Statistical analysis of high-order Markov dependencies

The paper deals with parsimonious models of integer valued time series. Such models are special cases of high-order Markov chain with a small number of parameters. Two new parsimonious models are presented. The first is Markov chain of order s with r partial connections, and the second model is called Markov chain of conditional order. Theoretical results on probabilistic properties and statistical inferences for these models are given

Optimization of the simulation of stress-assisted hydrogen diffusion for studies of hydrogen embrittlement of notched bars

The stress-strain assisted hydrogen diffusion in metals under variable loading is concerned as a key element of elucidation of hydrogen embrittlement (HE). The suitability of simplified treatments of hydrogen diffusion in notched solids under monotonic loading is addressed comparing various 1D and 2D modeling approaches with the purpose to assess if generated approximate solutions can provide acceptable results along the diffusion depth towards prospective rupture sites, so that quite more expensive simulations may be eluded. For different geometry-and-loading cases, respective time-depth domains are revealed where certain simplified procedures can be fairly suitable to carry out calculations of metal hydrogenation for the purposes of HE analysis and control, while the choice of the optimum strategy for the stress-strain assisted diffusion simulations in notched members is case- and purpose-dependent.Проаналізовано дифузію водню в металах за наявності напружень і деформацій, зумовлених змінними навантаженнями. Шляхом порівняння серії одно- і двовимірних модельних підходів зроблено висновок про можливість застосування спрощених процедур до розв’язування задач про дифузію водню в тілах з вирізами, щоб уникнути громіздких обчислень. Для різних геометрії і навантаження виявлено відповідні області змінних часу і глибини дифузії, за яких деякі спрощені підходи можуть дати прийнятні результати для визначення наводнювання металів. Вибір оптимального шляху вивчення дифузії за впливу напружень і деформацій залежить від конкретної мети моделювання.Проанализирована диффузия водорода в металлах при наличии напряжений и деформаций, вызванных изменяющимися нагружениями. Путем сравнения одно- и двумерных модельных подходов сделан вывод о возможности применения упрощенных процедур к решению задач о диффузии водорода в телах с вырезами, чтобы избежать громоздких вычислений. Для разных геометрии и нагружения выявлены соответствующие области переменных времени и глубины диффузии, когда некоторые упрощенные подходы могут дать приемлемые результаты для определения наводороживания металлов. Выбор оптимального способа изучения диффузии при воздействии напряжений и деформаций зависит от конкретных целей моделирования

Hydrogen embrittlement of cold drawn prestressing steels: the role of the die inlet angle

Cold-drawn prestressing steel wires are susceptible to hydrogen embrittlement (HE) in aggressive environments, and residual stress-strain states generated in wires by the drawing process play the key role there. Correspondingly, alterations of the stress-strain fields due to peculiarities of the drawing procedure affect the serviceability of wires under HE. On the basis of performed numerical simulations of the process of cold drawing with the use of different drawing dies, the paper addresses the effect of the inlet angle of the die on residual stress-strain fields in wires, and derives their consequences for wires hydrogenation and their susceptibility to HE. The reduction of the die inlet angle is shown to be beneficial for the wires performance.Встановлено, що холоднодеформовані сталеві дроти для арматури попередньо напружених залізобетонів чутливі до водневого окрихчення (ВО) в агресивних середовищах. Залишкові напружено-деформовані стани, які утворюються в цих дротах внаслідок холодного волочіння, відіграють при цьому ключову роль. Зміна цих напружено-деформованих станів через особливості процесу волочіння впливає на роботоздатність дротів під час ВО. На основі числового моделювання холодного волочіння з використанням відмінних фільєрів розглянуто дію вхідного кута фільєра на напружено-деформовані стани в дротах і зроблено висновки про наслідки їх впливів на наводнення дротів в агресивному середовищі і схильність до ВО. Показано, що зменшення вхідного кута фільєра волочіння має позитивний вплив на роботоздатність дротів.Установлено, что холоднодеформированные стальные проволоки для арматуры предварительно напряжeнных железобетонов являются чувствительными к водородному охрупчиванию (ВО) в агрессивных средах. Остаточные напряженно-деформированные состояния, которые создаются в этих проволоках вследствие холодного волочения, играют при этом ключевую роль. Изменение этих напряженно-деформированных состояний вследствие особенностей процесса волочения влияет на работоспособность проволок при ВО. На основе численного моделирования холодного волочения с использованием различных фильеров рассмотрено воздействие входного угла фильера на напряженно-деформированые состояния в проволоках и сделаны выводы относительно последствий их влияния на наводороживание проволок в агрессивной среде и склонность к ВО. Показано, что уменьшение входного угла фильера волочения имеет положительное влияние на работоспособность проволок

Numerical analysis of hydrogen-assisted rolling-contact fatigue of wind turbine bearings

Offshore wind parks at locations further from the shore often involve serious difficulties, e.g. the maintenance. The bearings of offshore wind turbines are prone to suffer hydrogen-assisted rolling-contact fatigue (HA-RCF). Three important aspects linked with bearing failures are being extensively researched: (i) rolling contact fatigue (RCF), (ii) influence of carbide particles on fatigue life, and (iii) local microplastic strain accumulation via ratcheting. However, there is no reference related to bearing failure in harsh environment. This way, this paper helps to gain a better understanding of the influence of hydrogen on the service life of offshore wind turbine bearings through a numerical study. So, the widely used RCF ball-on-rod test was simulated by finite element method in order to obtain the stress-strain state inside the bearings during life in service and, from this, to elucidate the potential places where the hydrogen could be more harmful and, therefore, where the bearing material should be improved

О ТЕСТИРОВАНИИ ВЫХОДНЫХ ПОСЛЕДОВАТЕЛЬНОСТЕЙ КРИПТОГРАФИЧЕСКИХ ГЕНЕРАТОРОВ НА ОСНОВЕ ЦЕПЕЙ МАРКОВА УСЛОВНОГО ПОРЯДКА

The paper deals with the Markov chain of conditional order, which is used for statisticaltesting of cryptographic generators. Statistical estimations of model parameters are given. Consistency of the order estimator is proved. Results of computer experiments are presented.Рассматривается цепь Маркова условного порядка, используемая для статистического тес-тирования криптографических генераторов. Приводятся статистические оценки параметров, доказывается состоятельность оценки порядка цепи Маркова. Показываются результаты компьютерных экспериментов для модельных и реальных данных

Fast and slow precipitation responses to individual climate forcers: a PDRMIP multi-model study

Precipitation is expected to respond differently to various drivers of anthropogenic climate change. We present the first results from the Precipitation Driver and Response Model Intercomparison Project (PDRMIP), where nine global climate models have perturbed CO2, CH4, black carbon, sulfate, and solar insolation. We divide the resulting changes to global mean and regional precipitation into fast responses that scale with changes in atmospheric absorption and slow responses scaling with surface temperature change. While the overall features are broadly similar between models, we find significant regional intermodel variability, especially over land. Black carbon stands out as a component that may cause significant model diversity in predicted precipitation change. Processes linked to atmospheric absorption are less consistently modeled than those linked to top-of-atmosphere radiative forcing. We identify a number of land regions where the model ensemble consistently predicts that fast precipitation responses to climate perturbations dominate over the slow, temperature-driven responses

Robust skill of decadal climate predictions

There is a growing need for skilful predictions of climate up to a decade ahead. Decadal climate predictions show high skill for surface temperature, but confidence in forecasts of precipitation and atmospheric circulation is much lower. Recent advances in seasonal and annual prediction show that the signal-to-noise ratio can be too small in climate models, requiring a very large ensemble to extract the predictable signal. Here, we reassess decadal prediction skill using a much larger ensemble than previously available, and reveal significant skill for precipitation over land and atmospheric circulation, in addition to surface temperature. We further propose a more powerful approach than used previously to evaluate the benefit of initialisation with observations, improving our understanding of the sources of skill. Our results show that decadal climate is more predictable than previously thought and will aid society to prepare for, and adapt to, ongoing climate variability and change.D.M.S., A.A.S., N.J.D., L.H. and R.E. were supported by the Met Office Hadley Centre Climate Programme funded by BEIS and Defra and by the European Commission Horizon 2020 EUCP project (GA 776613). L.P.C. was supported by the Spanish MINECO HIATUS (CGL2015-70353-R) project. F.J.D.R. was supported by the H2020 EUCP (GA 776613) and the Spanish MINECO CLINSA (CGL2017-85791-R) projects. W.A. M. and H.P. were supported by the German Ministry of Education and Research (BMBF) under the project MiKlip (grant 01LP1519A). The NCAR contribution was supported by the US National Oceanic and Atmospheric Administration (NOAA) Climate Program Office under Climate Variability and Predictability Program Grant NA13OAR4310138 and by the US National Science Foundation (NSF) Collaborative Research EaSM2 Grant OCE-1243015. The NCAR contribution is also based upon work supported by NCAR, which is a major facility sponsored by the US NSF under Cooperative Agreement No. 1852977. The Community Earth System Model Decadal Prediction Large Ensemble (CESM-DPLE) was generated using computational resources provided by the US National Energy Research Scientific Computing Center, which is supported by the Office of Science of the US Department of Energy under Contract DE-AC02-05CH11231, as well as by an Accelerated Scientific Discovery grant for Cheyenne (https://doi.org/10.5065/D6RX99HX) that was awarded by NCAR’s Computational and Information System Laboratory.Peer ReviewedPostprint (published version

Requirements for a global data infrastructure in support of CMIP6

The World Climate Research Programme (WCRP)’s Working Group on Climate Modelling (WGCM) Infrastructure Panel (WIP) was formed in 2014 in response to the explosive growth in size and complexity of Coupled Model Intercomparison Projects (CMIPs) between CMIP3 (2005–2006) and CMIP5 (2011–2012). This article presents the WIP recommendations for the global data infrastruc- ture needed to support CMIP design, future growth, and evolution. Developed in close coordination with those who build and run the existing infrastructure (the Earth System Grid Federation; ESGF), the recommendations are based on several principles beginning with the need to separate requirements, implementation, and operations. Other im- portant principles include the consideration of the diversity of community needs around data – a data ecosystem – the importance of provenance, the need for automation, and the obligation to measure costs and benefits. This paper concentrates on requirements, recognizing the diversity of communities involved (modelers, analysts, soft- ware developers, and downstream users). Such requirements include the need for scientific reproducibility and account- ability alongside the need to record and track data usage. One key element is to generate a dataset-centric rather than system-centric focus, with an aim to making the infrastruc- ture less prone to systemic failure. With these overarching principles and requirements, the WIP has produced a set of position papers, which are summa- rized in the latter pages of this document. They provide spec- ifications for managing and delivering model output, includ- ing strategies for replication and versioning, licensing, data quality assurance, citation, long-term archiving, and dataset tracking. They also describe a new and more formal approach for specifying what data, and associated metadata, should be saved, which enables future data volumes to be estimated, particularly for well-defined projects such as CMIP6. The paper concludes with a future facing consideration of the global data infrastructure evolution that follows from the blurring of boundaries between climate and weather, and the changing nature of published scientific results in the digital age

Rapid Adjustments Cause Weak Surface Temperature Response to Increased Black Carbon Concentrations

We investigate the climate response to increased concentrations of black carbon (BC), as part of the Precipitation Driver Response Model Intercomparison Project (PDRMIP). A tenfold increase in BC is simulated by nine global coupled‐climate models, producing a model median effective radiative forcing of 0.82 (ranging from 0.41 to 2.91) W m⁻², and a warming of 0.67 (0.16 to 1.66) K globally and 1.24 (0.26 to 4.31) K in the Arctic. A strong positive instantaneous radiative forcing (median of 2.10 W m⁻² based on five of the models) is countered by negative rapid adjustments (−0.64 W m⁻² for the same five models), which dampen the total surface temperature signal. Unlike other drivers of climate change, the response of temperature and cloud profiles to the BC forcing is dominated by rapid adjustments. Low‐level cloud amounts increase for all models, while higher‐level clouds are diminished. The rapid temperature response is particularly strong above 400 hPa, where increased atmospheric stabilization and reduced cloud cover contrast the response pattern of the other drivers. In conclusion, we find that this substantial increase in BC concentrations does have considerable impacts on important aspects of the climate system. However, some of these effects tend to offset one another, leaving a relatively small median global warming of 0.47 K per W m⁻²—about 20% lower than the response to a doubling of CO₂. Translating the tenfold increase in BC to the present‐day impact of anthropogenic BC (given the emissions used in this work) would leave a warming of merely 0.07 K