Albert Strickler

Albert Strickler (25 July 1887 – 1 February 1963) was a Swiss mechnical engineer recognized for contributions to our understanding of hydraulic roughness in open channel and pipe flow. Strickler proposed that hydraulic roughness could be characterized as a function of measurable surface roughness and described the concept of relative roughness, the ratio of hydraulic radius to surface roughness. He applied these concepts to the development of a dimensionally homogeneous form of the Manning formula. 
Albert Strickler was the only child of Albert Strickler, Sr. (1853–1936) and Maria Auguste Flentjen (1863–1945) of Wädenswil, Canton of Zürich, Switzerland. He was married twice, the second time as a widower. Neither marriage produced children. 
Strickler graduated from ETH Zurich as a mechical engineer in 1911. He earned a Ph.D. in 1917 while serving as the principal assistant to Professor Franz Prasil (1857–1929). Throughout his career, he was involved in the development of hydropower with interests ranging from hydraulic machinery to the regulation of river flows for inland navigation. Prior to World War II, he was the vice president of the Association of Exporting Electricity and a member of the board of directors on the Gotthard Electricity Mains AG, Altdorf, Uri. He subsequently worked as a engineering consultant until illness forced his withdrawal from practice in 1950. 
In 1923, Strickler published a report examining 34 formulas for the computation of flow in pipes and open channels and related experimental data. The report validated the Gauckler formula and by inference, the Manning formula. Strickler proposed that Kutter’s n-value, used to characterize hydraulic roughness in the Manning formula, could be defined as a function of surface roughness. 
Strickler’s equation introduces a new emperical coefficient which must be determined experimentally to define n-value. However, unlike Kutter’s n-value, which has units of T/L1/3,The units of Kutter's n-value as applied in the Manning formula are a matter of debate. While both dimensional analysis and application of the Manning formula imply units of T/L1/3, other interpretations have been proposed. Chow examined the development of formulas using n-value and concluded that the historical record did not resolve the question has units of length, and at least in theory, is a measurable quantity. A measurable quantity is potentially useful for channel design and stream restoration engineering where the design value of hydraulic roughness may be unknown. 
Stricker proposed that for a fixed boundary, surface roughness could be defined by the median grain size of a river’s bed material. He also noted that the onset of sediment transport, the mobile boundary condition, increased the observed hydraulic roughness. 
Later researchers produced variations on Strickler’s equation proposing different measures of surface roughness and corresponding variations in the empherical coefficient. In 1933, Johann Nikuradse published a study of hydraulic roughness in pipes that validated Strickler’s observations of the influence of surface roughness in turbulent flows. 
Substituting Strickler’s equation for n-value and rearranging terms produces a dimensionally homogeneous form of the Manning’s formula: 
The first term on the right-hand side of the equation is the dimensionless ratio of hydraulic radius to roughness height, commonly referred to as relative roughness. The remaining term, known as the boundary shear velocity, approximates the flow of water downhill under the influence of gravity and has units of velocity, i.e., L/T. 
Category:1887 births
Category:Swiss people
Category:Mechanical engineers
Category:1963 deaths