Swiss

Swiss contribution to water hammer theory Contribution Suisse à la théorie du coup de bélier WILLI H. HAGER, VAW, ETH-Zentrum, CH-8092 Zurich, Switzerland KEY WORDS Fluid Transients, History, Hydraulics, Water Flow, Water Hammer. ABSTRACT Swiss hydraulic engineers have significantly contributed to the understanding of water hammer, based partly on the advances of the Italians Ménabréa and Allievi. The contributions of Michaud, Strickler, Schnyder and Jaeger are particularly discussed in the light of modern developments, and biographies on the latter two individuals are added. It is concluded that the phenomenon of water hammer has been developed within a short period, mainly due to the mathematical methods furnished by mechanical engineers and the experience collected by civil engineers for the design and execution of dams during the golden age of dam engineering. RÉSUMÉ Les ingénieurs hydrauliciens suisses ont contribués de façon significative à la compréhension du coup de bélier, en partie grâce aux développements des italiens Ménabréa et Allievi. Les contributions de Michaud, Strickler, Schnyder et Jaeger sont particulièrement traitées à la lumière des développements modernes, et les biographies des deux dernières personnes ci-dessus sont jointes. Il apparaît en conclusion que le phénomène du coup de bélier s’est précisé durant une très courte période, à cause surtout des méthodes mathématiques présentées par les ingénieurs mécaniciens et les expériences réunies par les ingénieurs civils pour la conception et la réalisation des barrages pendant l’âge d’or des constructions de barrages. Introduction Water hammer occurs due to hydraulic transients, i.e. any temporal change of a basic parameter such as gate operation or variation of discharge due to pipe rupture. Water hammer has been studied mainly from the middle of the 19th century and has come to stagnation about 100 years later, until new interest was initiated with the availability of computers. Water hammer involves unsteady pressurized fluid flow in an elastic pipe. Its features are described in excellent textbooks, such as Wylie and Streeter (1967), Sharp (1981) and Chaudhry (1987). In the following, the Swiss contributions to water hammer understanding are highlighted, with particular reference to the outstanding contributions of Schnyder (1904-1974) and Jaeger (19011989). Also, the significant contributions of the Lausanne hydraulicians are accounted for. Early contributions Michaud (1848-1920) presented a paper (1878) to design air compressors. He observed that air pockets are not a direct cause for pipe damage, but that air can lead to water hammer when not properly evacuated. Pipes must thus be filled carefully with water, and air pockets be removed from pipeline systems. By neglecting the effects of fluid compressibility and elasticity of pipe walls, Michaud studied successively abrupt and partial closure configurations. Also, indications on air compressors and their optimum location were provided. By accounting for the effects of elasticity and compressibility the maximum pressure increase HM was determined as HM = 2uL , gT (1) where u=flow velocity before abrupt closure, L=length of pipe from reservoir to orifice, g=gravitational acceleration and T=closure time. Michaud treated the water hammer process correctly, in principle, although the wave features of unsteady pipe flow were overlooked (Vischer 1983). These were correctly modelled in 1902 by Lorenzo Allievi (1856-1941). While still at ETH as a PhD student, Albert Strickler (1887-1963) first reviewed the generalized approach of water hammer by Allievi, as published in 1913 (Strickler 1914a) and conducted experiments on water hammer (Strickler 1914b). A steel pipe 70m long was subjected to linear variation of the outflow section, and the results compared well with the predictions of Allievi. The effect of the so-called water hammer characteristic ρ=avo/(2gyo) was particularly mentioned, where a=propagation velocity, vo=pipe flow velocity and yo=static pressure head. The effects of friction and additional head losses were stated to be insignificant for technical applications. Strickler was able to present a formulation for the extreme pressure head y’ as a function of only n=Lvo/(gyoτ) with τ=closure time. It is noteworthy that Strickler’s thesis had nothing to do with either water hammer nor his well known velocity formula for which he became famous. Schnyder’s approach Schnyder’s first paper (1929) is a mixture of theory and application, and is not simple to read. The graphical method for water hammer in connection with pumps and valves, as designed by his employer Von Roll iron plant, was outlined, but the solution procedure was not attractive enough for engineers. In Schnyder’s Revision received August 7, 1999. Open for discussion till August 31, 2001. JOURNAL OF HYDRAULIC RESEARCH, VOL. 39, 2001, NO. 1 3 (1932) key work the Schnyder-Bergeron method was outlined, using a generalized treatment of water hammer for arbitrary boundary conditions. The boundary conditions were graphically defined and the pressure and velocity distributions along the pipeline determined. The method applies for both pipelines of constant and variable diameters. Based on the governing system of equations in a simple pipeline, the pressure heads H at locations x, x1, and x2, for times t, t1 and t2 may be written in the original notation as H – H1 = + a (C – C1) g a (C – C2) g (2) H – H2 = – (3) The unknowns pressure head H and velocity C may thus be determined, provided conditions at points 1 and 2 are known. Eqs.(2) and (3) are referred to as the conjugate conditions of state. If these are known at two locations, the conditions at a third location 3 may be determined. Refering to an (H,C) coordinate system, straight lines of slope +(a/g) and –(a/g) are drawn, respectively, and the point of intersection defines the solution. The two points can of course be located at the end of the pipeline, and the successive development of velocity and pressure can be determined. Basic examples include the closure of a pipeline connected to a reservoir, from steady to zero discharge by including friction, water hammer in a pipeline containing a surge tanke, and resonance effects on pipelines. The results of these computations are so nicely illustrated, and the method outlined so straightforward, that Schnyder’s paper was popular among hydraulic engineers that were asked to compute unsteady pipe flows. Note that the contributions of the Frenchmen Camichel, Eydoux and Gariel from Toulouse university were cited, whereas Louis Bergeron (1876-1948) remained unmentioned at that time. The 1935 paper of Schnyder refered in particular to water hammer in pipe bifurcations added to surge tanks. His basic approach was extended to this significant application. Bergeron was cited for the first time, but Schnyder stated that Bergeron followed his own approach to account for frictional effects. In the same year 1935, Bergeron also published two papers, and cited Schnyder’s approach in the latter paper. Whereas Bergeron refered mainly to the analytical approach of Jaeger to be discussed below, Schnyder’s key reference was Allievi. It appears that the two researchers have had not too much sympathies for each other. The graphical method is actually referred to as the Schnyder-Bergeron method, a notation introduced by Jaeger. Obviously to attract Bergeron’s attention, Schnyder (1936a) published a paper in French, in the main engineering journal of Western Switzerland. He was able to demonstrate that Bergeron’s approach neglects the effect of velocity head on water hammer. An important contribution to this problem was also presented by Angus (1937), to which both Bergeron and Schnyder submitted discussions, among others, and Jaeger introduced the notation Method of Schnyder and Bergeron. In 1937 also, this notation was used in the introduction to a paper on water hammer (Schlag 1937) by the leading French hydraulics journal Revue Générale de l’Hydraulique. Bergeron (1950) proposed the graphical method for other physical phenomena, such as waves on electric lines or even lightnings. It is not clear whether Bergeron has ever met Schnyder, and both have stopped to work on water hammer after the mid thirties. Schnyder turned more to hydraulic machinery associated with Von Roll, such as pressure reduction valves (Schnyder and Büttiker 1936), pumps (Schnyder 1937), and pipe rupture security (Schnyder 1939). Schnyder returned to fundamental research in 1943, and summarized the water hammer theory in a textbook style. One year later, Gaden and Schnyder (1944) were able to discuss various shortcomings of the conventional approach by refering not only to the small, but also to the large amplitude assumption. The latter simplifies to the small amplitude theory whenever the ratio of pipe to propagation velocities is small. Schnyder (1944) also examined the relation between water hammer and gas dynamics. For small relative velocity, the equations are identical. Even for large velocities of a continuous flow, equations can be expressed in a generalized form. However, for discontinuous flows, shocks form that follow the Hugoniot equations in gas dynamics. Jaeger’s approach Jaeger (1933a) submitted a thesis published as a book by the well known French printer Dunod. In a summary paper, Jaeger (1933b) outlined the findings of his thesis. A generalization of Allievi’s approach seemed important for a pipeline system connected to a surge tank. Until then, substitute pipes were accounted for, which can lead to serious errors. A large surge tank is an excellent protection against pressure waves because all waves are totally reflected, and the additional pressures in the pipeline are always zero. Jaeger’s analysis involving a surge tank allows generalisation of Allievi’s system of equations. At the bifurcation of three pipes I, II and III starting at the reservoir, the surge tank and the orifice, respectively, the positive wave Fi and the negative wave fi just at the base of the surge tank are related to as fi=–αiFi with αi as reflection parameter. With ρi as Allievi’s characteristic previously introduced, Jaeger obtained for transmission ri and reflection si coefficients, respectively αi = rIII = ñ -1 + ñ -1 − ñ -1 I II III , 1 1 ñ -I1 + ñ -II + ñ -III (4) (5) sIII = 1 – rIII . Allievi’s result for the single pipeline is simply αi=1. At one time step, Jaeger’s analytical method involves a system of three equations. Computations are described to be lengthy and errors have significant consequences to subsequent time steps. Compared to the graphical method, this was a major disadvantage at Jaeger’s times when all calculations were manually made. Jaeger concluded that water hammer and mass oscillations can add to each other and result in larger pressure peaks, compared to a simple 4 JOURNAL OF HYDRAULIC RESEARCH, VOL. 39, 2001, NO. 1 superposition of oscillations. The review of Jaeger’s thesis by Schnyder (1934) was excellent, and the two main Swiss researchers on water hammer phenomena found a common basis of research. Collaboration between the two has not resulted, however, mainly because of too different professional backgrounds. Jaeger (1935a) stated that Schnyder introduced a method of computation for pipes with a variable diameter. He speculated that Bergeron was not aware of this generalisation but that Bergeron’s contribution to the problem was mainly inclusion of head losses. Jaeger also proposed that procedures for the prediction of water hammer should be presented in a generalized approach, including graphical methods of Schnyder and Bergeron, and analytical methods of Allievi and himself. He drew attention to the fact that the envelopes of all possible water hammer curves had not yet been determined, although thousands of observations were available. An introduction of Jaeger’s analytical water hammer theory was devised in 1937, in the leading German journal Wasserkraft und Wasserwirtschaft. It was stated that most engineers applied the graphical method of Schnyder-Bergeron, although the analytical method had advantages in defining the water hammer curves for complex pipelines. The governing equations for water hammer in a pipeline element based on the conservation equations for mass and momentum are ∂v g ∂y , = ∂x a 2 ∂t ∂v ∂y . =g ∂t ∂x (6) (7) The solution of this linear system of partial differential equations is known since Riemann. The solutions depend exclusively on the initial and boundary conditions. It can be demonstrated that function F describes a wave travelling from the closure device towards the reservoir and the function f is the reflection wave. At an arbitrary location x, the pressure head thus equals the sum of static and dynamic pressure heads. Whereas the approach of Allievi refers to a pipeline of constant diameter that is fed from a large reservoir, the general water hammer theory accounts for systems of pipes including also surge tanks. Jaeger presented his theory for both abrupt and continuous closure and opening scenarios. The latter can be analyzed with a simpler approach because temporal variations are so small that various terms remain constant. He then treated resonance of pipeline systems due to rhythmic opening and closure processes. When looking at his analytical approach, most engineers were happy to proceed with the graphical approach and the SchnyderBergeron method has been popular within the period until computers were available. From this time onwards, the analytical method as introduced by Allievi and generalized by Jaeger took over, until today. The first contribution to the theory of resonance in English was provided by Jaeger in 1939. By considering a pipeline connected with a surge tank the minimum pressure at the gate is H=0, and the maximum pressure head is H=2ho, i.e. the double static pressure head. Jaeger extended his considerations to systems of pipelines and verified his analytical results with French observations. Jaeger’s textbook (1949) originated from his habilitation thesis in 1944 and an almost complete draft was available in 1946. When presenting it to Prof. Meyer-Peter, Director of Versuchsanstalt für Wasserbau at ETH, the latter realized its value and suggested to be first author, a common European practise. Jaeger, however, disagreed and left the institute. He started working at Rugby U.K., for the English Electric Company, and finished his master work. The German version contains almost 500 pages, including each 170 pages on steady flows and unsteady flows, and another 110 pages on groundwater flow and appendices mainly on experimental procedures. The unsteady flow chapter is subdivided almost equally into surge tanks and water hammer. In the following, only the latter section is reviewed. After introducing the governing equations of water hammer, and Allievi’s solution for the basic pipe arrangement, the system reservoir-surge tank-penstock is considered. In addition, multiple pipeline systems are treated, and the effect of decreasing penstock diameter is discussed. Particular reference is made to Henry Favre (1901-1966), a close friend to Jaeger both during studying at ETH, and later at the Versuchsanstalt. During the years of Jaeger’s illness, collaboration was complicated, and when returning to Zurich in 1938, Favre became ETH professor in mechanics. Therefore, no common paper of the two main Swiss theoretical hydraulicians is available. The next section of the book deals with resonance in penstocks, and regulation of turbines. Only then, the method of Schnyder-Bergeron is introduced and recommended as engineering tool for practical applications. The basics of the method are outlined for standard opening and closure scenarios. Then, the effects of diameter reduction and friction are discussed. The water hammer section is completed with a comparison between the characteristics of surge tank oscillations and water hammer waves. Further Swiss contributions Jaeger’s contributions to water hammer are significant, particularly his analytical approach. He developed the Allievi approach and continued the (Swiss-French) hydraulics school of this research branch. After Daniel Gaden (1893-1966) had translated Allievi’s general water hammer theory in 1921, a center for water hammer established in the French part of Switzerland, obviously influenced by the Engineering School of Lausanne (today EPFL) and Charmilles and Vevey, furnishers for hydro machinery. Gaden, former director of Charmilles at Geneva and later professor for hydraulic machinery at Ecole Polytechnique Universitaire de Lausanne (EPUL), contributed largely to the regulation and stability of hydromachinery (Gaden 1945). He presented several papers together with Jules Calame (1891-1961), a consulting engineer of Geneva. The paper of Calame and Gaden (1935) was questioned by the young researcher Jaeger (1935b, 1936), mainly because of simplifications introduced into the computational procedure. The present author is unaware of any personal contacts between Schnyder and Jaeger, although both were working less than 100 km apart, and both have significantly developed the water hammer theory. Biographies of both persons follow below. JOURNAL OF HYDRAULIC RESEARCH, VOL. 39, 2001, NO. 1 5 References Angus, R.W. (1937). Water hammer in pipes, including those supplied by centrifugal pumps: Graphical treatment. Proc. Mechanical Engineers 136: 245-331. Bergeron, L. (1950). Du coups de bélier en hydraulique au coup de foudre en éléctricité (From water hammer in hydraulics to lightning in electricity). Dunod: Paris (in French). Calame, J., Gaden, D. (1935). Influence des reflexions partielles de l’onde aux changements de caracteristiques de la conduite et au point d’insertion d’une chambre d’equilibre (Influence of partial wave reflexions at changes of conduit characteristics and at the point of surge tank addition). Bulletin Technique de la Suisse Romande 61(19): 217-220; 61(24): 277-282; 62(5): 49-53 (in French). Chaudhry, M.H. (1987). Applied hydraulic transients. Van Nostrand Reinhold: New York. Gaden, D. (1921). Théorie du coup de bélier (Theory of water hammer). Dunod: Paris (in French). Gaden, D., Schnyder, O. (1944). Coups de bélier de petites et grandes amplitudes (Water hammer of small and large amplitudes). Bulletin Technique de la Suisse Romande 70(14): 173182 (in French). Gaden, D. (1945). Contribution à l’étude des regulateurs de vitesse - Considérations sur le problème de la stabilité. La Concorde: Lausanne (in French). Jaeger, C. (1933a). Théorie générale du coup de bélier: Application au calcul des conduites à caractéristiques multiples et des chambres d’équilibre (General theory of water hammer: Application of computation on pipelines with a multiple characteristic and on surge tanks). Dunod: Paris (in French). Jaeger, C. (1933b). Théorie générale du coup de bélier (General theory of water hammer). Le Génie Civil 103(26): 612-616 (in French). Ja e g er, C. (1935a). Über eine allgemeine graphische Berechnungsmethode der Druckstösse in Rohrleitungen (On a general graphical method for water hammer in pipelines). Wasserkraft und Wasserwirtschaft 30(17): 202-203; 30(23): 279-280 (in German). Jaeger, C. (1935b). Les coups de bélier dans les conduites simples et dans les conduites complexes (Water hammer in simple and complex conduits). Bulletin Technique de la Suisse Romande 61(22): 255-256 (in French). Jaeger, C. (1936). Quelques remarques en marge de la théorie du coup de bélier. Réponse aux considerations sur le coup de bélier, de MM. Calame et Gaden (Some remarks on the water hammer theory. Answer to considerations of Calame and Gaden). Bulletin Technique de la Suisse Romande 62(10): 113118 (in French). Jaeger, C. (1937). Die analytische Theorie des Druckstosses in Druckleitungen (Analytical theory of water hammer in pipes). Wasserkraft und Wasserwirtschaft 32(23): 269-276 (in German). Jaeger, C. (1939). Theory of resonance in pressure conduits. Trans. ASME 61: 109-115. Jaeger, C. (1949). Technische Hydraulik (Technical hydraulics). Birkhäuser: Basle (in German). Michaud, J. (1878). Coup de bélier dans les conduites - Etude des moyens employés pour en atténuer les effets (Water hammer in pipelines - Study of means to reduce the effects). Bulletin de la Société Vaudoise des Ingénieurs et des Architects 4(3): 56-64; 4(4): 65-77 (in French). Michaud, J. (1903). Intensité des coups de bélier dans les conduites d’eau (Intensity of water hammer in water pipelines). Bulletin Technique de la Suisse Romande 29(3): 35-38; 29(4): 49-51 (in French). Schlag, A. (1937). Le coup de bélier dans une conduite à caractéristique unique (The water hammer in a pipe with unique characteristic). Revue Universelle des Mines Series 8 13(10): 413-430 (in French). Schnyder, O. (1929). Druckstösse in Pumpensteigleitungen (Water hammer in pumping pipelines). Schweizerische Bauzeitung 94(22): 271-273; 94(23): 283-286 (in German). Schnyder, O. (1932). Über Druckstösse in Rohrleitungen (On water hammer in pipelines). Wasserkraft und Wasserwirtschaft 27(5): 49-54; 27(6): 64-70; 27(8): 96 (in German). Schnyder, O. (1934). Review of Théorie générale du coup de bélier, by Charles Jaeger. Schweizerische Bauzeitung 104(5): 54 (in German). Schnyder, O. (1935). Über Druckstösse in verzweigten Leitungen mit besonderer Berücksichtigung von Wasserschlossanlagen (On water hammer in bifurcated pipelines with particular consideration of surge tanks). Wasserkraft und Wasserwirtschaft 30(12): 133-142; 30(14): 172 (in German). Schnyder, O. (1936a). Considérations sur le coup de bélier (Considerations on water hammer). Bulletin Technique de la Suisse Romande 62(11): 121-123; 62(12): 133-137 (in French). Schnyder, O. (1936b). Über Druckstösse in Rohrleitungen, die zur bleibenden Rohrverformung führen (On water hammer in conduits resulting in lasting pipe deformations). Wasserkraft und Wasserwirtschaft 31(4): 37-40 (in German). Schnyder, O., Büttiker, W. (1936). Druckreduzierventile und Regler für Wasserversorgungsanlagen (Pressure reduction valves and regulators for drinking water supply). Bulletin der Gas- und Wasserfachmänner 16(2): 35-41 (in German). Schnyder, O. (1937). Comparisons between calculated and test results on water hammer in pumping plants. Trans. ASME 59(13): 695-700. Schnyder, O. (1939). Rohrbruchsicherheitsanlagen (Pipe rupture safety installations). Wasserkraft und Wasserwirtschaft 34(19/20): 230-238 (in German). Schnyder, O. (1943). Druckstösse in Rohrleitungen (Water hammer in conduits). Von Roll Mitteilung 2(3/4): 1-56 (in German). Schnyder, O. (1944). Zur Theorie der Druckstösse bei grosser Fliessgeschwindigkeit und die Zusammenhänge mit der Gasdynamik (Theory of large velocity water hammer and relations to gas dynamics). Wasserkraft und Wasserwirtschaft 39(5/6): 131-134 (in German). Sharp, B.B. (1981). Water hammer, problems and solutions. Arnold: London. Strickler, A. (1914a). Theorie des Wasserstosses (Review of 6 JOURNAL OF HYDRAULIC RESEARCH, VOL. 39, 2001, NO. 1 Theory of water hammer). Schweizerische Bauzeitung 63(25): 357 (in German). Strickler, A. (1914b). Versuche über Druckschwankungen in eisernen Rohrleitungen (Experiments on pressure variations in steel pipes). Schweizerische Bauzeitung 64(7): 85-87; 64(10): 123 (in German). Vischer, D. (1983). Schweizer Pioniere der Hydraulik (Swiss pioneers in hydraulics). Schweizer Ingenieur und Architekt 101(48): 1129-1134 (in German). Wylie, E.B., Streeter, V.L. (1967). Fluid transients. McGraw-Hill: New York. Othmar Schnyder (1904-1974) Born on 25th March 1904 at Kriens close to Lucerne, Switzerland, Schnyder obtained the degree of mechanical engineer at the Swiss Federal Institute of Technology (ETH) in 1926. He submitted a PhD thesis on the static computation of regulation rings for turbines and pumps (1928) to obtain the degree of Doctor of Technical Sciences. In mid 1928, he started working with Von Roll iron works at Klus, close to Solothurn, Switzerland. The professional career of Schnyder is thus subdivided into two parts: (1) His job as a design engineer for hydraulic machinery with Von Roll and later in his own office, and (2) his hobby or even his love: Water hammer. Schnyder’s (1930) typical contribution to his professional duties is characterized with a strong relation to mechanical design of security elements. In 1936, Schnyder combined in a way his job and hobby for security installations in hydraulic machinery. By this time, the Method of Schnyder-Bergeron became a simple means for hydraulic engineers to tackle fluid transients in pipes. Schnyder, however, seems to have been aside from the rapid development, because of his physical distance to any university. By the end of the thirties, Daniel Gaden, a professor of hydraulic machinery of EPUL at Lausanne (now EPFL) followed Schnyder’s outstanding work, and the two started collaboration, mainly during weekends. Schnyder, on the other hand, was firmely attached to Von Roll, and he was asked to develop hydraulic control elements for large presses and oil pumps (Schnyder 1942, 1946). He was even allowed to develop a hydraulic lab in 1947 at Von Roll with installations for both pressurized and free surface flows. However, Schnyder was pushed to consulting and management, which he did not really like as a researcher. Frustrated by the job prospect at Von Roll, Schnyder decided to start his own company as a consultant in 1950, and in 1954 as the head of Hydro-Progress, an engineering office for developing hydraulic machinery. Othmar Schnyder was a quiet person, he loved to be with his family, and his daughter seemed to be his best friend. During weekends, he often visited his chalet on lake of Lucerne, to be in nature and to elaborate new concepts for hydraulic machinery. During the week, he visited his clients all over Switzerland, as also in Germany and Austria. In 1962, he started with Hydro-Progress at Malters close to Lucerne, sufficiently far away from Von Roll. There, he collaborated with his brother-in-law, who has been head of Hydro-Progress since 1974. Schnyder was a natural talent in technical terms. His practical sense is demonstrated by the elegant development of his graphical method for water hammer. He was an authority in technical matters, and all his designs worked so nicely that clients hardly asked why. Schnyder was not a teacher: "Either you know how this works, or you will not learn it". He had always time for a new approach, and many details were developed during nights or weekends. He was working to his last day, and visited his HydroProgress from his residence at Rüschlikon, close to Zurich. A serious illness caused his death, but he was happy that the family did well. Othmar Schnyder died on October 28, 1974 after a fulfilled live for progress in hydraulic machinery. He left his wife Anna and a daughter. References Schnyder, O. (1930). Absperrorgane für Wasserkraftmaschinen (Arresting organs for hydraulic machinery). Schweizerische Technische Zeitschrift 27(10/11): 163-167 (in German). Schnyder, O. (1936). Rohrbruchsicherungen (Safety elements against pipe rupture). Schweizerische Bauzeitung 107(25): 281284 (in German). Schnyder, O. (1942). Sind Flanschen hoch beansprucht? (Are flanges highly stressed?). Schweizerische Bauzeitung 119(25): 298-299 (in German). Schnyder, O. (1946). Various notes. Von Roll Mitteilung 5: 5196; 5: 102-123 (in German). Schnyder, O. (1947). Die hydraulische Forschungsanstalt (The hydraulic laboratory). Von Roll Mitteilung 6: 102-119 (in German). Othmar Schnyder in 1935 JOURNAL OF HYDRAULIC RESEARCH, VOL. 39, 2001, NO. 1 7 Charles Jaeger (1901-1989) Time at ETH Charles Jaeger was born on March 26, 1901 in Zurich, Switzerland, townsman of Auboranges in canton of Fribourg. He left the Swiss Federal Institute of Technology in 1924 as a civil engineer and started working with an engineering company in Geneva. However, he was suffering from tuberculose and had to be in isolation because of infection danger. He spent 1926 to 1928 at the International University Sanatory at Leysin. The first recovery center at approximately 1400m a.o.d. was opened in 1922 and contained lecture rooms, libraries and study rooms. Jaeger could thus penetrate into the technical literature. From 1929 to 1931 he was the private assistant to Prof. Eugen Meyer-Peter (1883-1969), and presented a thesis on water hammer in 1932. His mother tongue was French, and he was fluent in German and Spanish. He got married in 1934, once his professional life was set. From 1934 to 1938 he was a consultant at Villars sur Ollons, located East of Montreux. There he was busy in writing state-of-the-art papers on various subjects, such as descriptions of the recently opened Versuchsanstalt für Wasserbau (Jaeger 1930), newly errected power plants (Jaeger 1932a, 1936a, 1937b), on the friction losses of tunnels, pipes and channels (Jaeger 1936b, c), on construction installations for dams (Jaeger 1936d) and even on economical problems of the thirties (Jaeger 1932b, 1937a). He started also to act as a scientific reporter for journals such as Wasserkraft and Wasserwirtschaft, the leading hydraulics journal in German language. From 1935 to 1938, all his papers and notes were signed by C. J., Villars sur Ollon, where his wife worked as a dentist. He still had contacts to the Versuchsanstalt at Zurich, and it was normally him that summarized research results of friends, such as of Henri Favre (1901-1966) and Hans Albert Einstein (1904-1973), or the ASME water hammer committee, of which he was associate member. He reported also on the activities of ETH and Ecole Polytechnique de l’Université de Lausanne (EPUL) because of his interest in international activities, much in contrast to most of the other Swiss hydraulic engineers. The main research topic until 1938, his return to ETH as a scientific collaborator, remained of course water hammer, and he was able to get two papers accepted by the ASME Transactions on resonance of pipe flow due to water hammer. His first topic after returning to the Versuchsanstalt was scour at plunge pools (Jaeger 1939, 1940). His proposal initiated the researches of Willi Eggenberger and Robert Müller on generalized scour equations (Hager 1998). Further research topics of Jaeger until 1946 involved the generalized energy equation for free surface flows, stability analysis of surge tanks, groundwater flow and history of hydraulics. These shall not be reviewed here, however. According to friends at ETH, Jaeger was a reticent person mainly writing reports, and not conducting lab works. He was by far the most internationally known person of the institute, and the director Eugen Meyer-Peter had obviously some problems of competition. The latter was a practitioner with excellent relations to Swiss industries, but with a small international engagement until the end of the war. This tension grew into a conflict when Jaeger presented Meyer-Peter his book draft Technische Hydraulik. Jaeger, since 1943 Privat-Dozent of ETH similar to a senior reader in the english university system, but without a leading role at the Versuchsanstalt, decided to leave Switzerland. Jaeger and his young family left for a rather unsafe future both in private and professional terms. From theory to applications After fifteen years of academic research, Charles Jaeger was thrown into the cold waters, as we say, with the English Electric Company at Rugby, close to London, U.K. He was suddenly in the center of applications. England had just finished the war, and lots of activities started in power engineering. As a specialist in water hammer and surge tanks analysis, Jaeger took actively part in the design of underground hydro-electric power stations. He also gave advice for complex designs all over Europe as a consulting engineer. Jaeger developed into a specialist for pressure tunnels, and started working on rock mechanics, a science that had not really developed yet. By the end of the fifties, so-called pumped storage was developed, and Jaeger again was an important contributor to such designs. His activities are set down in many contributions to English journals, such as in the Proc. of the Institution of Civil Engineers, Water Power, the English Electric Journal or the Engineering Journal. Jaeger was involved in various dam problems as an expert, such as Malpasset (France in 1959), Vajont (Italy in 1963), Tarbela (Pakistan) and Kariba (Central Africa). His knowledge was published in books, starting from the classical textbook Technische Charles Jaeger in 1936 8 JOURNAL OF HYDRAULIC RESEARCH, VOL. 39, 2001, NO. 1 Hydraulik (1949) of which French and English translations were published in the mid fifties. Later, he contributed to GuthrieBrown’s Hydro-Electric Engineering Practice (1970) and published the noteworthy Rock Mechanics and Engineering (1972). Jaeger summarized his immense knowledge on unsteady flows in Fluid Transients (1977). All these books evolved from his activities at Imperial College, where he served from 1946 to 1965 first as a special lecturer, and then as a visiting professor (Jaeger 1965). He stated that hydro-power engineering required wide technical knowledge ranging from hydrology and fluid mechanics to structures and architecture, a fact mainly responsible for the student’s interest in this branch of engineering, without fearing over-specialisation. After the war, a majority of students believed that hydraulic engineering was the best introduction to a career in civil engineering. He then referred to the graduate course in engineering fluid mechanics and hydro-power structures that started after war at Imperial College, London. This initiative was taken to fill in the gap for the future design of large hydro-power projects, mainly in Scotland and in the Commonwealth. These courses, which led to an engineering diploma, were an accepted feature of British universities. Jaeger offered rock mechanics as a particular course for graduate students at Imperial College. Such a course had become necessary as a supplement to dam foundations, tunneling methods and design of underground power stations. In his Preface to the rock mechanics book Jaeger (1979) stated that there is no better method to deal with technical problems than the close analysis of case histories. Jaeger was known as an engineer and not only a specialist, at least after his arrival at England. It is this outstanding quality that deserves particular attention in a time of overspecialisation. Rehabilitation at ETH In early 1980 Charles Jaeger came into contact with Prof. D.L. Vischer, former director of VAW, ETH Zurich. Jaeger submitted a curriculum vitae that served as the basis of a summary on Swiss hydraulicians (Vischer 1983). Indeed, Jaeger returned from England in 1968, after having been visiting professor at Colorado State University in 1966, and consultant for UNESCO in India, in 1967. His wife didn’t like the English weather, and the Jaegers were happy at Pully, on Lake Geneva. Under the leadership of Prof. Vischer again, Jaeger was honored by a special issue of the Schweizerische Bauzeitung, with contributions of various friends worldwide. In the introduction, Vischer refers to Jaeger as the known unknown person, because Jaeger had great influence on Swiss hydraulics but was not known in public. Jaeger received various honors including the Gotthilf-HagenMedal for his services for water power development in 1965, but his own country followed only in 1983, to honor him with the ETH Honorary Degree of Doctor. The laudatio reads Honor for his contributions to pipe and channel hydraulics and unsteady processes in pipelines of power plants in particular (Vischer 1989). Charles Jaeger was proud that ETH at last offered him this special recognition. He died after a rich life for the engineering profession on December 5, 1989 at Pully. Acknowledgements The preparation of the biographies depended largely on the help of Mrs. A. Schnyder, Rüschlikon, and Mrs. N. Hopkirk, Wallisellen, Charles Jaeger’s daughter. The author would like to acknowledge em.Prof. Dr. D.L. Vischer, ETH, and em.Prof. Dr. P. Novak, University of Newcastle, U.K., for reviewing the manuscript. References (1930) Die Versuchsanstalt für Wasserbau an der ETH in Zürich (The hydraulic lab at ETH Zurich). Schweiz. BaumeisterZeitung 30(1): 4-6 (in German). (1932a). Essai sur un modèle reduit de la galérie de fuite de Wettingen (Model test on outlet tunnel of Wettingen power plant). Bulletin Technique de la Suisse Romande 58: 289-291 (in French). (1932b). L’organisation du troc international au moyen de chambres de compensation d’industries (The organisation of international barter by industrial compensation chambres). Goemaere: Bruxelles (in French). (1936a) Die neueren französischen Wasserkraftwerke (Recent hydraulic power plants of France). Wasserkraft und Wasserwirtschaft 31(13): 162-166; 31(14): 175-177 (in German). (1936b). Italienische Messungen über Druckverluste in Druckrohren, Stollen und Kanälen (Italian observations on pressure losses in penstocks, tunnels and channels). Schweizerische Bauzeitung 108(14): 150-151 (in German). (1936c). Gleichförmige Strömung in grossen Rohrleitungen und Kanälen (Uniform flow in large penstocks and channels). Wasserkraft und Wasserwirtschaft 31(21): 273-275 (in German). (1936d). Baustelleninstallationen bei grossen Staumauern (Site installations for large dams). Hoch- und Tiefbau 35(20): 168171; 35(21): 175-179 (in German). (1937a). Le problème de la prévision en économique rationelle (The problem of forecast for rational economics). Zeitschrift für Schweizerische Statistik und Volkswirtschaft 73(2): 279-286 (in French). (1937b). Die französischen Versuchsanstalten für Wasserbau (The French hydraulic laboratories). Wasserkraft und Wasserwirtschaft 32(4): 44-46 (in German). (1939). Über die Ähnlichkeit bei flussbaulichen Modellversuchen (On similarity of river engineering models). Wasserkraft und Wasserwirtschaft 34(23/24): 269-270 (in German). (1940). Sur les équations des cours d’eau à fond mobile (On the equations of flow in mobile bed channels). Comptes Rendus de l’Académie des Sciences Paris 210(13): 472-474. (1965) A college course in hydroelectric engineering. Water Power 17(7): 267-272. (1970). Governing of water turbines. Hydro-Electric engineering practise 2: 799-816. J. Guthrie Brown, ed. Blackie & Son: Glasgow. (1972). Engineering and rock mechanics. Water Power 22(5/6): 203-209; 22(7/8): 253-259. JOURNAL OF HYDRAULIC RESEARCH, VOL. 39, 2001, NO. 1 9 (1977). Fluid transients. Blackie: Glasgow and London. (1979). Rock mechanics and engineering. 2nd ed. Cambridge University Press: Cambridge. Hager, W.H. (1998). Plunge pool scour: Early history and hydraulicians. Journal of Hydraulic Engineering 124(12): 1185-1187. Vischer, D. (1989). Zum Hinschied von Charles Jaeger (Obituary for Charles Jaeger). Wasser, Energie, Luft 81(11/12): 361 (in German). 10 JOURNAL OF HYDRAULIC RESEARCH, VOL. 39, 2001, NO. 1