Journal of Computational & Applied Research in Mechanical Engineering (JCARME)
https://jcarme.sru.ac.ir/
Journal of Computational & Applied Research in Mechanical Engineering (JCARME)endaily1Fri, 01 Mar 2024 00:00:00 +0330Fri, 01 Mar 2024 00:00:00 +0330Vibration characteristics of rotor systems with disk-shaft clearance
https://jcarme.sru.ac.ir/article_1950.html
Currently, the existing study on rotor system with disk-shaft clearance primarily focus on analyzing factors such as interference force and friction coefficient, while neglecting the vibration characteristics during the rotational states. Therefore, a finite element model is established by taking rotor systems with disk-shaft clearance as the research object. The vibration characteristics of rotor systems under different clearances or rotation speeds are analyzed. Increasing clearance leads to gradual fluctuations in the speed difference of shaft to disk, accompanied by an increasing periodicity of these fluctuations. In the time domain diagram, beat vibration characteristic become evident, and its period undergoes noticeable changes. The amplitude of rotation frequency increases, while that of multiple frequency decreases gradually and tends to a constant value. The presence of clearance causes the orbit of the disk center to become an irregular circle, and the shape of 8 appears. Additionally, collision and friction of shaft to disk result in apparent serrations in the orbit. As the rotational speed increases, the speed difference initially increases but eventually reaches a stable value. The beat vibration characteristic disappears due to the small speed difference, leading to a small amplitude of the multiple frequency. The orbit of the disk center tends to become circular, and the serrated phenomenon weakens and disappears. Finally, the experiments of rotor systems with disk-shaft clearance are carried out. The results are in good agreement with the simulations, which verifies the correctness of the dynamic model. The research results can provide a theoretical basis for understanding rotor systems with disk-shaft clearance.CFD simulation and exergy evaluation of geometrical characteristics effects of refrigeration tubes in a 3-fluid LAMEE
https://jcarme.sru.ac.ir/article_2086.html
Cooling tubes are inserted into the desiccant dehumidifier liquid of a 3-fluid liquid-to-air membrane energy exchanger (LAMEE) in order to regulate the temperature of the dehumidifier liquid. As a result, the 3-fluid LAMEE's performance is significantly influenced by the refrigerated tubes. The numerical analysis of the present work shows that the number of chilled tubes and their inner diameter affect the effectiveness (total, latent, and sensible) rate of moisture removal and adequate cooling power, and exergy loss. Additionally, the dehumidifier liquid channel receives the addition of wavy cooling tubes for the first time. The relationship between wave height and wave length is known as wave steepness, and its impact on efficiency and energy loss is also examined. Numerical studies show that the number and inner diameter of the cooling tubes have a direct correlation with the efficiency of the 3-fluid LAMEE. The improved the efficiency, the more cooled tubes there are and the larger their diameter. Furthermore, both exergy loss and without dimensions exergy loss increase with the quantity and diameter of refrigerated tubes. The sensible and latent effectiveness of the 3-fluid LAMEE is increased by the wavy refrigeration tubes as compared to straight tubes; the augmentation of the sensible and latent effectiveness increases with wave steepness.A comprehensive numerical investigation of the effects of inlet operating conditions on the performance of 3-fluid liquid-to-air membrane energy exchangers
https://jcarme.sru.ac.ir/article_2058.html
3-fluid liquid-to-air membrane energy exchangers (LAMEEs) are economic dehumidification systems; cooling tubes are put into dehumidifier liquid channels to regulate the internal temperature of the dehumidifier liquid. 3D computational fluid dynamics is used to simulate a 3-fluid LAMEE, and extra transfer of both heat and mass formulas, along with the essential equations that govern for viscous fluid flow, are compiled using external computer programs known as UDS (User Defined Scalar). This study thoroughly investigates the impact of the water inflow variables on system efficiency. The refrigeration fluid that runs inside the cooling tubes is water. The temperature distribution of the three fluids is investigated and the role of the refrigeration tubes based on their positions is evaluated on the desiccant solution cooling. Six tests are conducted to achieve the best arrangement of the inlet water conditions based on the tube&rsquo;s geometrical location. At an intake water mass flow rate of 4.67 g/s, the latent and sensible effectiveness rise from51% to 78% and 60% to 130%, respectively, when the input water temperature drops from 24.6 &deg;C to 10.1 &deg;C.Improvement of energy efficiency and heat recovery performance within the paper machine drying section
https://jcarme.sru.ac.ir/article_2059.html
In this study the energy assessment and heat recovery analysis of multi-cylinder drying section were carried out in a fluting paper machine. The specific heat consumption per unit of paper was determined to be about 4.7 GJ per ton of paper and accordingly, the machine consumed about 1.71 tons steam per ton of produced paper. The temperature efficiency of the heat exchanger and recovering efficiency of the heat recovery system of the paper machine have been determined to be about 50% and 4%, respectively. The results show that the steam use in the heat recovery system can be reduced by about 0.95 ton/h due to adjusting the supply air temperature to the optimum range, which corresponds to about 5.2% reduction in energy input and 4% improvement in dryer efficiency resulting nearly 31,000 $ savings per year. Also, the CO2 emission due to gas use can be decreased about 925 tons per year.Effect of exhaust gas recirculation and constant pre-heated air temperature on the homogeneous charge compression ignition combustion engine with diesel and wppo 20 blend
https://jcarme.sru.ac.ir/article_2018.html
This article describes an experimental study on fueling the port fuel injection homogeneous charge compression ignition (PFI-HCCI) combustion engine with plastic oil that is generated from waste plastics through the pyrolysis method. This study tested different exhaust gas recirculation (EGR) levels of 0%, 5%, 10%, and 15% using a modified PFI-HCCI computerised 4-stroke, single-cylinder, water-cooled, direct injection Kirloskar diesel engine connected to an eddy current dynamometer. Furthermore, an engine running at 1500 rpm and a constant pre heated air temperature (PHAT) of 140&deg;C were assessed. In this experiment, fuel, 20% biodiesel waste plastic pyrolysis oil (WPPO), and continuous PHAT 140&deg;C are used. The testing results show that the cylinder peak pressure and heat release rate for WPPO 20 with 15% EGR were attained at 39.70% and 15.09%, respectively. Additionally, port fuel injection with PHAT and WPPO 20% without EGR is reported to have a 45% higher brake thermal efficiency at full load than PFI-HCCI Diesel (D100). But when employed at full load with 15% EGR, WPPO 20 blend also reduced smoke opacity by 30.74% and Oxides of Nitrogen (NOx) emission by 52.17%. On the other hand, compared to the PFI-HCCI (D100), there are higher emissions of carbon monoxide (CO) (22.07%) and unburnt hydro carbon (UHC) (54.14%) with 15% EGR. Consequently, WPPO can be used to the PFI-HCCI engine.Numerical solution of unsteady incompressible nanofluid flow with mixed convection heat transfer using Jameson method on unstructured grid
https://jcarme.sru.ac.ir/article_1974.html
The purpose of this paper is to numerically simulate unsteady, incompressible and laminar flow with natural and mixed convection heat transfer in a square lid-driven cavity filled with Cu-Water nanofluid. Jameson method is used in conjunction with Artificial compressibility method on unstructured grid in a viscous flow. Effects of Grashof number and nanoparticle volume fraction on the flow and heat transfer characteristics are investigated. Two dimensional Navier-Stokes equations as the governing equations of the problem are discretized with finite volume method. Spatial discretization is performed with two order central scheme and Jameson artificial dissipation terms are added to equations to stabilize the solution. Unsteady terms are discretized with implicit two order scheme and are solved with fourth order explicit Runge-Kutta method in pseudo-time. It is found that Jameson method has good performance with reasonable convergence rate. Results show that increase in volume fraction of nanoparticles improves heat transfer characteristics while increase in Grashof number, weakens the heat transfer due to domination of natural convection.Evaluation of omega-shaped Coriolis mass flow meter for laminar flow
https://jcarme.sru.ac.ir/article_1904.html
Measuring flow rate precisely in laminar flow has been a difficult task, especially when utilizing a Coriolis mass flow meter (CMFM) for low flow rate measurements. The meter often under reads the mass flow rate, making it less useful in these conditions. The dominant factor affecting the CMFM's performance in laminar regions is secondary flow, which overshadows the generated Coriolis force, leading to an under-reading of flow rate. Previous studies have indicated that tube curvature is the most significant parameter affecting secondary flow generation and the overall performance of the meter. An omega-shaped tube configuration featuring a continuous curvature has been identified as the optimal shape for maximizing a CMFM device&rsquo;s performance in laminar flow. The purpose of the investigation is to study and compare the efficiency of various Omega tube designs that have undergone slight geometric alterations. Four different configurations were evaluated for maximum time lag by vibrating at their respective natural frequencies and keeping the sensor position along the centerline of the tube configuration.Effect of concentric and eccentric porous layer on forced convection heat transfer and fluid flow around a solid cylinder.
https://jcarme.sru.ac.ir/article_2055.html
In this paper, heat transfer and fluid flow around a solid cylinder wrapped with a porous layer in the channel were studied numerically by computational fluid dynamics (CFD). The homogeneous concentric and eccentric porous medium round a rigid, solid cylinder are supposed at local thermal equilibrium. The transport phenomena within the porous layer, volume averaged equations were employed, however the conservation laws of mass, momentum and energy were applied in the channel. The main purpose of this study is analyzed and compared the heat flux of concentric and eccentric porous layer in Reynolds number range of 1 to 40 and Darcy numbers of 10-2 to 10-6. It is found that with the decline of Darcy number, the vortex length is increased behind the solid cylinder surface. In addition, the heat flux rate of the cylinder is raised with the increase of Reynolds number. Finally, the results showed that the average Nusselt numbers in different Darcy and Reynolds numbers are higher in the eccentric porous layer than in the concentric porous layer. For example, our findings show that in Da=〖10〗^(-5), Re=40 and d=0.07 m, the average Nusselt number in the eccentric porous layer is 7.5% higher than the concentric porous layer.Fatigue analysis of the railway wheels of the CRH2 high speed train due to random parameters
https://jcarme.sru.ac.ir/article_1995.html
The most crucial parts that literally sustain the safety of railroad rolling stock from the subfloor are the wheels. However, during operation, several random parameters can impair their performance, resulting in the train's unsafety. These unpredictable characteristics can lead to fatigue failure, especially in a CHR2 high-speed train. This study aims to analyse the fatigue life of railway wheels for the CHR2 high-speed train due to different random parameters. Three scenarios with random parameters were considered: suspension system, passenger weight, and train speed. A 3D wheel model created by CAD and analyzed with finite element software ANSYS and nCode to validate the model by applying static force. A railway vehicle-track dynamics model with a 30t axle load using the vehicle-track dynamics theory. Then Monte Carlo simulations performed to produce random samples of sensitive parameters and analyze their effect distributions on wheel&ndash;rail contact under random wheel parameters. The findings demonstrate that the random parameters of the suspension system have more negative effects on fatigue life compared to random passengers&rsquo; weight and train speed, however, random passengers&rsquo; weight has a less negative impact compared to random suspension and passenger weight. But also, the dynamic results stress analysis showed that the random suspension system parameters have a high maximum stress compared to the stress obtained from random passengers&rsquo; weight and train speed. Moreover, the random suspension system parameters have high maximum stress compared to stress obtained from random passengers&rsquo; weight and train speed.Comparison of the performance of mesh and simple baffles in controlling the sloshing phenomenon based of the SPH simulation
https://jcarme.sru.ac.ir/article_2054.html
One of the main problems in liquid transfer tanks is the sloshing phenomenon. This phenomenon, which is associated with regular or irregular liquid waves inside the tank, can cause many risks. One of the most widely applied methods to control the fluctuations caused by the sloshing phenomenon is the use of baffles. Baffles are usually installed vertically or horizontally on the inner wall of the tank. In uniform samples (simple baffle), the hydrodynamic force on the baffle is significant. Therefore, in this research, mesh baffle from the category of permeable baffles is introduced and tested, which can significantly reduce the hydrodynamic forces on the baffle. Therefore, in the present work, the sloshing phenomenon in a rectangular tank is first modeled by Smoothed Particle Hydrodynamics (SPH) and validated. Then, the tank with a simple baffle and mesh baffle are modeled and examined. During the numerical solution (in each time interval), the hydrodynamic forces acting on the baffles are monitored and extracted. The comparison of the obtained results shows that in addition to reducing the fluctuations of the sloshing phenomenon, the mesh baffle also creates a lower hydrodynamic resistance force.Dynamic analysis of multi-body dynamics model of the mold oscillator including self-excitation of the supporting system
https://jcarme.sru.ac.ir/article_1996.html
A hydraulically driven mold oscillator is challenging to estimate the dynamic state variables precisely. Significantly, the additional stiffness effect of hydraulic oil is variable according to operating conditions, and it is hard to formulate it as a mathematical expression. This study investigates the dynamic characteristics of a mold oscillator operated by two hydraulic cylinders with other springs and dampers to determine the non-linear effect and estimate exact dynamic state variables to improve the accuracy control. The mold oscillator was excited in either step oscillation or sine-sweeping oscillation to measure its dynamic behaviors, including mold displacement and hydraulic cylinder pressure. Due to non-linear properties, the dynamic behaviors change according to excitation conditions during sine-sweeping oscillation. Primarily, peak frequencies around 50 Hz are founded from experimental pressure-displacement data in the frequency domain. To identify the oscillating mechanisms, equivalent 1-DOF and 2-DOF mass-damper-spring models for the mold oscillator are established. The fundamental system property is derived by experiment and a Finite Element multi-body dynamics model. In addition, inverse dynamics and numerical analysis were applied to derive the unknown force from the hydraulic servo system and structural characteristics. The unknown force is related to a friction problem and an elastic deflection by relative components near the mold. For high accuracy control, the unknown force model by an additional mass-spring model that causes high-frequency vibrations at 49, 48, 47, 46, or 45 Hz was suggested to formulate the equation of motion with the additional vibrations without any arbitrary modeling process.Application of combined mathematical modeling/optimization methods coupled pitch controller in wind turbine using hybrid MLP neural network and firefly algorithm
https://jcarme.sru.ac.ir/article_832.html
A common method utilized in wind turbines is pitch angle control whereby via varying the angle of wind turbine blades around their own axis, power generated at high speeds of wind is held around maximum amount and is kept away from the severe mechanical stress on wind turbine. In current study, in order to control pitch angle, a control method based on using PI controller is suggested. Therefore, gains of the PI controller are regulated through combining the Firefly evolutionary algorithm and MLP neural network in such a way that the controller at its output sends a suitable controlling signal to the pitch actuator to set the pitch angle and so by varying the blades pitch angle suitably at high speeds of wind, the produced generator power remains around its nominal value. A wind turbine 5MW made by NREL (National Renewable Energy Laboratory) has been utilized based on FAST software code to simulate and analyze the results. The simulation results show that proposed method has a good performance.