Large eddy simulation of heat and mass transport in turbulent flows. Part 1: Velocity field

Localized residual or subgrid-scale (SGS) models are presented for use in large eddy simulation of heat and mass transport in turbulent flows. In part (1) (this paper), we discuss the SGS stress models for the velocity field. The models for the scalar field are presented in part (2). The new SGS stress closures are compared with the dynamic-Smagorinsky model (DSM) and the dynamic two-parameter mixed model (DTMM). All models are applied “locally” and their performances are assessed via both a priori and a posteriori analyses with detailed comparisons against data obtained from direct numerical simulation of homogeneous isotropic, homogeneous shear and temporal mixing layer flows. The results of a priori assessments indicate that the new closures predict the SGS stresses better than both DSM and DTMM in all simulated flows. The results of a posteriori assessments also show that the SGS stresses and the statistics of the filtered velocity are more accurately predicted with the new models.     

Relationship between Deflection and Crack Mouth Opening Displacement of Self-Compacting Concrete Beams with and without Fibers

There are only a few research results for predicting the relationship between deflection and the crack mouth opening displacement (CMOD) of self-compacting concrete (SCC) beams with and without fibers. A series of bending beam tests on SCC, with different fiber types have been carried out. For this purpose, four SCC mixes—plain SCC, steel, polypropylene, and hybrid fiber reinforced SCC—are considered in the test program. Based on the experimental results, a model for predicting the relation between the deflection and CMOD of SCC has been established per each mix. These models rely on the load–deflection relation and the load–CMOD relation of bending beam. A well agreement has been found between the suggested model and the test results. The results of this study indicate that the load–deflection diagram is very similar to that of the load–CMOD diagram, and there is a linear relation between the mid-span deflection and CMOD of SCC.     

The effect of stiffener on behavior of reduced beam section connections in steel moment-resisting frames

Reduced Beam Section (RBS) connections are a new type of connection which have been used in steel moment-resisting frames since the 1994 Northridge earthquake. This study is primarily aimed at analyzing the effects of suitable web stiffeners on preventing the deterioration effect of the hysteresis curve for RBS connections. Results of more than 183 nonlinear finite element analyses on different IPE sections with radius cut, straight cut, and drilled-flange RBS connection showed that different web stiffeners considerably contribute to the enhancement of seismic performance of RBS connections. In this research, the effects of factors such as the geometry and the number of the stiffeners, the distance between the stiffener and column side, and the length and thickness of the stiffener on the seismic performance of RBS connections were also studied.     

Multiple damage detection in complex bridges based on strain energy extracted from single point measurement

Strain Energy of the structure can be changed with the damage at the damage location. The accurate detection of the damage location using this index in a force system is dependent on the degree of accuracy in determining the structure deformation function before and after damage. The use of modal-based methods to identify damage in complex bridges is always associated with problems due to the need to consider the effects of higher modes and the adverse effect of operational conditions on the extraction of structural modal parameters. In this paper, the deformation of the structure was determined by the concept of influence line using the Betti-Maxwell theory. Then two damage detection indicators were developed based on strain energy variations. These indices were presented separately for bending and torsion changes. Finite element analysis of a five-span concrete curved bridge was done to validate the stated methods. Damage was simulated by decreasing stiffness at different sections of the deck. The response regarding displacement of a point on the deck was measured along each span by passing a moving load on the bridge at very low speeds. Indicators of the strain energy extracted from displacement influence line and the strain energy extracted from the rotational displacement influence line (SERIL) were calculated for the studied bridge. The results show that the proposed methods have well identified the location of the damage by significantly reducing the number of sensors required to record the response. Also, the location of symmetric damages is detected with high resolution using SERIL.     

Biological and chemical redox transformations of mercury in fresh and salt waters of the high arctic during spring and summer

It is well-established that atmospheric deposition transports Hg to Arctic regions, but the postdepositional dynamics of Hg that can alter its impact on Arctic food chains are less understood. Through a series of in situ experiments, we investigated the redox transformations of Hg in coastal and inland aquatic systems. During spring and summer, Hg reduction in streams and pond waters decreased across a 4-fold increase in salinity. This alteration of Hg reduction due to chloride was counterbalanced by the presence of particles, which favored the conversion of oxidized Hg to its elemental form. In saline waters, biogenic organic materials, produced by algae, were able to promote oxidation of Hg(O) even under dark conditions. Overall these results point to the vulnerability of marine/ coastal Arctic systems to Hg, compared to inland systems, with oxidation processes enhancing Hg residence times and thus increasing its potential to enter the food chain.     

Desulfurization of high sulfur petroleum coke by molten caustic leaching

Desulfurization by molten caustic leaching (MCL) at 400–500 °C has been investigated in order to reduce the sulfur content of petroleum coke. Effective parameters on desulfurization of petroleum coke, other than temperature, include alkali to feed (petroleum coke) mass ratio, time and mesh size in the ranges of 0.5–1.5, 1–3 h and 200–600 µm, respectively. In this work, petroleum coke desulfurization conditions using solid KOH have been studied. Maximum petroleum coke desulfurization by MCL method has been obtained by Taguchi L9 design using alkali to feed mass ratio of 1, temperature of 600 °C, time of 2 h and mesh size of 200 µm. The changes in the main groups on the coke surface have been determined using FTIR spectroscopy. In addition, SEM-EDX, TGA and XRD analyses have been used to investigate the changes in coke physical and chemical properties.     

Manufacture of a mechanical test rig to simulate the movements of forces within the shoulder

The shoulder complex, also known as the glenohumeral joint is the most manoeuvrable and one of the most well used joints of the human body. Over time problems can occur with the glenohumeral joint and surrounding muscles, cartilage, tendons and ligaments caused by ageing or by over stressing the shoulder complex. This work examines the design of a new innovative glenohumeral test rig. The test rig was required to imitate the movement of the humerus in the human body and replicate all the ranges of motion, which it can move in when combined with the relevant bones, muscles, ligaments and tendons in the shoulder complex. A variable force also had to be applied to the glenoid in all ranges of motion. Research had to be undertaken in the ranges of motion of the shoulder complex and the forces acting on the glenoid. Concept designs were initially created to mimic specific ranges of motion; adduction, flexion, internal (medial) and external (lateral) rotation for example. The concepts were evolved and combined to develop a test rig that would replicate any axial movement of the shoulder. Research determined the most appropriate manufacturing processes and materials so that the test rig could be manufactured in the material laboratories.     

An Unsteady Oscillatory Flow of Generalized Casson Fluid with Heat and Mass Transfer: A Comparative Fractional Model

It is of high interest to study laminar flow with mass and heat transfer phenomena that occur in a viscoelastic fluid taken over a vertical plate due to its importance in many technological processes and its increased industrial applications. Because of its wide range of applications, this study aims at evaluating the solutions corresponding to Casson fluids’ oscillating flow using fractional-derivatives. As it has a combined mass-heat transfer effect, we considered the fluid flow upon an oscillatory infinite vertical-plate. Furthermore, we used two new fractional approaches of fractional derivatives, named AB (Atangana–Baleanu) and CF (Caputo–Fabrizio), on dimensionless governing equations and then we compared their results. The Laplace transformation technique is used to get the most accurate solutions of oscillating motion of any generalized Casson fluid because of the Cosine oscillation passed over the infinite vertical-plate. We obtained and analyzed the distribution of concentration, expressions for the velocity-field and the temperature graphically, using various parameters of interest. We also analyzed the Nusselt number and the skin friction due to their important engineering usage.     

Experiments on two-phase flow in hydraulic jump on pebbled rough bed: Part 1–Turbulence properties and particle chord time and length

This study reported and discussed turbulence characteristics, such as turbulence intensity, correlation time scales, and advective length scales. The characteristic air–water time scale, including the particle chord time and length and their probability density functions (PDFs), was investigated. The results demonstrated that turbulence intensity was relatively greater on a rough bed in the roller length, whereas further downstream, the decay rate was higher. In addition, the relationship between turbulence intensity and dimensionless bubble count rate reflected an increase in turbulence intensity associated with the number of entrained particles. Triple decomposition analysis (TDA) was performed to determine the contributions of slow and fast turbulent components. The TDA results indicated that, regardless of bed type and inflow conditions, the sum of the band-pass (T'_u) and high-pass (T″_u) filtered turbulence intensities was equal to the turbulence intensity of the raw signal data (T_u). T″_u highlighted a higher turbulence intensity and larger vorticities on the rough bed for an identical inflow Froude number. Additional TDA results were presented in terms of the interfacial velocity, auto- and cross-correlation time scales, and longitudinal advection length scale, with the effects of low- and high-frequency signal components on each highlighted parameter. The analysis of the air chord time indicated an increase in the proportion of small bubbles moving downstream. The second part of this research focused on the basic properties of particle grouping and clustering.     

Experiments on two-phase flow in hydraulic jump on pebbled rough bed: Part 2–Bubble clustering

A survey on bubble clustering in air–water flow processes may provide significant insights into turbulent two-phase flow. These processes have been studied in plunging jets, dropshafts, and hydraulic jumps on a smooth bed. As a first attempt, this study examined the bubble clustering process in hydraulic jumps on a pebbled rough bed using experimental data for 1.70 < Fr₁ < 2.84 (with Fr₁ denoting the inflow Froude number). The basic properties of particle grouping and clustering, including the number of clusters, the dimensionless number of clusters per second, the percentage of clustered bubbles, and the number of bubbles per cluster, were analyzed based on two criteria. For both criteria, the maximum cluster count rate was greater on the rough bed than on the smooth bed, suggesting greater interactions between turbulence and bubbly flow on the rough bed. The results were consistent with the longitudinal distribution of the interfacial velocity using one of the criteria. In addition, the clustering process was analyzed using a different approach: the interparticle arrival time of bubbles. The comparison showed that the bubbly flow structure had a greater density of bubbles per unit flux on the rough bed than on the smooth bed. Bed roughness was the dominant parameter close to the jump toe. Further downstream, Fr₁ predominated. Thus, the rate of bubble density decreased more rapidly for the hydraulic jump with the lowest Fr₁.