The study makes an attempt to model a complete vibrating guitar including its non-linear features, specifically the tension-compression of truss rod and tension of strings. The purpose of such a model is to examine the influence of design parameters on tone. Most experimental studies are flawed by uncertainties introduced by materials and assembly of an instrument. Since numerical modelling of instruments allows for deterministic control over design parameters, a detailed numerical model of folk guitar was analysed and an experimental study was performed in order to simulate the excitation and measurement of guitar vibration. The virtual guitar was set up like a real guitar in a series of geometrically non-linear analyses. Balancing of strings and truss rod tension resulted in a realistic initial state of deformation, which affected the subsequent spectral analyses carried out after dynamic simulations. Design parameters of the guitar were freely manipulated without introducing unwanted uncertainties typical for experimental studies. The study highlights the importance of acoustic medium in numerical models.

The trigeneration systems for production of cold use sorption refrigeration machines: absorption and adsorption types. Absorption systems are characterized namely by better cooling coefficient of performance, while the adsorptive systems are characterized by the ability to operate at lower temperatures. The driving heat source temperature can be as low as 60-70 °C. Such temperature of the driving heat source allows to use them in district heating systems. The article focuses on the presentation of the research results on the adsorption devices designed to work in trigeneration systems.

Results of 3-D of discharge channel displacement simulation, acquired by means of the Fluent program during one current half-period of AC arc, indicate that the obtained images of the phenomenon are qualitatively similar to those, recorded with a high-speed digital camera, while the computer simulation enables much a more comprehensive analysis of the acquired data. In addition to selected arc simulation frames and corresponding distributions of mass velocity vectors and current density vectors on a plane, the distributions of temperature, current density and mass velocity values are presented on the axis of the electrode arrangement model. The composite motion (continuous and jumping) of discharge channels was analyzed, taking into account mass displacement and matter state changes.