Development of Competitive Skills in Future Mechanical Engineers

Nowadays, the Web is a common tool for students searching information about the subjects taught in the different university courses. Although this is a good tool for the first rapid knowledge, a more deep study is usually demanded. After many years of teaching one course about ceramic and composite materials, the authors, used the Bologna reformulation of the mechanical engineering course to introduce new teaching methodologies based on continuous evaluation. One of the main innovations is one practical work that comprises the study of a recent ceramic scientific article, using all the actual available tools, elaboration of a scientific report, present the work and participate in a debate. With this innovative teaching method the enrolment of the students was enhanced with a better knowledge about the ceramics subject and the skills related with the CDIO competences.

Experimental Investigation on the Heat Transfer of a Portable Forced-Convection Solar Air Heater

A cross-corrugated portable forced-convection solar air heater has been designed, fabricated, and developed. A wavelike bottom plate has been positioned crosswise to the air flow while rectangular baffles have been attached to the flat-plate absorber. The relative corrugation height, (e/Dh) ranges between 0.24 and 0.4, and relative baffles distance (l/L) varies between 0.21 and 0.48. The air flow rate in the heater duct has been varied in the range of 0.001 kgs−1 to 0.01kgs−1 (Reynolds number ranges from 350 to 3500), while other thermal specifications such as inlet, outlet, and plate temperatures have varied due to weather changes. Results of this study have been compared with those related to smooth ducts and other literatures, and the maximum enhancement in Nusselt number is observed to be approximately five times of that of the smooth duct under similar flow conditions. Finally, thermal efficiency of the device for different case studies has been determined and compared with other researches.

Does a Predictive Minimal Model of Friction-Induced Vibration Exist?

Highly idealised models of friction-induced vibration have been motivated by an attempt to capture what is essential to the phenomenon. This approach has resulted in a few simple mechanisms that are thought to capture common routes to instability. This paper aims to determine how well these perform as approximations to a more complex system, and whether the essential ingredients needed for a minimal model can be identified. We take a reduced-order model that exemplifies ‘mode-coupling’ and explore the extent to which it can approximate predictions based on an experimentally identified test-system. For the particular test system under study, two-mode ‘mode-coupling’ is rarely a good approximation and three modes are usually required to model a limited frequency range. We then compare predictions with results from an extensive program of sliding contact tests on a pin-on-disc rig in order to identify which ingredients are needed to explain observed squeal events. The results suggest that several minimal models would be needed to describe all observed squeal initiations, but the ‘negative-damping’ route to instability, which requires a velocity-dependent friction law, convincingly accounts for one cluster.

Structural Analysis of Riveted Structures Using a New FE Modelling Technique

A theoretical approach, in order to define the structural behaviour of riveted joints, is presented. The closed form solutions lead to the definition of a Rivet Element useful to FE models of multi-riveted structures. The objective is an accurate evaluation of the local stiffness of riveted joints in FE analysis, which is fundamental to perform a reliable simulation of multi-joint structures and, consequently, a good estimate of loads acting on connections; this makes it possible to introduce new general criteria allowing, for example, to predict fatigue behaviour. On the other hand, a low number of degrees of freedom is needed when several connections are present in a complex structure. The goal is to reach a reliable model of the rivet region which can be used as the basis to develop a Rivet Element in FE analysis. The proposed Rivet Element combines the precision in the simulation with a very limited number degrees of freedom in the finite element model of a complex structure having several rivets. In the present paper the structural behavior of two simple riveted specimens is investigated experimentally and numerically using a new Rivet Element. A comparison with a joint model performed with very refined non-linear 3D models of rivet and with experimental data is performed and a good agreement is shown.

Development of a Computer Program for the Numerical Investigation of Heat Transfer in a Gasketed Plate Heat Exchanger

In this study, a computer program is developed to calculate characteristics of a Chevron type gasketed plate heat exchanger (CTGPHEX) such as: the number of plates, the effective surface area and total pressure drops. The main reason to prefer the use of CTGPHEXs to other various types of heat exchangers is that the heat transfer efficiency is much higher in comparison. Working conditions such as the flow rates and inlet and outlet temperature of both flow sides and plate design parameters are used as an input in the program. The Logarithmic Mean Temperature Method and the different correlations for convective heat transfer coefficient and Fanning factor that are found in the literature are applied to calculate the minimum necessary effective heat transfer area, the number of plate and pressure drops due to friction for both fluid sides of fulfill the desired heat transfer rate. This Turkish / English language optioned user friendly computer program is targeted to be used in domestic companies to design and select CTGPHEXs for any desired working conditions.

Coherent Flame Model to Predict Formation Pollutants in Turbulent Premixed Flame

The objective of this work is to analyze and to model the turbulent flames in the context of coherent flame model. We present a detailed description of equations and the flamelet regimes in turbulent premixed flame. A surface density models proposed here represents a good issue for numerical simulation. Extension of coherent flame model and homogenous stilled reactor model is proposed to consider the dynamics behavior of flame and pollutants formation. From the results of this work it is concluded that the coherent flame model allows surpassing difficulties of the turbulent reactive flow modeling. Calculations based on a semi-global kinetic scheme and flamelet formulation combined with a well stirred reactor analysis of the burnt gases are used and provided reasonably accurate values of CO and NO formation. Also, we have observed that CO is formed near the reaction zone (front flame) but emission of CO2, H2O and NO are formed in the hot gases.

Investigation of Heat Transfer Over a Rotating Disk in Case of Temperature and Velocity Jump Conditions by Using Differential Transform Method

The energy crisis in the last two decades has turned the attention of scientific and engineering communities to redesigned and developed heat-fluid interaction systems. All of the details in analyses are reconsidered to reduce energy consumption. The present work examines the effects of temperature and velocity jump conditions on heat transfer, fluid flow over a single rotating disk. The flow due to rotating disks is of great interest in thermal engineering as it appears in many industrial and engineering applications such as gas turbine engines and micropumps. The related equation of flow, which is nonlinear and coupled, and heat transfer governing equations are reduced to ordinary differential equations by applying the so-called classical approach which was first introduced by Von Karman. Instead of this approach, a pure numerical one, the recently developed popular semi numerical analytical technique differential transform method (DTM), with Benton transformation, is employed to solve the reduced governing equations under the assumptions of velocity-slip and temperature jump conditions on the disk surface. The solution is valid for continuum and slip-flow regime which has a Knudsen number smaller than 0.1. The results attained for various physical cases are interpreted by using non-dimensional parameters related to flow and temperature fields. Velocity and temperature profiles are presented graphically. The effect of various parameters such as the Knudsen Number (Kn), Reynolds Number (Re) and Nusselt Numbers (Nu) are examined. The observed physical consequences are the velocity slip and temperature jump at the wall becoming strongly dependant on the Knudsen number. It is also observed that the temperature jump and velocity jump conditions have nonlinear effects on slip; these effects are investigated with great details and presented graphically.

Natural Convective Characteristics of an Oblique Heat Source Module in the Closed and Ventilated Cabinets

A numerical analysis is performed to study the characteristics of heat transfer from a block heat source module at different angles in two-dimensional cabinets. Great efforts are carried out to conduct the effects of thermal interaction between the air steams inside and outside the cabinet on the conjugate conduction–natural convection phenomena. Moreover, the enhancement of cooling performance of the heat source module through the construction of air vents on cabinet wall is rigorously examined. The computation domain covers the cabinet and the surrounding area, and the temperature and velocity fields of the cabinet and surrounding area are solved simultaneously. Results show that the thermal interaction between the airs inside and outside the cabinet, the module angle and vent position can significantly affect the transfer characteristics. Comparing the results for cases with and without the consideration of thermal interaction between the air streams, the difference in hot spot temperature of module can be up to 26% for Pr = 0.7, Kbf = Kpf = Kwf = 100, 105 ≦ Ra ≦ 107 and φ = 0°, 90°, 270°. The maximum reduction in hot spot temperature is about 41% when two air vents are constructed on cabinet wall. The variation of module angle results in the maximum difference of the hot spot temperature is 15% for closed cabinet, and 10% for ventilated cabinet.

Coupled Axial-Flexural-Torsional Vibration of Internally Damped Timoshenko Frames

In this study, free in-plane and out-of-plane bending vibrations of frame structures have been analyzed together with torsional vibration. Axial extension, rotational inertia and shear effects have also been considered. The frame structure has been constructed as having two beams with doubly symmetric cross-sections and connected at any angle to each other. These types of frames frequently appear on ships as bridge wings which are probably the most problematic members experiencing severe vibration. Internal damping has been incorporated into the analyses by using a complex modulus of elasticity. Natural frequencies have been obtained analytically by solving simultaneous linear equations of complex coefficients. A finite element analysis has also been conducted to verify the analytical results. Furthermore, an experimental modal analysis has been carried out and the results have been compared with theoretical ones in tables for various connection angles and damping factors. The agreement among results has been found to be good.

The Performance of Bolted Slant Endplate Connections Subjected to Temperature Increase

In this paper the main goal is to evaluate the vertical and slant bolted endplate connections performance in steel moment frame structures under thermal effect in elastic field, and by a finite element software. the connections are simulated to complete and verify simple modeling of analytical and numerical analysis of the behavior of vertical and slant bolted endplate connections due to increase in temperature. The results that are obtained from performance of a vertical bolted endplate connection and a slant bolted endplate connection due to increase in temperature will be compared.