Janusz Kubrak

Scenarios of the spread of a waste heat discharge in a river — Vistula River case study

The problem of two-dimensional mathematical modelling of heated cooling water discharges into running waters is considered in the paper. Two models — one for the evaluation of 2D turbulent velocity field and the other, developed by authors of the study, for 2D heat transport in open-channels — were used in the calculations. Relevant scenarios of the spread of heated water discharged from a designed gas-stem power plant to be constructed at the Vistula River were presented. Environmentally most friendly variant of the discharge of the thermal pollution was selected from among four various variants.

Influence of a method of evaluation of the curvature of flexible vegetation elements on vertical distributions of flow velocities

Methods of computing the deflections of flexible vegetation elements under the dynamic pressure of water were presented in the paper. Two methods, based on Euler-Bernoulli beam theory, were discussed, one designed for small deflections and the other, generalized one, also for larger deflections. The choice of the method for computations of deflections was discussed from the perspective of the computation of flow velocities above flexible vegetation. Computational results were compared with laboratory experiments and it was found that the simplified, computationally less expensive method may be used in many practical situations without deterioration of the results.

Measurements of 3D Turbulence Structure in a Compound Channel

Experimental research was undertaken to investigate the changes in spatial turbulence intensity, water turbulent kinetic energy, the time and spatial macro-scale, scales of turbulent eddies (macro- and microeddies) in a compound channel. Three tests for two various roughness values were realized. The surface of the main channel bed was smooth and made of concrete, whereas the floodplains and sloping banks were covered by cement mortar composed of terrazzo. Instantaneous velocities were measured with the use of a three-component Acoustic Doppler Velocimeter (ADV). The distributions of relative turbulence intensity (u′/U, v′/U, w′/U) in the main channel and on the floodplains were presented. It was found that the longitudinal (u′/U) and transverse (v′/U) turbulence values decreased from the bottom upwards to the floodplain elevation (z/h = 0.56) in the main channel, but remained constant above the floodplain level. Vertical relative turbulence intensity (w′/U) increased going up from the bottom until z/h = 0.15, decreased until about z/h = 0.7, and then increased again upwards to the water surface. The distributions of relative turbulence intensities were described with regression equations. The distributions of turbulent kinetic energy at different water depths were described by regression equations. Vertical distributions of turbulent kinetic energy on the floodplains and over the banks of the main channel were divided into three zones. Over the bottom of the main channel, four zones were determined, containing the middle zone of the flow field divided into two zones of different trends. Measurements of instantaneous velocities are used to investigations of the longitudinal sizes of the smallest eddies (Kolmogorov’s microscale). Presented analyses were based on the already published results.

Application of one-dimensional model to calculate water velocity distributions over elastic elements simulating Canadian waterweed plants (Elodea Canadensis)

One-dimensional model for vertical profiles of longitudinal velocities in open-channel flows is verified against laboratory data obtained in an open channel with artificial plants. Those plants simulate Canadian waterweed which in nature usually forms dense stands that reach all the way to the water surface. The model works particularly well for densely spaced plants.

Experimental Investigation of Kinetic Energy and Momentum Coefficients in Regular Channels with Stiff and Flexible Elements Simulating Submerged Vegetation

The paper addresses the problem of determination of the energy and momentum coefficients for flows through a partly vegetated channel. These coefficients are applied to express the fluid kinetic energy and momentum equations as functions of a mean velocity. The study is based on laboratory measurements of water velocity distributions in a straight rectangular flume with stiff and flexible stems and plastic imitations of the Canadian waterweed. The coefficients were established for the vegetation layer, surface layer and the whole flow area. The results indicate that the energy and momentum coefficients increase significantly with water depth and the number of stems per unit channel area. New regression relationships for both coefficients are given.

Experimental and numerical investigation of non-submerged flow under a sluice gate

Abstract The problem of sluice gate flow is analyzed using two models: a simplified one, derived according to the concept of the Potential Field (PF), and a more complex form, based on the Reynolds Average Navier-Stokes (RANS) equations. The numerical solution is compared with experimental data, including measurements performed by authors and results acquired from literature. Despite its simplicity, the PF model provides a satisfactory agreement with the measurements. The slightly worse performance of the RANS model comes from an overestimation of energy losses.

Identification of vegetation parameters for compound channel discharge as inverse problem

Abstract In recent years many sophisticated models for discharge capacity of compound channels with vegetation have been developed. Despite the mature state of knowledge in this field, in a practice the simplest methods prevail and most of hydraulic models are based on the Manning formula. One of the reasons is that more complex methods require detailed characteristics on vegetation. The present study demonstrates that this issue can be solved by treating all such necessary variables as parameters to be identified in a sense of an inverse problem, using techniques of optimization. With a flume experiment as a case study, four models of a uniform flow were identified: Pasche, Mertens as complex methods, divided channel method (DCM) with Manning and Darcy–Weisbach equations as techniques used in a practice. Results showed that parameters for all methods can be found on the basis of minimization of model residuals, with the restriction that because of the larger number of parameters in complex methods, more observations are required. Methods of Pasche and Mertens with identified parameters provided a much better explanation of water depths than the Manning or Darcy–Weisbach based on the DCM. It is surprising that significant discrepancies between identified parameters and their real measured values were recorded. Even more, an almost perfect fit was obtained for different parameter sets.

Hydraulic Conditions of Flood Wave Propagation in the Valley of the Narew River after the Siemianówka Dam Overtopping Failure

In this paper, the results of the dam break wave forecast in the valley of the Narew River, after the failure of the Siemianowka Reservoir earth dam, are presented. The Siemianowka Reservoir was built in 1991 due to the planned agricultural management of the Narew Valley. It is located in the Upper Narew Catchment as a typical lowland reservoir of a low mean depth, equal to 2.5 m and the principal spillway of 145.00 m above sea level. The reservoir is located about 82 km upstream of the border of the Narew National Park and considerably influences the hydrological regime of the Narew River within that park. The total capacity of the reservoir is 79.5 million m3. The presented example of calculations for the Siemianowka Reservoir underlines the most important issues related with the forecast of the dam break, that is: the determination of maximum water levels and discharges in the valley downstream of the failure dam, the calculation of wave-front occurrence time at particular points of the valley, the inundation range along with the longitudinal profiles of water levels and velocities of water on inundated areas. The knowledge of the water depths on inundated areas, the duration of inundation and maximum water velocities enable as well the estimation of the damage degree on inundated areas. As it results from the calculations, the washout process of the Siemianowka Reservoir earth dam, which is 6 m high, happens very quickly, and after about 2 h the top of the triangular breach reaches the dam bed. The discharge from the reservoir after dam failure drops from 465 to 304 m3/s and the water level in reservoir decreases 1.36 m as fast as within 300 h. The occurrence of wave in the valley causes the increase of water levels by 0.1–4 m in comparison to the water level before the dam break, and a 4-time increase of discharge rate in relation to the design flow at the cross-section of the dam of the Siemianowka Reservoir. The velocity of the wave-front propagation in the Narew Valley does not exceed 5 km/h.