Local Losses Research Articles

Entropy generation rate analysis of turbocharger radial flow compressor in range from surge to choke

This study compares the local losses of a radial compressor in the range from surge to choke considering shock phenomena, boundary layer separation, and mixing mechanisms. For this purpose, formulation of the local entropy generation rate (EGR) is added to the computational fluid dynamics (CFD) solver, which models the turbulent flow field of the compressor through the RANS approach. For validation, the numerical pressure rise curve of the compressor is compared with the experimental data. The results indicate that at the design point, the impeller, diffuser, and the volute account for approximately 50.8%, 30.0%, and 12.3% of the EGR, respectively, with approximately 5% in the impeller backspace, 1% in the diffuser cavity, and less than 0.5% in the inlet duct. Approaching the surge condition, local losses due to mixing and shock waves decline while boundary layer losses increase. Based on comprehensive analysis of the leading-edge boundary layer, the largest dead-air zone is found at the design point, resulting in a lower diffusion entrance loss and a higher mixing loss. Furthermore, the EGR variation in the diffuser channel is investigated by shedding light on mixing dynamics and classification of the channel flow regime into three different zones based on mixing ratio (MR). The outcomes show that the flow regime tends to mix more quickly at a higher MR, resulting in a slight decrease in EGR, which benefits compressor performance. We demonstrate that the mixing rate of flow regimes decreases in both the leading-edge boundary layer and the radial diffuser approaching the surge margin.

Synergy principle and its application of endwall loss analyses in the turbine stator

The endwall flow significantly impacts the turbine performance behavior, and it is necessary to investigate the development of endwall secondary vortices and relevant losses. Inspired by the field synergy principle, the synergy between the velocity and the pressure gradient established by the three-dimensional mechanical energy conservation equation is innovatively applied to the endwall loss analysis in the stator of an axial-inflow turbine. In terms of the synergy equation, the loss is not only related to the viscous dissipation, but also the included angle (or the synergy angle) between the velocity vector and the pressure gradient vector. The physical content of the synergy angle suggests that the larger synergy angle is (i.e., the worse synergy), the higher losses should be. This conclusion has been validated by present numerical results, and an apparent positive correlation between the synergy angle and the losses could be perceived under time-averaged and transient conditions. The worse synergy could be observed at the passage rear part and the wake, where complex passage vortices and local separation exist. In these regions, the local velocity vector is not aligned with the bulk pressure gradient of the mainstream. Hence, the synergy angle has a marked rise, corresponding to the local high losses.

Abundance, Distribution and Mortality of Hydrobionts in the Section of the Gorky Reservoir Affected by Heated Waters of the Kostroma Hydroelectric Power Plant

The study was conducted in the river section of the Gorky reservoir in the zone affected by the heated water discharge from the Kostroma hydroelectric power plant during the growing season (May–November) 2021. The reduced species richness was observed in the sites of the maximum water heating, which, however, quickly returned to the initial values in the downstream section of the river. The lethal effect of warm waters on zooplankton is mainly manifested in the summer, when the natural warming of the river waters is influenced by the heated water discharge from the Kostroma hydroelectric power plant. In autumn, the warming effect of heated waters, on the contrary, promotes better survival of organisms. Fish reach a high abundance in the study area by the end of summer, when the grown juvenile sleave shallow waters. In the autumn period, the fish redistribution and a significant increase in the abundance occur in the area of heated waters compared to the back ground sites. The results obtained indicate the absence of an environmentally significant lethal effect. Local plankton losses are quickly compensated due to high reproduction rates and short-cycle development of invertebrates. The lethal effect of exposure to high temperatures on fish was not found.

Расчет коэффициента местного сопротивления при изотермическом течении неньютоновской несжимаемой жидкости в цилиндрическом канале с внезапным сужением

The engineering calculation and construction of the extrusion tool in the form of cylindrical forming channels with sudden narrowing is associated with the determination of the coefficient of resistance of sudden narrowing and local pressure losses. The available theoretical and experimental data on the values of the resistance coefficient of sudden narrowing are contradictory, approximate in nature and, in some cases, do not take into account the rheological properties of the liquid. Their use to calculate local pressure losses under laminar flow conditions leads to significant errors. To eliminate the indicated problems, a mathematical statement of the problem of isothermal stationary laminar flow of non-Newtonian non-compressible fluid in an axisymmetric channel with sudden narrowing was formulated. The mathematical model of flow in spatial formulation is formalized in the form of equations for preserving momentum and mass. As a rheological model, the Carreau model is taken, taking into account the presence of finite viscosity values at marginal shear rates. The numerical solution of the problem was performed by the finite element method using the Comsol MultiphysicsTM CFD modeling package. As a result of the solution, the picture of the current of the non-Newtonian medium was restored in the form of the distribution of current lines, kinematic and dynamic flow parameters. The impact of Reynolds number on change of geometric characteristics of flow structure, kinematic and dynamic flow parameters was evaluated. Values of local resistance coefficient and pressure losses for overcoming sudden narrowing for selected flow modes are calculated. The results of computational experiments are summarized in the form of a criterion ratio for calculating the coefficient of local resistances depending on the Reynolds number.

On-line milling tool wear monitoring under practical machining conditions

Accurate diagnosis of milling tool wear monitoring during high-speed cutting processes is essential for ensuring machining surface precision, enhancing tool efficiency, and extending the service life of machine tools. However, challenges in data screening during each stage of tool movement and signal migration caused by changes in machining parameters have not been sufficiently addressed. To tackle these issues, this paper presents a novel MB-DAAN model, which considers signals from each stage of tool movement and diagnoses tool wear under dynamic machining parameters. Firstly, the multi-branch classification module is introduced, incorporating two independent classifiers to form a multi-branch classification module. This module adaptively extracts features of tool wear states during the cutting stage. Subsequently, the dynamic adversarial factor adjusts the global and local losses between features, aligning conditional and edge distributions across different machining parameters. The models were evaluated in the milling tool wear data set. MB-DAAN achieving a diagnostic accuracy of 97.3%-a significant improvement compared to CNN, DAN, and DAAN models.

A framework for assessing variations in ecological networks to support wildlife conservation and management

Habitat fragmentation poses a considerable threat to global biodiversity loss, making the study of landscape connectivity and ecological networks essential in an ever-changing environment. Of particular importance is the assessment of network dynamics, as it can provide invaluable specific insights for conservation and management strategies. This research proposes a framework to assess variations in ecological networks and identify conservation priorities. In this framework, we applied multi-methods to collect species occurrence and create resistance surfaces based on habitat suitability from the MaxEnt model. By using diverse approaches such as the least-cost model, circuit model, and centrality mapper, we identified ecological corridors between core areas and determined their centrality. Furthermore, we employed multi-level metrics to measure changes within ecological networks. Additionally, we introduced two indices to evaluate human disturbance faced by core habitats. We proposed a novel method that considers core habitats’ centrality and human disturbance to identify conservation priorities. Specifically, using the Asiatic Black Bear (Ursus thibetanus) as a case species, we examined the variations in ecological network and human disturbance across 2000–2020 in Western Yunnan, China. Our study revealed overall improvement with local losses in the availability and connectivity of black bear habitats in Western Yunnan from 2000 to 2020. However, the core habitats have been facing an escalating human disturbance. Our approach provides a framework for assessing dynamic ecological networks that can be applied to diverse species, landscapes, and scenarios. Furthermore, this approach helps guide conservation and management to promote human-wildlife coexistence in a changing environment.

A general meta‐ecosystem model to predict ecosystem functions at landscape extents

The integration of ecosystem processes over large spatial extents is critical to predicting whether and how local and global changes may impact biodiversity and ecosystem functions. Yet, there remains an important gap in meta‐ecosystem models to predict multiple functions (e.g. carbon sequestration, elemental cycling, trophic efficiency) across ecosystem types (e.g. terrestrial‐aquatic, benthic‐pelagic). We derive a flexible meta‐ecosystem model to predict ecosystem functions at landscape extents by integrating the spatial dimension of natural systems as spatial networks of different habitat types connected by cross‐ecosystem flows of materials and organisms. We partition the physical connectedness of ecosystems from the spatial flow rates of materials and organisms, allowing the representation of all types of connectivity across ecosystem boundaries. Through simulating a forest‐lake‐stream meta‐ecosystem, our model illustrates that even if spatial flows induced significant local losses of nutrients, differences in local ecosystem efficiencies could lead to increased secondary production at regional scale. This emergent result, which we dub the ‘cross‐ecosystem efficiency hypothesis', emphasizes the importance of integrating ecosystem diversity and complementarity in meta‐ecosystem models to generate empirically testable hypotheses for ecosystem functions.

Numerical Study on Local Entropy Production Mechanism of a Contra-Rotating Fan.

Contra-rotating fans (CRFs) have garnered significant attention due to their higher power-to-weight ratio compared to traditional fans; however, limited focus has been given to the localization and development of local aerodynamic losses. Furthermore, there is a need for further research on the impact of load distribution along the radius on local entropy production. Therefore, this study aims to investigate a contra-rotating fan as the research subject. An optimal design for load distribution along the radius is achieved by constructing a surrogate model in combination with a genetic algorithm. The effectiveness of this design has been verified through experimentation using a specific test device. In this study, a local entropy production rate (EPR) model adapted to the shear stress transport-detached eddy simulation (SST-DES) technique is constructed to evaluate the loss distribution of the contra-rotating fan. This paper primarily focuses on comparing and analyzing the blade profile and overall performance of the CRFs before and after optimization. The EPR contribution of each interval along the radius is compared to the corresponding blade channel to identify the approximate range of high-EPR regions. Furthermore, an investigation is conducted to examine the distribution of EPR along the streamwise direction in these high-EPR regions. After that, by comparing the development of the flow structure near a stall before and after optimization, combined with the analysis of the EPR contours, the EPR mechanism of this CRF is revealed.

Stressed economies respond more strongly to climate extremes

Economies experience stress for various reasons such as the global Covid-19 pandemic beginning in 2020. The associated lock-downs caused local economic losses and the disruption of international supply chains. In addition, such stress alters the effects of short-term shocks as caused by climate extremes, especially their propagation through the economic network and the resulting repercussions. Here we show that adverse indirect impacts of tropical cyclones, river floods, and heat stress on global consumption are strongly enhanced when the economy is under stress. This compound effect results from aggravated scarcity causing higher consumer prices. Modeling climate impacts during Covid-19, we find that in a stressed economy with the current network structure, consumption losses due to climate extremes double in the USA and triple in China. The simulated effects intensify when climate shocks grow stronger. Our results emphasize the amplifying role of the interaction between climate change and its socioeconomic backdrop.

Mechanistic investigation on the voltage collapse of polymer electrolyte membrane fuel cell under high-temperature and low-humidity conditions

Polymer electrolyte membrane fuel cell (PEMFC) operating under high-temperature and low-humidity (HTLH) conditions enables more efficient and compact fuel cell system through smaller radiators (less parasitic power) and smaller humidifier, but exerts negative influence on conductivity of perfluorosulfonic acid (PFSA) membrane, which is the most commercial proton conductor for PEMFC at current state. Although great progress has been made on the R&D of advanced PFSA-based material, a huge gap from material to PEMFC still exists due to its complicated physico-chemical processes. In this work, after a slight rise of operation temperature, we observe the unexpected voltage collapse of PEMFC under HTLH conditions and non-active zone (nearly zero local current density) is found to fast propagate from air inlet to the rest area during this period. For the first time, temporal–spatial numerical reconstruction of this dynamic process reveals that the current in-plane redistribution raises the local mass transfer losses but make limited contribution. Instead, the water being transferred from anode to cathode due to proton's dragging effect leads to severe anode ionomer dehydration, dominating such process. Finally, suggestions are provided as following: (a) raising membrane conductivity under dry condition or reducing proton's dragging coefficient could significantly improve PEMFC's performance under HTLH condition; (b) particular attention should be paid to the water content of anode ionomer for PEMFC design and system control.

Aerodynamic Performance Optimization of Centrifugal Fan Blade for Air System of Self-Propelled Cotton-Picking Machine

To enhance the working efficiency and aerodynamic performance of the centrifugal fan in the air system of a cotton picker, a new type of centrifugal fan blade was designed by extracting the mid-arc section from the prototype blade and integrating an airfoil, which was transplanted and coupled to the mid-arc section. The design aimed to improve the airflow characteristics and performance of the centrifugal fan. By combining experimental data from centrifugal fans used in existing cotton-picker air systems and employing computational fluid dynamics (CFD) methods, the internal flow field structure of the centrifugal fan was simulated. This study focused on investigating the aerodynamic performance of the new centrifugal fan blade and its impact on improving the internal flow patterns within the centrifugal fan. The results of the flow field visualization analysis indicate that the new blade design exhibits excellent aerodynamic performance, improving the flow distribution within the centrifugal fan. It enhances the uniformity of the outlet airflow, reduces the occurrence of localized “jet-wake” phenomena at the impeller’s outlet, suppresses the generation and development of vortices in the flow channel, and reduces local energy losses within the impeller. These improvements contribute to an increase in the fan’s efficiency. Under rated operating conditions, the efficiency of the prototype fan was measured at 60.3%, while the optimized fan achieved an efficiency of 64.8%. This signifies a significant improvement in the efficiency of the centrifugal fan.

Enigmatic freshwater mussel declines could be explained by the biodiversity‐disease relationship

AbstractThe biodiversity‐disease relationship states that increased species richness leads to lower pathogen pressure (i.e. the dilution effect), an effect that erodes with biodiversity loss. However, whether losses of the dilution effect can trigger extinction cascades remains largely unexplored.To explore this idea, we consider declines in freshwater mussels, on average the most threatened non‐marine group of organisms in the world. We argue that anthropogenically stimulated declines in mussel richness amplify pathogens in remaining species. Pathogen amplification triggers further local losses in both mussel abundance and richness, explaining the observed so‐called “enigmatic” declines in freshwater mussels.Vulnerable communities could become trapped in cycles of pathogen amplification and host decline. We highlight knowledge gaps and provide key steps to assess the likelihood of this occurring; these key steps are applicable to any host group.Policy implications. Our argument constitutes a testable hypothesis that may explain richness or abundance declines in previously intact communities. We provide further impetus for the consideration and preservation of diversity at a local scale and show that effective conservation requires integration of both host and parasite ecology.

Flexible 3D Lane Detection by Hierarchical Shape Matching

As one of the basic while vital technologies for HD map construction, 3D lane detection is still an open problem due to varying visual conditions, complex typologies, and strict demands for precision. In this paper, an end-to-end flexible and hierarchical lane detector is proposed to precisely predict 3D lane lines from point clouds. Specifically, we design a hierarchical network predicting flexible representations of lane shapes at different levels, simultaneously collecting global instance semantics and avoiding local errors. In the global scope, we propose to regress parametric curves w.r.t adaptive axes that help to make more robust predictions towards complex scenes, while in the local vision the structure of lane segment is detected in each of the dynamic anchor cells sampled along the global predicted curves. Moreover, corresponding global and local shape matching losses and anchor cell generation strategies are designed. Experiments on two datasets show that we overwhelm current top methods under high precision standards, and full ablation studies also verify each part of our method. Our codes will be released at https://github.com/Doo-do/FHLD.

Memoryless Quantum Repeaters Based on Cavity‐QED and Coherent States

AbstractA quantum repeater scheme based on cavity‐quantum electrodynamics (QED) and quantum error correction of channel loss via rotation‐symmetric bosonic codes (RSBCs) is proposed to distribute atomic entangled states over long distances without memories and at high clock rates. In this scheme, controlled rotation gates, i.e., phase shifts of the propagating light modes conditioned upon the state of an atom placed in a cavity, provide a mechanism both for the entangled‐state preparations and for the error syndrome identifications. In order to assess the performance of this repeater protocol, an explicit instance of RSBCs—multicomponent cat codes—are studied quantitatively. It is found that the total fidelity and the success probability for quantum communication over a long distance (such as 1000 km) both can almost approach unity provided a small enough elementary distance between stations (smaller than 0.1 or 0.01 km) and rather low local losses (up to 0.1%) are considered. In a quantum key distribution application, secret key rates can become correspondingly high, both per channel use, beating the repeaterless bound, and per second thanks to the relatively high clock rates of the memoryless scheme. Based upon the cavity‐QED setting, this scheme can be realized at room temperature and at optical frequencies.

Community context mediates effects of pollinator loss on seed production

AbstractA critical goal for ecologists is understanding how ongoing local and global species losses will affect ecosystem functions and services. Diversity–functioning relationships, which are well‐characterized in primary producer communities, are much less consistently predictable for ecosystem functions involving two or more trophic levels, particularly in situations where multiple species in one trophic level impact functional outcomes at another trophic level. This is particularly relevant to pollination functioning, given ongoing pollinator declines and the value of understanding pollination functioning for single plant species like crops or threatened plants. We used spatially replicated, controlled single‐pollinator‐species removal experiments to assess how changes in bumble bee species richness impacted the production of fertilized seeds in a perennial herb—Delphinium barbeyi—in the Rocky Mountains of Colorado, USA. To improve predictability, we also assessed how traits and abundances in the plant and bumble bee communities were related to D. barbeyi reproductive success. We hypothesized that trait‐matching between pollinator proboscis length and D. barbeyi's nectar spurs would produce a greater number of fertilized seeds, while morphological similarity within the floral community would dilute pollination services. We found that the effects of pollinator removal differed depending on the behavioral patterns of pollinators and compositional features of the plant and pollinator communities. While pollinator floral fidelity generally increased D. barbeyi seed production, that positive effect was primarily evident when more than half of the Bombus community was experimentally removed. Similarly, communities comprising primarily long‐tongued bees were most beneficial to D. barbeyi seed production in tandem with a strong removal. Finally, we observed contrasting effects of morphological similarity in the plant community, with evidence of both competition and facilitation among plants. These results offer an example of the complex dynamics underlying ecosystem function in multitrophic systems and demonstrate that community context can impact diversity–functioning relationships between trophic levels.

Modeling of Switching Power Losses in Cascaded H-Bridges With Unipolar PWM

This paper studies the extraction of an equivalent resistance for calculation of the switching power losses in cascaded H-bridge multilevel inverters with unipolar pulse width modulation. The concept of local and global rms currents and switching power losses are introduced in each H-bridge considering different frequencies of the inverter output and the switching network, i.e., transistor and diode. Energy conservation law has been utilized to show that the equivalent averaged local and global resistances for switching power losses are functions of load power factor angle, load rms current, and modulation index. This dependency is then reduced to only load rms current when the equivalent resistances are transformed to the inverter output branch based on the reflection rule. Consequently, a resistive model of switching power losses of the inverter is deduced, which depends neither on the knowledge of the physics of the switch, nor on complicated nonlinear equations of the semiconductor devices, and loop inductances. Double-pulse tests are conducted to acquire reliable data on the switching characteristics of the devices for different operating points.

Observation of Hidden Polar Phases and Flux Closure Domain Topology in Bi2WO6 Thin Films.

Topological textures of ferroelectric polarizations have promise as alternative devices for future information technology. A polarization rotation inevitably deviates from the stable orientation in axial ferroelectrics, but local energy losses compromise the global symmetry, resulting in a distorted shape of the topological vortex or inhibiting the vortex. Easy planar isotropy helps to promote rotating structures and, accordingly, to facilitate access to nontrivial textures. Here, we investigate the domain structure of an epitaxial thin film of bismuth tungsten oxide (Bi2WO6) grown on a (001) SrTiO3 substrate. By using angle-resolved piezoresponse force microscopy and scanning transmission electron microscopy, we find the existence of a hidden phase with ⟨100⟩-oriented ferroelectric polarizations in the middle of the four variant ⟨110⟩-oriented polarization domains, which assists in the formation of flux closure domains. The results suggest that this material is one step closer to becoming an isotropic two-dimensional polar material.

Diagonal compression testing of masonry under fatigue loading and high static loads

Underground railway operations pose a significant impact on overlying, highly sensitive historic masonry structures. Here, the process of structural assessment involves fatigue actions, through induced ground-borne vibrations, from operating underground railways. Considering long-term exposure periods, fatigue can introduce local cracking and losses, which endanger the integrity of both structural and non-structural elements. The lack of experimental fatigue data on tensile actions in masonry and the apparent computational restraints from constitutive cementitious material models that do not account for damage due to repeated loading, increase the complexity of structural assessment, under combined fatigue actions and other hazards. The current paper aims at providing new experimental data on fatigue in historic brick and lime mortar masonry wallets, replicating realistic combinations of static and fatigue loading under diagonal compression. Material deterioration and stiffness degradation are monitored throughout the process. Hence, under moderate amplitudes of fatigue loading and high static loads, cracking occurred, at a relatively low number of cycles, demonstrating the need for more strict vibration thresholds to ensure the integrity of historic masonry buildings.

RetiFluidNet: A Self-Adaptive and Multi-Attention Deep Convolutional Network for Retinal OCT Fluid Segmentation.

Optical coherence tomography (OCT) helps ophthalmologists assess macular edema, accumulation of fluids, and lesions at microscopic resolution. Quantification of retinal fluids is necessary for OCT-guided treatment management, which relies on a precise image segmentation step. As manual analysis of retinal fluids is a time-consuming, subjective, and error-prone task, there is increasing demand for fast and robust automatic solutions. In this study, a new convolutional neural architecture named RetiFluidNet is proposed for multi-class retinal fluid segmentation. The model benefits from hierarchical representation learning of textural, contextual, and edge features using a new self-adaptive dual-attention (SDA) module, multiple self-adaptive attention-based skip connections (SASC), and a novel multi-scale deep self-supervision learning (DSL) scheme. The attention mechanism in the proposed SDA module enables the model to automatically extract deformation-aware representations at different levels, and the introduced SASC paths further consider spatial-channel interdependencies for concatenation of counterpart encoder and decoder units, which improve representational capability. RetiFluidNet is also optimized using a joint loss function comprising a weighted version of dice overlap and edge-preserved connectivity-based losses, where several hierarchical stages of multi-scale local losses are integrated into the optimization process. The model is validated based on three publicly available datasets: RETOUCH, OPTIMA, and DUKE, with comparisons against several baselines. Experimental results on the datasets prove the effectiveness of the proposed model in retinal OCT fluid segmentation and reveal that the suggested method is more effective than existing state-of-the-art fluid segmentation algorithms in adapting to retinal OCT scans recorded by various image scanning instruments.

Loss Analysis of a Transonic Rotor with a Differential Approach to Entropy Generation

The loss mechanism of transonic axial compressors is a long-standing problem that involves almost all types of entropy generation in fluid flows, such as skin friction, shock waves, shear flows, corner separation, and tip vortices. Primarily, sources need to be identified and quantitative comparisons of their contributions need to be made. For such determination, we propose herein a differential approach to entropy generation, called the “differential approach”. Two case studies are analyzed to determine the applicability of this approach: (1) laminar and turbulent incompressible flows in straight circular ducts and (2) turbulent compressible flows in convergent-and-divergent nozzles with shock waves. The results lead to the following conclusions: (a) Qualitatively, the differential approach works well, and the quantified measure is reliable if it is calculated with quality meshes and a suitable turbulence model. This means that the differential approach can be a good tool for predesign optimization. (b) When shocks occur within flow fields, the shock-induced boundary-layer separation can generate more loss than the shock loss alone. Subsequently, the differential approach is applied to complex flows in the NASA Rotor 67, which is a well-known bench-test transonic rotor. The results show that the differential approach not only determines the local losses and associates the source of losses with the flow structures but also qualitatively compares and identifies the largest contributors. These results provide a theoretical foundation for optimizing rotor design and enhancing stability.