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1.
在工程实践中,直墙拱应用较多。由于拱脚位移的存在,合理假设拱脚约束为转角约束、竖向约束和水平弹性约束,应用力法推导出了在弯矩、剪力和轴力共同作用下直墙拱沿弧长的弯矩公式。研究了竖向均布荷载、竖向三角形荷载和竖向集中力荷载作用下,直墙拱沿弧长的弯矩分布及反弯点形成的规律;发现在3种荷载作用下,使得拱脚弯矩为零时的圆心角依次减小。取弹簧支座刚度为等效的下端固支、上端允许水平位移的直墙的抗推刚度,得出了随着直墙高度增加,圆弧拱拱顶弯矩增大而拱脚弯矩减小的变化规律。在直墙拱的设计中,建议选取合适的直墙高度和使得圆弧拱拱脚弯矩为零的圆心角大小,从而有利于提高结构抗弯承载力及拱脚抗剪承载力。  相似文献   

2.
据1986、1987年在天津西郊大棚黄瓜系统调查,采用m—m回归法对茶黄螨在大棚黄瓜田间危害空间分布型及抽样技术进行了初步研究.结果认为田间受害株密度小于0.5271时,茶黄螨危害株的田间分布为聚集分布型;大于0.5271时则为均匀分布型.计算得出不同受害级别下相应的最适抽样数,随着受害程度的加重,抽样数明显减少.  相似文献   

3.
为了探讨黑龙江省不同穗型粳稻穗部稻曲病发生情况及其与病害的相关性,采用田间自然感病法,调查分析了不同穗型粳稻稻曲病病穴率、病穗率、病情指数、抗性频率、病粒空间分布以及一、二次枝梗特征等。结果表明,不同穗型稻曲病发生程度不同,弯穗型稻曲病病穴率、病穗率和病情指数最低,半直穗型次之,直穗型最高,稻曲病发生呈直穗型＞半直穗型＞弯穗型的规律。弯穗型中10.76%表现为免疫,70.59%表现为抗性,半直穗型52.13%表现为抗性,直穗型19.62%表现为抗性。不同穗型水稻上病粒分布规律不同,弯穗型和半直穗型水稻病粒分布规律为中部＞上部＞下部,直穗型水稻病粒分布规律为中部＞下部＞上部,且三种穗型病粒均主要着生在二次枝梗上。相关分析表明,弯穗型品种二次枝梗数与病情指数显著正相关,半直穗型品种二次枝梗长度与病情指数极显著负相关,直穗型品种二次枝梗数与病情指数呈极显著正相关。  相似文献   

4.
为了进一步探索生物发酵床发酵机理。分析发酵床不同断面温湿度的变化及与猪舍环境小气候的关联。结果表明：（1）发酵床不同断面温度变化差异显著(P<0.01),其中10 cm断面温度较表层提高2.56℃ (P<0.05),20~40 cm断面温度较表层提高7.10~9.42℃ (P<0.01);（2）发酵床10 cm断面垫料含水率较20 cm和30 cm断面分别高11.5% (P<0.05)和13.5% (P<0.05),20 cm断面含水率与30 cm断面差异不显著(P>0.05);（3）发酵床不同断面温度和含水率与环境小气候相关性不显著(P>0.05)。由试验结果可见,发酵床温度不会随外界环境温湿度的变化而有较大变化,其表层和内部温度能维持相对稳定。  相似文献   

5.
为了探究不同田间持水量对马铃薯根系生长的影响,提高西北地区马铃薯产量。于2018在大田遮雨棚内进行,以马铃薯品种海斯薯为试验材料,采用膜下滴灌的灌溉方式。根据不同田间持水量梯度设置6个处理(分别为T1:85%～95%、T2:75%～85%、T3:65%～75%、T4:55%～65%、T5:45%～55%和T6:不灌水处理),研究不同田间持水量对马铃薯根系特性、产量及其相关性的影响。结果表明,随着田间持水量的下降根系分布逐渐加深,在田间持水量大于45%,根系主要分布在垄面0～10 cm处;当田间持水量小于45%时,根系主要分布在垄侧20～40 cm处。持水量高于65%处理下的块茎产量和大薯率高于其他处理,补偿效应显著(P<0.05);其中,持水量75%～85%处理下产量最高,平均产量为884.06 g/株,较T6处理增产257.61%。相关性分析发现,田间持水量与垄面根长、根表面积、大薯率和块茎产量呈显著(P<0.05)正相关,垄面根系长度和表面积与马铃薯块茎产量显著正相关(P<0.05)。综上所述,田间持水量大于65%时,能显著提高垄面的根长、根表面积和产量,其中,持...  相似文献   

6.
为了减少七叶一枝花野生资源的消耗,满足市场需求,节约生产成本,提高林地的利用率,增加林农收入,保护生态环境,选择常绿林地（杉木林地）、阔叶林地（核桃林地）与灌木林地（金银花林地）3种类型的林地,采用湖南本地洪江八面山生产的七叶一枝花种子和根茎切块2种繁殖材料,开展了林下育苗和栽培技术研究。结果表明：选择繁殖材料时,应采用种子繁殖,可减少野生资源的消耗,大量提供种苗,有利于规模化种植;不同繁殖材料采用育苗移栽和直播直栽林下规模种植时,宜采用直播直栽,可节约生产成本,提早投产;3种不同类型林地种植时宜选择阔叶林地,符合七叶一枝花的生态习性和生长发育规律,获得更好的经济效益。  相似文献   

7.
马鹿肌肉组织学特性研究   总被引：1，自引：1，他引：0  
为了研究马鹿不同部位肌肉的肉质。采用石蜡切片对马鹿不同部位肌肉肌纤维直径、肌纤维密度、肌束内肌纤维根数和肌纤维密度进行了测定。结果表明：同一部位公鹿肌肉肌纤维直径小于母鹿,除胸浅前肌和腹直肌无显著差异外(P>0.05),其他部位公鹿均显著小于母鹿(P<0.05);肌肉肌纤维面积,公鹿均小于母鹿,且公鹿颈斜方肌、臂头肌、肋间肌、背最长肌和股外侧肌肌纤维面积显著小于母鹿(P<0.05);对于肌束内肌纤维根数,公鹿均大于母鹿,但差异不显著(P>0.05);肌纤维密度公鹿大于母鹿,其中颈斜方肌、胸浅前肌、腹直肌和臀中肌呈显著性差异(P<0.05)。同一性别不同部位肌肉间肌纤维特性值显著性差异(P<0.05)和非显著性差异(P>0.05)。对肌肉组织学特性值进行综合比较后发现,公鹿肉好于母鹿肉,部位间肉质的比较为背最长肌>股外侧肌>冈上肌>臀中肌>肋间肌>臂头肌>腹直肌>胸浅前肌>颈斜方肌。  相似文献   

8.
马鹿肌肉组织学特征与肉质关系的研究   总被引：1，自引：0，他引：1  
为了研究马鹿不同部位肌肉的肉质.采用石蜡切片对马鹿不同部位肌肉肌纤维直径、肌纤维密度、肌束内肌纤维根数和肌纤维密度进行了测定.结果表明:同一部位公鹿肌肉肌纤维直径小于母鹿,除胸浅前肌和腹直肌无显著差异外(P＞0.05),其他部位公鹿均显著小于母鹿(P＜0.05);肌肉肌纤维面积,公鹿均小于母鹿,且公鹿颈斜方肌、臂头肌、肋间肌、背最长肌和股外侧肌肌纤维面积显著小于母鹿(P＜0.05);对于肌束内肌纤维根数,公鹿均大于母鹿,但差异不显著(P＞0.05);肌纤维密度公鹿大于母鹿,其中颈斜方肌、胸浅前肌、腹直肌和臀中肌呈显著性差异(P＜0.05).同一性别不同部位肌肉间肌纤维特性值显著性差异(P＜0.05)和非显著性差异(P＞0.05).对肌肉组织学特性值进行综合比较后发现,公鹿肉好于母鹿肉,部位间肉质的比较为背最长肌＞股外侧肌＞冈上肌＞臀中肌＞肋间肌＞臂头肌＞腹直肌＞胸浅前肌＞颈斜方肌.  相似文献   

9.
高肥力土壤下氮素对水稻产量效应的影响   总被引：2，自引：1，他引：1  
为了掌握不同施氮水平下氮素对水稻产量的贡献率,采用田间小区试验方法,对高肥力土壤条件下氮素对水稻产量的影响进行研究。结果表明,在高肥力土壤上水稻生物产量随着施氮量增加而增加,当施氮量小于105 kg/hm2时,水稻籽粒和秸秆产量同步增加;当施氮量大于105 kg/hm2时,秸秆产量呈快速增加,而籽粒产量呈下降趋势。随着施氮量的增加,每增加1 kg氮素投入所带来的作物生物产量和籽粒产量的增加量均呈下降趋势,但是籽粒下降幅度明显大于生物产量。  相似文献   

10.
为研究空调房间室内环境参数对室外气象参数瞬时变化的动态响应,采用CFD中的标准k-ε模型对兰州地区某办公室在考虑非稳定传热情况下的室内气流组织和污染物浓度场进行数值分析,获得了顶送风/下回风和侧送风/下回风两种通风模式下室内流场、温度场及污染物浓度场的分布。结果表明：不同时刻的太阳辐射通过激励室内自然对流换热过程对室内污染物的空间分布及迁移特性产生了显著影响。同一送风模式下,16:00时室内的污染物浓度较8:00时均匀,而8:00时的污染物浓度平均水平较高;在同一送风参数下,采用顶送风方式时更有利于降低室内污染物浓度。  相似文献   

11.
To get the spatial distribution characteristic of roadway's surrounding rock stress, circular section roadway was taken as a case study. The solution of stress was got by using complex function method, and roadway's surrounding rock stress field was analysed after the solution of mapping space was transformed into the solution of roadway space. As a result, the visual diagram of stress field distribution of roadway's surrounding rock was obtained, which could describe intuitively stress distribution of roadway's surrounding rock at any position. Considering the influence of different radius and side pressure coefficients on surrounding rock stress field, the following conclusions have been obtainded: the peak value and direction of circular roadway's surrounding rock stress has nothing to do with the radius; when side pressure coefficient is less than 1/3,the roof can produce tensile stress; when side pressure coefficient is more than 3, the surrounding rock in two sides can produce tensile stress. And the change rule of hoop stress, radial stress, shear stress and the maximum and minimum of stress have also been generated.  相似文献   

12.
According to seepage body force, strain softening and rupture expansion of rock mass, elastic-plastic mechanics theory, distribution laws of stress and displacement of surrounding rock in seepage field are derived, and relationships between different zonation range of the surrounding rocks, pore water pressure, strain softening and rupture expansion are established. The results show that the pore water pressure and rupture expansion rock mass have a more obvious impact on the surrounding rock rupture area than the plastic zone. Both the plastic zone and the rupture area are larger when the seepage field is considered. The impact of strain softening on both the plastic zone and the rupture zone of surrounding rock is very significant, and both seepage and strain softening rupture expansion affect deformation of surrounding rock of roadways obviously. It provides certain reference values for the roadway support engineering in seepage field.  相似文献   

13.
深部逆断层圆弧形断面诱发煤岩动力灾害的力学分析   总被引：1，自引：0，他引：1  
为了探索逆断层附近易于发生煤岩动力灾害的力学机制,构建了由构造应力为主导的圆弧形断层面简化力学模型,得到了构造应力以及由其引起附加垂直应力的分布规律,进而建立了断层上盘逆冲滑动临界角度的数学模型。研究表明：水平构造应力与附加垂直应力随着断层倾角的增大而增大,当断层倾角接近90°时,附加垂直应力突然增大且其值数倍高于水平构造应力;基于逆断层滑动的力学分析,理论计算了煤层沿断层逆冲滑动的临界角度,这将对煤岩动力灾害的危险性预测有一定的参考意义。  相似文献   

14.
This paper is aimed at investigating the acoustic properties of rock mass under the three-dimentional different stress states, and is presented to discuss emphatically the characteristics of the acoustic wave propagation and the stress-velocity relation in both rocks (sandstone and limestone) under uniaxial and true triaxial compression. The results indicate three regions in which the acoustic velocities and the strains change with the stresses are approximately similar under different stress states; and the acoustic velocity-stress relations for elastic rocks may be represented by different interdependence coefficients under uniaxial compression. At a time, The acoustic measurement method of rock mass stresses and the horizontal tectonic stress are discussed.  相似文献   

15.
According to the strain nonlinear softening constitutive model having inflexion point after peak stress of practical rock and considering intermediate principal stress, the plastic zone of circular cavern with liner under the condition of uniform pressure is analyzed. The elasto - plastic boundaries both for the lining and surrounding rock are discussed. The stress distribution law is different due to the different position of elastic - plastic boundary. Based on this, different stress formulas are gained. The critical pressure caused by excavation of cavern leading to the yield zone and that caused by inner pressure leading to the yield of the liner and surrounding rock is introduced.  相似文献   

16.
Reasonable choice of rock strength criteria is crucial for stress and displacement prediction and support design in tunnel engineering. Based on Mogi-Coulomb strength criterion and elastic-perfectly plastic model, analytical solutions of stress and displacement for surrounding rocks around a circular tunnel were derived The intermediate principal stress coefficient was used to present the intermediate principal stress effect. The results in this study were compared with the current solutions in the literatures and the influence of intermediate principal stress and shear strength parameters of surrounding rocks was discussed. The results showed extensive applicability and the Mohr-Coulomb strength criterion and Matsuoka-Nakai criterion are two special cases; when the intermediate principal stress coefficient b was equals to 0.5, the results indicated that the intermediate principal stress effect and its range for rock strength; the influence of cohesion and internal friction angle on the plastic radius and tunnel wall displacement was significant; Care should be taken to the effects of intermediate principal stress and shear strength parameter variations of surrounding rocks on tunnel design and construction.  相似文献   

17.
Basic on the FEM numerical analysis, the contour maps stress of rocksalt cavity's surrounding rock and the major principal stress's law changed with the depth and horizontal direction are analyzed. The influencing factors to the distribution of the stress surrounding rocksalt cavity, such as cavity's span, water pressure and the depth of rocksalt layer is also studied. The results show that major principal stress becomes big with the increase of rocksalt's depth. The cavity's influence to the stress's distribution will be clearer with the nearer to the cavity. The stress's centralization will be weaker with the accretion of water pressure in rocksalt's cavity. But the stress's centralization will be stronger, and the stress's value increases.  相似文献   

18.
A mathematical model of rock breaking under pulsed jet is established by introducing the Johnson-Holmquist-Concrete constitutive relation and the smoothed particle hydrodynamics method. Based on this model, the formation, propagation and attenuation of stress wave during rock breaking by pulsed jet are simulated. The relations between pressure and time at different points on rock surface and the curve of peak stress wave versus distance to action spot are obtained. Destruction behaviors of rock under pulsed jet and effects on stress wave effect from jet velocity and lithology are studied according to the above calculation results, analysis results show that stress wave effect of pulsed jet acts locally and the peak stress wave shrinks sharply as the acting distance increases. The rock breaking mechanism of stress wave is tensile failure during the high speed process of load-unload. Power and effect range of stress wave is in high direct proportion with jet velocity. There is a threshold velocity before the macroscopic failure. Rocks of different lithologies have different destruction types under pulsed stress wave of pulsed jet. Destruction type of low strength rock like sandstone is crack propagation under the tensile stress during the high speed process of load-unload, while the destruction type of high strength brittle rocks like granite and limestone is vertical failure of stress concentration.  相似文献   

19.
An analysis is made for various kinds of possible breakdown modes during hydrofracture,and the corresponding breakdown pressure,from which a method is given to distinguish which kind of failure mode practically occured. The analysis shows that the initial failure mode at the wellbore wall may be the pure tension failure or shear failure according to different stress states and mechanical properties of rock,therefore there are two different stress state configurations resulting in vertical shear fractures.  相似文献   

20.
In the partially mixed part of the Volkerak Estuary current speed and salt concentration are measured in several stations for periods of 13 hours on August 16 and 17, 1977. The freshwater discharge on those days and during the preceding six months is kept constant at a rate of 50 m3·s−1. In spite of different wind conditions, the longitudunal distribution of the tidally- and cross-sectionally averaged salt concentration is the same for both days. The vertical structure of circulation and salt concentration differ significantly. A similar set of measurements is carried out on March 18, 1980 with a constant freshwater discharge of 100 m3·s−1. The doubling of freshwater discharge leads to a relatively small increase in vertical circulation and stratification.In this study, the vertical circulation and stratification is examined in terms of the external forcings, freshwater discharge and wind, with special emphasis on wind. Tide conditions, for the three measurement days are similar. The estuary is schematized to a prismatic channel with a rectangular cross-section. In the schematized channel the tidally averaged salt concentration and velocity distribution are laterally uniform. To account for salt fluxes in the actual estuary associated with lateral and time-variations in current velocity and salt concentration, a diffusive salt flux is introduced. The effect of wind and longitudinal density gradients on the vertical circulation and stratification in the schematized channel is investigated using a simplified form of the two-dimensional conservation of momentum and salt equations. Using observed values along the axis of the estuary a scaling analysis shows that in the two-dimensional conservation of momentum equation the longitudinal pressure gradient and horizontal turbulent shear are the dominant terms, closely followed by the tidal stress. In the conservation of salt equation, the dominant terms are those associated with advective fluxes resulting from the horizontal and vertical tidal mean velocities, a horizontal flux associated with tidal variations in the longitudinal velocity and salt concentration and the vertical turbulent flux. Retaining only first order terms, the equations are solved using the similarity solution of Hansen and Rattray. Comparing calculated and observed vertical circulation and stratification it is shown that wind mixing significantly increases the vertical exchange of momentum, thereby reducing the density-driven vertical circulation (=gravitational circulation) and stratification. At the same time, through the wind surface stress, wind generates its own vertical circulation and, therefore, stratification. An expected increase in vertical exchange of mass with increasing wind speed and accompanying reduction in stratification could not be confirmed by the analysis. It is concluded that on the days of the measurements wind is as important as the longitudinal salt concentration gradient in forcing vertical circulation and stratification. Care should be taken in generalizing this conclusion as on the days of the measurements the axial component of the wind velocity is always in the down estuary direction.  相似文献   

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