This paper reviews analytical solutions for the accelerated flow of an incompressible Newtonian fluid in a pipeline. This problem can be solved in one of two ways according to the (1) imposed pressure gradient or (2) flow rate. Laminar accelerated flow solutions presented in a number of publications concern cases where the two driving mechanisms are described by simple mathematical functions: (a) impulsive change; (b) constant change; (c) ramp change, etc. The adoption of a more complex and realistic description of the pressure gradient or flow rate will be associated with a profound mathematical complexity of the final solution. This is particularly visible with the help of the universal formula derived by several researchers over the years and discussed in this paper. In addition to the solutions strictly defined for laminar flow, an interesting extension of this theory is the theory of underlying laminar flow for the analysis of turbulent accelerated pipe flows (TULF model developed by García García and Alvariño). The TULF model extends the Pai model developed more than 60 years ago, which has been previously used for steady flows only. The discussed solutions extend the theory of analytical solutions of simplified two-dimensional Navier–Stokes equations and can be used not only to study the behavior of liquids during accelerating pipe flow but they can also be used to test the accuracy of commercial CFD codes.

The article presents the theoretical research on hydraulic processes occurring in hydraulic drives of transport machines. The research analysed the influence of hydrodynamic processes on the fluid flow characteristics following installation of angular fitting connections in pipeline systems. The analysis was based on the numerical simulations by Reynolds-averaged Navier–Stokes equations in 3D. The fluid flow in the hydraulic system pipeline connections were investigated for fluid flow rate up to 100 l/min. For numerical simulation, a mesh independence study was performed. By modeling. we obtained results of pressure drops, turbulence models, flow coefficients and energy losses at 45° and 90° angular fitting connections. The article compares the results obtained using the calculation method based on the standard of equivalent length fitting with the findings presented. The research conducted indicated that using the equivalent length method is not appropriate for studying angular fitting connections. It was found that additional investigations are necessary for each type of angular fitting connection.

This paper identifies mechanical vibrations occurring in the operating environment of hydraulic systems used in marine engineering. Particular attention was paid to the influence of periodic vibrations on changes in the amplitude-frequency spectrum in a marine hydraulic system. For the case of analysing the effect of vibration on changes in the pressure pulsation spectrum with a proportional directional valve, a modified mathematical model was used. Experimental results were presented and compared with the results obtained from the mathematical model. A way of limiting the transmission of vibrations to the directional control valve body was proposed.

With the prevalence of obesity and overweight increasing at an alarming rate, more and more researchers are focused on identifying effective weight loss strategies. The ketogenic diet (KD), used as a treatment in epilepsy management for over 100 years, is additionally gaining popularity as a weight loss method. Although its efficacy in weight loss is well documented, the areas where it may be beneficial to other dietary approaches need to be carefully examined. The objective of this paper is to identify the potential benefits of the KD over alternative dietary weight loss strategies based on a comprehensive literature review. It has been shown that the KD may be more bioenergetically efficient than other dietary strategies, inter alia owing to its effect on curtailing hunger, improving satiety and decreasing appetite (influence on hunger and satiety hormones and the sensation of hunger), inducing faster initial weight loss (associated with lower glycogen levels and reduced water retention), and controlling glycaemia and insulinemia (directly attributable to the low-carbohydrate nature of KD and indirectly to the other areas described). These effects are accompanied by improved insulin sensitivity, reduced inflammation (through ketone bodies and avoidance of pro-inflammatory sugars), reduced need for pharmacological obesity control (the diet’s mechanisms are similar to those of medication but without the side effects), and positive impacts on psychological factors and food addiction. Based on the authors’ review of the latest research, it is reasonable to conclude that, due to these many additional health benefits, the KD may be advantageous to other diet-based weight loss strategies. This important hypothesis deserves further exploration, which could be achieved by including outcome measures other than weight loss in future clinical trials, especially when comparing different diets of equal caloric value.