Flexible Wall Research Articles

Experimental study on impermeability of Loess liner mixed with bentonite-HDTMA

Permeability tests are performed by using the flexible wall permeameter to study the influence of bentonite-HDTMA (hexadecyl trimethyl ammonium bromide) on the permeability performance of Loess as a lining material in the solid waste landfill. Results show, the impermeability of compacted Loess in the middle and lower reaches of the Yellow River in China does not meet the standard requirement as the landfill liner. The permeability of Loess mixed with more than 10% bentonite ratio is less than 1.0 × 10−7 cm·s−1. The permeability of Loess increases slightly after mixing a small amount of HDTMA. The impermeability of Loess mixed with some bentonite-HDTMA ratio still meet the standard requirement. The HDTMA may destroy the soil aggregate structure and increase the soil permeate channel. The SEMs show that the bentonite clay particle can fill the pores between Loess coarse particles and improve the impermeability performance of the material. The digital photos show that HDTMA can effectively resist the development of soil macro-cracks induced by wetting–drying cycles, better for liner to maintain good impermeability. On this basis, the relationship between the hydraulic conductivity of bentonite-HDTMA modified Loess and dry density is constructed. From this study, Loess can be used as a lining material for landfills, when mixed with bentonite/HDTMA at ratios of 10%/0% or 14%/2%.

Modeling of Advanced Helmholtz Resonator Liners with a Flexible Wall

Acoustic liners are an effective way to dampen aircraft noise. Conventional single-degree-of-freedom liners consist of a perforated facesheet backed with a honeycomb structure and a rigid end plate. Their damping excels near their resonance frequency, which is antiproportional to the cavity depth (-resonator) or the cavity volume (Helmholtz resonator). However, this is a challenge for low-frequency noise with long wavelengths due to the limited installation space. We therefore propose a resonator in which the back cavity is divided into two cavities by a flexible plate. The aim is to combine the damping mechanisms of the Helmholtz resonator with the material damping of the flexible plate. With carefully chosen parameters, this flexible plate resonates well below the Helmholtz frequency. We derived an analytic model based on waveguide theory to predict the impedance of the resonator concept. The Helmholtz equation was solved to (numerically) determine the scattering coefficients of a channel section in which one wall is lined with the predicted resonator impedance. The predicted dissipation agreed well with experimental data from measurements at the aeroacoustic wind tunnel DUCT-R.

Numerical Evaluation of Dynamic Earth Lateral Pressure on Basement Walls in Cohesionless Soils (A Case Study of Iranian Earthquakes)

Various earth-retaining structures are extensively used in different civil engineering projects. Using the results of experimental and numerical modeling, the effect of the earthquake loading on the distribution of the earth lateral pressures on basement walls was investigated. The UBCHYST constitutive model was used in the performed numerical simulations, and using the results of 12 centrifuge dynamic model tests, a calibration process was conducted to obtain the proper input parameters for numerical models. Based on the results, some correlations between the dynamic increment coefficient of earth lateral pressure (ΔKae) and the free-field peak ground acceleration (PGAff) were established. The correlations are different for stiff and flexible basement walls. In the end, the results of the model calibration process were verified by the examination of 12 major earthquakes that occurred in the Iran plateau. The results showed that the proposed ΔKae-PGAff correlations are precise enough for the applied design projects.

Experimental investigation on water/gas resistance and strength properties of clinoptilolite/Na-PAA amended compacted clay cover

Compacted clay is an effective and economical engineering barrier for seepage prevention and gas blocking in landfills (including tailings pond, landfill, etc.). In addition to the lack of durability such as desiccation cracks of compacted clay modified by clinoptilolite and sodium polyacrylate, it is also necessary to consider the changes of engineering properties such as water holding capacity, water and gas resistance, and strength of compacted clay. Therefore, through oven evaporation test, flexible wall permeability test and unconfined compressive strength test, this paper studies the water retention, permeability and strength characteristics of compacted clay with different amounts of clinoptilolite and sodium polyacrylate. Orthogonal experiment L16(45) was used to optimize the amount of clinoptilolite and sodium polyacrylate and the compaction conditions, and further combined with the analytic hierarchy process (AHP), the factors affecting the water retention, permeability and strength of the compacted clay before and after the modification of clinoptilolite and sodium polyacrylate were discussed simply and quickly, and the applicability of the orthogonal experiment traditional analysis method and the analytic hierarchy process in the modified compacted clay of clinoptilolite and sodium polyacrylate was studied.

Experimental Study on Microstructure and Hydraulic Performance of Bentonite Modified Loess

The impact of natural sodium bentonite on the microstructure, permeability and strength characteristics of bentonite-modified loess (BML) were evaluated by scanning electron microscope (SEM) test, triaxial flexible wall permeability test, uniaxial compression test and direct shear tests. The experimental results indicate that bentonite can be used for loess solidification attributed to its effective particle filling, water absorption and expansion characteristics. The quantitative parameters of SEM images such as the average pore area, width, length and surface porosity of BML declined first and then increased with bentonite content, and the lowest was observed at a bentonite content of 15%. The hydraulic conductivity of BML declined with increasing bentonite content and was lower than the maximum allowable limit of 1.0 × 10−9 m/s. The uniaxial compressive strength and shear strength parameters of BML increased initially and subsequently declined as bentonite content increased. A normalized prediction model was established for modified loess based on the correlation between mechanical characteristics and the microscopic pore parameters, which was verified to be rational in estimating the macro- and micro-scale properties of BML. Therefore, when the anti-seepage landfill layers are constructed in the Loess Plateau area, 15% of bentonite is recommended in modified loess, which has optimal impermeability and mechanical properties.

Permeability Characteristics and Mechanism of Silicone-Hydrophobic-Powder-Modified Compacted Loess

This paper proposes the addition of an environmentally friendly silicone hydrophobic powder (SHP) to compacted loess to enhance its impermeability and reduce the settlement caused by wetting deformation. A flexible wall permeability test was conducted to examine the permeability coefficient of compacted loess with different dry densities mixed with different proportions of the SHP. Water drop infiltration testing, low-temperature drying testing, low-field nuclear magnetic resonance testing, and scanning electron microscopy were performed to clarify the occurrence state and permeability reduction mechanism of the SHP between loess particles from the microscopic viewpoint of the loess structure. The permeability coefficient of the compacted loess decreases significantly after adding 1–3% SHP. Specifically, the permeability coefficient of the loess with low compaction degree (1.35 g/cm3) decreases by 87% after the addition of 3% SHP. Moreover, the permeability coefficient of the loess with a compaction degree of 1.50 g/cm3 decreases from 1.58 × 10−6 to 7.9 × 10−8 cm/s. When the SHP is added to compacted loess, filling and adsorption effects occur: The filling effect decreases the proportion of large pores in the loess. The adsorption effect allows the SHP to encapsulate the loess particles to form a hydrophobic film layer, which leads to the formation of a non-closed hydrophobic structure. This phenomenon decreases the water flow capacity while ensuring the water evaporation capacity inside the loess. The findings demonstrate the potential of adding SHP to enhance the loess impermeability and facilitate and optimize the anti-seepage treatment of various loess filling projects.

Stress–strain behavior and constitutive relation of rubberized plastic concrete under uniaxial and triaxial compression

AbstractPlastic concrete is a kind of flexible concrete cutoff wall material, which is used to solve the problem of poor coordinated deformation ability between ordinary concrete cutoff wall and surrounding soil. It has the characteristics of small elastic modulus and large limit strain, which greatly improves the operation condition of cutoff wall. In order to save bentonite resources and recycle waste automobile tires, this paper crushed waste automobile tires into rubber particles and mixed them into plastic concrete, through the uniaxial compression test and triaxial compression test, obtained the corresponding stress–strain curve, rubberized plastic concrete strength and deformation properties are studied and the rubber particles and the relationship between dosage. The test results show that the compressive strength of rubberized plastic concrete decreases with the increase of rubber particles content, but the deformation capacity increases with the increase of rubber particles content. In this paper, the regression analysis of rubberized plastic concrete constitutive relation and failure criterion including the influence factor of rubber particles are helpful to promote the engineering application of rubberized plastic concrete and reduce the exploitation of natural resources and environmental pollution.

Unsteady free convection in a composite enclosure having flexible wall

Transient free convection in a composite enclosure having a cold flexible plate and a hot rigid plate is simulated numerically. It is assumed that the flexible plate is hyper-elastic. A porous layer with various sizes and permeabilities is attached to the rigid plate. The enclosure is filled with water. Fluid flow in the fluid domain was governed by the Navier–Stokes equations, and the flow within a saturated porous layer was governed by the Brinkman-Forchheimer extended Darcy model. The unsteady continuity, momentum, and energy equations are solved using the Arbitrary-Lagrangian-Eulerian (ALE) approach based on the fluid-structure interaction (FSI). It is found that the development of convective flow goes through initial, transitional, and stationary states. Each state interval is shifted by varying the Darcy number and Rayleigh number. In the transitional state, the deformation of the flexible parts reaches its maximum bending. The profile of the flexible plate at steady state is in a sinusoidal shape for the non-Darcy regime, while it is in an asymmetric parabolic shape for the Darcy regime. The steady state is reached for [Formula: see text], [Formula: see text], and [Formula: see text] before [Formula: see text].

Open questions in plant cell wall synthesis.

Plant cells are surrounded by strong yet flexible polysaccharide-based cell walls that support the cell while also allowing growth by cell expansion. Plant cell wall research has advanced tremendously in recent years. Sequenced genomes of many model and crop plants have facilitated cataloging and characterization of many enzymes involved in cell wall synthesis. Structural information has been generated for several important cell wall synthesizing enzymes. Important tools have been developed including antibodies raised against a variety of cell wall polysaccharides and glycoproteins, collections of enzyme clones and synthetic glycan arrays for characterizing enzymes, herbicides that specifically affect cell wall synthesis, live-cell imaging probes to track cell wall synthesis, and an inducible secondary cell wall synthesis system. Despite these advances, and often because of the new information they provide, many open questions about plant cell wall polysaccharide synthesis persist. This article highlights some of the key questions that remain open, reviews the data supporting different hypotheses that address these questions, and discusses technological developments that may answer these questions in the future.

Clinical experience of thoracoplasty with absorbable rib substitutes

PurposeMalignant chest wall tumors are rare in pediatrics. They require multimodal oncological treatment and local surgical control. Resections are extensive; therefore, thoracoplasty should be planned to protect intrathoracic organs, prevent herniation, future deformities, preserve ventilatory dynamics, and enable radiotherapy.MethodsWe present a case series of children with malignant chest wall tumors and our surgical experience with thoracoplasty using absorbable rib substitutes (BioBridge®), after local surgical control. BioBridge® is a copolymer made of a polylactide acid blend (70% L-lactic acid y 30% DL-lactide).ResultsIn 2 years, we had three patients with malignant chest wall tumors. Resection margins were negative, without recurrence at follow-up. We achieved good cosmetic and functional results, and no postoperative complications.ConclusionAlternative reconstruction techniques such as absorbable rib substitutes provide protection, guarantee a flexible chest wall, and do not interfere with adjuvant radiotherapy. Currently, there are no management protocols in thoracoplasty. This option represents an excellent alternative for patients with chest wall tumors. Knowledge of different approaches and reconstructive principles is essential to offer children the best onco-surgical option.

Experimental and finite element analysis: Out-of-plane mechanical performance of infill walls with flexible connection

Flexible connection between the wall and the frame can improve the seismic performance of the structure, thus minimizing the pushing effect of the infill wall on the main frame. Masonry infill walls with flexible connection have lower out-of-plane stability than walls with rigid connection. However, local collapses are more likely to occur. A comparative study was conducted on the load-carrying capacity, initial stiffness, deformation and ductility of different wall structures based on a monotonous static load test, and the out-of-plane mechanical properties exhibited by flexible masonry infill walls were investigated. A simplified separated finite element model of masonry infill wall was built in accordance with the test results, and then the monotone out-of-plane static loading was performed. The structural configuration, the wall-frame connection method, and the spacing between structural columns were found to have significant effects on the out-of-plane mechanical behavior of the infill wall. The wall structural configuration was found to have the strongest effect, followed by the wall-frame connection method. Under the conditions of flexible connection, when the wall structure was in the “grid-beam” form, and the spacing between structuring columns was 2.5–3.0 m, the frame-infill wall was found with the best restraint effect, so the optimal out-of-plane comprehensive mechanical performance would be achieved.

Radiation damping effect on the sound pressure response in a structural-acoustic cavity

A structural-acoustic system consisting of an enclosed cavity with flexible wall panels is considered to evaluate the effect of sound radiation-damping resulting from the panel vibration on the sound pressure level in the cavity. The interior cavity pressure can excite the flexible wall panels that will radiate noise to the exterior that in turn can reduce the interior noise due to the energy loss to the exterior surroundings. This energy loss is described as radiation damping of the interior cavity system. An enclosed rectangular cavity-plate system subjected to external random pressure excitation is used to evaluate the effect. The radiation damping is evaluated using a modal approach (FEM, BEM) to determine the radiation efficiency of the vibrating panels. The effect of the radiation damping for the example of a box-plate structure is evaluated using the CMA (classical modal analysis) method for the low-frequency range and the AMA (asymptotic modal analysis) method for the mid- and high-frequency ranges. The inclusion of radiation damping due to rigid body cavity mode excitation is shown to provide an improved prediction of the sound transmission loss especially in the low-frequency range.

Effect of the lid-driven on mixed convection in an open flexible wall cavity with a partially heated bottom wall

The FSI-mixed convection heat transfer in a lid–driven vented cavity is studied in the present work. The heat source is set partially on the base of the cavity; the left flexible wall is cold, while the remaining walls are adiabatic. The top wall of the cavity moves in different cases depending on its movement; stationary wall (case 0), moving to the left (case I) and moving to the right (case II). The arbitrary Lagrangian-Eulerian formulation and finite element method are utilized to solve the governing equations. A two-dimensional incompressible laminar flow with an unsteady-state condition is used in the present model. The effects of relevant factors like the Richardson number 0.01≤ Ri ≤ 100 and the ratio of the velocities of moving top wall to that of the air entering the cavity, which is governed by Reynolds numbers ratio 1 ≤ Rer ≤ 4 have been studied. The outcomes demonstrate the feasibility of using a flexible wall and a special movement of the top wall. The percentage increase of the Nusselt number due to the flexible wall alone is about 4.5% while when the top wall moving to the left (case I), the augmentation rises to 28%.

Direct measurement of unsaturated permeability of kaolin-sand mixtures

Unsaturated permeabilities of six different kaolin-sand mixtures named as 100K0S, 90K10S, 80K20S, 50K50S, 20K80S, and 10K90S were directly measured using a modified flexible wall triaxial permeameter system. 90K10S means that the soil mixture contains 90% kaolin and 10% sand by dry mass. Soil–water characteristic curves (SWCC) of the kaolin-sand soil mixtures were also measured for a wide range of suctions using a Tempe pressure cell, 5-bar pressure plate, 15-bar pressure plate, and saturated salt solutions. The unsaturated permeabilities of the soil mixtures were also estimated using ten different theoretical models using (1) the measured SWCC data over a complete suction range and (2) the measured SWCC data up to 100 kPa suction in combination with the estimated SWCC data at higher suction values. The directly measured unsaturated permeability of the soil mixtures was used to validate the estimated values of unsaturated permeability. The results showed that the unsaturated permeability estimation models could reasonably fit the directly measured unsaturated permeability data when both the data from the complete measurement of SWCC and the measured SWCC data up to 100 kPa suction in combination with the estimated SWCC data at higher suction values were used.

Surrounding rock activity law and support optimization of double flexible formwork wall gob-side entry retention in stratified mining coal seams

To ensure gas control in the layered mining of extra-thick coal seams in Baijigou Coal Mine—in addition to reducing the loss of coal resources and amount of roadway driving—this article proposes the gob-side entry retention technology of flexible formwork concrete, and retains the 010202 working face four-layered return air roadway as the 010203 working face gas drainage lane. By combining theory and field practice, a flexible formwork concrete wall + anchor cable joint support scheme is proposed to strengthen small coal pillars. Further, the design scheme for the aforementioned framework at the bottom of the layered mining region of an extra-thick coal seam is proposed. Then, field tests are carried out, and the surrounding rock activity law of the double flexible formwork wall entry retention in a layered mining coal seam is obtained. The results show that (i) 010202 the whole process of overburden collapse to stability at the stratified mining face is completed 60--200 m behind the face and (ii) the roadway deformation of the extra-thick coal seam in the Baijigou Coal mine can be divided into four stages, and the mining pressure of the gas drainage roadway basically presents a dynamic change of “pressurized stage – peak stage – stabilized pressure stage”. Based on this, three mechanical stages of roadway deformation are derived: (1) δz< Nmz<< Nwz; (2) Nmz < δz << Nwz; and (3) Nmz < δz< Nwz. Three repeated mining support optimization schemes are provided, one for each stage. Finally, the deformation and damage of the surrounding rock are effectively controlled, and the requirement that the gas drainage roadway is still intact under the influence of the 010203 working face mining is realized. This study has certain reference significance for gob-side entry retention in the bottom layer of stratified mining in extra-thick coal seams.

Flow-induced surface instabilities in a flexible-walled channel with a heavy wall

We consider the stability of laminar high-Reynolds-number flow through a planar channel formed by a rigid wall and a heavy compliant wall under longitudinal tension with motion resisted by structural damping. Numerical simulations indicate that the baseline state (with Poiseuille flow and a flat wall) exhibits two unstable normal modes: the Tollmien–Schlichting (TS) mode and a surface-based mode which manifests as one of two flow-induced surface instabilities (FISI), known as travelling wave flutter (TWF) and static divergence (SD), respectively. In the absence of wall damping the system is unstable to TWF, where the neutrally stable wavelength becomes shorter as the wall mass increases. With wall damping, TWF is restricted to long wavelengths through interaction with the most unstable centre mode, while for wall damping greater than a critical value the system exhibits an SD mode with a two branch neutral stability curve; the critical conditions along the upper and lower branches are constructed in the limit of large wall damping. We compute the Reynolds–Orr and activation energy descriptions of these neutrally stable FISI by continuing the linear stability analysis to the following order in perturbation amplitude. We find that both FISI are primarily driven by the working of normal stress on the flexible wall, lower-branch SD has negative activation energy, while upper-branch SD approaches zero activation energy in the limit of large wall damping. Finally, we elucidate interaction between TS and TWF modes for large wall mass, resulting in stable islands within unstable regions of parameter space.

Analytical study of a model of fluid flow through a channel with flexible walls

The present paper is devoted to mathematical analysis of the model that describes fluid flow moving in a channel with flexible walls, which are subject to traveling waves. Experimental data show that the energy of the flowing fluid can be consumed by the structure (the walls) inducing “traveling wave flutter.” In the problems involving two‐media interactions (fluid/structure), flutter‐like perturbations can occur either in the fluid flowing in the channel with harmonically moving walls, or in the solid structure interacting with the flow. In the present research, it is shown that there are no abrupt (or flutter‐like) changes in the flow velocity profiles. Using the mass conservation law and incompressibility condition, we obtain the initial boundary value problem for the stream function. The boundary conditions reflect that (i) there is no movement in the vertical direction along the axis of symmetry and (ii) there is no relative movement between the near‐boundary flow and the structure (“no‐slip” condition). The closed form solution is derived for the stream function, which is represented in the form of an infinite functional series.

Performances of the Soil–Bentonite Cutoff Wall Composited with Geosynthetic Clay Liners: Large-Scale Model Tests and Numerical Simulations

The geosynthetic clay liner (GCL) overlap plays a key role in maintaining hydraulic performance of the barrier systems, e.g., the bottom liner and cover systems. However, its influences on the behavior of the vertical barrier have been rarely investigated. This paper aims to address this issue using the large-scale model test and 3-dimensional finite element (FE) modeling. In the model test, the GCL overlap at the width of 500 mm was tested under a constant hydraulic head of 1 m and confining stress ranging from 10 to 150 kPa using a newly developed large-scale apparatus. Compared with the flexible wall permeameter, this apparatus could guarantee full field-scale GCL overlap to be tested. Results showed that the effective hydraulic conductivity of the GCL overlap decreased from 10−8 to 10−9 cm/s as the confining stress increased from 10 to 150 kPa. The addition of supplemental bentonite paste in between the overlap with a water-to-bentonite ratio of 19:1 contributed to reducing the effective hydraulic conductivity by 60% compared with that for a GCL overlap without bentonite paste. The breakthrough time for the soil-bentonite (SB) cutoff wall composited with GCLs was 64% longer in comparison with that for the single SB wall. Additionally, the breakthrough after 50 years is made for the entire depth of the single SB wall while at the depth no more than 0.9 m for the composite wall with bentonite paste at the GCL overlap. With consideration that the depth of the groundwater table is generally greater than 1 m, the GCL–SB composite cutoff wall will exhibit a good performance in containing groundwater contaminants in the field, especially when applying bentonite paste at the GCL overlap.

The Numerical Simulation of Nanofluid Flow in Complex Channels with Flexible Wall

The Numerical Simulation of Nanofluid Flow in Complex Channels with Flexible Wall

The influence of fluid-structure interactions 2-ways on dynamic characteristics of flexible tank

This paper investigates the influence of two-way fluid-structure interactions (FSI) on the dynamic characteristics of flexible storage liquid tanks. A coupled finite volume method FVM and finite element method FEM (FVM/FEM) was developed to simulate a flexible water tank subjected to seismic loading. FVM is used to simulate the fluid domain and FEM is used to capture the structural domain. The two-dimensional interaction equation is solved at the contact surface between the elastic tank wall and the fluid by tuning the relaxation parameter and convergence conditions. The model investigates the influence of considering two-way FSI on the dynamic characteristics of a tank flexible to a rigid tank wall. The results show that the frequency of flexible tank walls differs from that of rigid walls, especially the hydrodynamic pressure of liquid motion acting on the tank. A “threshold value” is revealed to distinguish flexible or rigid tanks. If the tank stiffness exceeds this threshold, then the thicker the tank is, the lower the hydrodynamic pressure. However, if the tank stiffness is less than this threshold, the thinner the tank is, the lower the hydrodynamic pressure. Further experiments on a fluid container under harmonic excitation are carried out using a shaking table to verify the dynamic behavior in comparison to numerical results. Good agreement is observed between numerical, analytical, published, and experimental data.