Smooth Slope Research Articles

Experimental investigation of dissolved oxygen improving aeration efficiency by hydraulic jumps

The dissolved oxygen (DO) level in water is vital for water quality and supporting aquatic life. Hydraulic jumps involve rapid flow changes from super-critical to sub-critical, visible at abrupt bed slope shifts, like at spillway bases in rivers or canals. The hydraulic jump efficiently mixes oxygen from air into water and offers a cost-effective method of aeration by entraining air bubbles in the stream to improve oxygen transfer compared to traditional systems. The objective of this experimental research is to investigate the aeration performance with hydraulic jump parameters and establish correlations crucial to measuring aeration (or transfer) efficiency. Relationships between transfer efficiency, jump height, jump length, sequent depth ratio, discharge, inlet Froude number, and channel bed slope were determined. To investigate the nature of such relationships, a series of experiments were conducted in a rectangular tilt flume to test the aeration performance of forced submerged hydraulic jumps with five different discharges and five different smooth bed slopes. The inlet Froude number before the jump varied from 2.18 to 8.23. Experimental observation confirms a positive relationship between transfer efficiency and jump control parameters. During experimentation, transfer efficiency was found to vary between 9.4 % and 34 %. This research includes estimating the optimal transfer efficiency due to hydraulic jumps, which can help hydraulic engineers in building structures that can revitalize any degraded stream.

Numerical Evaluation of Wave Dissipation on a Breakwater Slope Covered by Precast Blocks with Different Geometrical Characteristics

Slopes suffer damage from waves in coastal environments. Precast blocks with well-designed geometrical characteristics can benefit the construction of revetments by mitigating the issue of wave overtopping and dissipating wave energy. In this study, we numerically studied the effect of the geometrical characteristics of precast blocks on wave overtopping by carrying out a numerical simulation of wave overtopping on a slope covered with precast blocks. A total of three different types of blocks were considered in this study to determine the optimal geometric shape using a validated numerical model. Our numerical investigation demonstrated that the roughness of the precast block plays an important role in lessening the height of the wave run-up. Concave and embedded regular hexagons could reduce the wave run-up height by 44.6% compared with smooth slopes within a 2 s wave period. Herein, we evaluate and discuss the influence of the geometrical characteristics of a given precast block, such as thickness, aperture, and wave dissipation notch, on wave run-up. We also present an empirical formula for predicting wave run-up on a slope covered by a concave and embedded regular hexagon-type prefabricated block. This study provides valuable insights into the design of prefabricated revetment blocks.

Stability analysis for passive robots walking on inclined surfaces with local angles

For common-legged robots with a kind of stiff joints, the human-like and consecutive gait shown by passive walking robots is a bit difficult to achieve because of varying degrees of control, which is usually accompanied by computational cost. Of course, passive dynamic walking undoubtedly has its inevitable disadvantages because of the lack of control, which is stability. At the same time, the significant nonlinearity of the passive gait increases the difficulty of realizing the walking stability of the passive robot. Therefore, the passive robot still needs certain control to achieve stable walking even on the natural plane or smooth slope. In this paper, a passive robot model walking on an inclined plane with a local angle is studied. First of all, the approximate solution of the nonlinear dynamic equation is given by the perturbation method, and the conditions for the robot to achieve stable walking without external forces are obtained. Further, the input-output feedback linearization control based on hybrid zero dynamics is employed to carry out virtual constraints on the passive robot during the swing stage of walking, facilitating the transition from the unstable state to the stable periodic state. From the result of the experiments, the walking stability of the passive robot is improved over a larger range of walking status values compared with the condition without external force control, and the use of this method reduces the complicated work of solving the fixed point. These findings possibly have reference value in passive walking stabilization control. Meanwhile, the simulation results obtained by designing and studying the minimum controlled walking model show that human walking is based on the uncontrolled mechanical process. The exploration of the mechanism of passive gait can provide some enlightenment to the research of human texture and the application of exoskeleton.

Empirical Predictions on Wave Overtopping for Overtopping Wave Energy Converters: A Systematic Review

Over the past three decades, the development and testing of various overtopping wave energy converters (OWECs) have highlighted the importance of accurate wave run-up and overtopping predictions on those devices. This study systematically reviews the empirical formulas traditionally used for predicting overtopping across different types of breakwaters by assessing their strengths, limitations, and applicability to OWECs. This provides a foundation for future research and development in OWECs. Key findings reveal that empirical formulas for conventional breakwaters can be categorized as mild or steep slopes and vertical structures based on the angle of the slope. For the same relative crest freeboards, the dimensionless average overtopping discharge of mild slopes is larger than that of vertical structures. However, the formula features predictions within a similar range for small relative crest freeboards. The empirical formulas for predicting overtopping in fixed and floating OWECs are modified from the predictors developed for conventional breakwaters with smooth, impermeable and linear slopes. Different correction coefficients are introduced to account for the effects of limited draft, inclination angle, and low relative freeboard. The empirical models for floating OWECs, particularly the Wave Dragon model, have been refined through prototype testing to account for the unique 3D structural reflector’s influence and dynamic wave interactions.

Response of Hydrodynamic Characteristics to Tillage-Induced Microtopography of Rill Erosion Processes under Heavy Rainfalls

Response of Hydrodynamic Characteristics to Tillage-Induced Microtopography of Rill Erosion Processes under Heavy Rainfalls

A Novel Direct Current Circuit Breaker with a Gradually Increasing Counter-Current

A reliable and cost-effective mechanical direct current circuit breaker (DCCB) is a promising solution for DC interruption. However, the typical mechanical DCCB has difficulty in interrupting a rated current, because the high oscillating current superimposed on the rated current generates a steep current slope at current zero-crossing (CZC) points, which makes it difficult for the vacuum interrupter to extinguish the arc. The objective of this paper is to present a novel DCCB topology with a gradually increasing counter-current. It utilizes a full-controlled converter, a semi-controlled full bridge, and an LC oscillation branch to generate a gradually increasing counter-current, which is superimposed on any fault current and generates a smooth current slope at CZC points. The proposed DCCB topology is modeled with PSCAD, and the current slope and the initial transient interruption voltage (ITIV) at CZC are analyzed and compared with the typical mechanical DCCB. The results indicate that the current slope at CZC decreases by 57–84% in full-range current interruptions, and the ITIV can be reduced by the same extent. Additionally, the performance of the proposed DCCB is evaluated in a four-terminal HVDC system. A cost and performance comparison is conducted among the main topologies. The obtained results show that the proposed DCCB is a reliable solution for the multi-terminal HVDC system.

Vineyard Microclimatic Zoning as a Tool to Promote Sustainable Viticulture under Climate Change

Understanding microclimate spatial variability is crucial for sustainable and optimised grape production within vineyard plots. By employing a combination of a microclimate model (NicheMapR) and multiple climate data sources, this study aimed to achieve microclimatic analysis in two vineyard plots, Quinta do Bomfim (northern Portugal) and Herdade do Esporão (southern Portugal). This approach provides an innovative 10 m spatial resolution for climate variables. This study incorporated local station hourly data with quantile mapping bias correction on the ERA5-land data. The microclimate model output was employed to perform bias correction on a EURO-CORDEX model ensemble. Climate extreme and bioclimatic indices specifically targeted to viticulture were calculated for each vineyard plot. The 10 m scale was analysed to identify potential shifts in temperature extremes, precipitation patterns, and other crucial climatic variables for grape cultivation within each specific plot. The significance of microclimate analyses was higher in areas with intricate topography, while in areas with smooth slopes, the variation of climatic variables was determined to be negligible. There was a projected increase in the median temperature of approximately 3.5 °C and 3.6 °C and a decrease in precipitation of approximately 98 mm and 105 mm in Quinta do Bomfim and Herdade do Esporão, respectively, when comparing a future scenario for the period 2071–2100 against the historical period (1981–2010). Hence, this study offers a comprehensive and future-oriented method for analysing microclimates in vineyard plots. By incorporating geospatial data, ERA5-land data, and the microclimate NicheMapR model, this research aimed to enhance the understanding of current microclimates and future climate scenarios for viticulturists.

Swash-flow induced forces on human body standing on a smooth and impermeable slope: A numerical study with experimental validations

ABSTRACT Swash flow poses a significant hazard to pedestrians standing on the slope of the seawall. Unlike the forces of overtopping flow or open channel flow on the human body, which have been studied before, swash flow has two distinct cycles within one wave period: onshore flow and offshore flow. Both cycles can risk human safety by exerting hydrodynamic forces on the body. This paper presents a numerical study to examine the hydrodynamic forces exerted on the human body when subjected to swash flow on a smooth and impermeable slope. A Reynolds-averaged Navier-Stokes (RANS) model is set up in OpenFOAM, where the numerical results are compared with experimental data obtained from wave tank tests. Reasonable agreement has been achieved, which validates the numerical model. We examine the kinematics of swash flow generated by plunging and surging breakers. In the case of a plunging breaker, we observe that the instantaneous runup height exhibited asymmetry, whereas it is nearly symmetric for a surging breaker. The velocity profile is then used to compute the momentum flux of the swash flow, which is shown to be associated with the inline forces exerted on the human body. We have defined an instability index to assess the risk of pedestrian mobilisation by swash flow, demonstrating its dependence on the Iribarren number and the body's position. The analysis reveals that the associated risk is substantially reduced as the Iribarren number increases and when the body moves towards the shoreline.

Effect of microrelief features of tillage methods under different rainfall intensities on runoff and soil erosion in slopes

Tillage methods play a crucial role in controlling rainwater partitioning and soil erosion. This study utilized rainfall simulation experiments to investigate the impact of four tillage methods (manual digging (MD), manual hoeing (MH), traditional ploughing (TP), and ridged ploughing (RP)) on runoff and soil erosion at the plot scale. The smooth slope (SS) was used as a benchmark. Rainfall intensities of 30, 60, 90, and 120 mm h−1 were considered. The study revealed that tillage altered rainwater distribution into depression storage, infiltration, and runoff. Tillage reduces runoff and increases infiltration. The four tillage methods (30–73%) increased the proportion of rainwater converted to infiltration to varying degrees compared to the SS (22–53%). Microrelief features influenced the role of tillage methods in soil erosion. Surface roughness and depression storage accounted for 79% of the variation in sediment yield. The four tillage methods reduced runoff by 2.1–64.7% and sediment yield by 2.5–77.2%. Moreover, increased rainfall intensity weakens the ability of tillage to control soil erosion. When rainfall intensity increased to 120 mm h−1, there was no significant difference in runoff yield among RP, TP, MH, and SS. Therefore, assessing the effectiveness of tillage in reducing soil erosion should consider changes in rainfall intensity. Additionally, the cover management (C) factor of the RUSLE was used to assess the effects of different tillage methods on soil loss. Overall, the C factor values for tilled slopes are in the order MH > TP > RP > MD with a range of 0.23–0.97. As the surface roughness increases, the C factor tends to decrease, and the two are exponential functions (R2 = 0.86). These studies contribute to our understanding of how different tillage methods impact runoff and soil erosion in sloped farmland and provide guidance for selecting appropriate local manual tillage methods.

New Settlement of Holercani-Hansca Cultural Horizon in Republic of Moldova

As a result of field surveys of the last years, the new site of Holercani-Hansca cultural group – Andreevca-I settlement has been found. The purpose of this research paper is the characteristics of the mentioned site and the interim results of its study.
 Results. Andreevca-I settlement is located in Orhei raion of the Republic of Moldova, at the lands of Chiperceni Community. The site is located 0.38 km northeast of the village of Andreevca and 0.28 km northwest of the pond of the village of Andreevca; on the left bank of the stream Vorotet. The settlement is located on a smooth slope. The land area of the settlement along the line North-West-South-East is 100x200 m. Fragments of ceramics, bones of animals, pieces of burnt clay, and different stones, some of them with traces of processing, were found on the plowed surface. The settlement is multilayered. The ceramics of the Late Bronze Age prevail in the materials of the settlement. It is associated with Holercani-Hansca cultural group (12th – 10th century BCE), interim between the cultures of the early Hallstatt, and the Late Bronze Age.
 According to O.G. Levitskiy, Holercani-Hansca group fills the gap between the cultural formations of Pre-Babadag and Tămăoani type and Balta group of sites of the Late Bronze Age. In addition, Hallstatt horizon with prevailing incised ceramics, which can be conventionally called Tămăoani-Holercani-Balta, is distinguished. Chronological framework of this horizon according to analogues of Balta group and Tămăoani can be the end of the 12th – 10th century BCE. The closest analogues to this cultural formation could be the cultures of the Lower Danube region – Sihleanu, Tămăoani, Pre-Babadag, Babadag-I, and early Belozerka culture sites, including Balta group of the Late Bronze Age. The role of Chisinau-Corlateni type sites, of which Holercani-Hansca group had got a number of material borrowings while forming its cultural entity, is doubtless.

Effects of microtopography change driven by seepage and slope gradients on hillslope erosion of purple soil

Seepage is the prominent hydrological process on tilled hillslopes covered by purple soil, which can easily exacerbate slope instability and soil loss. Laboratory simulated experiments with a seepage intensity of 4 L min−1 under different slope gradients (5°, 10°, and 15°) were conducted to analyze how seepage induced the erosion impacts the microtopographic change during water erosion process. Three tillage practices, i.e., smooth slope (CK), artificial diffing (AD) and ridge tillage (RT) with different initial microrelief were designed in this study. Results showed that the variation of soil surface roughness (SSR) to seepage erosion showed CK > AD > RT, and the most severe on the midslope and downslope, fluctuating from −4.23% to 12.40%. The sharpness of soil surface microtopography (SSM) on RT and AD decreased as the slope gradient increased. Compared to CK, AD and RT effectively controlled runoff loss. Both AD and RT were unable to reduce soil loss when the seepage duration exceeded 45 min, that was, the sediment yield increased by 815.50% and 730.25%, respectively. The response of surface runoff and sediment yields to microtopography changes was characterized applying multivariate linear equation. The applicability of multifractal parameters was weakened in the terms of the response to soil erosion caused by seepage. In contrast, the contribution rate of RUp to soil erosion was 69.40% and that of RDown was 58.76% in SSR indexes under seepage condition, which were the optimal parameters assessing the changes of surface runoff and sediment yields. This study contributes to elucidating seepage erosion effects in purple soil slope and understanding hydrological processes based on SSM changes.

Gneissic tors in the central European upland: Complex Late Pleistocene forms?

Bedrock outcrops punctuating regolith-covered surfaces in the summit/upper slope and hillside positions (tors and crags) have long been a subject of inquiry in geomorphology for their evolutionary trajectories and now also as valuable geoheritage sites. Methodological advances in research, such as DTM-based geomorphological analysis and terrestrial cosmogenic nuclide inventories, create new perspectives to decipher the spatial and temporal context of tor emergence and decay. The shape, structural controls, 10Be inventories and relation to surrounding medium-scale landforms were studied at thirteen conspicuous bedrock outcrops developed in metamorphic and sedimentary lithologies in the Bohemian-Moravian Highland, Czechia. The shapes of studied bedrock outcrops indicate significant litho-structural controls. The general outline is mainly governed by (sub)vertical joints, whereas the inclination of foliation or bedding planes dictates summit and cliff morphology. Some of the tors described in this study developed in exceptionally densely foliated and jointed gneiss, which does not comply with the generally accepted view of tors as massive rock compartments resisting weathering. A series of rock hardness measurements performed at three gneissic tors using Schmidt hammer show statistically significant within-tor variability of R-values, indicating different exposure times to subaerial weathering. The complexity of landform assemblages, within which studied tors/crags are developed, varies from isolated bedrock outcrops surrounded by smooth slopes covered with debris-rich soils to outcrops accompanied by low rock cliffs, debris-covered steps, slope benches, boulder fields and isolated large blocks. The 10Be inventories reveal ages mostly from the Late Pleistocene and rarely from the Holocene. Summit/upper slope tors and hillside crags show considerable variability in maximum denudation rates ranging from 6.4 ± 0.2 to 105.6 ± 4.8 m/Ma. Paired samples from the summits and cliffs of eight outcrops indicate three possible post-emergence evolutionary scenarios with summit downwearing while keeping the outcrop outline, balanced cliff and summit degradation rate, and backwearing as the dominant degradation process.

Multi-temporal spatial modelling to assess runoff and sediment dynamics under different microtopographic patterns

Soil erosion is a multi-scale geographical interface process with high spatiotemporal variability. This study aimed to assess runoff and sediment dynamics under different microtopographic patterns based on wavelet analysis and SIMulated Water Erosion model (SIMWE). Three rainfall intensities of 1.0 mm min−1, 1.5 mm min−1, and 2.0 mm min−1, combined with three slope gradients of 10°, 15°, and 20°, were utilized to conduct rainfall simulations on three soil boxes measuring 4 m in length and 0.8 m in width. The soil boxes exhibited distinct microtopographic patterns, including smooth slope (CK), artificial digging (AD), and ridge tillage (RT). The results showed that the runoff and sediment reduction benefits of different tilled slopes decreased with an increase in both slope and rainfall intensity. The AD and RT slopes reduced runoff yields by 8.4% − 50.2% and 17.3% − 75.0% respectively compared to CK slope. Although sediment yields from AD and RT slopes were reduced by 4.2% − 51.6% and 1.8% − 53.0%, respectively, the sediment control benefits of AD and RT slopes were basically lost when the slope gradient increased to 20°. The rill erosion was the main source of soil erosion on different tilled slopes, accounting for 72% − 87% of the total soil loss. And the rates of both soil erosion and rill erosion exhibited a power function relationship with an increase in rainfall intensity and slope. The impact of slope gradient on soil erosion on the RT slope was greater than those on the CK and AD slopes. During the development of rill erosion, non-stationary and multi-scale periodic phenomena exist in the time series of runoff and sediment on different microreliefs. As surface microrelief increased, the fluctuations in runoff and sediment on tilled slopes intensified, resulting in a gradual shortening of the variation period. And this study verified the feasibility of the SIMWE model to simulate the runoff and sediment dynamics on microtopographic scale under a single rainfall event. The results can provide a theoretical basis for the scientific layout of soil and water conservation practices in sloping farmland and the construction of soil erosion model in purple soil area.

Pit-mound microrelief on a forested slope drives infiltration and preferential flow after heavy rainfall – experiments with soil resistance monitoring and dye tracing

With the changing climate, short heavy rainfalls (SHRs) are becoming more frequent and intensive. The distribution of rainwater and subsurface runoff formation in forest soils can be strongly affected by soil disturbances and surface microrelief. Rainwater redistribution and the formation of preferential flow in response to natural and simulated SHRs were investigated in soil profiles on slopes forested by Norway spruce with a pit-mound microrelief formed by historical tree uprooting using two independent methods; soil electrical resistance monitoring and the application of dye tracer. In the deepest soil layers, resistance decreased in responses to natural SHRs on average by 46% in pits and by 11% on ‘smooth slope’ controls, reflecting the deeper redistribution of infiltrated water in pits. Dye tracing in the simulated rainfall revealed the formation of shallow biomat flow at the control plot. In contrast, the shallow lateral flow was focused by the pit and redirected into funnel flow underneath the pit bottom. The sum of medium and high dye concentration classes obtained with the support vector machine classification of profile photographs indicated a higher water entry into topsoil and subsoil layers in pit (44% and 31% of area, respectively) as compared to the control profile (16% and 8% of area, respectively). Leaving pit-mound microrelief as the natural legacy in forest soils can mitigate some of the negative hydrological effects of intensive forest management and may improve the water yields on forested slopes by redirecting shallow subsurface runoff and facilitating deep distribution of infiltrated water. Such beneficial effects of pit-mounds on the hydrology of forested slopes should be considered in future hydrological modelling and land management.

SPH modeling of dam-break bores on smooth and macro-roughness slopes

Understanding the kinematics and hydrodynamics of long waves in nearshore zones is currently one of the more pressing aims motivating research in the coastal engineering community. Owing to the simplicity of its setup, the dam-break mechanism is frequently adopted in laboratories to generate bores and model long-wave dynamics, kinematics, and runup processes in coastal regions. Numerical simulations have been used to replicate the results of laboratory experiments using a dam-break system. In this study, we aimed to evaluate the effect of different macro-roughness slopes owing to dam-break driven swash using an open-source particle-based program, DualSPHysics, based on smoothed particle hydrodynamics. To serve as a reference case, the swash flows of a dambreak-generated bore on a uniform slope were performed, and model–data comparisons were made for time-series analysis of the surface elevation, runup process and velocity profiles at selected points. Simulations of dam-break bores passing over slopes containing various configurations of macro-roughness elements were performed to replicate long waves impacting an array of structures in a waterfront area. Different configurations of slope roughness have varying effects on the flow hydrodynamics in the swash zone, which were examined in this study.

Raking over the Ashes—The Analysis of the LBA Ashmounds from NE Romania

During the end of the Bronze Age, the territory of present-day eastern Romania was occupied by Noua communities, belonging to the Noua-Sabatinovka-Coslogeni (NSC) cultural complex. Although these communities have left us a large number of archaeological sites, this period is rather poorly known and understood, mostly because the investigation of Late Bronze Age (LBA) sites is very rare, usually consisting of small test trenches or fieldwalks. The main characteristic of these communities and the subject of our study is represented by the so-called ashmounds (grey, quasi-circular spots, visible on the soil surface, with small elevations and diameters of 25–30 m), present inside most settlements. Our paper aims at highlighting the spatial characteristics of these sites, using GIS (Geographic Information System) tools, as well as aerial photographs, LiDAR (Light Detection and Ranging) measurements, magnetometry and geo-electrical methods, in order to identify the relationship existing between Noua communities and the inhabited environment, in the area known as the Jijia River catchment. Thus, our approach was able to outline the way in which the geographical peculiarities determined the establishment of new settlements, revealing that the human groups from the end of the Bronze Age preferred low terrains with smooth slopes, located in the immediate vicinity of the most important watercourse of the inhabited micro-area. Additionally, our geophysical studies allowed us to confirm the lack of ash located within the ashmound, as well as to signal the possibility that these features have become visible on the soil surface only due to the irreversible damage caused by intensive agricultural processes. Despite the small number of excavations, to this day an important number of studies have been dedicated to the communities and features in question; however, no analysis has yet been performed that unites the tools specific to GIS software with the usage of non-invasive methods (such as aerial photographs, LiDAR measurements and geophysical techniques).

Slovenská terminológia travertínov, penovcov a príbuzných terestrických vápencov

The paper follows on a review articles on Slovak travertines and tufa published in English in 2021. Geomorphological terms such as ‘fissure ridge’, ‘coalesced mound’, ‘self-buiding channel’, ‘keeled waterfall’, ‘smooth slope’, ‘terrased slope’, ‘dams along stream’, ‘peached springline deposits’, ‘moss pillow’ were defined as new in Slovak terminology. Travertine forms are formed by defined facies: ‘crystalline crusts’ with different crystal types, ‘radiating dendrites’, ‘coated bubbles’, ‘rafts’, and ‘breccias’ of various origin. Biogenic facies such as ‘microphyte mats’, ‘microphyte crusts’, ‘microphyte shrubs’, and ‘macrophyte facies’ appear in various tufas and travertines. In lakes, fens and marshes, the ‘lime-mudstones’ and the terms ‘mottling (marmorisation)’ and ‘pseudomikcokarst’ were defined. ‘Travertinized tufa’ was established as a transitional form between travertine and tufa.

Comparison of deep-water-parameter-based wave overtopping with wirewall field measurements and social media reports at Crosby (UK)

Wave overtopping formulae, which often underlie coastal hazard early warning systems, are typically parameterised using wave conditions at the toe of the structure. For very shallow conditions where significant wave breaking occurs over the foreshore, this usually requires computationally-demanding numerical models—and practitioners skilled in their application—to accurately transform offshore waves to the structure toe. An additional concern is that overtopping formulae are scarcely validated in the field due to the very limited availability of in-situ overtopping data obtained at actual structures. Here, we validate a set of deep-water-parameter-based formulae for mean overtopping discharge (q) at smooth slopes, which remove the need for nearshore measurements or additional numerical modelling but require that a single representative foreshore slope angle (m) be defined. The validation is carried out against field data gathered at Crosby (UK) using two novel approaches: i) a new overtopping measurement system called “WireWall”; and ii) crowd-sourced data in the form of overtopping images obtained from a community Facebook page (social media). A method is introduced to define m for irregular bathymetries, based on the location where the local water depth is equal to the offshore significant wave height. The overtopping formulae proved accurate—with estimates of q being within a factor of 4 of observations—when compared to both 1-h averaged and 15-min averaged overtopping data, suggesting that the approach can be used for both design and assessment and now-casting hazard information. Finally, hindcasts made using the newly validated formulae for the events reported by the community indicate that q can exceed 10 l/s/m under yearly winter conditions, posing a serious hazard to pedestrians. This highlights the pressing need to update the current hazard warning system at Crosby, which estimates q to be a factor of 3 lower than the deep-water-parameter-based approach, on average.

Low-Reynolds-number oscillating boundary layers on adiabatic slopes

We investigate the instabilities and transition mechanisms of Boussinesq stratified boundary layers on sloping boundaries when subjected to oscillatory body forcing parallel to the slope. We examine idealized forms of boundary layers on hydraulically smooth abyssal slopes in tranquil mid- to low-latitude regions, where low-wavenumber internal tides gently heave isopycnals up and down adiabatic slopes in the absence of mean flows, high-wavenumber internal tides, shelf breaks, resonant tide–bathymetry interactions (critical slopes) and other phenomena associated with turbulence ‘hot spots’. In non-rotating low-Reynolds-number flow, increased stratification on the downslope phase has a relaminarizing effect, while on the upslope phase we find transition-to-turbulence pathways arise from shear production triggered by gravitational instabilities. When rotation is significant (low slope Burger numbers) we find that boundary layer turbulence is sustained throughout the oscillation period, resembling stratified Stokes–Ekman layer turbulence. Simulation results suggest that oscillating boundary layers on smooth slopes at low Reynolds number ($\textit {Re}\leqslant 840$), unity Prandtl number and slope Burger numbers greater than unity do not cause significant irreversible turbulent buoyancy flux (mixing), and that flat-bottom dissipation rate models derived from the tide amplitude are accurate within an order of magnitude.

An Insect-Inspired Terrains-Adaptive Soft Millirobot with Multimodal Locomotion and Transportation Capability.

Inspired by the efficient locomotion of insects in nature, researchers have been developing a diverse range of soft robots with simulated locomotion. These robots can perform various tasks, such as carrying medicines and collecting information, according to their movements. Compared to traditional rigid robots, flexible robots are more adaptable and terrain-immune and can even interact safely with people. Despite the development of biomimetic principles for soft robots, how their shapes, morphology, and actuation systems respond to the surrounding environments and stimuli still need to be improved. Here, we demonstrate an insect-scale soft robot with multi-locomotion modes made by Ecoflex and magnetic particles, which can be actuated by a magnetic field. Our robot can realize four distinct gaits: horizontal tumbling for distance, vertical tumbling for height, imitation of gastropod writhing, and inchworm-inspired crawling for cargo delivery. The soft compliant structure and four locomotion modes make the robot ideal for maneuvering in congested or complex spaces. In addition to linear motion (~20 mm/s) and turning (50°/s) on a flat terrain, the robot can also maneuver on various surface conditions (such as gaps, smooth slopes, sand, muddy terrain, and water). These merits, together with the robot’s high load-carrying capacity (5 times its weight), low cost, obstacle-crossing capability (as high as ~50% its length), and pressure resistance (70 kg), allow for a wide variety of applications.