Vol. 56, No. 1-2 (2009)
Rafał Ostrowski1, Zbigniew Pruszak1, Grzegorz Różyński1, Marek Szmytkiewicz1, Pham Van Ninh2, Do Ngoc Quynh2, Nguyen Thi Viet Lien2
1Institute of Hydro-Engineering of the Polish Academy of Sciences (IBW PAN),
Kościerska 7, 80-328 Gdańsk, Poland, email: rafi@ibwpan.gda.pl
2Institute of Mechanics, Center for Marine Environment, Survey, Research and Consultation
(CMESRC), 264 Doi Can, Hanoi, Vietnam
Abstract
| The paper presents a comparative analysis of physical processes occurring at two different coasts, which belong to two different geographic zones, namely a subtropical region exposed to monsoons and typhoons and a region of temperate climate with ice-snowy winter season. The former coast comprises sandy shores nearby Lubiatowo and the Hel Peninsula, located at the south Baltic Sea in Poland. The shore at Lubiatowo is relatively stable in the long run, while the shore along Hel Peninsula is mostly vulnerable to erosion and strongly protected by use of various measures (groins, seawall and artificial beach nourishment). The second site is the eroded (and partly protected by dikes) coast at Hai Hau in the Gulf of Tonkin (the South China Sea, Vietnam). This shore segment is built of mixtures of sandy and cohesive material, comprising both marine sands and river-borne sediments which nourish the coastal zone at the Red River mouth, located northwards of the Hai Hau beach. The present analysis is focused on differences and similarities of hydro- and morphodynamics between the above coastal zones in various time and spatial scales. The analysis shows that regional climatic and environmental conditions, associated with geographical zones, play a key role in dynamic evolution of the coastal regions and necessitate different engineering activities against erosion and flooding. |
Key words: non-tidal and tidal coast, waves and currents, sediment transport, morphodynamics
Full text link: http://www.ibwpan.gda.pl/docs/ahem/ahem56str003.pdf
The occurrence of s-shaped velocity profiles in gravel-bed river flows
Mario J. Franca1, Urlich Lemmin2
1Departmento de Engenharia Civil Faculdade de Ciencias e Tecnologia, Universidade Nova de Lisboa
Quinta da Torre, 2829-516 Caparica, Portugal, e-mail: mfranca@dec.uc.pt
2Laboratoire d’Hydraulique Environnementale (LHE), Ecole Polytechnique Federale de Lausanne CH
1015 Lausanne, Switzerland, ulrich.lemmin@epfl.ch
Abstract
| Based on ADVP field measurements, we discuss velocity profiles observed in two shallow gravel-bed rivers with low blockage ratio. In these flows, log-shaped profiles and s-shaped profiles simultaneously exist, indicating the possibility of 3D flow inside the roughness layer. However, a quasi-2D layer is generally found in an intermediate region of the flow outside the roughness layer. Therefore a best-fit log-law approach may lead to estimates of a roughness parameter which are reasonably correlated with the local flow resistance. Above a certain limit of the ratio roughness parameter/water depth (≈ 0.6 from our measurements), the velocity distribution in the lower regions corresponds to an s-shaped profile. We also investigate the velocity distribution throughout the flow depth and conclude that the mean of the velocity profile roughly occurs at a normalized distance of the riverbed of 0.40, for both log- and s-shaped profiles. |
Key words: field measurements, gravel-bed river flows, velocity profiles, depth-averaged velocity
Full text link: http://www.ibwpan.gda.pl/docs/ahem/ahem56str029.pdf
Strains in sand due to cyclic loading in triaxial conditions
Andrzej Sawicki, Jacek Mierczyński, Waldemar Świdziński
Institute of Hydro-Engineering PAS, ul. Kościerska 7, 80-328 Gdańsk-Oliwa, Poland,
e-mail: as@ibwpan.gda.pl
Abstract
| The experimental results dealing with the cyclic loading of sand samples in triaxial conditions are presented. These results show the development of both the volumetric and deviatoric permanent strains due to a large number of loading cycles. The analysis of experimental data has led to the formulation of semi-empirical constitutive equations, expressed in the incremental form, for these strains as functions of the cyclic shear stress amplitude, number of loading cycles and the initial stress state, around which the cyclic shearing takes place. |
Key words: cyclic loadings, granular soils, premanent strains, triaxial conditions
Full text link: http://www.ibwpan.gda.pl/docs/ahem/ahem56str085.pdf
A Lagrangian finite element analysis of gravity waves in water of variable depth
Ryszard Staroszczyk
Institute of Hydro-Engineering PAS, ul. Kościerska 7, 80-328 Gdańsk-Oliwa, Poland,
e-mail: rstar@ibwpan.gda.pl
Abstract
| The paper is concerned with the problem of gravitational wave propagation in water of variable depth. The problem is formulated in the Lagrangian description, and the ensuing equations are solved numerically by a finite element method. In computations a convecting mesh that follows the material fluid particles is used. As illustrations, results of numerical simulations carried out for plane gravity waves propagating over bottoms of simple geometry are presented. For parameters typical of a laboratory flume, the transformation of a transient wave, generated by a single movement of a piston-like wave maker, is investigated. The results show the evolution of the free-surface elevation, displaying steepening of the wave over sloping beds and its gradual attenuation in regions of uniform depth. |
Key words: gravity water wave, variable water depth, transient problem, Lagrangian formulation, finite element method
Full text link: http://www.ibwpan.gda.pl/docs/ahem/ahem56str043.pdf
On the description of long water waves in material variables
Kazimierz Szmidt, Benedykt Hedzielski
Institute of Hydro-Engineering of the Polish Academy of Sciences (IBW PAN),
ul. Waryńskiego 17, 71-310 Szczecin, Poland, email: jks@ibwpan.gda.pl
Abstract
| Shallow water equations formulated in material variables are presented in this paper. In the model considered, a three-dimensional physical problem is substituted by a two-dimensional one describing a transformation of long waves in water of variable depth. The latter is obtained by means of the assumption that a vertical column of water particles remains vertical during the entire motion of the fluid. Under the assumption of small, continuous variation of the water depth, the equations for gravity waves are derived through Hamilton’s principle formulated in terms of the material coordinates. This formulation ensures the conservation of mechanical energy. The approximation depends on the wave parameters as well as on the bed bathymetry. The latter may influence a solution of the model decisively; thus, one should be careful in applying the description to complicated geometries of fluid domains encountered in engineering practice. |
Key words: long wave, shallow water, unsteady motion, sloping beach
Full text link: http://www.ibwpan.gda.pl/docs/ahem/ahem56str063.pdf