Valve-controlled electro-hydraulic technology is widely used in heavy-duty linear actuator, but its energy efficiency is low. The electro-mechanical actuator (EMA) has high energy efficiency, but its ...output force is small. In order to achieve high efficiency, high power-to-weight ratio, and high performance linear drive, a hydraulic-electric hybrid linear drive principle integrating hydraulic cylinder and EMA is proposed, and a prototype of electromechanical hydraulic hybrid actuator (EMHA) is designed and developed. In the hybrid drive system, EMA is responsible for actuator motion control and hydraulic cylinder is used for force control. In the study, an extended state observer (ESO) was first designed to estimate the external load torque of the EMA permanent magnet synchronous motor (PMSM) in real time. Combining the detected pressures, the load force of the EMHA can be estimated. Then, according to the estimated load force, the hydraulic system is controlled to make the hydraulic cylinder balance most of the actuator load force, maintaining the PMSM within the required load range. A sliding-mode controller is further designed to compensate the external load torque acting on the PMSM to ensure that the system has good motion control characteristics. The results show that under the same driving force and velocity, the power density of the EMHA is 154% higher than that of the EMA. In this article, the proposed system can achieve equivalent control performance as the valve-controlled system, while reducing energy consumption by 58%.
•A general BEST method is presented for estimating soil hydraulic parameters without the need for particle-size distribution data.•Estimation of soil hydraulic parameters can be performed directly by ...using the quasi-exact implicit formulation of Haverkamp et al. (1994).•Kosugi and van Genuchten soil hydraulic parameters are satisfactorily retrieved with the methodology.
Soil hydraulic characterization is crucial to describe the retention and transport of water in soil, but current methodologies limit its spatial applicability. This paper presents a cost-effective general Beerkan Estimation of Soil Transfer parameters (BEST) methodology using single ring infiltration experiments to derive soil hydraulic parameters for any unimodal water retention and hydraulic conductivity functions. The proposed method relies on the BEST approach. The novelty lies in the use of Kosugi hydraulic parameters without need for textural information. In addition, the method uses a quasi-exact formulation that is valid for all times, which avoids the use of approximate expansions and related inaccuracy. The new BEST methods were tested against numerically generated data for several contrasting synthetic soils, and the results show that these methods provide consistent hydraulic functions close to the target functions. The new BEST method is accurate and can use any water retention and hydraulic conductivity functions.
Given increasing water deficits across numerous ecosystems world-wide, it is urgent to understand the sequence of failure of leaf function during dehydration.
We assessed dehydration-induced losses ...of rehydration capacity and maximum quantum yield of the photosystem II (F
v/F
m) in the leaves of 10 diverse angiosperm species, and tested when these occurred relative to turgor loss, declines of stomatal conductance g
s, and hydraulic conductance K
leaf, including xylem and outside xylem pathways for the same study plants. We resolved the sequences of relative water content and leaf water potential Ψleaf thresholds of functional impairment.
On average, losses of leaf rehydration capacity occurred at dehydration beyond 50% declines of g
s, K
leaf and turgor loss point. Losses of F
v/F
m occurred after much stronger dehydration and were not recovered with leaf rehydration. Across species, tissue dehydration thresholds were intercorrelated, suggesting trait co-selection. Thresholds for each type of functional decline were much less variable across species in terms of relative water content than Ψleaf.
The stomatal and leaf hydraulic systems show early functional declines before cell integrity is lost. Substantial damage to the photochemical apparatus occurs at extreme dehydration, after complete stomatal closure, and seems to be irreversible.
Soil hydraulic properties are required in various modelling schemes. We propose a consistent spatial soil hydraulic database at 7 soil depths up to 2 m calculated for Europe based on SoilGrids250m ...and 1 km datasets and pedotransfer functions trained on the European Hydropedological Data Inventory. Saturated water content, water content at field capacity and wilting point, saturated hydraulic conductivity and Mualem‐van Genuchten parameters for the description of the moisture retention, and unsaturated hydraulic conductivity curves have been predicted. The derived 3D soil hydraulic layers (EU‐SoilHydroGrids ver1.0) can be used for environmental modelling purposes at catchment or continental scale in Europe. Currently, only EU‐SoilHydroGrids provides information on the most frequently required soil hydraulic properties with full European coverage up to 2 m depth at 250 m resolution.
•The three-chamber hydraulic cylinders integrated with driving and energy recovery functions.•The proposed method is applicable to all sizes of machines without mechanical structure changes.•The ...potential energy is directly recovered and reused.•The flow demand and throttling losses when lifting the boom is reduced.•Both energy consumption and peak power of power source is reduced.
When the hydraulic excavator boom drops, the gravitational potential energy accumulated during the lifting process is converted into heat energy and dissipated through the throttling effect of hydraulic valve, which results in poor energy efficiency and higher temperature of hydraulic oil. A cooling system must be installed to lower the temperature, increasing the cost and complexity of the system. In order to solve the above problems, an integrated drive and energy recuperation system based on a three-chamber hydraulic cylinder is proposed. In the proposed system, one chamber of the three-chamber cylinder is directly connected to a hydraulic accumulator, storing and reusing the potential energy of the boom. The other two chambers are connected to the main driving circuit. The proposed system is first studied with an integrated co-simulation of the mechanical and hydraulic systems. Through the simulation, the energy saving performance of the new system is verified, and the initial pressure of the hydraulic accumulator is determined. In addition, the new system is tested on a 6-ton hydraulic excavator, and the results are compared with the ones of double-chamber hydraulic cylinder driving system. The test results show that with the proposed system, the energy consumption of the boom is reduced by 50.1% and the peak power of the power source is reduced by 64.9%. It is worth noting that the new method can be widely applied to all types of heavy lift device driven by hydraulic cylinders.
The most applied pedotransfer functions (PTFs) often suffer from two main limitations: (a) the soil hydraulic models (SHMs) only account for capillary forces and/or the models show an unrealistic ...decrease near saturation for fine‐textured soils; (b) the observations of soil hydraulic properties (SHPs) used to generate the PTF generally do not cover very dry conditions. In this paper, we first present a simple method for predicting SHPs in the dry range from soil texture information. Together with measurements that cover only a relatively high matric potential range, the method yielded a good prediction of the complete SHPs from saturation to oven dryness. With this method, we extended a public dataset to cover dry conditions, and then applied it to develop a new PTF for a SHM that accounts for both capillary and adsorption forces and overcomes the unrealistic decrease near saturation for fine‐textured soils. A comparison with other PTF that was developed for the capillary‐based soil hydraulic model showed that the new PTF provided the most accurate predictions of SHPs. It reduced the root‐mean‐square‐error value from 0.055 to 0.045 cm3 cm−3 in predicting water content and from 0.84 to 0.66 log10 (cm d−1) in predicting hydraulic conductivity. We further applied this method to extend an existing capillary‐based PTF to dry conditions. The results showed an improved performance, with reported RMSE reduced from 0.058 (original) to 0.056 (extended) cm3 cm−3 and from 1.43 (original) to 1.20 (extended) log10 (cm d−1) for prediction of water content and hydraulic conductivity, respectively.
Key Points
A simple method is presented for predicting a complete SHP with limited measurements covering only high matric potential range
A new PTF was developed by considering limitations of model structure and observation, which significantly improved the prediction of SHPs
A method is proposed to extend an existing capillary‐based PTF to dry conditions
With the development of large‐scale wind power generation and offshore wind energy, reducing the nacelle weight and the gear failure rate is increasingly important. Hydraulic transmission is ...characterized by its flexible layout and transmits large energy with small volume and weight, which suits the demands of wind power generation. In this paper, a thorough review of hydraulic technology application in wind energy is carried out, in the aspect of pitch, brake, yaw, transmission, new applications, and the potential problems.
Within vascular plants, the partitioning of hydraulic resistance along the soil‐to‐leaf continuum affects transpiration and its response to environmental conditions. In trees, the fractional ...contribution of leaf hydraulic resistance (Rleaf) to total soil‐to‐leaf hydraulic resistance (Rtotal), or fRleaf (=Rleaf/Rtotal), is thought to be large, but this has not been tested comprehensively. We compiled a multibiome data set of fRleaf using new and previously published measurements of pressure differences within trees in situ. Across 80 samples, fRleaf averaged 0.51 (95% confidence interval CI = 0.46−0.57) and it declined with tree height. We also used the allometric relationship between field‐based measurements of soil‐to‐leaf hydraulic conductance and laboratory‐based measurements of leaf hydraulic conductance to compute the average fRleaf for 19 tree samples, which was 0.40 (95% CI = 0.29−0.56). The in situ technique produces a more accurate descriptor of fRleaf because it accounts for dynamic leaf hydraulic conductance. Both approaches demonstrate the outsized role of leaves in controlling tree hydrodynamics. A larger fRleaf may help stems from loss of hydraulic conductance. Thus, the decline in fRleaf with tree height would contribute to greater drought vulnerability in taller trees and potentially to their observed disproportionate drought mortality.
Summary Statement
In trees, we found that leaves contribute a large and varying fraction of the total hydraulic resistance within the soil‐to‐leaf continuum that feeds the transpiration stream.
Journal of Hydraulic Research Discussion: Backwater effects of Jambor weir sillby M. GEBHARDT, U. PEROMMER, F. BELZNER and N. EISENHAUER, J. Hydraulic Res. 50(3), 2012, pp. 344-349.
PDF
