Review of Suspended Sediment Transport Mathematical Modelling Studies

This paper reviews existing studies relating to the assessment of sediment concentration profiles within various flow conditions due to their importance in representing pollutant propagation. The effects of sediment particle size, flow depth, and velocity were considered, as well as the eddy viscosity and Rouse number influence on the drag of the particle. It is also widely considered that there is a minimum threshold velocity required to increase sediment concentration within a flow above the washload. The bursting effect has also been investigated within this review, in which it presents the mechanism for sediment to be entrained within the flow at low average velocities. A review of the existing state-of-the-art literature has shown there are many variables to consider, i.e., particle density, flow velocity, and turbulence, when assessing the suspended sediment characteristics within flow; this outcome further evidences the complexity of suspended sediment transport modelling.

Seaweed ingress of cooling water intakes with predictions for Torness power station

Seaweed ingress into the cooling water intakes of nuclear power stations has caused several disruptions to electricity supply. Seaweed is transported by tidal and wave-induced currents after dislodgement from the sea bed following stormy conditions but ingress will be shown to be not only determined by wave conditions. An integrated model system has been developed to predict such ingress and applied at the Torness power station in Scotland where the mass of seaweed recovered was measured for some ingress cases. Prior to each case, seaweed is assumed initially to be distributed in areas surveyed within the surrounding coastal domain with a mass per unit area based on local measurements. Criteria for dislodgement are based on near-bed velocity. Six cases where the mass of ingress was measured and two cases with no ingress have been modelled and predicted by adjusting a dislodgement factor (a multiplier on the threshold velocity) within a relatively narrow range.

The Impacts of Climate Variability on the Wind Erosion Potentials in the Western Region of Makran Coastal Plain, Iran

Coastal plains are prone to various degrees of wind erosion due to their characteristics. This study aimed to investigate the effect of climatic factors in the western region of Makran coastal plain in a southeastern region of Iran on the wind erosion potential. The study period was 1993-2018. First, the data related to wind velocities, relative humidity and precipitation, and the granulometric data of plain surface sediments were obtained. Then, the wind erosion threshold velocity in humid air conditions was determined. Finally, the Mann-Kendall test was applied to analyze the probability of wind erosion and its temporal variability. The results indicated that the wind erosion threshold, in terms of humidity changes, varied from 7.21 to 12.31 meters per second during the study period. The highest probability of wind erosion was in February, March, and April, with 24.69%, 21.51%, and 20.41%, respectively. The lowest probability of wind erosion was in October, November, and September with 4.00%, 4.12%, and 6.00%, respectively. Finally, the erosion trend analysis indicated that wind erosion was a temporal phenomenon that increased significantly in January (winter solstice) and July (summer solstice). These months were characterized by an increase in the wind blowing at speed above the threshold. Otherwise, the months were not different from other months of the year in terms of precipitation or the number of dry days. Therefore, wind erosion is expected to maximize in the early winter and the early summer.

Biofilms for Turbidity Mitigation in Oil Sands End Pit Lakes

End pit lakes (EPLs) have been proposed as a method of reclaiming oil sands fluid fine tailings (FFT), which consist primarily of process-affected water and clay- and silt-sized particles. Base Mine Lake (BML) is the first full-scale demonstration EPL and contains thick deposits of FFT capped with water. Because of the fine-grained nature of FFT, turbidity generation and mitigation in BML are issues that may be detrimental to the development of an aquatic ecosystem in the water cap. Laboratory mixing experiments were conducted to investigate the effect of mudline biofilms made up of microbial communities indigenous to FFT on mitigating turbidity in EPLs. Four mixing speeds were tested (80, 120, 160, and 200 rpm), all of which are above the threshold velocity required to initiate erosion of FFT in BML. These mixing speeds were selected to evaluate (i) the effectiveness of biofilms in mitigating turbidity and (ii) the mixing speed required to ‘break’ the biofilms. The impact of biofilm age (10 weeks versus 20 weeks old) on turbidity mitigation was also evaluated. Diverse microbial communities in the biofilms included photoautotrophs, namely cyanobacteria and Chlorophyta (green algae), as well as a number of heterotrophs such as Gammaproteobacteria, Desulfobulbia, and Anaerolineae. Biofilms reduced surface water turbidity by up to 99%, depending on the biofilm age and mixing speed. Lifting and layering in the older biofilms resulted in weaker attachment to the FFT; as such, younger biofilms performed better than older biofilms. However, older biofilms still reduced turbidity by 69% to 95%, depending on the mixing speed. These results indicate that biostabilization is a promising mechanism for turbidity mitigation in EPLs.

Resonant Instability of Kink Oscillations in Magnetic Flux Tubes with Siphon Flow

We study kink oscillations of a straight magnetic tube in the presence of siphon flows. The tube consists of a core and a transitional or boundary layer. The flow velocity is parallel to the tube axis, has constant magnitude, and confined in the tube core. The plasma density is constant in the tube core and it monotonically decreases in the transitional layer to its value in the surrounding plasma. We use the expression for the decrement/increment previously obtained by Ruderman and Petrukhin (Astron. Astrophys.631, A31, 2019) to study the damping and resonant instability of kink oscillations. We show that, depending on the magnitude of siphon-velocity, resonant absorption can cause either the damping of kink oscillations or their enhancement. There are two threshold velocities: When the flow velocity is below the first threshold velocity, kink oscillations damp. When the flow velocity is above the second threshold velocity, the kink oscillation amplitudes grow. Finally, when the flow velocity is between the two threshold velocities, the oscillation amplitudes do not change. We apply the theoretical result to kink oscillations of prominence threads. We show that, for particular values of thread parameters, resonant instability can excite these kink oscillations.

Depth of penetration of Dyneema® HB26 hard ballistic laminates

Analysis of depth of penetration (DoP) experimental data of Dyneema® HB26 hard ballistic laminates is presented using an energy approach. Several DoP experimental parameters have been identified and calculated including the threshold velocity of penetration ([Formula: see text]), the characteristic time ([Formula: see text]), the DoP damping coefficient ([Formula: see text]), and the dynamic pressure per unit impact speed ([Formula: see text]). For the first time, a simple penetration model is developed from the energy approach to predict the projectile motion and penetration resistance force during depth of penetration experiments.

Energy absorption of composite materials under high velocity impact

Many studies were directed toward understanding damage patterns in composite laminates and determining the damage development sequence upon high velocity impact. Damage accumulation depends on projectile velocity and on a number of other parameters, so that it is not possible to set strict limits between the different regimes. However, experiments show that, for a given set of experimental conditions where the impact speed is the only variable, there is a certain threshold velocity below which no detectable damage occurs. Above the threshold velocity, no surface damage is observed except for a small indentation at the contact point, but significant internal damage consisting of delaminating and matrix cracks is introduced. As the impact velocity increases further, surface damage due mainly to fiber breakage is introduced. For very high speeds, the target does not have time to deform, and perforation occurs, leaving a clean hole in the sample. The objective of this study is to develop a mathematical model that corresponds to the deformed geometry under high velocity impact applications for composite laminates. A total of 100 tests were conducted on composite laminates, struck by cylindrohemispherical projectiles at normal incidents with velocities up to about 100 mls. The types of materials, used this study, are AS4/3051, IM7/5250 CarbonlEpoxy and TI003 Glass/Epoxy. The strain energy was obtained by derivation of the proposed deflection function. The strain energy was plotted with respect to the deflection of the mid-plane and, then correlated through dynamic correlation factors to actual kinetic energy during the impact. The dynamic correlation factors were determined using a genetic algorithm regression analysis. Two types of materials were tested, namely plain graphite composites and hybrid composites. The growth of the delamination and also the effect of varying the stacking sequence were investigated for the different type of materials and various orientations. The mathematical model appears to provide a reasonable representation of the deformation of composite laminates during the penetration by a cylindro-hemispherical projectile. Furthermore, hybrid composites appear to provide more resistance to the impact, whereas plain composites have less resistance with respect to the higher velocities. It was concluded that, the change of the material in a hybrid composite affects the growth of the damaged area and also reduces the impact penetration resistance. Hence, IM7/E-Glass hybrid has a higher resistance to the penetration. Measurements of the energy levels of the hybrid composites indicated that they offer the highest resistance to ballistic perforation. The hybrid composites perforated at velocities between 77 mls and 83 (mls), whereas the graphite composites perforated at velocities between 48 m/s and 59 (mls). The higher perforation resistance is attributed to the reduced level of delamination generated during the impact, and also the addition of the E-Glass, which was capable of absorbing more energy during the impact. In studying the graphite composites, the best orientation in terms of the stacking sequence was found to be [(45, -45, 0, 90) 2 ] S , which indicates that this stacking sequence withstand higher velocity and hence absorbs more energy during the impact. Therefore, the quasi-isotropi corientation [(45, -45, 0, 90) 2 ] S is best for impact resistance if a laminate is not combined with E-Glass. The ballistic-limit velocity prior to perforation for the Quasi-isotropic laminate was measured as 58.9 m/s. This is a significant increase compared to the other plain graphite samples. The energy required for the complete perforation is approximately 48% higher in this stacking sequence as compared to other plain Graphite specimens. It was also found that the energy absorption capability is reduced significantly in the cross-ply laminates. The penetration resistance of the [(0,90,0,90) 2 ] S laminate and the energy required for perforation are approximately 50% less than the other plain graphite specimens.

Energy absorption of composite materials under high velocity impact

Many studies were directed toward understanding damage patterns in composite laminates and determining the damage development sequence upon high velocity impact. Damage accumulation depends on projectile velocity and on a number of other parameters, so that it is not possible to set strict limits between the different regimes. However, experiments show that, for a given set of experimental conditions where the impact speed is the only variable, there is a certain threshold velocity below which no detectable damage occurs. Above the threshold velocity, no surface damage is observed except for a small indentation at the contact point, but significant internal damage consisting of delaminating and matrix cracks is introduced. As the impact velocity increases further, surface damage due mainly to fiber breakage is introduced. For very high speeds, the target does not have time to deform, and perforation occurs, leaving a clean hole in the sample. The objective of this study is to develop a mathematical model that corresponds to the deformed geometry under high velocity impact applications for composite laminates. A total of 100 tests were conducted on composite laminates, struck by cylindrohemispherical projectiles at normal incidents with velocities up to about 100 mls. The types of materials, used this study, are AS4/3051, IM7/5250 CarbonlEpoxy and TI003 Glass/Epoxy. The strain energy was obtained by derivation of the proposed deflection function. The strain energy was plotted with respect to the deflection of the mid-plane and, then correlated through dynamic correlation factors to actual kinetic energy during the impact. The dynamic correlation factors were determined using a genetic algorithm regression analysis. Two types of materials were tested, namely plain graphite composites and hybrid composites. The growth of the delamination and also the effect of varying the stacking sequence were investigated for the different type of materials and various orientations. The mathematical model appears to provide a reasonable representation of the deformation of composite laminates during the penetration by a cylindro-hemispherical projectile. Furthermore, hybrid composites appear to provide more resistance to the impact, whereas plain composites have less resistance with respect to the higher velocities. It was concluded that, the change of the material in a hybrid composite affects the growth of the damaged area and also reduces the impact penetration resistance. Hence, IM7/E-Glass hybrid has a higher resistance to the penetration. Measurements of the energy levels of the hybrid composites indicated that they offer the highest resistance to ballistic perforation. The hybrid composites perforated at velocities between 77 mls and 83 (mls), whereas the graphite composites perforated at velocities between 48 m/s and 59 (mls). The higher perforation resistance is attributed to the reduced level of delamination generated during the impact, and also the addition of the E-Glass, which was capable of absorbing more energy during the impact. In studying the graphite composites, the best orientation in terms of the stacking sequence was found to be [(45, -45, 0, 90) 2 ] S , which indicates that this stacking sequence withstand higher velocity and hence absorbs more energy during the impact. Therefore, the quasi-isotropi corientation [(45, -45, 0, 90) 2 ] S is best for impact resistance if a laminate is not combined with E-Glass. The ballistic-limit velocity prior to perforation for the Quasi-isotropic laminate was measured as 58.9 m/s. This is a significant increase compared to the other plain graphite samples. The energy required for the complete perforation is approximately 48% higher in this stacking sequence as compared to other plain Graphite specimens. It was also found that the energy absorption capability is reduced significantly in the cross-ply laminates. The penetration resistance of the [(0,90,0,90) 2 ] S laminate and the energy required for perforation are approximately 50% less than the other plain graphite specimens.