Sandwich structures have been widely used in marine applications due to their properties such as high weight/strength ratio. In contrast, the failure mechanism of these structures has a significant ...effect on the local and global dynamic responses. In the present study, sandwich panels with polymeric skins and PVC foam cores subjected to slamming impact are investigated experimentally and numerically. A high speed shock machine is used to keep approximately a constant velocity during the impact event. The dynamic resistance was analysed in terms of hydrodynamic loads, dynamic deformation and failure mechanisms for different impact velocities. On the other hand, the slamming model was implemented in Abaqus/Explicit software based on Coupled Eulerian Lagrangian model approach. In addition, different damage modes are incorporated in the numerical model, including the intralaminar, debonding in skin/core interface, and core shear to cover all possible damage modes throughout structures. Two failure criteria (Hashin criteria for the laminate composite and Christensen criteria for the core in sandwich structure) are defined and integrated into VUMAT sub-routine. In addition, the cohesive zone model is used to predict the debonding skin/core. A good agreement in both hydrodynamic loads and damage prediction were found between numerical and experimental results.
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•UHMWPE Tensylon is successfully thermaly spraying coated by 200 µm thick Alumina by using an intermediate Zn layer.•LASAT method has been successfully experienced to assess the ...coating adhesion at high strain rates.•The obtained hybridized structure reduces the rear face velocity under shock by more than half, very effective for impact resilience.
Composite materials are increasingly inescapable in engineered systems in various industrial fields, given their high strength to weight ratio for increasing autonomy, reducing energy consumption and enhancing mechanical strength of high added value products. However, their out-of-plane resistance could be improved by multimaterial assembly for structural hybridization. The purpose of this study is to explore the possibility of upgrading the shock resistance of UHMWPE Tensylon® by alumina coating. Thermal spraying was used for alumina deposition on UHMWPE and bond strength assessment of the obtained assembly was performed by Laser Adhesion Test (LASAT). During experiments, free surface velocities of specimens were recorded by the use of Photonic Doppler Velocimetry (PDV) allowing relevant observations complementary to optical observations. From the PDV analysis and cross section observations by microscopy, a diagnostic of the decohesion of the interface is proposed. The study shows the possibility of assembling alumina on UHMWPE to strengthen its shock resistance and makes now possible the improvement of the study of deposition process parameters thanks to LASAT evaluations.
The 1,3-dipolar cycloaddition reaction of benzaldehyde with diazomethane is investigated, in gas phase and in diverse polar solvents, using the molecular electron density theory through density ...functional theory calculations at the B3LYP(+D3)/6-31G(d) level. Analysis of the reaction pathway reveals that this reaction takes place along a concerted but asynchronous mechanism. Computations show that the acetophenone product is kinetically and thermodynamically more favored than 2-phenylacetaldehyde product in agreement with experimental outcomes. The favored cyclization mode and the observed regioselectivity of this cycloaddition are rationalized by both activation energy calculations, frontier molecular orbital analysis and reactivity indices. Also, polar solvents effect favors the reaction. Furthermore, we performed electron localization function (ELF) topological analysis. The ELF topological analysis of diazomethane indicates that this reactant presents an allenic
pseudoradical
electronic structure.
Figure: Composite panels under slamming impact: panels and Servo-test machine.
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•Dynamic structural response of composite structures under slamming impact.•Experimental investigation ...on the slamming impact water of composite wedge.•Damage progressive in composites under slamming impact is presented.•Assessment to meet the specific requirements of marine vessels.
Generally, when marine vessels encounter the water surface on entry and subsequently re-enter the water at high speed, this can subject the bottom section of the vessels to high hydrodynamic loads, especially over very short durations. This phenomenon generates high hydrodynamic loads, which can cause a catastrophic failure in the structure. In contrast, the interaction between deformable structures and free water surface can be modified the fluid flow and changed the estimated hydrodynamic loads comparing with rigid body, due to appearance of hydroelastic effects. These effects are considered active challenge areas in structural ship design. This work presents an experimental study of the water impact for composite laminate wedge at different constant entry velocities. The aim of this study is to investigate the dynamic structural response of panels and predicts the hydrodynamic loads to meet the specific requirements of marine vessels. In order to better describe hydroelastic influence, two composite panels with different thicknesses namely 8 mm and 13 mm are subjected under constant impact velocities of 4, 6 and 8 m/s with the deadrise angle of 10°. The obtained experimental results were indicated that more flexible panels had a higher peak force and significant dynamic noise compared with higher stiffness panels. In addition, the maximum deformation occurred in the centre and close to the chine edge of the panel due to changes in local velocity and local deadrise angle. For this reason, special attention requires in both design phase and operation phase.
•Experimental study and the help of numerical methods the structural behavior and the effect of the flexibility of composite panels on hydrodynamic loads and the dynamic deformation response.•A high ...velocity shock machine was used to perform a constant velocity during water entry on composite panels.•The numerical model was implemented using Coupled Eulerian–Lagrangian (CEL) approach for modeling of a three dimensional slamming impact.•The numerical results give a good correlation with the executed experimental results in both hydrodynamic force and deformation response.•Results of this study can be assisting vessel designers to understand the influence of the elastic structural behavior on hydrodynamic loads.
The interaction between deformable structures and free water surfaces can modify the fluid flow and change the estimated hydrodynamic loads in relation to rigid bodies, due to the appearance of hydroelastic effects. The flexibility and damage failure modes in composite materials introduce additional complexity for predicting hydrodynamic loads when interactive with water. This is considered to be a key challenge when using these materials in marine applications. Therefore, particular attention should be paid to this fact in the design phase and over their period of use. The aim of this work is to study the structural behavior and the effect of the flexibility of composite panels on hydrodynamic loads and the dynamic deformation response experimentally and numerically. To study these effects, composite panels with two different rigidities were subjected to various impact velocities and investigated. It should be noted that all the panels tested at a10° deadrise angle. A high velocity shock machine was used to maintain constant velocity during water entry at impact velocities of 4 m/s, 6 m/s, 8 m/s and 10 m/s. The general analysis of experimental results indicated that compared to the higher stiffness panels, the more flexible panel has a higher peak force as velocity increases. This has been attributed to the change in local velocity and local deadrise angle along the water-panel interface. The numerical model was implemented based on the Coupled Eulerian–Lagrangian Model (CEL) built-in Abaqus/Explicit finite element software. The numerical results showed a good agreement compared with experimental data for both the hydrodynamic force and the deformation response. These quantitative structural-loading data can provide a clear guide for maritime ship design.
Figure: Water-entry problem: Experimental shock machine and numerical model. Display omitted
In the maritime environment slamming is a phenomenon known as short duration impact of water on a floating or sailing structure. Slamming loads are local and could induce very high local stresses. ...This paper reports a series of impact test results and investigate the slamming loads and pressures acting on a square based pyramid. In this study the slamming tests have been conducted at constant velocity impact with a hydraulic high speed shock machine. This specific experimental equipment avoids the deceleration of the structure observed usually during water entry with drop tests. Three velocities of the rigid pyramid have been used (10, 13 and 15ms−1). Time-histories of local pressures, accelerations and slamming loads were successfully measured. The relationship between the pressure magnitude and the impact velocity is obtained and the spatial distribution of pressures on pyramid sides is characterized. The impact velocity was found to have a negligible influence in predicting the maximum pressure coefficient.
•Variation of quality and maturity index was influenced by the phenol compounds, ripeness or their interaction according to grapes varieties.•The different quality parameters and content in ...grapevines are largely depended upon grape genotypes.•The timing of harvest (maturity stages) had a marked effect on grape maturity.•The phenol compounds, the rapport of sugar/acidity remain the principals’ attributes determinant the ripeness of grapes.
The time of the maturity and the picking of the grapes remains one of the most important parameters to obtain high grapes or wine quality. Harvest decision is taken traditionally by viticulturists only after sugar, acids, °Brix and pH of grapes overlooking the phenol maturity despite they are valuable parameters in determining the quality of table grapes. In this work technological maturity (sugar/acidity) and phenolic maturities were investigated during grapes ripening varieties. Three of them are allochthonous (triploids: Superior, Early sweet and Flam) while two are autochthonous (diploids: Abbou and Adari). The varieties samples were investigated by 12 parameters which three are morphological: weight, density (ρ) and the form coefficient (Cs), while 10 other are physicochemical related to the quality proprieties: °brix, titratable acidity, pH, juice content, water content, capacity of rehydratation, phenols, flavonoids and tannins compounds. A PCA analyze to classify grapes ripeness according maturities factors were performed. The descriptive quality panels showed that both maturities of the attributes grapes were different among varieties of samples (P ≤ 0.05). The phenol compounds decreased for the triploid varieties during ripeness whereas they increase in the diploids. The morphological proprieties: weight and density increase in parallel to the °brix, juice content accompanied in the other hand by the acids content. The statistics established that the variation of quality factors generally and maturity index (°brix/acidity) especially was influenced by the phenol compounds, stage of ripeness or their interaction according to grape varieties. Thus revealed that the phenol compounds, the ratio of sugar/acidity remain the principal attributes determinant the ripeness of grapes.
Nitric oxide (NO), a small free radical molecule, turned out to be pervasive in biology and was shown to have a substantial influence on a range of biological activities, including cell growth and ...apoptosis. This molecule is involved in signaling and affects a number of physiologic functions. In recent decades, several processes related to cancer, such as angiogenesis, programmed cell death, infiltration, cell cycle progression, and metastasis, have been linked with nitric oxide. In addition, other parallel work showed that NO also has the potential to operate as an anti-cancer agent. As a result, it has gained attention in cancer-related therapeutics. The nitric oxide synthase enzyme family (NOS) is required for the biosynthesis of nitric oxide. It is becoming increasingly popular to develop NO-releasing materials as strong tumoricidal therapies that can deliver sustained high concentrations of nitric oxide to tumor sites. In this paper, we developed NO-releasing materials based on sodium alginate hydrogel. In this regard, alginate hydrogel discs were modified by adsorbing layers of polyethyleneimine and iNOS-oxygenase. These NO-releasing hydrogel discs were prepared using the layer-by-layer film building technique. The iNOS-oxygenase is adsorbed on the positively charged polyethyleneimine (PEI) matrix layer, which was formed on a negatively charged sodium alginate hydrogel. We show that nitric oxide is produced by enzymes contained within the hydrogel material when it is exposed to a solution containing all the components necessary for the NOS reaction. The electrostatic chemical adsorption of the layer-by-layer process was confirmed by FTIR measurements as well as scanning electron microscopy. We then tested the biocompatibility of the resulting modified sodium alginate hydrogel discs. We showed that this NOS-PEI-modified hydrogel is overall compatible with cell growth. We characterized the NOS/hydrogel films and examined their functional features in terms of NO release profiles. However, during the first 24 h of activity, these films show an increase in NO release flux, followed by a gradual drop and then a period of stable NO release. These findings show the inherent potential of using this system as a platform for NO-driven modulation of biological functions, including carcinogenesis.
•BBFEM is extended to solve elastic wave problems.•Analytical rules are used to set up the local FE matrices for affine triangular elements.•The tensorial construction of Bernstein polynomials is ...exploited via sum factorisation for curved triangular elements.•The p BBFEM is more effective in coping with the pollution effect and resolving high order evanescent P and S wave modes.•Non uniform p refinement reduces the computational cost and enhances accuracy.
This work presents a high-order Bernstein-Bézier finite element (FE) discretisation to accurately solve time harmonic elastic wave problems on unstructured triangular mesh grids. Although high-order FEs possess many advantages over standard FEs, the computational cost of matrix assembly is a major issue in high-order computations. A key ingredient to address this drawback is to resort to low complexity procedures in building the local high order FE matrices. This is achieved in this work by exploiting the tensorial property of Bernstein polynomials and applying the sum factorisation method for curved elements. An efficient implementation of the analytical rules for affine elements is also proposed. Furthermore, element-level static condensation of the interior degrees of freedom is performed to reduce the memory requirements. Additionally, the applicability of the method with a variable polynomial order, based on a simple a priori indicator, is investigated.
The computational complexities of sum factorisation, analytical rules and standard quadrature are first evaluated, in terms of the CPU time against the polynomial order. The analysis shows that the achieved numerical complexities compare favourably to those expected theoretically. A significant runtime saving is also obtained by using analytical rules and sum factorisation. The performance of the Bernstein-Bézier FEs is then assessed on various benchmark tests, over a wide range of frequencies. Results from the elastic wave scattering problem demonstrate the effectiveness of this method in coping with the pollution error, and its accuracy in resolving high order evanescent wave modes. Additionally, a wave transmission problem with high wave speeds contrast and a curved interior interface is considered, where a simple a priori indicator is proposed to assign the variable polynomial order. The study provides evidence of the great benefit of a non uniform p-refinement in reducing the computational cost and enhancing accuracy.
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