Multi-branch Artificial Neural Network-based decomposition of Ship’s Added Resistance using on-board measured data

A simple calculation tool for added resistance in waves is developed to utilize for initial design or embedded module for navigation support system. In order to select an appropriate calculation method for added resistance in waves, three methods (drift method, integrated pressure method, radiated energy method) based on strip method are applied to Wigley I and KVLCC2. The methods for added resistance in waves give the underestimated results because it is difficult to consider nonlinear effects due to reflected wave. We apply asymptotic (Faltinsen's method) and empirical formula (NMRI's method) to improve the accurac y for short wave length region. In comparison with experimental results, the combination of radiated energy method and short wave correction method of NMRI is the most reasonable. However, a simple sum of results calculated by two methods gives rise to the overestimation of added resistance for short wave length region because added resistance of radiated energy method exits in total reflection region. To overcome this problem, modified radiated energy method is proposed using correction coefficient defined by reflection coefficient of NMRI's method. Finally, added resistance in regular waves is composed of added resistance of modified radiated energy method and that of short wave correction method of NMRI. Estimated added resistance in regular waves is validated by comparison with experimental results of other research groups.

Prediction of the added resistance or corresponding speed loss in real sea conditions is essential to evaluate the performance of a ship. Assessment of the environmental impact on vessel performance is essential for route and cargo planning, optimization of fuel consumption and design, and configuration of engines and the main propulsion system. In the present study, added resistance and speed loss in real sea conditions are evaluated from1 year of onboard monitoring data of a platform supply vessel (PSV) operating in the North Sea. The true sea margin is shown on an annual basis. Relative contributions from environmental conditions and vessel operation control are presented. Results are compared with model experiments and existing numerical methods for prediction of added resistance and speed loss in waves. The study shows that added resistance due to waves for this PSV is significantly larger than predicted by conventional frequency-domain calculations or model tests. No reason for the deviation is found, but it is anticipated that a combination of effects of longitudinal mass radius of gyration, differences in wavelength and steepness in model tests and reality, and nonlinear effects (not accounted for in the numerical calculations) is partly responsible for the deviations. For ships having similar main dimensions, the conventional ways of predicting added resistance or speed loss in waves is nonconservative, and improved methods should be sought.

The characteristics of wave conditions with large tidal ranges and small wave heights in China's coastal waters limit the operation time of traditional single-stage overtopping devices, while the multi-stage overtopping wave energy converters can increase the overall operation time of the device by distributing the upper and lower reservoirs. To study the overtopping performance of the multi-stage overtopping wave energy converter under real sea conditions, a two-dimensional numerical model of the device is developed and verified by physical model tests. The effects of the lower reservoir opening width, slope angle combination, and slope inundation length on the overtopping performance are investigated under regular wave conditions. It is found that a smaller opening width and two 30° slope angles improve the overtopping performance of the device, while the slope inundation depth has less effect. Further, based on the full-scale prototype device, the database of overtopping in a complete tidal cycle (12h) were constructed under real sea conditions in different seasons to provide the basic data for the Wave-to-wire model of power generation simulation.

The International Maritime Organization (IMO) has established the Energy Efficiency Design Index (EEDI) as the most important policy measure to reduce greenhouse gas (GHG) emissions from shipping. A vessel’s EEDI is based on sea trials at delivery, and vessels cannot exceed a threshold for emitted CO2 per ton-mile, depending on vessel type and size. From other industries such as cars we have learnt that testing methods must reflect realistic operating conditions to deliver the desired emission reductions. Present sea-trial procedures for EEDI adjust to ‘calm water conditions’ only, as a comparative basis, despite calm sea being the exception at sea. We find that this adjustment procedure excessively rewards full bodied ‘bulky’ hulls which perform well in calm water conditions. In contrast, hull forms optimized with respect to performance in realistic sea-conditions are not rewarded with the current EEDI procedures. Our results indicate that without adjusting the testing cycle requirements to also include a threshold for performance in waves (real sea), the desired reductions will be short on targets and GHG emissions could potentially increase.

Wave energy, as a significant renewable and clean energy source with vast global reserves, exhibits no greenhouse gas or other pollution during real-sea operational conditions. However, throughout the entire lifecycle, wave energy convertors can produce additional CO2 emissions due to the use of raw materials and emissions during transportation. Based on laboratory test data from a wave energy convertor model, this study ensures consistency between the model and the actual sea-deployed wave energy convertors in terms of performance, materials, and geometric shapes using similarity criteria. Carbon emission factors from China, the European Union, Brazil, and Japan are selected to predict the carbon emissions of wave energy convertors in real-sea conditions. The research indicates: (1) The predicted carbon emission coefficient for unit electricity generation (EFco2) of wave energy is 0.008–0.057 kg CO2/kWh; when the traditional steel production mode is adopted, the EFco2 in this paper is 0.014–0.059 kg CO2/kWh, similar to existing research conclusions for the emission factor of CO2 for wave energy convertor (0.012–0.050 kg CO2/kWh). The predicted data on carbon emissions in the lifecycle of wave energy convertors aligns closely with actual operational data. (2) The main source of carbon emissions in the life cycle of a wave energy converter, excluding the recycling of manufacturing metal materials, is the manufacturing stage, which accounts for 90% of the total carbon emissions. When the recycling of manufacturing metal materials is considered, the carbon emissions in the manufacturing stage are reduced, and the carbon emissions in the transport stage are increased, from about 7% to about 20%. (3) Under the most ideal conditions, the carbon payback period for a wave energy convertor ranges from 0.28 to 2.06 years, and the carbon reduction during the design lifespan (20 years) varies from 238.33 t CO2 (minimum) to 261.80 t CO2 (maximum).

A reliable prediction of attainable ship speed at actual seas is essential from economical and environmental aspects. At this paper a methodology for estimating the attainable speed and related fuel consumption and carbon dioxide (CO2) emissions in moderate and severe sea is proposed. The irregular sea is handled as a series of regular waves with different amplitudes and frequencies. The added resistance in regular waves is obtained by either a direct pressure integration method or an asymptotic small wavelength formula. The in-and-out-of-water-effect and ventilation of a propeller in severe seas is accounted for by a quasi-steady averaging of experimental data for different propeller submergences. The propulsion results for regular waves are used in simulating results in irregular waves. It is shown that for higher sea states this effect has much more influence on the speed loss than the added resistance in waves. The speed loss is calculated by taking into account the engine and propeller performance in actual seas as well as the mass inertia of the ship. The numerical model used for main propulsion engine modeling is based on a zero-dimensional model of an internal combustion engine. The main propulsion engine is represented by number of control volumes interconnected with links for mass and energy transfer between them. This model provides excellent prediction of engine dynamic response during transients with rather short computational time. Also, engine fuel consumption can be precisely determined which represents the basic presumption for estimation of carbon-dioxide emission. Furthermore, use of such model can be extended to determination of the lowest fuel oil consumption strategy for given sea condition and ship speed with resulting lowest possible CO2 emissions. The attainable ship speed is obtained as time series. Correlation of speed loss with sea states allows predictions of propulsive performance in actual seas.

Calculation of embodied GHG emissions in early building design stages using BIM and NLP-based semantic model healing

Comparative study on computation of ship added resistance in waves

Wave overtopping at berm breakwaters: Development of prediction formula and a study on the impact of sea level rise on the overtopping rate

Regression analysis of experimental data for added resistance in waves of arbitrary heading and development of a semi-empirical formula

ABSTRACTThe seakeeping behavior of a ship in waves is different from its behavior in calm water. The resistance and seakeeping performance of a ship must be considered in the early-stage design. Therefore, this paper proposes a hull form optimization framework aiming to achieve the minimum total resistance in waves using a computational fluid dynamics (CFD) technique. A sinusoidal wave is adopted to establish the numerical wave tank and the overset mesh technique is used to facilitate the motions of the ships in question. The total resistance of the hull in waves is regarded as the objective function which is calculated using the Reynolds averaged Navier–Stokes (RANS) method. The arbitrary shape deformation (ASD) technique is used to change the geometry. Under displacement and design variables, a hybrid algorithm is developed to evaluate the objective function combining the optimal Latin hypercube design (Opt LHD) and the non-linear programming by quadratic Lagrangian (NLPQL) algorithm. Finally, two examples of hull form optimization are presented and discussed for David Taylor Model Basin (DTMB) model 5512 and WIGLEY III cases. The results show the effectiveness of the optimization framework developed in the present study, which can lay the foundation for further optimization of full-scale ships.

Effect of sand grain size on simulated mining-induced overburden failure in physical model tests

This paper reports the results of two model test programs conducted on ship-shape vessels to determine current drag forces and moments on the hulls and to assess thruster and main propulsion efficiencies as a function of current intensity and angle of attack. Tests conducted on a drillship with below and through-hull thrusters and a main propulsion system, and an icebreaker with a through-hull thruster and a main propulsion system reveal that operating a propulsor in a current significantly alters the fluid flow and resulting pressure distribution around the hull. This creates different effective hydrodynamic restoring forces and moments than would be predicted by treating the propulsors purely as thrust producing devices and computing restoring forces and moments using their thrust capability and location. These forces and moments are a function of the propulsor, the current velocity and angle of attack and can affect the vessel's performance and station keeping capabilities. The results of these test programs demonstrate that in order to assess accurately the effectiveness of propulsor devices on a ship-shape body for station keeping in a current, model tests using a full hull model are necessary for those devices aft of amidships. Estimation of bow thruster effectiveness at low speeds in a current appears amenable to mathematical techniques. INTRODUCTION Recently there has been increased interest in maneuverability and station keeping capabilities of shipshape vessels. This interest has fueled the need for more information concerning current drag forces and moments and the select ion of thruster or propulsion assist systems. Considerable work has been done in the area of thruster design and the prediction of effective thrust for various types of systems. However, only limited work has been performed on predicting the performance or efficiency of such systems in a current for various current speeds and angles of attack. Estimation of Resistance, Side Force and Yaw Moment Determination of the current forces and moments are required to estimate the average requirements of a thruster system and to determine the resulting response of the vessel in a current field. There appears to be no reliable numerical method currently available for determining hydrodynamic coefficients for this analysis according to a survey of the state of- the-art conducted by the Naval Civil Engineering Laboratory summarized by Palo [1]. The hydrodynamic coefficients are usually determined by physical model tests and used in preliminary static analyses to size the respective propulsive system and in dynamic, nonlinear, time domain simulations to predict the motions of a moored or dynamically assisted vessel. A catalogue of hydrodynamic coefficients for tankers was developed from physical model tests performed for the Oil Companies International Marine Forum. The results of these tests were compiled into a document titled "Prediction of Wind and Current Loads on VLCC's" [2]. These coefficients are used extensively in the offshore industry and are referred to almost exclusively as a source of semi-empirical data on current hydrodynamic coefficients. Additional work was conducted by Edwards [3] in 1985 concerning the effects of Reynold's number on the determination of these hydrodynamic coefficients.

The present study is focused on performance issues of underwater vehicles near the free surface and gives insight into the analysis of a speed loss in regular deep water waves. Predictions of the speed loss are based on the evaluation of the total resistance and effective power in calm water and preselected regular wave fields w.r.t. the non-dimensional wave to body length ratio. It has been assumed that the water is sufficiently deep and that the vehicle is operating in a range of small to moderate Froude numbers by moving forward on a straight-line course with a defined encounter angle of incident regular waves. A modified version of the Doctors & Days [1] method as presented in Skejic and Jullumstrø [2] is used for the determination of the total resistance and consequently the effective power. In particular, the wave-making resistance is estimated by using different approaches covering simplified methods, i.e. Michell’s thin ship theory with the inclusion of viscosity effects Tuck [3] and Lazauskas [4] as well as boundary element methods, i.e. 3D Rankine source calculations according to Hess and Smith [5]. These methods are based on the linear potential fluid flow and are compared to fully viscous finite volume methods for selected geometries. The wave resistance models are verified and validated by published data of a prolate spheroid and one appropriate axisymmetric submarine model. Added resistance in regular deep water waves is obtained through evaluation of the surge mean second-order wave load. For this purpose, two different theoretical models based on potential flow theory are used: Loukakis and Sclavounos [6] and Salvesen et. al. [7]. The considered theories cover the whole range of important wavelengths for an underwater vehicle advancing in close proximity to the free surface. Comparisons between the outlined wave load theories and available theoretical and experimental data were carried out for a submerged submarine and a horizontal cylinder. Finally, the effective power and speed loss are discussed from a submarine operational point of view where the mentioned parameters directly influence mission requirements in a seaway. All presented results are carried out from the perspective of accuracy and efficiency within common engineering practice. By concluding current investigations in regular waves an outlook will be drawn to the application of advancing underwater vehicles in more realistic sea conditions.

The building sector contributes to 50.9 percent of China’s carbon emissions. Due to the complexity of the assessment process, it is difficult to predict the entire life cycle carbon emissions of a building at the early stage of design. In this study, a whole-life carbon emission estimation model for the early stage of building design is developed based on comparison of the standard calculations and an analysis of stock cases. Firstly, the standard calculation methods in China, Japan and Europe were compared, and the boundary of the model was defined in three parts: production, construction and demolition and operation. Second, information on 68 examples of Chinese buildings was collected and divided into a training set and a test set at a ratio of 7:3. In the training set, the relationship between carbon emissions and the design parameters was searched, and a carbon emission estimation model applicable to different stages was constructed. Finally, the model was applied to the test set for validation. The results show that the calculation error of the model is within ±15%, and it can quickly estimate carbon emissions based on the design factors, which is helpful for carbon emission assessment work in the early stages of design.