The majority of natural Lithuanian rivers were regulated during intensive land reclamation period. Straightening of rivers caused unfavourable conditions for biodiversity. Four tributaries of the Merkys River in the South Lithuania were selected to explore changes in biodiversity patterns and determine the relationships between flow energy distribution in beds and ecological status of selected rivers. The research has shown that variation of cross sections area was usually 1.2 to 2.3 times higher in natural beds as compared to regulated ones. The range of rivers flow energy, estimated by Froude number, values were characterized as higher in natural (0.0 to 0.35) streams than in regulated (0.0 to 0.20) ones. This is the reason why the biggest number of macroinvertebrate taxa during the research period was recorded in natural riverbeds and the lowest - in the fields of the regulated segments. The assessing the abundance of fish revealed that total fish density in natural river sections was four times higher than in regulated ones. The research has approved the importance of naturalness for biodiversity and rehabilitation of regulated rivers in Lithuania.

This paper investigates the effect of intake runner design on pressure wave propagation and reflection in sparkignited internal combustion (IC) engine. These events are known to leave a noticeable influence on the overall engine performance therefore the aim of this study is to evaluate how changes in intake runner geometry affect pressure oscillations and volume flow rate. Time-dependent computational fluid dynamics (CFD) analysis was carried out to determine how these changes affect the pressure oscillations during a full engine cycle at constant crankshaft speed. Steady state CFD analysis at constant pressure differential was carried out to evaluate the effect on volume flow rate. The simulations were carried out in SolidWorks Flow Simulation environment. Honda CRF450R motorcycle engine was used to define the initial conditions and basic intake runner design. Intake air speed at port entrance cross-section was calculated based on engine parameters and operating speed. The average pressure values with respect to physical time were measured and graphed across the intake port opening cross-section. Six different intake runner designs were compared. It was concluded that the runner taper angle has influence on pressure wave-length but internal geometry (steps, curvature and taper angle) has influence on volume flow rate. It was observed that cylindrical intake runner design produced an increase in pressure wave-length but a cylindrical section of the intake runner with a stepped transition to tapered extension produced a slight increase in pressure wave amplitude.