نشریه مهندسی مکانیک مدرس
سال بیست و یکم شماره 12 (آذر 1400)

Homogeneous charge compression ignition (HCCI) has attracted lots of attention due to the high thermal efficiency, lower NO x, and Soot exhaust emissions. Heat transfer from the gases to the combustion chamber walls has effective impact on the combustion process and the formation of engine-out emissions in HCCI engine. In this study for the first time a zero-dimensional single-zone model coupled with detailed chemical kinetics was used to evaluate the semi-empirical heat transfer models of Annand, Woschni, Hohenberg along with Assanis and Hensel to calculate heat flux in an HCCI engine fueled with natural gas. For this purpose, the 3D-CFD model coupled with detailed chemical kinetics was firstly validated by using experimental data, and then the 3D derived model was used as a base model for evaluating zero-dimensional model. Furthermore, the response surface model (RSM) was employed for investigating the effect of input parameters of engine including intake pressure (1, 1.25, and 1.5bar), equivalence ratio (0.3, 0.5, and 0.7), and engine speed (800, 1100, and 1400rpm) on the output parameters i.e., in-cylinder pressure and heat flux. In most cases were assessed, the zero-dimensional simulation results indicated that Annand technique provided the best model for heat flux simulation. Besides, the model of Hohenberg overpredict the heat flux in comparison with the calculated values derived from the 3D model, while Assanis and Hensel models underpredict the heat flux compared with the evaluated value of the 3D model. Furthermore, Woschni’s model cannot be used to model the heat flux in HCCI engine.

The fibers of date palms, which are widely available in the south of Iran, are a variety of natural fibers that can be used as a reinforcement in polymer composites. This work investigates the effect of alkali treatment on the mechanical properties of date palm fibers and their adhesion to thermoset polymer. The sodium hydroxide (NaOH) solution at three different concentrations (1 wt%, 3 wt%, and 5 wt%) was used to treat the fibers. The single fiber tensile test and fiber pull-out tests were performed to measure the mechanical properties and fiber/matrix interfacial share strength, respectively. Comparing the SEM images of the untreated and treated fibers showed that the 3% NaOH treatment could effectively remove non-cellulosic materials, i.e. lignin and wax, with minimum damage to the fiber surface. The experimental results showed a clear improvement of the mechanical properties and fiber/matrix adhesion after treatment. It was found that the 3% NaOH solution is the optimal concentration to achieve the maximum improvement in the fiber and bonding properties.

Wave conditions have a significant effect on the hydrodynamic behavior of OWC. As the interactions of the WEC and the incident waves are important, therefore, due to the importance of coefficients in evaluating the performance of the OWC, in this paper, the experimental evaluation of dimensionless hydrodynamic coefficients of a MC-OWC is applied. To define the experimental tests, considering the installation location of the converter on the break water, the conditions of the Caspian Sea implemented. Calibration and uncertainty analysis have performed, experimental tests have been carried out in the wave tank of the BNUT. According to the results, assuming a dimensionless water depth, with increasing dimensionless frequency of the wave, the dimensionless coefficient of transmitted wave, the dimensionless coefficient of reflected wave, dimensionless coefficient of discharge and the dimensionless coefficient of pressure increase. The results showed that due to the change of dimensionless wave number from 1.9 to 3.3, discharge coefficients, reflected wave, pressure and transmitted wave are 1.6 times, 2.2 times, 2.8 times, respectively, are 3.5 times, the dimensionless coefficient of the transmitted wave is highly sensitive to the wave conditions; the dimensional coefficient of discharge will have less changes compared to other coefficients. On the other hand, the results showed that the OWC in this study has an efficiency of 41.8% in the best case. This efficiency occurs at the dimensionless natural frequency of 0.88 and the dimensionless water intake depth of 0.032; under these conditions, the amplitude of water fluctuations inside the OWC reaches 9.6 cm.

The increasing consumption of non-renewable energy sources such as oil and gas and reducing their reserves make it more necessary to pay attention to clean and renewable resources. In this situation, wind energy is known as one of the safest options for generating electrical energy. In this study, with the aim of evaluating the impact of climate change on the economic and environmental characteristics of wind turbines, numerical modeling was developed in MATLAB software. In order to evaluate the effects of the mentioned parameters as a case study, this numerical modeling for the parameters expressed in 4 cities of Iran, including Rasht, Tehran, Abadan, and Sanandaj, as the representatives of the main climates of Iran has been analyzed. According to the results of the economic point of view, which represents the Levelized cost of the energy production unit, Abadan was recognized as the most economical case with a   Levelized cost of  1.04 $ per kilowatt-hour of energy. Also, the environmental aspect of the analysis, which is based on the life cycle assessment method, considering the amount of carbon dioxide produced during the system life cycle and its pricing based on penalty policies, Rasht with a mild climate and emissions of 156 kg. Carbon dioxide per year and the lowest fine cost (annual cost $ 2.26) showed the most suitable option among other cities.

Today, polyether ether ketone composites are widely used in the medical and aerospace industries due to their high strength-to-weight ratio, anti-allergic properties, high buckling resistance and fatigue. Grinding has a high specific energy among traditional cutting processes. Usually a high portion of energy will converts to heat. Because heat has an important role in polymer grinding, the heat modeling of it is necessary. In addition to the energy of chip formation during material removal, there are other energies such as plowing and friction energy. The contribution of each of these energies affects the efficiency of the process. By theoretical calculating of the cutting energy and comparing it with the experimental specific grinding energy, the portion of chip formation energy versus friction and plowing energy can be calculated. By performing differential scanning calorimetry test and theoretical calculations, the amount of chip formation energy was 0.089 and 0.119 J/mm^3 for GFRP and CFRP, respectively. While the experimental results of grinding showed a minimum specific energy of 2.2 J/mm^3 and 2.4 J/mm^3 for GFRP and CFRP, respectively. This difference indicates the very high portion of plowing energy in the grinding of this material and especially polymeric materials. The percentage of the chip-forming energy that enters the workpiece as heat was calculated to be 27%. Therefore, it can be stated that all energy except 73% of the chip formation energy enters the workpiece.

Sports simulation mechanisms practically have a lot of appeal and application to implement virtual reality environments. Cycling simulator has a more special place in sports and urban transportation due to the popularity of cycling activities. In this paper, the design and construction of a new motion generating mechanism for an interactive cycling simulator is presented. First, by using the references, the range of velocity and acceleration that the user should experience while cycling has been extracted, and by analyzing other cycling simulators, the required degrees of freedom and its range have been determined. Then, a new motion generating mechanism with two degrees of freedom is designed. Genetic algorithm has been used for dimensional optimization of the mechanism parameters. Kinematics and dynamic equations of the mechanism have been extracted. According to the dynamic model of the mechanism, a controller has been designed using the feedback linearization method and the performance have been investigated. Finally, the designed motion generating mechanism has been constructed and the position control has been implemented on the platform.