Numerical investigation of the turbulence characteristics and energy dissipation mechanism of baffle drop shafts

The baffle drop shaft is widely used in deep tunnel drainage system due to its fine applicability and high energy dissipation. To fully study the turbulence characteristics and energy dissipation mechanism of baffle drop shafts, a 1:25 scale physical model test and the numerical simulation based on the Realizable k-ε model and Volume of Fluid (VOF) method were performed. The results showed that a baffle spacing that is too dense or too sparse is not conducive to energy dissipation and discharge. The minimum baffle spacing is the optimal structural design at the design flow rate when the flow regime is free-drop flow. The energy dissipation calculation model established in this paper has high accuracy for calculating the energy dissipation rate on the baffles in free-drop flow. The energy dissipation modes of the shaft can be divided into inlet energy dissipation, baffle energy dissipation, and shaft-bottom energy dissipation. Baffles play a major role in the energy dissipation at low flow rates, and the proportions of inlet and shaft-bottom energy dissipation increase with the increase in flow rate.

Simulation and Verification of Hydraulic Performance and Energy Dissipation Mechanism of Perforated Drip Irrigation Emitters

Drip irrigation has become an application trend of water-saving irrigation technology due to its excellent water-use efficiency. However, the energy dissipation form of the commonly used labyrinth channel is relatively simple, and the corresponding energy dissipation mechanism research is inadequate. This article proposes a new kind of channel structure of drip irrigation emitters based on the structure of scalariform perforation plates in plant xylem vessels. We establish a total of 16 sets of orthogonal structure schemes. Using numerical simulation and physical experiments, the hydraulic performance and energy dissipation mechanism of the perforated drip irrigation emitters (PDIE) are studied. The results show that the flow index of PDIE is 0.4665–0.5266. The hydraulic performance of PDIE in the high-pressure zone is the best, and the flow index is 0.4665–0.5046. As the pressure increases, the velocity of the flow of the upper perforation increases rapidly, the flow ratio decreases, the flow index decreases, and the hydraulic performance improves. To further verify the energy dissipation mechanism, a lower flow ratio and a better hydraulic performance were obtained through appropriately expanding the upper part of the upper perforation inlet to the channel boundary. The research sheds new insights for optimizing the hydraulic performance of PDIE. Results reported here provide a theoretical basis for the structural design of drip irrigation emitters and the energy dissipation mechanism research.

Planar arrangement of permanent magnets in design of a magneto-solid damper by finite element method

This article studies the energy dissipation mechanism of a proposed magneto-solid damper using a three-dimensional finite element model developed in COMSOL Multiphysics software. The energy dissipation mechanism of the magneto-solid damper dissipates energy through combined actions of friction and eddy current damping. The key components of the magneto-solid damper are a steel plate, two copper plates placed on two sides of the steel plate in parallel, and two planar arrays of permanent magnets each one placed between the steel plate and one of the copper plates. These arrays are kept away from the steel and copper plates through narrow gaps; the gaps between them and the steel plate are filled with thin friction pads made of non-magnetic materials. The attractive magnetic interaction between the permanent magnet arrays and the steel plate provides the normal force for the friction developed between the friction pads and the steel plate when the permanent magnet arrays move relative to the steel plate. The motion of the permanent magnet arrays relative to the copper plates, on the other hand, provides the eddy current damping. The main contribution of this article is to optimize the pole arrangement of the permanent magnets and demonstrate that how the optimum pole arrangement can affect the energy dissipation capacity of the magneto-solid damper. The analysis results show that, for a given number and size of the permanent magnets, alternate arrangement of the poles of permanent magnets along the direction of their motion is the most optimal case resulting in large and smooth hysteresis force–displacement loops. This pole arrangement has also been used to find the optimum size of the steel and copper plates by addressing edge and skin effects in the design of the damper.