Deltar

Tidal calculations had been a focus of engineering research in the Netherlands for much of the early 20th century. In 1916, Gerard Henri de Vries Broekman had suggested a practical method for the calculation of tidal levels.{{Cite journal |last=de Vries Broekman |first=G.H. |date=1916 |title=Invloed van eb en vloed op de benedenrivieren |trans-title=Influence of ebb and flow on the lower rivers |journal=De Ingenieur |language=nl |issue=29}} In 1926, Hendrik Lorentz had developed two methods for the prediction of tidal levels for the Zuiderzee Works.{{cite book | last1 = Lorentz | first1 = H.A. | author-link1 = Hendrik Lorentz |author-link2=Hendrik Wortman | last2 = Wortman | first2 = H. | last3 = van Everdingen | first3 = E. | last4 = Stoel | first4 = W.F. | title = Verslag van de commissie Lorentz (gevolgen afsluiting Zuiderzee op het getij) | trans-title = Report of the Lorentz Committee (Effects of the Closure of the Zuiderzee on the Tide) | language = nl | year = 1926 | publisher = Algemene Landsdrukkerij | url = http://resolver.tudelft.nl/uuid:f5a4fe20-b26a-4875-9f96-6be04ba16c59 | access-date = 2023-12-28 }}

The methodologies for solving differential equations of tidal motion were continuously researched and improved in the years after this, notably by J.P. Mazure,{{cite thesis |last=Mazure |first=J.P. |title=De berekening van getijden en stormvloeden op benedenrivieren |trans-title=The Calculation of Tides and Storm Surges in Lower Rivers |language=nl |url=http://resolver.tudelft.nl/uuid:42258e53-ce1d-4cee-b197-025374e857e6 |year=1937 |access-date=28 December 2023 |degree=PhD |publisher=TU Delft}} H.J. Stroband,{{Cite web |last=Stroband |first=H.J. |date=1945 |title=De voortplanting van het getij bepaald met behulp van de electrotechniek : 1e stuk |trans-title=The propagation of the tide determined using the electro technique: 1st piece |url=https://open.rijkswaterstaat.nl/zoeken/@178262/voortplanting-getij-bepaald-behulp/ |access-date=28 December 2023 |website=Rijkswaterstaat Publications Platform |language=nl}}{{Cite web |title=Verklaring overbrenging collectie Van Veen van Rijksinstituut voor Kust en Zee te Den Haag naar het Nationaal Archief te Den Haag |trans-title=Declaration transfer collection Van Veen of the National Institute for Coast and Sea in The Hague to the National Archives in The Hague |url=https://open.rijkswaterstaat.nl/overige-publicaties/2005/verklaring-overbrenging-collectie-veen/ |access-date=28 December 2023 |website=Rijkswaterstaat Publications Platform |language=nl}}{{Cite journal |last=Stroband |first=H.J. |date=1943 |title=Stormvloedsberekening met de sinusoidale methode |trans-title=The calculation of tidal surges by the sinusoidal method |journal=Rapport Studiendienst |language=nl |publisher=Rijkswaterstaat |publication-place='s-Gravenhage}} Jo Johannis Dronkers,{{Cite journal |last=Dronkers |first=J.J. |author-link=Jo Johannis Dronkers |date=1949 |title=De exacte methode voor getijberekening met als toepassing de berekening van de getijvoortplanting bij enkele theoretische stormvloeden |trans-title=The exact method of tidal calculation with examples of its application to the calculation of several theoretical tide surges |journal=Rapport Studiendienst |language=nl |location='s-Gravenhage |publisher=Rijkswaterstaat}} H. Holsters,{{Cite journal |last=Holsters |first=H. |date=1953 |title=Le calcul du mouvement non permanent dans les rivières par la méthode dite des "lignes d'influence" |trans-title=Calculation of non-permanent flow in rivers by the method known as "influence lines" |journal=La Houille Blanche |language=fr |volume=39 |issue=4 |pages=495–509 |doi=10.1051/lhb/1953044 |issn=0018-6368 |doi-access=free |bibcode=1953LHBl...39..495H }} and Johan Christoph (J.C.) Schönfeld.{{Cite book |last=Schönfeld |first=J.C. |url=http://resolver.tudelft.nl/uuid:9ec412b4-26b3-40bf-a6f6-ecb2e069fa17 |title=Propagation of tides and similar waves |publisher=Staatsdrukkerij en Uitgeversbedrijf |year=1951 |access-date=28 December 2023}}

In the 1930s, Johan van Veen worked on a model to compare tidal currents with electrical currents. Despite initial scepticism about its reliability, van Veen continued to develop his 'electrical method', which he described in an article in the Dutch journal {{lang|nl|De Ingenieur}} as a 'simple engineering method' with 'relatively great accuracy'.{{Cite journal |last=van Veen |first=J. |date=1947 |title=Analogy between tides and AC electricity |url=http://resolver.tudelft.nl/uuid:e66ed3f0-a349-44a7-b548-ccb6785aba70 |journal=The Engineer |issue=Oct/Dec 1947 |pages=498–499; 520–521; 544–545 |access-date=28 December 2023 |via=TU Delft Repository}}{{Cite journal |last=van Veen |first=J. |author-link=Johan van Veen |date=1937 |title=Getijstroomberekening met behulp van wetten analoog met die van Ohm en Kirchhoff |trans-title=Tidal current calculation using laws analogous to those of Ohm and Kirchhoff |journal=De Ingenieur |language=nl |issue=19}}

His method stood in opposition to the more mathematical methods for tidal calculations, such as those of Dronkers, which required complicated mathematical effort. Dronkers had published several papers on tidal calculations, leading up to his magnum opus, Tidal computations in rivers and coastal waters, in 1964. It remains a benchmark in the field of tidal calculation theory, and led to the award of the Conrad Medal by the Royal Netherlands Institute of Engineers to Dronkers in 1965.{{cite book |last=Dronkers |first=J.J. |url=https://archive.org/details/tidalcomputation0000dron/page/n9/mode/2up |title=Tidal computations in rivers and coastal waters |publisher=North-Holland Pub. Co.; Interscience Publishers |year=1964 |location=Amsterdam; New York |accessdate=28 December 2023}}

Dronkers' computational approach, though rigorous, was criticised by van Veen for its complexity and computational demands, which he believed could hinder timely practical applications. The Deltar, by comparison, offered a fast and accurate method to undertake tidal calculations.{{cite journal |last=Van Veen |first=J. |date=1946 |title=Electrische nabootsing van getijden: Commentaar van dr J. J. Dronkers, met naschrift van de auteur |trans-title=Electrical Simulation of Tides: Commentary by Dr. J. J. Dronkers, with Postscript from the Author |url=https://open.rws.nl/open-overheid/onderzoeksrapporten/@17005/commentaar-dronkers-naschrift-auteur/ |journal=De Ingenieur |language=nl |publisher=Koninklijk Instituut van Ingenieurs |issue=17 |pages=70–78 |access-date=28 December 2023}}

After the North Sea flood of 1953, the {{lang|nl|Deltacommissie}} (English: Delta Commission), led by A.G. Maris, the Director-General of Rijkswaterstaat, was established. This commission was tasked by the Minister of Transport and Water Management to develop plans to prevent such disasters in the future. Although a Delta Plan had been conceived by van Veen before the flood, this event expedited the decision to progress it, with the Dutch coastline to be shortened by approximately 700 kilometres. The scale and complexity of the Delta Works meant that the reduction in calculation time offered by the Deltar, compared with manual calculation methods, would be advantageous.{{Cite web |last1=Maris |first1=A.G. |last2=Van Veen |first2=J. |last3=De Vries |first3=J.W. |last4=Dibbits |first4=H.A.M.C. |title=Het deltaplan en zijn verschillende facetten |url=http://resolver.tudelft.nl/uuid:acb4bafc-6e81-416b-a059-04d9c4a04ef6 |publisher=KiVI-NIRIA |date=1956-02-24 |trans-title=The Delta Plan and Its Various Aspects |language=nl |access-date=27 December 2023}}

==System overview==

File:Deltar table1.jpg

File:Deltar units.jpg

File:Deltar module.jpg

The Deltar was an advanced system designed for simulating tides and analysing river environments by converting tidal data, river flows, and environmental factors into electrical analogue signals. This approach enabled dynamic modelling of time-varying parameters, which was essential for fluid dynamics simulations in natural settings.{{Cite journal |last1=Schönfeld |first1=J.C. |last2=Stroband |first2=H.J. |date=1961 |title=Rijkswaterstaat getijonderzoek door middel van de hydraulisch-elektrische analogie |trans-title=Rijkswaterstaat tide research by means of the hydraulic-electric analogy |url=http://resolver.tudelft.nl/uuid:e32906b8-a248-412a-9611-ea28d8a08231 |journal=Rapport Deltacommissie. Deel 4. Bijdragen 3: Beschouwingen over Stormvloeden en Getijbeweging (Deltacommission Report. Part 4. Contributions 3: Considerations on Storm Surges and Tidal Movement). |language=nl |location=Delft |publisher=Rijkswaterstaat |volume=4 |issue=3 |pages=209–231 |url-access= |via=TU Delft Repository |doi-access=}}

Divided into multiple sections, each corresponding to a distinct part of the studied river system, the Deltar required initial configuration with precise values to simulate each segment accurately. Inputs such as fluctuating tide levels and wind conditions, often encoded on punched tapes, were translated into electrical signals to drive the simulation.

Its output system recorded the resulting data, providing insights into water flow and currents. The Deltar's computing speed was managed via a time-scale setting, balancing computational capacity with the rate of data input and output. Each module of the Deltar represented water flow and levels at both ends of a river segment using electrical currents and voltages. The primary computing elements were the operational amplifiers which continuously solved interconnected first-order differential equations.

The system was organised in three groups of 40 units. Each unit corresponded to a particular section of a river, enabling up to three tidal problems to be investigated simultaneously. The analogue sections were configured so that a river section’s hydraulic properties such as length, width, depth, and resistance coefficient were immediately reflected within the simulation.{{Cite journal |last1=Schönfeld |first1=J.C. |last2=Verhagen |first2=C.M. |date=1957 |title=Development of the tidal analogue technique in Holland |journal=Second International Analogue Computation Meeting |publication-place=Strasbourg}}{{Cite journal |last=Schönfeld |first=J.C. |date=1951 |title=Propagation of tides and similar waves |url=http://resolver.tudelft.nl/uuid:9ec412b4-26b3-40bf-a6f6-ecb2e069fa17 |journal=Staatsdrukkerij- en Uitgeversbedrijf den Haag |access-date=28 December 2023 |via=TU Delft Repository}}

The Deltar accommodated both manual and automatic adjustments. Basic settings were entered manually, while changes in water height triggered automatic alterations via servomotor-controlled resistors in each module, ensuring dynamic reflection of changing water levels in the simulation.

A mechanical function generator, driven by a servomotor spindle, was integral to accurately modelling water behaviour in each river segment. The low drift and high common-mode rejection required by the amplifiers were achieved using mirror galvanometer-based designs. Each module contained four such amplifiers and a ECC81 dual triode vacuum tube in the servo circuit.{{Cite journal |last=Van Den Ende |first=J. |date=1992 |title=Tidal calculations in the Netherlands, 1920-60 |url=https://ieeexplore.ieee.org/document/150066 |journal=IEEE Annals of the History of Computing |volume=14 |issue=3 |pages=23–33 |doi=10.1109/85.150066 |issn=1058-6180 |access-date=28 December 2023 |via=IEEE Computer Society}} The system was capable of running simulations at up to 100 times real-time speed.{{Cite journal |last=Verhagen |first=C.M. |date=1957 |title=Symposium over elektronische analogon machines: I - Principes en mogelijkheden van elektronische analogon machines |trans-title=Symposium on Electronic Analogue Machines: I - Principles and Possibilities of Electronic Analogue Machines |journal=De Ingenieur |language=nl |volume=69 |issue=27 |pages=61–69}}{{Cite journal |last=Verhagen |first=C.M. |date=1957 |title=Symposium over elektronische analogon machines: II - De fouten in elektronische analogon machines |trans-title=Symposium on Electronic Analogue Machines: II - Errors in Electronic Analogue Machines |journal=De Ingenieur |language=nl |volume=69 |issue=30 |pages=71–74}}

The Deltar's first major assignment was to study the tidal movement in the North Delta area during and after the execution of the Delta Plan. It was also used for:{{cite journal |title=Getijonderzoek door middel van de hydraulisch-elektrische analogie |trans-title=Tidal Research through Hydraulic-Electric Analogy |author= |language=nl |journal=Rapport Deltacommissie Deel 4 Bijdrage III.8 |year=1960}}{{cite journal |title=De getijrekenmachine Deltar |trans-title=The Tidal Computing Machine Deltar |first1=J.C. |last1= Schönfeld |language=nl |journal=Natuurkundige Voordrachten, Nieuwe Reeks |issue=41 |volume=1962 - 1963}}{{cite journal |title=De Deltar |trans-title=The Deltar |first1= H.J. |last1= Stroband |language=nl |journal=Weg en Waterbouw |issue=30/12 |pages=429–431 |year=1970}}{{cite journal |last1=Maris |first1=A.G. |last2=De Blocq van Kuffeler |first2= V.J.P.|last3= Harmsen |first3= W.J.H. |last4= Jansen |first4= P.P. |last5= Nijhoff |first5= G.P. |last6= Thijsse |first6= J.T. |last7= Verloren van Themaat |first7= R. |last8= De vries |first8= J.W. |last9= Van der Wal |first9= L.T. |date= 1961 |title=Rapport Deltacommissie. Deel 1: Eindverslag en interimadviezen |trans-title=Report of The Delta Commission. Part 1: Final report and interim advice |url=http://resolver.tudelft.nl/uuid:0e28dfd8-4e67-4267-a443-54b74a062bcb |language=nl |journal=Deltacommissie |volume= |issue= |pages= |doi= |access-date=28 December 2023}}{{Cite book |url=http://resolver.tudelft.nl/uuid:fb90981f-5a61-479f-9b09-ab59cac1612d |title=The Closure of tidal basins: closing of estuaries, tidal inlets, and dike breaches |date=1987 |access-date= 28 December 2023 |publisher=Delft University Press |last1= Huis in 't Veld |first1= J. C. |last2= Stuip |first2= J. |last3= Walther |first3= A.W. |last4= van Westen |first4= J.M. |isbn=90-6275-287-X |edition=2nd |location=Delft, the Netherlands |oclc=18039440}}

• Operational guidance for the closures of the Volkerak (the Volkerakdam), Grevelingen (the Grevelingendam), and the Brouwershavense Gat (the Brouwersdam).
• Research on the occurrence of seiches in the sea ports of Den Helder, IJmuiden, and Scheveningen.
• Investigations into water levels during storm surges along the North Sea Canal and the IJ.
• Studies on water movement on the Hollandse IJssel during various closure manoeuvres with the Stormvloedkering Hollandse IJssel.

Despite its advanced capabilities, the advent of digital computing, exemplified by the Electrologica X1, soon overshadowed the Deltar's analogue methodology. After 1984, the system was dismantled and almost entirely lost. However, four units are known to have been preserved, three of which are on display at Deltapark Neeltje Jans, and one at the Computer Museum of the University of Amsterdam.{{Cite web |title=Deltar computer |url=https://ub.fnwi.uva.nl/computermuseum/deltar.html |access-date=28 December 2023 |website=University of Amsterdam}}

• Delta Works
• Flood control in the Netherlands
• Ishiguro Storm Surge Computer
• Rijkswaterstaat

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Category:Analog computers

Category:Delta Works