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This study investigated the shear resistance and damage evolution of glass fiber-reinforced polymer (GFRP)-reinforced concrete short columns. Five circular concrete short columns reinforced with GFRP bars and spiral stirrups were fabricated and tested under lateral thrust in the laboratory. The test variables involved the stirrup reinforcement ratio, the longitudinal reinforcement ratio and the type of stirrups. The failure modes, load-displacement curves, strain responses and crack characteristics of these columns were documented and discussed. The accuracy of shear design equations in predicting shear capacity of such columns was evaluated. In addition, the digital image correlation (DIC) instrument was used to identify the full-field strain and damage zones of circular concrete short columns. Several smart aggregate (SA) transducers coupled to the surface of these columns were used to monitor its damage status. The energy ratio index (ERI) and the damage index based on smart aggregate were established to characterize damage level of such columns. The test results indicate that the shear capacity is improved 5.6% and 31.1% and the lateral ultimate displacement is increased 67.7% and 400% as the stirrup reinforcement ratio of the concrete short column is increased from 0 to 0.19% and 0.47%, respectively. The shear capacity equation proposed by Ali and his co-workers, considering a strain limit of 0.004Efv, gives accurate predictions of the shear capacity of circular concrete short columns reinforced with GFRP bars and spiral stirrups. The variation in ERI values is explained by the development of damage zones of the column obtained with DIC technology and with the proposed damage index based on the smart aggregate it is feasible to evaluate the damage level of circular short concrete columns.

This paper extends previous studies concerning the structure of wind in tropical cyclones (TCs) approaching land mass over coastal waters. New sets of field measurements from wind observation towers and Doppler SODARS at levels between the land surface and 100 m height are presented. The measured mean (over 10-min periods) of the horizontal velocity U(r) shows the usual eye, eyewall and outer vortex structure. But very significantly they also exhibit that the mean vertical profile, U(z), does not increase monotonically as in a usual surface boundary layer in the backside eyewall regions. Rather, it is in the form of a jet, with a maximum velocity, U L L J , at a height z L L J , lying between 40 and 60 m. The data also show that the mean velocity gradient, defined by the ratio U L L J / U ( 10 ) , is typically smaller in the front side of a tropical cyclone in the direction of its motion as compared to the backside. This asymmetric distribution does not vary significantly with the radius. The mechanisms that result in the asymmetric distribution of the low-level jet are complex. One possible source is the downward transportation of convective turbulence. In the backside of a TC, the downflow is dominated, and it transports high velocity flow downward and enhances the mean momentum of wind flow at lower heights. Another factor may be the influence of the swell translation in different azimuth of a TC structure. These mechanisms need further investigation based on high resolution observations through a collaborative multiplatform measurement involving, e.g., Doppler SODAR, conventional sensors and numerical simulations.

Optimization design assisted with advanced additive manufacturing techniques opens an effective gate for us to create novel, lightweight, mechanically robust cellular materials. Among them, lattice materials with an ordered cellular architecture have been known for their high mechanical properties, low density and energy absorption capacity. Limitedly, what kinds of topologic architecture have the best performance? And how could we obtain the optimized architecture? To answer them, we here took up two challenging tasks to achieve a novel compression-resistant lattice: ① The topology optimization method was introduced to design the optimized topologic architecture. ② Metallization was used to form lattice composites to further enhance the mechanical properties of pristine polymer. The topology optimization-guided lattice with only 20% volume of solid materials quite resembles the microstructure of cuttlebone, giving an indication of a good compression-resistant ability. Furthermore, the synthesized composites exhibit high specific compressive modulus of 5417.02 MPa kg−1 and energy absorption efficiency of 78%. By in situ compressive tests, digital image correlation, finite element simulation and fracture analysis, the deformation mechanism, and fracture modes were unambiguously revealed. The design strategies and findings shed light on the realization of advanced materials with tailored mechanical properties.

Alkali-activated materials (AAMs) are widely recognized as potential alternatives to ordinary Portland cement (OPC) due to their lower carbon footprint. However, like OPC, AAMs can also generate some durable problems when exposed to aggressive environments and the mechanisms and possible improvements are still not fully clear in existing investigations. Furthermore, the corrosion mechanisms of AAMs are different from OPC due to the discrepant reaction products and pore structures. Thus, this study’s aim is to review the chemical reaction mechanisms, factors, and mitigation methods when AAMs are attacked by carbonation and chloride ions, along with a summative discussion regarding instructive insights to durable problems of AAMs.

The temperature-dependent mechanical behaviors of open-hole composite plates are essential for composite design and structures. Here, tensile experiments of shallow straight-link-shaped 2.5D woven composites (abbr. 2.5DWC) with/without a center hole are first conducted at different temperatures (20 °C, 180 °C and 240 °C). Failure modes are examined by scanning electron microscope (SEM). Thermal property of QY8911-IV resin is investigated by DMA analysis. It is noted for samples without the center hole that with the increase of temperature, the tensile stress–strain curves exhibit a linear response until that a slight nonlinearity at the end stage. The strength retention rates at 180 °C and 240 °C are totally equal. For the open-hole samples, it is interestingly found that the strength retention rates are higher than that of samples without the hole at 180 °C, resulting from the stress concentration accommodation and fiber-dominated failure mode. Even at 240 °C, there is no necking phenomenon for all the failed samples, but more broom-like damage extent is observed in the cross-section. Due to the primary load-bearing warp yarns and hole-edge stress concentration, obvious pull-out warp yarns emerge near the hole edge.

Water inside and between cells with dimensions on the order of 101–103 nm such as synaptic clefts and mitochondria is thought to be important to biological functions, such as signal transmissions a...

Apart from the rapid development in macroscale green energies, such as wind energy and hydro energy, micro/nanoscale self-powered energy systems are increasingly attractive in wearable energy systems. To utilize the energy harvester more conveniently and effectively, an energy harvester, viz., single-electrode textile-based triboelectric nanogenerator (ST-TENG), is reported in this study. The ST-TENG is a polydimethylsiloxane (PDMS)/Ag-coated chinlon fabric (PACF) composite film with the surface microstructures induced by sandpapers. The PACF composite is self-powered based on the triboelectrification and electrostatic induction. The merits of ST-TENG include: (1) all the basic materials are flexible and scalable; (2) the resultant PACF is a free-standing composite film, which can be easily peeled off from the sandpaper substrate; (3) an extremely low-cost method was first introduced to fabricate the surface microstructures in flexible triboelectric nanogenerator though sandpapers; and (4) the as-fabricated PACF composite film can directly harvest energy though squeezing, warping and folding. Experimental results demonstrate that the ST-TENG can generate an average maximum output voltage of 46.52 V and a high-power density of 613 mW m−2 at the external resistance of 20 MΩ. Additionally, the ST-TENG can also be utilized to detect the variation of contact area, frequency and force.

The conventional UV/Vis spectroscopy methods recommended by the European Pharmacopoeia (EP) for determining hexosamine, hexonic acid and methylpentose in pneumococcal polysaccharide vaccine (PPSV) hydrolates are time-consuming due to derivatization process (typically, an analysis cycle is more than 4 h) and improvements of selectivity and precision of the methods are in demand. In this study, a new approach based on hydrophilic interaction liquid chromatography and triple quadrupole mass spectrometry (HILIC-MS/MS) was optimized to overcome the drawbacks of the EP methods for simultaneous determination of methylpentose, hexose, hexosamine and hexonic acid in PPSV hydrolysates. The chromatographic, MS and sample hydrolysis conditions were systematically investigated. A zwitterionic column, Click Cys, using a gradient elution with a mobile phase of 10 mM ammonium formate (pH 4.3) in acetonitrile from 72% to 21% in 6 min was applied for separating the targets, which exhibited low column bleeding, easy equilibration and long-term stability. The HILIC-MS/MS method showed a high sensitivity (LOD = 0.98 μg L−1 for hexonic acid), a good repeatability (RSD of peak area less than 1.669%), accuracy (92.9%–104.2%), recovery (97.6%–99.3%) and a wide linear range. The RSD of retention time obtained from more than 3000 injections in three months was less than 1.64%. The new method was compared with the EP method for determining hexosamine in 23 serotypes of PPSV hydrolysates. The results indicated that the new HILIC-MS/MS method was highly selective, accurate, stable and extremely fast due to without need of derivatization, as compared to the conventional EP methods.

How to design energy-efficient building materials, theoretically requiring a balance of mechanical properties and thermal conductivity , remains a crucial challenge in construction & building fields. Recently there is an increased interest in using 3D concrete printing technology to automatically manufacture complicated and customized constructions. Nevertheless, majority of printed constructions are still solid and have a low quality in the interface performance. Inspired by the lightweight lattice architecture, 3D core-framework lattice cementitious composites (CS-LCCs) is proposed in this work, which consists of printed polymeric framework and cement mortar . Results show that although the average compressive strength of CS-LCCs is lower than that of the cubic sample fabricated using the cement mortar (40 × 40 × 40 mm 3 ), the specific strength of CS-LCCs approaches that of cubic one. The ductility of CS-LCCs is obviously improved due to the effect of polymeric framework. According to the test and finite element analysis , a hinging and stretching couple deformation mechanism is used to elaborate the deformation mechanism of CS-LCCs. Additionally, the CS-LCCs also exhibit low thermal conductivities at various temperatures owing to the ordered porous characteristic of lattice.

This study deals with the mechanical behavior of a shear thickening fluid–sliding friction (STF–SF) isolator, and investigates the feasibility of its application in anti-seismic engineering from a theoretical perspective. The STF–SF isolator is composed of a conventional sliding friction (SF) material and a smart shear thickening fluid (STF) material. When the excitation energy is small, the SF material keeps the structure static or only has a small vibration. However, when the excitation energy is large, the STF material results a huge damping force and dissipation of the external energy, eventually reducing the relative motion between the base and the upper structure. To better understand this phenomenon, a mechanistic study of the STF–SF isolator is proceeded by an analytical model which is derived from flow momentum equations. After that, the seismic protective effect of the STF–SF isolator is evaluated at harmonic excitation with different accelerations through a single degree of freedom (SDOF) structure. Furthermore, the effects of layer gap, layer number and friction coefficient of the STF–SF isolator on the seismic protective effect are investigated. The results show that the STF–SF isolator can significantly decrease both the displacement response and the acceleration response of the SDOF structure. This theoretical study indicates the STF–SF isolator can be used in anti-seismic engineering.

Wind characteristics (e.g., mean wind speed, gust factor, turbulence intensity and integral scale, etc.) are quite scattered in different measurement conditions, especially during typhoon and/or hurricane processes, which results in the structural engineer ambiguously determining the wind parameters in wind-resistant design of buildings and structures in cyclone-prone regions. In tropical cyclones (including typhoons and hurricanes), the inconsistent wind characteristics may be in part ascribed to the complex flow structure with the coexistence of both mechanical and convective turbulence in the boundary layer of tropical cyclones. Another significant contribution to the scattered wind characteristics is due to various measurement conditions (e.g., terrain exposure and height) and data processing schemes (e.g., averaging time). The removal of the inconsistency in the field-measurement system may offer a more rational comparison of measured wind data from various observation platforms, and hence facilitates a better identification scheme of the wind characteristics to guide the urban planning design and wind-resistant design of buildings and structures. In this study, an analytical framework was firstly proposed to eliminate the potential observation-related effects in wind characteristics and then the wind characteristics of seven field measured tropical cyclones (four typhoons and three hurricanes) were comparatively investigated. Specifically, field measurements of wind characteristics were converted to a standard reference station with a roughness length of 0.03 m, observation duration of 10 min for mean wind and averaging time of 3 s for gusty wind at a 10 m height. The differences of the measured wind characteristics between the typhoons and hurricanes were highlighted. The standardized turbulent wind characteristics under the analytical framework for typhoons and hurricanes were compared with the corresponding recommendations in standard of American Society of Civil Engineers (ASCE 7-10) and Architectural Institute of Japan Recommendations for Loads on Buildings (AIJ-RLB-2004).

Lightweight and thermal insulative cementitious materials with large porous structures for improving energy efficiency have rapid development currently. However, the design of cementitious materials for energy-efficient building system in terms of low thermal conductivity, excellent mechanical properties and lightweight remains a crucial challenge in construction & building fields. Recently, the polymer-based lattice-inspired structures fabricated by 3D printing technology (3DPT) show a rapid development that achieves a balance of thermal and mechanical properties due to their ordered and large-scale cellular architecture. In this work, a novel category of lattice-inspired cementitious lattice materials was first proposed for applying in the energy-efficient building systems by integrating the 3DPT and traditional casting technology. Taking face-centered cubic (FCC) lattice as an example, the advantages of the proposed fabrication technology and FCLMs are follows: (i) ultralight weight; (ii) enhanced ductility of brittle cementitious materials; (iii) low thermal conductivity. Through the structural and material design, the proposed fabrication technology could effectively overcome the current issues of 3DPT, such as the weakness of interlayer performance and low accuracy (Extrusion-based 3DPT) as well as limited feasible materials (Powder-bed-based 3DPT), in the civil engineering. Statement of Significance How to design cementitious materials for energy-efficient building system in terms of thermal conductivity, mechanical properties and lightweight requirement remains a crucial challenge in construction & building fields. Inspired by the low thermal conductivity and lightweight structure of metamaterials in the previous researches (Song et al., Materials & Design, 2019. 173: 107773-86; Nicholas et al. Nano letter, 2018. 18: 4755-61), here a novel category of lattice-inspired cementitious materials with ordered porous structures has been proposed for energy-efficient building materials with lightweight, low thermal conductivity and good mechanical properties characteristics. Additionally, recently there is increased interest to use 3D concrete printing technology (3DCPT) to automatically manufacture complicated and customized structure. However, currently, 3DCPT encounters many sticky issues, involving that (i) weak interlayer performance induced by cold joints between layers; (ii) deformation under self-weight due to the low yield stress of fresh mix; (iii) probable shrinkage under the low water/cement ratios typically used in printed mortars; (iv) geometrical instability owing to creating suspended structures. It is not a trivial to directly print cementitious porous materials, and therefore this work also achieved a breakthrough in developing cementitious porous materials combining advanced SLA 3D printing and traditional casting technology for the first time. It is worth mention that compared to Extrusion-based 3DCPT and Powder-bed-based 3DCPT, the advantages of the manufacture technology include that (i) automatically printing 3D complex structure; (ii) Optional cementitious materials; (iii) Good interlayer performances of prepared materials. We expect that the proposed design idea and novel manufacture strategy could serve as the guideline to develop material-structural-functional integrated energy-efficient building materials combining 3D printing technology, advanced structure design and high-performance cementitious materials.

Due to the complexity of crosswind vibrations of rectangular cylinders, current research on crosswind vibrations of rectangular cylinders mainly relies on expensive wind tunnel tests and time-consuming numerical simulation techniques. In this study, in order to evaluate crosswind vibrations of rectangular cylinders, machine learning method was used to build an efficient and effective prediction model for supplementing the above two research tools. 5 machine learning models based on decision tree regression, k-nearest neighbor regression, random forest, gradient boosting regression tree (GBRT) and histogram gradient boosting regression tree algorithms were trained based on the existing high-quality and reliable wind tunnel test datasets of crosswind responses of rectangular cylinders. The hyper-parameters were optimized by using particle swarm optimization method. 4 types of crosswind vibration phenomena, including over-coupled, coupled, semi-coupled and decoupled, were predicted. It was found that the GBRT model is capable of predicting crosswind responses of rectangular cylinders at side ratios from 0.75 to 3 and Scruton numbers from 0 to 150 under wind flow with turbulence intensities from 0 to 16%. Evidently, GBRT model can be an effective and economical method to study crosswind vibrations of rectangular cylinders and hence supplement traditional wind tunnel tests and numerical simulation techniques.

Inflow conditions play a key role in the Computational Fluid Dynamics (CFD) simulation of wind environment. Taking the micro wind climate of Hong Kong Kowloon Bay costal town as a research object, two kinds of widely used inflow condition determination methods are adopted to test their performances. One is to fit the velocity profile into the empirical (logarithmic/exponential) law, hereafter referred to as the Fitted Empirical Profile (FEP) method. The other is to interpolate the outflow velocities and turbulence properties from a pre-simulation of the upstream region, hereafter referred to as the Interpolated Multiscale Profile (IMP) method. The GIS data of this mountainous/ urban area are digitalized and simplified into the CFD geometry model. Computational treatments for numerical algorithms, domain size, grid systems and boundary conditions are carefully configured according to the published CFD Best Practice Guidelines (BPGs). By validating with one year of real scale wind measurement data from two meteorological stations, it is found that these two inflow conditions lead to considerably different results. Having less consideration for the blockage effects of terrain/buildings, the FEP method tends to predict higher wind speed. As more thermal effects are removed by increasing wind speed thresholds, the results of IMP method demonstrate an incremental agreement with the measurement data. Finally, the validated simulation results are applied to the spatial representativeness assessment of two meteorological stations. Both the point-to-surface consistency indicator and point-centered semivariance are employed. The results show that the meteorological stations show a good representation within a range of 400 m.

After 30 years of development, 3D printing technology (3DPT) is becoming increasingly popular in civil engineering field. However, weak interlayer performance and lack of reinforcement significantly limit its application. Nowadays, structural-functional integrated energy-efficient building materials, theoretically requiring a balance of mechanical properties and thermal resistance, are an emerging interdisciplinary research area in civil engineering field. This work proposed a novel digital cement-based manufacture technology by integrating 3D printing technology with casting technology. By incorporating tension-resistant polymeric truss network (PTN), a category of 3D face-centered cubic-inspired cement-based hybrid composites (FCHCs) is proposed. Results show the printed PTN can effectively improve the tension-resistant capacity of cement mortar. The FCHCs not only exhibit a multiple cracking damage characteristic but also a low thermal conductivity compared to traditional cement-based materials. A building energy simulation program was performed to evaluate the effectiveness of FCHCs on the energy savings. It is found that 34% heating energy could be saved for FCHCs building.

Atmospheric boundary layer (ABL) is generated due to frictions induced by obstacles on the Earth’s surface, such as terrains, vegetation, buildings, etc … Inspired by this physical mechanism, horizontally homogeneous ABL flow in computational fluid dynamics is achieved by proposing an enriched canopy drag (ECD) model, which is more flexible in reproducing the effects of various physical roughness ground, not limited to vegetation types. The multi-objective evolutionary algorithm is employed to determine the appropriate near-ground drag and the acting height of the proposed ECD model. Furthermore, the evolutionary algorithm is adopted to minimize the discrepancies of mean wind velocity and turbulence kinetic energy (TKE) between the inflow condition and the flow at a target downstream location. A set of simulations using logarithmic- and power-law inlet flows over rural, suburban, and urban terrains based on the shear-stress transport k-ω turbulence model are conducted to demonstrate the effectiveness of the ECD model. The results show that the proposed ECD model is capable of reproducing the Earth’s roughness numerically and improving the homogeneities of mean velocity and TKE in streamwise direction and applicable to different mesh resolutions, near-wall treatment methods, standard k-e turbulence model and simulation dimension.

Elevated fatigue behaviors of resin matrix composites are considerable key to the application of aeroengine that requires fatigue resistance at elevated temperature. However, undeniably, very few studies are focused on this issue, thereby resulting in limitation applications of resin matrix composites in aeroengine components, i.e. blades and case. In this work, the fatigue responses of layer-to-layer 3D angle-interlock woven composites (2.5DWC) were experimentally and numerically studied at room and elevated temperatures. Experimental results show that the weft direction fatigue lives at 20 °C and 180 °C experienced a relatively short cycle (less than 104 cycles) prior to the failure. But, once the stress level declined to a threshold value (dropped by 1–2%), the fatigue limitation would be activated, regardless of temperature. Moreover, the residual strength at 20 °C or 180 °C was reinforced compared to the static strength. Considering the fatigue data and fracture morphology, probable damage mechanisms corresponding to temperature-dependent weft direction fatigue behaviors of 2.5DWC were proposed. A temperature-dependent fatigue life prediction model of 2.5DWC was proposed, based on which the weft direction fatigue lives, damage propagation processes and residual stiffnesses of 2.5DWC at 20 °C and 180 °C were predicted.

Calcium leaching is a degradation progress inside hardened cement composites, where Ca2+ ions in cement pore solution can migrate into the aggressive solution. In this work, calcium leaching of graphene oxide (GO) reinforced cement composites was effectively characterized by combined techniques of electrochemical impedance spectroscopy (EIS) and scanning electron microscope (SEM). Inhibiting mechanism of GO on calcium leaching of the composites was also examined. The obtained results show that the diameter of the semi-circle of the Nyquist curves of leached samples with GO addition decreased less than that of controlled samples. After leaching for 35 days, loss rate of model impedance RCCP of leached samples with 0, 0.05, 0.1, 0.15, and 0.2 wt.% GO addition was 94.85%, 84.07%, 79.66%, 75.34%, and 68.75%, respectively. Therefore, GO addition can significantly mitigate calcium leaching of cement composites, since it can absorb Ca2+ ions in cement pore solution, as well as improve the microstructure of the composites. In addition, coupling leaching depth and compressive strength loss were accurately predicted by using the impedance RCCP.

Partial degradation products (PDPs) of herbal medicine (HM) polysaccharides with precolumn derivatization using 1-phenyl-3-methy-5-pyrazolone (PMP) were mapped by high performance liquid chromatography (HPLC), and three groups of confusable HMs were differentiated using the PDP fingerprints assisted with cluster analysis (CA). Three variables of HPLC mobile phase, i.e. acetonitrile proportion, buffer concentration and pH value were optimized with PDP of β-cyclodextrin. Radix Glehniae and Radix Adenophorae; Radix Sophorae Tokinensis and Rhizoma Menispermi; Radix Achyranthis Bidentatae and Radix Cyathulae were successfully distinguished by the method, respectively. The results involving mass spectrometry analysis showed that these PDPs primarily included oligosaccharides and a few monosaccharides. The method can be used as an effective approach for the identification and quality control of HMs, and can also facilitate the in-depth study of biological activity and further development of HM polysaccharides to some extent.

Tropical cyclones are referred to as typhoons and hurricanes in the South China Sea/North Pacific and the Atlantic Ocean, respectively. As the genesis of these storms results from different basins and latitudes, the wind field characteristics may differ in these storms and differ with the recommendations in current wind codes, which are mainly based on extratropical winds. In order to delineate any differences, based on wind data measured at fixed/deployable towers in four typhoons and three hurricanes, turbulent wind characteristics, e.g., turbulence ratio and intensity, integral scale, gust factor, peak factor, skewness and kurtosis, were comparatively investigated and compared with the recommendations in ASCE7-10. In this comparison, the influences of roughness length and mean wind speed on the turbulent wind characteristics were also examined.

In this paper, an Ytterbium-doped V-shape photonic crystal fiber (Yb-VPCF) with low dispersion and high nonlinearity is designed and fabricated in our laboratory. Through coupling femtosecond pulses into the fundamental mode of Yb-VPCF, the tunable anti-Stokes signals at the visible wavelength are efficiently generated based on the phase-matching four-wave mixing. When the pump wavelength is changed from 810, to 820, and to 830 nm and the input average power is increased from 0.4, to 0.5, and to 0.6 W, respectively, the anti-Stokes signals are generated within the wavelength range of 562–477 nm. The wavelength-tunable range is over 100 nm, and the maximum power ratio of anti-Stokes signal at 477 nm and the residual pump at 830 nm can be up to 23.9:1. The anti-Stokes signals generated can be used as the ultrashort pulse sources for ultrafast optoelectronics and spectroscopy.

Reinforcement corrosion is a major cause of degradation in reinforced concrete structures. The fragile rust layer and cracking and spalling of the cover caused by splitting stress due to rust expansion can alter bond behaviors significantly. Despite extensive experimental tests, no stochastic model has yet incorporated randomness into the bond parameters model. This paper gathered published experimental data on the bond-slip parameters of pull-out specimens and beam-end specimens. Regression analysis was carried out to identify the best fit of bond strength and the corresponding slip value in the context of different corrosion levels from the recollected test results. An F-test confirmed the regression effect to be significant. Residual data were also analyzed and found to be well described by a normal distribution. Crack width data of the tested specimens were also collected. A regression analysis of the bond strength and maximum crack width was carried out given the comparative simplicity of measuring crack width versus rebar area loss. Results indicate that maximum crack width can also be used to predict bond strength degradation with similar variation magnitude.

A conceptual model is proposed for the characteristic sub-ranges in the velocity and temperature spectra in the boundary layer of tropical cyclones (hurricanes or typhoons). The model is based on observations and computation of radial and vertical profiles of the mean flow and turbulence, and on the interpretation of eddy mechanisms determined by shear (namely roll and streak structures near the surface), convection, rotation, blocking and sheltering effects at the ground/sea surface and in internal shear layers. The significant sub-ranges, as the frequency increases, are associated with larger energy containing eddies, shear and blocking, inertial transfer between large and small scales, and intense small-scale eddies generated near the surface caused by waves, coastal roughness change, and the buoyancy force associated with the evaporation of spray droplets. These sub-ranges vary with the locations at which the spectra are measured, i.e. the level \(z\) in relation to the height \(z_{max}\) of the peak mean velocity and the depth \(h\) of the boundary layer, and the radius \(r\) in relation to the eyewall radius \(R_{ew}\) and the outer-vortex radius \(R_{ov}\). For two tropical cyclones (Nuri and Hagupit), experimental data were analyzed. Spectra were measured where \(r\) is near to \(R_{ew}\) and \(R_{ov}\) using four 1-h long datasets at coastal towers, at 10- and 60-m heights for tropical cyclone Nuri, and at 60-m height for tropical cyclone Hagupit at the south China coast. The field measurements of spectra within the boundary layer show significant sub-ranges of self-similar energy spectra (lying between the length scale 1,000 m and the smallest scales less than 40 m) that are consistent with the above conceptual model of the surface layer. However, with very high wind speeds near the eyewall, the energy of the independently generated intense surface eddy motions, associated with surface waves and water droplets in the airflow, greatly exceeds the energies of the small scales in the inertial sub-range of the boundary layer, over scales less than about 3–40 m depending on the height \(z\) and the radius \(r\). This rise in the small-scale frequency weighted spectra (\(nS_u (n)\), where \(n\) is natural frequency, and \(S_u (n)\) is the energy spectrum of the longitudinal wind component) is consistent with the hypothesis that these processes are only weakly correlated with the main boundary-layer turbulence.

3D woven composite structures are increasingly replacing metal structures in astronautics and aeronautics areas, due to their excellent mechanical properties and structure integrity. Limitedly, the comprehensive influences of notch and temperature on the mechanical behavior of 3D woven composites have not been completely understood, especially those at elevated temperatures. In this work, the thermo-mechanical behavior and failure mechanisms of centrally notched layer-to-layer 3D angle-interlock woven composites (commonly called notched 2.5DWC, N-2.5DWC) were elaborated by experiment and simulation. Experimental results revealed the elevated temperature strength of N-2.5DWC approximately dropped by 26% compared to the room temperature one. The drop extension of strength was more severe than un-notched 2.5DWC at the same temperature, indicating that the mechanical properties of N-2.5DWC are significantly affected by notch and temperature. A brittle fracture mode without no necking phenomenon was noted, regardless of temperature. However, there was an obvious pull-out damage of yarn near the notch edge, attributed to the comprehensive effect of notch-edge stress concentration and load-bearing warp yarns. Furthermore, a thermo-mechanical predication model for N-2.5DWC was proposed. The mechanical properties at 20 °C and 180 °C were predicted and the damage propagation characteristics were identified, which clearly revealed the damage mechanisms of N-2.5DWC at different temperatures.

This study evaluated the performance of wind energy harvesters with multiple shape-optimized circular cylinders in tandem via computational fluid dynamics simulations. The circular cylinders were optimized by attaching triangular protrusions on their surface. The circumferential location of the protrusion plays a crucial role in the efficiency of this kind of wind energy harvester. The protrusions at the circumferential angles of α = 60°and 90°significantly extend the wind velocity range with remarkable energy generation. When the reduced wind velocity is lower than 10, the harvester with three plain cylinders in tandem generates the most power. However, when the speed is higher than 10, the most power is generated by the harvester having three cylinders in tandem with protrusions at α = 60°. Therefore, in a low wind velocity environment, the harvester with three plain circular cylinders in tandem is superior to other tested configurations, whereas in a high wind velocity environment, the harvester with three circular cylinders with protrusions at α = 60°in tandem outstands from other tested configurations. The associated flow mechanisms are detailed as well.

Fatigue behavior, notch sensitivity and environmental effect are three of the principal concerns in composite applications, especially those for aeroengines that require mechanical fastening and fatigue resistance at elevated temperatures. As a new generation of woven composites, 2.5D woven composites (2.5DWC), have drawn increasing amounts of interest due to the excellent fatigue resistance of these materials. However, the lack of temperature-dependent fatigue explorations into centrally notched 2.5DWC (N-2.5DWC) significantly limits the engineering applications of these materials. Therefore, the objective of this paper is to investigate the temperature-dependent fatigue behavior of N-2.5DWC. Warp direction tension-tension fatigue tests of N-2.5DWC were performed at 20 °C and 180 °C for the first time. The fatigue lives and the related failure mechanisms were obtained experimentally. Interestingly, the fatigue life at the same temperature exhibited a sudden increase with a decreasing stress level. A temperature-dependent fatigue life prediction model was established, and the fatigue lives and damage propagation processes at various temperatures and stress levels were predicted. The predicted damage propagation process was a “L” shaped, which was consistent with the corresponding experimental fracture morphologies. Finally, the effects of temperature and warp arranged density on the warp direction fatigue life were discussed.

Understanding fluid and interfacial properties in extended nanospace (10-1000 nm) is important for recent advances of nanofluidics. We studied properties of water confined in fused-silica nanochannels of 50-1500 nm sizes with two types of cross-section: (1) square channel of nanoscale width and depth, and (2) plate channel of microscale width and nanoscale depth. Viscosity and wetting property were simultaneously measured from capillary filling controlled by megapascal external pressure. The viscosity increased in extended nanospace, while the wetting property was almost constant. Especially, water in the square nanochannels had much higher viscosity than the plate channel, which can be explained considering loosely coupled water molecules by hydrogen bond on the surface within 24 nm. This study suggests specificity of fluids two-dimensionally confined in extended nanoscale, in which the liquid is highly viscous by the specific water phase, while the wetting dynamics is governed by the well-known adsorbed water layer of several-molecules thickness.

This study focuses on enhancing our understanding of the spectral features of typhoon winds with critical implications on the mitigation of disproportionate damage experienced in typhoons-prone coastal regions. Examination of data suggests that generally used empirical models of wind power spectrum for extratropical storms may not adequately represent the tropical cyclone winds. In this paper, a data-driven model is proposed for wind power spectrum in tropical cyclone winds over the sea surface. Rather than fitting data to a universal spectral description, first the physical meaning of parameters in such a model is carefully examined and the contribution of each parameter is delineated. With these backgrounds, field measurements in typhoon Hagupit are used to model these spectral parameters in terms of the Monin–Obukhov length, mean wind speed and roughness length. Finally, the proposed spectral model is validated using arbitrarily selected four hours of data in different sectors of typhoon Hagupit wind field. The model shows a good agreement with the measurements.

The recent development of Doppler radar sensor has allowed to study the typhoon wind structure more accuracy and systematic. In order to obtain more wind data near typhoon eye-wall, vehicular Doppler radar emerge as the times require. Based on two typhoon observed results carried out by vehicular Doppler radar in category A terrain, firstly the 10min mean wind profiles under 1000m height in different regions of typhoon were analyzed. The typhoon mean wind speeds increase a logarithmic law with height at nearly lower two hundred meters in all regions of typhoons. Using the power law to fit wind profiles, the exponential index α in pre-eye-wall region is greater than it in post-eye-wall region, and it decreases with increasing the mean wind speed. Secondly, based on analyzing the relationship between mean wind speed and wind ratio, the calculation formula for nominal gradient height were established in category A terrain. Finally introducing the probability method to study the mean wind profile, the exponential index α was established in category A terrain.

Wearable triboelectric nanogenerators (TENGs) have attracted interest in recent years, which demand highly flexible, scalable, and low-cost features. Here, we report an ultra-flexible, large-scale and textile-based TENG (T-TENG) for scavenging human motion energy. The triboelectric layer was derived from the polydimethylsiloxane (PDMS) film with a cost-effective paper-induced rough surface via a facile doctor-blending technology. Ag-coated chinlon fabric (ACF) with ultra-flexible, large-scale and conductive characteristics was used as the electrode. The as-fabricated PDMS-based ACF (PACF) composites possess a 240 &times, 300 mm2 superficial area and remain highly flexible under mechanical squeezing, folding and even tearing deformation. The maximum output charge of ~21 &mu, C and voltage of 80.40 V were therefore achieved to directly power 100 LEDs based on the high surface area of 762.73 mm2 which was rationally replicated from the sandpaper of the T-TENG. Moreover, the output voltage signal can be also used as a trigger signal of a movement sensor. Importantly, the explicit theoretical model corresponding to T-TENG was quantitatively investigated under different applied force, frequency and effective surface factor.

The ultraviolet to visible continuum generations are experimentally demonstrated by coupling femtosecond pump pulses around 800 nm into the normal dispersion region close to the zero-dispersion wavelength in the fundamental mode of a silica photonic crystal fiber (PCF). The ultraviolet to visible continuum is generated through a combination of nonlinear effects including degenerate four-wave mixing, cross-phase modulation, and stimulated Raman scattering. When pump pulses with the wavelength of 800 nm and the input average power of 500 mW are used, more than 40% of the incident pump power is converted to the ultraviolet to visible spectral region. The evolution of the output spectra for different PCF lengths is studied to understand the nonlinear propagation dynamics during the process of the continuum generation. The ultraviolet to visible continuum generation will find important applications in the ultraviolet and visible-based biophotonics and spectroscopy.

In this paper, a dual-core polymer-filled photonic crystal fiber (PCF) is designed for broadband dispersion compensation. Large negative dispersion value from −255 to −823 ps/(nm•km) over the entire C band is achieved. Furthermore, the effective refractive index of the polymer-filled outer core can be well tuned by changing the temperature. This PCF can be used for the dynamical dispersion compensation in wavelength-division-multiplexing (WDM) systems.