Analytical characterisation of amplitude-dampening and phase-shifting in air/soil heat-exchangers

This article presents the complete analytical solution for the heat diffusion of a cylindrical air/soil heat-exchanger with adiabatic or isothermal boundary condition, submitted to constant airflow with harmonic temperature signal at input. It will be shown that, depending on its thickness, the soil layer will induce either one of two kinds of amplitude-dampening and phase-shifting regimes of the periodic input signal. In particular, for a thin layer submitted to adiabatic boundary condition, it is possible to completely phase-shift the periodic input while barely dampening its amplitude, a phenomenon apparently unexploited up to now, which might give rise to interesting energy handling techniques. Analytical results are validated against a finite-difference numerical simulation model as well as against an experimental setup.     

Tests and Analysis of Cantilevered GFRP Tubular Poles with Partial Concrete Filling

In this study, six glass fiber-reinforced polymer (GFRP) cantilevered tubular poles were tested in flexure. Four poles were filled with varying amounts of concrete; within 13, 30, 51, and 72% of their lengths, from the fixed point. Two poles, namely, a hollow and a totally concrete-filled tubes, were also tested as control specimens. The filament-wound prismatic tubes were 3,660 mm long, including a 700 mm clamped length at the fixed end, with a 220 mm outer diameter, and 4.15 mm wall thickness. The study aims at increasing flexural strength of thin-walled GFRP tubular poles by using a small amount of concrete at the vicinity of maximum moment near the base. Test results showed that flexural strength increases as the length of concrete fill is increased, until it reaches a plateau corresponding to about double the strength of the hollow tube, when the concrete fill is about one third of the clear length. This is considered the optimal condition for this tube that provides the largest strength-to-weight ratio. Poles with a shorter filling length failed prematurely, by a combined local buckling and crushing of the hollow part, while poles with a longer filling length failed at the base by rupture of the tube in tension. An analytical model was developed, validated, and used in a parametric study. The correlations between the optimal filling length ratio and both “diameter-to-thickness” ratio, and laminate structure of the tube, have been demonstrated for both angle-ply and cross-ply tubes.     

预失真线性化器的仿真研究

根据级联网络理论,基于行波管的非线性特性推导出预失真器模型,并在Matlab仿真平台上从三个角度验证了该模型的可行性和有效性,包括增益特性、相移特性和三阶交调特性,其中三阶交调系数的提取采用了计算精度高的自相关函数法。仿真结果显示,在饱和输入功率条件下加入预失真器后的系统相比行波管的三阶交调改善了6．947dBc。     

NO2 gas sensing properties of amorphous InGaZnO4 submicron-tubes prepared by polymeric fiber templating route

One-dimensional (1D) amorphous InGaZnO₄ (a-IGZO) submicron-tubes were synthesized in a method involving an electrospun polymeric fiber template and the direct RF-sputter-coating of a-IGZO films combined with subsequent calcination at 450 °C. The a-IGZO hollow fibers with a diameter of 300 nm and a shell thickness of 20–30 nm showed an amorphous structure, as confirmed by XRD and HR-TEM analyses. Gas sensors using semiconducting a-IGZO tube networks exhibited n-type gas sensing characteristics and a 3.7-fold higher gas response (R_gas/R_air = 109.5 at 2 ppm NO₂) compared to (R_gas/R_air = 29.4) planar a-IGZO thin films at an operating temperature of 300 °C. The enhanced gas response of a-IGZO tubes is attributed to the greater space charge modulation depth associated with the thin shell structures and the porous networks which are readily accessible by gas.     

大直径薄壁无缝管材对接试验样机的研发

研究了专门用于大直径薄壁管材对接装置,可实现ф1500mm~ф3500mm薄壁管材的对接,对接装置包含管材运送装置和整形装置,运输装置包括水平调节装置和垂直调节装置,可实现两根管材端部中心的对正,和管材的周向角度调节,实现管材运送和对接功能。该装置解决了大直径薄壁管材容易变形造成运输及对接困难,提高了对接效率和成品率,填补了国内技术空白,为进一步研究更大直径薄壁管材的运输及对接方案奠定了基础。     

Analytical Models for Concrete Confined with FRP Tubes

Concrete columns encased in fiber-reinforced polymer (FRP) tubes offer an attractive solution to enhance behavior of concrete in terms of strength as well as ductility. Analytical models for development of stress-strain curves for concrete confined with FRP are proposed in this paper. The predicted stress-strain curves for confined concrete using the proposed models are compared with those of tests for concrete specimens confined with FRP. It is demonstrated that the proposed models predict the stress-strain behavior of confined concrete very well. Based on the confidence gained in the proposed models, the effects of using different fibers, the presence of voids, and the number of layers are established.     

Combined Shear and Flexural Behavior of Hybrid FRP-Concrete Beams Previously Subjected to Cyclic Loading

Concrete-filled fiber-reinforced polymer (FRP) tubes (CFFTs) were initially proposed for bridge substructures in corrosive environments in the early 1990s. Systematic studies have since demonstrated the feasibility and merits of CFFTs with or without internal mild steel reinforcement. However, the experimental database in this field is still quite limited. This paper enhances the test database through a series of monotonic bending tests on one control RC specimen and five CFFT specimens previously subjected to reverse cyclic loading. Although the control RC specimen suffered shear-flexural cracks, specimens with carbon fibers experienced flexural failure by longitudinal splitting of the FRP tube in tension and its crumpling in compression. Specimens with glass or hybrid (glass/carbon) fibers, on the other hand, all failed by local buckling of FRP with either burst crushing or crumpling cracks. The specimen with hybrid fibers had higher normalized initial stiffness primarily because of its higher FRP/concrete stiffness ratio. The tests showed that the ductility of CFFT increases with FRP rupture strain. Further synthesis of flexural strength with FRP and mild steel reinforcement indexes reveals the existence of an optimized overall reinforcement index to achieve a design moment without overconfining concrete. Finally, the study confirms that shear failure is not critical for CFFT specimens at short shear span-to-depth ratios, even with internal mild steel reinforcement, as long as the FRP architecture is designed properly.     

Composite Tube Hinges

This paper is concerned with self-powered, self-latching tube hinges, made by cutting three parallel slots in a thin-walled carbon fiber reinforced plastic tube with a circular cross section. Thus, a hinge consists of two short tubes connected by three transversally curved strips of material (known as tape springs). A particular tube hinge design is considered, with a diameter of about one-third that of the hinges used previously; this requires the tape springs to reach strains close to failure when the hinge is folded. Three analyses of the peak strains in a tube hinge are presented. The first analysis obtains general analytical expressions for the longitudinal fold radius of a tape spring and the associated peak fiber strains. The second analysis is a finite-element simulation of the folding of a single tape spring and the third analysis is a simulation of a complete tube hinge. It is found that the largest fiber strains in one- and two-ply hinges can be predicted analytically with very good accuracy. It is also found that the contact and interaction between the three tape springs that form a tube hinge, modeled in the third analysis, do not affect the peak strains significantly.     

Testing and modeling of a novel FRP-encased steel–concrete composite column

A composite column consisting of steel, concrete and fiber reinforced polymer (FRP) is presented and assessed through experimental testing and analytical modeling. The composite column utilizes a glass FRP (GFRP) composite tube that surrounds a steel I-section, which is subsequently filled with concrete. The GFRP tube acts as a stay-in-place form in addition to providing confinement to the concrete. This study investigates the behavior of the proposed composite columns under axial loading. A total of seven specimens were tested. The influence of concrete shrinkage on the compressive behavior of the composite columns was also investigated. Significant confinement and composite action resulted in enhanced compressive behavior. The addition of a shrinkage reducing agent was found to further improve the compressive behavior of the composite columns. An analytical model was developed to predict the behavior of the composite columns under axial loading.