Motion Responses of a Berthed Tank under Resonance Coupling Effect of Internal Sloshing and Gap Flow

The growth of global energy transportation has promoted the rapid increase of large-scale LNG (liquefied natural gas) carriers, and concerns around the safety of LNG ships has attracted significant attention. Such a floating structure is affected by the external wave excitation and internal liquid sloshing. The interaction between the structure’s motion and the internal sloshing under wave actions may lead to the ship experiencing an unexpected accident. In this research, a hydrodynamic experiment is conducted to investigate the motion responses of a floating tank mooring, both close to and away from a dock. The resonance coupling effect of the internal sloshing and gap flow on the tank’s motion is considered. Based on the measured motion trajectory of the floating tank, the stability and safety of the floating tank are estimated. The results show that the sloshing resonance and narrow gap resonance are beneficial to the stability of the ship. This is helpful for controlling the motion of a berthed ship under wave action with a reasonable selection of the gap distance and the liquid level.

Simulation and Experiment Research on Liquid Channel of Diffuser Blade by Electrochemical Machining

Aiming to solve the problems of the low electrolyte flow rate at leading edge and trailing edge and poor uniformity of the end clearance flow field during the electrochemical machining (ECM) of diffuser blades, a gap flow field simulation model was established by designing three liquid-increasing channels at the leading edge and the trailing edge of the cathode. The simulation results indicate that the liquid-increasing hole channel (LIHC) with an outlet area S of 1.5 mm2 and a distance L from channel center to edge point of 3.2 mm achieves optimal performance. In addition, the experiment results show that the optimized cathode with liquid-increasing hole channel (LIHC) significantly improves the machining efficiency, accuracy and surface quality. Specifically, the feed speed increased from 0.25 mm/min to 0.43 mm/min, the taper decreased from 4.02° to 2.45°, the surface roughness value of blade back reduced from 1.146 µm to 0.802 µm. Moreoever, the roughness of blade basin decreased from 0.961 µm to 0.708 µm, and the roughness of hub reduced from 0.179 µm to 0.119 µm. The results prove the effectiveness of the proposed method, and can be used for ECM of other complex structures with poor flow field uniformity.

AERODYNAMICS AND HEAT TRANSFER INSIDE A GAS TURBINE MID-PASSAGE GAP

Gas turbine blades and vanes are typically manufactured with small clearances between adjacent vane and blade platforms, termed the midpassage gap. The midpassage gap reduces turbine efficiency and causes additional heat load into the vane platform, as well as changing the distribution of endwall heat transfer and film cooling. This paper presents a low-order analytical analysis to quantify the effects of the midpassage gap on aerodynamics and heat transfer, verified against an experimental campaign and CFD. Using this model, the effects of the gap can be quantified, for a generic turbine stage, based only on geometric features and the passage static pressure field. It is found that at present there are significant losses and a large proportion of heat load caused by the gap, but that with modified design this could be reduced to negligible levels. Cooling flows into the gap to prevent ingression are investigated analytically and with CFD. Recommendations are given for targets that turbine designers should work toward in reducing the adverse effects of the midpassage gap. A method to estimate the effect of gap flow is presented, so that for any machine the significance of the gap may be assessed.

Motion Model of Spent Fuel Rack Considering Two-dimensional Gap Flow

A free-standing rack system, in which each rack is not fixed to the floor or the wall, is proposed and is in use in European countries and the US as a storage method for spent fuel from nuclear power stations. Although this system can reduce the influence of an earthquake's excitation force by using the frictional force between the rack's bottom surface and the floor surface, together with the fluid force excited by each rack's motion, design guidelines are not yet established. In this research project, to evaluate the fluid force more precisely, the gap between the racks is treated as a two-dimensional gap flow, and the pressure loss coefficient at the flow path junction and the top of the flow path were estimated based on the steady CFD calculation and incorporated into the motion model. Our primary concern in this paper is rocking motion. As a result, we concluded that increasing the pressure loss coefficient at the fuel rack's top suppressed rocking motion.

Research on Ultrasonic Vibration Assisted Electrical Discharge Machining SiCp/Al Composite

In this paper, ultrasonic-vibration assisted electrical discharge machining (UEDM) is used to process SiCp/Al composite materials in order to achieve a higher material removal rate (MRR) and lower surface roughness, width overcut, and relative tool wear rate (RTWR). FLUENT software was used to simulate the gap flow field. The simulation results of the gap flow field show that the ultrasonic vibration of the tool electrode is conducive to the removal of chips, which makes the discharge more stable and improves the machining efficiency. Based on the single factor experiment, the effects of peak current, reference voltage, pulse width, and pulse interval on MRR, surface roughness, width overcut, and RTWR of the workpiece are studied. Then, based on the orthogonal experiment, the grey relational analysis method was used to optimize the process parameters, and the order of the influence of the 4 process indicators on the comprehensive performance and the optimal processing parameter combination was obtained. The reliability of the process optimization was verified with experiments.

SEAM-ECM Jet Milling TC4 Titanium Alloy Using Gas-Liquid Mixed Medium

A novel combined machining approach combining short electric arc machining and electrochemical machining (SEAM-ECM) is proposed in this study. It aims to improve the surface integrity of TC4 titanium alloy by adding compressed air and electrolyte into the SEAM. This approach can change the material removal mechanism of the conventional SEAM and improve the gap flow field distribution and discharge state using the dual fluid properties of electrolyte and air mixed medium. The effects of gas addition on the state of the gap flow field and the electrical conductivity of the mixed medium are illustrated by flow field simulation. The effects of the presence or absence of air and the electrical conductivity of the solution on the machining performance are compared by experiments. The results show that the recast layer is weakened by using electrolyte and air mixed medium in SEAM-ECM compared to SEAM alone. The addition of high-speed air reduces defects such as melt drops, particles, holes. It performs with higher precision and finishes than ECM alone, the overall surface integrity has been significantly improved.

3D Flow Simulation of a Twin-Screw Pump for the Analysis of Gap Flow Characteristics

Unsteady 3D flow simulations on a twin-screw pump are performed for an assessment of the radial, circumferential and flank gap flow effect on the pump performance. By means of the overset grid technique rigid computational grids around the counter-rotating spindles yield a high cell quality and a high spatial resolution of the gap backflow down to the viscous sublayer in terms of y^+ < 1 . An optimization of the hole-cutting process is performed on a generic gap flow and transferred to the complex moving gaps in the pump. Grid independence is ensured, and conservation properties of the overset grid interpolation technique are assessed. Simulation results are validated against measured pump characteristics. Pump performance in terms of pressure build-up along the flow path through the spindles and volume flow rate is presented for a wide range of spindle speed and pump head. Flow rate fluctuations are found to depend on head but hardly on speed. By a profound assessment of the respective radial, circumferential and flank gap contribution to the total backflow, the importance of the most complex flank gap is pointed out. Backflow rate characteristics in dependence on the pump head and the pump speed are presented.