System Resilience and Stability Index Calculator

Calculate the composite System Resilience and Stability Index (SRSI) using redundancy level, mean time to recovery (MTTR), failure rate (λ), and average system load. The index ranges from 0 (no resilience) to 100 (perfect resilience).

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Formulas Used

1. Single-Component Availability
A = MTBF / (MTBF + MTTR)

2. System Availability (N parallel redundant components)
A_sys = 1 − (1 − A)N

3. Failure Rate
λ = 1 / MTBF

4. Recovery Speed Score
RSS = 1 / (1 + ln(1 + MTTR)) — logarithmic penalty for long recovery times

5. Load Stress Factor
LSF = 1 − (Load / 100)² — quadratic penalty for high operational load

6. Redundancy Bonus
RB = ln(N) / ln(10) — logarithmic benefit of additional redundant components

7. Composite SRSI (0–100)
SRSI = 100 × (0.35·A_sys + 0.25·RSS + 0.20·LSF + 0.10·RB + 0.10·Diversity)

Assumptions & References

  • Components are assumed to fail and recover independently (parallel redundancy model).
  • Availability formula follows the standard IEC 60050-191 steady-state availability definition.
  • The parallel availability model A_sys = 1 − (1−A)N assumes identical, independent components — a standard result from reliability engineering (Billinton & Allan, Reliability Evaluation of Engineering Systems, 1992).

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