Dimensioning of the intermediate states of the machined phases “DISMP” approach

In manufacturing practice for each machining operation, transfer techniques are extensively used for the allocation of manufacturing specification tolerance type and value. This paper focuses more on tolerance type which is the basis for a coherent and complete tolerancing process. We developed an algorithmic method called “DISMP” in order to generate the necessary types of manufacturing specifications that guarantee the respect of the functional requirements. A geometric variation model, based on the invariants degrees of freedom (DOFs) of the datum reference frames (DRF) and the toleranced surfaces serves to specify the two extremities of the tolerance chain. The identification of the controlled DOFs (Cont-DOFs) of the positioning reference frames in each machining phases and also the constrained DOFs (Cons-DOFs) of each machined surface contributes to the development of the way linking between the functional toleranced surface and its functional DRF. To generate the appropriate manufacturing geometric specifications, our method can be divided in five steps. We started by the translation of the ISO functional specification using the topologically and technologically related surfaces rules “TTRS” (Step 1: M1). Mapping the manufacturing process (Step 2: M2 and M3) requires the identification of the Cons-DOFs of the machined surfaces and those controlled by the positioning surfaces “Cont-DOFs” in each phase. The search of all chain links, which constitute the tolerance chain, is realized on Step3 (M4 and M5). Then, in step 4 (M6), we generate ISO standardized manufacturing specification. The fifth step (M7) draft technological constraints related to the manufacturing process, i.e., the case where there are inversion in the order between the toleranced surfaces and its DRF. Finally, we present the manufacturing process phases with ISO standards requirements.     

Viscothermal fluid effects on vibro-acoustic behaviour of double elastic panels

This paper deals with the vibro-acoustic behaviour of two vibrating plates coupled to a viscothermal fluid cavity. The acousto-elastic model is established in dimensionless appropriate form including the effects of viscosity and thermal conductivity of fluid and taking into account the fluid–structure interaction. The finite element method is used for the discretization of the functional of energy, which gives after minimization a symmetrical coupled matrix system in which the acoustic matrices are frequency dependent. For this purpose, an iterative procedure is derived to determine the eigenmodes of the coupled system. The modal approach is adopted to determine the vibro-acoustic system's response which the numerical results show the importance of the viscothermal effects in the case of thin fluid layers.     

Shape and Thickness Optimization Performance of a Beam Structure by Sequential Quadratic Programming Method

Successful performance of beam structures is critical to failure prevention, and beam performance can be optimized by careful consideration of beam shape and thickness. Shape and thickness optimization of beam structures having linear behaviour is treated. The first problem considered is the thickness distribution of the beam where the optimization variable is the thickness of the control points. The second problem is the shape optimization where the optimization variables are the ordinates of the control points. The optimization criterion (function objective to be minimized) is defined starting with the Von Mises criterion expressed in plane constraints. The resolution of the mechanical problem is made by the finite element method, and the optimization algorithm is the sequential quadratic programming (SQP) method.     

Failure analysis of a misaligned and unbalanced flexible rotor

Shaft misalignment and rotor unbalance are major concerns in rotating machinery. In order to understand the dynamic characteristics of these machinery faults, a model of a complete motor flexible-coupling rotor system capable of describing these failures was developed. Generalized system equations of motion for a rotor under misalignment and unbalance conditions were derived using the finite element method. A spectral method was developed for resolving the equation of motion. This allows one to obtain and analyze the dynamic response and consequently to identify misalignment and unbalance faults.     

A theoretical model for analyzing the dynamic behavior of a misaligned rotor with active magnetic bearings

The dynamic response of a misaligned rotor, mounted in two identical active magnetic bearings (AMBs) was numerically investigated in this work. Three simplified models of current biased radial active magnetic bearings were presented, where four, six and eight electromagnets were powered by the bias current i₀ and respective control current. The magnetic forces acting on the rotor, the coil currents and the displacement of the rotor were obtained through an electromagnetic theory. The AMBs’ dynamics support parameters were modelled by linearised direct cross axes stiffness and damping coefficients. These are strongly dependent on the air gap between the stator and the shaft. A spatial model of a misaligned rotor with two degrees of freedom was presented. The motion equations were established for the rotor bearing system and simulated with Newmark method. Simulations results were carried out to survey the dynamic behavior of spatial misaligned rotor mounted in AMBs. The angular misalignment was such that the 2× and 4× running speed components are predominant. Their magnitudes varied with the number of magnets in the bearing and with the air gap between the stator and the shaft.     

Literature review of reuse in business process modeling

Business process models play an important role in the analysis and improvement of the performance of an enterprise. Evidently, the quality of a business process model has a direct effect on the business performance. This evidence has motivated both the academic and industrial communities to look for suitable methods for creating good quality business process models. In particular, there is a wide agreement that reuse can accelerate the design process and produce high quality solutions by adopting best practices and agreed-up-on solutions. However, faced with various types of reusable artifacts, business process designers need a set of criteria to determine which type would suit best their needs and design context. To assist designers in their choice, we first present a set of criteria influencing the design phase in terms of effort required and the quality of the resulting model. Secondly, we use this set of criteria to present a state of the art on the most significant reusable design artifacts.     

Backlash effect on dynamic analysis of a two-stage spur gear system

Gearbox dynamics are characterized by a periodically changing stiffness due to multiple teeth contacts. In real gear systems, a backlash also exists that can lead to a loss in contact between the teeth. Due to this loss of contact, the gear has piecewise linear stiffness characteristics. This paper examines the effect of backlash in the two-stage gear system. A purely torsional gear system is formed by three shafts connected to each other by two spur gear pairs. Using standard methods for nonlinear systems (Newton-Raphson algorithm), the dynamic behavior of a gear system with backlash is examined. Amplitude jumps in systems due to backlash are observed.     

Numerical and experimental analysis of a gear system with teeth defects

The modelling of a one-stage spur gear transmission by a two degrees of freedom system produces two modes: rigid body and elastic. The time varying meshing stiffness is the main internal excitation source for the transmission and governs the behaviour of the elastic mode. Deterioration of one or several teeth, which affects the gear mesh stiffness, is considered in this work. The beginning of crack or spalling are modelled respectively by tooth having localised and distributed defect and are taken into account in the model. Simulation results are analysed by cepstrum and spectrum techniques. It is found that cepstrum and spectrum techniques are very efficient for localised and distributed defects, respectively. Series of tests are made in the experimental setup. Spectrum and cepstrum analysis of the recorded responses, with and without defects, are compared with numerical results and confirms their usefulness in gear monitoring .