A Two-Dimensional Eight-Node Quadrilateral Inverse Element for Shape Sensing and Structural Health Monitoring.

The inverse finite element method (iFEM) is a powerful tool for shape sensing and structural health monitoring and has several advantages with respect to some other existing approaches. In this study, a two-dimensional eight-node quadrilateral inverse finite element formulation is presented. The element is suitable for thin structures under in-plane loading conditions. To validate the accuracy and demonstrate the capability of the inverse element, four different numerical cases are considered for different loading and boundary conditions. iFEM analysis results are compared with regular finite element analysis results as the reference solution and very good agreement is observed between the two solutions, demonstrating the capability of the iFEM approach.

Appraisal of surface-groundwater anthropogenic indicators and associated human health risk in El Sharqia Governorate, Egypt.

The aim of this study was to integrate hydrogeochemistry with a multivariate statistical approach to understand the various processes that control the evolution/contamination of water resources in El Sharqia Governorate, Egypt with a particular emphasis on direct/indirect risks to human health. To achieve this, a representative collection of 21 groundwater and 35 drainage samples was taken and examined for physical, chemical, and trace element measurements. Results indicated that in shallow groundwater and drainage water samples, the relative abundance of major cations is Na+ > Mg2+ > Ca2+ > K+, and for anions it is HCO3- > Cl- > SO42- (on a molar basis). Natural processes involving the dissolution/precipitation of some minerals and other processes including leaching of solid waste, overuse of agricultural fertilizers application, and high loads of discharged sewage water are responsible for the evolution of water resources in El Sharqia Governorate. Ammonia, nitrate, biological oxygen demand (BOD), phosphate, turbidity, iron, manganese, lead, and aluminum concentrations were found to be higher than the limits set by internatio2nal drinking water regulations. The health risk index (HRI) values for children were found to be higher than those for adults when the water resources are used for drinking purposes, which poses a risk to human health.

Integration of groundwater vulnerability with contaminants transport modeling in unsaturated zone, case study El-Sharqia, Egypt.

Nowadays, irrigation uses large amount of marginal wastewater due to continuous decline in fresh water supply. As a consequence, using this wastewater for different purposes can cause some adverse environmental impacts. Anthropogenic activities such as septic tanks, sewage ponds, and polluted drains have large influence on deterioration of shallow groundwater aquifers. So, construction of many wastewater treatment plants in these areas is mandatory to control and mitigate this deterioration. Groundwater vulnerability assessment maps and contamination simulation in unsaturated zone can be beneficial in understanding contaminants pathways and groundwater quality evolution. This work is mainly focused on aquifer vulnerability assessment to pollution and the role of vadose zone in attenuation of contaminants transport through it prior to groundwater seepage. Therefore, about 56 drainage and groundwater samples were collected and analyzed for potentially toxic elements. The most vulnerable sector was determined using GOD method revealing that central parts of the study area are the most threatened zones with some scattered sporadic zone of sensitivity to pollution and this was verified through the zonation of Pb, Fe, and Mn spatial concentrations. The leakage of these elements through the unsaturated zone was further simulated using HYDRUS-1D model for the next 10-year period to determine the extent of the pollution plumes and maximum concentration of these elements that percolate to the groundwater directly. The concentration of Fe, Pb, and Mn at the end of the simulation reached low concentrations at the bottom layer of the unsaturated zone.

Two-dimensional finite-difference time-domain formulation for sound propagation in a temperature-dependent elastomer-fluid medium.

This study focuses on the two-dimensional (2-D) finite-difference time-domain (FDTD) formulations to investigate the acoustic wave propagation in elastomers contained in a fluid region under different thermal conditions. The developed FDTD formulation is based on a direct solution of the time-domain wave equation and the Havriliak-Negami (H-N) dynamic mechanical response of the elastomers. The H-N representation, including double fractional derivative operators, can be accurately transferred from the frequency-domain to the time-domain by using Riemann-Liouville theory and the Grunwald-Letnikov operator for fractional derivative approximations. Since the Williams-Landel-Ferry shift function is related to the relaxation time for different thermal conditions, the proposed scheme represents a simple and accurate prediction of acoustic wave propagation for varying thermal conditions. The pulse-wave propagation in a viscous fluid field is simulated by investigating the Navier-Stokes equations. The acoustic properties of different elastomers in a variety of temperatures are obtained by means of the proposed FDTD formulation and validated by a good agreement with the experimental data over a wide frequency range. Additionally, the 2-D examples relevant to wave propagation in different elastomers contained in a fluid field are implemented. The proposed FDTD formulation can be used to predict 2-D acoustic wave propagation in different thermal conditions accurately.

Mechanical and acoustic performance prediction model for elastomers in different environmental conditions.

This study focuses on the constitutive model, including temperature and pressure effects, to investigate the dynamic, mechanical, and acoustic properties of elastomers in the frequency domain under different underwater conditions. The developed constitutive relation is based on the Havriliak-Negami (H-N) model by implementing experimental Young's modulus data and using the Williams-Landel-Ferry (WLF) shift function for relaxation time calculation. The H-N model accurately captures the dynamic mechanical modulus for a wide range of frequencies for constant temperature and pressure based on measured dynamic mechanical thermal analysis data. Since the WLF shift function is related with the relaxation time for different temperatures and pressures, the proposed model represents a simple and accurate prediction of the dynamic modulus for varying external conditions. The relationship between Young's modulus and the acoustic properties of the rubber structure can be established by investigating the hydro-wave propagation process. The predictions from the proposed model are verified by comparing with mechanical and acoustic experimental data at different temperatures and pressures. Additionally, the parametric study is conducted to investigate the effect of H-N parameters on mechanical and acoustic properties of elastomer materials. The proposed model can be used to predict the mechanical and acoustic properties in different environmental conditions accurately.