A salutary note at the end of Rutherford Aris’ Mathematical Modelling Techniques: When a model is being used as a simulation an obvious comparison can be made between its predictions and the results of the experiment. We are favourably impressed with the model if the agreement is good and if it has not been purchased […]

Don’t Try to Predict Physics (or Much of Anything Else) Without a Model — Chet Aero Marine

Don’t Try to Predict Physics (or Much of Anything Else) Without a Model — Chet Aero Marine

Posted in Academic Issues

A Salutary Reminder About the Limitations of Data and Statistics

In a culture that imputes statistical studies with authority they don’t deserve, this warning, from Numerical Recipes in FORTRAN 77, is very salutary:

Data consist of numbers, of course. But these numbers are fed into the computer, not produced by it. These are numbers to be treated with considerable respect, neither to be tampered with, nor subjected to a numerical process whose character you do not completely understand. You are well advised to acquire a reverence for data that is rather different from the “sporty” attitude that is sometimes allowable, or even commendable, in other numerical tasks.

The analysis of data inevitably involves some trafficking with the field of statistics, that grey area which is not quite a branch of mathematics —and just as surely not quite a branch of science. In the following sections, you will repeatedly encounter the following paradigm:

  • apply some formula to the data to compute “a statistic”
  • compute where the value of that statistic falls in a probability distribution
    that is computed on the basis of some “null hypothesis”
  • if it falls in a very unlikely spot, way out on a tail of the distribution,
    conclude that the null hypothesis is false for your data set

If a statistic falls in a reasonable part of the distribution, you must not make the mistake of concluding that the null hypothesis is “verified” or “proved.” That is the curse of statistics, that it can never prove things, only disprove them! At best, you can substantiate a hypothesis by ruling out, statistically, a whole long list of competing hypotheses, every one that has ever been proposed. After a while your adversaries and competitors will give up trying to think of alternative hypotheses, or else they will grow old and die, and then your hypothesis will become accepted. Sounds crazy, we know, but that’s how science works!

Posted in Deep Foundations

Amsterdam has been collapsing for years. Now it’s paying the price

Amsterdam’s day of reckoning shouldn’t really have come as a surprise.
The city’s children grow up with a verse: “Amsterdam, die grote stad / Die is gebouwd op palen / Als die stad eens ommeviel / Wie zou dat dan betalen?
Loosely translated: “Amsterdam, big city / It is built on piles / If the city would collapse / Who would pay for that?”
The city is now collapsing — and the Dutch are paying.

Amsterdam has been collapsing for years. Now it’s paying the price–from CNN

This is a new paper to update and expand on part of the first technical paper presented by a Vulcan employee: the paper “A Proposal for a Simplified Model for the Determination of Dynamic Loads and Stresses During Pile Driving,” originally presented at the 1987 Offshore Technology Conference. The abstract is here: Warrington (1987) was […]

via OTC 5397 Revisited: Analysis of Cushioned Pile Hammers — vulcanhammer.info

OTC 5397 Revisited: Analysis of Cushioned Pile Hammers — vulcanhammer.info