Academic

In this project we aim to predict the morphology evolution of a porous solid due to chemical reactions between a solid and a penetrating gas phase. The oxidation of soot by diluted oxygen and NO2, passing through a porous soot layer, will serve as an example of practical relevance. This basic phenomenon during the regeneration of soot filters for cleaning the exhaust of diesel engines and is so far not sufficiently understood. It is well known that the overall oxidation rate during soot filter regeneration is a strong function of time, even under isothermal conditions. By combining experimental investigations and detailed numerical simulations we will try to show from first principles if (and to what extent) the change in the overall reaction rate primarily originates from morphological changes of the soot.

Within the project a special reactor will be constructed that allows to oxidize a soot layer stepwise under isothermal conditions. From analysis of exhaust gas, we retrieve the instantaneous overall reaction rate. After subsequent steps of partial soot oxidation, the overall BET surface will be measured without dismounting the sample. Thus, we can simultaneously obtain effective reaction rates and surface areas. Detailed information of the porous soot structure has recently become assessable by Focused Ion Beam - Scanning Electron Microscope (FIB-SEM) images. This allows to reconstruct the porous medium in microscopic scale with high resolution and provides initial conditions for numerical simulations.

A detailed 3D Lattice-Boltzmann (LB) model will be developed to simulate the soot morphology change during soot oxidation. While the reaction of multicomponent inside pores will be considered homogeneous and simulated using the discrete form of the Boltzmann kinetic equation, the heterogeneous soot morphology change during soot oxidation will be modeled as new boundary condition. As LB method can handle complex geometries efficiently, it is suited to model solid-gas phase transition. We can compare the calculated effective oxidation rate to experimental values, assuming a constant surface reaction rate at the evolving soot surface. Furthermore, FIB-SEM images obtained from soot samples after partial oxidation can be compared to simulations. Once a detailed model is available, this will serve as a basis for the development of an extended application-oriented model. For deriving anisotropic macroscopic transport parameters asymptotic homogenization will be used. The derived macroscopic model comprises the classical mass and energy balances as well as balance equations for characteristic structural properties such as BET surface.

From left to right a sample of backscattered images, its three-dimensional reconstruction of FIB-SEM images (Hasegawa et al. 2018), as well as images pores detection and numerically reconstruction (Muntean et al. 2003). 

Marine currents transfer a lot of kinetic energy during their movement. These currents can be caused by tides. The energy extraction for this situation is similar to that of wind and can be achieved by using a turbine similar to the wind turbine. Due to the much higher water density than air, this energy is about 1000 times more. The tidal turbine with a power of 100 watts has been designed and constructed according to the needs defined for our group.

In this project, in the first step, computer-aided numerical simulation and computational fluid dynamics (CFD) were used to design, investigate and optimize a horizontal axis tidal turbine (HATT). This was the first step of R&D for implementation in the Persian Gulf condition. To do so, suitable locations were reviewed. Then, the optimization is focused on determining the optimum fixed pitch angle of a 3-bladed HATT based on widespread multiple reference frame technique to calculate power and thrust coefficients at different operational rotating speeds. To simplify the problem and reducing the computational costs due to cyclic symmetry only one blade, accordingly 1/3 of the whole computational domain, is considered in the modeling. Due to flow's nature involving rotating, separation and recirculation, realizable κ-ε turbulence model with standard wall function is selected to capture flow characteristics influenced by the rotor and near the wall region. Moreover, the major phenomenon, cavitation occurrence, is also checked at the critical situation where it is found to be safe. Finally, by comparing and evaluating the results to other HATTs, it implies that the proposed rotor is feasible and proved by CFD evaluation at this step. 

After performing numerous simulations and assuring of turbine performance, the model was designed and constructed. In the next step, the turbine was tested under various conditions namely: pitch angle, electrical load, carriage speed, and immersion depth to improve efficiency. Our experiment indicated the turbine performance to be the best being close to the surface of the water at different flow speeds. The optimum electrical load was found to be 20 Ω adding 16-40% to efficiency. By fixing the optimum load and tip immersion depth, the maximum efficiency of the whole rotor achieved around 0.265 at less than 0.56 m/s as towing speed while at the speed of 1.1 m/s, the maximum output power was more than 120 W having the pitch of the blades fixed at 20.4°.  The picture of the model and the testing operations are shown in below.

The marine and ocean energies are part of renewable energy that Wave energy converters (WECs) are used to extract them. Experimental modeling will be useful in evaluating their performance. In this project, the experimental model of an attenuator WEC, called Centipede, was designed and built in the Sea-Based Energy Research Group of the Babol Noshirooni University of Technology. The system utilizes six 36cm spherical floaters, all of which are steel and mounted on the system with a 1m long arm connection. The arms used in the system are screw type and the floater position can be adjusted by moving along the axis of the arm. In this converter, mechanical Power Take-Off System type is used for this WEC. The flywheel is used to keep the axle rotation uniform because it can withstand rotational speed changes when an irregular torque is applied. The length of a row of floaters is at least equivalent of a wavelength, and by passing the waves over the floaters, the floaters move up or down depending on the position and causing the axis to rotate. Then, in the next step, after passing the wave, the floaters move downwards without affecting the rotational speed to repeat the function of the vessels as the next wave enters. 

The performance of this WEC was studied and evaluated in the wave tank by applying the sea waves conditions. In this evaluation, the effects of wave amplitude and wave period on the average and maximum net power of the Centipede WEC were investigated. According to the results, it was observed that the maximum net power from this experimental system was more than 60 W considering the wave conditions of the Caspian Sea. 

The oscillating water column (OWC) converter is one of the most widely used devices in the field of sea electricity generation. Physically, the device is a rigid, hollow chamber designed to be floating and stationary. In this project, various designs have been investigated and researched. Finally, the design that confirms the results of numerical simulations and laboratory tests is a multi-chamber OWC in which the chambers are aligned in a wave direction. The results of simulations and tests suggest the optimal number of 5 chambers.

In this project which was also my PhD Thesis, an offshore point-absorber wave energy converter (WEC), called IRWEC1 was designed, manufactured and tested in our group (Sea-Based Energy Research Group). The initial concept of the IRWEC1 is based on French SEAREV WEC ; however the PTO mechanism is entirely altered by applying a chain-and-gear system. The mechanical and electrical systems of this WEC are placed in an outer shell for complete sealing. Its mechanical system consists of a pendulum and a power take-off system. Important motion for the WEC is the pitch motion, so a pendulum is designed for converting this oscillation. The WEC pitch oscillation causing the movement of the pendulum and this motion is transmitted to generator by power take-off system. The PTO consists of several gears for rectifying the reciprocating rotation at first stage and then converts them to an appropriate torque and angular velocity for transmitting it to generator. By generator rotation, electricity is produced.  The electrical part of the IRWEC1 consists of a brushless generator. The brushless generators are known for their durability, reliability, less losses, less weight and volume and high efficiency. The generator of IRWEC1 is completely designed and built in our Lab. 

In this project, this WEC is experimented for a wide range of waves in the wave tank. The wave characteristics are presented by which the system had appropriate pitch motion and acceptable extracted electrical energy. Extracted power from this experimental WEC when system has suitable pitch angle was more than 100 watts. 

In the next step, the geometry of the IRWEC1 was optimized. For the optimization process, the multi-objective GA was used with mean absorbed power and submerged surface area as the objective functions. The mean absorbed power was calculated with regards to the wave characteristics of the Caspian Sea. For the hydrodynamic simulation of the wave-body interaction, the boundary element method was employed as it is one of the most useful methods for modelling the boundary value problems, particularly for problems related to the hydrodynamic of marine structures. For the optimization, various shapes were considered for WEC geometry. The parallelepipedic hull shape was selected as the basic shape for the optimization process. All other geometries were obtained by implementing modifications on the upside and bottom part of this geometry and also changing the dimensions. After implementing the optimization process for these geometries, the Pareto fronts obtained from each shape were compared and the superior shape between these geometries was introduced for further investigation and optimization. 

Exploiting wind energy, which is a complex nature in urban areas, requires turbines suitable for unfavorable weather conditions, to trap the wind from different direction; savonius turbines are suitable for these conditions.  In this project, first a savonius vertical wind turbine (VWT) is designed and by using numerical simulation, its performance is evaluated. Then, the designed model was constructed and its efficiency is assessed by applying different wind speeds.

In the numerical simulations, the effect of overlap ratios and the position of blades on the turbine is studied and analyzed. For this purpose, two positive and negative overlap situations are first defined along the x-axis and examined in the different tip speed ratios of the blade, while maintaining the size of the external diameter of the rotor, to find the optimum point; then, the same procedure is done along the y-axis. Two-dimensional numerical simulations are performed using URANS equations and sliding mesh method. Turbulence model is realizable K-ε. According to the values of the dynamic torque and power coefficient, while investigating horizontal and vertical overlaps along the x and y-axis, the blades with overlap ratios of HOLR = +0.15 and VOLR = +0.1, show better performances when compared to other corresponding overlaps. Accordingly, the average Cm and Cp improvement were 16% and 7.5%, respectively, compared to the base with zero overlap ratio.

After performing numerous numerical simulation to assure of the turbine performance, the model was designed using the Solidworks software. The construction of the turbine was done by our group. With using wind turbine, the turbine was operated and multiple LEDs was used to show the electricity generated by the turbine.