Multi-Period Dynamic Optimization for Large-Scale Differential-Algebraic Process Models under Uncertainty
Abstract
:1. Introduction
2. Problem Statement
3. Proposed Solution Approach
3.1. Multi-Period Multiple-Shooting Discretization
3.2. First-Order Derivative Generation
3.3. Second-Order Derivative Generation
3.4. Implementation Details
Algorithm 1 Multi-period gradient-based non-linear program (NLP) solution approach with embedded differential-algebraic equations (DAE). QP, quadratic programming. |
Input: initial primal and dual variable guesses and tolerances |
1: generate scenario realizations: |
2: define initial guesses for primal, , and dual variables |
3: provide optimality (tol) and feasibility (tol) tolerances |
Output: primal/dual solution , to a local minimum of the NLP satisfying tolerances |
4: procedure NLP_SOLVE(, , tol) |
5: |
6: initial eval of objective/constraints and 1st derivatives (gradient, Jacobian) |
7: ⊳explicit function eval |
8: DAE_SOLVE() ⊳implicit function eval |
9: ⊳explicit function eval |
10: initial Lagrangian Hessian approximately (or eval exactly via DSOA_SOLVE()) |
11: repeat until termination criteria satisfied |
12: check KKTconditions (and other termination criteria) |
13: compute search direction of primal/dual variables () via QP solver |
14: compute step size via a line search (requires objective/constraint eval) |
15: |
16: |
17: re-evaluate function derivatives (used to construct the next QP) |
DAE_SOLVE() |
18: update Hessian approximately (or eval exactly via DSOA_SOLVE()) |
19: end |
20: end procedure |
Algorithm 2 Parallel multi-period DAE and first-order sensitivity function evaluation. |
Input: state initial conditions, control parameters and invariant model parameters |
1: specified scenario realizations |
2: NLP variables , d, |
3: provide relative (tol) and absolute (tol) integration tolerances for DAE solution |
Output: differential state solution , |
4: procedure dae_solve(x, θ, tol) |
5: for i 1 to do ▹ in parallel using OpenMP for tasks |
6: for j 0 to do |
7: set initial differential and algebraic DAE variables:
|
8: set initial differential DAE sensitivity variables:
|
9: solve DAE and 1st order sensitivity system |
{, } ← sundials_dae_solver |
10: end for |
11: end for |
12: end procedure |
4. Example Problems
4.1. Batch Reactor Problem
Total Program Solution Time (s) | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|
m | vars | cons | iter | ||||||||
1 | 25 | 78 | 53 | 24 (60) | −1.4911 | 0.7683 | 0.389 | 0.251 | 0.235 | 0.201 | – |
40 | 1000 | 3081 | 2081 | 40 (1239) | −1.5235 | 0.7785 | 17.48 | 8.87 | 7.01 | 6.26 | 6.24 |
80 | 2000 | 6161 | 4161 | 46 (2244) | −1.5463 | 0.7868 | 45.41 | 21.61 | 16.88 | 15.20 | 14.87 |
160 | 4000 | 12,321 | 8321 | 49 (4395) | −1.5340 | 0.7823 | 90.00 | 42.37 | 34.74 | 30.87 | 30.35 |
320 | 8000 | 24,641 | 16,641 | 49 (8718) | −1.5200 | 0.7772 | 188.69 | 82.60 | 65.10 | 56.74 | 55.67 |
iter | Total (s) | NLP (s) | FSA(s) | DSOA(s) | ||||||
---|---|---|---|---|---|---|---|---|---|---|
qn | ex | qn | ex | qn | ex | qn | ex | ex | ||
1 | −1.4911 p | 52 | 48 | 0.793 | 22.96 | 0.311 | 0.111 | 0.482 | 0.297 | 22.56 |
40 | −1.5235 p | 70 | 66 | 27.81 | 632.42 | 2.277 | 0.591 | 25.54 | 12.27 | 619.56 |
80 | −1.5463 p | 65 | 64 | 48.61 | 1218.46 | 3.697 | 1.060 | 44.91 | 23.57 | 1193.82 |
160 | −1.5340 p | 71 | 65 | 107.3 | 2204.61 | 8.023 | 1.920 | 99.32 | 47.12 | 2155.57 |
320 | −1.5200 p | 49 | 44 | 151.2 | 4397.64 | 11.70 | 3.962 | 139.5 | 92.78 | 4300.90 |
4.2. Air Separation Problem
Total solution time (s)/ | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|
n | m | vars | cons | iter | |||||||
6 | 1 | 6 | 3184 | 3194 | 9 (1308) | 1.0159 | 0.0079 | – | – | – | – |
20 | 120 | 63,680 | 63,974 | 14 (42,704) | 1.0134 | 0.1908 | 0.0535 | 0.0420 | 0.0426 | 0.0501 | |
40 | 240 | 127,360 | 127,955 | 16 (85,672) | 1.0181 | 0.5146 | 0.1785 | 0.1589 | 0.1596 | 0.1688 | |
80 | 480 | 254,720 | 255,915 | 17 (170,391) | 1.0156 | 1.3808 | 0.7166 | 0.6669 | 0.6720 | 0.6882 | |
12 | 1 | 12 | 5914 | 5930 | 12 (3221) | 1.0141 | 0.0135 | – | – | – | – |
20 | 240 | 118,280 | 118,808 | 18 (81,273) | 1.0114 | 0.7163 | 0.1955 | 0.1558 | 0.1491 | 0.1474 | |
40 | 480 | 236,560 | 237,628 | 11 (162,037) | 1.0159 | 0.9167 | 0.5179 | 0.4891 | 0.4732 | 0.4714 | |
80 | 960 | 473,120 | 475,268 | 17 (322,952) | 1.0129 | 7.7468 | 3.2047 | 2.8156 | 2.7239 | 2.6748 |
Total Solution Time (s)/ | ||||||||||
---|---|---|---|---|---|---|---|---|---|---|
m | vars | cons | iter | |||||||
23/57 | 6 | 566 | 568 | 19 (184) | 0.8559 | 0.0006 | – | – | – | – |
480 | 45,280 | 45,915 | 22 (16,326) | 0.8560 | 0.0824 | 0.0230 | 0.0247 | 0.0368 | 0.0416 | |
59/153 | 6 | 1490 | 1492 | 12 (616) | 1.0111 | 0.0011 | – | – | – | – |
480 | 119,200 | 119,835 | 18 (38,928) | 1.0110 | 0.2185 | 0.0896 | 0.0870 | 0.0881 | 0.1052 | |
125/329 | 6 | 3184 | 3194 | 10 (1294) | 1.0159 | 0.0079 | – | – | – | – |
480 | 254,720 | 255,915 | 17 (170,391) | 1.0156 | 1.3808 | 0.7166 | 0.6669 | 0.6720 | 0.6882 |
5. Concluding Remarks
Acknowledgements
Author Contributions
Conflicts of Interest
References
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Washington, I.D.; Swartz, C.L.E. Multi-Period Dynamic Optimization for Large-Scale Differential-Algebraic Process Models under Uncertainty. Processes 2015, 3, 541-567. https://doi.org/10.3390/pr3030541
Washington ID, Swartz CLE. Multi-Period Dynamic Optimization for Large-Scale Differential-Algebraic Process Models under Uncertainty. Processes. 2015; 3(3):541-567. https://doi.org/10.3390/pr3030541
Chicago/Turabian StyleWashington, Ian D., and Christopher L.E. Swartz. 2015. "Multi-Period Dynamic Optimization for Large-Scale Differential-Algebraic Process Models under Uncertainty" Processes 3, no. 3: 541-567. https://doi.org/10.3390/pr3030541
APA StyleWashington, I. D., & Swartz, C. L. E. (2015). Multi-Period Dynamic Optimization for Large-Scale Differential-Algebraic Process Models under Uncertainty. Processes, 3(3), 541-567. https://doi.org/10.3390/pr3030541