Computer Simulation Research Articles

Hydraulic investigation of flows at high-head overflow spillway with multiple aerators: a physical and numerical study of Mohmand Dam, Pakistan

ABSTRACT A spillway is the essential part of the dam body, which releases surplus flows. At higher floods, the spillway operates at high heads, which results in high flow velocities along the chute and may cause negative pressures and cavitation. Therefore, to minimize such issues, aerators are provided along the spillway's chutes. This study aims to analyze the performance of the high-head overflow spillway of Mohmand Dam, Pakistan, having a steep chute of 32° with multiple aerators. Based on Froude's law of similitude, the physical model study was carried out at Irrigation Research Institute, Nandipur, on a scale of 1:60, while FLOW-3D numerical models were used to compare different hydraulic parameters, i.e., flow depth, velocity and pressure. The numerical models were validated with the results of a physical model, which were found in an acceptable range (i.e., 4.93%), and the hydraulic performance of two aerators was evaluated at different discharges. The models indicated negative pressures inside the aerator cavity, which allowed the suction of air to the lower nappe. The maximum air entrainment at the first aerator was about 8.5%. The results also showed that air entrainment to the lower nappe decreased when discharge was increased, whereas the maximum air detrainment reached 11.3% downstream of the second aerator.

On the uncertainty in numerical modeling of wireless communication devices operating at frequencies of 900 MHz, 1800 MHz, and 28 GHz.

Some of the difficulties in numerical modeling of wireless communication devices for dosimetric evaluations arise from, e.g. incomplete documentation available for the numerical model, such as missing information on dielectric materials or the antenna matching circuitry. This study investigates the impact of these difficulties on the dosimetric results, such as the peak spatial average specific absorption rate at 900 and 1800MHz and the peak spatial average power density at 28GHz. The impact of dielectric losses, detuning, and mesh resolution is quantified using different generic and Computer Aided Design (CAD) based models of wireless transmitters. The findings show that the uncertainties of the numerical results due to detuning and mesh resolution can be reduced by normalization to the antenna feedpoint power instead of the feedpoint current. Uncertainties due to variations in dielectric losses can largely be compensated by normalization to the radiated power.

Advanced method for estimating the volumetric intensity along tunnels using ANN

ABSTRACT Simulating realistic scenarios with numerical models often demands substantial computational resources, which can be excessively time-consuming. In complex Discrete Fracture Network (DFN) simulations where mutual influence among fracture parameters is crucial, efficient Artificial Intelligence (AI) algorithms offer a promising solution. This study focuses on the Monte Seco tunnel in Brazil, employing Artificial Neural Networks (ANN) with the Levenberg-Marquardt Algorithm (ANN-LM) to estimate Volumetric discontinuity intensity (P32). Comparative analysis with traditional DFN-based methods reveals superior predictive performance of the ANN model over Multiple Linear Regression (MLR). MATLAB was utilized for implementation, considering the interdependence of geometric parameters across fracture sets to estimate P32 values. Sensitivity analysis identified correlations between F1 parameters (density and trace length) and P32 estimates for F2, aiding in predicting potential tunnel instability. A Graphical User Interface (GUI) was developed to streamline calculations, replacing cumbersome spreadsheet methods.

Integrated monitoring and prediction of thermal discharge from nuclear power plants using satellite, UAV, and numerical simulation.

Global nuclear power is surging ahead in its quest for global carbon neutrality, eyeing an anticipated installed capacity of 436 GW for coastal nuclear power plants by 2040. As these plants operate, they emit substantial amounts of warm water into the ocean, known as thermal discharge, to regulate the temperature of their nuclear reactors. This discharge has the potential to elevate the temperature of the surrounding seawater, potentially influencing the marine ecosystem in the discharge vicinity. Therefore, our study area is on the Qinshan and Jinqimen Nuclear Power Plants in China, employing a blend of Landsat 8/9, and unmanned aerial vehicle (UAV) imagery to gather sea surface temperature (SST) data. In situ measurements validate the temperature data procured through remote sensing. Leveraging these SST observations alongside hydrodynamic and meteorological data from field measurements, we input them into the MIKE 3 model to prognosticate the three-dimensional (3D) spatial distribution and temperature elevation resulting from thermal discharge. The findings reveal that (1) satellite remote sensing can instantly acquire the horizontal distribution of thermal discharge, but with a spatial resolution much lower than that of UAV. The spatial resolution of UAV is higher, but the imaging efficiency of UAV is only 1/40,000 of that of satellite remote sensing. (2) Numerical simulation models can predict the 3D spatial distribution of thermal discharge. Although UAV and satellite remote sensing cannot directly obtain the 3D spatial distribution of thermal discharge, using remotely sensed SST as the temperature field input for the MIKE 3 model can reduce the quantity of measured temperature data and lower the cost of numerical simulation. (3) In the process of monitoring and predicting the thermal discharge of nuclear power plants, achieving an effective balance between monitoring accuracy and cost can be realized by comprehensively considering the advantages and costs of satellite, UAV, and numerical simulation technologies.

Modeling Contaminant Transport from a Red Mud Pond – A Case Study from South India

The present study focused on impact assessment of redmud pond on groundwater using numerical groundwater flow and contaminant transport modeling using pertinent data including water quality and 2D electrical resistivity imaging data. The observed groundwater depths range from 1.2 to 25.8 meters below ground level with deeper levels observed in upstream and higher elevated regions in the study area. Elevated pH and electrical conductivity (>3000 μS/cm) characterize the Redmud ponds, while other groundwater samples meet BIS drinking water standards. Major ion concentrations contouring indicates high total dissolved solids (TDS) around Redmud ponds due to leakage and in the downstream due to domestic sewage pollution. Most locations adhere to BIS drinking water limits except for one downstream site. The resistivity data indicated hard formations (>18 m depth) with resistivity >500 Ohm.m, weathered basalt (12-18 m, 60-150 Ohm.m), and saturated water (12 m, 1-5 Ohm.m). Contaminated aquifers (<1 Ohm.m) are detected up to 3 m depth, and noticed accumulating contaminated water (27 m depth) in the NW corner of the Redmud pond from seepage. Predominant groundwater flow from the Redmud pond towards public water bodies and streams is highlighted by simulated contaminant transport model. Collaboration and comprehensive management are recommended to protect the watershed’s environmental integrity and public health.

Rainfall-induced Landslide in the Lesser Himalaya: A Case Study of the Pallotari Landslide, Lamjung, Central-West Nepal

The Pallotari area, located in the Marsyangdi Rural Municipality, Lamjung, central-west Nepal, within the Lesser Himalaya, was impacted by a series of rainfall-induced landslides in July 2020. This study focuses on the Pallotari landslide, one of the major landslides in the area. Geological and engineering geological studies were performed to identify the causes of this landslide, and its impacts to the local community. Our results indicate the major causative factors to be intensive rainfall, steep topography with loose colluvial soil, and some anthropogenic activities such as the construction of the rural roads through the crown area. The study area still has hanging colluvial material on the crown as well as on the left flank of the landslide, and the numerical model for slope stability analysis indicates it to be unstable even in the unsaturated condition. The colluvial material in the middle portion of the landslide also has the risk of failure in the saturation condition which can be due to intensive rainfall. However, the rock slope stability analysis using the kinematic analysis does not show any contribution to the orientation of discontinuities on the slope failure. The presence of several transverse and longitudinal cracks in the surrounding of the landslide are signs of future failure.

Symmetry-preserving modeling for lithographic imaging.

In computational imaging and lithography, it has been a challenge for a numerical model to faithfully preserve symmetries in the physical imaging system. In this Letter, we present a project-to-symmetry-subspace (PTSS) method to prevent symmetry loss during the iterative generation of optical kernels. Essentially, PTSS is to project iterative vectors onto a predefined symmetric subspace when decomposing the transmission cross coefficient (TCC). Simulation results demonstrate the PTSS-generation of a truncated set of optical kernels that are substantially free of symmetry error, regardless of the order of truncation.

Management of Plastic Wastes through Recent Advanced Pyrolysis Processes

Plastics are predominant in numerous sectors like packaging, agriculture, hardware, electronics, and many others. Annual plastic demand has been rapidly growing in the last few decades because of the increasing dependency on plastics. As a consequence, massive amounts of plastic waste are being generated every year. These plastic wastes are non-biodegradable, and hence their disposal poses a serious threat to the ecosystem and causes significant environmental problems such as endangering the safety of marine life, wildlife, air, water, and soil, etc. A large portion of plastic waste ends up in landfills, and only a small fraction is recycled. The continuous dependence on landfills as the main disposal method for plastic waste is costly and ineffective. Common solutions to plastic waste management are incineration and recycling; however, incineration emits harmful pollutants and greenhouse gases that contribute to ozone layer depletion and global warming; moreover, recycling is expensive and inefficient. As an alternative to recycling and incineration, the pyrolysis process can convert plastic wastes into more valuable fuel products. Pyrolysis is a thermal process that converts raw material into pyrolysis liquid, solid wax, and non-condensable gases in the absence of oxygen. This process is attractive because it is economical and energy-efficient, and it can be used to convert various types of plastic waste into valuable products. In recent years, there have been significant developments in pyrolysis applications in liquid fuel production from plastic wastes. This work reviews recent advances in and challenges for the pyrolysis process for converting plastic wastes into a valuable alternative fuel, focusing on studies of advanced pyrolysis processes published over the last five years. The paper also highlights the numerical modeling of pyrolysis of plastic wastes and the potential impact of pyrolysis on the future of sustainable waste-management practices of plastics.

Physics of microscale freeform 3D printing of ice

Ice is emerging as a promising sacrificial material in the rapidly expanding area of advanced manufacturing for creating precise 3D internal geometries. Freeform 3D printing of ice (3D-ICE) can produce microscale ice structures with smooth walls, hierarchical transitions, and curved and overhang features. However, controlling 3D-ICE is challenging due to an incomplete understanding of its complex physics involving heat transfer, fluid dynamics, and phase changes. This work aims to advance our understanding of 3D-ICE physics by combining numerical modeling and experimentation. We developed a 2D thermo-fluidic model to analyze the transition from layered to continuous printing and a 3D thermo-fluidic model for the oblique deposition, which enables curved and overhang geometries. Experiments are conducted and compared with model simulations. We found that high droplet deposition rates enable the continuous deposition mode with a sustained liquid cap on top of the ice, facilitating smooth geometries. The diameter of ice structures is controlled by the droplet deposition frequency. Oblique deposition causes unidirectional spillover of the liquid cap and asymmetric heat transfer at the freeze front, rotating the freeze front. These results provide valuable insights for reproducible 3D-ICE printing that could be applied across various fields, including tissue engineering, microfluidics, and soft robotics.

Dust storms and cardiorespiratory emergency department visits in three Southwestern United States: application of a monitoring-based exposure metric

Climate change is projected to increase the risk of dust storms, particularly in subtropical dryland, including the southwestern US. Research on dust storm’s health impacts in the US is limited and hindered by challenges in dust storm identification. This study assesses the potential link between dust storms and cardiorespiratory emergency department (ED) visits in the southwestern US. We acquired data for 2005–2016 from eight IMPROVE (Interagency Monitoring of PROtected Visual Environments) sites in Arizona, California, and Utah. We applied a validated algorithm to identify dust storm days at each site. We acquired patient-level ED visit data from state agencies and ascertained visits for respiratory, cardiovascular, and cause-specific subgroups among patients residing in ZIP codes within 50 km of an IMPROVE site. Using a case-crossover design, we estimated short-term associations of ED visits and dust storms, controlling for temporally varying covariates. During 2005–2016, 40 dust storm days occurred at the eight IMPROVE sites. Mean PM10 and PM2.5 levels were three to six times greater on dust storm days compared to non-dust storm days. Over the study period, there were 2 524 259 respiratory and 2 805 925 cardiovascular ED visits. At lags of 1, 2, and 3 days after a dust storm, we observed 3.7% (95% CI: 1.0%, 7.6%), 4.9% (95% CI: 1.1%, 8.9%), and 5.0% (95% CI: 1.3%, 8.9%) elevated odds of respiratory ED visits compared to non-dust storm days. Estimated associations of dust storm days and cardiovascular disease ED visits were largely consistent with the null. Using a monitoring-based exposure metric, we observed associations among dust storms and respiratory ED visits. The results add to growing evidence of the health threat posed by dust storms. The dust storm metric was limited by lack of daily data; future research should consider information from satellite and numerical models to enhance dust storm characterization.

Seismic Isolation Layout Optimized of Mid-Rise Reinforced Concrete Building Frame Structure

Seismic isolation technology plays a crucial role in enhancing earthquake resistance and mitigating disasters for building structures. In this study, the ETABS analysis software V21.0.1 is utilized to establish a numerical model of a six-story steel reinforced concrete frame structure. Both the time-history analysis method and response spectrum method are employed to calculate the seismic response of the model under earthquake actions. The placement of an isolation layer on the foundation and from the first to fifth floor is considered, with separate calculations conducted for each scenario. Subsequently, a comprehensive comparison and analysis of the dynamic response characteristics among different design schemes are performed. The results demonstrate that the most favorable isolation effect is achieved when the isolation layer is implemented on the foundation or first floor. Compared to non-isolated structures, the natural period of the structure can be extended by 2.2 times and 2 times under the base isolation and first-floor top isolation schemes, respectively. The damping coefficients can reach 0.35 and 0.36, respectively, while the inter-story drift angles can be reduced by 66% and 67%, respectively.

Interpass temperature strategies for compressive residual stresses in cladding low-transformation-temperature material 16Cr8Ni via wire arc additive manufacturing

Low-transformation-temperature (LTT) materials induce compressive residual stresses within an effective depth in wire arc additive manufacturing (WAAM), which is well suited for cladding applications. However, this role was found to be sensitive to the phase transformation sequence. We developed an LTT material—16Cr8Ni (16Cr8Ni-LTT)—and to explore its potential, it was clad onto a KA36 substrate via WAAM. Three different interpass temperature strategies were designed as follows: (1) no interpass temperature control; (2) interpass temperature controlled at approximately 270 °C above the martensite transformation start temperature (Ms = 200 °C) for simultaneous phase transformation; and (3) interpass temperature controlled at approximately 50 °C below the martensite transformation finish temperature (Mf = 60 °C) for sequential phase transformation. A thermal elastic-plastic numerical model considering the phase transformation-induced plasticity (TRIP) was developed using in-house software, JWRAIN-Hybrid, to reproduce the temperature field and residual stresses of 16Cr8Ni-LTT cladding. X-ray diffraction (XRD) and contour methods were employed for residual stress measurements. The high accuracy of the model was validated in terms of the temperature, deformation, and residual stress. The reproduced maximum historical temperature distributions were combined with hardness tests to identify the depths and temperatures of the heat-affected zone (HAZ). The measured maximum compressive residual stresses induced by the three interpass temperature strategies for cladding 16Cr8Ni-LTT were −503, −420, and −720 MPa. Moreover, irrespective of the adopted interpass temperature strategy, both longitudinal and transverse residual stresses were compressive in the 16Cr8Ni-LTT cladding. This study provides scientific insights into LLT-induced compressive residual stresses and highlights the superiority and flexibility of cladding LTT materials via WAAM for improving the resistance of large metal components to fatigue and corrosion.

Boundary Layer Analysis of a Transonic High-Pressure Turbine Vane Using Ultra-Fast-Response Temperature-Sensitive Paint

Abstract The focus of this article is the impact of surface roughness on the boundary layer caused by a 7YSZ thermal barrier coating (TBC). Experimental investigations are conducted on a NGV installed inside the wind tunnel for Straight Cascades Göttingen (EGG). The shape of the vane has been altered in a way that eliminates the influence of TBC's thickness. Therefore, it is expected that only the surface roughness is influencing the location of the separation and boundary layer transition. The transition next to the roughness can also be affected by positive and negative pressure gradients, separation, and interacting shocks. The impact of TBC on the turbulent wedges' appearance, separation bubble's position and length, and transition location is examined in this study. This research, combined with prior investigations, provides a comprehensive understanding of a turbine vane's aerothermodynamics. To investigate unsteady flow phenomena on a TBC-coated NGV, ultra-fast-response temperature-sensitive paint (iTSP) is utilized. This dataset will serve as a reference point for developing new turbine vane designs that include TBC and extensive cooling. Furthermore, the findings will be employed as a benchmark for improving numerical models.

Analysis and Comparison of Three Bending Tests on Phosphogypsum-Based Material According to Peridynamic Theory

Phosphogypsum-based materials have gained much attention in the field of road infrastructure from the economic and sustainable perspectives. The Three-point bending test, the Four-point bending test and the Semi-circular bending test are three typical test methods applied for fracture energy measurement. However, the optimal test method for fracture energy evaluation has not been determined for phosphogypsum-based materials. To contribute to the gap, this study aims to analyze and compare the three test methods for fracture energy evaluation of phosphogypsum materials based on the peridynamic theory. For this purpose, the load–displacement, vertical displacement–Crack Mouth Opening Displacement (CMOD) and fracture energy of the phosphogypsum-based materials were measured and calculated from the three test methods. The simulated load–displacement and vertical displacement–CMOD by PD numerical models, with different fracture energy as inputs, were compared to the corresponding tested values according to simulation error results. The results showed that the Four-point bending test led to minimized errors lower than 0.189 and indicators lower than 0.124, demonstrating the most optimal test method for the fracture energy measurement of phosphogypsum-based material. The results of this study can provide new methodological references for the selection of material fracture energy measurement tests.

Numerical investigation on ground and structure response of ancient site in complex strata caused by groundwater fluctuation and rainfall

As more and more ancient sites are discovered around the world, protecting them in situ has become a challenge due to issues such as ground settlement and masonry wall leaks caused by groundwater fluctuation or rainfall. In this study, laboratory tests, borehole tests and field high‐density resistivity detections are conducted to obtain information for numerical modelling, including design parameters. A complex three‐dimensional hydrological–mechanical coupling model is then established to investigate ground settlement and wall deformation caused by groundwater fluctuation and rainfall. The seepage simulation results for the initial state are accurately verified by high‐density resistivity imaging. Both measured data and numerical results indicate that changes in a single water head point mainly result in wall settlement. The pattern of wall deformation changes from settlement to lateral deformation with an increase in the drawdown rate of groundwater level. Furthermore, delayed rainfall and high‐intensity rainfall can increase foundation settlement and wall deformation. Settlement deformation determines the upper limit of the global deformation when wall nodes are mainly affected. In contrast, if lateral spreading dominates wall deformation, it determines the lower limit of the global deformation. This study provides reference for in situ protection and foundation reinforcement of ancient sites.

Development of embedded bioprinting for fabricating zonally stratified articular cartilage

Embedded bioprinting enables direct deposition of bioinks in three dimensions inside a support bath with shear-thinning and self-healing capabilities, and it has been used to fabricate complex tissues and organs for several biomedical applications. In this study, a support bath comprising gelatin/alginate microparticles and oxidized alginate solution was developed and crosslinked in situ with carbonyl hydrazide-modified gelatin bioink via the Schiff base reaction. The numerical model of embedded printing was established to analyze the extrusion process and disturbance of the support bath. The process window (e.g., extrusion pressure, nozzle moving speed, nozzle size, and support bath composition) was established experimentally to ensure stable fiber formation. In addition, the compressive modulus of the printed construct has been reinforced due to the formation of interpenetrating polymer networks in the microparticles. Based on the process investigation, a zonally stratified artificial cartilage with a three-layered structure was designed: vertically printed fibers in the bottom, oblique fibers in the middle, and horizontally printed fibers in the superficial layer. The bioprinted cartilage supported cell survival, proliferation, and spreading, with the observed deposition of cartilage-specific proteins, offering a new strategy for developing tissue-engineered cartilage constructs with biological and histological relevance.

A numerical oxidation model for SiC‐coated thermal protection systems in hypersonic applications

AbstractSilicon carbide (SiC) is a widely used component for thermal protection system (TPS) design. This material is often used either as a coating layer to protect beneath carbon‐based material against oxidation or as a ceramic matrix for composite materials used in the hypersonic leading edges. A numerical equilibrium model for SiC‐coated material ablation is developed in this study to compute the material response of coated TPS in hypersonic relevant aerothermal environment. The developed model is based on an equilibrium approach similar to the carbon graphite oxidation framework for ablative charring materials. The equilibrium wall composition is calculated based on the minimization of the Gibbs free energy. The proposed method can capture numerically the transition from passive to active oxidation while maintaining a low computational cost and good numerical stability. Implementation of the model in the Porous Material Analysis Toolbox based on OpenFOAM code permits to compare against previous literature test cases. By comparing the surface temperature obtained from the model with the experimental data, it is observed that the numerical model gives a good estimation providing accurate surface temperature prediction.

Nonlinear composition dependence of hydrogen bond lifetime in water-DMSO binary mixtures: The role of hydrophobic interaction.

The lifetime of a hydrogen bond between water and dimethyl sulfoxide (DMSO) is found to be considerably longer than that between two water molecules in neat water. This is counter-intuitive because the charge on the oxygen in DMSO is considerably less than that in water. Additionally, the strength of the water-dimethyl sulfoxide (w-D) hydrogen bond is found to be strongly composition dependent; the lifetime of the hydrogen bond is ten times larger at 30% than at very low concentrations. Using computer simulations, we perform microscopic structural and dynamic analysis to find that these anomalies arise at least partly from an "action-at-a-distance" effect where the attraction between the hydrophobic methyl groups results in the self-aggregation of DMSO molecules that "cages" both the rotational and linear motions of the molecules involved. This is reflected in the observed strong correlation of the lifetime with the local coordination number of the associated methyl groups. The elongated w-D h-bond lifetime causes a slowdown of collective dynamics and affects the lifetime of the w-w h-bond. This nonlinear feedback mechanism explains the strong composition dependence of viscosity and is anticipated to play a dominant role in many self-assemblies. Furthermore, the w-D hydrogen bond breaking mechanism changes from low to high DMSO concentration, a phenomenon not anticipated a priori. We introduce a new order parameter-based free energy surface of the bond breaking pathway. A two-dimensional transition state rate theory calculation is performed for the lifetime of the w-D h-bond that is found to be semi-quantitatively accurate.

Thermal performance of phase-change wall of a hotel building under hot-summer and cold-winter climate

ABSTRACT In China, the energy consumption in the building sector has increased tremendously in the past decades. It is important to investigate advanced passive energy-saving technologies for buildings. By applying phase-change materials in walls, the peak cooling/heating load can be significantly reduced. In the present study, a numerical model of one-dimensional heat transfer within a phase-change wall was developed and solved by Matlab, which was successfully validated with published data. Subsequently, the model was used to simulate the thermal performance of a phase-change wall in a hotel building in Shanghai, China. Simulation results demonstrate that the performance of the phase-change wall is optimized when the phase-change material is applied to both sides of the wall. Year-round heat transfer is minimized using layers of paraffin (C16-C28) and capric acid (2 cm), with phase-change temperatures of 43℃ and 16.3℃, respectively. The PCM wall reduces inwardthe inward heat transfer by 26.9% compared with a common wall without phase-change material. The outward heat loss is also reduced by 15.7% during the heating season. This study demonstrates that the PCM wall can effectively reduce indoor heat gain in summerin the summer and heat loss in winterin the winter. The numerical model has proven to be feasible for optimizing construction design.

Hydromechanical modelling of the influence of water saturation on the penetration performance of concrete target

The objective of the present paper is to study numerically the hydro-mechanical behaviour of concrete targets subjected to a rigid projectile, with special attention to the influence of water saturation. An elastoplastic model, encompassing two primary plastic mechanisms (shear and pore collapse), is improved to capture the influence of water saturation. The adopted model is implemented in the finite element code Abaqus/Explicit and validated by simulating two dynamic compression tests at the material point level and two penetration tests at the structure level. Not only a strong influence of water saturation on both volumetric and deviatoric behaviours of concrete is observed at material point level, but also the time-evolutions of projectile velocity, projectile deceleration and penetration depth in concrete targets are also satisfactorily reproduced by the numerical simulations. After that, a series of parametric studies are performed to understand the influence of water saturation on the penetration performance of concrete. It is found that with the presence of pore water, penetration resistance of concrete increases with decreasing water saturation, indicating a higher projectile deceleration and lower penetration depth obtained in saturated targets. Numerical modelling and analysis will enhance our understanding of the vulnerability of concrete infrastructures subjected to near-field detonations or impacts.