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A. Cano Alvarez
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Master thesis
(2026)
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A. Cano Alvarez, D. Zappalá, Moritz Johann Gräfe, Vasilis Pettas, Nikolay Dimitrov
Offshore wind operation and maintenance is modelled by two families of tools that do not meet. Discrete-event simulation carries the mechanisms that drive offshore downtime but costs many runs per converged answer, whereas the published analytical models answer for a fraction of the computational cost yet are exponential, steady-state, and window-based, and the effects of these assumptions have not been benchmarked against a modern simulator.
This thesis develops a hierarchy of analytical availability models that occupies that gap, establishing what each member can be trusted to estimate, at what accuracy, and at what cost. The family pairs steady-state and time-marching solvers under Continuous Time Markov Chain and a Semi-Markov Process frameworks, plus two simulator twins, all consuming one shared input pipeline. The reference case is a bottom-fixed 12MW turbine with 22 corrective failure modes over twenty years of hourly ERA5 weather, and the discrete-event reference, NREL’s WOMBAT (0.13.3), is audited, minimally patched, and characterised through a pre-registered mechanism-accretion ladder.
Under aligned conditions the steady-state semi-Markov model reproduces the reference raw, at z = +0.20 over 200 seeds and z = −1.02 against the thousand-seed population, certifying 97.9903% time-based availability, 97.8243% production-based availability, and an annual direct cost of 576,393.60USD for the selected case study turbine. The memoryless simplification is evaluated and proves adequate for mean-determined steady-state quantities, although it cannot express production-based availability accurately, overstates the cold-start boundary credit by 46%, and is blind to the replacement waves that make a twenty-year life
at β = 2 one long transient, missing 1.47 percentage points of year-one availability. Process interruptibility treatment is also evaluated, with results indicating a second-order convention worth 0.167 percentage points for the short repairs, and the enabling assumption for heavy replacement modelling, whose contiguous execution diverges at the reference site.
Finally, the 13 ms solve enables rapid scenario screening and sensitivity analysis, being used to propagate forty thousand joint uncertainty samples, price vessel capability, lifting envelopes, mobilisation lead time, and component reliability with break-evens attached, therefore turning the validated hierarchy into a decision instrument at a cost measured in seconds. ...
This thesis develops a hierarchy of analytical availability models that occupies that gap, establishing what each member can be trusted to estimate, at what accuracy, and at what cost. The family pairs steady-state and time-marching solvers under Continuous Time Markov Chain and a Semi-Markov Process frameworks, plus two simulator twins, all consuming one shared input pipeline. The reference case is a bottom-fixed 12MW turbine with 22 corrective failure modes over twenty years of hourly ERA5 weather, and the discrete-event reference, NREL’s WOMBAT (0.13.3), is audited, minimally patched, and characterised through a pre-registered mechanism-accretion ladder.
Under aligned conditions the steady-state semi-Markov model reproduces the reference raw, at z = +0.20 over 200 seeds and z = −1.02 against the thousand-seed population, certifying 97.9903% time-based availability, 97.8243% production-based availability, and an annual direct cost of 576,393.60USD for the selected case study turbine. The memoryless simplification is evaluated and proves adequate for mean-determined steady-state quantities, although it cannot express production-based availability accurately, overstates the cold-start boundary credit by 46%, and is blind to the replacement waves that make a twenty-year life
at β = 2 one long transient, missing 1.47 percentage points of year-one availability. Process interruptibility treatment is also evaluated, with results indicating a second-order convention worth 0.167 percentage points for the short repairs, and the enabling assumption for heavy replacement modelling, whose contiguous execution diverges at the reference site.
Finally, the 13 ms solve enables rapid scenario screening and sensitivity analysis, being used to propagate forty thousand joint uncertainty samples, price vessel capability, lifting envelopes, mobilisation lead time, and component reliability with break-evens attached, therefore turning the validated hierarchy into a decision instrument at a cost measured in seconds. ...
Offshore wind operation and maintenance is modelled by two families of tools that do not meet. Discrete-event simulation carries the mechanisms that drive offshore downtime but costs many runs per converged answer, whereas the published analytical models answer for a fraction of the computational cost yet are exponential, steady-state, and window-based, and the effects of these assumptions have not been benchmarked against a modern simulator.
This thesis develops a hierarchy of analytical availability models that occupies that gap, establishing what each member can be trusted to estimate, at what accuracy, and at what cost. The family pairs steady-state and time-marching solvers under Continuous Time Markov Chain and a Semi-Markov Process frameworks, plus two simulator twins, all consuming one shared input pipeline. The reference case is a bottom-fixed 12MW turbine with 22 corrective failure modes over twenty years of hourly ERA5 weather, and the discrete-event reference, NREL’s WOMBAT (0.13.3), is audited, minimally patched, and characterised through a pre-registered mechanism-accretion ladder.
Under aligned conditions the steady-state semi-Markov model reproduces the reference raw, at z = +0.20 over 200 seeds and z = −1.02 against the thousand-seed population, certifying 97.9903% time-based availability, 97.8243% production-based availability, and an annual direct cost of 576,393.60USD for the selected case study turbine. The memoryless simplification is evaluated and proves adequate for mean-determined steady-state quantities, although it cannot express production-based availability accurately, overstates the cold-start boundary credit by 46%, and is blind to the replacement waves that make a twenty-year life
at β = 2 one long transient, missing 1.47 percentage points of year-one availability. Process interruptibility treatment is also evaluated, with results indicating a second-order convention worth 0.167 percentage points for the short repairs, and the enabling assumption for heavy replacement modelling, whose contiguous execution diverges at the reference site.
Finally, the 13 ms solve enables rapid scenario screening and sensitivity analysis, being used to propagate forty thousand joint uncertainty samples, price vessel capability, lifting envelopes, mobilisation lead time, and component reliability with break-evens attached, therefore turning the validated hierarchy into a decision instrument at a cost measured in seconds.
This thesis develops a hierarchy of analytical availability models that occupies that gap, establishing what each member can be trusted to estimate, at what accuracy, and at what cost. The family pairs steady-state and time-marching solvers under Continuous Time Markov Chain and a Semi-Markov Process frameworks, plus two simulator twins, all consuming one shared input pipeline. The reference case is a bottom-fixed 12MW turbine with 22 corrective failure modes over twenty years of hourly ERA5 weather, and the discrete-event reference, NREL’s WOMBAT (0.13.3), is audited, minimally patched, and characterised through a pre-registered mechanism-accretion ladder.
Under aligned conditions the steady-state semi-Markov model reproduces the reference raw, at z = +0.20 over 200 seeds and z = −1.02 against the thousand-seed population, certifying 97.9903% time-based availability, 97.8243% production-based availability, and an annual direct cost of 576,393.60USD for the selected case study turbine. The memoryless simplification is evaluated and proves adequate for mean-determined steady-state quantities, although it cannot express production-based availability accurately, overstates the cold-start boundary credit by 46%, and is blind to the replacement waves that make a twenty-year life
at β = 2 one long transient, missing 1.47 percentage points of year-one availability. Process interruptibility treatment is also evaluated, with results indicating a second-order convention worth 0.167 percentage points for the short repairs, and the enabling assumption for heavy replacement modelling, whose contiguous execution diverges at the reference site.
Finally, the 13 ms solve enables rapid scenario screening and sensitivity analysis, being used to propagate forty thousand joint uncertainty samples, price vessel capability, lifting envelopes, mobilisation lead time, and component reliability with break-evens attached, therefore turning the validated hierarchy into a decision instrument at a cost measured in seconds.