Preliminary Parametric Study Research Articles

Discrete element simulations to predict the response of bio-cemented sands

Discrete element method (DEM)-based numerical models in the YADE environment are used to simulate the constitutive response of uncemented and bio-cemented sands to investigate the influence of boundary conditions, loading and testing conditions, and material types. Both the classical DEM model and the pore scale finite volume (PFV)-coupled DEM model are used to simulate the response of saturated uncemented and lightly cemented sands with a rigid wall boundary under both drained and undrained triaxial compression. A DEM model with flexible boundaries created using particle facet (PFacet) elements is used to simulate undrained triaxial compression of moderately cemented sands, including the influence of confining stress. The PFacet-based model is used to predict the transition from barreling failure to shear banding when the confining stress or the cementation degree increases. The classical DEM model with cohesive bonds of uniform strength is also used to successfully simulate the uniaxial compression response of a sand with an extremely high degree of cementation. Finally, this paper presents a particle-packing model consisting of multiple solid phases for cemented sands based on the understanding that not all particle types will have the same cohesive properties. This multiple solid-phase model is a refinement of the classical DEM model that represents the particle physics more realistically, especially for heterogeneous systems. A preliminary parametric study is carried out considering varying cohesive properties and volume fractions for the different solid phases.

Numerical Modeling of the Walls Perforation Influence on the Accuracy of Wind Tunnel Experiments Using Two-Dimensional Computational Fluid Dynamics Model

The presented work is dedicated to the development of the mathematical model of a closed-type wind tunnel (WT) in a two-dimensional (2D) formulation based on the computational fluid dynamics (CFD) Unsteady Reynolds Averaged Navier Strokes Equations (URANS) method. The influence of the WT walls perforation percentage on the aerodynamic characteristics of the SC1095 (SC is an abbreviation for “supercritical”) airfoil in a wide range of pitch angles from 0 to 28 degrees has been studied. The obtained data are compared with the aerodynamic characteristics of the airfoil in free flow conditions. It is shown that the use of perforation makes it possible to significantly reduce the influence of the wind tunnel walls on the obtained aerodynamic characteristics of the airfoil bringing them closer to the airfoil characteristics under free flow conditions. The developed low resource-intensive 2D CFD WT model can be used to determine the optimal ratio between the walls perforation percentage, the WT test section dimensions, and the experimental model dimensions for various test modes. Support of WT experiments with the help of preliminary parametric studies based on the 2D CFD model could significantly reduce material costs and increase the accuracy of the obtained results.

Development of a solar device for jute filling based humidification dehumidification desalination

ABSTRACT It is predicted that the ground water sources which are currently termed as sustainable will also begin to deteriorate, and this may lead to the degradation of the cropland and may severely affect food production, smooth colonial expansion and also damage the balance of ecosystem. Since 2011, much of the interest has been laid upon the concepts of Ecohydrology, which dwells upon the interconnectivity of ecosystem and hydrology. This study emphasises on the recycling of waste water and desalination of sea water. Among various desalination techniques, humidification–dehumidification (HDH) technique, using solar energy as the heat source for evaporation of salt water, has gathered attention in recent years. A conventional solar reflector HDH desalination plant requires a humidifier, where saline water is fed and made to evaporate in running air, when drizzled through nozzles and passed through the jute surface, which will be further reduced due to a fan which will be installed at the end of a humidifier region. Therefore, there will be enhancement in vapour formation and then sent to a dehumidifier where pure water is separated from moist air through condensation. The proposed unit in which latent heat can be recovered, which may yield 20 L/day on floor area of 2 m2 and adopting jute as filling in humidifier. The latent heat that is extracted from the moist air may be further utilised in the preheating of the saline water. Here, a prediction model was developed over data collected for 25 days and net gain obtained from the experimentation will be used to calculate gained output ratio. A preliminary parametric study to explore the technical feasibility of the HDH reveals that a fixed bed column filled with EDTA provides a longer working duration to assure the overall system’s performance and to remove surplus salt.

Numerical & experimental investigation of slotted-hidden-gap connection for square HSS brace members

The Slotted-Hidden-Gap (SHG) connection represents an attractive alternative to the conventional knife plate connection for HSS braces of steel braced frames as it allows the brace to yield along its length without having to reinforce the connection. Prior studies have proven the effectiveness of this detail for circular and square HSS braces. However, no encompassing seismic design method or detailing rules exist for SHG square HSS members. To gain deeper insight into the behaviour of the SHG connection, a preliminary numerical parametric study of square HSS braces under a monotonic tension loading protocol was done to further investigate key factors influencing the connection's performance. The weld size and length as well as the gusset plate thickness are critical in the design of SHG connections and may hinder the connection performance if poorly designed or fabricated. A laboratory testing program, of four SHG HSS ASTM A1085 (254 × 254 × 13) brace specimens with different weld configurations, was also carried out. Keeping a 20 mm overlap length despite changing the overall weld size and length was sufficient to develop the yield resistance of the braces and to force fracture away from the connection region. Utilizing longer length smaller sized welds granted an additional 3.1% of brace strains compared to connections with shorter welds.

A continuum damage approach to spallation and the role of microinertia

Spall failure is of interest due to its prevalence in high strain rate problems in which the spallation is driven by the interaction of release waves. In this article, a porosity-based damage model that includes microinertial effects is used to examine spall failure. The model is successfully calibrated to plate impact-driven experiments and then used to evaluate experimental conditions producing more extreme strain rate conditions, such as those in laser-driven experiments. The incorporation of microinertia allows us to better understand the increase in apparent macroscopic spall strength seen at high strain rates. Correspondingly, we conclude that the incorporation of microinertial effects improves the model’s predictive capabilities. Microinertial effects result in more severe local tensile stresses that affect the damage evolution, and microinertia can play a significant role in the approach to the material’s ideal strength at extreme loading rates. A preliminary parametric study is also carried out to investigate the role of microstructural aspects such as nucleation volume fraction and initial pore radius. One counter-intuitive result from the microinertial effects is that, for a given nucleation site volume fraction, having larger initial pore nucleation sites can lead to an improved macroscopic spall strength.

Experimental and numerical study of the seismic behavior of cold-formed steel walls with diagonal braces

In this paper, the seismic performance of cold-formed thin-walled steel walls with diagonal braces is studied by means of experiments and finite element analysis. In total, horizontal hysteretic loading tests were carried out on six full-scale cold-formed thin-walled steel walls. The influence of diagonal bracing, the screw spacing, wall panels and vertical loads on the seismic performance of the walls was investigated from the aspects of hysteretic curves, skeleton curves, the lateral stiffness degradation and the energy dissipation capacity. It was found that diagonal bracing could significantly improve the load-bearing capacity, stiffness, and energy dissipation capacity of the walls. However, the lateral resistance increased slightly because of premature buckling of the transverse braces at the connection between the diagonal and transverse braces. In addition, finite element models of the wall specimens were established by ABAQUS software and validated against the experimental data. A preliminary parametric study was also conducted to further examine the influence of essential parameters on the behavior of cold-formed steel walls with diagonal braces.

Optimization of muscle activation schemes in a finite element neck model simulating volunteer frontal impact scenarios

Neck muscle activation is increasingly important for accurate prediction of occupant response in automotive impact scenarios and occupant excursion resulting from active safety systems such as autonomous emergency braking. Muscle activation and optimization in frontal impact scenarios using computational Human Body Models have not been investigated over the broad range of accelerations relevant to these events. This study optimized the muscle activation of a contemporary finite element model of the human head and neck for human volunteer experiments over a range of frontal impact severities (2 g to 15 g). The neck muscles were grouped as flexors and extensors, and optimization was undertaken for each group based on muscle activation level and activation time. The boundaries for optimization were defined using data from the literature and a preliminary parametric study. A linear polynomial method was used to optimize the model head kinematics to the volunteer experiments for each impact severity. The optimized models predicted muscle activation to increase with higher impact severities, and improved the average cross-correlation by 35% (0.561–0.755) relative to the Maximum Muscle Activation (MMA) scheme in the original model. Importantly, a newly proposed Cocontraction Muscle Activation (CMA) scheme for maintaining the head in a neutral posture provided a 23% on average improvement in correlation compared to the MMA scheme. In conclusion, this study identified a new scheme to obtain more accurate response kinematics across multiple impact severities in computational Human Body Models as well as contributing to the understanding of muscle influence during frontal impact scenarios.

Flexure Behavior of a Two Layer Reinforced Concrete Beam

This paper presents an overview of the research on flexural behavior of a two layer high strength reinforced concrete beam compared with a single layer high strength reinforced concrete beam. The experimental program consisted in testing the reaction to a flexural load of a reinforced concrete beam with two different concrete classes and a reinforced concrete beam made of the highest concrete class was made to compare the flexural behavior of the two layer beam with the single layer beam. Design and properties of the two beams in study was considered according to a preliminary economic parametric study. The two beams in study were modeled also in a finite element analysis program using experimental data.

A semi-analytical approach for the analysis of variable-stiffness panels with curvilinear stiffeners

A semi-analytical method is developed for the analysis of composite stiffened panels, where stiffness variability is achieved through a combination of fiber steering and curvilinear stringers. The approach relies upon a 2D plate model for the skin and a 1D beam description for the stiffeners, according to first-order shear deformation theory. The approach is developed in the framework of a displacement-based formulation, where Legendre polynomials are used for approximating the displacement field, and the Ritz method is used for the solution strategy. The resulting tool is characterized by its excellent computational efficiency, and allows problems in free-vibrations, buckling and thermal buckling to be solved with reduced effort. The quality of the results is assessed by an extensive set of comparison against results from the literature, demonstrating the potential of the tool as a means for performing preliminary parametric studies for these variable-stiffness, variable-geometry structures.

A multiphase SPH framework for supercooled large droplets dynamics

Purpose This paper aims to introduce a three-dimensional smoothed particle hydrodynamics (SPH) framework for simulating supercooled large droplets (SLD) dynamics at aeronautical speeds. Design/methodology/approach To include the effects of the surrounding air, a multiphase model capable of handling high density-ratio problems is adopted. A diffusive term is incorporated to smooth the density field and avoid numerical instabilities. Additionally, a particle shifting technique is used to eliminate anisotropic particle distributions. Findings The framework is validated against low-speed droplet impingement experimental results and then applied to the droplet impingement at high speeds typical of SLD conditions. Preliminary parametric studies are conducted to investigate the post-impact splashing. It is observed that a thicker water film can decrease the crown diameter and a smaller impact angle can suppress upward and forward splashing. Originality/value A three-dimensional multiphase SPH framework for SLD dynamics at a wide range of impact speed is developed and validated. The effects of particle resolution, water film thickness and impact angle on the post-impact crown evolution are investigated.

Evaluation of theranostic perspective of gold-silica nanoshell for cancer nano-medicine: a numerical parametric study.

Using gold-silica nanoshell as a reference nano-agent, this work has performed preliminary numerical parametric study to investigate the feasibility and if feasible the efficiency of using a single nano-agent to achieve theranostic goals. In total, seven generics of gold-silica nanoshells have been tested including the R[50,10] (radius of the silica core is 50 nm and thickness of the gold shell is 10 nm), R[40,15], R[55,25], R[40,40], R[75,40], R[104,23], and R[154,24] nanoshells. A planar tissue model has been constructed as the platform for parametric study. For mathematical modeling, radiant transport equation (RTE) has been applied to describe the interactions among laser lights, the hosting tissue, and the hosted nanoshells and Penne's bio-heat equation has been applied to describe the hyperthermia induced by such interactions. Effects of different nanoshell generics on the diffuse reflectance signal and hyperthermia temperature transition have been simulated, basing on which the potential of a certain nanoshell generic as theranostic nano-agent has been evaluated. It has been found that it is highly feasible for gold-silica nanoshells to be engineered for theranostic purpose and nanoshell generics that are preferentially scattering should be explored for good theranostic candidates. On the condition that nanoshell generic with the right optical properties has been located, a moderate nanoshell retention in the target tissue site is already sufficient to induce effective theranostic effects, which indicates that theranostic nano-medicine might not have a stringent requirement for the delivery technique. Among nanoshells that have been tested, the R[55,25] nanoshell seems to be a promising candidate as theranostic nano-agent. Further testing on it is highly recommended. Nanoshells that are preferentially absorbing such as the R[50,10] and R[40,15] nanoshells are efficient photothermal agent and could be used for therapeutic purpose only. However, it is not recommended that preferentially absorbing nanoshells being used for theranostic purpose due to possible negative effects such nanoshells might bring to the diffuse reflectance signal.

A coupled model on energy conversion in laser power beaming

The light-to-electricity conversion efficiency is of critical interest for the laser power beaming technology. The coupled interaction between electricity conversion and heat generation determines the actual light-to-electricity conversion efficiency. In this paper, a coupled model is established to describe such coupled interaction and the equilibrium point of laser illuminated Photovoltaic (PV) cells. A simplified equation is developed to solve the equilibrium temperature and the electricity conversion efficiency of a thin-film PV cell evenly illuminated by a laser. Numerical examples are provided for typical conversion conditions and a preliminary parametric study with sensitivity analysis is carried out for future system design.

Experimental assessment of a new combined flow control approach in compressor cascade

A new combined flow control approach is put forward in this paper using blade slot and vortex generator, which increase the flow control benefits by the combining their effects. A preliminary parameter study is conducted to select the geometry parameters of the vortex generator, and then experiments are performed to assess the gains and to reveal the mechanisms. The measured flow fields show that the cascade separation is significantly reduced and the outlet flow field is more ordered due to the combined approach. The cascade performance, the total pressure loss, the flow turning angle and the static pressure rise averagely increase by −30.9%, +2.0°, and +69.9% respectively. The stable margin of the cascade rises +3° regarding the incidence angle. The mechanisms should be concluded that high-speed slot jet induced reduces trailing edge separations and concentrates remaining separations to the cascade corner, and the vortex generator further decreases the corner separations by deflecting the passage vortex. Combining the benefits of two devices, the combined approach achieves better flow control effects than the individual two.

A numerical approach for the evaluation of particle-induced erosion in an abrasive waterjet focusing tube

In this work, a numerical approach to study erosion phenomena inside a focusing tube for Abrasive Water Jet (AWJ) is presented. The goal of this approach is to capture the erosive action of the particle-laden flow developing inside the focusing tube as a result of cumulated impact phenomena. This is fundamental in the research and development of this sector in order to optimize cost and reliability of the AWJ system. With this purpose, a multiscale algorithm for CFD-DEM is used in combination with erosion models presented in the literature so to retrieve erosion profiles comparable to the one obtained by the most common experiments in this field. The approach is shown to provide insight into the process of wear development as the identification of areas characterized by brittle and cut phenomena. Preliminary parametric studies on the influence of impact models and particle diameters are proposed to show the potentialities of the method in describing the physics of the nozzle.

Ultraviolet radiation modelling from ground-based and satellite measurements on Reunion Island, southern tropics

Abstract. Surface ultraviolet radiation (SUR) is not an increasing concern after the implementation of the Montreal Protocol and the recovery of the ozone layer (Morgenstern et al., 2008). However, large uncertainties remain in the prediction of future changes of SUR (Bais et al., 2015). Several studies pointed out that UV-B impacts the biosphere (Erickson et al., 2015), especially the aquatic system, which plays a central part in the biogeochemical cycle (Hader et al., 2007). It can affect phytoplankton productivity (Smith and Cullen, 1995). This influence can result in either positive or negative feedback on climate (Zepp et al., 2007). Global circulation model simulations predict an acceleration of the Brewer-Dobson circulation over the next century (Butchart, 2014), which would lead to a decrease in ozone levels in the tropics and an enhancement at higher latitudes (Hegglin and Shepherd, 2009). Reunion Island is located in the tropics (21° S, 55° E), in a part of the world where the amount of ozone in the ozone column is naturally low. In addition, this island is mountainous and the marine atmosphere is often clean with low aerosol concentrations. Thus, measurements show much higher SUR than at other sites at the same latitude or at midlatitudes. Ground-based measurements of SUR have been taken on Reunion Island by a Bentham DTMc300 spectroradiometer since 2009. This instrument is affiliated with the Network for the Detection of Atmospheric Composition Change (NDACC). In order to quantify the future evolution of SUR in the tropics, it is necessary to validate a model against present observations. This study is designed to be a preliminary parametric and sensitivity study of SUR modelling in the tropics. We developed a local parameterisation using the Tropospheric Ultraviolet and Visible Model (TUV; Madronich, 1993) and compared the output of TUV to multiple years of Bentham spectral measurements. This comparison started in early 2009 and continued until 2016. Only clear-sky SUR was modelled, so we needed to sort out the clear-sky measurements. We used two methods to detect cloudy conditions: the first was based on an observer's hourly report on the sky cover, while the second was based on applying Long and Ackerman (2000)'s algorithm to broadband pyranometer data to obtain the cloud fraction and then discriminating clear-sky windows on SUR measurements. Long et al. (2006)'s algorithm, with the co-located pyranometer data, gave better results for clear-sky filtering than the observer's report. Multiple model inputs were tested to evaluate the model sensitivity to different parameters such as total ozone column, aerosol optical properties, extraterrestrial spectrum or ozone cross section. For total column ozone, we used ground-based measurements from the SAOZ (Système d'Analyse par Observation Zénithale) spectrometer and satellite measurements from the OMI and SBUV instruments, while ozone profiles were derived from radio-soundings and the MLS ozone product. Aerosol optical properties came from a local aerosol climatology established using a Cimel photometer. Since the mean difference between various inputs of total ozone column was small, the corresponding response on UVI modelling was also quite small, at about 1 %. The radiative amplification factor of total ozone column on UVI was also compared for observations and the model. Finally, we were able to estimate UVI on Reunion Island with, at best, a mean relative difference of about 0.5 %, compared to clear-sky observations.

Production of composite particles using an innovative continuous dry coating process derived from extrusion

Dry particle coating is used to modify surface properties and monitor the end use properties of powders. These processes are mainly running in batch mode. In certain cases, continuous processes may present interest for specific applications (limitation of investments, stability, versatility…). In this study, the feasibility of dry coating particles by an innovative way derived from the well-known extrusion process was investigated. Adhesion between host and guest particles is induced by mechanical shear stress during processing. A preliminary parametric study on microcrystalline cellulose particles as host particles was carried out in order to determine the operating condition range. Then, coating was successfully performed using talc and a microcrystalline cellulose system, which demonstrates the feasibility of this novel process and led to different morphologies according to the operating conditions.

Pseudo-static stability analysis of rock slopes reinforced by passive bolts using the generalized Hoek–Brown criterion

The stability analysis of passive bolt-reinforced rock slopes under seismic loads is investigated within the framework of the kinematic approach of limit analysis theory. A pseudo-static method is adopted to account for the inertial forces induced in the rock mass by seismic events. The strength properties of the rock material are described by a modified Hoek–Brown strength criterion, whereas the passive bolts are modeled as bar-like inclusions that exhibit only resistance to tensile-compressive forces. Taking advantage of the ability to compute closed-form expressions for the support functions associated with the modified Hoek–Brown strength criterion, a rotational failure mechanism is implemented to derive rigorous lower bound estimates for the amount of reinforcement strength to prevent slope failure. The approach is then applied to investigating the effects of relevant geometry, strength and loading parameters in light of a preliminary parametric study. The accuracy of the approach is assessed by comparison of the lower bound estimates with finite element limit analysis solutions, thus emphasizing the ability of the approach to properly predict the stability conditions and to capture the essential features of deformation localization pattern. Finally, the extension of the approach to account for slipping at the interface between reinforcements and surrounding rock mass is outlined.

Passive Control of Piston Secondary Motion Using Nonlinear Energy Absorbers

The impulsive behavior of the piston in the cylinder liner plays a key role in the noise, vibration, and harshness (NVH) of internal combustion engines. There have been several studies on the identification and quantification of piston impact action under various operation conditions. In the current study, the dynamics of the piston secondary motion are initially explored in order to describe the aggressive oscillations, energy loss, and noise generation. The control of piston secondary motion (and thus, impacts) is investigated using a new passive approach based on energy transfer of the highly transient oscillations to a nonlinear absorber. The effectiveness of this new method for improving the piston impact behavior is discussed using a preliminary parametric study that leads to the conceptual design of a nonlinear energy absorber.

Improving Residential Wind Environments by Understanding the Relationship between Building Arrangements and Outdoor Regional Ventilation

This paper explores the method of assessing regional spatial ventilation performance for the design of residential building arrangements at an operational level. Three ventilation efficiency (VE) indices, Net Escape Velocity (NEV), Visitation Frequency (VF) and spatial-mean Velocity Magnitude (VM), are adopted to quantify the influence of design variation on VE within different regional spaces. Computational Fluid Dynamics (CFD) method is applied to calculate VE indices mentioned above. Several residential building arrangement cases are set to discuss the effect of different building length, lateral spacing and layouts on four typical space patterns under wind directions oblique or perpendicular to the main (long) building facade. The simulation results prove that NEV, VF and VM are useful VE indices, which can reflect different features of flow pattern in studied regional domains. Preliminary parametric studies indicate that wind direction might be the most important factor for improving spatial ventilation. When the angle between main building facade and wind direction is more than 30°, ventilation of different exterior spaces could improve evidently. When wind direction is perpendicular to main building façade, decreasing building length can increase NEV of the middle space by 50%, while decreasing lateral spacing would decrease NEV of the intersection space by 35%.

Parametric seismic evaluation of highway overpass bridges in moderate seismic areas

Prior to modern seismic provisions, several bridges were not designed for seismic actions in moderate seismic areas. Precast multi-girder and slab bridges are typical highway overpass structures; they have a significant contribution to national bridge stocks. Since the seismic behavior is questionable, a preliminary parametric study is conducted to determine critical configurations and components. The results indicate that the behavior of the abutments, backfill soil, superstructure and foundation is normally satisfactory; however, the superstructure-abutment joints are critical for both single- and multi-span bridges, while the piers are also critical for longer multi-span configurations. The parametric results provide a solid basis both for detailed seismic assessment and development of design concepts of newly built structures in moderate seismic zones.