Volume 1 Issue 1
Authors: Qing H. Qin; Kun Cai
Abstract: A new design method in hydraulic engineering is presented for the construction of a lightweight submerged radial gate (SRG) with two vertical arms. In the analysis, the structure is decomposed into several main components and each component is shaped using a topology optimization approach. In particular, a SRG can be divided into three major parts: the water-retaining face plate, the support frame, and the arms. The whole design process for the SRG generally includes five steps: (1) the optimal position of arms is determined in terms of avoiding bending moment of arm adjacent to the support frame; (2) using the topology optimization method, the shape of each arm is determined subject to the symmetry condition with respect to the whole structure; (3) a frame made of horizontal and vertical ribs is constructed to support the face plate; (4) the new radial gate is assembled based on these optimized components, e.g., two arms, the face plate and its support frame; and (5) the sizes of these components are verified using size optimization by considering the stiffness and strength of the new structure under a critical loading condition. To show the validity of the method, a traditional SRG in a real project is adopted as an example and is redesigned using the present method. The evaluation result shows that the new structure is about 27% lighter than the original. At the same time, the mechanical properties of the SRG are significantly improved.
Keywords: Radial Gate; Optimal Design; Topology Optimization; Size Optimization; Lightweight Structure
Authors: Jan Kicinski
Abstract: The paper presents author’s opinions concerning capabilities and limitations of the model based diagnostics. Present development in computer science and methodology of modelling has increased those capabilities considerably. It is obvious that talking about model based diagnostics assumes possessing not only an advanced theoretical model of the examined object but also models of irregular states and mutual relations between defects and their symptoms. Acquiring sufficiently reliable relations of defect-symptom type is a difficult, and frequently an extremely difficult task. The opinions presented in the paper concern one of the most intriguing phenomena, namely the formation of whirls and whips in slide bearings of a rotating machine. Although those phenomena are being the object of investigation in many research centers all over the world, their physics has not been satisfactorily recognized yet. The paper presents the abilities of computer simulation of the development of oil whirls and whips using the methods characteristic for model based diagnostics. Another very interesting issue is an assessment of the influence of a random character of certain input data – in this case – changes of external excitations of the system. This problem is related to the so-called heuristic models often placed in opposition to widely used algorithmic models. The main issue concerned the question whether the heuristic methodology can move to the techniques, in this case, the rotor dynamics. Heuristic approach may be the future of model based diagnostics. The objects of investigations were the high-speed rotor of a micro turbine being an element of the micro power plant in dispersed power engineering based on renewable energy sources. In both cases (whirls and heuristics), it is necessary to have very powerful tools for analyzing the behavior of objects, especially in the non-linear range. These tools are the basis of modern model based diagnostics.
Keywords: Model-Based Diagnostic; Oil Whirl and Whip; Hydrodynamic Instability; Rotor Dynamics; Nonlinear Vibrations; Heuristic Problems
Authors: Serguei G. Psakhie; Andrey I. Dmitriev
Abstract: The response of materials under intensive shear loading was investigated by help of numerical modelling at micro- and meso-scale levels. At micro-scale the simulation was performed on the basis of molecular dynamics method where the interatomic interactions were calculated in framework of embedded atom approach. At meso-scale level method of movable cellular automata was used. This method is based on the discrete conception and can be considered as a result of cellular automata concept development by means of incorporation of some basic postulates and relations of discrete element method. In the paper it was shown that the loading with the gradient of velocity in areas near the surface leads to formation of low density and fragmented areas. The behaviour of material in such areas differs from behaviour of solids. So, this effect is accompanied by the failure of crystal lattice stability and intensive mixing process at the atomic level. The mechanisms of mass transfer in contact area were discussed. The results allow us to explain a host of experimental data of mechanochemistry such as phase formation at friction surface, alloy formation due to contact interaction under “pressure plus shear” loading conditions.
Keywords: Modelling; Pressure Plus Shear Conditions; Low-Density Layer; Mass Mixing; Meso and Atomic Scales