鱼类通过混流式水轮机转轮时受压强及剪切损伤的概率分析

鱼类在通过混流式水轮机流道时会遭遇最低压强及压强梯度引发的压强损伤以及剪切应力引发的剪切损伤。为了辨识混流式转轮中压强损伤和剪切损伤的主次关系,进而有针对性的开展混流式转轮的鱼类生态友好性能优化,该文基于计算流体动力学分析方法研究了不同水头条件下混流式转轮内超出压强以及剪切损伤阈值的体积分布规律,并获得了不同工况下混流式转轮内压强、压强梯度以及剪切应力引发鱼类受损的概率。结果表明:鱼类受压强及剪切损伤的概率与流量成正相关关系,对于该文分析的混流式转轮,鱼类受最低压强损伤的概率在最小水头的最大流量工况下达到最大值9.1%,剪切损伤及高压强梯度损伤的概率在额定工况下达到最大,分别为0.823%和8.31%。在相同工况下进行3种损伤概率的对比后发现,在大流量工况下,鱼类受最低压强和高压强梯度损伤的概率更大,在小流量工况下则是压强梯度损伤概率相对较高,所以综合分析结果可知最低压强和高压强梯度是开展亲鱼型混流式转轮优化时需要考虑的主要因素,而剪切应变率则是次要因素。

水轮机转轮结构与过机幼鱼受压强损伤相关性研究

大坝阻隔了洄游性鱼类的洄游通道,鱼类通过水轮机下行或误入水轮机流道将遭受水轮机流道复杂水动力特性及水轮机结构的影响,导致过机鱼体的损伤甚至死亡。为有效保护鱼类资源,本文在对大型轴流式水轮机进行全流道三维数值模拟的基础上,以鱼类受压强和压强梯度损伤阈值作为评价指标,对水轮机流道转轮叶片数目及转轮泄水锥尺寸进行降低幼鱼损伤概率的优化研究。研究结果表明,在满足水轮机出力要求的前提下,大型轴流式水轮机转轮叶片数目增多将增大下行幼鱼受压力及压力梯度损伤的概率,转轮泄水锥相对高度的减小将增加幼鱼受压力及压力梯度损伤的概率。该研究成果可为减小鱼体损伤的环境友好型水轮机优化设计提供参考。

Thermal damage constitutive model for rock considering damage threshold and residual strength

With the gradual depletion of mineral resources in the shallow part of the earth,resource exploitation continues to move deeper into the earth,it becomes a hot topic to simulate the whole process of rock strain softening,deformation and failure in deep environment,especially under high temperature and high pressure.On the basis of Lemaitre’s strain-equivalent principle,combined with statistics and damage theory,a statistical constitutive model of rock thermal damage under triaxial compression condition is established.At the same time,taking into account the existing damage model is difficult to reflect residual strength after rock failure,the residual strength is considered in this paper by introducing correction factor of damage variable,the model rationality is also verified by experiments.Analysis of results indicates that the damage evolution curve reflects the whole process of rock micro-cracks enclosure,initiation,expansion,penetration,and the formation of macro-cracks under coupled effect of temperature and confining pressure.Rock thermal damage shows logistic growth function with the increase of temperature.Under the same strain condition,rock total damage decreases with the rise of confining pressure.By studying the electron microscope images(SEM)of rock fracture,it is inferred that 35.40 MPa is the critical confining pressure of brittle to plastic transition for this granite.The model parameter F reflects the average strength of rock,and M reflects the morphological characteristics of rock stress–strain curves.The physical meanings of model parameters are clear and the model is suitable for complex stress states,which provides valuable references for the study of rock deformation and stability in deep engineering.

Meso-damage evolution and mechanical characteristics of low-porosity sedimentary rocks under uniaxial compression

Low pore sedimentary rocks(from Guangxi, China) were subjected to uniaxial compression loading experiment under different initial stresses. The rock samples were investigated by nuclear magnetic resonance before and after the loading. The relationships between the mesoscopic rock damage and macroscopic mechanical parameters were established, and the initial damage stress of the low-porosity sedimentary rock was determined. The results showed that this type of rock has the initial stress of damage. When the initial loading stress is lower than the initial stress of damage, the T2 spectrum area of the rock sample gradually decreases, and the primary pores of the rock are further closed under the stress. The range of the initial stress of damage for this type of rock is 8-16 MPa. When the loading stress exceeds the initial stress of damage, the T2 spectrum area gradually increases, indicating that the porosity of the rock increases and microscopic damage of the rock appears. The rock damage degree is defined, and the nonlinear function between the rock damage degree and the initial loading stress is established.

Rabbit lung injury induced by explosive decompression

Objective: To study the mechanism of rabbit lung injury caused by explosive decompression. Methods: A total of 42 rabbits and 10 rats were served as the experimental animals. A slow recompression decompression test and an explosive decompression test were applied to the animals, respectively. And the effects of the given tests on the animals were discussed. Results: The slow recompression decompression did not cause an obvious lung injury, but the explosive decompression did cause lung injuries in different degrees. The greater the decompression range was, the shorter the decompression duration was, and the heavier the lung injuries were. Conclusions: Explosive decompression can cause a similar lung injury as shock wave does. The primary mechanical causes of the lung injury might be a tensile strain or stress in the alveolar wall and the pulmonary surfaces impacts on the inside wall of the chest.

Flavonoid-rich fraction of the Monodora tenuifolia seed extract attenuates behavioural alterations and oxidative damage in forced-swim stressed rats

The antidepressant effects of the flavonoid-rieh fraction of Monodora tenuifolia seed extract were examined by assess- ing the extent of attenuation of behavioural alterations and oxidative damage in the rats that were stressed by forced swim test. Com- pared with the model control group, the altered behavioural parameters were attenuated significantly （P 〈 0.05） in the group treated with the flavonoid-rich fraction （100 and 200 mg·kg^-1）, comparable to the group treated with the standard drug, fluoxetine （10 mg·kg^-1）. The flavonoid-rich fraction and fluoxetine improved significantly （P 〈 0.05） the activities of the antioxidant enzymes such as superoxide dismutase and catalase as well as other biochemical parameters such as reduced glutathione, protein, and nitrite in the brain of the stressed rats. These results suggested that the flavonoid-rich fraction of Monodora tenuifolia seed extract exerted the antidepres- sant-like effects which could be useful in the management of stress induced disease.