Simulations were also conducted to investigate effects of track gage, curve radius, guardrail height and lubrication on vehicle dynamic performances. The following conclusions can be drawn from the parametric studies:
- The optimal guard/restraining rail installation, leading to a balance of lateral wheel/rail forces as well as a balance of wear between the high rail and the guard/girder/restraining rail can be achieved through the control of flangeway width and wheel/rail friction coefficients.
- The optimal flangeway width depends on the wheel profile shape, including flange back profile, wheel back to back distance, track gage, guard/restraining rail profile shapes, installation height and wheelset angle of attack (AOA) or the track curvature.
- The flangeway width should increase with the wheelset AOA and track curvature for AOA larger than 20 mrad (corresponding to curves with about 290-foot radius) if the 3-dimensional flange back fattening effect is larger than that on the maximum flange angle face.
- The flangeway width should increase approximately the same amount as the gage increase to keep the flange front clearance equal to the flange back clearance. Increasing only the gage leads to excessive wear on the guard/girder/restraining rails.
- The flangeway width should increase with the increase of guard/restraining rail height to keep the flange front clearance equal to the flange back clearance.
- Lubrication on the high rail gage face and guard/girder/restraining rail significantly reduces the wheel/rail wear and rolling resistances. To achieve similar wear rates between the high rail and the guardrail, the guideline for rail lubrication with guardrail is to produce low friction coefficients on the contact patches in the presence of high contact angles and relative high friction coefficients on the contact patches in the presence of low contact angles.
COMPARISONS OF TWO INSTALLATION PHILOSOPHIES
Steady-state curving simulations on a number of constant radius curves without perturbations were conducted to evaluate performance trends of the two philosophies. Two wheel/rail interaction performance indices, wheel lateral forces and wear on leading axles, were used for comparison.
Figure 7 shows more than twice the lateral force acts on just the guardrail using philosophy II than the lateral force acts almost equally on both rails using philosophy I. Figure 8 shows that both philosophies resulted in a larger wear index on leading axle wheels (the sum of the wear index from all contact points on both wheels of the lead axle) than the case with no guardrail, with a lower wear index from philosophy I.
The simulations show that philosophy I leads to better vehicle dynamic performance than philosophy II (no high rail flange contact and with the guardrail contact on the low rail wheel) in terms of lower lateral forces on rails, lower vehicle rolling resistance, and lower leading axle wear.
FLANGE CLIMB DERAILMENT SIMULATION
NUCARS steady-state and dynamic curving simulations of four types of transit vehicles on single cosine wave shape, with three levels of severity of perturbations, were conducted to investigate guardrail effects on increasing resistance to flange climbing derailment.
Figure 9 shows the wheel lateral to vertical ratio on tight curves with a radius less than 500 feet increases with the increase of the wheel/rail friction coefficient. The vehiclederailed on curves with a radius less than or equal to 250 feet at a friction coefficient of 0.6, which indicates that a guardrail is needed even on perfect track without perturbations.
As expected, the dynamic curving L/V ratios on perturbed track without a guardrail increase with the wheel/rail friction coefficient and amplitude of the perturbations, as Figures 10 and 11 show. The dynamic L/V ratios approach or exceed the Nadal limit (shown as a solid red line) at a friction coefficient of 0.5. The vehicle derailed for all simulated cases (100 ~3,000 ft radii curves), with a friction coefficient 0.6 and the most severe track perturbations.
The following guardrail guidelines are recommended for two types (Type 1 and Type 2) of transit railcars and two types (Type 1 and Type 2) of light rail vehicles implemented with 75-degree flange angle wheels: