Fluid Dynamics  is the science that studies the 
motion of the fluids, among which water and air play a fundamental role. 
Fluids can flow in man-made structures or freely in nature. The interaction 
of the water and air with natural obstacles or within artificial structures 
is the topic of 
Hydrodynamics and 
Aerodynamics, respectively. 
Ocean and Atmosphere Dynamics, also called 
Dynamic Oceanography 
and 
Dynamic Meteorology, study the dynamics of the Ocean and the 
Atmosphere. 
 
This classification is not always respected, and many other disciplines are 
quoted, such as: 
 
 - Physics of Fluids, Fluid Mechanics, 
Hydrodynamics, Hydraulics, Water Wave Mechanics, Aerodynamics, 
 - 
Physical Oceanography, Marine Hydrodynamics, Coastal Oceanography, 
Theoretical Oceanography, 
 - Physics of the Atmosphere, Physical 
Meteorology, Meteorological Fluid Dynamics, Theoretical Meteorology, 
 - 
Atmospheric Thermodynamics, Atmospheric Diffusion, Boundary Layer 
Meteorology, Coastal Meteorology, 
 - Atmospheric-Ocean Interaction, 
Atmosphere-Ocean Dynamics, Geophysical Fluid Dynamics,  Astrophysics, 
 
 with meanings which are slightly different from time to time, from 
author to author. This is the consequence of the fact that the various parts 
of Fluid Dynamics are so strictly related to each other that a clear 
subdivision of the topic is not possible yet. 
 
This situation suggested to the author of this web site the derivation of the 
 Principles of Fluid Dynamics  at the basis of all 
these disciplines in a systematic way, with a particular attention to the 
scientific rigor and clarity of the exposition. A simplified version of the 
first notions, entitled 
 Elements of Fluid Dynamics 
 is published as well, to provide the largest number of basic results with the 
minimal effort, without sacrificing rigor and clarity. 
Any comment about my work will be highly appreciated. I am at the disposal of 
every reader for clarifications and discussions about the published material. 
 
                
  
                  
                  
                 
                Franco Mattioli,
                 
                 e-mail: franco.mattioli@unibo.it  
                 
                 
Bologna, 1 jan 2010. 
                 
 
 An exhortation.  The chapters of my book may be 
downloaded free and printed, but cannot be modified or edited. In particular, 
do not mix material taken from my book with other material taken elewhere.
The use of complete chapters is not only permitted, but also recommended. 
Thank you. 
 
                 
                 
Publication Plan  
                 
                 
                 
The book is organized in a series of Chapters that should be read 
sequentially and a series of Appendices that should be consulted when 
necessary. 
 
The appendices are transversal to the main text, so that you can find in them 
references to material dealt with in the course of the whole book. 
Furthermore, appendices do not aim at being complete and detailed. Many 
notions are only quoted to inform the reader about the scientific background 
he needs to be able to understand the main text. However, the appendices do 
not limit themselves to quote classical results, but also include 
considerations and problems that are particularly oriented to the 
understanding of the fluid dynamics, but cannot be easily found elsewhere.
 
With the exception of the first introductory part, the chapters aim at being 
as complete as possible, proving all the derived laws with a few exceptions 
relative to particularly long demonstrations of little physical relevance. At 
the end of some chapters and appendices we provide the reader with 
information about the time and the authors of the main discoveries dealt with 
in the text, along with recent references to which the reader is addressed to 
deepen the various topics. They make no pretence to be accurate or complete. 
They have been introduced especially to stress that this text follows a 
logical, and not a historical order. 
 
The date in front to the chapters refers to the first publication of the 
material in the context of the relative book. Later this material can have 
been corrected, modified, expanded, split in two or moved in another place. 
In the future other chapters can be inserted between two already published 
chapters, even if the publication is normally sequential. For this reason 
sometimes the sequential number of pages, chapters and parts has been 
interrupted, in order tho make easier future arrangements of the material. 
The same can be repeated for the appendices. 
 
If you want to quote my work, you should refer to the single chapters, 
providing the interval of time in which the chapter has been elaborated. For 
example:
Mattioli, F. Principles of fluid dynamics (www.fluiddynamics.it) Vol. I
The states of the matter (01 jan 2010 - 01 jan 2023).
Here, the former date is the date on the left of the title of the quoted 
chapter and the latter date is the date in which you consulted the chapter.  
 
For the same reason we publish a 
 News  page, in 
order to help the reader in the identification of the new material from the 
momentt of his last access. The Index will be updated as frequently as 
possible, but some incoherence might exist for a short lapse of time, 
especially regarding the page numbering.  
 
 
                 
                 
The role of Fluid Dynamics in Mathematics and Physics 
                 
                 
                 
 
Fluid Dynamics is one of the older and difficult branches of Physics. At 
present, it seems a still underestimated sector of physics for several 
reasons as stated, for example, at the beginning of the book 
 Fluid 
Dynamics for Physicists.  Cambridge University Press, 1995, by Faber, 
T.E. : "
Nowadays [fluid dynamics] is partially obscured 
from view by branches of more recent origin, such as relativity, atomic 
physics and quantum mechanics, and students of physics pay rather little 
attention to it.  This is a pity, for several reasons. Firstly, 
because of the engineering applications of the subject, which are many and 
various: the design of airplanes and boats and automobiles, and indeed of any 
structure intended to move through fluid or propel fluid or simply to 
withstand the forces exerted by fluid, depends in a critical way upon the 
principles of the subject. Secondly, because fluid dynamics has important 
applications in other branches of physics and indeed in other realms of 
science, including astronomy, meteorology, oceanography, zoology and 
physiology: dripping tabs, solitary waves on canals, vortices in liquid 
helium, seismic oscillations of the Sun, the great Red Spot on Jupiter, small 
organisms that swim, the circulation of the blood - these are just a few of 
the very varied topics involving fluid dynamics which have been occupying 
research scientists and mathematicians of international reputation over the 
past few decades. Thirdly, because most other subjects in the physics 
curriculum are almost exclusively concerned with 
  
linear   processes, whereas fluid dynamics leads one into the 
  non-linear   domain. And lastly, because 
there are so many curious and beautiful natural phenomena, visible every day 
in the world about us, which a physicist with no knowledge of fluid mechanics 
in unable to appreciate to the full." 
The necessity to understand the behavior of a fluid forced several authors of 
the past to discover new mathematical tools suitable for the scope. Thus 
Fluid Mechanics led to the introduction of the 
 Partial 
Differential Equations,  to the 
 Singular 
Perturbation Theory,  to the 
 Method of Multiple 
Scale Analysis,  to the 
 Inverse Scattering 
Transform,  and of other advanced mathematical techniques. Later, 
these techniques spread over other fields of Mathematics and Physics. 
 
For a long time the solutions proposed for the flows of a fluid seemed very 
far from reality. Indeed, the interpretation of many of the most common 
phenomena of our everyday life involving fluids is still very poor. While 
Physics evolved in fields very far from the possibility of a direct 
observation, but rich of important applications. 
 The 
field of Fluid Dynamics was essentially abandoned by physicists  
because of its difficulties. The development of the discipline relied on the 
important civil and military applications of engineering. The advent of 
computers revived interest in this topic, not only in its numerical aspects, 
but also in its theoretical and experimental components. 
 
Today, 
 Fluid Dynamics appears as one of the most advanced 
fields of Physics,  characterized by a boundless number of problems 
linked to each other in various ways. The role of a problem inside this 
complex network is difficult to establish, but essential for its full 
understanding. Unfortunately, the complication of this matter leads very 
often to the presentation of the discipline as a set of uncorrelated 
phenomena, very far from each other, thus generating a misunderstanding not 
only of the discipline, but also of its true importance. 
 
In particular, 
 the meteo-oceanographic system  
appears to be as the most complicated system present in physics as stated, 
for example, at the beginning of their book 
 Introductory Physics of the 
Atmosphere and Ocean.  D. Reidel Publishing Company, 1986, by Hasse, L. 
& Dobson, F. : "
Atmosphere and ocean are probably the 
most complex system which is treated in physics,  since the scales of 
motions involved span such a wide range: 10,000 km for long planetary waves, 
through a few millimeters for the scale of decaying turbulent eddies.". 
Within this system many phenomena superimpose and interact in a complicated, 
bidirectional way, so that their satisfactory understanding is still very 
far. At present we know only some of the main processes, which can partially 
justify a certain number of important phenomena, but we are still unable to 
interpret a large number of many other phenomena, and especially the 
unpredictability of the so-called 
 extreme events  
or the possible transitions to 
 new climatic equilibria, 
 threatening the safety of the life of humankind on our planet.