Compression failure conditions of concrete-granite combined body with different roughness interface

Bedrock and concrete lining are typical composite structures in the engineering field and the stability of the geological body and engineering body is directly connected to the mechanical properties of the composite body.Under this background,the study provides the transverse isotropic equivalent model of concrete-granite double-layer composite based on the notion of strain energy equivalence.Assuming that the strength failure of concrete and granite meets the Mohr-Coulomb criterion,then the strength failure model of the combined body considering the joint roughness coefficient(JRC)is derived,and the influences of JRC,the height ratio of concrete to granite,and confining pressure on the strength failure characteristics of the combined body are emphatically analyzed.Finally,the model applicability is illustrated by the uniaxial and triaxial compression tests on concrete monomer,granite monomer and concretegranite composite samples(CGCSs)with different JRCs.The results revealed that the compressive strength of the composite is closer to the concrete with lower strength in the combined body under different confining pressures.Adding interface roughness causes to raise the compressive strength of the composite due to interfacial adhesion between concrete and granite,and a slowing growth trend is observed in compressive strength as roughness.The model can provide a certain reference for the stability design and evaluation of engineering rock mass.

The deteriorated degradation resistance of Mg alloy microtubes for vascular stent under the coupling effect of radial compressive stress and dynamic medium

The degradation of Mg alloys relates to the service performance of Mg alloy biodegradable implants.In order to investigate the degradation behavior of Mg alloys as vascular stent materials in the near service environment,the hot-extruded fine-grained Mg-Zn-Y-Nd alloy microtubes,which are employed to manufacture vascular stents,were tested under radial compressive stress in the dynamic Hanks'Balanced Salt Solution(HBSS).The results revealed that the high flow rate accelerates the degradation of Mg alloy microtubes and its degradation is sensitive to radial compressive stress.These results contribute to understanding the service performance of Mg alloys as vascular stent materials.

Effects of I-EGR and Pre-Injection on Performance of Gasoline Compression Ignition(GCI)at Low-Load Condition

Gasoline compression ignition(GCI)has been considered as a promising combustion concept to yield ultralow NOX and soot emissions while maintaining high thermal efficiency.However,how to improve the low-load performance becomes an urgent issue to be solved.In this paper,a GCI engine model was built to investigate the effects of internal EGR(i-EGR)and pre-injection on in-cylinder temperature,spatial concentration of mixture and OH radical,combustion and emission characteristics,and the control strategy for improving the combustion performance was further explored.The results showed an obvious expansion of the zone with an equivalence ratio between 0.8∼1.2 is realized by higher pre-injection ratios,and the s decreases with the increase of pre-injection ratio,but increases with the increase of i-EGR ratio.The high overlap among the equivalentmixture zone,the hightemperature zone,and the OH radical-rich zone can be achieved by higher i-EGR ratio coupled with higher preinjection ratio.By increasing the pre-injection ratio,the combustion efficiency increases first and then decreases,also achieves the peak value with a pre-injection ratio of 60%and is unaffected by i-EGR.The emissions of CO,HC,NOX,and soot can also be reduced to low levels by the combination of higher i-EGR ratios and a pre-injection ratio of 60%.

Effect of Processing Conditions on the Compression Elasticity of Three Dimensional Crimp Staple

The multi-hollow three dimensional(3-D)crimp sta-ple were prepared by the non-symmetrical cooling spin-ning technology.The material properties,spinneret shape,drawing conditions,heat-setting conditions and silicon finishing conditions that influence the compression elasticity of the staple have been investigated.It is found that the compression elasticity of 3-D crimp PET staple is larger than that of 3-D crimp PP staple.The com-pression elasticity of the 5-hollow staple is much

Effect of Deformation Condition on Axial Compressive Precision Forming Process of Tube with Curling Die

The effect of the deformation condition on the axial compressive precision forming process of tube with curling die was investigated by using a rigid-plastic FEM. The results show that the forming accuracy depends mainly on geometric condition rp/d0, little on tube material properties and friction condition; the relative gap △/2rp of double-walled tubes obtained decreases with Increasing rp/d0, and there is a parameter k for a given to/do or rp/t0, when rp/d0 >k, △/2rp< 1, otherwise △/2rp>1.

微小型压缩空气储能系统用涡旋压缩机流动特性研究

以空气为工质,基于计算流体动力学方法,对无油空气涡旋压缩机在变工况运行条件下进行了三维非稳态数值模拟。研究发现:动静涡旋齿之间存在的径向间隙,会使得压缩机工作腔内温度、流速和压力的分布不规律;增大转速,不但可以增加涡旋压缩机的质量流量,而且还可以减小切向泄漏量,进而提高压缩机的工作效率;排气压力过大,会降低涡旋压缩机的基本输出性能;在低转速下,过高的排气压力会使得压缩机排气口出现“净回流”现象。

可压缩边界层的入口合成湍流生成方法

在壁湍流中开展RANS-LES方法混合模拟时,入口处添加合理的湍流脉动能够缩短流场向完全湍流的发展距离,提高数值模拟精度以及节省计算资源.采用SA-IDDES方法对槽道湍流和可压缩湍流边界层开展了数值模拟研究,对比了3种较为常用的合成湍流方法对流场发展的影响,包括合成湍流生成器(STG)、数字滤波法(DFM)和合成涡方法(SEM);研究了不同合成湍流入口条件下流场壁面摩阻、流场结构、雷诺应力的发展过程,评估了各方法在壁湍流中的表现.其中在不可压槽道湍流和可压缩湍流边界层的模拟中,STG方法展现了较短的摩阻恢复距离,流场结构与雷诺应力发展相比DFM也有一定的优势.在高马赫数湍流边界层的数值模拟中,忽略热力学量脉动可能会降低合成边界层脉动恢复到物理真实脉动的速度.因此,文章进一步基于STG给出的速度脉动,在入口处通过若干强雷诺比拟方法(SRA,GSRA和HSRA)添加热力学脉动量,对比研究了对可压缩湍流边界层流场发展的影响,结果显示是否添加热力学脉动对于流场摩阻和雷诺应力发展影响较小,但对流场中的热力学量影响显著,其中GSRA下流场热力学量恢复得最快.

简单立方点阵结构静态平压性能分析

为了提高简单立方(SC)点阵结构的平压力学性能,在ABAQUS中对SC单胞建立了周期边界约束方程,并通过ESO算法对周期边界条件下的SC单胞进行了拓扑优化设计。随后对优化SC单胞的等效弹性模量进行了求解,发现优化SC单胞的等效弹性模量明显优于传统SC单胞,从外部去除单胞材料可使优化单胞等效压缩模量提高27.14%,从内部去除单胞材料可使单胞等效剪切模量提高46.18%。最后将优化SC单胞从单胞层面扩展到宏观结构中,探究了三类SC点阵结构的静态平压性能。研究表明,周期边界条件与ESO相结合的拓扑优化方法,可使SC结构静态平压时的抵抗力得到明显提升。相比传统SC点阵结构,优化后的SC点阵结构抵抗力提高了20%以上。

基于无侧限抗压强度试验的不同养护环境对水泥土强度影响研究

以福建省宁德市连城路(疏港路-学院路段)道路工程项目为依托,采用无侧限抗压强度试验系统研究了不同养护条件、不同水泥掺量、不同养护龄期对水泥土强度的影响。结果表明:当水泥掺量和养护龄期均相同时,试验箱中水泥土的无侧限抗压强度均小于标养箱;在同一水泥掺量下,试验箱和标养箱中水泥土的无侧限抗压强度均与养护龄期成正相关,即随着养护龄期的增加而增长,但其强度增长幅度随着养护龄期的增加逐渐降低;同一养护龄期下,不同养护条件下水泥土的无侧限抗压强度均随着水泥掺量的增加而增长,且试验箱和标养箱中试样的强度差值随着水泥掺量的增加逐渐加快。

基于最优动态功率补偿的先进绝热压缩空气储能一次调频控制策略

随着大规模新能源接入电网,新型电力系统“低惯量、弱支撑”特征凸显,电网频率调节资源日益稀缺,系统频率稳定问题愈发严峻。先进绝热压缩空气储能(advanced adiabatic compressed air energy storage,AA-CAES)具有容量大、寿命长等优势而受到广泛关注,但由于其储能和释能过程涉及气-热动态耦合过程,调频特性较为复杂,调频潜力还有待挖掘。因此,首先建立AA-CAES系统全工况动态仿真模型,进而基于期望频率动态曲线设计AA-CAES系统调频传递函数,优化目标传递函数关键参数,实现AA-CAES最小动态功率补偿下满足系统频率调节需求。最后通过仿真实验,验证了所提控制策略可优化AA-CAES调频容量的同时减小系统的稳态频率偏差与频率超调量,显著改善频率响应特性,为建设电网友好型AA-CAES电站提供技术支撑。

基于CRF的分区倒排索引压缩算法

倒排索引是大型搜索引擎的核心数据结构,本质是倒排列表中整数序列的集合。倒排索引压缩可以有效减少倒排索引所占空间,提高对关键词的检索效率。本文提出的基于条件随机场(CRF)的分区倒排索引压缩算法主要关注域值分区的分区方式。该算法对序列进行预分区,并且使用条件随机场对预分区进行标注并重组,有效减少了压缩时间。根据分区类型,该算法使用相应的编码方式,进一步减少了压缩后的空间占用。与其他倒排索引压缩算法进行对比实验分析,结果表明本文算法在压缩率上超过目前一些域值分区的算法,并且在解压时间上与其他域值分区算法相当。该算法在时间和空间上取得了较好的平衡。

土的压缩模量与变形模量的理论关系

在实际工程中经常用到土的变形模量,由于测试变形模量需要花费较多的时间和费用,故常常通过压缩模量来估算变形模量,但这种估算有很大争议。本文首先指出长期公认的变形模量与压缩模量间的关系式E_(0)=βE_(s)中存在的问题,然后重新推导了它们的关系式E_(0)=β′E_(s),考虑到土的结构性、应力历史条件以及土体扰动,最后建立了一种新的变形模量与压缩模量的关系式E_(0)=αE_(s)。

养护条件对地聚物胶凝材料的力学性能影响

以矿渣、粉煤灰和沸石粉为主要原料,NaOH和水玻璃为碱激发剂,在标准养护和室温养护条件下制备地聚物。采用三个因素三个水平进行正交试验设计,揭示三个因素对地聚物28 d抗压强度的影响并以28 d抗压强度为指标,确定制备地聚物的最佳配合比。试验结果表明:在标准养护和室温养护条件下,水胶比对试件抗压强度有显著影响。标准养护条件制备地聚物最佳配合比组合即矿渣、粉煤灰和沸石粉配合比分别为50%、25%和25%,水胶比为0.35,水玻璃模数为1.4,最高强度为68.4 MPa。室温养护条件制备地聚物最佳配合比组合即矿渣、粉煤灰和沸石粉配合比分别为50%、25%和25%,水胶比为0.40,水玻璃模数为1.4,最高强度为60.35 MPa,可见不同养护条件对抗压强度影响较大。

非补燃式地下含水层压缩空气储能地质研究及发展前景

非补燃式地下含水层压缩空气储能是借助于自身的储热特点和区域地质优势将过剩电力转换存储的新型储能方式,间接的解决了能源浪费问题,成为现今能源储备方向的热题。通过现有的压缩空气储能成功案例和正在建设项目工程,对非补燃式地下含水层压缩空气储能(CAESA)原理和未来发展前景进行简易介绍,对储气库选址工作中所需的地质条件和经济效益以及安全性等3重因素进行详细阐述。储层的地质条件包括储层地质完整性、含水储层渗透性、盖层密封性及储层稳定性4个方面,经济效益着重工程地质选址成本、工程建设成本及运营维护成本等,其中选址环节利用现有各项资料能节省部分项目支出。项目安全性旨在建设期地下工程喷井等安全事故及运行期内固井和井筒腐蚀性等可能存在的安全隐患分析。结合国内地理优势、城市经济及油气田的分布等,针对性研究含水储层对空气压缩储能的发展有重大的实际性意义。

基于灰色关联理论现场商品混凝土强度的影响因素分析

为了研究现场施工中混凝土强度的影响因素,使用粉煤灰掺量分别为75kg/m^(3)、70kg/m^(3)、68kg/m^(3)、91kg/m^(3),水胶比分别为0.36、0.46、0.45、0.39,砂率分别为0.48、0.53、0.52、0.45的现场同条件试件,经过不同振捣程度成型后,进行不同累计温度、不同龄期养护后,将试件进行轴心抗压试验,以混凝土抗压强度为评价指标,采用灰色关联分析理论,对现场施工中混凝土强度的影响因素进行研究。结果表明:随着累计温度增加,混凝土强度整体呈增长趋势,影响现场施工混凝土强度因素按照重要程度排序为累计温度>养护天数>振捣程度>粉煤灰>水胶比>砂率。

An Experimental Investigation on Low Load Combustion Stability and Cold-Firing Capacity of a Gasoline Compression Ignition Engine

Gasoline compression ignition (GCI) is one of the most promising combustion concepts to maintain low pollutant emissions and high efficiency. However, low load combustion stability and firing in cold-start operations are two major challenges for GCI combustion. Strategies including negative valve overlap (NVO), advanced injection strategies, fuel reforming, and intake preheating have been proposed in order to solve these difficulties;however, the cold start is still an obstacle. The objective of this work is to study effective methods to achieve GCI engine cold start-up. This work combines NVO, in-cylinder fuel reforming, and intake preheating to achieve quick firing under cold-start conditions and the subsequent warmup conditions. The results show that start of injection (SOI) during the intake stroke yields the best fuel economy, and injection during the compression stroke has the potential to extend the low load limit. Furthermore, SOI during the NVO period grants the ability to operate under engine conditions with cold intake air and coolant. With highly reactive products made by in-cylinder fuel reforming and fast heat accumulation in the combustion chamber, the NVO injection strategy is highly appropriate for GCI firing. An additional assisted technical method, such as intake preheating, is required to ignite the first firing cycle for a cold-start process. With the combination of NVO, in-cylinder fuel reforming, and intake preheating, the GCI engine successfully started within five combustion cycles in the experiment. After the firing process, the engine could stably operate without further intake preheating;thus, this method is appropriate for engine cold-start and warm-up.

Near optimal condition of OMP algorithm in recovering sparse signal from noisy measurement

This paper analyzes the performance of the orthogonal matching pursuit （OMP） algorithm in recovering sparse signals from noisy measurement. Considering the fact that some matrices satisfy some restricted isometry properties （RIPs） but not the coherence condition, a superior RIP-based condition is proposed, which means that if the measurement matrix satisfies δk＋1 〈 1/（2 ＋ √k） and the minimum component signal-to-noise ratio （MCSNR） is bounded, the OMP algorithm can exactly identify the support of the original sparse signal within k iterations. Finally, the theoretical results are verified by numerical simulations con- cerning different values of MCSNR and noise levels.

Pre-Compression Volume on Flow Ripple Reduction of a Piston Pump

Axial piston pump with pre-compression volume（PCV） has lower flow ripple in large scale of operating condition than the traditional one. However, there is lack of precise simulation model of the axial piston pump with PCV, so the parameters of PCV are difticult to be determined. A finite element simulation model for piston pump with PCV is built by considering the piston movement, the fluid characteristic（including fluid compressibility and viscosity） and the leakage flow rate. Then a test of the pump flow ripple called the secondary source method is implemented to validate the simulation model. Thirdly, by comparing results among the simulation results, test results and results from other publications at the same operating condition, the simulation model is validated and used in optimizing the axial piston pump with PCV. According to the pump flow ripples obtained by the simulation model with different PCV parameters, the flow ripple is the smallest when the PCV angle is 13~, the PCV volume is 1.3 ~ I0-4 m3 at such operating condition that the pump suction pressure is 2 MPa, the pump delivery pressure 15 MPa, the pump speed 1 000 r/min, the swash plate angle 13~. At the same time, the flow ripple can be reduced when the pump suction pressure is 2 MPa, the pump delivery pressure is 5 MPa,15 MPa, 22 MPa, pump speed is 400 r/min, 1 000 r/rain, 1 500 r/rain, the swash plate angle is ll~, 13~, 15~ and 17~, respectively. The finite element simulation model proposed provides a method for optimizing the PCV structure and guiding for designing a quieter axial piston pump.

Multivariable fuzzy control of residential inverter-driven air conditionings

A model free intelligent multivariable fuzzy controller (MFC) designed for modulating the vapor compression cycles in a residential inverter-driven air conditioning is proposed. The novel controller combines a traditional fuzzy controller (TFC) and an additional coupling fuzzy controller,the coupling fuzzy controller is introduced to compensate for the unknown cross-coupling effects of this multivariable system. In order to evaluate the control performance of the MFC,it is digitally implemented in terms of regulating the desired evaporating temperature and superheat. The experimental results show the effectiveness of the MFC for improvement of system performance and energy efficiency.

不同超低温作用工况混凝土受拉受压强度间关系试验研究

通过常温降至给定超低温(-40℃、-80℃、-120℃、-160℃和-190℃)以及经历超低温再直接和以1℃/min匀速地回至常温共3种工况混凝土的轴心受压和劈裂抗拉试验,探讨不同超低温作用工况下混凝土受拉受压强度间关系及其离散性变化情况。结果表明,随作用的超低温降低,混凝土超低温时相对受拉受压强度及其差值比分别呈先增后减、波动地增大和先增后减的变化趋势;经历超低温再直接回至常温工况混凝土相对受拉受压强度及其差值比分别呈波动状但较为平稳、先增大后平稳和先减后增的变化趋势;而经历超低温再以1℃/min匀速地回至常温工况混凝土相对受拉受压强度则均呈波动状且稍有增大的变化趋势。混凝土超低温时受拉受压强度离散性随作用的超低温降低分别呈先迅速后缓慢减小和缓慢增大的变化趋势;而经历超低温再直接和以1℃/min匀速地回至常温工况混凝土的受拉强度离散性却总是大于受压强度,但两者均呈波动性减小的变化趋势。