Turbulent Events Research Articles

Dissipation-range fluid turbulence and thermal noise.

We revisit the issue of whether thermal fluctuations are relevant for incompressible fluid turbulence and estimate the scale at which they become important. As anticipated by Betchov in a prescient series of works more than six decades ago, this scale is about equal to the Kolmogorov length, even though that is several orders of magnitude above the mean free path. This result implies that the deterministic version of the incompressible Navier-Stokes equationis inadequate to describe the dissipation range of turbulence in molecular fluids. Within this range, the fluctuating hydrodynamics equationof Landau and Lifschitz is more appropriate. In particular, our analysis implies that both the exponentially decaying energy spectrum and the far-dissipation-range intermittency predicted by Kraichnan for deterministic Navier-Stokes will be generally replaced by Gaussian thermal equipartition at scales just below the Kolmogorov length. Stochastic shell model simulations at high Reynolds numbers verify our theoretical predictions and reveal furthermore that inertial-range intermittency can propagate deep into the dissipation range, leading to large fluctuations in the equipartition length scale. We explain the failure of previous scaling arguments for the validity of deterministic Navier-Stokes equationsat any Reynolds number and we provide a mathematical interpretation and physical justification of the fluctuating Navier-Stokes equation as an "effective field theory" valid below some high-wave-number cutoff Λ, rather than as a continuum stochastic partial differential equation. At Reynolds number around a million, comparable to that in Earth's atmospheric boundary layer, the strongest turbulent excitations observed in our simulation penetrate down to a length scale of about eight microns, still two orders of magnitude greater than the mean free path of air. However, for longer observation times or for higher Reynolds numbers, more extreme turbulent events could lead to a local breakdown of fluctuating hydrodynamics.

Robust Portfolio Optimization based on Evidence Theory

During the past few years, there have been some turbulent events in the world's economy, which have significantly influenced the performance of companies. Therefore, there is an urgent need to use a robust method to handle the existing uncertainties on the performance of the companies. This paper uses Evidence Theory (ET) to present an innovative and practical approach to consider the experts’ opinions which are based on the available evidence regarding the factors that influence the stock market. Subsequently, the study proposes a way to determine the changes in these factors from possible scenarios on historical data to find the return range of different investment alters to be used in robust optimization. Moreover, in a case study, the study examined the sensitivity of the Iranian capital market to exchange rate fluctuations under different scenarios which were due to the lack of a unified view of that rate’s value among experts as one of the mentioned factors. The preliminary results of a real-life case study reveal that the submitted approach is productive and practically useful.

Effect of inclined angle on a wall-mounted finite-height square cylinder with a passive vertical suction

Drilling a vertical cavity from the bottom to the free-end surface has been a passive method of controlling wake flow around a wall-mounted square cylinder. The mean flow field around a wall-mounted finite-height square cylinder with a vertical rectangular cavity was studied experimentally in a water tunnel to explore the effects of inclined angle α. Measurements were conducted using an acoustic Doppler velocimeter at the Reynolds number of Reh = 17,525, in which the incidence angles of the cylinder were α = 0, 10°, 30°, and 45°. Results depict the presence of a recirculation zone in the cavity and a near-wake zone. As α increases from 0 to 10°, the mean wake behind the cylinder shifts in the opposite position, and a single peak is observed. When α changes from 10° to 45°, the mean wake regains its symmetry, and two peaks are observed at the wake. Self-similarity in terms of the streamwise velocities and Reynolds shear stress can be achieved by properly selecting the velocity and length scales irrespective of the angle of incidence. For the wake flow with a higher value of α, the length of the mean recirculation zone, momentum exchange, and turbulence kinetic energy increase, whereas the mean and variance values of the vortex shedding frequency reach a smaller one. In this study, the cavity flow and wake flow are also observed in terms of velocity distribution, turbulent kinetic energy budget, and turbulent events.

Remaining mission-focused amid both turbulence and transition.

In Brief Preface to the 2022 Military Supplement. We review the turbulent events of the past year–withdrawal from Afghanistan and the war in Ukraine–and reflect on transitions in the MHS and beyond.

Female Public Employees during a Post-Imperial Transition: Gender, Politics and Labour in Fiume after the First World War

After the demise of the Habsburg Empire in 1918, Fiume's long political transition provided women with new challenges and opportunities. This was especially true for female public employees who had to adapt to a weak and fluid state that provided them with social security and benefits in exchange for loyalty and control. Beginning with two case studies of women elected to the Fiume city council in 1919, this paper explores how the two professional cohorts they represented – teachers and tobacco workers – learned to cope with the turbulent national and political events, as well as with the rapidly deteriorating economic conditions.

Extreme events in transitional turbulence.

Transitional localized turbulence in shear flows is known to either decay to an absorbing laminar state or to proliferate via splitting. The average passage times from one state to the other depend super-exponentially on the Reynolds number and lead to a crossing Reynolds number above which proliferation is more likely than decay. In this paper, we apply a rare-event algorithm, Adaptative Multilevel Splitting, to the deterministic Navier-Stokes equations to study transition paths and estimate large passage times in channel flow more efficiently than direct simulations. We establish a connection with extreme value distributions and show that transition between states is mediated by a regime that is self-similar with the Reynolds number. The super-exponential variation of the passage times is linked to the Reynolds number dependence of the parameters of the extreme value distribution. Finally, motivated by instantons from Large Deviation theory, we show that decay or splitting events approach a most-probable pathway. This article is part of the theme issue 'Mathematical problems in physical fluid dynamics (part 2)'.

Large-Eddy and Flight Simulations of a Clear-Air Turbulence Event over Tokyo on 16 December 2014

Abstract In this study, a clear-air turbulence event was reproduced using a high-resolution (250 m) large-eddy simulation in the Weather Research and Forecasting (WRF) Model, and the resulting wind field was used in a flight simulation to estimate the vertical acceleration changes experienced by an aircraft. Conditions were simulated for 16 December 2014 when many intense turbulence encounters (and one accident) associated with an extratropical cyclone were reported over the Tokyo area. Based on observations and the WRF simulation, the turbulence was attributed to shear-layer instability near the jet stream axis. Simulation results confirmed the existence of the instability, which led to horizontal vortices with an amplitude of vertical velocity from +20 to −12 m s−1. The maximum eddy dissipation rate was estimated to be over 0.7, which suggested that the model reproduced turbulence conditions likely to cause strong shaking in large-size aircraft. A flight simulator based on aircraft equations of motion estimated vertical acceleration changes of +1.57 to +0.08 G on a Boeing 777-class aircraft. Although the simulated amplitudes of the vertical acceleration changes were smaller than those reported in the accident (+1.8 to −0.88 G), the model successfully reproduced aircraft motion using a combination of atmospheric and flight simulations.

A network intervention for natural resource management in the context of climate change

As climate change impacts the Great Lakes region, the increased frequency and intensity of precipitation events are dramatically increasing the erosive effects of stormwater in the ravine ecosystem. Because formal governance structures may not be effective in providing coordination during turbulent and dynamic events, those seeking to manage natural resources during climate change may turn to resources located in their social networks. In this study network analysis was used to visualize collegial ties and self-reported consideration of climate change among those managing ravines along southwestern Lake Michigan. Professional development then leveraged the visualizations to modify the network, potentially increasing knowledge flows and coordination. Those who were targeted by the intervention increased their engagement in the network and contributed to bridging between subgroups to fill structural holes. This provides insight into the potential for interventions that leverage baseline network analysis for the management of natural resources in the context of climate change.

Overturning Instabilities Across a Warm Core Ring From Glider Observations

AbstractThis work presents new evidence for conducive conditions for the existence of overturning instabilities in the mixed layer across a mesoscale anticyclonic Loop Current Eddy (LCE) and surrounding cyclonic eddies in the Gulf of Mexico (GoM). The LCE was intensively sampled using four gliders during 12 months. The LCE is characterized by a strong anomaly of fresh and warm water in the center and strong strain at the periphery. Mixed layers prone to overturning instabilities are diagnosed from the gradients of buoyancy. In the GoM, the reduction of potential vorticity (PV) in the mixed layer is driven by surface cooling by year‐round persistent negative turbulent heat fluxes, eventually reaching −700 W m−2 during extreme winter wind events. Lateral buoyancy gradients associated with submesoscale filaments and fronts at the periphery of the LCE enhance the frictional torque supplied by the wind stress when aligned with the geostrophic jet current. Negative PV in the mixed layer occurs simultaneously with negative turbulent heat fluxes and events of Ekman buoyancy fluxes that reduce the stratification. These regions are susceptible to mixed‐layer gravitational‐symmetric instability preferentially in winter. Extreme Ekman equivalent heat flux (≤−10,000 W m−2) associated with wind stress of 1.2 N m−2 coincides with the development of inertial‐symmetric instability across anticyclonic vorticity. These observations might have several implications for the restratification processes, kinetic energy budget, and biogeochemical cycles inside LCEs and can contribute to the formation of low‐PV waters that could feed mode water formation inside the GoM.

Observational Characteristics of Wintertime Extreme Surface Turbulent Heat Flux Events in the North Pacific Subtropical Region

Surface turbulent heat flux is the most direct variable denoting air-sea interactions. In wintertime North Pacific, in addition to the Kuroshio-Oyashio extension (KOE) region, high-resolution observations show that the North Pacific subtropical region (NPSR) is also characterized with high surface heat flux, whose characteristics need systematic investigation. In this study, the extreme surface turbulent heat flux events in the NPSR are investigated using daily observational data. Our results show that the extreme events exhibit dipolar changes of surface flux over NPSR and KOE regions, lasting for several days. Though with a spatially correlated pattern, the occurrence of extreme events in NPSR and KOE is found greatly independent. In the extreme events, both surface sensible and latent heat fluxes display evident changes in north NPSR, while in south NPSR the change in surface latent heat flux dominates. The formation of extreme events in the NPSR is mainly determined by anomalous atmospheric circulation. Changes in the intensity of subtropical high influence the surface air wind speed, humidity, and temperature, contributing to the formation of extreme events in the NPSR. Our results further suggest that the processes through which the extreme events affect the atmospheric precipitation may be different in south and north NPSR. In south NPSR, the change of precipitation in extreme events is very likely attributed to the change of surface latent heat flux. In north NPSR, the change of water vapor transport by atmospheric circulations is found to play a major role.

Machine learning-based turbulence-risk prediction method for the safe operation of aircrafts

This study has proposed a method for detecting turbulence, a primary factor that influences safe aircraft operation. The number of observed turbulence events is limited, thereby indicating the requirement of an appropriate flow for detecting turbulence events from a small number of samples. In addition, the opinions and experiences of pilots must be reflected at the initial stage to address the high risk of turbulence occurrence, which can result in airline operations being cancelled. Thus, this study proposed a method for predicting turbulence occurrence based on the turbulence occurrence date information provided by airlines as well as meteorological data sets obtained from open data available in Japan as teacher data. However, because commonly used machine learning methods are unable to detect the turbulence occurrence date, the proposed method employed principal component analysis coupled with the K-Means method to generate risk clusters with a high likelihood of turbulence occurrence and consequently perform statistical checks. Subsequently, the risk clusters were utilized as supervisory data for turbulence occurrence, while the support vector machine was used for predicting turbulence occurrence. Furthermore, the results obtained with the proposed method were statistically checked as well as practically verified by a pilot to confirm the appropriateness of the turbulence occurrence date predicted.

Employees’ Belief in a Just World and Sustainable Organizational Citizenship Behaviors: The Moderating Effect of Interpersonal Intelligence

To both survive and develop continuously, enterprises must overcome many kinds of competition and challenges. Cultivating employees’ active and sustainable organizational citizenship behavior is important for enterprises to successfully cope with turbulence and uncertain events during their development. Building on social exchange theory, this study proposes a theoretical framework. In this framework, belief in a just world has a certain predictive effect on organizational citizenship behavior, and this effect is affected by interpersonal intelligence. In this study, we investigated the development level of and factors influencing employees’ organizational citizenship behavior in current organizations. This research adopted the empirical research method of a questionnaire survey, and investigated 230 employees from 15 different enterprises by using the Belief in a Just World Scale, Organizational Citizenship Behavior Scale, and Interpersonal Intelligence Scale. After excluding the questionnaires that did not meet the requirements, a total of 193 valid questionnaires were obtained. To estimate the proposed relationships in the conceptual model, we analyzed the data through SPSS-21. The results showed that belief in a just world, interpersonal intelligence, and organizational citizenship behavior were significantly positively correlated. Interpersonal intelligence played a moderating role between belief in a just world and organizational citizenship behavior; the belief in a just world of individuals with high interpersonal intelligence had a more significant positive predictive effect on organizational citizenship behavior. This meant that under a certain level of belief in a just world, a high level of interpersonal intelligence was more conducive to promoting employees’ sustainable organizational citizenship behavior.

Study of Suspended Sediment Diffusion Coefficients in Submerged Vegetation Flow

AbstractThe traditional profile model of the sediment diffusion coefficient (), which is parabolic along the water depth, cannot precisely predict the vertical distribution of in vegetated flow. Therefore, in this study, a series of flume experiments were conducted to clarify the influence of submerged vegetation on the diffusion characteristics of suspended load particles. First, the submerged canopy increases the efficiency of momentum exchange but restrains the vertical diffusion of suspended sediment, indicating that the presence of submerged plants promotes the siltation of solid particles. Second, the depth‐averaged sediment diffusion coefficient () monotonically decreases with increasing relative water depth, while the depth‐averaged momentum exchange coefficient () presents two opposite trends, likely owing to the dominant turbulence event changing from ejections to sweeps and the different variation tendencies of the velocity gradient and Reynolds shear stress with increasing vegetation density. Compared with the ratio () of to the momentum exchange coefficient in nonvegetated flow, in submerged canopy flow is significantly less than 1, which means that the solid particles diffuse less readily than liquid particles because of the stem‐scale vortices generated by the vegetation. In addition, vertical profile models of and suspended sediment concentration were proposed and validated by experimental data. The models exhibit a high accuracy, correlation and applicability and can provide critical information to promote research on riverbed deformation and nutrient dynamics in vegetated rivers, wetlands and estuaries.

The energy cascade as the origin of intense events in small-scale turbulence

This work presents evidence of the relation between the dynamics of intense events in the dissipative range of turbulence and the energy cascade. The generalised (Hölder) means are used to construct signals that track the temporal evolution of intense enstrophy and dissipation events in direct numerical simulations of isotropic turbulence. These signals are remarkably time-correlated with the average dissipation signal, and with its large-scale surrogate, despite describing only a small fraction of the flow domain, and they precede the dissipation signal with a temporal advancement that grows with their intensity and that scales in integral time units. Interpreted from a causal perspective, these results point to the energy cascade as the driver of the intense events in the dissipative range. Moreover, it is shown that the temporal advancements of the generalised means are consistent with a local energy cascade, whereby eddies cascade in a time proportional to their turnover time, causing intense eddies to reach the dissipative scales before weak eddies. These results shed light on the dynamics of intense and extreme events in small-scale turbulence, and provide empirical support to the phenomenological foundations of a broad class of intermittency models based on the turbulence cascade.

Радіотелеграфний зв’язок Української Народної Республіки (УНР) 1917-1921 років як фундаментальна основа становлення суспільного радіомовлення України

The purpose of the article is to study the issues related to the unexplored period of formation of the Ukrainian national radio broadcasting. It is about the proclamation and foundation of the Ukrainian People's Republic (UNR)1917–1921; to prove that radiotelegraph content serves as a prototype of modern public radio broadcasting in Ukraine.The research methodology involved the use of methods belonging to two groups: scientific and practical methods –method of studying archival materials, observation and description; scientifiс theoretical methods –formalization, axiomatization, analysis and synthesis, analogy.One of the first steps of the UNR government was creation of the Ministry of Posts and Telegraphs, which was engaged in the production of radiotelegraph content. It allowed for effective internal and external communication of the UNR government. The main form of content was numerous orders, orders, speeches, appeals, explanatory notes, which we consider a prototype of primary information messages.Results. One of the first steps of the UNR government was creation of the Ministry of Posts and Telegraphs, which was engaged in the production of radiotelegraph content. It allowed for effective internal and external communication of the UNR government. The main form of content was numerous orders, orders, speeches, appeals, explanatory notes, which we consider the primary information messages.Given the high social significance of radiotelegraph content, its extreme relevance in a controversial historical era, prompt delivery to the audience, a balanced approach to information, there is every reason to believe that radiotelegraph communication is a precursor to modern public radio broadcasting in Ukraine.Conclusions. Radiotelegraphic content of the Ukrainian People's Republic of the period 1917–1921 became the first information product of the young country's activity. Thanks to the production of this content, the first steps in providing it have been taken domestic and foreign institutions, communities with reliable, comprehensive information about the turbulent events of the First World War and the postwar years. Dissemination of important socio-political information by radiotelegraph and radio communication was considered a strategic task of the state. Having passed a long and painful way of its formation, the radiotelegraphic content of the period of the Ukrainian People's Republic of 1917–1921 later managed to produce purely radio methods and techniques of presenting information, which could not but affect the quality and effectiveness of providing the community with important and necessary socially significant information, which is the basis for the development of public broadcasting in Ukraine. Key words: radiotelegraph, radiocommunication, radiotelegraphic content, information message, public radio broadcasting.

Territorial narratives: Talking claims in open moments

In the rural inland of northern Sweden, three mining projects are making the future of the land uncertain. Based on ethnographic fieldwork, we show how these potential mining interventions create ‘open moments’, turbulent events that destabilizes established claims to land. We analyse how actors such as reindeer herders, indigenous groups, local and national government and mining companies make claims to land, (i.e territorialising it) by drawing on discourses on environmental responsibility, sustainability, indigeneity or growth. By paying attention to language and knowledge production, we show how a multiplicity of actors narrate territory into being, allowing us to go beyond conventional notions of territory as produced ‘from above’ by the state or by counter-territorial movements ‘from below’. By ‘freezing time’ in the unfolding of the open moments we lend all these ‘territorial narratives’ equal space, in order to analyse the connection between actors and their relation to land. This allow us to show connections between what might otherwise be perceived as locked and antagonistic positions, but also how ongoing processes of territorialisation are influenced by and change peoples’ subject positions as the open moment unfolds on the ground.

ISTOČNO PITANjE I FAKTORI INTEGRACIJE SRPSKOG NARODA U PERIODU OD 1774. DO 1807. GODINE

The period from the Peace of Kuchuk-Kaynardji to the armistice in Slobozia was marked by turbulent events in the Eastern Question, embodied in the reorientation of Habsburg foreign policy, under the influence of Russia’s stronger ascendant in the Eastern Question. These factors, together with the reforms of Maria Theresa and Emperor Joseph II on the one hand and the collapse of the Ottoman order in the Balkans on the other, led to key changes in the integration of the Serbian people. The Russo-Turkish war of 1768-1774 apparently indirectly affected the Serb people. However, during this period, the Habsburg Monarchy prescripted a series of border regulations that were most directly related to the Serb people. Also, the change of priorities in its eastern policy led to the fact that in 1774, as a reward for mediation in peace concluding, the Habsburg Monarchy received Bukovina instead of Belgrade. Russia gained the right to protect Christians in the Ottoman Empire with the Peace of Kuchuk-Kainardji, which gave it the opportunity to influence in Ottoman internal affairs. The mentioned clause turned out to be an important factor in the future development of Russian -Turkish relations, which, despite the change of priorities and reorientation to Italy and the German states, the Habsburg Monarchy had to count on, which significantly reflected on the historical past of the Serbian people. Based on relevant sources and literature, the paper discusses the factors that influenced the integration of the Serbian National Corps in the period before the Serbian Revolution and the change in the aims of the uprising from improving the situation in Belgrade Pashalik to full independence.

ОБОГАТИТЬ СЛОЖНУЮ ИСТОРИЮ СМУТЫ В РОССИИ [Рец. на кн.: Кабанов А.Ю., Рабинович Я.Н. «Прямые» и кривые» Cмутного времени в России. – М.: Квадрига, 2022

This article reviews A.Yu. Kabanov and Ya.N. Rabinovoch’s book “The Honest and the Unscrupulous in the Time of Troubles in Russia” published in 2022, which is a vivid description of the most prominent figures during the Russian political crisis of the early 17th century. It is argued that the book is timely, as well as highly important and influential for further evolution of history as a field of study. The connection of the authors’ historical narrative with the earlier historiographic traditions is traced. The structure and content of the book are analyzed in detail. It is concluded that the book stands out by its organization and approach. The authors contribute a lot into both a better understanding of the general situation in Russia of the 17th century and to disentangling the complicated issues associated with the Time of Troubles. They describe the dramatic and turbulent events through the fates of specific individuals, thereby proving the key role of the behavioral aspect in historical research. At the end of the review, the need to keep on analyzing historical problems from this angle in modern Russian historiography is substantiated.

The Lord of Time: Temporal Discourses of the Enlightenment in Russia

The article deals with the perception of temporal processes in Russia during the Enlightenment and their regulation by the power structures. Several levels and forms of this perception are investigated, from individual experience to reflect on the dimensions of the historical process, from philosophical comprehension to ways of measuring and symbolic representation of time constants. Particular attention is paid to the system of conventions in the perception of time and ways of expressing the sequence and logic of historical processes. Examples of calendar and clock reforms and experiments in cultural history show that temporal rhythms were set by power structures and were perceived by society not only as natural but also as social realities. Turbulent events in Russia at the beginning of the 18th century made the problem of time urgent. The perception of changing and qualitatively defined time was associated with the reforms of Peter the Great, including the calendar reform and the reform of “timekeeping”. The calendar reform moved the starting point 5,508 years from the beginning of the world to the Nativity of Christ. The introduction of New Year’s Day on January 1 instead of September 1 fixed the annual cycles and linked the country to the European calendar. The time reform changed not only the number of divisions on the dial (12 instead of 17) but also the quality of time, giving equal rights to “day” and “night” time. These reforms created a feeling of change, of transition from one time to another, of the “novelty” of time and its dependence on the sovereign’s will. The ruling circles commanded not only the change in the way time was measured, but also the time of their subjects. This is analyzed in the article with examples of corvée as the alienation of the time of serfs, recruitment military service, and compulsory nobility service.

Российское общество 2020-х гг.: попытка идейного самоопределения

Addressing the works of V.V. Petukhov, dedicated to the study of public opinion dynamics, including on issues of political self-determination, the author examines the impact of changes in the socio-economic and political situation on the preferences of Russians. In current sociological data, the author finds confirmation of the ideas of V.V. Petukhov about consistent attempts at ideological self-determination of Russians, despite the constant impact on society of crisis events of various origins, social turbulence and limited opportunities for political representation. Although the request of Russian society in the 1990s for democratic reforms was replaced in the 2000s by skepticism about the applicability of Western models of development, key democratic principles remained socially significant: the lifting of the ban on public criticism of senior officials, the expansion of publicity and freedom of speech, the elimination of censorship, the democratisation of elections, etc. The focus of many Russians on private problems by the time of election campaigns in 2019-2021 was replaced by a growing interest in political participation and ideological self-determination, and in 2021 about a third of citizens could clearly define their own ideological and political views. If the limited possibilities of party-political representation in the 2000–2010s stimulated public demand for ideological self-determination, then the categories of identity circulating in the official discourse gave many people a reason to think about their meanings, and even change their own ideas. This happened with the category “Russian”, the content of which has become clearer over the past few years, and the subtle components of identity have lost popularity. The idea that Russians are all those who honestly work for the benefit of Russia has ceased to be popular. The proportion of those who agree with the most popular logic of interpreting Russian identity, that suggests that a Russian is one who grew up and was brought up in the traditions of Russian culture, has slightly decreased, while the popularity of defining Russian identity through the native Russian language, Russian origin and self-determination after 2014 increased. It is possible that the search for meaningful attributes of Russian identity, coinciding in the view of many with Russian civil identity, along with support for the ideas of national diversity, is an attempt by Russian society to “assemble” a new social consensus and search for the foundations of a new national mythology.