanism. In contrast to previous work, the focus of our study is placed on product degradation prognosis by implementing an ensemble learning method. This method combines the stochastic process modeling approach and the machine learning approach, taking advantage of these approaches to gain a more accurate and stable degradation prediction. The proposed method is demonstrated by some simulation examples and by a case study of lithium-ion battery accelerated degradation test. Both the simulation study and the real case verify the superiority of the proposed method. The case study indicates that the ensemble learning method can further help to effectively manage the energy storage and energy distribution of battery packs.     

Influence of the valve lubricant on the aerodynamic particle size of a metered dose inhaler

Presented in this work are the results of a study designed to investigate the impact of valve lubricant (i.e., silicone oil) on the aerodynamic particle size distribution (PSD) of a steroid suspension metered dose inhaler (MDI) containing propellant HFA-227. The objective of this study was to explore whether the valve lubricant, which is often used in MDI products to prevent valve sticking, can enter an MDI product and potentially impact the aerosol spray dynamics. The results of this work have shown that samples containing valves with high silicone levels produced a larger aerodynamic particle size (by cascade impaction) than samples with low-silicone or silicone-free valves. It is postulated that the presence of silicone in the product may increase the propensity for drug aggregation, thereby leading to an increase in the aerodynamic particle size of the emitted aerosol. These findings stress the importance of evaluating the effects of valve lubricant on the aerodynamic PSD in the early formulation development stage of an MDI.     

Effect of particle size distribution and subgrade condition on degradation of railway ballast under impact loads

Ballasted rail tracks are generally exposed to impact loads generated from abnormal wheel-rail interface as well as sudden variations in support rigidity. These induced impact loads can lead to railway ballast degradation by attrition of the angular edges of the aggregate and breakage of single particle into finer fragments. In the present study, the degradation of ballast particles under impact loads is investigated by considering various fouling and breakage indices. For this purpose, impact test is conducted on ballast aggregates obtained from different quarries (rock types of basalt, marl, dolomite and trachyte) by varying the gradation of ballast aggregates, impact energy and subgrade type. According to the obtained results, the degradation of ballast specimens under impact loading is less for more broadly-graded ballast. In addition, providing a flexible subgrade as support condition leads to reduction in ballast degradation resulted from diminishing impact energy. Furthermore, the axial strain of ballast specimens reduces with decrease in degradation of aggregates under repeated impact loads.     

Optical turbulence on underwater image degradation in natural environments

It is a well-known fact that the major degradation source on electro-optical imaging underwater is from scattering by particles of various origins and sizes. Recent research indicates that, under certain conditions, the apparent degradation could also be caused by the variations of index of refraction associated with temperature and salinity microstructures in the ocean and lakes. The combined impact has been modeled previously through the simple underwater imaging model. The current study presents the first attempts in quantifying the level of image degradation due to optical turbulence in natural waters in terms of modulation transfer functions using measured turbulence dissipation rates. Image data collected from natural environments during the Skaneateles Optical Turbulence Exercise are presented. Accurate assessments of the turbulence conditions are critical to the model validation and were measured by two instruments to ensure consistency and accuracy. Optical properties of the water column in the field were also measured in coordination with temperature, conductivity, and depth. The results show that optical turbulence degrades the image quality as predicted and on a level comparable to that caused by the particle scattering just above the thermocline. Other contributing elements involving model closure, including temporal and spatial measurement scale differences among sensors and mitigation efforts, are discussed.     

Influence of different sources of microstructural heterogeneity on the degradation of asphalt mixtures

The response and degradation of the hot mix asphalt (HMA) materials used in pavement structures are affected by their inherent heterogeneity. The objective of this work is to study the impact of two different sources of HMA heterogeneity in the uncertainty of the mechanical moisture degradation of HMA. The first source of heterogeneity is the spatial variability of the properties of the bulk fine aggregate matrix (FAM) of the mixture, and the second is the location and shape of the coarse aggregate particles. The heterogeneity of the bulk FAM phase was modelled using a random field technique, while that of the coarse aggregates was accounted for by randomly generating realistic probable sets of aggregate particles. Thus, ‘computational replicates’ of HMA microstructures were generated and subjected to moisture diffusion and mechanical loading using a finite element approach. In the mechanical simulations, a non-linear viscoelastic moisture damage constitutive relationship based on continuum damage mechanics theory was selected to characterise the response of the bulk FAM phase. The results show that conducting computational simulations with realistic HMA microstructures that properly capture the heterogeneity of the material is useful to quantify the mean values and dispersion (i.e. uncertainty) associated with the response and degradation of the mixture. This information, which cannot be easily obtained in the field or in the laboratory due to the difficulty of acquiring a sufficient amount of data, is useful to conduct structural reliability analysis and to predict the life cycle behaviour of the material.     

Dynamic particle analysis for the evaluation of particle degradation during compounding of wood plastic composites

A dynamic image analysis method was applied for particle characterisation to study the effect of different process conditions during twin-screw compounding of WPC. The use of distributions based on different types of quantity is discussed with respect to their sensitivity to reveal the effects of different process conditions on particle degradation. Distributions based on length proved to be most suitable to represent the initially broad length distribution of the particles before processing. Sensitivity was strong enough to show differences in particle size after processing depending on process conditions. Particle size was reduced by more than 97% compared to initial size. Degradation was stronger with increasing wood content and when the screw design contained more mixing elements. The effect of screw speed and feed rate was dependent on filler content and screw design.     

On the role of temperature fluctuations during microstructural degradation of the Cd-Zn eutectic

The purpose of this work was to explore the influence of various types of temperature fluctuations on the microstructural stability of the Cd-Zn eutectic which is treated as a model for certain potential high-temperature, turbine-blade materials. The main conclusion was that the holding period at the highest cycle temperature had a significant, and previously unrecognized, influence upon the rate of microstructural degradation. The mechanism of degradation is discussed and it is noted that considerably more work is needed in this area if such alloys are to fulfill their potential applicability.     

Evaluation of Particle Degradation Due to High-Speed Impacts in a Pneumatic Handling System

Particle degradation can be a significant issue in particulate solids handling and processing, particularly in pneumatic conveying systems, in which high-speed impact is usually the main contributory factor leading to changes in particle size distribution (comparing the material to its virgin state). However, other factors may strongly influence particles breakage as well, such as particle concentrations, bend geometry, and hardness of pipe material. Because of such complex influences, it is often very difficult to predict particle degradation accurately and rapidly for industrial processes. In this article, a general method for evaluating particle degradation due to high-speed impacts is described, in which the breakage properties of particles are quantified using what are known as “breakage matrices.” Rather than a pilot-size test facility, a bench-scale degradation tester has been used. Some advantages of using the bench-scale tester are briefly explored. Experimental determination of adipic acid has been carried out for a range of impact velocities in four particle size categories. Subsequently, particle breakage matrices of adipic acid have been established for these impact velocities. The experimental results show that the “breakage matrices” of particles is an effective and easy method for evaluation of particle degradation due to high-speed impacts. The possibility of the “breakage matrices” approach being applied to a pneumatic conveying system is also explored by a simulation example.     

Analysis of correlated multivariate degradation data in accelerated reliability growth

Modern engineering systems have become increasingly complex and at the same time are expected to be developed faster. To shorten the product development time, organizations commonly conduct accelerated testing on a small number of units to help identify failure modes and assess reliability. Many times design changes are made to mitigate or reduce the likelihood of such failure modes. Since failure-time data are often scarce in reliability growth programs, existing statistical approaches used for predicting the reliability of a system about to enter the field are faced with significant challenges. In this work, a statistical model is proposed to utilize degradation data for system reliability prediction in an accelerated reliability growth program. The model allows the components in the system to have multiple failure modes, each associated with a monotone stochastic degradation process. To take into account unit-to-unit variation, the random effects of degradation parameters are explicitly modeled. Moreover, a mean-degradation-stress relationship is introduced to quantify the effects of different accelerating variables on the degradation processes, and a copula function is utilized to model the dependency among different degradation processes. Both a maximum likelihood (ML) procedure and a Bayesian alternative are developed for parameter estimation in a two-stage process. A numerical study illustrates the use of the proposed model and identifies the cases where the Bayesian method is preferred and where it is better to use the ML alternative.     

Micromechanics based ply level material degradation model for unidirectional composites

The damaged response of a composite lamina depends on various mechanisms that take place at the microlevel, i.e., at the level of the fiber and matrix. The present work focuses on developing a ply level continuum damage model for point-wise stiffness degradation through simplified representation of the microlevel damage. A three dimensional micromechanical analysis of a single cell representative volume element is carried out for various volume fraction, and levels of damage. The model brings out the coupled effect of damage on the effective point-wise ply level stiffness. Further, the numerical results are employed to develop a functional continuum representation of stiffness degradation as a function of the damage parameters and fiber volume fraction perturbations. The micromechanics model is consistent with experimentally observed stiffness degradation, i.e., a strong influence of fiber breakage and fiber matrix debond, and a weak influence of normal cracking of matrix. The proposed model can be considered as an improved version of the widely accepted diffused (meso) damage models, i.e., DML. The study also gives a generalized and consistent definition for the free energy, which can be used for modeling growth of damage.     

An investigation of segregation and mixing in dense phase pneumatic conveying

Pneumatic conveying of bulk materials has become an important technology in many industries: from pharmaceuticals to petro-chemicals and power generation. Particulate segregation has been investigated in many solids handling processes. However, little work has been published on the segregation and mixing in pneumatic conveying pipelines, particularly in dense phase pneumatic conveying. Due to the character of dense phase flow, it is difficult to investigate the segregation in a flowing plug. A sampling device was designed and built to take samples from the pneumatic conveying pipeline after “catching a plug”. Several experiments were conducted over a range of gas–solids flow conditions with 3 mm nylon pellets and 3 mm ballotini as a segregating mixture. Experimental data combined with video footage were analysed to describe the segregation and mixing of solids plugs in pipes. This investigation provides initial research on establishing a segregation index in a flowing plug. A gas–solids two-dimensional mathematical model was developed for plug flow of a nylon-glass particulate mixture in a horizontal pipeline in dense phase pneumatic conveying. The model was developed based on the discrete element method (DEM). The model was used to simulate the motion of particles both in a homogeneous flow and as binary mixtures taking into account the various interactions between gas, particles and pipe wall. For the gas phase, the Navier Stokes equations were integrated by the semi-implicit method for pressure-linked equations (SIMPLE) using the scheme of Patankar employing the staggered grid system. For the particle motion the Newtonian equations of motion of individual particles were integrated, where repulsive and damping forces for particle collision, the gravity force, and the drag force were taken into account. For particle contact, a model with a simple non-linear spring and dash pot model for both normal and tangential components was used. This model employed a mixture of 3 mm pellets and ballotini as virtual materials with properties of nylon and glass. The results from the model are discussed and compared with experimental work and show qualitative agreement. Further modelling and experimental work in key areas is proposed.     

Designing optimal degradation tests via multi-objective genetic algorithms

The experimental determination of the failure time probability distribution of highly reliable components, such as those used in nuclear and aerospace applications, is intrinsically difficult due to the lack, or scarce significance, of failure data which can be collected during the relatively short test periods. A possibility to overcome this difficulty is to resort to the so-called degradation tests, in which measurements of components' degradation are used to infer the failure time distribution. To design such tests, parameters like the number of tests to be run, their frequency and duration, must be set so as to obtain an accurate estimate of the distribution statistics, under the existing limitations of budget. The optimisation problem which results is a non-linear one. In this work, we propose a method, based on multi-objective genetic algorithms for determining the values of the test parameters which optimise both the accuracy in the estimate of the failure time distribution percentiles and the testing costs. The method has been validated on a degradation model of literature.     

On the relevance of electrochemical diffusion for the modeling of degradation of cementitious materials

Reactive solute transport models have been broadly used over the last years to evaluate the durability of cementitious materials because they provide a mechanistic approach to cope with the complex diffusion–reaction phenomena involved in cement and concrete degradation processes. However, most of the numerical models published in the scientific literature use Fick’s law as the constitutive equation for the diffusive transport of dissolved ions, neglecting the electrochemical constraints imposed by the various ionic fluxes, which conspire against the local electroneutrality of the system.In this work, the relevance of electrochemical diffusion and its impact on the nonlinear coupled phenomena concerned by cement degradation were evaluated, on the basis of its influence on the simulation of deterioration of concrete exposed to weak sulfate solutions.Results obtained show that diffusive approaches based on Fick’s law may not be accurate enough for modeling the degradation of cementitious materials since, for the case considered, when ignored, electrochemical interactions in the diffusion process may lead to the inability of reactive transport models to reproduce key phenomena such as gypsum precipitation near the exposed cement surface.     

Experimental and simulation study of the effect of gravity on the solid-liquid two-phase flow and erosion of ball valve

The ball valve is an important control component in the pipeline hydraulic transmission system. Its internal solid-liquid two-phase flow and erosion characteristics have an important effect on the safety and stability of the entire pipeline system. Therefore, the erosion characteristics and positions of the ball valve body, the spool flow channel, and the pipeline surface behind the valve should be accurately predicted to ensure the safety of the pipeline. In this study, the experimental setup of the ball valve was designed. The experimental study on the erosion caused by the solid-liquid two-phase flow on the inner surface of the ball valve was conducted. And the numerical calculation research based on the CFD-DEM simulation method was performed. Results show that the placement of the ball valve has a great effect on the two-phase flow and erosion distribution inside the valve; the surface of the erosion plate will form a corrugated texture under the impact of particles at small openings; the placement method changes from vertical to horizontal due to the change in the direction of gravity. As a result, the particle distribution easily gathers near some wall surfaces to form a protective layer, which reduces the erosion rate.     

Best practice for the assessment of defects in pipelines – Corrosion

Corrosion is a common form of degradation in pipelines that reduces both the static and cyclic strength of a pipeline. In this paper, the best practices for the assessment of corrosion in pipelines are presented. Small scale and full scale tests, theoretical analyses and assessment methods are discussed and best practice in terms of assessment methods are described. The work stems from the results of a joint industry project, documenting the best techniques currently available for the assessment of pipeline defects (such as corrosion, dents, gouges, weld defects, etc.) in a simple and easy-to-use manual, and gives guidance on their use.     

Reliability modeling for competing failure processes considering degradation rate variation under cumulative shock

Most systems experience both random shocks (hard failure) and performance degradation (soft failure) during service span, and the dependence of the two competing failure processes has become a key issue. In this study, a novel dependent competing failure processes (DCFPs) model with a varying degradation rate is proposed. The comprehensive impact of random shocks, especially the effect of cumulative shock, is reasonably considered. Specifically, a shock will cause an abrupt degradation damage, and when the cumulative shock reaches a predefined threshold, the degradation rate will change. An analytical reliability solution is derived under the concept of first hitting time (FHT). Besides, a one-step maximum likelihood estimation method is established by constructing a comprehensive likelihood function. Finally, the reasonability of the closed form reliability solution and the feasibility and effectiveness of the proposed DCFPs modeling methodology are demonstrated by a comparative simulation study.     

Modeling the behavior of natural gas pipeline impacted by falling objects

A numerical approach, based on the finite-element method was established in this paper to simulate impact behavior of buried gas pipeline. A three-dimensional elastic perfectly plastic soil model with plane strain conditions was employed in this analysis. The influence of relative stiffness of pipeline–soil, buried depth of pipeline and impact energy on the stress distribution of buried pipelines was discussed. The analysis results showed that the maximum pipeline stress decreased with the increase of the relative stiffness of pipeline–soil; however, the penetration depth was independent of the relative stiffness of pipeline–soil. Pipeline stress decreased with the increase of buried depths and began to stabilize when the buried depth was more than 3 m. The results of impact load and penetration depth considering the plasticity of soil were much larger than those not considering it. To minimize the discrepancy of results between the current approaches and the actual situation, a new method was put forward to improve the accuracy of the proposed formula computing impact load and penetration depth. The results from the new theoretical method were closer to those from the finite element analysis and tests.     

Probabilistic life analysis of vital components considering multistage degradation under variable working conditions

The lifespan of a mechanical product is related to its working conditions; the product's performance typically shows a multistage degradation pattern throughout its life profile. The performance degradation is generally researched under constant test conditions, while the effects of different working conditions on life are seldom considered. This paper proposes a staged recursive derivation method for the multistage degradation under variable working conditions. The proposed method works by merging measured degradation data with an empirical degradation model. The measured degradation data of a new prototype are utilized to update the staged degradation model based on a Bayesian posterior probability analysis. The staged degradation model is derived stage by stage, and then the probabilistic life of the new prototype is predicted. The degradation data of a machine‐gun barrel are used as a case study to demonstrate and validate the proposed method. The results show that the probabilistic life of the test prototype can be predicted effectively in the case of relatively little measured degradation data at the product development stage. Furthermore, the proposed method appears to be especially suited to mechanical components requiring short test periods or low test costs.