Davis resistance formula

Davis resistance formula is as follows:

Davis resistance formula is a formula for calculating train resistance, which was put forward by British engineer Davis in the 1930s. The formula is based on the following assumptions:

1. The train is subjected to various resistances during operation, including mechanical resistance, friction resistance, air resistance and pressure resistance.

These resistances are directly proportional to the train speed.

3. Mechanical resistance and frictional resistance are directly proportional to the square of speed, and air resistance and pressure resistance are directly proportional to the cube of speed.

The calculation steps of Davis resistance formula are as follows:

1. List the coefficients in the formula: inertia resistance coefficient (a), rolling resistance coefficient (b), aerodynamic resistance coefficient (c) and speed (v).

2. Determine the values of these coefficients through the actual train operation test.

3. Use the following formula to calculate the total resistance (R) of the train:

R = A + BV + CV^2

Among them, A, B and C are the coefficients determined by the actual train operation test, and V is the train speed.

4. Divide the calculated total resistance by the train speed to get the unit resistance (t):

T = R / V

5. Finally, add the unit resistance and the inertia resistance coefficient (a) to obtain the mechanical resistance (Tm):

Tm = ( 1/2)(A + BV)

Davis resistance test:

For example, for small-scale water droplets, Davis formula only considers the volume of the water droplets themselves, but ignores the influence of the interaction between the water droplets and the surrounding environment. Therefore, people have developed a micro-hydrodynamic model, which can predict the behavior of tiny water droplets more accurately. For example, in these models, people can consider various factors such as surface tension, humidity, electrostatic force and charge coupling to better describe the behavior of tiny water droplets.

In addition, Davis formula can not describe the complex flow process and nonlinear motion well. In these cases, people need to rely on more complex mathematical models and experimental techniques to better explore these complex physical phenomena.

Davis resistance formula is widely used in train design and performance analysis, but its calculation results are affected by experimental errors and calculation methods, which need to be revised and verified in practical application.