Search Results (11)

Compared with real fish, bionic fish have significant gaps in terms of swimming speed and efficiency, turning performance, and agility. The complicated underwater working environment necessitates monitoring equipment that can deal with the dynamic interference of dense fish schools and aquatic vegetation. An agile and flexible bionic fish with a fast swimming speed would be better suited to underwater monitoring tasks. In this study, a bionic greenfin fish robot is designed in detail, and a hydrodynamic simulation analysis of the designed bionic greenfin fish robot is carried out using STAR CCM+ and Fluent software to analyze the effects of different parameters on the propulsion performance of the pectoral fins, the steering of the caudal fins, and the emergency stop function. The swimming efficiency was found to be highest when the angle of attack was changed sinusoidally by 10° and the frequency was the same as that of the pectoral fin flutter. The feasibility of an emergency stop of the tail fin with negative-phase swinging and the adjustment of the pectoral fin uneven flutter monitoring position were also confirmed. Full article

This paper aims to solve the problem of erosion sediment that negatively affects the quality of fallowed soil through the development of a new type of agricultural machinery. The transported erosion sediment will be quantified locally to evaluate the danger of these negative effects on the fallowed soil and on the functionality of the grass cover. Subsequently, a new type of machinery will be proposed for the remediation of eroded sediment and conservation of the fallowed soil. In various fallow research areas with different management methods (such as biobelts, grassed valleys, and grassed waterways), agricultural land affected by eroded sediment was examined, and appropriate machinery was designed to rehabilitate the stands after erosion events. By identifying the physical and mechanical properties of the soil, as well as the eroded and deposited sediment/colluvium, the shape, material, attachment method, and assembly of the working tool for the relevant mobile energy device were designed. The developed tool, based on a plow–carry system using a tractor, features flexible tools that separate the eroded sediment from the fallow land surface, transfer it over a short distance, and accumulate it in a designated area to facilitate subsequent removal with minimal damage to the herbaceous vegetation. The calculated erosion event was 196.9 m³ (179.0 m³ ha⁻¹), corresponding to 295 tons (268.5 t ha⁻¹) deposited from the area of 90 ha. Afterward, the proposed machinery was evaluated for the cost of the removal of the eroded sediment. Based on experience from the field, we calculated that 174 m³ per engine hour results in EUR 0.22 m⁻³. From the performed experiment, it is evident that the proposed machinery offers a suitable solution for eroded sediment removal locally, which prevents further erosion and subsequent sediment deposition in water bodies where the costs for sediment removal are higher. Moreover, we have proven the potential negative impact of invasive plant species because their seeds were stored in the sediment. Finally, it is credible to state that the proposed agricultural machinery offers an effective solution for the eroded sediment relocation, which subsequently can be used for other purposes and monetized. This results in an increase in the profitability of the erosion sediment removal process, which is already in place at the source before further transportation to aquatic systems where the costs for removal are significantly higher. Full article

Aquatic vegetation in the littoral zone plays a crucial role in attenuating wave energy and protecting coastal communities from hazardous events. This study contributes to the development of numerical models aimed at designing nature-based coastal defense systems. Specifically, a novel numerical application for simulating wave–vegetation interactions at the stem scale is presented. The numerical model employed, DualSPHysics, couples the meshfree Smoothed Particle Hydrodynamics (SPH) fluid solver with a structural solver to accurately capture the two-way interactions between waves and flexible vegetation. The proposed numerical model is validated against experimental data involving a submerged rubber cylinder representing an individual vegetation stem, subjected to regular waves. The results demonstrate excellent agreement in hydrodynamics, force transfer, and the swaying motion of the flexible cylinder. Importantly, the approach explicitly captures energy transfer between the fluid environment and the individual stem. The numerical results indicate persistent turbulent flow along the vegetation stem, even when its swaying speed matches that of the surrounding environment. This reveals the presence of vortex shedding and energy dissipation, which challenges the concept of passive swaying in flexible aquatic vegetation. Full article

Curved channels and aquatic vegetation are commonly present in the riverine environment. In this study, the effects of vegetation density and distribution on the hydrodynamic characteristics of a mixed layer developed over a 180-degree curved channel were investigated through flume experiments. Wooden sticks were used to simulate rigid vegetation distributed along the half side of the channel, and a 200 Hz acoustic Doppler velocimeter (ADV) was employed to measure the three-dimensional instantaneous velocity at five selected cross sections along the curved channel. Experimental results show that the vegetation covering the half of the channel significantly affects the hydrodynamic structure of the curved channel flow, and the unequal vegetation resistance induces the K-H instability at the vegetation and non-vegetation interface, resulting in a standard hyperbolic tangent function of streamwise velocity distribution along the lateral direction. The influence of curve position on turbulence kinetic energy is far greater than that of vegetation density and vegetation distribution. The peak value of turbulent kinetic energy is comprehensively affected by vegetation density and distribution, and the peak position of turbulent kinetic energy at the interface is changed by different vegetation distribution. The combined effect of the curve and the partly covered vegetation increases the mixing between the water bodies, enhancing turbulent kinetic energy, and vegetation along the concave bank plays a more significant role. For turbulent bursting, the inward and outward interactions are mainly bursting events in the vegetation area, while ejections and sweeps are dominant in the non-vegetation area. However, the critical vegetation condition to initiate large-scale coherent structure (LSS) in the mixed layer and the influence of flexible vegetation need to be further studied in the future. Full article

Aquatic vegetation plays a critical role in aquatic environments and provides various valuable services. To characterize vegetation, vegetation density and flexibility are usually used as parameters, but aquatic vegetation found in nature may have a non-uniform distribution of density in the vertical direction. Studies have shown that this non-uniformity could impact the flow structure and flow resistance. With the aim of studying the effect of vertical variation of submerged vegetation density on the flow resistance and bulk flow characteristics, the hydrodynamics of three types of wooden model vegetation elements were compared in the laboratory. Vegetation models had the same density but different vertical distributions of density. All other influential parameters were kept constant so that any differences in the flow structure and the flow resistance would be attributable to the distribution of density in the vertical direction. The results show that the vertical distribution of submerged vegetation density impacts the flow field, bed shear stress, and flow resistance. There was a 41% difference in the value of the drag coefficient produced by the models. The distance between the bed and the geometrical center of vegetation elements was introduced as a parameter to quantify the effect of the vertical distribution of vegetation. There is a direct relation between this parameter with both the drag and Manning’s coefficients. The findings of this can study help researchers and practitioners use relevant vegetation parameters. Full article

Bottom friction is an important process in coastal and estuarine environments because it can reduce wave heights and moderate tidal currents. When modeling large systems with spatially varying hydraulic properties, bottom friction values are commonly derived from land use classification products. However, estimation of bottom friction for vegetated areas can be more challenging due to the complicated and time-varying geometry of the roughness elements. This is particularly true of flexible, buoyant submerged aquatic vegetation (SAV) species, such as seagrasses and kelps, that deform under waves and currents. In this study we incorporate a dynamic friction model that includes the temporal variation in SAV drag forces into a depth-integrated coupled circulation-wave model. In vegetated areas, the bottom friction is continuously updated based on plant geometry, water depth, and combined wave-current velocities. Taking a multi-scale approach, we use the model to investigate the impact of SAV dynamics on both the localized and the integrated bay-wide hydrodynamics of a riverine and tidally influenced estuary. First, we investigate SAV modification of velocity fields and its implications for sediment transport and circulation pathways. Then, we show how SAV can modify tidal behavior throughout the estuary. Full article

Despite being recognized as a key component of shallow-water ecosystems, submerged aquatic vegetation (SAV) remains difficult to monitor over large spatial scales. Because of SAV’s structuring capabilities, high-resolution monitoring of submerged landscapes could generate highly valuable ecological data. Until now, high-resolution remote sensing of SAV has been largely limited to applications within costly image analysis software. In this paper, we propose an example of an adaptable open-sourced object-based image analysis (OBIA) workflow to generate SAV cover maps in complex aquatic environments. Using the R software, QGIS and Orfeo Toolbox, we apply radiometric calibration, atmospheric correction, a de-striping correction, and a hierarchical iterative OBIA random forest classification to generate SAV cover maps based on raw DigitalGlobe multispectral imagery. The workflow is applied to images taken over two spatially complex fluvial lakes in Quebec, Canada, using Quickbird-02 and Worldview-03 satellites. Classification performance based on training sets reveals conservative SAV cover estimates with less than 10% error across all classes except for lower SAV growth forms in the most turbid waters. In light of these results, we conclude that it is possible to monitor SAV distribution using high-resolution remote sensing within an open-sourced environment with a flexible and functional workflow. Full article

The monitoring of Global Aquatic Land Cover (GALC) plays an essential role in protecting and restoring water-related ecosystems. Although many GALC datasets have been created before, a uniform and comprehensive GALC dataset is lacking to meet multiple user needs. This study aims to assess the effectiveness of using existing global datasets to develop a comprehensive and user-oriented GALC database and identify the gaps of current datasets in GALC mapping. Eight global datasets were reframed to construct a three-level (i.e., from general to detailed) prototype database for 2015, conforming with the United Nations Land Cover Classification System (LCCS)-based GALC characterization framework. An independent validation was done, and the overall results show some limitations of current datasets in comprehensive GALC mapping. The Level-1 map had considerable commission errors in delineating the general GALC distribution. The Level-2 maps were good at characterizing permanently flooded areas and natural aquatic types, while accuracies were poor in the mapping of temporarily flooded and waterlogged areas as well as artificial aquatic types; vegetated aquatic areas were also underestimated. The Level-3 maps were not sufficient in characterizing the detailed life form types (e.g., trees, shrubs) for aquatic land cover. However, the prototype GALC database is flexible to derive user-specific maps and has important values to aquatic ecosystem management. With the evolving earth observation opportunities, limitations in the current GALC characterization can be addressed in the future. Full article

Flow resistance, velocity distribution, and turbulence intensity are significantly influenced by aquatic vegetations (AV) in riparian zones. Understanding the hydraulics of flow with planted floodplains is of great significance for determining the velocity distribution profile and supporting the fluvial processes management. However, the traditional flume experiment method is inefficient. Therefore, the multigroup simultaneous flume test method was carried out to describe the flow patterns affected by emerged rigid (reed and wooden stick) and submerged flexible vegetations (grass and chlorella). The Acoustic Doppler Velocimeter (ADV) was utilized to measure the velocity at one point for different experimental conditions. The results showed that hydraulic features were influenced by different types of vegetation. Furthermore, the relative depth (z/h) was a determining factor of those variations. In addition, the time-averaged velocity distributions of planted floodplains are not logarithmic. Instead, they represented “s-shape” profiles. In detail, for the vegetated floodplains, reed and wood followed an s-shape profile, but for grass and chlorella, they followed reverse s-shape profile. For all cases, turbulence is not isotropic and the change law of turbulence intensity is different in different sections. The flow resistance, turbulence intensities, and Reynold stresses influenced by different types of vegetation were also analyzed. Full article

In this paper, the problem of the interaction between a periodic linear wave and offshore aquatic vegetation is investigated. The aquatic vegetation field is considered as a flexible permeable system. A vegetation medium theory is proposed based on Lan–Lee’s poro-elastomer theory, in which linearizing vegetation friction resistance is used to describe fluid motion in the vegetation medium. The study involves boundary conditions for free surface water in emergent vegetation media that have been of less concern in previous studies. The analytical solutions of the vegetation medium and wave fields are derived by the partitioning method combined with matching boundary conditions for neighboring regions. An estimation formula for a modification factor is proposed to evaluate the linear vegetation friction coefficient, which can reasonably compare the analytical solution with relevant past cases in terms of wave transmission. Wave reflection, transmission, and attenuation induced by the effects of the characteristics of the vegetation are studied. The results indicate that an increase in the drag coefficient, stem diameter, stem density, spatial coverage, and plant stiffness leads to the emergency vegetation inducing higher wave energy dissipation and reducing the wave transmission. Vegetation stiffness is a significant factor affecting the drag coefficient. Full article

Vegetation in riparian zones has a significant influence on resistance, velocity distribution and turbulence intensity. This study experimentally investigated the effect of emergent bending riparian zone vegetation on the flow. The results showed that the frond and stem parts of Acorus calami had different influences on hydraulic features and that the relative depth ratio of water depth h to stem height h_s was a key determinant of those influences. Manning coefficient n varied greatly with the variation of vegetation densities, relative depth ratio of water depth h to stem height h_s, Re and Fr. Manning coefficient n increased with increasing vegetation density, particularly in cases when h/h_s > 1. The velocity distributions did not follow logarithmic profiles, but they instead exhibited double logarithmic profiles. In addition, vegetation characteristics were shown to influence the height of maximum velocity. The position of maximum velocity is further away from the bed in cases with denser vegetation distribution. Finally, turbulence intensity showed more significant variation in the stem part and peaked near the middle of the stem, at z/h_s = 0.5, where z was the distance from the bottom. Full article