Flexible Barrier Research Articles

Effects of flow-bed interactions on barrier impact

Debris flow mobility is governed by complex interactions at the flow-bed interface. These interactions may cause flow bulking and increase in momentum. Both factors need to be considered for the design of barriers installed along the flow path. In this study, channelized debris flow over a wet erodible bed impacting a terminal flexible barrier is modelled in a 28-m-long and 2-m-wide flume facility with 20o slope inclination in Hong Kong. Tests with flow volumes of 6 m3 and 9 m3 overriding both erodible and non-erodible beds are conducted. The change in normalised flow energy over the erodible bed section, the change in flow momentum and the impact dynamics on the terminal barrier is assessed.

Flexible Organic Light-Emitting Diodes: Structure and Fabrication

Flexible organic light-emitting diodes (OLED) technology with thin, light in weight, and free in design have been developed and perfected rapidly. The versatility of flexible OLED technology has been effectively proved in the sectors of displays, lighting, and medicine. In this article, the structure and fabrication of flexible OLED were introduced. Normal flexible OLED device construction includes flexible OLED substrate, barrier layers, electrode and organic layer. The flexible OLED is made on the substrate. The barrier layer is used to shield the OLED material from airborne oxygen and humidity. The electrodes are used for electricity, and the organic layer is used for light. The production processes of flexible OLED include coat-debond with advantages such as good stability and thermal conductivity, bond-debond with the advantage of simple and convenient and roll-to-roll [R2R] method with advantages of low cost, and mass production. Additionally, the application fields of these methods have been highlighted.

Analysis of Fire Development in a Road Tunnel Equipped with Transformable Elements by Using Numerical Modeling Method

As it is known, in case of strong fires initiated and developed in road tunnels with properly functioning longitudinal ventilation systems, at some moment, the air flows induced by mechanical ventilation can no longer affect the traction forces and flows formed as a result of combustion. Consequently, the smoke formation in the air on both sides of the tunnel is so intense that the environment becomes practically unsuitable for human life. In case of such a fire scenario, the only way to save people from the emergency is well-organized and timely self-evacuation from the dangerous environment [1]. The success depends on the duration of self-evacuation. Naturally, the longer the evacuation time is, the more the chances of saving the people are. In this case, the efficient use of flexible elements of transformable systems (flexible ventilation fire-proof barriers) allows significantly prolonging the evacuation time.

Rockfall trajectory reconstruction: a flexible method utilizing video footage and high-resolution terrain models

Abstract. Many examples of rockfall simulation software provide great flexibility to the user at the expense of a hardly achievable parameter unification. With sensitive site-dependent parameters that are hardly generalizable from the literature and case studies, the user must properly calibrate simulations for the desired site by performing back-calculation analyses. Thus, rockfall trajectory reconstruction methods are needed. For that purpose, a computer-assisted videogrammetric 3D trajectory reconstruction method (CAVR) built on earlier approaches is proposed. Rockfall impacts are visually identified and timed from video footage and are manually transposed on detailed high-resolution 3D terrain models that act as the spatial reference. This shift in reference removes the dependency on steady and precisely positioned cameras, ensuring that the CAVR method can be used for reconstructing trajectories from witnessed previous records with nonoptimal video footage. For validation, the method is applied to reconstruct some trajectories from a rockfall experiment performed by the WSL Institute for Snow and Avalanche Research SLF. The results are compared to previous ones from the SLF and share many similarities. Indeed, the translational energies, bounce heights, rotational energies, and impact positions against a flexible barrier compare well with those from the SLF. The comparison shows that the presented cost-effective and flexible CAVR method can reproduce proper 3D rockfall trajectories from experiments or real rockfall events.

Bi‐Linear Laws Govern the Impacts of Debris Flows, Debris Avalanches, and Rock Avalanches on Flexible Barrier

AbstractGeophysical mass flows impacting flexible barriers can create complex flow patterns and multiway solid‐fluid‐structure interactions, wherein estimates of impact loads rely predominantly on analytical or simplified solutions. However, an examination of the fundamental relations, applicability, and underlying mechanisms of these solutions has been so far elusive. Here, using a coupled continuum‐discrete method, we systematically examine the physical laws of multiphase, multiway interactions between geophysical flows of variable natures, and a permeable flexible ring net barrier system. This model well captures the essential physics observed in experiments and field investigations. Our results reveal for the first time that unified bi‐linear laws underpin widely used analytical and simplified solutions, with inflection points caused by the transitions from trapezoid‐shaped to triangle‐shaped dead zones. Specifically, the peak impact load increases bi‐linearly with increasing Froude number, peak cable force, or maximum barrier deformation. Flow materials (wet vs. dry) and impact dynamics (slow vs. fast) jointly drive the patterns of identified bi‐linear correlations. These findings offer a physics‐based, significant improvement over existing solutions to impact problems for geophysical flows.

Noncontact vision-based impact force reconstruction and spatial-temporal deflection tracking of a flexible barrier system under rockfall impact

Flexible barrier systems are significant for natural disasters (e.g., rockfalls, mudslides) prevention in mountainous areas. However, monitoring the dynamic behavior of flexible barrier systems subjected to rockfall impact is difficult in practice due to the unpredictability of disasters and the problem of easily broken contact-type sensors. Therefore, this paper proposed a noncontact vision-based methodology, in which deep learning and computer vision techniques are developed to reconstruct impact forces induced by falling rocks and to identify the spatial–temporal deflection of a flexible barrier system from remotely captured image sequences by a high-speed camera. The contribution of this paper lies in two aspects: (1) a lightweight neural network is trained to detect falling rocks from captured images for motion information extraction and impact force reconstruction; (2) a two-dimensional distribution map of velocity amplitude is constructed for tracking the full-field spatial deflection pattern of the flexible barrier system under rockfall impact, and multipoint temporal deflection curves of the studied system are also extracted for maximum elongation calculation. The effectiveness of the proposed method is validated by full-scale experiments of a three-span flexible barrier system under rockfall impact with energies of 250 kJ and 750 kJ. The results show that the reconstructed impact forces, tracked full-field spatial deflection pattern, and extracted multipoint temporal deflection curve by the proposed method agree well with reference values, verifying the correctness and robustness of the proposed method. The obtained results can be directly used for the reliable design and condition assessment of flexible barrier systems under rockfall disasters.

Investigations of Thermal, Mechanical, and Gas Barrier Properties of PA11-SiO2 Nanocomposites for Flexible Riser Application.

Acidic gas penetration through the internal pressure sheath of a flexible riser tends to cause a corrosive environment in the annulus, reducing the service life of the flexible riser. Nanoparticles can act as gas barriers in the polymer matrix to slow down the gas permeation. Herein, we prepared PA11/SiO2 composites by the melt blending method. The effect of adding different amounts of SiO2 to PA11 on its gas barrier properties was investigated by conducting CO2 permeation tests between 20 °C and 90 °C. As the temperature increased, the lowest value of the permeability coefficient that could be achieved for the PA11 with different contents of SiO2 increased. The composites PA/0.5% SiO2 and PA/1.5% SiO2 had the lowest permeation coefficients in the glassy state (20 °C) and rubbery state (≥50 °C). We believe that this easy-to-produce industrial PA/SiO2 composite can be used to develop high-performance flexible riser barrier layers. It is crucial for understanding riser permeation behavior and enhancing barrier qualities.

Nacre-inspired biodegradable nanocellulose/MXene/AgNPs films with high strength and superior gas barrier properties

Super strength and high barrier properties are the bottleneck of the application of cellulose film materials. Herein, it is reported a flexible gas barrier film with nacre-like layered structure, in which 1D TEMPO-oxidized nanocellulose (TNF) and 2D MXene self-assembled to form an interwoven stack structure with 0D AgNPs filling the void space. The strong interaction and dense structure endowed TNF/MX/AgNPs film with mechanical properties far superior to PE films and acid-base stability. Importantly, the film presented ultra-low oxygen permeability confirmed by molecular dynamics simulations and better barrier properties to volatile organic gases than PE films. It is here considered the tortuous path diffusion mechanism of the composite film responsible for the enhanced gas barrier performance. The TNF/MX/AgNPs film also possessed antibacterial properties, biocompatibility and degradability (completely degraded after 150 days in soil). Collectively, the TNF/MX/AgNPs film brings innovative insights into the design and fabrication of high-performance materials.

Water wave interaction with dual unequal horizontal flexible porous barriers using integral equations

ABSTRACT Under the assumption of linear wave theory, this work investigates the interaction of surface gravity waves with two asymmetric horizontal flexible porous barriers. Three types of barriers are considered, namely, (i) step barriers, (ii) partially overlapped barriers and (iii) fully overlapped barriers. Green's integral theorem and the boundary condition on the barriers are utilised to produce four integral equations for functions related to potential difference and normal velocity of fluid across the barriers which are solved numerically by an expansion-collocation method. As a result, the role of asymmetric flexible porous barriers with an additional comparison between dual and single horizontal flexible porous barriers is studied by analysing numerical solutions of different hydrodynamic quantities. This study shows that the upper barrier plays a major role compared to the lower one in the propagation of surface waves. The current analysis is validated by reviving previous results and utilising energy balance relationship.

Numerical investigation on the dynamic response of rockfall impacts on flexible barrier under seismic loading

Numerical investigation on the dynamic response of rockfall impacts on flexible barrier under seismic loading

A Case Study on the Energy Capacity of a Flexible Rockfall Barrier in Resisting Landslide Debris

Landslides frequently occur in forest areas with a steep hillside, especially when severely disturbed by human activities. After sustained heavy rainfall, a landslide occurred near the Tianwan tunnel entrance of the Chongqing-Huaihua railway in China. Fortunately, the landslide debris was successfully intercepted by a flexible barrier originally installed to stop rockfalls, which is, to date, the first publicly reported case of landslide debris having been successfully intercepted by a flexible barrier without any damage, in mainland of China. A field investigation was first conducted, and then a back analysis of the landslide mobility and the interaction between the landslide and the flexible barrier was carried out. The back analysis showed that the impact energy was three-times larger than the rated energy capacity of the flexible barrier. It also showed that the elongation of the brake rings and the deflection of the flexible barrier from the numerical simulation was comparable to that from the field measurements. The fact that these brake rings were not elongated to their limit indicated that the capacity of the flexible barrier still had a surplus. Finally, to investigate the maximum energy capacity of a flexible rockfall barrier in resisting landslide debris, parametric analyses of a flexible barrier impacted by landslide debris with different impact energies and velocities were carried out using a coupled ALE-FEM modeling technique. The results showed that the flexible barrier dissipated less than 40% of the total energy of the landslide debris. With an increase of impact energy, the energy dissipation ratio of the flexible barrier decreased linearly. The maximum energy capacity of a flexible rockfall barrier in resisting landslide debris is four-times that of resisting a rockfall.

A computational study of electrical contacts to all-inorganic perovskite CsPbBr3

All-inorganic halide perovskites are promising candidates for optoelectronic devices due to their excellent physicochemical properties and better thermal stability than their hybrid counterparts. The electrical contact to perovskite plays a crucial role in determining the device’s performance. This paper investigated the contacts of two types of CsPbBr3 surface to a series of metals (Pd, In, Pb, Zr, Ti, Zn, graphene, and Ti3C2) through first-principles calculations. On the PbBr2-terminated surface, all the studied metals form Schottky contacts with minimum barriers ranging from 0.63 to 0.97 eV. On the CsBr-terminated surface, Ti and Ti3C2 forms n-type Ohmic contacts while others form Schottky contacts with minimum barriers ranging from 0.25 to 0.97 eV. Ti3C2, considering the small Schottky barrier, large tunneling barrier, and high electronic localization function, is found to be proper ohmic metal contacts with the CsBr-terminated surface. In addition, a −16.4% to 15.1% change in the size of the CsPbBr3 band gap is found because of the interfacial interaction. The Fermi pinning factor of the CsPbBr3-metal contact is estimated via a modified method considering the gap change, and that of the PbBr2-terminated one is slightly larger than that of the CsBr-terminated one, indicating a more flexible Schottky barrier in the former through changing the metal work function. This work presents a comprehensive understanding of metal contacts to all-inorganic perovskite CsPbBr3 and offers theoretical guidance for preparing high-performance inorganic perovskite photoelectric devices.

Graphene Oxide and Metal-Organic Framework-Based Breathable Barrier Membranes for Toxic Vapors.

Garments protective against chemical warfare agents (CWAs) or accidently released toxic chemicals must block the transport of toxic gases/vapors for a substantial time and allow moisture transport for breathability. These demands are challenging: either the barriers block CWAs effectively but have poor breathability or barriers have excellent breathability but cannot block CWAs well. Existing protective garments employ large amounts of active carbon, making them quite heavy. Metal-organic framework (MOF)-based adsorbents are being investigated as sorbents for CWAs. Breathable laminate of graphene oxide (GO) flakes supported on a porous membrane reduces permeation rates of CWA simulants substantially. We developed a multilayered membrane-based flexible barrier: GO laminate-based membrane over a MOF nanocrystal-filled expanded polytetrafluorethylene (ePTFE) membrane having submicrometer pores. The GO laminate-based layer developed a steady breakthrough concentration level almost 2 orders of magnitude below the usual breakthrough level. This highly reduced level of CWA was blocked by the MOF nanocrystal-filled membrane substrate layer over a highly extended period. We demonstrated the blocking of CWAs, mustard (HD), soman (GD), a sarin simulant [dimethyl methyl phosphonate (DMMP)], and ammonia for an extended period while the moisture transmission rate was substantial. The times for complete blockage of ammonia, HD, GD, and DMMP were 2750 min, 1075 min, 176 min, and 7 days, respectively. This remarkable performance resulted from a very low steady-state penetrant permeation through GO-laminate membrane and substantial penetrant sorption by MOF nanocrystals; furthermore, both layers show high moisture vapor transmission.

Study of dynamic debris impact load on flexible debris-resisting barriers and the dynamic pressure coefficient

The use of steel flexible barriers to mitigate landslide risk on natural hillsides is becoming common in the past decade in Hong Kong. The current design approach for this kind of barrier structure involves the adoption of the hydrodynamic load model to predict dynamic impact forces, followed by non-linear structural analyses of flexible barriers using numerical programs based on the pseudo-static force method. From local design guidelines, the dynamic pressure coefficient, a critical input parameter in the hydrodynamic load model, is taken as 2.0. This empirically considers the effect of impacts from boulders up to 2.0 m in diameter. With a view to rationalising the design approach, a series of physical impact tests and numerical analyses was conducted to investigate the dynamic debris impact on flexible barriers and the resulting barrier response. The physical impact tests involved up to 9 m3 of debris resisted by a 1.5 m high steel ring-net barrier. The tests were conducted in the 28 m long large-scale flume facility at the Kadoorie Centre in Hong Kong. Numerical modelling using computer programs LS-DYNA and NIDA-MNN was conducted to analyse the dynamic response of flexible barriers with different structural forms. The study aims to evaluate the dynamic pressure coefficient and to verify the current design approach based on the suggested dynamic pressure coefficient from this study. Results indicate that a dynamic pressure coefficient of 1.0 is, in general, appropriate for design purposes if the debris comprises primarily water and fine-grained particles.

Chemical Vapour Deposition Graphene-PMMA Nanolaminates for Flexible Gas Barrier.

Successful ways of fully exploiting the excellent structural and multifunctional performance of graphene and related materials are of great scientific and technological interest. New opportunities are provided by the fabrication of a novel class of nanocomposites with a nanolaminate architecture. In this work, by using the iterative lift-off/float-on process combined with wet depositions, we incorporated cm-size graphene monolayers produced via Chemical Vapour Deposition into a poly (methyl methacrylate) (PMMA) matrix with a controlled, alternate-layered structure. The produced nanolaminate shows a significant improvement in mechanical properties, with enhanced stiffness, strength and toughness, with the addition of only 0.06 vol% of graphene. Furthermore, oxygen and carbon dioxide permeability measurements performed at different relative humidity levels, reveal that the addition of graphene leads to significant reduction of permeability, compared to neat PMMA. Overall, we demonstrate that the produced graphene–PMMA nanolaminate surpasses, in terms of gas barrier properties, the traditional discontinuous graphene–particle composites with a similar filler content. Moreover, we found that the gas permeability through the nanocomposites departs from a monotonic decrease as a function of relative humidity, which is instead evident in the case of the pure PMMA nanolaminate. This work suggests the possible use of Chemical Vapour Deposition graphene–polymer nanolaminates as a flexible gas barrier, thus enlarging the spectrum of applications for this novel material.

Seabed influence on wave scattering by a porous flexible barrier in a two-layer oblique sea

Seabed influence on wave scattering by a porous flexible barrier in a two-layer oblique sea

How Flexible, Slit and Rigid Barriers Mitigate Two‐Phase Geophysical Mass Flows: A Numerical Appraisal

AbstractFlexible, slit, and rigid barriers are common countermeasures to mitigate natural geophysical mass flows, but presently, quantitative comparisons of their performance are lacking, due to the challenges involved in accurately representing the multi‐body and multi‐phase interactions. This study presents a numerical appraisal on this issue using a physics‐based coupled computational fluid dynamics and discrete element method (CFD‐DEM). A geophysical flow is considered as a mixture of discrete gap‐graded particles (DEM) and a continuous viscous slurry (CFD), whereas a permeable and deformable barrier structure can be modeled by DEM. The in‐flow multiphase interactions and flow‐barrier interactions can be rigorously modeled by a coupling scheme between DEM and CFD. Our numerical simulations reasonably capture both field and experimental observations on key features of flow‐barrier interactions and barrier responses. The different intercepting mechanisms of three barriers via pile‐up and runup modes are revealed by qualitative and quantitative characterizations. Flexible barriers perform the best under runup mode regarding much larger peak load reduction ratios (up to 89%) due to their high permeability and Fr‐dependent load‐deflection behavior. We further compile a barrier‐specific design diagram that suggests existing analytical models calibrated by limited experiments may underestimate the peak impact for slit and rigid barriers due to their neglect of large solid particles in the impinging flows while leading to overestimations for flexible barriers owing to inappropriate representations of barrier permeability and structural deformability. Our findings may offer a basis for model improvements and developments in practical barrier selection and design.

A Gaussian wavelet-based method for extracting rockfall motion information in consecutive impact tests on flexible barrier systems

Flexible barriers are vulnerable to consecutive rockfall impacts, particularly in mountainous areas. The barriers deformation, energy absorption, and anti-impact performance can be evaluated from the rockfall motion information. However, a slight interference in rockfall displacement signals, generated during the actual measurement, could result in a distortion of the rockfall velocity and acceleration extracted through conventional derivative calculations. Consecutive impact tests on steel-wire ring nets were conducted, and the motion of the impact rock was captured from a high-speed video. The random noise in the impact signal was quantified using the signal-to-noise ratio and was distinguished in the frequency domain. Furthermore, to increase the derivative calculation accuracy, a Gaussian wavelet-based method is proposed, and an amplitude parameter is introduced into the wavelet transform procedure. The self-consistency of the proposed method was achieved using a combined differentiation–integration iteration process. Analytical signals of a single-degree-of-freedom system under a sine-wave impulse were used to validate the proposed method. We observed that the wavelet scale parameters were strongly related to the impact signal frequency band, which accounted for 90% – 99% of the total energy in the frequency domain. Finally, the Gaussian wavelet-based method was applied to the real impact signals of a rockfall. The results indicated that the proposed method is an effective and reliable tool for extracting the velocity and acceleration information of falling rocks during the consecutive impact process.

MPM modelling of debris flow entrainment and interaction with an upstream flexible barrier

Flexible barriers may be installed upstream in debris flow channels to reduce entrainment of bed material. Simulating both the entrainment and the impact on a barrier by the same numerical tool remains challenging. For this purpose, a three-dimensional one-phase material point method (MPM) software is used herein to back-calculate two large-scale flume experiments. These experiments were conducted to measure the entrainment of an erodible bed and the impact on a flexible barrier. To simulate the entrainment of the wet bed, a Mohr–Coulomb softening model is introduced. In the model, the apparent friction angle of the bed material decreases as a function of the distortional strain, effectively reproducing the pore pressure increase observed in the experiments. From the tests and the numerical simulations, we identify two main mechanisms leading to entrainment: (i) the direct rubbing and colliding effect of the flow on to the bed and (ii) a significant bed shear strength reduction. Concerning the first mechanism, existing models only consider the rubbing of the bed surface by a shear stress parallel to the slope. However, we observe that a ploughing-type erosion occurs due to normal stresses acting on the bed in the flow direction. The additional ploughing explains why beds which are mechanically stronger than the flow can also be partly entrained. Larger entrainment volumes are found when the bed material loses shear strength due to pore pressure buildup that eventually leads to a self-propelled entrainment where the bed no longer has frictional strength to carry its own weight.

Debris flow overflowing flexible barrier: physical process and drag load characteristics

Debris flow overflowing flexible barrier: physical process and drag load characteristics