Turbulent Conditions Research Articles

Enhancing the Stability of Small Rescue Boats: A Study on the Necessity and Impact of Hydraulic Interconnected Suspensions

Aiming to solve the problem that existing small rescue boats cannot realize the effective and stable rescue of human lives under high sea turbulence conditions, this paper proposes a parallel decoupled hydraulic interconnected suspension system for actual sea state. The system dynamics model is established, and its damping characteristics are analyzed by joint simulation. The results show that compared with the truss-type rescue ship, the suspension system can improve the transverse rocking resistance by 81.5% and the longitudinal rocking resistance by 25.0%, and the system has excellent transverse rocking resistance.

The method to improve the accuracy of experiment using helium instead of hydrogen

Based on the hydrogen-helium similarity theory, the leakage experiments using helium instead of hydrogen can effectively reduce the risk of hydrogen deflagration, but the experimental results show that there is a large difference between the concentration of hydrogen and helium in initial period of leakage base on this theory. This paper focuses on leakage experiments under turbulent conditions in enclosed spaces. Based on the hydrogen-helium similarity theory, helium is used to replace hydrogen to find out the concentration of helium at multiple leakage speeds. A comparison is made between helium concentration values and hydrogen concentration values, and a polynomial correction algorithm is used to shrink the difference. The results show that this correction method can reduce the concentration average error between the helium and the hydrogen from 14.06% to 7.94% for the Reynolds number range of 3500–9500. Therefore, a polynomial fitting algorithm based on this theory can improve the accuracy of experiment using helium instead of hydrogen.

Settling velocity of microplastics in turbulent open-channel flow

The settling behavior of microplastics (MPs) plays a pivotal role in their transport and fate in aquatic environments, but the dominant mechanisms and physics governing the settling of MPs in rivers remain poorly understood. To gain mechanistic insights into the velocity lag of MPs in an open-channel flume under different turbulent flow conditions, an experimental study was conducted using three types of MPs: polystyrene, cellulose acetate, and acrylic, of sphere-shaped particles with diameters ranging from 1 mm to 5 mm. A particle tracking technique was employed to record and analyze the MPs velocity within turbulent flows. The results showed a variation in the vertical settling velocity of MPs ωMP ranging from −26 % to +16 %, when compared to their counterparts in still water (ωs). A new formula for the drag coefficient (Cd) of MP particles was developed by introducing the suspension number (u∗/ωs). The developed Cd formula was used to calculate the resultant velocity lag VMP, with a mean relative error of 16 % compared with the measured values. Further, the study highlighted that the MPs with large Stokes numbers are mainly driven by their own inertia and turbulence has less influence on their settling behavior. This study is crucial for understanding the settling behavior of MPs in turbulent flows and developing their transport and fate models for MPs in riverine systems.

RUSSIAN CONSTITUTION AS A GUARANTEE OF CIVILIZATIONAL IDENTITY AND SOVEREIGN DEVELOPMENT OF THE RUSSIAN STATE (ON THE 30TH ANNIVERSARY)

The Constitution of Russia, despite pessimistic forecasts during its adoption, caused, among other things, by the idea of the targeted, anticrisis nature of this document, was a reliable basis for the formation of national consent, reconciliation of society, and became the most important guarantee of the preservation of Russian socio-cultural identity based on traditional spiritual and moral values. In modern socio-historical and geopolitical conditions, the consolidating role of the Russian Constitution and its potential associated with ensuring the sovereign development of Russian statehood is increasing. Designed to ensure state development in conditions of historical turbulence, the Russian Constitution enshrined exible, self-adjusting mechanisms for balancing the interests of the individual, society and the state, based both on respect for the heritage and traditions of our ancestors, and on the desire for social progress. It is necessary to consistently reveal the normative, value-semantic content of the current Constitution of Russia, for which an essential prerequisite should be its demythologization in the sense of abandoning its distorted interpretations inspired by the currents of liberal-individualistic globalism. Some judgments on this matter, concerning, in particular, the ideological side of state development, the rights and freedoms of man and citizen in the system of constitutional values, spiritual, moral and legal education in the education system, are set out in the article with the expectation of further scienti c dialogue and the formation of a new constitutional paradigms of Russian statehood.

Optimizing Flow Conditions and Fish Passage Success in Vertical Slot Fishways: Lessons from Fish Behavior Observations

This study investigates the behavior of chubs (Squalius cephalus) of mid-body length (9.7–15.6 cm) with respect to turbulent flow conditions in a pool representing an experimental vertical slot fishway. Velocity and turbulence were characterized using PIV data. The influence of turbulent flow on fish behavior was assessed through the number of successful fish passage attempts, the associated passage times, and the spatial distribution of fish in the pool. Turbulence conditions were modified by the addition of one or three vertical rigid cylinders inside the pool. The results show that these adaptations may facilitate the passage of chubs. Results provide valuable insights and information to understand the relationship between fish behavior and hydraulic conditions, especially in the context of improving the design of fishways.

Enhancing information transmission in FSO-OAM systems through multiscale interpretable neural networks under turbulent conditions

The paper proposes a solution to improve the information transmission efficiency of FSO-OAM systems under turbulent conditions by combining a multiscale interpretable neural network model, 4RK-MSNN. We use a multiscale structure to design the overall architecture of the neural network, which enables the comprehensive analysis of information in different dimensions. Based on the fourth-order Runge-Kutta correlation theory, a core network module, 4RK, is constructed, which can be explained in terms of dynamical systems. The 4RK-MSNN model, which couples the multiscale structure and the 4RK module, has a lower number of parameters, allowing for layered feature extraction in an interpretable framework. This facilitates low-cost, rapid sharing and transmission of feature information at different scales. The proposed solution is validated by transmitting image data under different turbulence intensities and transmission distances. The results indicate the feasibility of the proposed information transfer system. After adding redundant training data, the 4RK-MSNN model significantly improves the quality of the transmitted data and maintains satisfactory results even under strong turbulence and long distances.

Increasing complexity in Aerodynamic Gradient flux calculations inside the roughness sublayer applied on a two-year dataset

Over tall canopies such as forests the atmospheric surface layer is subdivided into an inertial sublayer (ISL) and a roughness sublayer (RSL). Inside the RSL the classic aerodynamic gradient method using Monin-Obukhov similarity theory (MOST) by itself does not represent the gradient well and is insufficient to calculate fluxes. Over the past decades multiple studies have proposed methods to extend MOST to account for the different turbulent conditions within the RSL, containing a wide range of approaches and complexity. In this study we investigate how much complexity is necessary to calculate the flux more accurately and what we can learn from the respective complexity. A large dataset is required to assess the statistical robustness of the respective complexity during different environmental conditions. To this end, we study and apply the effect of forest roughness and directional heterogeneity in our flux calculations on a two-year dataset (2009-2010) of the sensible heat flux measured over a Douglas fir forest in the Netherlands. We apply standard MOST, an observational based method (the α-factor) and a physically based method (Harman and Finnigan, 2007, 2008) (hereafter HF07/08) together with a range of methods for the displacement height (d). Our results show that both a simple method (the α-factor) and a complex method (HF07/08) are able to more accurately represent the flux but that, as expected, standard MOST (regardless of the method estimating d) alone is insufficient. Both the α-factor and (HF07/08) allow to analyze large scale patterns in canopy turbulence. Differences between the methods lie in the level of detail and practical usability.

Aerodynamic analysis of vertical axis wind turbines at various turbulent levels: Insights from 3D LES simulations

This study provides novel insights into the aerodynamic performance of vertical axis wind turbines (VAWTs) in diverse turbulent environments using 3D large eddy simulations (LES). The research aims to understand how turbulence affects VAWT aerodynamics across different operational conditions, including varying wind speeds, tip speed ratios (TSRs), and turbulence intensities. Validation against wind tunnel test data from literature enhances the reliability of the findings. The study utilizes the consistent discrete random flow generation (CDRFG) technique to create homogeneous turbulence in the approaching flow. Through a detailed examination of the rotor aerodynamics and flow fields, critical insights are gained into the impact of turbulence on VAWT performance. The results highlight that local wind speed fluctuations influence the onset of dynamic stall, with turbulence significantly affecting lift forces, while having negligible effects on drag. Notably, fluctuations in the one-cycle power coefficient CP,sgl are primarily attributed to variations in lift. Furthermore, under turbulent conditions, substantial improvements in power performance are observed as wind speed increases from 5 m/s to 10 m/s, with minimal further enhancements at higher wind speeds. These findings contribute valuable insights for optimizing turbine design and operation, particularly in regions characterized by varying wind speeds and turbulence.

Modelling the impact of turbulent economic conditions on non-audit services provision and audit quality during the global financial crisis

PurposeMotivated by concerns and the ongoing debate regarding auditors’ independence and impartiality, this paper aims to examine the impact of the financial crisis on non-audit services (NAS) provision and audit quality (main and robust variables) in the four largest Eurozone countries together during the global financial crisis (GFC).Design/methodology/approachThe authors used a time trend OLS model with a dummy variable as well as a baseline model with a dummy and control variables accounting for multicollinearity, considering the characteristics of the GFC.FindingsIt documented a positive (negative) relationship between NAS provision (audit quality) and crisis in four Eurozone countries, Germany, France, Italy and Spain, in the context of a baseline approach, supporting the hypotheses that there are higher non-audit fees and a lower audit quality. Moreover, it is revealed that NAS provision and audit quality behave similarly, using a time trend approach, during the GFC. Considering the role of the auditor specialization or not (Big4 vs non-Big4) in companies, a significant effect from crisis on non-audit fees and audit quality for the four countries under the baseline approach is found. In general, the findings persist for NAS provision and audit quality using the robust methods of the time trend and panel OLS approaches. Multicollinearity was not found to affect the findings of the regressions.Practical implicationsThe study provides important implications for firm managers, auditors and regulatory authorities.Originality/valueTo the best of the author’s knowledge, it is the first time that the impact of the crisis on non-audit fees and audit quality is investigated during the GFC with two sets of OLS models (a time trend OLS with a dummy and a panel OLS with a dummy and control variables) in four largest Eurozone countries together.

Intelligent towing and pushing system for unmanned tugboats under wind and wave disturbances

ABSTRACT Intelligent unmanned tugboats have the potential to significantly improve the efficiency of barge manipulation. This paper investigates the kinetic modelling, optimal force distribution, and cooperative control within the unmanned tugboat towing and pushing system. A practical kinetic model for the towing and pushing system has been developed, precisely taking into account factors like physical cable forces and disturbances caused by wind and waves in turbulent sea conditions. Following this, an optimal force allocation approach is investigated to allocate the desired force and determine the towing and pushing angles. Furthermore, a cooperative model predicted control strategy is proposed for the dual unmanned tugboats' towing and pushing systems. This strategy aims to ensure the barge quickly reaches its designated location, maintaining the desired heading and velocity. Simulation results indicate that unmanned tugboats can collaboratively tow and push the unpowered barge to the specified location with the desired heading and speed.

Flash precipitation of random copolymers in a micro-mixer for controlling the size and surface charge of nanoparticles.

Precisely controlling the size and surface chemistry of polymeric nanoparticles (P-NPs) is critical for their versatile engineering and biomedical applications. In this work, various NPs of amphipathic random copolymers were comparatively produced by the flash nanoprecipitation (FNP) method using a tube-in-tube type of micro-mixer up to 330 mg min-1 in production scale in a kinetically controlled manner. The NPs obtained from poly(styrene-co-maleic acid), poly(styrene-co-allyl alcohol), and poly(methyl methacrylate-co-methacrylic acid) were concurrently controlled in the range 51-819 nm in size with narrow polydispersity index (<0.1) and -44 to -16 mV in zeta potential, by depending not only on the polymeric chemistry and the concentration but also the mixing behavior of good solvents (THF, alcohols) and anti-solvent (water) under three flow regimes (laminar, vortex and turbulence, turbulent jet). Moreover, the P(St-MA) derived NPs under turbulent jet flow conditions were post-treated in the initial solution mixture for up to 16 h, resulting in lowering of the zeta potential to -52 mV from the initial -27 mV and decreasing size to 46 nm from 50 nm by further migration of hydrophilic segments with -COOH groups on the outer surface, and the removal of THF trapped in the hydrophobic core.

Enhanced heat transfer in a two-dimensional serpentine micro-channel using elastic polymers

Elastic turbulence has emerged as a promising method to enhance heat transfer performance at the microscale. However, previous studies have mainly focused on the overall convective heat transfer performance in curved channels, overlooking the fact that the chaotic flow intensity varies along the streamline, leading to diverse local heat transfer characteristics. In this study, we systematically investigate the hydraulic and thermal properties of a dilute polymer solution under elastic turbulence conditions, where the inflow conditions exhibit a vanishing Reynolds number (Re) and high Weissenberg number (Wi), enabling a comprehensive understanding of the influence of polymers on the system. Through extensive direct numerical simulations using Rheotool, a two-dimensional curvilinear channel flow of an Oldroyd-B viscoelastic fluid is analyzed. By examining the variations of the friction factor and Nusselt number along the serpentine channel, we unveil both global and local characteristics of elastic turbulence. Based on the Wi value, we identify three distinct regimes. In the first regime (0<Wi≤3), we observe approximately 10% heat transfer enhancement accompanied by a roughly 5% reduction in the friction factor compared to laminar flow, known as polymer-induced thermal conductivity enhancement. In the second regime (3<Wi≤5), we observe a steep linear increase in heat transfer (around 30%) at the expense of up to 15% enhanced friction factor. Finally, in the fully developed elastic turbulence regime (Wi>5), we observe a remarkable heat transfer enhancement of up to 60% along with a reduced friction factor. The significant enhancement of heat transfer with increasing Wi can be attributed to the intensifying elastic instability resulting from the balance between normal stresses and streamlined curvatures.

Collective movement of schooling fish reduces the costs of locomotion in turbulent conditions

Collective movement of schooling fish reduces the costs of locomotion in turbulent conditions

Enhancing transmission and coupling efficiency in Cassegrain optical systems with four-petal Gaussian beams

This study investigates the propagation characteristics of four-petal Gaussian beams through Cassegrain optical systems. With the properties of this new type of beam, the problem of masking loss in the Cassegrain optical system can be well solved. Analytical expressions of the optical field for beams after propagating the optical system are derived, considering atmospheric turbulence effects and random jitter on coupling efficiency. Simulation tests explore various factors affecting transmission efficiency. Acceptable axial mounting error tolerance and significant efficiency drops beyond specific communication distances under different turbulence conditions (). Achieving over 80 coupling efficiency is feasible with specific lens parameters (f = 0.4 − 0.5 mm, receiving position after 4 km) using standardized lenses. This work offers a theoretical model for four-petal Gaussian beams, aiding optical communication design and application, with practical engineering implications.

Development of Technology and a Convertеr for Neutralizing Greenhouse Gases Emitted from Automobiles

The article touches upon the issues of global warming associated with carbon dioxide (CO2) emissions into the atmosphere from vehicle internal combustion engines (ICE). To neutralize existing greenhouse gases emitted by ICE, in particular CO2, the interaction of the latter with various chemicals has been studied. The dynamics of exhaust gas emissions from ICE cylinders were observed. The experimental research was conducted to develop a greenhouse gas neutralization technology. Carbon dioxide neutralization converter with three neutralization batteries and a homogenization device is presented. This converter can guarantee CO2 neutralization of up to 92%. The formation of CO2 in the cylinders of modern petrol engines is due to the final combustion of the air-petrol fuel mixture. The combustion of the latter in the cylinder can be heterogeneous and diffusive. In addition, CO2 is generated in large quantities during diffusion combustion. The most effective method of diffusive combustion was chosen by the constructors of modern ICE, which is the formation of an artificial turbulent gas-dynamic condition for the fuel mixture due to the increase in the temperature of the air adsorbed in the cylinder, which ensures the engine's thermal energy efficiency coefficient of up to 35%. The CO2 volume in the exhaust gases of such engines reaches up to 16%. Thus, considering the perfection of modern ICE design for providing a high-efficiency reaction for the hydrocarbon oxidation in the fuel mixture in the combustion chamber, it becomes apparent that the presence of about 16% CO2 in the fractional composition of emitted dissolved gases is a serious problem in terms of increasing the volume of greenhouse gases in the atmosphere. Therefore, the goal of this article is to develop a reduction technology.

Error performance and capacity of subcarrier BPSK modulated THz wireless systems with pointing errors

Terahertz (THz) technology is poised to play a pivotal role in the future sixth-generation (6 G) wireless systems, offering substantial benefits with its extremely high bandwidth and rapid transmission speeds. This paper explores subcarrier-modulated THz wireless systems, analyzing their performance under the log-normal and gamma-gamma models. It provides a detailed examination of how composite turbulence and pointing errors impact the system performance. Closed-form solutions for the bit error rate and outage probability are derived for various conditions of turbulence and pointing errors. Furthermore, the paper delves into the asymptotic error performance, presenting numerical results that confirm the accuracy of the derived solutions across different propagation distances, turbulence strengths, and pointing error scenarios. The study offers critical insights into how different conditions affect the system performance, which is essential for characterizing subcarrier THz links in forthcoming 6 G deployments.

Turbulence image correction using focused light field camera

Under turbulent conditions, the images of objects may be severely blurred and become unrecognizable because of the complex aberrations introduced by turbulence. Using adaptive optics (AO) to compensate for these wavefront aberrations can theoretically solve the problem of image blurring under turbulent conditions. However, due to its small field of view and high cost, the AO system is difficult to widely use. In recent years, using the technology of light field photography to correct turbulence images has been proposed. However, the current studies are either based on the structure of the non-focused light field camera, which makes it hard to achieve good image quality, or on the need to redesign the core sensor of the non-focused light field camera, which greatly increases the cost and complexity. We believe that the structure of a focused light field camera has a good potential for turbulence image correction and propose a new method of achieving a corrected focused image using a focused light field camera in this paper. We propose to use phase estimation instead of depth estimation for a focused light field camera and phase maps instead of a depth map as the basis for achieving a focused image. By the proposed method, a corrected focused image with a large field of view under turbulent conditions is achieved without using independent wavefront correction devices or redesigning the light field camera. The experiments are given to verify the effectiveness of the proposed method under strong turbulent conditions in the laboratory and real turbulent conditions in the outdoors. The proposed method in this paper provides a new and low-cost solution for image correction for optical imaging systems under turbulent conditions, so it has a high application value.

How accurate are ultrasonic anemometers, calibrated in a laminar wind tunnel, under turbulent conditions?

Two ultrasonic anemometers, namely the Gill HS-100 and the Anemoment TriSonica Mini, were placed in the VKI L-1A wind tunnel to assess their accuracy and precision. A comparison was made between these instruments and a Prandtl probe, using a range of wind speeds up to 20 m/s, eighteen azimuth angles (wind directions) at 20° intervals, five tilt angles ranging from -10 to 10°, and two levels of turbulence. As the normal level of turbulence in the wind tunnel, determined by hot wire anemometry, is less than 1%, a grid was installed to allow a second level of turbulence of 6.1% to be evaluated. The analysis shows that the Gill HS-100 accurately measures wind speed in low turbulence conditions in accordance with the manufacturer’s specifications. However, in a turbulent atmosphere, the measured wind speeds are not only overestimated by 2-8% compared to the Prandtl probe but also show a systematic shift compared to the low turbulence case. As expected from the manufacturer’s specifications, the TriSonica Mini is less accurate and precise than the HS-100. In a low-turbulence environment, it fails to meet the manufacturer’s specifications. In a more turbulent atmosphere, however, it matches and even outperforms the HS-100, making it suitable for real-world applications. However, it did show reduced accuracy at non-horizontal wind angles, requiring careful consideration for drone-based measurements. More complex calibrations involving multiple turbulence levels could be considered for both anemometers. However, the feasibility of this approach remains uncertain in light of the results obtained.

Seasonal patterns and processes of migration in a long-distance migratory bird: energy or time minimization?

Optimal migration theory prescribes adaptive strategies of energy, time or mortality minimization. To test alternative hypotheses of energy- and time-minimization migration we used multisensory data loggers that record time-resolved flight activity and light for positioning by geolocation in a long-distance migratory shorebird, the little ringed plover, Charadrius dubius. We could reject the hypothesis of energy minimization based on a relationship between stopover duration and subsequent flight time as predicted for a time minimizer. We found seasonally diverging slopes between stopover and flight durations in relation to the progress (time) of migration, which follows a time-minimizing policy if resource gradients along the migration route increase in autumn and decrease in spring. Total flight duration did not differ significantly between autumn and spring migration, although spring migration was 6% shorter. Overall duration of autumn migration was longer than that in spring, mainly owing to a mid-migration stop in most birds, when they likely initiated moult. Overall migration speed was significantly different between autumn and spring. Migratory flights often occurred as runs of two to seven nocturnal flights on adjacent days, which may be countering a time-minimization strategy. Other factors may influence a preference for nocturnal migration, such as avoiding flight in turbulent conditions, heat stress and diurnal predators.

Wind tunnel investigation on the recovery and dynamics of the wake of a floating offshore wind turbine subjected to low inflow turbulence

Floating offshore wind turbines (FOWT) operate in various turbulent conditions, including low turbulence intensity situations (TI∞ ≤ 5%). In this paper, we investigate experimentally the wake of a model floating wind turbine subjected to inflow turbulence up to TI∞ ≈ 3%. We consider idealised surge platform motion and analyse wake measurements at different downstream positions x ∈ [4D, 8D]. The results show that rotor movements enhance wake recovery compared to the fixed wind turbine, especially for TI∞ ≤ 2%. The recovery of the moving wind turbine wake is progressively less affected by motion with increasing TI∞ . Both amplitude and frequency of motion are key parameters that drive wake recovery and dynamics. We found in the wake large coherent structures induced by the platform movements, which allow a faster transition to the far wake but may cause increased loading on downstream turbines.