A coupled dynamic leakage loss and flood routing model for ephemeral rivers with complex sections

Ephemeral rivers commonly occur in regions with a shortage of water resources, and their channel configuration tends to change substantially owing to cultivation, tree planting and sand extraction. There is an urgent need to restore degraded river ecosystems. During short-term water conveyance, water storage in sand pits and leakage in dry riverbeds retards the flow of water, which is detrimental for ecological restoration of the riparian zone. A coupled dynamic leakage loss and flood routing model was established to predict the flow processes in the complex river channel of the Yongding River in China. The model mainly included three sub-models of flow dynamics, dynamic leakage loss, and water balance along multiple cross sections of the river channel. The complex section is reflected in the different infiltration properties for each section, and the existence of sand pits. The water head was dominated by flow velocity and the overflow from sand pits. Owing to the difference in landforms and the deposited sediment size of the riverbed bottom, the river channel was divided into 11 cross sections and a sand pit to ascertain the respective infiltration or leakage loss processes. The input parameters of the model came from field surveys of sand pits, river geometry and hydrogeology. The model was also calibrated and validated using monitoring data from ecological water releases into the Yongding River in 2019 and 2020. This coupled model can predict the water leakage loss and flow process of the water head and also provide important guidance for river reconstruction and ecological restoration.

Performance Analysis and Optimization for Irreversible Combined Carnot Heat Engine Working with Ideal Quantum Gases

An irreversible combined Carnot cycle model using ideal quantum gases as a working medium was studied by using finite-time thermodynamics. The combined cycle consisted of two Carnot sub-cycles in a cascade mode. Considering thermal resistance, internal irreversibility, and heat leakage losses, the power output and thermal efficiency of the irreversible combined Carnot cycle were derived by utilizing the quantum gas state equation. The temperature effect of the working medium on power output and thermal efficiency is analyzed by numerical method, the optimal relationship between power output and thermal efficiency is solved by the Euler-Lagrange equation, and the effects of different working mediums on the optimal power and thermal efficiency performance are also focused. The results show that there is a set of working medium temperatures that makes the power output of the combined cycle be maximum. When there is no heat leakage loss in the combined cycle, all the characteristic curves of optimal power versus thermal efficiency are parabolic-like ones, and the internal irreversibility makes both power output and efficiency decrease. When there is heat leakage loss in the combined cycle, all the characteristic curves of optimal power versus thermal efficiency are loop-shaped ones, and the heat leakage loss only affects the thermal efficiency of the combined Carnot cycle. Comparing the power output of combined heat engines with four types of working mediums, the two-stage combined Carnot cycle using ideal Fermi-Bose gas as working medium obtains the highest power output.

Applications of a Novel Lost Circulation Additive

Lost circulation is a complicated situation in the drilling operation, wasting a lot of time and mud during processing. A serious lost circulation can cause hazards, such as sticking, blowout and collapse of well. There are some problems in conventional plugging technology, such as particle size of plugging material does not match crack width, slip of the blocking zone, and weak adhesion of lost circulation additive to the rock, which restricts the success rate of lost circulation operation. Regular and elastic polyhedron structure material compounds elastic variable network plugging material and rigid plugging materials to form a loss circulation materials (LCM)plugging mixture for different leakage speed and crack width affected by stress. Through plugging and HTHP sand bed experiment loss circulation materials(LCM) and amount of gel were optimized and improved. Through indoor simulation about leakage process of different leakage speed and different crack sizes, the on-site construction formula suitable for wells under different temperature is formed and determined. Scanning electron microscope shows the plugging gel has a variable network structure. By changing the ratio of elastic plugging material, rigid plugging material and gel, a LCM plugging formula for high temperature and high pressure formations can be formed to meet the pressure requirement of 7.5MPa. Leakage simulation formed on-site plan under different leakage rate to adapt to 180°C. The novel CPM material has been well-field tested and used for HPHT reservoirs. When the rate of leakage less than 30 m3/h and 30-60 m3/h, success rate of single plugging is more than 95% and rate of leakage greater than 60 m3/h success rate of single plugging beyond 80%. Leakage loss time is more than 80% shorter than conventional plugging techniques.

Q-Factor Enhancement of Thin-Film Piezoelectric-on-Silicon MEMS Resonator by Phononic Crystal-Reflector Composite Structure

Thin-film piezoelectric-on-silicon (TPoS) microelectromechanical (MEMS) resonators are required to have high Q-factor to offer satisfactory results in their application areas, such as oscillator, filter, and sensors. This paper proposed a phononic crystal (PnC)-reflector composite structure to improve the Q factor of TPoS resonators. A one-dimensional phononic crystal is designed and deployed on the tether aiming to suppress the acoustic leakage loss as the acoustic wave with frequency in the range of the PnC is not able to propagate through it, and a reflector is fixed on the anchoring boundaries to reflect the acoustic wave that lefts from the effect of the PnC. Several 10 MHz TPoS resonators are fabricated and tested from which the Q-factor of the proposed 10 MHz TPoS resonator which has PnC-reflector composite structure on the tether and anchoring boundaries achieved offers a loaded Q-factor of 4682 which is about a threefold improvement compared to that of the conventional resonator which is about 1570.

The Development and Applications of a Loading Distribution Based Tip Leakage Loss Model for Unshrouded Gas Turbines

The prediction of tip leakage flow aerothermal loss plays a crucial role in turbine preliminary design, which strongly affects the turbine performance. A new tip leakage loss model for unshrouded turbine is developed in this paper, considering the compressible flow aerothermal process inside the clearance. By coupling with a parameterized loading distribution model proposed in this work, in which the blade loading can be described by four independent parameters, Zweifel coefficient (Zw), diffusion factor (DF), peak velocity location (PVL), and leading edge acceleration (LEA), the loss model can evaluate the tip leakage loss in aerodynamic design process conveniently and accurately. The proposed models are validated by numerical simulations and the results show that, compared with the other acknowledged loss models, the loss model can reduce the deviations by more than 50%. Based on the models, the effects of blade loading design parameters on tip leakage losses are discussed via analysis of variance (ANOVA). The results show that Zw has the most significant influence. As Zw decreases from 1.0 to 0.7, tip leakage losses can be reduced by about 16%. Under lower Zw conditions, the joint effect of PVL and LEA is remarkable. However, under higher Zw conditions, the joint effect of the DF and PVL is more important.