Effectiveness of ECP Brakes in Reducing the Risks Associated with HHFT Trains

Transcription

1 Effectiveness of ECP Brakes in Reducing the Risks Associated with HHFT Trains Presented To The National Academy of Sciences Review Committee October 14, 2016 Slide 1 1

2 Agenda Background leading to HM-251 Enhanced tank Car Standards Approach- Evaluation of Risk Reduction Measures- Reduced Tank Car Punctures Key Parameters Assessed for Risk Reduction Models Applied Input Data Process Validation with historical data and simulations Results of Analysis Expected Risk Reductions Summary and Conclusions Review of Analysis and Test Plan to Assess the Effectiveness of ECP Brakes in Reducing the Risks Associated with HHFT Trains Wrap-up Review of Action Items Slide 2 2

3 Background Govt and Industry had been updating tank car standards for more than a decade when a series of accidents spurred more aggressive action beginning in 2011 Eventual proposals for reducing risk included -Stronger tank cars -Reduced speeds -Improved brakes Slide 3 3

4 Evaluating Benefits of Risk Reduction Measures -General Approach Taken- 1) Tank Cars derailed and tank cars punctured as the primary measures of risk 2) Assess likely tank impacts from past accidents 3) Assess likely risk reduction from -Stronger tank cars -Reduced speeds -Enhanced braking systems 4) Estimate risk reduction with historical data and dynamic simulations Slide 4 4

5 Process for Evaluating Likelihood of Puncture Derailment Scenario Simulations Estimate Collision Load Spectrum Car Strength Capacities From Design Criteria Derailment Evidence from Past Events Likely Impactor Size Distribution Likely No. of Derailed Cars and Punctures Adjust impactor Distribution Actual No. of Derailed Cars and Punctures Process Validation Slide 5 5

6 Key Parameters evaluated for contributions to Risk Reduction Train Speed 30, 40 and 50mph Tank car design variations in strength Brake system type (conv, EOT / DP, ECP) 18 simulations for each derailment speed for each brake system type 3 COF, 3 initiations, 2 lateral track stiffness Slide 6 Slide #: 66

7 Models Applied LS DYNA: Collision Dynamics and Finite Element Stress Analysis Program of choice for crashworthiness simulations, across multiple industries, for a wide variety of crash, blast, and impact applications Non-linear, explicit, finite element code Widespread acceptance in the engineering community Commercially available and supported by the Livermore Software Technology Corporation (LSTC) Based on the public domain, DYNA3D finite element code developed at the Lawrence Livermore National Laboratory Extensive user community that applies and validates the code for a variety of problems, including derailment simulations Slide 7 77

8 Models Applied cont d TEDS for Brake System Performance Train Energy Dynamic Simulation Model developed under contract to FRA/DOT Using industry accepted data for brake signal propagation and brake cylinder pressure and shoe force build up TEDS now being made available to public users Slide 8 DRAFT as of 1/3/14 8 8

9 LS Dyna Post Derailment Simulation Sample Animation 30 mph Slide 9 9

10 LS Dyna Post Derailment Simulation Sample Animation 40 mph Slide 10 10

11 Derailment Load Spectrum (From simulations) These histograms are cumulated and averaged over 18 simulations at each speed. In line with physics expectations, both the number of impacts and the magnitude of the impacts rise, with increasing speed. Slide 11 11

12 Car Strength Capacities Car strength capacities are based on prior industry analysis Slide 12 12

13 Impactor Size Distribution Qualitative comparison from past accidents In general terms: - Broken rail impactors are likely to be around 2 to 7 - Coupler shanks are likely to be around 4 to 8 - Coupler heads are likely to be around 10 to 12 - Truck components could be in the range of 9 to 16 - Bulk impact could be larger than 24 - Any of the above impactors could present a smaller face under oblique impact angles. Slide 13 13

14 Comparing Puncture Risk Mitigation Strategies Base Case Alternate 3 (DOT 117) Tank Type 7/16" A No Jacket 9/16" TC128B 11 Gauge Jacket 1/2 Head Shield Most Likely Number of Punctures % Improvement Compared to Base Case 30 mph 40 mph 30 mph 40 mph % Improvement Due to Speed Reduction 40 to 30 mph ~ ~ 38% % 52% 42% These results are derived by combining the load histograms, with the car strength capacity, and the impactor distribution. The impactor distribution is held constant for all cases. As evident from above, the methodology can be used to evaluate the relative risk of an improved car design or a speed restriction. Slide 14 14

15 Model Validation Simulations validated against past accidents The number of cars derailed The number of punctures Gross layout of the pileups Comparisons to event recorder data from the rear locomotive Simulations compared well with real life observations. Slide 15 Slide #: 15 15

16 Process Validation The spread of the simulations reasonably represents the spread seen in actual derailment data. Slide 16 Number of Derailed Cars vs. Train Speed 16

17 Process Validation Derailments Comparison of tank car derailment histories vs simulation results Note: there is variation in real-world data; the model predicts the average. Slide 17 Number of Derailed Cars vs. Train Speed 17

18 Simulated Derailment Pileups 30 mph Several realistic pileup configurations are seen among the 18 simulations. This gives us confidence that the resulting force spectrum represents a variety of derailments. A comparison of these simulated pileup images to real derailments shows reasonable similarities. Slide 18 18

19 Process Validation Punctures Comparison of tank car puncture histories vs simulation results Note: there is more variation in real-world puncture data than there is for derailment data. Slide 19 Number of Punctures vs. Train Speed 19

20 Other Validation Attributes LS-Dyna simulations yielded stopping distance within 4% of Aliceville rear end locomotive s event recorder data Slide 20 Slide #: 20 20

21 Enhanced Braking Assessment Simulations with enhanced braking systems Electronically Controlled Pneumatic (ECP) braking, where all cars are braked simultaneously End-of-Train (EOT) braking, in which the emergency brake signal is initiated simultaneously at both the front and rear of the train, were simulated. Slide 21 Slide #: 21 21

22 Enhanced Braking Slide 22 Number of Cars Derailed 22

23 Enhanced Braking Assessment Number of Punctures & Brake System Improvement Slide 23 23

24 Risk Reduction Based on 100 cars behind POD for speeds 30, 40 & 50 mph. Benefits from multiple strategies Car Construction Alternate 3 (DOT 117) offers a 53% reduction in risk over a legacy car (on average) Enhanced Braking ECP offered a 30% risk reduction (on average) DP/EOT offered a 16% risk reduction (on average) Reduced Speeds 50 mph to 40 mph: 34% 40 mph to 30 mph: 41% Slide 24 Slide #: 24 24

25 Train Length Considerations Benefits calculated for the enhanced braking systems are lower for shorter train lengths Simulations conducted for: 80 car trains 50 car trains 20 car trains These results were built into the DOT s risk evaluations, accounting for the likely train lengths and POD positions Slide 25 Slide #: 25 25

26 Summary An objective methodology was used to assess likely risk reductions from tank car design, train operations and improved brake systems. Modelling results validated by comparison to actual accident events and outcomes Addressed key parameters relevant to tank car puncture: Multiple derailment scenarios Derailment dynamics Impactor sizes Tank car designs Operating speeds Brake system performance Probabilistic framework used to estimate the relative merit of proposed mitigation strategies. Slide 26 Slide #: 26 26

27 Conclusions The gross dynamics of a tank car train derailment, and the resulting puncture performance of the tank cars are captured well by this approach. Number of cars derailed and number of punctures, as a function of train speed, compare favorably with observed derailment data. Puncture risk reduction correlates well with increased tank shell thickness and material strength. This approach provides a basis for comparing the relative benefits of various mitigation strategies. Slide 27 Slide #: 27 27

28 Conclusions cont d ECP Braking reduces risk of puncture from a derailment by 30% on average, based on past accident scenarios. Improved operating practices and tank car design improvements can provide similar reductions in risk. Slide 28 Slide #: 28 28

29 Thank You! Slide 29 29