Vishveshwar R. Mantha

The feasibility of biomass pellets production in Portugal.

Abstract The production of pellets represents the possibility of using different biomass residues in a standardized fuel. In this article, the economic feasibility of pellets production is analyzed in the Portuguese scenario according to the key indicators of biomass availability, costs, and legal framework. The potential of biomass residues in Portugal is significant and mainly from forestry. However, several limitations to its utilization for pellets production may arise since they are already put to other uses, such as biomass power plants. The combination of the biomass power plants with pellet production plants seems to be the best option for pellet production in the actual Portuguese scenario. The main constrains for the pellets market has been to convince small-scale customers that pellets are a good alternative fuel, mainly due to the investment needed and the strong competition in terms of fuel price with natural gas. These market problems need incentives at a political level bringing the value added tax for the same level of natural gas.

Computational Fluid Dynamics Study of Swimmer's Hand Velocity, Orientation, and Shape: Contributions to Hydrodynamics

The aim of this paper is to determine the hydrodynamic characteristics of swimmers scanned hand models for various combinations of both the angle of attack and the sweepback angle and shape and velocity of swimmers hand, simulating separate underwater arm stroke phases of freestyle (front crawl) swimming. Four realistic 3D models of swimmers hand corresponding to different combinations of separated/closed fingers positions were used to simulate different underwater front crawl phases. The fluid flow was simulated using FLUENT (ANSYS, PA, USA). Drag force and drag coefficient were calculated using (computational fluid dynamics) CFD in steady state. Results showed that the drag force and coefficient varied at the different flow velocities on all shapes of the hand and variation was observed for different hand positions corresponding to different stroke phases. The models of the hand with thumb adducted and abducted generated the highest drag forces and drag coefficients. The current study suggests that the realistic variation of both the orientation angles influenced higher values of drag, lift, and resultant coefficients and forces. To augment resultant force, which affects swimmers propulsion, the swimmer should concentrate in effectively optimising achievable hand areas during crucial propulsive phases.

The Effect of Depth on Drag During the Streamlined Glide: A Three-Dimensional CFD Analysis

The Effect of Depth on Drag During the Streamlined Glide: A Three-Dimensional CFD Analysis The aim of this study was to analyze the effects of depth on drag during the streamlined glide in swimming using Computational Fluid Dynamics. The Computation Fluid Dynamic analysis consisted of using a three-dimensional mesh of cells that simulates the flow around the considered domain. We used the K-epsilon turbulent model implemented in the commercial code Fluent® and applied it to the flow around a three-dimensional model of an Olympic swimmer. The swimmer was modeled as if he were gliding underwater in a streamlined prone position, with hands overlapping, head between the extended arms, feet together and plantar flexed. Steady-state computational fluid dynamics analyses were performed using the Fluent® code and the drag coefficient and the drag force was calculated for velocities ranging from 1.5 to 2.5 m/s, in increments of 0.50m/s, which represents the velocity range used by club to elite level swimmers during the push-off and glide following a turn. The swimmer model middle line was placed at different water depths between 0 and 1.0 m underwater, in 0.25m increments. Hydrodynamic drag decreased with depth, although after 0.75m values remained almost constant. Water depth seems to have a positive effect on reducing hydrodynamic drag during the gliding. Although increasing depth position could contribute to decrease hydrodynamic drag, this reduction seems to be lower with depth, especially after 0.75 m depth, thus suggesting that possibly performing the underwater gliding more than 0.75 m depth could not be to the benefit of the swimmer.

Effect of wearing a swimsuit on hydrodynamic drag of swimmer

The purpose of this study was to analyse the effect of wearing a swimsuit on swimmers passive drag. A computational fluid dynamics analysis was carried out to determine the hydrodynamic drag of a female swimmers model (i) wearing a standard swimsuit; (ii) wearing a last generation swimsuit and; (iii) with no swimsuit, wearing light underwear. The three-dimensional surface geometry of a female swimmers model with different swimsuit/underwear was acquired through standard commercial laser scanner. Passive drag force and drag coefficient were computed with the swimmer in a prone position. Higher hydrodynamic drag values were determined when the swimmer was with no swimsuit in comparison with the situation when the swimmer was wearing a swimsuit. The last generation swimsuit presented lower hydrodynamic drag values, although very similar to standard swimsuit. In conclusion, wearing a swimsuit could positively influence the swimmers hydrodynamics, especially reducing the pressure drag component.

Study of external air flow for an AURORA

Purpose – The purpose of this current study is to identify the optimal stable position of airship, with reference to spatial variation of atmospheric wind flow, so as to reduce the vibrations and thus aid in the development of control mechanism of airship dynamics.Design/methodology/approach – Study of uniform flow under steady‐state conditions was carried out through the measurements of pressure and velocity in a wind tunnel at low Mach numbers on airship model (in order of size, 1:13) inclined to the uniform air stream at various angles. The measurements have been made for a range of angles of incidence, in both vertical and horizontal planes, with a Reynolds number, based on the free stream velocity and a body cross‐sectional dimension, of order of four and six, respectively. Steady‐state numerical simulations were performed, serving comparative investigation with experimental data for the specific case of the model inclined to the free stream, with orientation of side‐slip (yaw) angle β=0 and angle of...

The 3D CFD study of gliding swimmer on passive hydrodynamics drag

The aim of this study was to analyze the effect of depth on the hydrodynamic drag coefficient during the passive underwater gliding after the starts and turns. The swimmer hydrodynamics performance was studied by the application of computational fluid dynamics (CFD) method. The steady-state CFD simulations were performed by the application of k - omega turbulent model and volume of fluid method to obtain two-phase flow around a three-dimensional swimmer model when gliding near water surface and at different depths from the water surface. The simulations were conducted for four different swimming pool size, each with different depth, i.e., 1.0, 1.5, 2.0 and 3.0 m for three different velocities, i.e., 1.5, 2.0 and 2.5 m/s, with swimmer gliding at different depths with intervals of 0.25 m, each starting from the water surface, respectively. The numerical results of pressure drag and total coefficients at individual average race velocities were obtained. The results showed that the drag coefficient decreased as depth increased, with a trend toward reduced fluctuation after 0.5m depth from the water surface. The selection of the appropriate depth during the gliding phase should be a main concern of swimmers and coaches.

Analysis of wind velocity and release angle effects on discus throw using computational fluid dynamics

The aim of this paper is to study the aerodynamics of discus throw. A comparison of numerical and experimental performance of discus throw with and without rotation was carried out using the analysis of lift and drag coefficients. Initial velocity corresponding to variation angle of around 35.5° was simulated. Boundary condition, on the top and bottom boundary edges of computational domain, was imposed in order to eliminate external influences on the discus; a wind resistance was calculated for the velocity values of 25 and 27 m/s. The results indicate that the flight distance (D) was strongly affected by the drag coefficient, the initial velocity, the release angle and the direction of wind velocity. It was observed that these variables change as a function of discus rotation. In this study, results indicate a good agreement of D between experimental values and numerical results.

CFD ANALYSIS OF THE BODY POSITION DURING THE GLIDING IN SWIMMING

Background The swimmers body position after immersion determines the success of the start rather than his/her starting body position in the block or during the fly.1 There are swimmers gliding in a lateral position whereas others prefer a prone one. Moreover, during this phase, swimmers may alter their body posture and, as far as some techniques are concerned, swimmers must change the position of the limbs.2 The purpose of this study was to analyze the effects of body positions in drag coefficient during the glide in swimming using computational fluid dynamics. Methods In order to create the three-dimensional digital model computer tomography scans of a human body of a male swimmer were applied3. The swimmer was modelled as if he were gliding underwater in a streamlined position, at four different body positions: (i) in the prone position, (ii) in a side position with an absolute angle between the horizontal plane with the body coronal plane of 45°, (iii) in a side position with 90° of rotation and, (iv) in the dorsal position. The boundary conditions of the model were designed to represent the geometry and flow conditions of a part of a lane in a swimming pool. Steady-state computational fluid dynamics analyses were performed using the Fluent® code and the drag coefficient was computed for velocities of 1.5, 2.0 and 2.5 m/s. Results Drag coefficient reaches its lowest value in the prone position, followed by the side position with 45° of rotation (0.29%, 0.15%, 0.01% drag increment for 1.5, 2.0, and 2.5 m/s, respectively), the side position with 90° of rotation (1.03%, 0.94%, 0.64% increment), and the dorsal position (2.21%, 1.42%, 0.96% increment), in which the highest value of drag coefficient is obtained. Discussion/Conclusions Main data shows that the prone position presented the lowest drag coefficient values, whereas dorsal position presented the highest values during the underwater gliding. The prone position seems to be the one that should be adopted after the starts and turns phases of a competitive swimming event, especially during freestyle events and after pushing-off from the wall during the turn where swimmers can freely choose the best body position.

Modelling propelling force in swimming using numerical simulations

Daniel A. Marinho1,2, Tiago M. Barbosa2,3, Vishveshwar R. Mantha2,4, Abel I. Rouboa2,5 and Antonio J. Silva2,4 1University of Beira Interior, Department of Sport Sciences, Covilha 2Research Centre in Sports, Health and Human Development, Vila Real 3Polytechnic Institute of Braganca, Department of Sport Sciences, Braganca 4University of Tras-os-Montes and Alto Douro, Department of Sport Sciences, Exercise and Health, Vila Real 5University of Tras-os-Montes and Alto Douro, Department of Engineering, Vila Real Portugal

Momentum and Heat Transfer in Power‐Law Fluids Across a Rotating Cylinder: A Numerical Study

The momentum and energy equations describing the steady cross‐flow of power‐law fluids past a rotating heated cylinder have been solved numerically. The results highlight the influence of dimensionless rotational velocity (0≤α≤6), power‐law index (0.5≤n≤1.5), Prandtl number (1≤Pr≤100) on the drag and lift coefficients for Reynolds number of Re = 40, surface‐averaged values of the Nusselt number, detailed flow and temperature fields.