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N.S. Dangi
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2 records found
1
Master thesis
(2026)
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M. Garcia Bravo, W. Yu, Taeseong Kim, S.J. Watson, Alan Wai Hou Lio, N.S. Dangi
Wind turbine fatigue assessments commonly represent load histories as independent 10-minute records, although slow atmospheric and operational changes can generate cycles that cross these boundaries. The resulting fatigue error and its dependence on structural response and material sensitivity remain insufficiently established.
This thesis determined how independent 10-minute processing affects fatigue estimates compared with longer continuous histories and whether the missing cycles can be recovered efficiently. Six months of load and operational measurements from a 7 MW offshore turbine were analysed for blade root flapwise and edgewise bending, and for two tower-bottom bending directions. Continuous rainflow counting, conventional independent-block processing and residue-aware low-frequency fatigue dynamics (LFFD) processing were compared across observation periods and Wöhler exponents. BHawC aeroelastic simulations compared 600 and 3600 s histories, continuous and segmented operating-state sequences, and concatenated short simulations.
LFFD reproduced the continuous reference while enabling analysis of the full six-month record. Independent 10-minute processing underestimated the flapwise damage equivalent load (DEL) by approximately 16% to 20%, and the tower bottom DELs by 3% to 20%, depending on the Wöhler exponent, while the edgewise difference remained below 0.2%. Daily residue aggregation recovered approximately 95%–96% of the full-record flapwise DEL and weekly aggregation about 99%. Cycles connecting different operating regimes contributed approximately 61% of the residue-aware flapwise fatigue contribution.
Extending stationary simulations from 600 to 3600 s increased the combined DEL by 3.62% for flapwise and 1.76% for fore-aft tower bending, whereas continuously processing an idling–startup–production–shutdown sequence increased them by 19.19% and 9.74%, respectively. Concatenated short simulations did not consistently reproduce directly simulated one-hour histories.
The results show that 10-minute storage remains practical, but processing those blocks independently can produce non-conservative estimates for aerodynamically driven responses. Residue-aware processing and targeted continuous transition simulations therefore provide more reliable fatigue estimates.
...
This thesis determined how independent 10-minute processing affects fatigue estimates compared with longer continuous histories and whether the missing cycles can be recovered efficiently. Six months of load and operational measurements from a 7 MW offshore turbine were analysed for blade root flapwise and edgewise bending, and for two tower-bottom bending directions. Continuous rainflow counting, conventional independent-block processing and residue-aware low-frequency fatigue dynamics (LFFD) processing were compared across observation periods and Wöhler exponents. BHawC aeroelastic simulations compared 600 and 3600 s histories, continuous and segmented operating-state sequences, and concatenated short simulations.
LFFD reproduced the continuous reference while enabling analysis of the full six-month record. Independent 10-minute processing underestimated the flapwise damage equivalent load (DEL) by approximately 16% to 20%, and the tower bottom DELs by 3% to 20%, depending on the Wöhler exponent, while the edgewise difference remained below 0.2%. Daily residue aggregation recovered approximately 95%–96% of the full-record flapwise DEL and weekly aggregation about 99%. Cycles connecting different operating regimes contributed approximately 61% of the residue-aware flapwise fatigue contribution.
Extending stationary simulations from 600 to 3600 s increased the combined DEL by 3.62% for flapwise and 1.76% for fore-aft tower bending, whereas continuously processing an idling–startup–production–shutdown sequence increased them by 19.19% and 9.74%, respectively. Concatenated short simulations did not consistently reproduce directly simulated one-hour histories.
The results show that 10-minute storage remains practical, but processing those blocks independently can produce non-conservative estimates for aerodynamically driven responses. Residue-aware processing and targeted continuous transition simulations therefore provide more reliable fatigue estimates.
...
Wind turbine fatigue assessments commonly represent load histories as independent 10-minute records, although slow atmospheric and operational changes can generate cycles that cross these boundaries. The resulting fatigue error and its dependence on structural response and material sensitivity remain insufficiently established.
This thesis determined how independent 10-minute processing affects fatigue estimates compared with longer continuous histories and whether the missing cycles can be recovered efficiently. Six months of load and operational measurements from a 7 MW offshore turbine were analysed for blade root flapwise and edgewise bending, and for two tower-bottom bending directions. Continuous rainflow counting, conventional independent-block processing and residue-aware low-frequency fatigue dynamics (LFFD) processing were compared across observation periods and Wöhler exponents. BHawC aeroelastic simulations compared 600 and 3600 s histories, continuous and segmented operating-state sequences, and concatenated short simulations.
LFFD reproduced the continuous reference while enabling analysis of the full six-month record. Independent 10-minute processing underestimated the flapwise damage equivalent load (DEL) by approximately 16% to 20%, and the tower bottom DELs by 3% to 20%, depending on the Wöhler exponent, while the edgewise difference remained below 0.2%. Daily residue aggregation recovered approximately 95%–96% of the full-record flapwise DEL and weekly aggregation about 99%. Cycles connecting different operating regimes contributed approximately 61% of the residue-aware flapwise fatigue contribution.
Extending stationary simulations from 600 to 3600 s increased the combined DEL by 3.62% for flapwise and 1.76% for fore-aft tower bending, whereas continuously processing an idling–startup–production–shutdown sequence increased them by 19.19% and 9.74%, respectively. Concatenated short simulations did not consistently reproduce directly simulated one-hour histories.
The results show that 10-minute storage remains practical, but processing those blocks independently can produce non-conservative estimates for aerodynamically driven responses. Residue-aware processing and targeted continuous transition simulations therefore provide more reliable fatigue estimates.
This thesis determined how independent 10-minute processing affects fatigue estimates compared with longer continuous histories and whether the missing cycles can be recovered efficiently. Six months of load and operational measurements from a 7 MW offshore turbine were analysed for blade root flapwise and edgewise bending, and for two tower-bottom bending directions. Continuous rainflow counting, conventional independent-block processing and residue-aware low-frequency fatigue dynamics (LFFD) processing were compared across observation periods and Wöhler exponents. BHawC aeroelastic simulations compared 600 and 3600 s histories, continuous and segmented operating-state sequences, and concatenated short simulations.
LFFD reproduced the continuous reference while enabling analysis of the full six-month record. Independent 10-minute processing underestimated the flapwise damage equivalent load (DEL) by approximately 16% to 20%, and the tower bottom DELs by 3% to 20%, depending on the Wöhler exponent, while the edgewise difference remained below 0.2%. Daily residue aggregation recovered approximately 95%–96% of the full-record flapwise DEL and weekly aggregation about 99%. Cycles connecting different operating regimes contributed approximately 61% of the residue-aware flapwise fatigue contribution.
Extending stationary simulations from 600 to 3600 s increased the combined DEL by 3.62% for flapwise and 1.76% for fore-aft tower bending, whereas continuously processing an idling–startup–production–shutdown sequence increased them by 19.19% and 9.74%, respectively. Concatenated short simulations did not consistently reproduce directly simulated one-hour histories.
The results show that 10-minute storage remains practical, but processing those blocks independently can produce non-conservative estimates for aerodynamically driven responses. Residue-aware processing and targeted continuous transition simulations therefore provide more reliable fatigue estimates.
H2GO H2ERMES Launch Vehicle
Design Report for the H2ERMES Reusable Launch Vehicle for Hydrogen Refueling
Bachelor thesis
(2025)
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D.F. Cravo da Costa, L. García Gutierrez, A. Orban, T.J. van Haarst, G. Homoki, M. Karásek, S. Katewale, J. Kovář, A. Krishnamoorthi, A.E. Lupei, D. Maggon, B.V.S. Jyoti, L.A. Afilal, N.S. Dangi
The H2GO project presents the design of H2ERMES, a reusable launch vehicle developed to autonomously deliver liquid hydrogen (LH2) to orbital fuel depots, supporting the advancement of nuclear thermal rocket (NTR) propulsion for deep space missions. The vehicle, optimized for environmental and economic sustainability, features a reusable second stage with novel technologies, including a regeneratively cooled heat shield, aerospike-effect propulsion, and cryogenic LH2 storage integrated with structural elements. H2ERMES is designed for 25 or more missions with minimal refurbishment, meeting stringent performance, safety, and sustainability requirements. A comprehensive systems engineering approach defined user and stakeholder requirements, conducted risk analyses, and performed extensive subsystem trade-offs. The final design includes high-efficiency LH2 tanks, a 24-chamber aerospike engine using an expander bleed cycle, actively cooled heat shield, autonomous docking systems, and reliable recovery mechanisms. The project addresses growing market needs for sustainable space infrastructure, with first operational flights planned by 2032 to enable economical, reusable, and low-emission LH2 transport to orbit.
...
The H2GO project presents the design of H2ERMES, a reusable launch vehicle developed to autonomously deliver liquid hydrogen (LH2) to orbital fuel depots, supporting the advancement of nuclear thermal rocket (NTR) propulsion for deep space missions. The vehicle, optimized for environmental and economic sustainability, features a reusable second stage with novel technologies, including a regeneratively cooled heat shield, aerospike-effect propulsion, and cryogenic LH2 storage integrated with structural elements. H2ERMES is designed for 25 or more missions with minimal refurbishment, meeting stringent performance, safety, and sustainability requirements. A comprehensive systems engineering approach defined user and stakeholder requirements, conducted risk analyses, and performed extensive subsystem trade-offs. The final design includes high-efficiency LH2 tanks, a 24-chamber aerospike engine using an expander bleed cycle, actively cooled heat shield, autonomous docking systems, and reliable recovery mechanisms. The project addresses growing market needs for sustainable space infrastructure, with first operational flights planned by 2032 to enable economical, reusable, and low-emission LH2 transport to orbit.