Experimental investigation on axial velocity distribution for ship’s twin-propeller jets

Abstract

The investigation of twin-propeller jets as ships undergo acceleration is essential. This form of jet has been triggering problematic consequences such as seabed scouring. In order to prevent such scouring, near-bed velocities must first be analyzed in order to design the necessary protection when the under keel clearance of a ship is low when it is near port structures. This paper presents experimental work performed by Laser Doppler Anemometry. It is noticed that research into twin-propeller jet profiles still remains limited in the literature. Therefore, we intend to analyze twin-propeller axial velocity profiles and look into several flow characteristics such as efflux velocity and its decay pattern. Also, the measured velocity profile is compared to that of a single-propeller jet. Current results show that scouring is more severe in the case of the twin-propeller jets.     

Electrochemical impedance spectroscopy evaluation of behaviour of Pb–Ag anodes for zinc electrowinning

Abstract

Pb–0·5–0·7Ag anodes are widely used in the industry of zinc electrowinning. Two commercial lead anodes containing 0·56 and 0·69%Ag were studied by electrochemical impedance spectroscopy to evaluate their electrochemical activity. An industrial acid zinc sulphate electrolyte containing glue and chloride ion, but without manganese addition, was considered. In this study, 5 h of electrolysis at a density of 50 mA cm^?2 (currently used in practice) and also 6 h of potential decay were made to represent electrowinning periods of maintenance both at 38°C. During the 5 h polarisation, the average double layer capacity of Pb–0·56Ag alloy was higher (～9%) than that of Pb–0·69Ag alloy. During the first hour of potential decay, the Warburg impedance controls the electrochemical reaction. For the period from the second to sixth hour, the double layer capacity decreased with immersion time, and the charge transfer resistance increased with time. During the potential decay, the average charge transfer resistance of Pb–0·69Ag anode was higher (～52%) than that of Pb–0·56Ag anode.     

Above-ground HTGR design for passive decay heat removal

The design of a small high-temperature gas-cooled reactor (HTGR) for passive decay heat removal which could be located deeply underground was proposed previously. In the present work, analogue design analyses of passive decay heat removal for an above-ground long-life small prismatic HTGR was carried out to obtain the conditions for successful decay heat removal by radiation and conduction inside the reactor building, and by radiation and natural cooling by air at the outer surface of the reactor building. Sensitivity analysis of the peak temperatures of both the core and the reactor building after reactor shutdown was performed by changing the physical characteristics of the reactor regions. Enlarging the reactor building was found to be an effective way to reduce the peak reactor building temperature to within its design limit. By using the obtained condition for design parameters, the appropriate sizes of reactor core and reactor building were evaluated for some reactors. Consequently, criticality and burnup analyses for the proposed reactors were performed to confirm the possibility of designing a long-life core for the core size and reactor power which meet the condition of removing decay heat successfully. Using our design, all the reactors with 20 wt% uranium enrichment could be critical for over nine years.     

Computer Analysis on Steady State Separation Characteristics of Hydrogen Isotope Separation System by Cryogenic Distillation

A computer code is developed for effective and exact simulation of cryogenic distillation columns. The simulation model incorporates the differences of latent heat of vaporization among the six molecular species, pressure drop, decay heat of tritium, heat transfer through the column wall, Raoult's law deviation of the solutions of hydrogen isotopes, multiple feeds and multiple sidestreams. The calculational procedure developed by Tomich for general equilibrium stage processes is further modified to match this complicated simulation model.

A computer simulation study is performed for the typical cryogenic distillation column cascade and separation characteristics of each column are clarified. The effects of pressure drop are found not significant. If the tritium concentration in the column is considerably high, the lower performance caused by decay heat effects cannot be neglected any longer. Increase of the reflux ratio or refrigeration of the stripping section, is required for improvement.

The present study provides a great help to development of exact simulation models and simulation procedures of cryogenic distillation columns.     

Dryout Heat Flux for Core Debris Bed, (I)

For gaining basic data on decay heat coolability of debris bed in the post-accident heat removal, measurement of dryout heat flux was made, with stagnant water as coolant, in a 50mm I. D. pyrex glass cylinder vessel. The fuel debris bed subjected to decay heat was simulated by steel ball particles which were inductively heated with a power supply of 20 kHz and 30 kW. The bed was made of homogeneous size particles. An emphasis was placed on the influence of system pressure and particle size. The experiment covered the ranges over the steel ball diameters of 0.3–4.0 mm and the system pressure of 0.02–0.5 MPa.

The experimental results, as a whole, agreed fairly well with the prediction based on Lipinski's 0-D model with respect to the dependence of dryout heat flux both on pressure and on particle size. In detail, however, the dryout heat flux deviates toward a lower value at a higher pressure while to a higher value for a smaller size particle bed. Comparison of the results between the free and fixed beds suggests that the deviation to the higher side will be attributed to the channeling and/or levitation.     

Evaluation of Shutdown Gamma-ray Dose Rates around the Duct Penetration by Three-Dimensional Monte Carlo Decay Gamma-ray Transport Calculation with Variance Reduction Method

For the evaluation of gamma-ray dose rates around the duct penetrations after shutdown of nuclear fusion reactor, the calculation method is proposed with an application of the Monte Carlo neutron and decay gamma-ray transport calculation. For the radioisotope production rates during operation, the Monte Carlo calculation is conducted by the modification of the nuclear data library replacing a prompt gamma-ray spectrum with a decay gamma-ray spectrum. By multiplying each correction factor, which is ratio of the actual activation level after shutdown to the production rate during operation, with each decay gamma-ray flux due to each radioisotope, the decay gamma-ray dose rate is evaluated. In order to improve the statistical error, a variance reduction method is proposed by the application of the weight window importance technique and the specification of the decay gamma-ray generation location. We identify the cell producing the decay gamma-ray which can contribute the decay gamma-ray flux in evaluation locations, and forcibly terminate the gamma-ray transport calculation in the cells except for the identified cells. In order to validate the effectiveness of the method, shielding calculation for actual ITER (International Thermonuclear Experimental Reactor) configuration is performed, and small statistical errors below criteria are obtained. The effectiveness of the proposed method for ITER design analysis is demonstrated.     

洁净室气密性检测方法研究——国标《洁净室施工及验收规范》编制组研讨系列课题之八

分析了在正、负压洁净室进行洁净室气密性验证的重要性,对洁净室气密性相关问题进行了理论计算,给出了具体检测方法,并进行了实验研究.结果表明,一个密封很好的洁净室,500 Pa压力的半衰期不足5 min,小时泄漏率不到10%.     

The CUORE Experiment: Bolometric Detectors in 1-Ton Scale Projects

CUORE is the first of a new generation 1-ton scale cryogenic detectors for rare events physics. CUORE, a detector to search neutrinoless Double Beta Decay of ¹³⁰Te, is an array of 988 TeO₂ bolometers that will work at 10 mK. Latest developments on detectors performances are reported together with improvements reached in background reduction. Results of CUORICINO, a single CUORE tower running since 2003, that widely showed the feasibility of the project are also reported and discussed. P. Gorla on behalf of the CUORE collaboration.     

超声激励陶瓷材料非局部弹性核函数理论研究

对各种非局部弹性核函数进行分析比较,通过考虑超声激励参量的影响因素,建立了超声激励下的非局部弹性核参量公式,推导出了超声激励下的非局部弹性核函数公式,并对弹性核函数的衰减特性和作用条件进行了研究,并依据此公式对非局部超声振动下的应力进行预测计算,得出应力衰减现象能够通过频域内的非局部核函数衰减来解释。     

混凝土建筑拆除时振动衰减规律的试验研究

对某混凝土建筑拆除过程中土体振动的速度、加速度进行实时监测,结果表明,楼房拆除产生的振动不大,低于振动预估值;振动波随着传播距离的增加,振动势衰减十分明显。