复杂结构六联筒仓控制爆破拆除

采用定向爆破拆除了某厂房6联体砖混筒仓,该筒仓立筒相互连接处由钢筋混凝土柱与砖混材料组成且形状不规则.介绍了筒仓爆破切口尺寸计算、复杂结构部位的爆破参数设计和预处理措施.取得了理想的爆破效果,为同类构筑物的爆破拆除提供了参考和依据.     

复杂结构立筒库控制爆破拆除

介绍了某面粉厂内由2排共6个联体砖混结构筒仓组成的立筒库的爆破拆除.对立筒库采用分段延期定向爆破拆除方案,并取得了理想效果.着重论述了立筒库爆破切口高度计算、药孔参数设计、安全防护措施,为同类建筑物爆破拆除提供参考和依据.     

复杂结构六联筒仓控制爆破拆除

采用定向爆破拆除了某厂房6联体砖混筒仓,该筒仓立筒相互连接处由钢筋混凝土柱与砖混材料组成且形状不规则。介绍了筒仓爆破切口尺寸计算、复杂结构部位的爆破参数设计和预处理措施。取得了理想的爆破效果,为同类构筑物的爆破拆除提供了参考和依据。     

联体水泥筒仓定向爆破拆除

某公司的大型水泥联体筒仓,由于城市建设要求,需要进行爆破拆除。针对联体筒仓刚性大重心偏低等特点,对圈梁、漏斗和积灰平台提前进行了处理,降低了筒体刚性,提高了重心高度,保证了筒仓顺利倾倒。着重论述了筒仓爆破切口高度计算、炮孔参数设计、施工方法和安全防护措施,为同类建筑物爆破拆除提供参考和依据。     

联体水泥筒仓定向爆破拆除

某公司的大型水泥联体筒仓,由于城市建设要求,需要进行爆破拆除。针对联体筒仓刚性大重心偏低等特点,对圈梁、漏斗和积灰平台提前进行了处理,降低了筒体刚性,提高了重心高度,保证了筒仓顺利倾倒。着重论述了筒仓爆破切口高度计算、炮孔参数设计、施工方法和安全防护措施,为同类建筑物爆破拆除提供参考和依据。     

两联体钢筋混凝土结构筒仓定向爆破拆除

介绍了采用控制爆破技术拆除两联体钢筋混凝土结构筒仓的设计。施工及爆破效果。受施工条件的限制，拆除爆破在距地面5.3m高的承台上进行，采用预处理。秒延期，控制切口高度等措施。爆破效果达到预期目的。     

复杂环境下连体筒仓的控制拆除爆破

为了实现大型连体筒仓的定向拆除爆破，根据筒仓结构特点及周边环境情况，对筒仓顶部输煤栈桥和筒仓内部结构及切口范围进行了预拆除，在切口范围内的圈梁上部开凿了竖向切缝，并设计了合理的爆破切口范围和参数，采取了有效的安全防护措施。爆破效果表明，筒仓倒塌方向精准，爆破飞石和振动未对周边保护物造成破坏，确保了爆破期间电厂机组的正常运行发电，达到了预期效果，可为类似工程提供参考。     

高耸薄壁结构联体筒仓的爆破拆除

介绍了复杂环境下12只高耸薄壁结构联体筒仓的爆破拆除方法.通过分析比较,采用了定向倾倒的爆破方案,在对其进行了较为充分的预处理的基础上,选择合理的切口高度、布孔参数、药量和延期等确保了本次爆破的成功.     

210m高烟囱爆破拆除技术

介绍了在复杂环境下采用定向控制爆破技术,成功拆除210m高钢筋混凝土烟囱的实例.重点阐述了高耸烟囱成功爆破拆除中的几个关键技术、爆破参数、安全措施和爆破效果等.该烟囱的成功爆破促进了国内爆破拆除技术的发展,为今后高耸烟囱爆破拆除提供了参考.     

两座100m高薄壁结构冷却塔控制爆破拆除

根据冷却塔高、质量大、壁厚薄以及周围环境复杂等特点,制定了安全可靠的爆破方案。通过采用高卸荷槽复式切口爆破拆除技术,选择合适的爆破参数,采取合理的预处理措施和相应的安全防护措施,对两座100m高薄壁结构冷却塔成功实施了控制爆破拆除。降低了冷却塔爆破振动效应,实现了冷却塔爆破拆除精准定向。振动测试结果显示,冷却塔爆破拆除产生的振动速度均在安全允许范围内,证实了振动控制措施的有效性和实用性,可为同类爆破拆除工程提供参考。     

Diffraction of cylinders with longitudinal surface structures

We present a model to determine the light scattered by a metallic cylinder with longitudinal structures when the cylinder is illuminated by a Gaussian light beam in oblique incidence. The model is based on an approximate solution to the Helmholtz-Kirchhoff integral by means of the stationary-phase method. We have studied the variations of the diffraction pattern in terms of the size of the defect and other geometrical parameters. The width of the beam and the misalignment between the beam and the cylinder have also been considered, as well as the optical properties of the surface.     

Microstructures and mechanical properties of an investment cast gamma titanium aluminide

Abstract

Investment castings have been produced in γ-TiAl of composition Ti–48Al–2Nb–2Mn (at.-%) using induction skull melting. The microstructures of the bars were studied in the as cast condition and after hipping and heat treatment. Heat treatment at 1200°C led to a near γ structure whereas treatment at 1350°C resulted in a nearly lamellar structure. However, a duplex structure was retained after treatment at 1300°C. Tensile, fracture toughness, and fatigue crack growth resistance tests have been carried out on specimens machined from different sized bars. The tensile properties increased with decreasing bar diameter but, conversely, both the fracture toughness and fatigue crack growth resistance improved as the bar diameter increased. It has been found that the fracture toughness and fatigue crack growth resistance in nearly lamellar structures were better than those in near γ structures, whereas duplex structures had intermediate properties. However, the tensile properties of duplex structures were better than both near γ and nearly α₂ /γ lamellar structures, with optimum values at 35 ± 5% α₂ /γ lamellae of ～400 MPa 0·2% proof strength, 470 MPa tensile strength, and 0·9% elongation.     

Comparison between symmetric and asymmetric hot rolling techniques performed on duplex stainless steel 2205

The use of duplex stainless steel represents one possible efficient alternative of austenitic grade and an interesting resources for its high performance against stress corrosion cracking. Unfortunately such material shows some limitations in their use: for instance the sheets or plates of duplex stainless steels present anomalous and poor formability for plastic deformation processes. Such problems are mainly related to an unsuitable normal anisotropy coefficient, which might cause the “necking” and “earing” phenomena, especially during hot rolling. The study deals with the comparison of symmetric and asymmetric rolling technique on stainless steel duplex 2205 specimens. All the experiments were carried out using a laboratory mill, properly equipped with an individual engine for each rolling cylinder. The experimental parameters considered include three different pre-heating temperatures and two asymmetry ratios, while the reduction level is maintained constant for both rolling configurations. Moreover, the study involves also the analysis of the influence of solubilization quenching and the SEM, SEM-EBSD investigation dedicated to establish the microstructure modifications. The specimens were also studied through tensile tests to determine the influence of the rolling techniques on the mechanical properties of the product, focusing on the definition of the average anisotropy coefficient. The results of the experimental trials allow to conclude that the use of asymmetric rolling process induces an improved formability and increases duplex 2205 tensile properties.     

三维实体结构NURBS等几何分析

等几何分析是近年来在有限元法基础上发展起来的一种新的数值方法,它消除了有限元的几何误差,具有高阶连续性。该文研究了三维结构等几何分析中NURBS几何体的表示方式及载荷、约束的施加方法,分别从计算精度和仿真效率两个方面对比了等几何分析的计算结果与有限元法一阶单元和二阶单元的计算结果,展示了等几何分析相对于标准有限元法的优势,并以厚壁圆筒模型算例验证了等几何分析的实用性。将NURBS单元应用于几何形状精度要求高的齿轮和变截面圆筒,数值结果表明三维NURBS等几何分析方法在复杂三维结构的仿真计算中具有较好的灵活性和适用性,可得到连续的应力场,有望在工程中得到广泛应用。     

Analytical Estimation of Radar Cross Section of Infinitely Long Conducting Cylinder Coated with Metamaterial

Aerospace structures can be approximately modeled as a combination of canonical structures such as cylinder, cone and ellipsoid. Thus the RCS estimation of such canonical structures is of prime interest. Furthermore metamaterials possess peculiar electromagnetic properties which can be useful in modifying the RCS of structures. This paper is aimed at calculating the RCS of an infinitely long PEC circular cylinder coated with one or two layers of metamaterial. The incident and scattered fields of coated cylinder are expressed in terms of series summation of Bessel and Hankel functions. The unknown coefficients of summation are obtained by applying appropriate boundary conditions. The computations are carried out for both principal polarizations. The computed results are validated against the numerical-based method of moments. Further, the variation of RCS of the metamaterial coated PEC cylinder with material parameters, frequency, aspect angle and polarization is analyzed.     

不同粗糙表面的圆柱风压分布试验研究

通过风洞试验研究了不同表面粗糙度、不同雷诺数条件下二维圆柱的压力分布和阻力特性。结果表明:通过合理地增大表面粗糙度,在相对较低的风速下有效地模拟了圆柱的超临界绕流特性,满足了工程应用对超临界雷诺数的要求。     

水下多层结构目标体的高频回声特性研究

水下装置很多都是多层结构。为准确预报其高频回声特性,提出平面元方法结合基于传递矩阵的多层结构反射特性计算方法的混合方法研究水下三维多层结构目标体的高频回声特性,并研究多层圆板、圆球和有限长圆柱等水下多层结构三维目标体的回声特性。计算结果表明,水下目标体的第一Fresnel波带表面的曲率变化平缓时,采用的方法和局部反应表面处理方法的结果是基本一致的。而第一Fresnel波带表面的曲率变化不平缓时,方法的计算结果更符合实际声学特性。     

Structural analysis of tape-wrapped structures

The present study investigates the method of structural analysis and failure prediction of tape-wrapped structures that have been used in the conventional nozzle structures of rockets. Four-point bending test and its finite element analysis were performed to study how to model tape-wrapped structures and to investigate the failure characteristics of tape-wrapped structures. For dynamic characteristics, the natural frequencies of an inclined stacked plate and a tape-wrapped cylinder were measured and compared with the analytical characteristics.     

Wave interaction with a perforated circular breakwater of non-uniform porosity

Wave interaction with a porous cylindrical breakwater is studied analytically by linear potential wave theory. The breakwater is assumed to have a thin skin, is bottom-mounted and surface-piercing. The porosity of the breakwater is uniform vertically but varies in the circumferencial direction. This allows the choice of a partially impermeable wall or a vertical slot in the breakwater. Three different basic configurations of the breakwater are investigated, namely, (1) uniformly porous cylinder; (2) porous cylinder with partial impermeable wall; and (3) porous cylinder with an opening. The performance of these types of breakwaters is studied vs. wave parameters and breakwater configurations including angle and position of opening or partial impermeable wall as well as porosity. Parametric studies with regard to the wave-amplification factor, wave forces, and elevation contours are made. The results should be found useful in the design of coastal and offshore structures.     

Hall—Petch relation in two-Phase TiAl alloys

The Hall—Petch relation in lamellar—gamma duplex structures of TiAl alloys has been evaluated using Fan and Miodownik's model, by assuming that the friction stress varies linearly with the lamellar volume fraction. The results reasonably predict the strength of lamellar—gamma duplex structures at various grain sizes and volume fractions. The individual contributions from three constituting boundaries, lamellar—lamellar (-), gamma—gamma (γ-γ), and lamellar—gamma (-γ) boundaries to the overall strengthening have been calculated as a function of volume fraction: the -γ phase boundaries are not effective obstacles to dislocation motion. The - grain boundaries are rather the strongest obstacles to dislocation motion.