How can train speed and acceleration be controlled to reduce drag and resistance?

1 Drag sources

Drag is the aerodynamic force that acts on a train as it moves through the air and is dependent on the shape, size, and surface of the train, as well as the speed, density, and viscosity of the air. Some of the sources of drag on a train are frontal drag, skin friction drag, interference drag, and induced drag. Frontal drag is caused by the pressure difference between the front and rear of the train due to air flow around it. Skin friction drag is caused by the boundary layer of air that sticks to the train. Interference drag is caused by the interaction of air flow around different parts of the train. And induced drag is caused by vortices that form at the edges of the train.

2 Resistance sources

Resistance is the mechanical force that acts on a train as it moves along the track. This force depends on characteristics like the weight, length, and configuration of the train, as well as the slope, curvature, and condition of the track. Rolling resistance is caused by friction between the wheels and rails due to deformation and deformation recovery. Curve resistance comes from centrifugal force and wheel-rail contact geometry. Grade resistance is a result of gravity force and track inclination. Lastly, acceleration resistance is caused by the inertia of the train mass.

3 Speed control

One of the ways to control drag and resistance is to optimize the speed of the train. Speed affects both drag and resistance, but in different ways. Drag increases with the square of the speed, while resistance increases linearly with the speed. This means that at low speeds, resistance is more dominant, while at high speeds, drag is more dominant. Therefore, to minimize drag and resistance, the optimal speed of a train depends on the balance between these two forces, as well as the power output and fuel consumption of the train. Generally, the optimal speed of a train is lower on curved or sloped tracks, and higher on straight or level tracks.

4 Acceleration control

Another way to control drag and resistance is to optimize the acceleration of the train. Acceleration affects both drag and resistance, but also in different ways. Acceleration increases drag by creating more vortices and turbulence around the train, while it increases resistance by requiring more force to overcome the inertia of the train mass. Therefore, to minimize drag and resistance, the optimal acceleration of a train depends on the trade-off between these two forces, as well as the time and distance required to reach the desired speed. Generally, the optimal acceleration of a train is lower when starting from rest or changing speed, and higher when maintaining a constant speed.

5 Drag reduction

In order to reduce drag, there are some methods that can be used to improve the aerodynamics of a train. Streamlining involves designing the front and rear of the train to have a smooth and tapered shape which reduces frontal and induced drag. Additionally, gap sealing involves filling or covering the gaps between the cars or between the car and the track to reduce interference drag and induced drag. Lastly, surface smoothing can be used by applying a smooth and glossy coating or material to the surface of the train to reduce skin friction drag and interference drag.

6 Resistance reduction

To reduce resistance directly, certain methods can be used to improve the mechanics of the train. Lightweighting is one such method, which involves reducing the weight of the train by utilizing lighter materials or components that minimize rolling and grade resistance. Shortening is another method that involves reducing the length of the train with fewer cars or shorter cars to decrease rolling and curve resistance. Lastly, configuring is a method that adjusts the arrangement of the cars or the coupling system to reduce rolling resistance and interference drag.

7 Here’s what else to consider

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