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Antti Ritari
Department of Mechanical Engineering, Aalto University, Otakaari 4, 02150 Espoo, Finland

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Journal article
Published: 30 August 2021 in Journal of Marine Science and Engineering
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This paper evaluates the effect of a large-capacity electrical energy storage, e.g., Li-ion battery, on optimal sailing routes, speeds, fuel choice, and emission abatement technology selection. Despite rapid cost reduction and performance improvement, current Li-ion chemistries are infeasible for providing the total energy demand for ocean-crossing ships because the energy density is up to two orders of magnitude less than in liquid hydrocarbon fuels. However, limited distance zero-emission port arrival, mooring, and port departure are attainable. In this context, we formulate two groups of numerical problems. First, the well-known Emission Control Area (ECA) routing problem is extended with battery-powered zero-emission legs. ECAs have incentivized ship operators to choose longer distance routes to avoid using expensive low sulfur fuel required for compliance, resulting in increased greenhouse gas (GHG) emissions. The second problem evaluates the trade-off between battery capacity and speed on battery-powered zero-emission port arrival and departure legs. We develop a mixed-integer quadratically constrained program to investigate the least cost system configuration and operation. We find that the optimal speed is up to 50% slower on battery-powered legs compared to the baseline without zero-emission constraint. The slower speed on the zero-emission legs is compensated by higher speed throughout the rest of the voyage, which may increase the total amount of GHG emissions.

ACS Style

Antti Ritari; Kirsi Spoof-Tuomi; Janne Huotari; Seppo Niemi; Kari Tammi. Emission Abatement Technology Selection, Routing and Speed Optimization of Hybrid Ships. Journal of Marine Science and Engineering 2021, 9, 944 .

AMA Style

Antti Ritari, Kirsi Spoof-Tuomi, Janne Huotari, Seppo Niemi, Kari Tammi. Emission Abatement Technology Selection, Routing and Speed Optimization of Hybrid Ships. Journal of Marine Science and Engineering. 2021; 9 (9):944.

Chicago/Turabian Style

Antti Ritari; Kirsi Spoof-Tuomi; Janne Huotari; Seppo Niemi; Kari Tammi. 2021. "Emission Abatement Technology Selection, Routing and Speed Optimization of Hybrid Ships." Journal of Marine Science and Engineering 9, no. 9: 944.

Journal article
Published: 01 July 2021 in Journal of Marine Science and Engineering
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We present a novel convex optimisation model for ship speed profile optimisation under varying environmental conditions, with a fixed schedule for the journey. To demonstrate the efficacy of the proposed method, a combined speed profile optimisation model was developed that employed an existing dynamic programming approach, along the novel convex optimisation model. The proposed model was tested with 5 different ships for 20 journeys from Houston, Texas to London Gateway, with differing environmental conditions, which were retrieved from actual weather forecasts. As a result, it was shown that the combined model with both dynamic programming and convex optimisation was approximately 22% more effective in developing a fuel saving speed profile compared to dynamic programming alone. Overall, average fuel savings for the studied voyages with speed profile optimisation was approximately 1.1% compared to operation with a fixed speed and 3.5% for voyages where significant variance in environmental conditions was present. Speed profile optimisation was found to be especially beneficial in cases where detrimental environmental conditions could be avoided with minor speed adjustments. Relaxation of the fixed schedule constraint likely leads to larger savings but makes comparison virtually impossible as a lower speed leads to lower propulsion energy needed.

ACS Style

Janne Huotari; Teemu Manderbacka; Antti Ritari; Kari Tammi. Convex Optimisation Model for Ship Speed Profile: Optimisation under Fixed Schedule. Journal of Marine Science and Engineering 2021, 9, 730 .

AMA Style

Janne Huotari, Teemu Manderbacka, Antti Ritari, Kari Tammi. Convex Optimisation Model for Ship Speed Profile: Optimisation under Fixed Schedule. Journal of Marine Science and Engineering. 2021; 9 (7):730.

Chicago/Turabian Style

Janne Huotari; Teemu Manderbacka; Antti Ritari; Kari Tammi. 2021. "Convex Optimisation Model for Ship Speed Profile: Optimisation under Fixed Schedule." Journal of Marine Science and Engineering 9, no. 7: 730.

Journal article
Published: 11 September 2020 in Energies
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We present a novel methodology for the control of power unit commitment in complex ship energy systems. The usage of this method is demonstrated with a case study, where measured data was used from a cruise ship operating in the Caribbean and the Mediterranean. The ship’s energy system is conceptualized to feature a fuel cell and a battery along standard diesel generating sets for the purpose of reducing local emissions near coasts. The developed method is formulated as a model predictive control (MPC) problem, where a novel 2-stage predictive model is used to predict power demand, and a mixed-integer linear programming (MILP) model is used to solve unit commitment according to the prediction. The performance of the methodology is compared to fully optimal control, which was simulated by optimizing unit commitment for entire measured power demand profiles of trips. As a result, it can be stated that the developed methodology achieves close to optimal unit commitment control for the conceptualized energy system. Furthermore, the predictive model is formulated so that it returns probability estimates of future power demand rather than point estimates. This opens up the possibility for using stochastic or robust optimization methods for unit commitment optimization in future studies.

ACS Style

Janne Huotari; Antti Ritari; Jari Vepsäläinen; Kari Tammi. Hybrid Ship Unit Commitment with Demand Prediction and Model Predictive Control. Energies 2020, 13, 4748 .

AMA Style

Janne Huotari, Antti Ritari, Jari Vepsäläinen, Kari Tammi. Hybrid Ship Unit Commitment with Demand Prediction and Model Predictive Control. Energies. 2020; 13 (18):4748.

Chicago/Turabian Style

Janne Huotari; Antti Ritari; Jari Vepsäläinen; Kari Tammi. 2020. "Hybrid Ship Unit Commitment with Demand Prediction and Model Predictive Control." Energies 13, no. 18: 4748.

Journal article
Published: 24 April 2020 in Energies
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This study investigates the potential of improving the energy efficiency and reducing the lifecycle costs of electric city buses with multispeed gearboxes. A two-speed dual clutch gearbox and a continuously variable transmission were studied and compared to a reference fixed gear ratio powertrain. A novel two-level optimization model was introduced. The top level involves an exhaustive search algorithm and quasi-static vehicle dynamic model for optimizing the two-speed gearbox gear ratios, utilizing efficiency maps for the electric motor and the inverter. The second level is an integer programming model, which finds an optimal gear shifting policy subject to constraints on hysteresis and gear shifting induced losses. The model was applied with a standard driving cycle and additionally with three measured cycles acquired from a prototype battery electric city bus operating on a daily schedule on a suburban route in Espoo, Finland. The results showed that a two-speed gearbox reduced energy consumption by 2–3.2%, depending on the driving cycle characteristics. On the other hand, the continuously variable transmission was found to increase consumption by 1.9–4.0% due to large losses of the belt mechanism. It was concluded that the two-speed gearbox is a cost-effective investment for electric city buses characterized by operation profiles with frequent acceleration and braking events.

ACS Style

Antti Ritari; Jari Vepsäläinen; Klaus Kivekäs; Kari Tammi; Heikki Laitinen. Energy Consumption and Lifecycle Cost Analysis of Electric City Buses with Multispeed Gearboxes. Energies 2020, 13, 2117 .

AMA Style

Antti Ritari, Jari Vepsäläinen, Klaus Kivekäs, Kari Tammi, Heikki Laitinen. Energy Consumption and Lifecycle Cost Analysis of Electric City Buses with Multispeed Gearboxes. Energies. 2020; 13 (8):2117.

Chicago/Turabian Style

Antti Ritari; Jari Vepsäläinen; Klaus Kivekäs; Kari Tammi; Heikki Laitinen. 2020. "Energy Consumption and Lifecycle Cost Analysis of Electric City Buses with Multispeed Gearboxes." Energies 13, no. 8: 2117.

Journal article
Published: 16 October 2019 in Energy
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The inclusion of a battery system for a diesel mechanical short sea ship was investigated. The main benefits of the battery were assumed to emerge from shaving thruster generated power peaks, rather than starting additional generating sets to accommodate the power demand and additionally from replacing a diesel engine as a reserve power source. To support the analysis, an auxiliary engine power output dataset of a roll-on/roll-off passenger ferry operating in the Baltic Sea was acquired. Required capacity for the battery system was derived by considering power availability requirements and battery safety margins for performance deterioration. A multi-period mixed-integer linear programming model was developed to derive a globally optimal power management strategy for the auxiliary engines and the battery, with the goal of minimizing the battery installation total cost. The battery system was found to reduce fuel oil consumption by 257.5 tons annually due to improved auxiliary engine efficiency alone. Furthermore, the battery system total cost advantage was found to vary from -€0.61 to €2.82 million during the ten-year investment period, depending on fuel oil and battery system costs applied in the modeling. For the studied case ship, the hybrid electric topology was concluded to be economically feasible.

ACS Style

Antti Ritari; Janne Huotari; Jukka Halme; Kari Tammi. Hybrid electric topology for short sea ships with high auxiliary power availability requirement. Energy 2019, 190, 116359 .

AMA Style

Antti Ritari, Janne Huotari, Jukka Halme, Kari Tammi. Hybrid electric topology for short sea ships with high auxiliary power availability requirement. Energy. 2019; 190 ():116359.

Chicago/Turabian Style

Antti Ritari; Janne Huotari; Jukka Halme; Kari Tammi. 2019. "Hybrid electric topology for short sea ships with high auxiliary power availability requirement." Energy 190, no. : 116359.

Journal article
Published: 23 November 2018 in Energies
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Uncertainty in operation factors, such as the weather and driving behavior, makes it difficult to accurately predict the energy consumption of electric buses. As the consumption varies, the dimensioning of the battery capacity and charging systems is challenging and requires a dedicated decision-making process. To investigate the impact of uncertainty, six electric buses were measured in three routes with an Internet of Things (IoT) system from February 2016 to December 2017 in southern Finland in real operation conditions. The measurement results were thoroughly analyzed and the operation factors that caused variation in the energy consumption and internal resistance of the battery were studied in detail. The average energy consumption was 0.78 kWh/km and the consumption varied by more than 1 kWh/km between trips. Furthermore, consumption was 15% lower on a suburban route than on city routes. The energy consumption was mostly influenced by the ambient temperature, driving behavior, and route characteristics. The internal resistance varied mainly as a result of changes in the battery temperature and charging current. The energy consumption was predicted with above 75% accuracy with a linear model. The operation factors were correlated and a novel second-order normalization method was introduced to improve the interpretation of the results. The presented models and analyses can be integrated to powertrain and charging system design, as well as schedule planning.

ACS Style

Jari Vepsäläinen; Antti Ritari; Antti Lajunen; Klaus Kivekäs; Kari Tammi. Energy Uncertainty Analysis of Electric Buses. Energies 2018, 11, 3267 .

AMA Style

Jari Vepsäläinen, Antti Ritari, Antti Lajunen, Klaus Kivekäs, Kari Tammi. Energy Uncertainty Analysis of Electric Buses. Energies. 2018; 11 (12):3267.

Chicago/Turabian Style

Jari Vepsäläinen; Antti Ritari; Antti Lajunen; Klaus Kivekäs; Kari Tammi. 2018. "Energy Uncertainty Analysis of Electric Buses." Energies 11, no. 12: 3267.