Natural Flow Research Articles

Climate-driven differences in flow regimes alter tropical freshwater ecosystems with consequences for an endemic shrimp

Climate-driven shifts in the natural flow regime can threaten species persistence in stream systems, and anticipating such shifts before they occur is critical for conservation. We can explore how climate change may impact biota by examining natural systems that differ in terms of climate yet are similar in terms of other landscape features such as geology, size, and elevation. Across an established precipitation and hydrologic gradient on the east coast of Hawaii Island, we sampled stream habitat and populations of the endemic migratory mountain shrimp Atyoida bisulcata over three years and examined how habitat as well as population metrics and individual condition respond to differences in stream flow. Along the precipitation gradient, baseflow declined and streams shifted from run/riffle systems with moss cover to those with predominately pools and limited available habitat. Across years, baseflow conditions were relatively consistent within streams while measures of stream flow stability and the duration of high flows were more variable. Streams with high and persistent baseflow had greater atyid biomass density with larger individuals less prone to disease. Within-stream interannual variation in baseflow was low relative to differences across streams, and most A. bisulcata metrics also had low within-stream interannual variability, making average baseflow an appropriate surrogate for differences in suitability. However, extremes in annual rainfall may result in high variability in A. bisulcata metrics within a single stream due to seasonal drying or persistent high flows, highlighting the importance of long-term monitoring to fully understand population responses to climate-mediated stream flow. Our study suggests that changes in rainfall patterns will alter stream flow and may ultimately negatively influence tropical stream organisms.

Distinctive approach for MHD natural bioconvection flow of Reiner–Rivlin nano-liquid due to an isothermal sphere

The analysis of heat excess through non-Newtonian fluid is noticed proper and promising arena for biomedical technological applications than Newtonian liquid. Herein, a type of non-Newtonian (Reiner–Rivlin) nanomaterial has been scrutinized with gyrotactic microorganisms around an isothermal sphere with surface of zero mass flux. Being mindful of that the model of Buongiorno’s nanofluid is utilized. Non-dimensional formulas for the basic dimensional partial differential equation system are obtained using appropriate non-similarity transformations. MATLAB function bvp4c code is adopted to get the non-similar solutions. The computations disclosed that the velocity of Reiner–Rivlin nanofluid and its gradient accelerate away from the surface of sphere to infinity and reduces in proximity to the sphere surface for higher values of Reiner–Rivlin factor K. The rate of surface density transport, rate of surface heat transport, and gradient of velocity diminish as the stream wise coordinate boosts. As the problem is subjected to special circumstances, there is a remarkable agreement between the acquired and prior numerical calculations resulting from the comparison.

A Simulation–Optimization System to Assess Dam Construction with a Focus on Environmental Degradation at Downstream

AbstractThe present study proposes and evaluates an integrated framework to assess dam construction and removal, encompassing the simulation of downstream river habitats and reservoir operation in three distinct statuses: conventional reservoir operation optimization, optimal release considering environmental aspects within the optimization model, and natural flow conditions. Fuzzy physical habitat simulation was employed to assess physical habitats, while an ANFIS-based model was utilized to simulate thermal tension and dissolved oxygen tension at downstream habitats. Particle swarm optimization was applied in the optimization models. To evaluate the effectiveness of the proposed framework, results from the optimization system as well as habitat suitability models in the natural flow and current condition were compared using various measurement indices, including the reliability index, vulnerability index, the Nash–Sutcliffe model efficiency coefficient (NSE), and root mean square error (RMSE). The case study results suggest that the reliability of water supply may be diminished under optimal release for environmental and demand considerations. Additionally, optimal release for the environment may not adequately protect downstream aquatic habitats. Therefore, in cases where the preservation of downstream habitats is a priority, dam removal may be a logical solution. Moreover, it is essential to acknowledge that the main limitation of the proposed method is its high computational complexity.

Transition mutation bias is crucial to adaptive extended spectrum beta lactamase (ESBL) resistance evolution

The importance of slow accumulation of mutation in the nucleic acids of bacteria and the possibility of organismal transcriptional modification to suit their adaptation are key drivers favouring natural selection and subsequently adaptive evolution. This study was aimed at providing insight into factors influencing adaptive extended spectrum beta lactamase (ESBL) resistance evolution. A total of twenty-six (26) extended spectrum beta lactamase-producing Gram-negative bacteria isolated in our previous study were subjected to uniplex and multiplex polymerase chain reaction (PCR) and sequencing prior to mutation discovery analyses, while the maximum likelihood value, transition-transversion ratio, tajimas neutrality test, nucleotide diversity and selection analyses were estimated following standard recommended protocols. Results obtained depict the PCR discriminated ESBL alleles as; TEM (n = 11.5 %), CTX-M (n = 15.4 %), SHV (n = 19.2 %) while the co-occurred ESBL alleles were estimated as CTX-M and TEM (n = 3.85 %), CTX-M and SHV (n = 15.4 %), TEM and SHV (n = 23.1 %), CTX-M, TEM and SHV (n = 11.5 %). The transition, transversion, deletion and insertion distribution pattern were evaluated as; TEM (46, 39,11 and 4 %), SHV (50, 31, 8 and 11 %) and CTX-M (60, 21,12 and 7 %) (p < 0.05) respectively. The maximum likelihood value, transition-transversion ratio, tajimas neutrality test, nucleotide diversity and selection analyses for TEM, SHV and CTX-M were (−8436, 1.18, 5.2, 62 % and 84.9 %,), (−8321, 1.60, 5.4, 68.9 % and 97.8 %) and (−7284, 2.86, 6.0, 55.2 % and 77.2 %) sequentially. Our findings therefore have shown that adaptive ESBL resistance evolution is driven by transition mutation, positive natural selection and ESBL gene flow. It is thus imperative to state that understanding these adaptive resistance driven factors and how they operate is crucial to deciphering the fundamental principles of adaptive evolution that might help circumvent the global challenges of antibiotic resistance.

Joint optimal operation of the South-to-North Water Diversion Project considering the evenness of water deficit

Abstract. Inter-basin water transfer projects are the main measure to address the water deficit crisis caused by uneven distribution of water resources. The current water transfer operation mainly tends to be present in areas with small water transfer costs and is prone to encounter the problem of spatial and temporal imbalances in water allocation. To address these issues, this paper defines a water deficit evenness index (WDEI), aimed at minimizing regional differences in water scarcity and sharing the pressure of water scarcity as a social demand objective. This index is incorporated into a joint optimization model for the Jiangsu section of the South-to-North Water Diversion Project (J-SNWDP), which comprises both the ecological objective of the total water deficit (TWD) and the economic objective of the pumping water (PW). Further, the Nondominated Sorting Genetic Algorithm III (NSGA-III) and multi-attribute decision-making were applied to solve the model and obtain an optimal operation strategy. The results showed the following: (1) the WDEI defined in this paper can mitigate the synchronized water scarcity in certain water users. In typical normal years (wet year and dry year), the WDEI shows a reduction of 94.2 % (81.8 %, 76.7 %) compared to the historical operation strategy. (2) The optimized operation strategy can significantly reduce TWD and PW by 82.06% (37.69 %, 52.36 %) and 45.13 % (3.25 %, 21.51 %) compared with the historical values, respectively, which can improve the water supply satisfaction and reduce the project cost. At the same time, the lake storage capacity of the optimal operation strategy performs well, and the water transfer efficiency of the river is significantly improved. (3) In this paper, targeted optimal operation strategies and potential ways to secure the project tasks are proposed for different natural flow. Overall, it is of great significance to study the water supply equity in the J-SNWDP to alleviate the concentrated water deficit in Jiangsu Province and other similar regions.

Towards the mechanical characterisation of unruptured intracranial aneurysms: Numerical modelling of interactions between a deformation device and the aneurysm wall

Intracranial aneurysm is a critical pathology related to the arterial wall deterioration. This work is an essential aspect of a large scale project aimed at providing clinicians with a non-invasive patient-specific decision support tool regarding the rupture risk assessment. A machine learning algorithm links the aneurysm shape observed and a database of UIA clinical images associated with in vivo wall mechanical properties and rupture characterisation. The database constitution is derived from a device prototype coupled with medical imaging. It provides the mechanical characterisation of the aneurysm from the wall deformation obtained by inverse analysis based on the variation of luminal volume. Before performing in vivo tests of the device on small animals, a numerical model was built to quantify the device’s impact on the aneurysm wall under natural blood flow conditions. As the clinician will never be able to precisely situate the device, several locations were considered. In preparation for the inverse analysis procedure, artery material laws of increasing complexity were studied (linear elastic, hyper elastic Fung-like).Considering all the device locations and material laws, the device induced relative displacements to the Systole peak (worst case scenario with the highest mechanical stimulus linked to the blood flow) ranging from 375 μm to 1.28 mm. The variation of luminal volume associated with the displacements was between 0.95 % and 4.3 % compared to the initial Systole volume of the aneurysm. Significant increase of the relative displacements and volume variations were found with the study of different cardiac cycle moments between the blood flow alone and the device application. For forthcoming animal model studies, Spectral Photon CT Counting, with a minimum spatial resolution of 250 μm, was selected as the clinical imaging technique. Based on this preliminary study, the displacements and associated volume variations (baseline for inverse analyse), should be observable and exploitable.

Framework for comprehensive assessment of ecological water conveyance based on long-term evolution forecast of riparian forests in arid floodplains: synergistic consideration of flood inundation and groundwater

Ecological water conveyance (EWC) is a crucial measure to address ecological degradation in arid regions. To scientifically formulate ecological water conveyance pattern (WCP), and provide a basis for ecological flow management of reservoirs, this study proposes a framework to assess the effect of EWC, and applied it to the Irtysh River basin as a case study. Following the framework, we first developed a calculation method to assess the evolution of the reproduction and growth of riparian forests caused by hydrological variations. Additionally, simulations of surface water and groundwater conditions under different scenarios of water resources development were conducted based on hydrodynamic and groundwater models. The study further predicted the long-term evolution of riparian forest reproduction and growth based on the simulation results. The results indicated that when EWC was not carried out (reservoirs operating according to the designed rules), after 30 years, floodplain flood (FF) inundation area decreased by 47%, duration shortened by 73%, and groundwater levels in 80% of the region declined by 1.5–2 m, causing severe and moderate impacts on the reproduction and growth of riparian forests, respectively. Alternatively, adopting EWC (reservoirs operating according to ecological rules) led to a 24% decrease in FF inundation area, a 63% reduction in its duration, and a groundwater level decline of 0.5–1 m in 87% of the region, and these changes caused severe impacts on riparian forest reproduction, while growth remained unaffected. These findings indicate that the current EWC effectively safeguards the growth of riparian forests but fall short of mitigating the impacts of water conservancy project construction and operation on the reproduction of riparian forests. Given the current trajectory, riparian forests are anticipated to undergo a gradual decline. Consequently, a sustainable EWC should ensure that the water volume discharged into the region exceeds 53% of the natural inflow and urgently requires measures to extend the duration of FF inundation. This study can provide new insights for the early evaluation, comparison and optimization of various WCPs before their implementation.

Talking to Multi-Party Conversational Agents in Advisory Services: Command-based vs. Conversational Interactions

Interacting with a conversational agent (CA) is becoming a major paradigm for human-technology interaction. Yet, ways for interacting with CAs are still forming, especially in situations involving more than one human. Starting an interaction with a CA might involve a wakeword and command. Alternatively, it could become active based on implicit requests and context information. Hence, CA designers face a serious dilemma: explicit commands disturb a natural conversation flow, while implicit requests might cause inadequate CA behavior. This study explores this dilemma and discusses observations from a project featuring a CA for financial advisory services. Advisors initially envisioned a CA that ''blends with the background'' and acts on context information. However, when engaging with a CA, they used conversational interactions in one part of the encounter and command-based interactions in another. We discuss this observation and contrast it against previous literature. This insight has implications for design and research.

Vegetation responses to large dam removal on the Elwha River, Washington, USA

Large dam removal can trigger changes to physical and biological processes that influence vegetation dynamics in former reservoirs, along river corridors downstream of former dams, and at a river’s terminus in deltas and estuaries. We present the first comprehensive review of vegetation response to major fluvial disturbance caused by the world’s largest dam removal. After being in place for nearly a century, two large dams were removed along the Elwha River, Washington, USA, between 2011 and 2014. The exposure, erosion, transport, and deposition of large volumes of sediment and large wood that were impounded behind the dams created new fluvial surfaces where plant colonization and growth have occurred. In the former reservoirs, dam removal exposed ~290 ha of unvegetated sediment distributed on three main landforms: valley walls, high terraces, and dynamic floodplains. In addition to natural revegetation in the former reservoirs, weed control and seeding and planting of desirable plants influenced vegetation trajectories. In early years following dam removal, ~20.5 Mt of trapped sediment were eroded from the former reservoirs and transported downstream. This sediment pulse, in combination with transport of large wood, led to channel widening, an increase in gravel bars, and floodplain deposition. The primary vegetation responses along the river corridor were a reduction in vegetated area associated with channel widening, plant establishment on new gravel bars, increased hydrochory, and altered plant community composition on gravel bars and floodplains. Plant species diversity increased in some river segments. In the delta, sediment deposition led to the creation of ~26.8 ha of new land surfaces and altered the distribution and dynamics of intertidal water bodies. Vegetation colonized ~16.4 ha of new surfaces: mixed pioneer vegetation colonized supratidal beach, river bars, and river mouth bars, and emergent marsh vegetation colonized intertidal aquatic habitats. In addition to the sediment-dominated processes that have created opportunities for plant colonization and growth, biological processes such as restored hydrochory and anadromous fish passage with associated delivery of marine-derived nutrients may influence vegetation dynamics over time. Rapid changes to landforms and vegetation growth were related to the large sediment pulse in the early years following dam removal, and the rate of change is expected to attenuate as the system adjusts to natural flow and sediment regimes.

Real-scale measurements of debris-flow run-ups

Rapid mass movements, such as debris flows, endanger alpine areas due to their destructive nature. In order to counteract these dangerous flows, it is necessary to design appropriate mitigation measures. A particular problem is the run-up of debris flows that impact on such structures. We provide in situ measurements of the run-up of three natural debrnis flows, each with multiple surges, in Gadria Creek, resulting from interaction with a mid-channel structure monitoring station. Four models were checked against data from other studies and the in situ measurements of the natural debris flows. The natural debris-flow measurements are all located in low Froude areas (Fr < 3) typical of Alpine granular debris flows. Sediment-laden pre-surges with Froude values greater than 2 produced the largest run-up factors in terms of run-up heights standardized to flow heights. Nevertheless, ensuing debris-flow surges exhibited a notable granular behavior and occurred at low Froude values. The findings indicate that the use of an energy conservation-based prediction model yields the most accurate estimates of the observed run-up factors. However, this smooth, gradual run-up can also be enhanced by preceding debris deposition and the formation of ramps. This can also prevent the formation of a reflection or shock wave, as assumed in models based on conservation of mass and momentum. These models have mainly overestimated the run-up factors of the observed debris flows.

Application of Novel Phase Change Material Constructive Solution for Thermal Regulation of Passive Solar Buildings

A comprehensive investigation regarding the hygrothermal behavior of a constructive solution containing phase change materials (PCMs) was performed on a full-scale test cell, divided into two similar compartments. This involved hygrothermal monitoring (indoor air temperature) of the two compartments, in which one had PCM incorporated into the floor mortar. The main goal of this research was to investigate the potential of this kind of solution for overheating mitigation. The numerical study was conducted using EnergyPlus® software (version 9.0), exploring different natural ventilation flow rates to gauge the novel solution’s potential to reduce overheating rates. The results from the monitoring studies revealed prolonged periods of thermal discomfort in both test cells, particularly overheating. However, it was proven that the PCM application in one of the test cells led to a reduction of almost 10 °C in the maximum peak of air temperature. In the simulation analysis, the increase in the ventilation rate led to a linear decrease in the overheating hours of up to one renovation per hour, and then the reductions were attenuated.

Reassessing the indicator value of the EPT group in karst rivers under hydromorphological pressure

Abstract Hydromorphological degradation is one of the most common stressors to freshwater ecosystems nowadays. Rivers lose riparian vegetation, habitat heterogeneity, natural flow velocity, etc., due to hydromorphological alterations. We analyzed macroinvertebrate communities in a wide range of hydromorphological conditions – from near natural sites to significantly altered water bodies, focusing on Ephemeroptera, Plecoptera, and Trichoptera (EPT). Considering that the EPT group is a quite sensitive and generally stenovalent group, we wanted to examine which of the hydromorphological pressures affects them the most. We also wanted to identify indicator taxa for different levels of degradation: minor, moderate, and severe. We collected samples from 84 karst rivers sites in Croatia. We found 52 taxa of EPT (Ephemeroptera – 21, Plecoptera – 11, Trichoptera – 20). Changes in river morphology proved to be the most important stressor affecting the distribution of the EPT group. Hydrological regulation did not show significance toward the EPT community, possibly due to the karst nature of the rivers studied. The most sensitive EPT taxa were those with the greatest preference for macrophytes and lithal habitats. More tolerant EPT taxa were those with a wide range of habitat preferences and/or taxa that feed on particulate organic matter.

Wall-resolved large eddy simulation of mixed-size sand-laden flow

Most of the existing numerical studies on wind-blown sand flow simplify sands into single-size particles, whereas natural wind-blown sand flow is a two-phase flow with mixed-size particles, thus, the simulation of mixed-size sand-laden flow is necessary. In the present work, wall-resolved large eddy simulations of mixed-size sand-laden flows are realized. Each sand in the wind field is tracked using the Lagrangian point-particle model. The transport characteristics of sand particles in mixed-size sand-laden flow are investigated under the premise of considering bed erosion. Considering the significant influence of sand-bed collision on simulation, the splash function is modified in the present simulation according to the previous experimental results. It reveals that in mixed-size sand-laden flow, the fraction of rebound sand particles in all the saltation particles is approximately 0.6, which is twice times of the ejected sand particles, and the modification of the sand rebound angle greatly affects the simulation results of mixed-size sand-laden flow. Meanwhile, the mean size of the saltation sand particles decreases with height and is 20% lower at the top of the saltation layer than that near the sand bed in the present simulation. Further analysis by grouping of sands with their size shows that the sand transport intensity of small sands decreased more rapidly with increasing height. The volume fraction and sand transport intensity of small sand particles exceed those of medium and large sand particles at heights y/δ = 0.05 and y/δ = 0.1.

The influence of inlet flow asymmetry on the carotid bifurcation hemodynamics

Arterial bifurcations are known to be high-risk areas for the initiation of atherosclerosis. The appearance and growth of atherosclerotic plaques in the bifurcation of the carotid artery can result in severe consequences such as cerebrovascular accidents. The common signs of an atherogenic risk center around the surpassing critical values by certain hemodynamic indices, which are distributed over the artery wall. These indices are related to the effect of blood flow on the arterial wall, and their distribution is influenced by both the bifurcation’s geometric shape and the flow structure at its inlet. The objective of this study is to carry out a comparative analysis of hemodynamic indices in personal-specific models of carotid bifurcation with centrally symmetric and asymmetric input flows. The examined geometric models of bifurcation are based on computed angiography data obtained from the individuals free of apparent pathology. By using computational fluid dynamics within these models, the distribution of hemodynamic indices in a steady periodic flow is calculated and critical zones are determined for them. All the models are divided into two groups – those with symmetric and those with asymmetric input flows. For each model with asymmetric input flow, an alternative geometry is designed to ensure inlet flow symmetry, and comparative numerical calculations of the blood flow are carried out. The results of comparative analysis reveal that the distribution of hemodynamic indices is simpler for the group with symmetric input flow. A comparison of the averages between these two groups with symmetrical and natural asymmetric input flows indicates a 55% better result for the latter group. Furthermore, for almost all models with asymmetric input flow, their alternative models give worse hemodynamic results. Thus, hemodynamic indices in simpler models with symmetrical input flow can serve as an upper estimate for indices in models with natural asymmetric flow. A total of 89 models are included in the study.

River pattern influences the composition of small indigenous species (SIS) of fish in deltaic Rajbari district, Bangladesh

Bangladesh is endowed with diverse rivers providing huge ecosystem services, but the diversity status and the abundance of the small indigenous species (SIS) are not identical in all rivers due to the natural water flow regime and anthropogenic challenges. Therefore, the present study endeavors to elucidate the composition and conservation status of SIS fish from four rivers namely, the Padma, the Gorai, the Chandana and the Horai rivers of Rajbari District, Bangladesh. Data were meticulously collected through fish sampling in each season, field observations, focus group discussions, and individual interviews by using a semi-structured questionnaire spanning from May 2021 and April 2022. The number of SIS in the Padma, the Gorai, the Chandana and the Horai rivers of Rajbari were 60, 36, 33 and 26, respectively, whereas a predominant concentration of fishes was notably observed in the benthopelagic zone of these rivers. Among the 60 riverine SIS, 23 fish were common in the four rivers. Additionally, Cyprinidae (>30%) was observed to be the most abundant SIS in the studied rivers. The fishermen in the research area used seven major fishing equipment of which cast nets are the most common for catching fish species. The abundance of SIS during the rainy season was the highest for all the studied rivers than the other seasons and 12 SIS were available throughout the year. Notably, the least concerned SIS outnumbered the other categories whereas, more than 10% was under the vulnerable category in the four rivers. The leading threats to the fish diversity were pollution followed by illegal and overfishing, siltation, reduced depth, degeneration of rivers and others. Consequently, to safeguard the existing SIS, reducing human pressure, implementing fishing regulations strictly, establishing and administering fish sanctuaries, and raising public awareness can be helpful for the sustainability of aquatic resources in deltaic areas.

Natural laminar flow leading edge: Requirements, design, and experimental validation under operational loads

To unlock the potential of natural laminar flow aircraft wings, novel structural designs are necessary for the wing leading edge and its attachment. Those designs may not impinge on operability and maintenance of the aircraft. This paper presents a leading edge and attachment design for the natural laminar flow environment as well as the testing of this design on a large-scale ground-based demonstrator. The leading edge design is numerically verified by considering operational loads. For operational viability, the replacement of damaged leading edges without alterations to the spare part is desirable. In a series of tests, such interchange trials are made with two ▪ full complexity leading edge segments and the aerodynamic step height at the interface of leading edge and wing cover is assessed in both ground and cruise deformation. The leading edge design and its attachment concept were proven to support natural laminar flow step height requirements even under global part deformations of a multi-material structure under thermal loading both numerically and experimentally. Interchangeability of the leading edge is demonstrated with very low mean variation in step height between different installations.

Water velocity shapes fish movement behavior.

Stream and river ecosystems present fluvial fishes with a dynamic energy landscape because moving water generates heterogeneous flow fields that are rarely static in space and time. Fish movement behavior should be consistent with conserving energy in these dynamic flowing environments, but little evidence supporting this hypothesis exists. Here, we tested experimentally whether three general movement behaviors-against the current, with the current, or holding position (i.e., staying in one position and location)-were performed in a way consistent with minimizing the cost of swimming in a heterogeneous flow field. We tested the effects of water velocity on movement behavior across three age classes (0, 1, and 5 years) of two different fluvial specialist fishes, the pallid sturgeon (Scaphirhynchus albus) and shovelnose sturgeon (Scaphirhynchus platorynchus). Individuals from the three age classes were exposed to a continuous and dynamic velocity field ranging from 0.02 to 0.53 m s-1, which represented natural benthic flow regimes occupied by these species in rivers. Both sturgeon species exhibited the same pattern with regard to their tendency to hold position, move upstream, or move downstream. Moving downstream was positively associated with velocity for all age groups. Moving upstream was inversely related to velocity for young fish, but as the fish aged, moving upstream was not related to water velocity. The oldest fish (age 5) moved upstream more frequently compared to the younger age classes. Holding position within a water current was the most frequent behavior and occurred with similar probability across the range of experimental velocity for youngest fish (age 0), but was inversely related to velocity in older fish. Our experiment across age classes suggests that the suite of swimming behaviors exhibited by fluvial specialists might have evolved to mitigate the energetic costs of complex energy landscapes generated by moving water to ultimately maximize net energy gain.

A conical spiral piezoelectric energy harvester with parallel beams for all-directional flow energy harvesting

Piezoelectric energy harvesting technology using flow-induced vibration is a type of interference-resistant and miniaturizable power generation technology, which is promising on powering the wireless micro electromechanical system in flow filed. However, the flow direction of the natural flow field is changeable while most existing flow-induced piezoelectric energy harvesters (PEHs) are limited by their working direction. In this paper, we propose a conical spiral piezoelectric energy harvester with parallel beams (CSPEH-PB) that can collect energy under flow excitation in all directions. Based on the multi-dimensional vibration analysis of conical spiral structure, we investigate the resonance mode and effective flow velocity range of the CSPEH-PB through numerical analysis. In comparative experiments with a bimorph flat PEH, we verify the effective flow velocity range and voltage of the CSPEH-PB and polyvinylidene fluoride (PVDF) films attached. The results demonstrate that the CSPEH-PB generates an effective voltage greater than 0.53 V through the PVDF films under any direction of the water flow, and has a wider resonance bandwidth than PEH with straight beam. This study provides a practical solution for adapting PEHs to changeable flow direction.

Evaluation of Subdaily Hydrological Regime Alteration Characteristics for Hydro–Photovoltaic Complementary Operation in the Upper Yellow River

The complementary operation of hydropower and photovoltaic power, aimed at meeting real-time demand, has led to frequent adjustments in power generation, causing significant fluctuations in hydrological systems and adversely affecting fish reproduction. The traditional hydrological regime alteration assessment index is based on index of hydrologic alternation (IHA) and mostly focuses on annual and daily runoff alterations. This study proposes a new set of indicators considering the characteristics of subdaily hydrological regime alterations, including magnitude, rate of change, duration, frequency, and timing. Using the hourly outflow from Longyangxia, an analysis of indicator redundancy was conducted. The alteration of the indicators before and after hydropower and photovoltaic operation was then analyzed using the cumulative probability distribution curve. Additionally, a concentration index was introduced to analyze the variations in hydrological impacts during different months. The results show that the hydro–photovoltaic complementary operation changed the subdaily natural flow regime, significantly increasing the rate of flow increase or decrease and the duration, with most indexes increasing by more than 100% compared with the natural flow regime. Furthermore, the concentration values of the indexes for the hydro–photovoltaic complementary operation were less than 10, indicating a more significant impact on the subdaily flow regime throughout the year. This research provides crucial data for mitigating ecological impacts under multi-source complementary scheduling.

Passive Cooling of Glazing Surfaces Using Solar Chimneys

The aim of this project is to reduce the cooling loads in spaces by decreasing the window temperature and solar radiation entrance through the use of a passive evaporative cooler combined with a solar chimney and with no additional energy consumption. The cooler provides heat and mass exchange that render the air capable of cooling the space in front of the window. On the other hand, the solar chimney works based on principles of buoyancy driven natural flows. Mathematical models of the evaporative cooler, glazing section, solar chimney are developed and integrated with a space model in an algorithm where the entire system is tested under different outdoor temperature and solar radiation conditions. As the outer glass temperature typically represents the temperature of the window without the installation of this system, reductions of 8% to 12% in the window temperatures were seen for an outdoor temperature of 30oC and a solar radiation of 300Wm2 and for small chimney sizes.