High Tech Pressure Safety

 Huang’s limit  vs. Nadal’s limit  

Nadal’s limit L/V ratio is a criterion for an object going down a slope while Huang’s limit L/V ratio is a criterion for an object going up a slope. The fact is that wheel climb is a wheel going up not down. See “The Boundary of Nadal’s Limit (L/V ratio) and Commencing Wheel Derailment for Railroad Truck” ---   paper by Dr. Jack Y. Huang

Derailment mechanism introduced by Nadal’s limit is imaginary. Thus, many erroneous wheel-rail interaction models were created based on that mechanism currently in the railroad industry.

Lubrication (on gauge face) will invite wheel climb derailments. However, field tests show that a train would pass a curved rail with lubrication but derail at the same rail without lubrication. Does that mean Nadal’s limit is correct---lubrication prevents wheel climb derailments? The answer is NO. The root cause of this derailment is not the action of L/V. That is, L/V is not important in this derailment mode. 

Truck hunting is a geometry problem that can be simulated by a centrifugal pendulum. Truck hunting induces reaction forces, however reaction forces, or any other kinds of forces, cannot induce hunting. See “Dynamic Analysis for Railroad Truck Design” --- paper by Dr. Jack Y. Huang

Curving resistance has two parts: 1). Rotational resistance which is produced due to the relative rotation of the carbody towards the truck, and 2). The resistance which is produced by the constraint of rail on the wheel.

Curving resistance can be calculated theoretically, depending on velocities of the vehicle; truck centers; the radius of curvature of the rail and coefficients of friction. Curving resistance has a unit of force (Newton) or moment (N-M). However, the unit used in the railroad industry for curving resistance is: lbs/ton/degree. It is obvious that this measurement (lbs/ton/degree) is not scientific or may be in error. Because curving resistance depends heavily on velocities of vehicles. That is to say, with every other conditions remained the same, curving resistance will be different with different velocities.

Department of Rail Technology

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Department of Pressure Relief