《固体力学学报》征稿简则北大核心CSCD

1．本刊是同体力学学科的学术性刊物。主要登载具有创造性的固体力学理论、实验和应用研究论文、各重要分支问题的评述和展望以及研究简报与学术讨论等,广泛交流学术界所取得的新研究成果,以促进固体力学学科的发展。读者对象是从事固体力学工作的科研与工程技术人员、高等院校教师和研究生。本刊有中、英文两个版本,向国内外公开发行。     

Analytical solution of a double moving boundary problem for nonlinear flows in one-dimensional semi-infinite long porous media with low permeability简

Based on Huang＇s accurate tri-sectional nonlin- ear kinematic equation （1997）, a dimensionless simplified mathematical model for nonlinear flow in one-dimensional semi-infinite long porous media with low permeability is presented for the case of a constant flow rate on the inner boundary. This model contains double moving boundaries, including an internal moving boundary and an external mov- ing boundary, which are different from the classical Stefan problem in heat conduction： The velocity of the external moving boundary is proportional to the second derivative of the unknown pressure function with respect to the distance parameter on this boundary. Through a similarity transfor- mation, the nonlinear partial differential equation （PDE） sys- tem is transformed into a linear PDE system. Then an ana- lytical solution is obtained for the dimensionless simplified mathematical model. This solution can be used for strictly checking the validity of numerical methods in solving such nonlinear mathematical models for flows in low-permeable porous media for petroleum engineering applications. Finally, through plotted comparison curves from the exact an- alytical solution, the sensitive effects of three characteristic parameters are discussed. It is concluded that with a decrease in the dimensionless critical pressure gradient, the sensi- tive effects of the dimensionless variable on the dimension- less pressure distribution and dimensionless pressure gradi- ent distribution become more serious; with an increase in the dimensionless pseudo threshold pressure gradient, the sensi- tive effects of the dimensionless variable become more serious; the dimensionless threshold pressure gradient （TPG） has a great effect on the external moving boundary but has little effect on the internal moving boundary.     

Linear stability of a fluid channel with a porous layer in the center简

We perform a Poiseuille flow in a channel linear stability analysis of a inserted with one porous layer in the centre, and focus mainly on the effect of porous filling ratio. The spectral collocation technique is adopted to solve the coupled linear stability problem. We investigate the effect of permeability, σ, with fixed porous filling ratio ψ = 1/3 and then the effect of change in porous filling ratio. As shown in the paper, with increasing σ, almost each eigenvalue on the upper left branch has two subbranches at ψ = 1/3. The channel flow with one porous layer inserted at its middle （ψ = 1/3） is more stable than the structure of two porous layers at upper and bottom walls with the same parameters. By decreasing the filling ratio ψ, the modes on the upper left branch are almost in pairs and move in opposite directions, especially one of the two unstable modes moves back to a stable mode, while the other becomes more instable. It is concluded that there are at most two unstable modes with decreasing filling ratio ψ. By analyzing the relation between ψ and the maximum imaginary part of the streamwise phase speed, Cimax, we find that increasing Re has a destabilizing effect and the effect is more obvious for small Re, where ψ a remarkable drop in Cimax can be observed. The most unstable mode is more sensitive at small filling ratio ψ, and decreasing ψ can not always increase the linear stability. There is a maximum value of Cimax which appears at a small porous filling ratio when Re is larger than 2 000. And the value of filling ratio 0 corresponding to the maximum value of Cimax in the most unstable state is increased with in- creasing Re. There is a critical value of porous filling ratio （= 0.24） for Re = 500; the structure will become stable as ψ grows to surpass the threshold of 0.24; When porous filling ratio ψ increases from 0.4 to 0.6, there is hardly any changes in the values of Cimax. We have also observed that the critical Reynolds number is especially sensitive for small ψ where the fastest drop is observed, and there may be a wide range in which the porous filling ratio has less effect on the stability （ψ ranges from 0.2 to 0.6 at σ = 0.002）. At larger permeability, σ, the critical Reynolds number tends to converge no matter what the value of porous filling ratio is.     

ACOUSTOELASTIC THEORY FOR FLUID-SATURATED POROUS MEDIA

Based on the finite deformation theory of the continuum and poroelastic theory, the aeoustoelastic theory for fluid-saturated porous media （FSPM） in natural and initial coordi- nates is developed to investigate the influence of effective stresses and fluid pore pressure on wave velocities. Firstly, the assumption of a small dynamic motion superimposed on a largely static pre- deformation of the FSPM yields natural, initial, and final configurations, whose displacements, strains, and stresses of the solid-skeleton and the fluid in an FSPM particle could be described in natural and initial coordinates, respectively. Secondly, the subtraction of initial-state equations of equilibrium from the final-state equations of motion and the introduction of non-linear constitu- rive relations of the FSPM lead to equations of motion for the small dynamic motion. Thirdly, the consideration of homogeneous pre-deformation and the plane harmonic form of the small dynamic motion gives an acoustoelastic equation, which provides analytical formulations for the relation of the fast longitudinal wave, the fast shear wave, the slow shear wave, and the slow longitudinal wave with solid-skeleton stresses and fluid pore-pressure. Lastly, an isotropic FSPM under the close-pore jacketed condition, open-pore jacketed condition, traditional unjacketed condition, and triaxial condition is taken as an example to discuss the velocities of the fast and slow shear waves propagating along the direction of one of the initial principal solid-skeleton strains. The detailed discussion shows that the wave velocities of the FSPM are usually influenced by the effective stresses and the fluid pore pressure. The fluid pore-pressure has little effect on the wave velocities of the FSPM only when the components of the applied initial principal solid-skeleton stresses or strains are equal, which is consistent with the previous experimental results.     

焙烧温度对纳米级SO4^2-／TiO2固体超强酸性能的影响

用锐钛型纳米TiO2制备了纳米级SO4^2-／TiO2固体超强酸，考查了焙烧温度对酸强度、比表面积、红外光谱及其催化活性的影响．结果显示该催化剂在450℃焙烧3h，可以形成纳米级SO4^2-／TiO2固体超强酸的结构，用该催化剂催化乙酸和丁醇酯化反应可使酯化率达到98．4％。     

CO2在气体水合物结构特性的固体核磁共振波谱与拉曼光谱实验研究

天然气水合物是蕴含着巨大能源潜力的非常规能源,2017年和2020年两次我国南海探索性试采的成功,加快了天然气水合物项目的进展。二氧化碳置换开采法,既能开发CH₄,又能封存CO₂。同时水合物法分离烟气中CO₂具有很好的应用前景,而CO₂在气体水合物的微观结构和特性尚不明确,实际应用存在一定的未知影响。为了考察其特性,利用13C固体核磁技术（NMR）和拉曼光谱（Raman）进行CO₂置换CH₄水合物、合成13CO₂-H₂-CP混合水合物实验表征,讨论CO₂在水合物中的定量问题,研究CO₂分子在笼型结构中的分布,探讨CO₂分子在气体水合物中的结构类型和特性。结果表明：（1）利用Raman费米低频共振1 277.5 cm-1峰积分得到CO₂在I型大笼（51262笼）的占有率为0.978 2,CH₄在Ⅰ型小笼（512笼）和大笼（51262笼）的占有率为0.059 3和0.009 5,水合数7.61,Raman费米高频共振1 381.3 m-1峰积分得到CO₂在51262笼的占有率为0.984 3,CH₄在512笼和51262笼的占有率为0.023 7和0.003 3,水合数7.70,CO₂几乎占满了大笼,CO₂气体的加入会导致水合物中,CH₄的大、小笼占有率均大幅度降低,置换后水合数略低于纯甲烷水合物,未标记的CO₂水合物在核磁中较难测出信号,CO₂气体置换后CH₄在小笼的占有率仅0.097 5,大笼占有率为0.317 2,两种方法差异主要原因为核磁的CO₂未出峰。（2）利用拉曼费米低频共振1 273.4 cm-1峰积分得到H₂、CO₂在512笼、CP在51262的占有率分别为0.124 8,0.304 2和0.997 8,水合数9.16;Raman费米高频共振1 380.6 cm-1峰积分得到H₂、CO₂在512笼、CP在51262的占有率分别为0.123 6,0.577 1和0.985 1,水合数7.12。13C标记CO₂分子在水合物中达到较好的固体核磁分辨率,首次确认CO₂在Ⅱ型小笼中的化学位移为124.8 ppm,计算得到CO₂的小笼占有率为0.783 1,CP的大笼占有率为0.971 8,水合数6.70,Raman高频频费米共振峰（1 380.6 cm-1）定量计算与13C NMR结果更接近。（3）对CO₂的13C NMR化学位移进行了归属,并结合Raman与13C NMR的对比分析,为CO₂水合物的13C NMR研究和拉曼定量提供参考。     

SSZ-13分子筛上甲醇转化过程中甲氧基物种的生成与活性研究

本文使用固体核磁共振（NMR）技术研究了SSZ-13分子筛上甲醇制烯烃反应过程中表面甲氧基物种的生成以及反应活性.通过二维¹³C-²⁷Al HMQC NMR方法确证了甲醇在分子筛骨架Brønsted酸位上生成的甲氧基物种,以及在Lewis酸位上生成的另外一种表面甲氧基物种.¹³C NMR结合气相色谱-质谱（GC-MS）实验结果表明,这两种甲氧基物种在甲醇制烯烃反应中均具有较高的反应活性,既可以导致烃池物种的生成,也可以参与烃池反应生成碳氢化合物.     

含两个圆孔电致伸缩材料的二维应力集中问题研究

应用复变函数方法,研究了含有两个圆孔无限大电致伸缩材料的二维应力集中问题。基于精确的电学和力学边界条件以及复变函数级数表示法,给出了孔边电场和应力场的一般解;在具体数值计算中,通过令两孔相距足够远得到单孔问题的近似解,并与已有单孔精确解比较,验证了本文解的正确性;通过改变孔内介质的介电常数和孔的位置讨论了孔周应力的分布规律。结果表明:当两孔距离很大时,圆孔孔周应力分布不受另一孔的影响;一般情况下孔内的电场很微弱,对孔周应力影响很小,可略去不计;当两孔圆心连线垂直于外加电场时,孔周应力峰值达到最大。     

梯度多孔材料单轴压缩弹塑性变形的宏微观数值分析

针对闭孔的密度梯度多孔材料,建立含球形孔洞的三维数值分析模型,研究其单轴压缩力学行为。首先,研究密度梯度对多孔材料宏观力学行为(如弹性模量和屈服强度)的影响;其次,研究密度梯度与材料局部力学性能的关系,得到了沿梯度方向弹性模量和屈服强度的分布规律;最后,讨论梯度多孔材料单轴压缩变形局部化机制。结果表明:当梯度材料与均质材料的总体相对密度相同时,梯度材料的宏观弹性模量和屈服强度均低于均质材料水平,其宏观应力-应变关系曲线降低;梯度多孔材料沿梯度方向的力学性能发生急剧变化,等效弹性模量沿梯度方向呈线性分布,屈服强度呈非线性曲线分布,导致沿梯度方向应力、应变呈现高度的不均匀性;多孔材料的变形局部化产生于孔隙率较大的薄弱位置,再逐渐向孔隙率较小的位置发展。由此可知,孔隙率的梯度变化影响多孔材料的力学性能,通过改变孔隙率的分布可实现材料预期的力学性质。     

闭孔泡沫金属变形模式的有限元分析

运用有限元软件ABAQUS/Explicit模拟了三维Voronoi闭孔泡沫金属在不同的冲击速度下的变形行为。随着冲击速度的提高,得到了3种变形模式:准静态均匀模式、过渡模式和冲击模式,并以相对密度和冲击速度为坐标建立了变形模式图。引入应力均匀性指标和变形局部化指标,确定了模式转化的临界速度,并与已有的冲击速度预测公式进行了比较。根据临界速度的数值和理论结果,提出了一种确定锁定应变的方案,结果介于压实应变和完全密实应变之间。