A thermal stress loading technique for large-sized hot dry rock mechanical tests

Testing of large-sized specimens is becoming increasingly important in deep underground rock mechanics and engineering.In traditional mechanical loading,stresses on large-sized specimens are achieved by large host frames and hydraulic pumps,which could lead to great investment.Low-cost testing machines clearly always have great appeal.In this study,a new approach is proposed using thermal expansion stress to load rock specimens,which may be particularly suitable for tests of deep hot dry rock with high temperatures.This is a different technical route from traditional mechanical loading through hydraulic pressure.For the rock mechanics test system of hot dry rock that already has an investment in heating systems,this technology may reduce the cost of the loading subsystem by fully utilizing the temperature changes.This paper presents the basic principle and a typical design of this technical solution.Preliminary feasibility analysis is then conducted based on numerical simulations.Although some technical details still need to be resolved,the feasibility of this loading approach has been preliminarily confirmed.

Lake-Based Nursery Rearing of Nile Tilapia (Oreochromis niloticus) Fingerlings in Nylon Hapas: Effects of Stocking Density on Growth, Survival and Profitability

The inadequate supply of tilapia fingerling is a major limitation to cage culture development in Ghana. Lake-based hapa systems are very efficient in nursing fingerlings although the process can be tricky due to inherent effects of stocking densities and environmental factors. This study aimed at assessing the growth, survival and profitability of Nile tilapia (Oreochromis niloticus) fingerlings of the Akosombo strain reared in nine 1 m3 Lake-based hapas at different densities. Each hapa was stocked with 2.12 ± 0.14 g sex-reversed tilapia fingerlings at varying stocking densities of 400 fish/m3, 800 fish/m3 and 1200 fish/m3 serving as treatments T1, T2 and T3 respectively. Each treatment was replicated thrice. Bi-weekly samplings were done and water quality parameters were measured. After the experiment, analysis of variance showed significant differences (p

Distribution and exploration direction of medium-and large-sized marine carbonate gas fields in Sichuan Basin, SW China

Based on the analysis of the basic characteristics of medium-and large-sized marine gas fields in Sichuan Basin, combined with the division of major reservoir forming geological units in the marine craton stage and their control on key hydrocarbon accumulation factors, the distribution law of medium-and large-sized marine carbonate gas fields in the basin was examined and the exploration direction was pointed out. Through the analysis of the periodic stretching-uplifting background, it is concluded that five large scale paleo-rifts, three large scale paleo-uplifts, five large scale paleo erosion surfaces were formed in the marine craton stage of Sichuan Basin, and these geological units control the key reservoir forming factors of medium and large sized gas fields:(1) Large-scale paleo-rifts control the distribution of high-quality hydrocarbon generation centers.(2) The margin of large-scale paleo-rifts, high position of paleo-uplifts and paleo erosion surfaces control the distribution of high-quality reservoirs.(3) Large-scale paleo-rifts, paleo-uplifts, paleo erosion surfaces and present tectonic setting jointly control the formation of many types of large and medium-sized traps.(4) Natural gas accumulation is controlled by the inheritance evolution of traps in large geological units. Based on the comparative analysis of the distribution characteristics of medium-and large-sized gas fields and large geological units, it is proposed that the superimposition relationship between single or multiple geological units and the present structure controls the distribution of medium-and large-sized gas fields, and the "three paleo" superimposed area is the most advantageous. According to the above rules, the main exploration fields and directions of medium-and large-sized marine carbonate gas fields in Sichuan Basin include periphery of Deyang-Anyue paleo-rift, eastern margin of Longmenshan paleo-rift, margins of Kaijiang-Liangping oceanic trough and Chengkou-western Hubei oceanic trough, the high part of the subaqueous paleo-uplifts around Central Sichuan, paleo erosion surfaces of the top boundary of Maokou Formation in eastern and southern Sichuan Basin, paleo erosion surfaces of the top boundary of the Leikoupo Formation in central and western Sichuan Basin.

Modeling and simulation of 3D thermal stresses of large-sized castings in solidification processes

When heavy machines and large scaled receiver system of communication equipment are manufactured, it always needs to produce large-sized steel castings, aluminum castings and etc. Some defects of hot cracking by thermal stress often appear during solidification process as these castings are produced, which results in failure of castings. Therefore predicting the effects of technological parameters for production of castings on the thermal stress during solidification process becomes an important means. In this paper, the mathematical models have been established and numerical calculation of temperature fields by using finite difference method (FDM) and then thermal stress fields by using finite element method (FEM) during solidification process of castings have been carried out. The technological parameters of production have been optimized by the results of calculation and the defects of hot cracking have been eliminated. Modeling and simulation of 3D thermal stress during solidification processes of large-sized castings provided a scientific basis, which promoted further development of advanced manufacturing technique.

Rolling Fatigue Test of Large-Sized UHPC Member for Cable Stayed Bridge

Recently, research strives to apply Ultra High Performance Concrete (UHPC) to large-sized structures owing to its remarkable mechanical performance and durability compared to normal concrete. The Korea Institute of Construction Technology proposed SuperBridge800, an edge girder type UHPC cable stayed bridge with central span of 800 m, through its detailed design. The bridge is designed to be erected through the connection of precast UHPC segments. The precast UHPC segment is monolithically composed of one ribbed deck slab and edge girders at each side. The connection between the precast segments is achieved by steel bars at the edge girders and by UHPC cast-in-place wet joint at the slab. Despite of the outstanding mechanical performance of UHPC, the fabrication of large-sized members is a difficult task since UHPC hardens faster than normal concrete and requires a special curing process. Therefore, the constructability of large-sized UHPC segment should be secured to achieve SuperBridge800. Besides, the performance of the connection between segments should also be guaranteed, especially in terms of the fatigue performance of the UHPC cast-in-place joint, which constitutes a weak point. To that goal, two half-scaled UHPC segments are manufactured and the constructability is examined by fabricating a large-sized UHPC member connected with respect to the design conditions. This study conducts rolling fatigue test on the so-fabricated large-sized UHPC member. Rolling fatigue test is carried out up to 2 million cycles considering actual vehicle load at each center and quarter points of the member. The test results confirm that the service limit state is satisfied.

Effects of Pawpaw Seed Powder as an Additive on Growth of Catfish Fingerlings Reared in an Indoor Tanks

Since the demand of African Catfish （Clarias gariepinus） is on increase there is need to increase its production so as to meet the protein requirement of the populace. An investigation was conducted for six weeks feeding trial to determine the performance of African catfish （Clarias gariepinus） fingerlings feed diets containing varying replacement level of fish meal with pawpaw seed powder meal （Carica papaya）. Fingerlings of Clarias gariepinus were subjected to five different dietary treatments with varying levels of pawpaw seed powder meal. The diets I-V contained 0, 20%, 40%, 60% and 80% replacement levels, respectively. The experiment was carded out in an 80 litres circular plastic bowls, the treatments were in triplicate. Each bowl contained 12 fingerlings. Feeding was done at 3% body weight per day and fishes were weighed every week. Growth parameters such as specific growth rate （SGR）, weight gained （WG）, food conversion ratio （FCR）, protein efficiency ratio （PER） and mortality were determined. Therefore, it could be concluded that fish meal could be replaced up to 80% with pawpaw seed powder meal in the diet of Clarias gariepinus fingerlings to encourage growth, while at 40% pawpaw seed powder meal inclusion mortality was reduced.

Experimental investigation and numerical simulation of large-sized aluminum tube extrusion forming

Large-sized aluminum tube has big section effect, aspect ratio and thin thickness, so that the extrusion technology is complex and the large specific pressure is generated in extrusion cavity. The temperature variation and velocity effect is difficult to control. The extrusion forming of large-sized aluminum tube was researched and simulated. Three-dimensional thermo-mechanical coupled finite element model was constructed and appropriate boundary conditions were given out. The results show that large-sized aluminum tube can be formed by isothermal extrusion through controlling the extrusion velocity and founding the relationship between extrusion velocity and extrusion temperature.

Replacement of Fish Meal with Graded Levels of Earthworm Meal in the Diet of Fingerlings： Effect on Feed and Growth Parameters

The study was aimed at evaluating growth response of Heteroclarias fingerlings fed diet in which fish meal was substituted with graded levels of earthworm meal. The replacement levels were 0.00%, 25%, 50%, 75% and 100% designated as Eo, E25, Es0, E75 and El00, respectively. Fingerlings used for the work were obtained through artificial insemination of brood stock （purchased from local farmers） with ovaprim in the laboratory. The resulting fry were reared and fed with cultured plankton for 2 weeks followed by 100% fish meal for another two weeks. Thereafter sixteen fingerlings weighing 4.73 g and measuring 6.512 mm standard length （on the average） were starved over night and reared in five indoors tanks （0.8 ~ 0.5 ~ 0.5 m） in duplicate for eight weeks. Fingerlings were fed on graded earthworm meals of 40% protein twice daily at 08：00 and 16：00. The highest mean weight （6.77 g）, specific growth rate （0.86） and protein efficiency ratio （0.6） were obtained at 50% replacement level. Also, Food conversion ratio was the highest at 50% substitution level and lowest at 0.00% substitution, indicating that fingerlings use earthworm containing meal more efficiently. Furthermore, cost benefit analysis revealed that the profit index for 50% inclusion of earthworm meal was the highest （1.71） and the highest net profit of N374.32 （circa $2.3） was achieved at this level. Water quality parameters observed were within tolerable values for the fingerlings well being. Consequently, farmers are advised to use 50% earthworm meal in place of fish meal for formulation of Heteroclarias fingerlings diet. This will drastically reduce production cost, increase farmers profit and enhance the biological value of our menu.

Determine the Optimal Density of Nile Tilapia (<i>Oreochromis niloticus</i>) Fingerlings Cultured in Floating Cages

The objective of the study was to determine the optimal density of fingerlings of the Nile tilapia (Oreochromis niloticus) culture in floating cages with respect to growth performance and to know the effect of temperature on growth during the winter period. Tilapia fingerlings (mean weight 8.5 ± 0.36 g) were stocked at densities of 120, 180 and 360 fish/m3 for 10 weeks. During culture, fish were fed a diet contains 35% protein made of peanut seed, cottonseed, wheat bran, and Sorghum. The results showed that the increase in fish density reduced the final weight of the fish. The percentage of the fish weight increased and reached 111% ± 1.45% in the lowest fish density (120 fish/m3), 79% ± 1.87% in the medium density (240 fish/m3), and 63% ± 2.03% of high fish density (360 fish/m3), therefore the daily growth rate was better in the lowest density. The rate of food conversion ratio was also better in the lowest density with 2.17 ± 0.33, followed by the medium density with 2.79 ± 0.28 and then the highest density with 3.09 ± 0.21. However, the total production in the cage increased with increasing fish density, and the return to the cost of food was better with higher fish density. According to various performance evaluation criteria, it can be concluded that the medium density 240 fish/m3 is the best for growing Nile tilapia fingerlings in floating cages. It was observed that the growth rates of the three treatments were low due to the decrease in water temperature in most of the study period, which may indicate the useless of culture in cages in the winter season.

A method of manufacturing process modeling based on activity network for large-sized and complex products

Simulation technique is an efficient approach to realize the planning and scheduling of manufacturing process of products. An appropriate and efficient manufacturing process model is the basis and key of manufacturing process simulation. By analyzing the features of large-sized and complex products, a method of manufacturing process modeling based on activity network is presented and a mapping algorithm of translating BOM/BOP into the manufacturing process model is designed in detail.

Production Cost of Heterobranchus longifilis (Valenciennes, 1840) Fingerlings in the Ponds Fertilized with Poultry Droppings

This study aims to evaluate the production cost of Heterobranchus longifilis larvae reared in fertilized fish ponds. Experiment was carried out in two fish ponds. Each fish pond was filled with 200 liters of water and fertilized with dry poultry droppings (dose: 0.6 g.L-1) and zooplankton was inoculated with 83±13 individuals/L. Six days after inoculation of zooplankton, larvae of H. longifilis of 2 days after post-hatching were directly introduced into ponds with 300 individuals/m3. These larvae used exclusively zooplankton during the first 7 days. From the 8th day, larvae were fed with Coppens feed until 30 days. At the end, the survival rates were ranged between 58.33% and 56.67%. Final mean weights were brought up to all the ponds and were notsignificantly different (p > 0.05). The production costs ranged between 2.55 FCFA and 2.60 FCFA per fingerling with ratio production cost/weight gain around 0.80 FCFA/g in each pond. Then, this production system of fingerlings in fertilized ponds is very efficient and could be popularized in the rural fish farms.

Effect of Temperature and Ram Speed on Isothermal Extrusion for Large-size Tube with Piece-wing

Heat energy change during the extrusion of 7075 aluminium alloy large-size tube with piece-wing in a container was analyzed. Extrusion load vs ram displacement diagrams and exit temperature vs ram displacement diagrams at various speeds were obtained by 3D FEM simulation. Results show that the exit temperature becomes higher as the ram speed and displacement increase. For large-size tube with piece-wing, there is certainly a curve of ram speed decreasing with increasing ram displacement, which enables isothermal extrusion to be achieved. Therefore,an attempt was made to divide the working stroke into five different zones. Each of them has a preset speed that decreases from the ram displacement beginning to the ending. And then, new exit temperature vs ram displacement diagram was obtained by 3D FEM simulation for the five different speeds. It is shown that the variation of exit temperature is very small. Through the above research, a basic method for realizing isothermal extrusion of 7075 large-size tube with piece-wing was obtained, that is, the working stroke was divided into several different zones with a decreasing speed during extrusion, each zonest speed was real-time adjusted on the feedback signal of exit temperature by proportional hydraulic valve through closed-loop control. The engineering experiment verification was carried out on 100 MN aluminium extrusion press with oil-driven double action. The experimental results of the exit temperature agrees with the simulation ones. The achievements of this study may serve as a significant guide to the practice of the relevant processes, particularly for isothermal extrusion. The verified method has been used in the design and manufacture of 125 MN aluminium extrusion press with oil-driven double action.

Study on scour around vertical large-size cylinder base due to combined action of wave and current

Based on the mechanism of local scour around vertical large-sized cylinder due to combined action of wave and current,the sour morphology,scour process and the maximum scour depth around the cylinders are studied experimentally.The influence of various ocean environmental parameters on local scour around the cylinder is considered in physical model test.The experimental results indicate that the principal effect factors on the scour in fine-sand seabed are wave height,wavelength,current velocity,ratio of diameter to wavelength and ratio of depth to wavelength when the ratio of cylinder diameter to wavelength is from 0.2 to 0.8.In this paper,dimensional analysis theory is utilized to establish a theoretical equation for forecasting maximum scour depth around large-sized round cylinder base due to the combined action of wave and current.The results computed with the theoretical equation are compared with the experimental results,and found to be in good consistency.The results in this studies can be used to estimate the maximum sour depth around analogous structures.

Design of a 70 MPa Two-Way Proportional Cartridge Valve for Large-Size Hydraulic Forging Press

For an ultra-high-pressure hydraulic transmission system of a large-size hydraulic forging press(LHFP),a 70 MPa two-way proportional cartridge valve has been developed to improve the power weight ratio of the hydraulic forging press.In this study,a nominal diameter 25 mm(DN25)cartridge valve is taken as the research object.A longer concentric cylindrical annular gap is set to effectively prevent the ultra-high-pressure oil from flowing to the pilot stage and a seated valve structure is set to form the linear sealing zone in the closing state of the main valve port.Electric-displacement feedback is adopted to realize precise control of the main valve port flow and the features of this valve are investigated.In order to verify the strength and static and dynamic characteristics,the finite element model and a simulation model of the valve proposed above are built.There is a little deformation which does not affect the main valve spool movement,and the main valve port flow meets the design demands.Then,the prototype of DN2570 TPCV is manufactured and a ultra-high-pressure experimental platform is developed.The experimental results show that the DN2570 TPCV designed in this study has the advantage of fast response,high control precision,and low leakage,which can meet the requirements of LHFPs.

Finite Element Analysis on the Uniaxial Compressive Behavior of Concrete with Large-Size Recycled Coarse Aggregate

To model the concrete with complex internal structure of concrete with large sized aggregates the effect of internal structure on uniaxial compression behavior are studied.Large-sized recycled aggregates behave differently in the concrete matrix.To understand the influence on concrete matrix,a finite element model was developed to model recycled aggregate concrete composed of multiple randomly distributed irregular aggregates and cement mortar.The model was used to calculate the effect of large-size recycled coarse aggregate(LRCA)on the strength of recycled aggregate concrete and simulate the compressive strength of cubes and prisms.The factors such as the strength of new concrete,the strength of old concrete,the defective element content,the shape of LRCA,the incorporation ratio of LRCA and the size of LRCA that can affect the strength of concrete are analyzed in this paper.Results showed that the influence of various factors on concrete strength are in the following desend-ing order:(i)strength of newly poured concrete;(ii)original strength of recycled aggregates;and(iii)defects.It can be seen that the cracking of the phase material elements starts along the bonding zones between gravel and mortar or the new and old mortar,then spreads to mortar and finally to LRCA.The cracking tendency is most significant in LRCA,which means that the fracturing is related to the fracture of the LRCA.After evaluating the variations in strength and quality of the recycled concrete,the influences on concrete strength and quality were studied.The results showed that the proposed concrete model with LRCA was successfully applied to studying the uniaxial compressive behavior of concrete with large-size recycled coarse aggregate.

Autonomous Formation Flight Control of Large-Sized Flapping-Wing Flying Robots Based on Leader–Follower Strategy

Birds in nature exhibit excellent long-distance flight capabilities through formation flight,which could reduce energy consumption and improve flight efficiency.Inspired by the biological habits of birds,this paper proposes an autonomous formation flight control method for Large-sized Flapping-Wing Flying Robots(LFWFRs),which can enhance their search range and flight efficiency.First,the kinematics model for LFWFRs is established.Then,an autonomous flight controller based on this model is designed,which has multiple flight control modes,including attitude stabilization,course keeping,hovering,and so on.Second,a formation flight control method is proposed based on the leader–follower strategy and periodic characteristics of flapping-wing flight.The up and down fluctuation of the fuselage of each LFWFR during wing flapping is considered in the control algorithm to keep the relative distance,which overcomes the trajectory divergence caused by sensor delay and fuselage fluctuation.Third,typical formation flight modes are realized,including straight formation,circular formation,and switching formation.Finally,the outdoor formation flight experiment is carried out,and the proposed autonomous formation flight control method is verified in real environment.

马口鱼秋片鱼种北方池塘培育试验

为实现北方地区马口鱼的池塘养殖,于2021年5—10月在辽宁省辽阳地区的2个池塘进行了马口鱼秋片鱼种培育试验。结果表明:马口鱼鱼苗自投放后,分别经30和33 d的培育,2个池塘夏花的平均全长为31.85 mm,平均体质量为0.28 g;再分别经123和125 d后,2个池塘秋片鱼种的平均体质量分别达到36.50和46.25 g,总计出塘秋片鱼种12300 kg,平均成活率61.9%,平均饵料系数1.62;7月份马口鱼幼鱼全长特定生长率最高值为4.00%/d,9月份马口鱼幼鱼体质量日增长最大值为0.49 g;马口鱼幼鱼从水花至秋片过程中全长与体质量呈幂函数关系。在马口鱼北方池塘养殖条件下,建议养殖水温保持在20~25℃,养殖密度控制在22.5万尾/hm^(2)左右。

水产苗种管理信息系统的研究与设计

为解决个体户、小微育苗场信息化管理滞后的问题,研究与设计一个使用方便的水产苗种管理信息系统是十分必要的。本文通过查阅文献对管理信息系统进行了研究,在实地调查研究、需求分析的基础上,提出了水产苗种管理信息系统的设计方案:根据使用者身份的不同,划分为系统管理员和操作员两类用户角色;根据需求分析,按照模块化的设计思路,设计了用户注册、系统登录、员工管理等9个模块;根据各个模块的功能需求,设计了相应的数据库表。应用表明,该系统界面友好,简单易用,可以满足日常的需要,能够提升个体户、小微育苗场的信息化水平。