Meshfree natural vibration analysis of 2D structures

Determination of resonance frequencies and vibration modes of mechanical structures is one of the most important tasks in the product design procedure. The main goal of this paper is to describe a pioneering application of the solution structure method (SSM) to 2D structural natural vibration analysis problems and investigate the numerical properties of the method. SSM is a meshfree method which enables construction of the solutions to the engineering problems that satisfy exactly all prescribed boundary conditions. This method is capable of using spatial meshes that do not conform to the shape of a geometric model. Instead of using the grid nodes to enforce boundary conditions, it employs distance fields to the geometric boundaries and combines them with the basis functions and prescribed boundary conditions at run time. This defines unprecedented geometric flexibility of the SSM as well as the complete automation of the solution procedure. In the paper we will explain the key points of the SSM as well as investigate the accuracy and convergence of the proposed approach by comparing our results with the ones obtained using analytical methods or traditional finite element analysis. Despite in this paper we are dealing with 2D in-plane vibrations, the proposed approach has a straightforward generalization to model vibrations of 3D structures.     

Mechanoenzymatic Transformations in the Absence of Bulk Water: A More Natural Way of Using Enzymes

Mechanochemical enzymatic reactions without bulk water have emerged as a low-waste and efficient method to access useful chemicals and to depolymerize biomass components in a single step. This emergent mechanoenzymatic reaction strategy is able to take advantage of the stereospecificity, regio- and stereoselectivity, as well as renewability of enzymes, while avoiding bulk solvents, offering the opportunity to control the direction of the reaction, bypassing reactant solubility issues, and enabling reactions with water-sensitive substrates or products. Enzymes are traditionally used in dilute aqueous solution, which is quite different from their crowded, water-depleted natural environment. This review outlines recent work which demonstrates that enzymes can be equally or even more efficient under mechanochemical conditions, without bulk aqueous or organic solvent.     

Electrocatalytic effects of Mo–Pt intermetallics singly and with ionic activators. Hydrogen production via electrolysis

The intermetallic phases along the Pt–Mo phase diagram, singly or in combination with specific ionic activators, have been investigated as cathode materials for the production of hydrogen by electrolysis from water KOH solutions in an attempt to decrease energy consumption. The influence of ionic activators (activating compounds) on energy consumption was significant. The intermetallic phases, as cathode materials, were activated by the surface deposition of activating compounds from electrolyte. The influence of these cathode materials on the electrolytic evolution of hydrogen was discussed in the context of transition metals features and their electronic configuration.     

New transformation polynomials for discretization of analogue systems

The novel transformation polynomials for discretization of analogue systems have been presented. A generalization of some of the existing transformation methods has also been done. A comparative analysis, through the corresponding examples involving several known discretization methods, has been carried out. It has been demonstrated that the application of these transformation polynomials allows the reduction of discretization error compared to other approximation methods. The response to an arbitrary excitation of the discrete system obtained by these transformations is approximately equal to that of the original analogue system. The transformations are rational since variable s ^{− n} ,n ∈ N, transforms to the quotient of two linear functions of variable z.     

Simple method for intermodulation products counting in multicarrier systems

This paper presents a novel algorithm for intermodulation products counting in multicarrier systems. Intermodulation products are caused by the nonlinearity of the amplifiers’ transfer characteristic. Along the transmission network, broadband amplifiers are needed to boost up the signal level and compensate the signal attenuation. When the number of carriers increases, the number of intermodulation products also increases extremely fast. In our approach, selective counting procedure by grouping intermodulation products was introduced. The presented solution shows considerable reduction in computational effort in counting the number of intermodulation products in the individual channel, especially if the number of products is very large.     

Calibration of 3D kinematic systems using orthogonality constraints

Processing images acquired by multi-camera systems is nowadays an effective and convenient way of performing 3D reconstruction. The basic output, i.e. the 3D location of points, can easily be further processed to also acquire information about additional kinematic data: velocity and acceleration. Hence, many such reconstruction systems are referred to as 3D kinematic systems and are very broadly used, among other tasks, for human motion analysis. A prerequisite for the actual reconstruction of the unknown points is the calibration of the multi-camera system. At present, many popular 3D kinematic systems offer so-called wand calibration, using a rigid bar with attached markers, which is from the end user’s point of view preferred over many traditional methods. During this work a brief criticism on different calibration strategies is given and typical calibration approaches for 3D kinematic systems are explained. In addition, alternative ways of calibration are proposed, especially for the initialization stage. More specifically, the proposed methods rely not only on the enforcement of known distances between markers, but also on the orthogonality of two or three rigidly linked wands. Besides, the proposed ideas utilize common present calibration tools and shorten the typical calibration procedure. The obtained reconstruction accuracy is quite comparable with that obtained by commercial 3D kinematic systems.     

A dynamic simulator for humanoid robots

Computer simulation is an essential step in the design and construction of various mechanical structures, including biped robots, because it enables rapid testing and virtual prototyping during the construction phase. Although many different simulators are available, this article gives an overview and a motivation for building a new dynamic multibody simulator. The simulator is especially adapted to humanoid robot Archie, developed at the IHRT Institute at the Technical University of Vienna. In addition, it is shown how the simulator can be used not only in the controller design, but also in the online control loop to extend the available sensors: a virtual sensors principle. This work was presented in part at the First European Workshop on Artificial Life and Robtics, Vienna, Austria, July 12–13, 2007     

Sensorless speed detection of squirrel-cage induction machines using stator neutral point voltage harmonics

In this paper a sensorless speed detection method of induction squirrel-cage machines is presented. This method is based on frequency determination of the stator neutral point voltage primary slot harmonic, which is dependent on rotor speed. In order to prove method in steady state and dynamic conditions the simulation and experimental study was carried out. For theoretical investigation the mathematical model of squirrel cage induction machines, which takes into consideration actual geometry and windings layout, is used. Speed-related harmonics that arise from rotor slotting are analyzed using digital signal processing and DFT algorithm with Hanning window. The performance of the method is demonstrated over a wide range of load conditions.