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• Estimates of modeled CH 4 emission (E) data for 1,325 U.S. landfills were reviewed. • Operators use two methods to estimate E from landfills with a gas collection system. • First-order decay (FOD) method shows increasing emissions. • Collection efficiency assumption method shows decreasing emissions. • FOD method shows some agreement to remotely sensed national estimates. As part of its commitment to the United Nations Framework Convention on Climate Change, the U.S. annually develops a national estimate of methane emissions from municipal solid waste (MSW) landfills by aggregating activity data from each facility. Since 2010, the U.S. has reported a 20 % decrease in MSW landfill emissions despite a 21 % increase in tons disposed. Operator-submitted data were investigated to understand the causes of this decline. In the U.S., operators of landfills with a gas collection and control system (GCCS) calculate their facility's emissions via two separate approaches – (1) first-order decay (FOD) and (2) collection efficiency assumption (CEA) − and select either result to feed into the annual inventory. The FOD model predicts methane generation proportional to waste disposal and that approach calculated a 19 % increase in total methane generated from 2010 to 2022, whereas generation via the CEA approach decreased by 8.9 %. The amount of measured methane collected has increased 7.5 % for the same years. Discrepancies between the two models' generated methane, assumed gas collection efficiencies, and oxidized methane compound into substantive differences in national estimates. Operators more frequently select the CEA method, which results in decreased national estimates. If only the FOD method was used, U.S. MSW landfill emissions would be 1.3-1.7 times greater than current estimates which is similar to recent extrapolations from remote sensing campaigns in the U.S. Both models contain parameters with large inherent uncertainty. Without measurement methods that continuously quantify both point-source and diffuse emissions, an assessment of either equation's accuracy cannot be made. [ABSTRACT FROM AUTHOR]

• PFAS sorb to and can diffuse through HDPE geomembranes. • Partition coefficients range from 3.8 to 98.3 L/kg. • The functional group and structure of PFAS affect partition and diffusion. • Diffusion coefficients vary from the order of 10-18 m2/s to 10-17 m2/s. • Estimated breakthrough times are more than 1500 years for intact 1.5 mm HDPE GM. The objective of this study is to investigate the fate and transport of per-polyfluoroalkyl substances (PFAS) through a high-density polyethylene (HDPE) geomembrane (GM) that is commonly used in landfill composite liner systems. Tests were conducted to measure the sorption and diffusion of per-polyfluoroalkyl substances (PFAS) with varying number of carbons in chain and functional groups on HDPE GM. Perfluoroalkyl carboxyl acids (PFCAs), perfluoroalkyl sulphonic acids (PFSAs), alkyl-sulfonamidoacetic acids (FOSAAs), fluorotelomer sulfonic acids (FtSAs), alkane sulfonamides (FOSA) and ether carboxylic acids (Gen X) were investigated in this study. The partition coefficients (K d) on HDPE GM ranged from 3.8 to 98.3 L/kg. PFAS with amide and sulfonic functional groups showed stronger sorption than that of PFAS with carboxylic acid functional groups. Molecular weight directly affected the K d for long-chained PFAS whereas the K d of short-chained PFAS was not sensitive to molecular weight. The diffusion coefficients (D g) of PFCAs and PFSAs through 0.1-mm HDPE GM were found to be in the orders of 10-18 to 10-17 m2/s. The D g decreased with increasing molar mass and were also observed to be dependent on the functional group. D g of PFSAs was lower than that of PFCAs for similar number of carbons in the chain. The estimated mass flux for PFAS in an intact 1.5-mm HDPE GM varied from 38.7 to 2080.8 ng/m2/year whereas the estimated diffusive breakthrough time for PFAS in intact 1.5-mm HDPE was 1526 years or longer. [ABSTRACT FROM AUTHOR]

This study investigated the impact of polymer elution on the interface shear strength between a smooth geomembrane (GMB) and two types of bentonite-polymer (B–P) geosynthetic clay liners (GCLs) containing linear and crosslinked polymers. Tests were also conducted with sodium bentonite (Na–B) GCLs as a control. Interface shear tests were conducted with dry, two-stage, and free hydration conditions with varying normal stresses. The results showed that under dry conditions, the displacement at peak strength and shear strength envelops of GMB/Na–B GCL and GMB/B–P GCLs were similar. However, the displacement at peak strength of GMB/B–P GCLs was higher than that of GMB/Na–B GCL under two-stage and free hydration. Meanwhile, the peak shear strength of the GMB/B–P GCLs showed a greater reduction than that of GMB/Na–B GCLs when transitioning from a dry condition to a free hydration condition at the same normal stress, particularly at higher normal stress. Loss on ignition (LOI) tests confirmed that there was a decrease in polymer loading of B–P GCLs after the shearing test, indicating polymer elution occurred during the shearing test. The result suggests that polymer elution had a significant effect on the GMB/B–P GCL interface shear strength, especially at higher normal stress. • Interface shear tests were conducted on bentonite-polymer (B-P) geosynthetic clay liners (GCLs) and one smooth geomembrane. • A two-stage hydration procedure and a free hydration procedure were used to simulate the subgrade hydration process of GCLs. • The GMBS/B-P GCLs interfaces had a lower peak and large displacement shear strength than that of GMBS/Na-B GCLs. • LOI test results confirmed that polymer elution from B-P GCLs after the shearing tests. • Retention of retain the polymer in B-P GCLs and minimizing polymer elution is critical to GMBS/GCLs interface. [ABSTRACT FROM AUTHOR]

This study focused on evaluating the longevity of Atactic Polypropylene (APP) used as a geomembrane (GM) to line ponds that collect runoff water from salt handling facilities. Samples of APP were exhumed from the ponds that have been in service for 6-, 25-, and 44-years and evaluated in the laboratory. Tests were conducted to analyze the surface cracks and textures, tensile properties, puncture resistance, and ability to hold water (permeability). Control tests were conducted with virgin APP GM. Results were compared based on the difference in the age of the APP, location of where the APP samples were obtained within the side slope of the pond (i.e., submerged, and above water level), and orientation of the side slope in relation to the sun (e.g., east, west, north, or south). Based on the field observations and laboratory evaluations, it was determined that exposure to sunlight accelerates the degradation more so than the chemical degradation that occurs due to the salt content within the pond water. The samples exhumed from the north slope (south-facing) had more severe degradation due to high solar radiation energy deposition. • This study focused on evaluating the longevity of APP GM used as pond liner to collect runoff in salt handling facilities. • APP GM were exhumed from the salt ponds after 6-, 25-, and 44-years service. • GMs were investigated by performing image analysis, tensile, puncture resistance, and permeability tests, and FTIR analysis. • APP GMs exhumed from region above water showed faster degradation than GMs exhumed from region below water at the same pond. • APP GMs exhumed from the north slope (south-facing) had the severe decay than the samples exhumed from the other slopes. [ABSTRACT FROM AUTHOR]

• OSP-HDT: A novel optimal sensor placement for the high-precision digital twin method. • An experiment of a complex shell validates the effectiveness of the OSP-HDT method. • OSP-HDT method has higher prediction accuracy than the uniform and random methods. • OSP-HDT method reduces the sensor number by 77.6% than full sensor placement method. The complex shape of the structure and the new needs for high-precision in digital twin modeling pose challenges for sensor placement optimization. A novel optimal sensor placement towards the high-precision digital twin (OSP-HDT) method is proposed for complex curved structures. It comprises three key aspects. Firstly, leveraging the spatial dimensionality reduction method, the complex curved surface is simplified into a planar representation. Subsequently, candidate sensor placement points can be easily identified by dividing the background mesh in the plane and screening them within the curved surface. These candidate points are then binary encoded to facilitate the subsequent optimization. Secondly, the method collects result data from the finite element model, treating it as virtual sensor data. Using this data, a surrogate model is constructed and then the objective function is formulated based on both the global and local critical areas precision of the surrogate model. Thirdly, the sensor placement optimization model is constructed, followed by optimization design using the efficient multi-objective covariance matrix adaptive evolutionary strategy. Through the steps above, the optimal sensor placement can be identified. To validate the proposed OSP-HDT method, an experiment is conducted on an S-shaped variable cross-section stiffened shell, with the construction of the corresponding digital twin. Compared to the uniform placement with an equivalent number of sensors, the OSP-HDT method demonstrated a significant 9.0% improvement in global precision and a remarkable 62.1% enhancement in local precision of critical areas. Furthermore, when compared to the random sensor placement strategies, the OSP-HDT method exhibited a 20.5% increase in global precision, together with a 44.2% increase in the local precision. Notably, even when compared to the full sensor placement, the OSP-HDT method can maintain comparable local precision, while significantly reducing the number of sensors by 77.6%. The above comparison indicates that the proposed OSP-HDT method can build a digital twin model with higher global and local precision for complex structures. [ABSTRACT FROM AUTHOR]

Hydraulic conductivity of conventional mock sodium bentonite (Na–B) and bentonite-polymer (B–P) geosynthetic clay liners (GCLs) were evaluated with three synthetic leachates that are chemically representative of aggressive leachates from coal combustion product (CCR) (I = 3179 mM), mining waste (MW) (I = 2127 mM, pH = 2.0), and municipal solid waste incineration ash landfill (MSWI) (I = 2590 mM). The mock B–P GCLs were created by dry mixing bentonite with branched, linear, or crosslinked polymer. The polymer loading of mock B–P GCLs ranged from 3 to 15%. Comparative tests were also conducted with Na–B GCLs. The mock Na–B GCLs cannot maintain low hydraulic conductivity to aggressive CCR, MW, and MSWI leachates. Mock B–P GCLs with 10% branched polymer had low hydraulic conductivity (< 1.0 × 10−10 m/s) to synthetic MW and MSWI leachates at 20 kPa effective confining stress, whereas the hydraulic conductivity of mock B–P GCLs with 10% linear or crosslinked polymer ranged from 1.5 × 10−9 to 1.4 × 10−7 m/s. As the effective stress increased, the B–P GCLs branched polymer showed a faster decreasing trend than that of Na–B and B–P GCLs with linear or crosslinked polymer. • Hydraulic conductivity tests were conducted up to 4 years to test long-term hydraulic conductivity of B-P GCLs. • The ratios of K L /K 6766 for B-P GCLs to synthetic CCP leachate were higher than that of Na-B GCLs (e.g., 3.5 to 14.7 vs. 1.7). • Polymer elution from B-P GCLs affects the long-term hydraulic conductivity of B-P GCLs. • The polymer elution should be measured and considered as an additional termination criterion in ASTM D6766. [ABSTRACT FROM AUTHOR]

Hydraulic conductivity tests were conducted on six bentonite-polymer (B–P) geosynthetic clay liners (GCLs) to investigate the effect of the slow cation exchange process and polymer elution on the long-term hydraulic conductivity of B–P GCLs. Tests were conducted up to 1458 days and as many as 443 pore volumes of flows (PVFs). Three B–P GCLs consist of linear polymer whereas the other three have crosslinked polymer. One sodium geosynthetic clay liner (Na–B GCL) was used as a control. Hydraulic conductivities (K 6766) of B–P GCLs (5.4 × 10−12 m/s to 3.7 × 10−11 m/s) per ASTM D6766 were approximately 2-3 orders of magnitude lower than that of Na–B GCL (2.3 × 10−9 m/s to 3.5 × 10−9 m/s). Tests were continued after hydraulic and chemical equilibrium to investigate the long-term hydraulic conductivity of GCLs. Hydraulic conductivities of GCLs had an increasing trend after hydraulic and chemical equilibrium. The ratio of K L /K 6766 for B–P GCLs was 3.5–14.7, whereas ratio of K L /K 6766 for Na–B GCLs was 1.0–1.7. Total organic carbon (TOC) tests results confirmed that polymer elution occurred during the entire permeation process. The higher ratio of K L /K 6766 for B–P GCLs was attributed to the effect of polymer elution. • Hydraulic conductivity tests were conducted up to 4 years to test long-term hydraulic conductivity of B–P GCLs. • The ratios of K L /K 6766 for B–P GCLs to synthetic CCP leachate were higher than that of Na–B GCLs (e.g., 3.5 to 14.7 vs. 1.7). • Polymer elution from B–P GCLs affects the long-term hydraulic conductivity of B–P GCLs. • The polymer elution should be measured and considered as an additional termination criterion in ASTM D6766. [ABSTRACT FROM AUTHOR]

In order to explore the global optimizing ability of the surrogate-based stacking sequence optimization of composite shells with multiple cutouts, a multi-fidelity competitive sampling (MFCS) method is developed in this paper, which is composed of a low-fidelity sampling level and a high-fidelity sampling level. In the low-fidelity sampling level, competitive sampling points are determined by means of the prior screening criterion and the further screening criterion in sequence. Based on the POD-based buckling method, a novel reduced-order model is established as the low-fidelity model for fast linear buckling analysis of composite shells with multiple cutouts. In the high-fidelity sampling level, the explicit dynamic method is employed to calculate the post-buckling response of competitive sampling points. Based on these sampling results, a surrogate model is built. Next, a surrogate-based stacking sequence optimization framework is established for minimum material cost of composite shells with multiple cutouts. A simple optimization example of Mishra's Bird test function is performed and the effectiveness of the MFCS method is demonstrated. Finally, the proposed method is used for the surrogate-based stacking sequence optimization of composite shells with multiple cutouts. The optimal result of total material cost by the MFCS method decreases by 23.0% than the optimal result by the traditional sampling method, which indicates that the MFCS method contributes to improving the global optimizing ability of the surrogate-based stacking sequence optimization of composite shells with multiple cutouts. [ABSTRACT FROM AUTHOR]

Abstract The hierarchical stiffened shell is a promising aerospace structure configuration with high load-carrying capacity, however, it is challenging to fully explore its optimal load-carrying efficiency. Therefore, a bi-level optimization framework is proposed for hierarchical stiffened shells. In the first level of the optimization framework, a parallel computing numerical-based smeared stiffener method (NSSM) is first introduced for the fast prediction of critical buckling load and mode, by combining the numerical implementation of asymptotic homogenization (NIAH) method with the Rayleigh-Ritz method. Then, a large-scale Latin hypercube sampling (LHS) is performed in the entire design space based on NSSM, and a set of competitive sampling points is collected from the Pareto front of LHS results according to a screening criterion of load-carrying efficiency. In the second level, a surrogate-based optimization using radial basis function (RBF) technique is performed based on generated competitive sampling points with high load-carrying efficiency. Finally, detailed comparisons between optimal results of the proposed optimization method based on the competitive sampling method and the traditional surrogate-based optimization method based on the RBF technique and the LHS sampling method are made from the viewpoint of computational efficiency and global optimizing ability. Spending an approximate computational time, the optimal buckling result of the proposed method increases by 23.7% than that of the traditional method. In order to achieve an approximate global optimization result, the proposed method is able to reduce the computational time by 74.4% than the traditional method. By evaluating competitive sampling results, it can also be concluded that the partial global buckling mode and global buckling mode are most dominant buckling modes for hierarchical stiffened shells with the thick skin and closely-spaced stiffeners, which are prone to obtain a higher load-carrying efficiency. Highlights • The highlights should be revised as 'An efficient parallel computing numerical-based smeared stiffener method is proposed. • The proposed competitive sampling method can increase sampling efficiency. • The bi-level buckling optimization framework has excellent global optimizing ability. [ABSTRACT FROM AUTHOR]

Aiming at obtaining an optimal configuration of curved shells in the compact design space, it is an effective way to perform the shape and topology optimization simultaneously. Considering the complexity in solving the coupled shape and topology optimization problem, this paper presents an easy-to-implement data-driven non-intrusive shape-topology optimization framework for curved shells, including two steps. In the off-line step, the shape equation-driven mesh deformation method is firstly proposed, contributing to using a small number of design variables for fast shape change and optimization of the skin of curved shell without re-modeling and re-meshing. Latin hypercube sampling is used to generate sample points as the input data in the design space, and the corresponding skin shape is obtained. In each design domain determined by different skin shapes, the topology optimizations are performed in parallel or by multiple optimization solvers, after that above multi-source optimization results are collected into the output dataset. The mapping relationship is trained between the input data and output data via surrogate modeling technique, and this non-intrusive concept contributes to integrating the independent shape and topology optimization into a single-loop data-driven optimization. The cross validation-Voronoi adaptive model updating method is used to improve the prediction accuracy. In the on-line step, the single-loop data-driven optimization is carried out using covariance matrix adaptive evolution strategy and adaptive optimization updating method, which can obtain optimized results more efficiently than direct topology optimization or shape optimization method. In order to verify the effectiveness of the proposed data-driven non-intrusive shape-topology optimization framework, three optimization examples are carried out. Example results show that compared with the results by the single topology optimization, the strain energy results by the proposed framework can be reduced by 20.55%, 15% and 51.6%, respectively, highlighting the outstanding optimization ability of the proposed framework. [ABSTRACT FROM AUTHOR]

The impact of α and β radiation on antioxidant depletion in smooth high-density polyethylene (HDPE) geomembranes (GMs) is described. Smooth HDPE GMs having different thickness (0.04-mm, 0.1-mm, 0.2-mm) were created by mechanically pulverizing sections of 2-mm-thick smooth HDPE GM and extruding the polymer at different thicknesses using a film blowing machine. The 2-mm-thick smooth HDPE GM was also used in the experiments. HDPE GM specimens were exposed to sealed sources of 241 Am and 99 Tc for 1–50 h to simulate the impact of α and β radiation from U and 99 Tc in low-level radioactive waste (LLW) leachate. Standard oxidative induction time (OIT) tests were conducted to determine antioxidant depletion. No change in OIT occurred in the 2-mm-thick HDPE GM after exposure to sealed sources of 241 Am and 99 Tc for 50 h. In much thinner GMs (e.g., 0.04 mm), however, significant antioxidant depletion occurred after exposure most likely due to penetration of α and β particles. Penetration depth of α and β particles and dose deposition in HDPE GMs were estimated with the GEometry ANd Tracking (GEANT4) program. Predictions from GEANT4 show that maximum dose deposition occurs at the surface of the HDPE GM and decreases with depth. A multilayer model is used to estimate antioxidant depletion in HDPE GMs for depth-dependent doses. These estimates suggest that radiation from LLW leachate has an insignificant effect on antioxidant depletion in HDPE GMs due to the low dose deposition (e.g., 2.42 Gy) expected over a 1000-yr service life, even if the level of activity in LLW leachate increases 10x to 100x the level typical of today. [ABSTRACT FROM AUTHOR]

Hydraulic conductivity and swell index tests were conducted on a conventional geosynthetic clay liner (GCL) containing sodium-bentonite (Na-B) using 5, 50, 100, 500, and 1000 mM ammonium acetate (NH 4 OAc) solutions to investigate how NH 4 + accumulation in leachates in bioreactor and recirculation landfills may affect GCLs. Control tests were conducted with deionized (DI) water. Swell index of the Na-B was 27.7 mL/2 g in 5 mM NH 4 + solution and decreased to 5.0 mL/2 g in 1000 mM NH 4 + solution, whereas the swell index of Na-B in DI water was 28.0 mL/2 g. Hydraulic conductivity of the Na-B GCL to 5, 50, and 100 mM NH 4 + was low, ranging from 1.6–5.9 × 10 −11 m/s, which is comparable to the hydraulic conductivity to DI water (2.1 × 10 −11 m/s). Hydraulic conductivities of the Na-B GCL permeated with 500 and 1000 mM NH 4 + solutions were much higher (e.g., 1.6–5.2 × 10 −6 m/s) due to suppression of osmotic swelling. NH 4 + replaced native Na + , K + , Ca 2+ , and Mg 2+ in the exchange complex of the Na-B during permeation with all NH 4 + solutions, with the NH 4 + fraction in the exchange complex increasing from 0.24 to 0.83 as the NH 4 + concentration increased from 5 to 1000 mM. A Na-B GCL specimen permeated with 1000 mM NH 4 + solution to chemical equilibrium was subsequently permeated with DI water. Permeation with the NH 4 + converted the Na-B to “NH 4 -bentonite” with more than 80% of the exchange complex occupied by NH 4 + . Hydraulic conductivity of this GCL specimen decreased from 5.9 × 10 −6 m/s to 2.9 × 10 −11 m/s during permeation with DI water, indicating that “NH 4 -bentonite” can swell and have low hydraulic conductivity, and that the impact of more concentrated NH 4 + solutions on swelling and hydraulic conductivity is reversible. [ABSTRACT FROM AUTHOR]

Influenced by numerous local features, the post-buckling analysis and optimization for hierarchical stiffened shells suffer from heavy computational costs. By smearing the minor stiffeners based on a novel numerical implementation of asymptotic homogenization (NIAH) method, a novel hybrid model for hierarchical stiffened shells is presented. Then, the high prediction accuracy and efficiency of the hybrid model for post-buckling analysis and imperfection sensitivity analysis are validated. Furthermore, a grid-pattern optimization framework of novel hierarchical stiffened shells allowing for imperfection sensitivity is established. The illustrative examples indicate that, the hierarchical stiffened shell with candidate sub-structures is more competitive in load-carrying capacity than that with the fixed grid-pattern, and the presence of imperfections would greatly affect the results of grid-pattern optimizations. [ABSTRACT FROM AUTHOR]

• An efficient buckling analysis and optimization method is proposed for rotationally periodic stiffened shells accelerated by Bloch wave method. • The theory derivation and implementation procedure of Bloch wave method for buckling analysis are presented. • Example results indicate the proposed method achieves high prediction accuracy and efficiency in buckling load and mode. Rotationally periodic stiffened shells have been widely used as load-bearing parts in engineering structures, however, the buckling analysis and optimization of stiffened shells suffer from large computational time owing to the large-scale and complex development tendency of engineering structures. Considering that most of the traditional equivalent buckling analysis methods do not retain the features of stiffeners and cannot capture local buckling, their prediction accuracies in buckling load and mode are not high enough although they can reduce the analysis cost. In this paper, an efficient buckling analysis and optimization method is proposed for rotationally periodic stiffened shells accelerated by Bloch wave method. Firstly, the derivation of Bloch wave boundary conditions for buckling analysis of the substructure is presented, along with the corresponding numerical implementation procedure. Based on the buckling analysis method accelerated by Bloch wave method, the Kriging-based Efficient Global Optimization method is used to improve the optimization efficiency. Then, typical examples are carried out for the buckling analyses of stiffened cylindrical shells with various grid patterns including orthogonal grids, triangle grids, rotated triangle grids, mixed triangle grids and hierarchical orthogonal grids, as well as the integrally stiffened shell with non-straight generatrix. Compared with buckling results from the direct finite element analysis, the proposed method achieves high prediction accuracy in buckling load and remarkable improvement in modelling and analysis efficiency simultaneously. Particularly, the proposed method succeeds in capturing both local buckling mode and global buckling mode. Finally, the optimization design of the integrally stiffened shell with non-straight generatrix is carried out based on the proposed method aiming at maximizing the buckling load. Results indicate that the proposed method can reduce the total optimization time significantly and improve the buckling load by 94.5%, contributing to providing meaningful references for the design large-scale engineering structures. [ABSTRACT FROM AUTHOR]

With regard to future heavy-lift launch vehicles, the buckling analysis and optimization of large-scale stiffened shells by finite element method (FEM) suffer from unbearable computational cost. In spite of the high analysis efficiency, the traditional smeared stiffener method (SSM) is still not accurate enough owing to the assumptions of analytical derivations. In this study, an effective and efficient numerical-based smeared stiffener method (NSSM) is proposed for the buckling analysis of stiffened shells. Firstly, the representative unit cell of stiffened shell is divided, and then it is equivalent using a novel numerical implementation of asymptotic homogenization (NIAH) method. The equivalent stiffness coefficients can be obtained accurately. Then, the buckling load is calculated by means of Rayleigh–Ritz method. Comparing with the prediction results of SSM and FEM, the high prediction accuracy and efficiency of NSSM are observed. Then, the effectiveness of NSSM for different loading conditions and model scales are discussed. Finally, numerical examples illustrate the high prediction accuracy and widespread applicability of NSSM for various grid-patterns, and the advantage of the rotated triangle grid-pattern in load-carrying capacity among various grid-patterns is demonstrated. [ABSTRACT FROM AUTHOR]

As a potential aerospace structural concept, hierarchical stiffened plates under axial compression are characterized by multiple local features, which lead to the buckling analysis and optimization suffering from heavy computational costs, by means of exact Finite Element Method (FEM). Thus, an efficient and simple hybrid framework for the buckling analysis and optimization of hierarchical stiffened plates is presented in this study. Firstly, the skin and minor stiffeners are equivalent to an unstiffened anisotropic plate based on a novel numerical implementation of asymptotic homogenization method (NIAH), which can be easily realized using commercial software as a black box, indicating a strong applicability for rather complicated minor stiffener configurations. Then, the equivalent plate together with major stiffeners can be treated as a hybrid model to be calculated by FEM. Further, a surrogate-based optimization based on this hybrid model is performed. Finally, three illustrative examples are established to demonstrate the effectiveness and simplicity of the proposed framework. [ABSTRACT FROM AUTHOR]

The test facility (TF) is one of the three major facilities of the International Fusion Material Irradiation Facility (IFMIF). Engineering designs of TF main systems and key components have been initiated and developed in the IFMIF EVEDA (Engineering Validation and Engineering Design Activities) phase since 2007. The related work covers the designs of a test cell which is the meeting point of the TF and accelerator facility and lithium facility, a series of test modules for experiments under different irradiation conditions, an access cell to accommodate remote handling systems, four test module handling cells for test module processing and assembling, and test facility ancillary systems for engineering support on energy, media, and control infrastructure. This paper summarizes the principle functions, brief specifications, and the current design status of the above mentioned IFMIF TF systems and key components. [ABSTRACT FROM AUTHOR]

As a widely used non-destructive buckling experimental technique, the vibration correlation technique (VCT) is able to determine the buckling load without reaching the collapse point. Following the experimental procedure, the numerical implementation of VCT can be easily realized. That is to say, the numerical VCT (NVCT) can be used for predicting buckling load. In this paper, the derivation of NVCT formulas is firstly presented for cylindrical shells under axial compression load. Aiming at accelerating the repeated eigenvalue analysis in NVCT, the combined approximation (CA) method is combined with NVCT. Then, the computational procedure of CA-NVCT is provided. Aiming at the verification of the effectiveness of the CA-NVCT, three analysis examples are carried out including variable-stiffness composite cylindrical composite shell, isotropic cylindrical shell and composite cylindrical shell with various types of imperfections. Finally, an optimization design is carried out to improve the buckling load of a composite cylindrical shell against imperfections based on the CA-NVCT. In comparison to results obtained by buckling experiments and typical buckling numerical methods, the high prediction efficiency and accuracy of the CA-NVCT in buckling analysis and optimization are verified. • Numerical VCT (NVCT) formulas are derived for axially loaded cylindrical shells. • Combined approximation method is combined with NVCT to develop CA-NVCT. • Five illustrative examples are carried out for comparison and verification. • The high prediction accuracy and efficiency of the CA-NVCT is verified. [ABSTRACT FROM AUTHOR]

Abstract: The IFMIF (International Fusion Material Irradiation Facility) test cell design has been further developed and optimized based on the existing modular test cell concept. Key features of the current test cell include actively cooled surrounding shielding walls with coverage of internal surfaces with stainless steel liner, independent two layer top shielding plugs for protecting the access cell from neutron and gamma radiation from the test cell, optimized piping and cabling plugs for accommodating pipe and cable penetrations and for minimizing neutron streaming, rearranged lithium quench tank to outside of the test cell, etc. According to preliminary neutronic calculation results, limited access to the quench tank area for maintenance after beam shut-off can be expected with the current arrangement. Maintenance of the lithium inlet and outlet pipes as well as the two beam ducts are also possible by introducing removable shielding plugs which can be removed and replaced in case of failure. [Copyright &y& Elsevier]

• This study was conducted to evaluate the hydraulic performance of GCL overlaps. • Na-B GCLs consisting of different geotextile combinations were tested. • Test were conducted with saline solutions at 20 to 500 kPa confining stress. • The GCL overlaps permeated with saline solutions had horizontal flow. • The horizontal flow through GCL overlaps reduced at higher confining stress. Hydraulic conductivity of the overlap region of two needle-punched sodium bentonite (Na-B) geosynthetic clay liners (GCLs) permeated with CaCl 2 solutions under confining stresses of 20, 100, 250, and 500 kPa were evaluated. One of the GCLs consisted of a uniform layer of Na-B encapsulated between a nonwoven (NW) and a woven (W) geotextile, and the other one consisted of NW geotextiles on both sides. Supplemental bentonite was placed within the overlap region. Experiments were conducted with 10, 20, and 50 mM CaCl 2 solutions representing dilute and aggressive leachates. The results indicate that in most of the scenarios there is a possibility that the flow is not completely vertical (meaning flow passes through the overlap region horizontally). As the confining stress increased, the horizontal flow through the overlap region for GCLs reduced effectively when permeated with deionized water and 10 mM CaCl 2 solution, whereas the reduction of horizontal flow was limited to 20 mM and 50 mM CaCl 2 solutions. [ABSTRACT FROM AUTHOR]

The Covariance Matrix Adaptation Evolution Strategy (CMA-ES) algorithm is one of the most successful continuous black-box optimization algorithms widely used in many fields. However, the algorithm would be computationally unaffordable due to the sharp increase in dimension and complexity of problems. To improve the computational efficiency and global optimizing ability, a competitive variable-fidelity surrogate-assisted CMA-ES (CVFS-CMA-ES) algorithm using data mining techniques is proposed in this paper. In the first data mining of CVFS-CMA-ES, the establishment method of the competitive variable-fidelity model (VFM) based on the fuzzy clustering algorithm is developed, aiming at making full use of high-fidelity information and focusing more on potential areas of design space. In the second data mining of CVFS-CMA-ES, the Lower Confidence Bound (LCB) method is modified by introducing the step size of CMA-ES to control the uncertain term adaptively, and the sample points are screened in each generation of CMA-ES based on the modified LCB method, which can make a balance between exploration and exploitation in the optimization process. The performance of CVFS-CMA-ES is compared with four known black-box optimization algorithms. Firstly, ten numerical examples of 10-dimensional and 30-dimensional benchmark functions are carried out, respectively. Moreover, a 20-dimensional engineering example of the aerospace variable-stiffness composite shell under combined loadings is studied in detail. Results of benchmark functions and engineering examples verify the high efficiency, robustness and high global optimizing ability of the proposed CVFS-CMA-ES in comparison to other algorithms. [ABSTRACT FROM AUTHOR]

Abstract: The relative optical density (ROD) method provides a means to measure three-dimensional information about soot aggregates from two-dimensional transmission electron microscopy (TEM) micrographs of soot. The method is dependent on accurate calibration of the relationship between the measured soot ROD in TEM images and the actual soot thickness perpendicular to the imaging plane. A novel calibration method based on the comparison between probability distributions of measured soot ROD in TEM images and that of virtual soot thickness of numerically simulated soot is introduced. Soot aggregates of various prescribed fractal structure parameters were numerically generated using a tunable cluster–cluster aggregation model. The probability histograms of the local soot thickness for the simulated soot aggregates and ROD of the TEM images of flame generated soot aggregates were found to be quite similar and were used as a basis to establish a quantitative relationship between ROD and the local soot thickness. The calibration constant obtained from the analysis of the simulated soot was found to be insensitive to the fractal structure parameters over a wide range. The calibrated ROD method is successfully applied to the morphology analysis of soot aggregates generated in an atmospheric laminar co-flow ethylene–air diffusion flame based on thermophoretic sampling (TS) and TEM analysis techniques. With the ROD method, an overlap coefficient is introduced to identify and eliminate non-soot-aggregate structures and the selection of a cut-off overlap coefficient was found to have little influence on the final results over a relatively wide range. ROD is independent of empirical constants and human judgments and has been found to be an accurate and reliable TEM image analysis method for studying the morphology of soot aggregates. [Copyright &y& Elsevier]

Abstract: The morphology of soot aggregates formed in a laminar coflow ethylene diffusion flame was studied by using the techniques of extractive thermophoretic sampling and subsequent image analysis of transmission electron microscopy (TEM) micrographs. A new image-analysis method, the relative optical density (ROD) method, is described in this paper and was used to obtain the morphological properties of soot aggregates. With this new method, the number of primary particles in each individual aggregate is determined by not only the projected area but also the optical density distribution within the projected area of the aggregate. As such, it attempts to address the three-dimensional nature of the aggregates. This method also calculates an overlap coefficient for each object in the TEM image that can be used to identify non-soot-aggregate structures. Unlike the conventional statistical method for fractal-like aggregate structure determination, ROD is independent of empirical constants based on correlations or numerical simulations. Using this new method, the parameters describing the morphology of soot aggregates generated in a laminar coflow ethylene diffusion flame, such as the geometric mean of the number of primary particles per aggregate, the fractal dimension, and the probability distribution function of aggregate size, were determined. ROD was found to be an accurate and reliable TEM image analysis method for studying the morphology of soot aggregates. [Copyright &y& Elsevier]

This paper provides a novel establishment method of the variable-fidelity surrogate model (VFSM) driven by transfer learning for shell buckling prediction problems such as buckling prediction of variable-stiffness composite shells, aiming at achieving higher prediction accuracy than the traditional VFSM constructed by the bridge function. The transfer learning based variable-fidelity surrogate model (TL-VFSM) includes two steps. In the first step, low-fidelity model and high-fidelity model points are calculated and collected into the source dataset and target dataset for transfer learning, respectively. Based on the source dataset, a Deep Neural Network (DNN) model is initialized. Then, the hyperparameter tuning of the DNN model is carried out based on Bayesian Optimization (BO), which uses the target dataset as the validation set. After the hyperparameter pre-tuning, the pre-trained DNN model is obtained. In the second step, early layers of the pre-trained DNN model are remained, while the last layer is replaced. Then, another hyperparameter tuning is carried out to fine-tune the pre-trained DNN model using BO. After that, the transfer learning is finished and the re-trained DNN model is obtained. Through above two steps, the TL-VFSM is constructed. The effectiveness and efficiency of the proposed TL-VFSM are verified by three test functions and two engineering examples of variable-stiffness composite shells and hierarchical stiffened shells. Example results indicate that, using the same computational cost, the proposed TL-VFSM achieves higher prediction accuracy than traditional VFSMs constructed by the bridge function, and it can be a potential method for time-consuming buckling prediction problems with multi-source data or variable fidelities. [ABSTRACT FROM AUTHOR]

[Display omitted] • Lycopene increases the bone mineral density of diabetic rats. • Lycopene prevents diabetic induced bone loss via anti-inflammatory, anti-oxidation, and regulating abnormal bone turnover. • This study provides a basis for the application of lycopene in the prevention of diabetic osteoporosis. Diabetic osteoporosis (DOP) is one of the complications of diabetes, with high morbidity, and high disability rate. Here, we established a diabetic rat model and administered lycopene to observe its effect on DOP. Our results showed that ten weeks lycopene treatment lowered blood glucose, improved diabetic induced polydipsia, overeating and body weight loss. Lycopene treatment also enhanced bone mineral density, restored bone mechanical and bone Micro-CT parameters of diabetic rats. Subsequently, lycopene decreased serum inflammatory cytokines levels and increased serum anti-oxidant indicators levels. Moreover, lycopene reduced the number of bone marrow adipocytes, and osteoclasts numbers of diabetic rats. The serum bone turnover markers levels were down-regulated after lycopene treatment. Meanwhile, the bone and serum OPG, RUNX 2 expression levels were up-regulated by lycopene in diabetic rats, and the OPG/RANKL ratio was also up-regulated. This study showed that lycopene could ameliorate diabetic induced bone loss via anti-inflammatory, anti-oxidation, and increasing OPG/RANKL ratio in diabetic rats. Lycopene could be used for nutritional intervention in patients with diabetic osteoporosis. [ABSTRACT FROM AUTHOR]

Vibration correlation technique (VCT) is an effective non-destructive buckling experimental technique for shell structures. In this study, VCT is studied from the point-of-view of being a buckling load numerical prediction method by numerically simulating the experimental procedure of VCT. Firstly, the formulas of VCT are introduced for axially loaded cylindrical shells and conical shells under the clamped–clamped boundary condition. According to the VCT formulas, the numerical procedure of VCT is provided. In order to accelerate the repeated eigenvalue analysis of VCT, the proper orthogonal decomposition (POD) method is integrated into VCT, and the POD-VCT is developed. Extensive examples are presented to verify the effectiveness of the proposed method, including unstiffened cylindrical shell with real measured imperfection, unstiffened conical shell with single perturbation load imperfection, composite cylindrical shell with eigenmode imperfection, and hierarchical stiffened cylindrical shell with combined imperfection. In comparison to buckling test results, high-fidelity explicit dynamic method and VCT method, the high prediction accuracy and efficiency of the proposed POD-VCT are fully demonstrated. Additionally, example results indicate the strong applicability of the proposed POD-VCT for various types of structural configurations, materials and imperfections. Above all, the POD-VCT is verified to be a fast buckling load numerical prediction method for imperfect shells. [ABSTRACT FROM AUTHOR]

Due to the high specific strength and stiffness, thin-walled shells are widely used in aerospace engineering structures. However, along with the increase of the structure size or the structure hierarchy, the computational cost of the post-buckling analysis of thin-walled shells would increase sharply and then the imperfection sensitivity analysis would become time-consuming. In this study, an accelerated Koiter method is proposed to improve the efficiency of post-buckling analysis and imperfection sensitivity analysis of thin-walled shells under axial compression. In the framework of the accelerated Koiter method, a single mode Koiter method considering pre-buckling nonlinear behavior is used to reduce the computational time of repeated imperfection analysis, which can accurately predict the effect of the small amplitude imperfection. Furthermore, in order to obtain the expanded point of Koiter method, a Combined Approximation (CA)-based iterative eigenvalue algorithm is constructed to obtain the pre-buckling state in the neighborhood of the bifurcation point and reduce computational cost by the reasonable step length prediction. Finally, the efficiency and accuracy of the proposed method are demonstrated by means of four illustrative examples, including the composite cylindrical shell, the isotropic cylindrical shell, the isotropic conical shell and the hierarchical stiffened cylindrical shell under axial compression. • Combined Approximation (CA) method is used to reduce the computational time of consistently eigenvalue problem. • The CA-based iterative eigenvalue algorithm is constructed to obtain the pre-buckling state near the buckling load. • The accelerated Koiter method is developed for fast imperfection sensitivity analysis of thin-walled shells. • Four representative examples are carried out to verify the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

Stiffened shells are widely used in aerospace structures such as launch vehicles and aircraft wings. This paper presents a novel two-scale topology optimization method to design the innovative grid-stiffened pattern for maximizing the critical buckling load of thin-walled cylindrical shells. On the micro-scale, the asymptotic homogenization method is employed to calculate the general stiffness coefficients of the cell. On the macro-scale, the maximum critical buckling load is set as the objective to drive the topology optimization on the micro-scale. Besides, the repeated eigenvalues are considered both in the sensitivity analysis of buckling loads and the optimization solver with a sub-problem based on the Method of Moving Asymptotes (MMA). Through the optimization, we can obtain the optimal configuration of the grid-stiffened cell. In this paper, an illustrative example of the grid-stiffened cylindrical shell for maximizing the critical buckling load is carried out to validate the effectiveness of the proposed optimization method. In comparison to the optimal orthogrid shell, the critical buckling load with the optimal pattern obtained by the proposed optimization method have a dramatically increase of 21.7%. It can be concluded that the proposed method has huge potential to design the configuration of the grid-stiffened cell of cylindrical shells. • A novel two-scale buckling topology optimization framework is established to design the innovative grid-stiffened pattern. • The repeated eigenvalue problem has been taken into consideration with a sub-problem based the Method of Moving Asymptotes. • In comparison to the optimal orthogrid shell, the optimal result obtained achieves a significantly increase of 21.7%. [ABSTRACT FROM AUTHOR]

In this paper, a concurrent multi-scale optimization framework is established for hybrid composite plates and shells, where fiber volume, fiber orientation and stacking sequence can be optimized simultaneously. Firstly, a finite element model of shell structure that contains patches is established. Then, the candidate material set of hybrid composites is calculated and assembled by different combinations of fiber volume, fiber orientation and stacking sequence at the material and laminate scales. Furthermore, the Discrete Material Optimization (DMO) method is employed to perform the concurrent multi-scale optimization. Two illustrative examples are used to verify the effectiveness of the proposed optimization framework, including a simple example of a hybrid composite plate and a complex engineering example of a double serpentine nozzle. In comparison to optimal results by the traditional constant-stiffness design method, the optimal results of the proposed framework achieve significant 19.8% and 14.0% improvements in the fundamental frequency under the constraint of material cost, respectively. It can be concluded that the proposed concurrent multi-scale optimization framework has huge potential in adaptive stiffness tailoring for hybrid composite plates and shells with complex multi-scale design variables, which can make full use of hybrid composite materials to improve the structural performance against vibration while maintaining the low material cost. [ABSTRACT FROM AUTHOR]

• Bentonite-polymer composite geosynthetic clay liners (BPC GCLs) may contain water-soluble (linear) or water-insoluble (crosslinked) polymers. • Generally, BPC GCLs with high initial polymer loading had relatively lower hydraulic conductivity than those with low initial polymer loading. • For BPC GCLs containing linear polymer, polymer elution occurred when permeated with water or leachate. • There was no correlation between the percentage of polymer retained and final hydraulic conductivity of the BPC GCLs containing linear polymer. A study was conducted to evaluate the hydraulic conductivity (k) of six bentonite-polymer composite (BPC) geosynthetic clay liners (GCLs) using five synthetic municipal solid waste incineration ash (IA) leachates with ionic strength (I) ranging from 174 to1978 mM. The BPC GCLs contained a dry blend of bentonite and proprietary polymers and had polymer loading ranging from 0.5 to 5.5%. The polymers used in the BPC GCLs were classified as linear polymer (LP) or crosslinked polymer (CP) based on the swelling characteristics of specimens extracted from the GCLs. Comparable hydraulic conductivity tests were also performed on two conventional bentonite (CB) GCLs as controls. The BPC GCLs had k of 2.6 – 6.7 × 10-11 m/s when permeated with IA leachate with I = 174 mM, whereas the CB GCLs had k > 5.0 × 10-8 m/s when permeated with the same leachate. However, k of the BPC GCLs ranged from the order of 10-10 to 10-7 m/s when permeated with IA leachates with I > 600 mM. BPC GCLs with high polymer loading generally had lower k compared to those with lower polymer loading when permeated with the same IA leachate, regardless of the polymer type. Polymer eluted from the BPC GCLs containing LP during permeation with DI water or IA leachate. Unlike CPs, LPs are water-soluble, therefore, they seem to easily migrate during permeation. There was no correlation between the percentage of polymer retained and the final hydraulic conductivity of the LPB GCLs used in this study. [ABSTRACT FROM AUTHOR]

Experiments were conducted to investigate how specimen preparation (crushing and sieving) affects the swell index (SI) of bentonite-polymer (B–P) composites and the relationship between SI and hydraulic conductivity of B–P GCLs. Seven B–P and one Na–B GCLs were used in this study. Tests were conducted using DI water and synthetic municipal solid waste incineration ash leachates. Specimens were prepared using the ASTM D5890 and two alternative methods prior to SI testing. For both Na–B and B–P composites, <100% of the specimen passed through the #100 sieve regardless of the amount of crushing performed using a mortar and pestle. SIs and loss on ignitions (LOI) of the portion of the B–P composites passing #100 sieve were comparable to the Na–B, whereas the B–P specimen retained on #100 sieve had very high SIs and LOIs. These observations indicate that crushing and sieving of the B–P composites lead to segregation of polymer. A stronger correlation (R2 = 0.90) was observed between SI and hydraulic conductivity, only when SI tests were conducted with B–P without any crushing and sieving, suggesting that SI tests should conduct with B–P composites retrieved from the GCLs without sieving to provide a better prediction of hydraulic compatibility. • There are limitations in the ASTM D5890 specimen preparation procedure. • < 100% of the Na–B and B–P specimens passed through the #100 sieve after crushing. • The portion of the B–P specimens retained on the #100 sieve mainly comprised polymer. • SIs of the uncrushed B–P specimens were higher than that of the ASTM D5890 specimens. • SI of uncrushed B–P specimens correlates well with hydraulic conductivity of B–P GCLs. [ABSTRACT FROM AUTHOR]

A concept of hybrid-stiffness stiffened shell is proposed based on sub-panel elements to achieve a simultaneous buckling pattern, which can provide enhanced design flexibility to fully explore the load-carrying capacity of structures. Then, a novel hybrid model is established to improve the computational efficiency of post-buckling analysis for stiffened shells, where the Numerical Implementation of Asymptotic Homogenization Method is utilized to smear out the stiffeners. On this basis, an integrated optimization framework of sub-panel configurations and weld lands for stiffened shells is presented. Illustrative examples with single and multiple cutouts demonstrate the effectiveness of the proposed framework based on the concept of hybrid-stiffness stiffened shell. [ABSTRACT FROM AUTHOR]