Hidrológiai Közlöny 1978 (58. évfolyam)

11. szám - Dr. Kovács György: A szivárgással kapcsolatos tudományos kutatás helyzetéről

Dr. Kovács Gy.: A szivárgással kapcsolatos Hidrológiai Közlöny 1978. 11. sz. 489 strebten die Forscher nach genauerer Beschreibung des Verhaltens des Strömungsfeldes, Vervollkommnung der kinematischen Zusammenhänge und der Berücksichtigung der Grenzbedingungen. Dies war mit Ausgestaltung des Lösungssystems der Beziehungen verbunden, die zur Suche nach einem besten Kompromiss zwischen den gegensätzlichen Ansprüchen von Genauigkeit und Lösbarkeit führte. Während den letzten zwei Jahrzehnten traten wir in die neue, dritte Entwicklungsphase. Bestimmend hierfür war die verbreitete Anwendung der Elektronenrechner in der Lösung der Sickeraufgaben. Dies modifizierte Richtung und Möglichkeit der Forschungen, weil der Rechnereinsatz die Anwendung der numerischen Methoden ermöglicht und somit den Widerspruch bedeutend oder wenigstens vermindert, dass einerseits der Prozess möglichst genau kinematisch zu beschreiben ist und die Grenzbedingungen genau zu berücksichtigen sind, aber die zur Berechnung dienenden Zusammenhänge dermassen zu vereinfachen sind, dass sie analytisch gelöst werden können. Analysen bestätigen, dass heute die moderne Richtung der Sickerforschungen in weitgehendster Anwendung der numerischen Prozesse liegt. Man muss bestrebt sein, die in den Bewegungsgleichungen figurierenden Faktoren und Bedingungen mit genügender Genauigkeit zu erkennen. Deshalb kann ihre physikalisch begründete und zahlenmässig verlässliche Erfassung als wichtigste Forschungsaufgabe gelten. Dabei müssen auch die natürlichen hydrologischen Prozesse berücksichtigt werden. Wegen Veränderlichkeit des den Strömungsraum bildenden Mediums und zufälligem Charakter der nie Sickerung beeinflussenden hydrologischen Erscheidungen müssen die die hydraulischen Bewegungsparameter in den meisten Fällen mit ihrem zu erwartenden Wert und ihrer Streuung beschrieben werden. Somit bezeichnet auch die Lösung der Aufgaben als Endergebnis einen mit bestimmter Wahrscheinlichkeit gekennzeichneten Wertbereich. The state of seepage research By Dr. Kovács, Oy. Doctor of Techn. Sciences Seepage hydraulics form a rather modest part of the mechanics of fluids and gases. The approach differs from the methods adopted in other chapters of hydromechanics, which can be traced back in part to the particular conditions of the seepage field, in part to the greater importance of natural influences. The seepage field is composed of a random, communicating network of pores and fissures, calling for the application of the principle of continuum also to describe the parameters of the seepage field. Moreover, the kinematic approach to the macroscopic movement of the water particle is adopted, which is a general, but often implicit application of the same theorem in hydromechanics. The interpretation of the continuum field imposes two limitations. It is possible to define the smallest size of the seepage field, below which the seepage relationships loose their validity and where the resistance of the individual water conveying elements must be taken into account. The other limitation is encountered, where the character of flow varies with pore size. In such instances the conveying ducts cannot be described any more in terms of the moan pore size, but the statistical model representing the probable distribution of pore diameters must be combined with the geometric and dynamic model. The exchange of water between soil moisture and ground water, as well as cross-currents establishing communication with adjacent layers are important relative to the seepage discharge. These processes are, however, materially influenced by natural factors, so that allowance for hydrological phenomena (randon natural events) assumes much greater significance in seepage hydraulics than in studios related to flow in pipes ,or open channels. Seepage problems may be classified according to practical, or theoretical objectives. Adopting the first aspect three basic types of problems can be distinguished : — In the coherent water conveying system a potential difference is created by a project, or group of projects, and flow is induced thereby in a rather confined, well defined seepage field. — The water exchange between soil moisture and ground water in influenced by natural processes, or human interference, and the problem consists of studying the vertical flow induced by these effects. — The direct aim is to withdraw water from the underground reservoir, and the problem is to describe the local, or regional changes triggered by this measure. None of the problems mentioned above can be solved, unless the main elements of the mathematical model describing the phenomenon can be explored, oF~determined by theoretical investigations. These elements include — the geometry of the seepage field, — the hydraulic parameters of the porous medium, — the exact boundary conditions prevailing along the perimeter of the seepage field, •— the kinematical description of flow within the seepage field, and — solution of the equations of movement. In the development of this domain of science three periods can be distinguished. The recognition of the linear relationship between velocity and gradient, establishing the foundations of seepage hydraulics is associated with the name of Darcy. In the ensuing first period research was concerned with the verification of this fundamental relation, with the determination of the validity limits, and with the development of a more general (non-linear) relationship. Efforts were also made at developing from the fundamental relationship equation of flow by wich both steady and time-variable seepage phenomena can be described at least approximately. The second period started in the first decade of this century, with development accelerating in the thirties. The objectives were to apply the basic principles explored earlier to the solution of practical problems, further, to improve the accuracy attainable by computation. In the interest thereof attempts were made at describing more exactly the behaviour of the seepage field and at introducing in a more correct manner the kinematic relations, together with the boundary conditions. Corrolary thereto schemes were devised for solving the equations obtained, leading to the quest of the optimum compromise betwen the demand for accuracy and the practical feasibility of solution. Research has entered into the recent, thirid period during the past two decades characterized by the advent and widespread application of computers to the solution of seepage problems. This device has changed the trends and scope of research, since it has permitted the introduction of numerical methods, eliminating, or at least substantially alleviating the conflict between striving on the one hand for the most perfect possible kinematic description of the process and for the exact introduction of the boundary conditions, and on the other hand to simplify the equations sufficienty to become accessible to an analytical solution. Surveys have revealed the recent trend in advanced seepage research to be directed at the widespread application of numerical methods. Attempts should be made at the sufficiently accurate understanding of the factors and conditions involved in the equations of movement. The physically sound and numerically reliable exploration thereof may be designated as the most important domain of research. In the course thereof allowance must be made also for the natural hydrological processes. Owing to the variability of the medium forming the seepage field and to the random nature of the hydrological phenomena influencing seepage, the hydraulic parameters describing seepage must be specif iced in the majority of cases by their expected value and standard deviation. The solution is thus obtained as a range of values having a specific probability.