Draft Conditions Research Articles

Bulbous Bow Shapes Effect on Ship Characteristics: A Review

Abstract Hydrodynamic optimization is an effective and robust design method that is indispensable in ship hull form performance. Marine engineering and naval architecture have displayed significant interest in integrating bulbous bows on combatant ships. This review aims to gather and assess the existing knowledge regarding the effects of bulbous bow shapes on the hydrodynamic characteristics of combatant ships in terms of historical background, design principles, and impacts of bulbous bow shapes on ship resistance, ship motion in seaways, squat, and seakeeping performance. The review evaluates the effects of bulbous bow shapes on hull hydrodynamics using computational fluid dynamics (CFD), model testing, and full-scale experiments. The text delves into the complexities of improving hull shape and how the bulbous bow design interacts with many operational factors like draft, speed, and sea conditions. This research offers scholars, naval architects, and marine engineers a comprehensive insight into the intricate effects of bulbous bow shapes on combatant ship performance. It aims to consolidate current material to enhance our comprehension of ship design and operation by identifying knowledge gaps and suggesting future research areas.

Estimation of the crop water stress index (CWSI) of sunflower (Helianthus annuus L.) using sensor-based irrigation scheduling for different irrigation levels

ABSTRACT The crop water stress index (CWSI) is an important technique for determining stress levels in the plant and directing irrigation management techniques. To determine the CWSI for sunflower, a pot-based research trial was carried out in the research field of the Department of Soil and Water Engineering, PAU, Ludhiana (India) during the summer of 2023. The sensor-based irrigation scheduling was carried out on the basis of the depletion of total available soil moisture (TASM). The drip irrigation treatments consist of I1 (full irrigation), I2 (20% depletion of TASM), and I3 (40% depletion of TASM). The results revealed that the highest amount of water applied under I1 was recorded at 484.4 mm, while I2 (387.5 mm) and I3 (290.7 mm) during the growing season of sunflower. The results revealed that for kernel diameter and seed weight, I1 and I2 were statistically non-significant to each other while I1 and I3 were statistically significant to each other. The highest water productivity recorded for I2, followed by I3. The overall findings revealed that an average CWSI value of 0.85 for the sunflower crop falls within the range of lower and upper baselines. The response of physico-chemical properties of sunflower seeds showed a high correlation with the draught condition.

Research on the effect of shallow draft on the performance of azimuth thruster under bollard conditions

For the azimuth thruster installed on shallow draft ships, the shallow water effect leads to a decrease in propulsive performance, especially under the bollard condition. In order to accurately predict the bollard propulsion performance of the azimuth thruster under shallow draft conditions, this paper firstly obtains the bollard thrust performance in several waters through the shallow water test, and then analyzes the effect of hull wake and cavitation on the bollard thrust performance of the azimuth thruster by using the CFD method. The results are consistent with the test results under the open water. When the water depth is less than 1.0D, the thrust coefficient increases with the increase of water depth, when the water depth is greater than 1.0D, the thrust coefficient basically does not change; Considering the influence of hull wake, the axial inlet velocity of the azimuth thruster is 7.27% higher than that of the open water condition; meanwhile considering the influence of the hull wake and cavitation, the leading edge of the bottom of the azimuth thruster conduit and the back of the paddle blade are susceptible to cavitation, which leads to average decrease of the thrust coefficient and torque coefficient by 7.03% and 6.12%, respectively.

CFD Simulation of Vortex Induced Motion of a Caisson during Installation Process

This paper presents the CFD investigation of the vortex induced motion (VIM) of a caisson model during the installation process. The simulations were performed by solving the unsteady 3D Navier-Stokes equation. The Dynamic Fluid-Body Interaction (DFBI) tool is utilized to simulate the motions. Typical draft conditions of a caisson during installation process are considered. The present methodology is verified through the free decay and the VIM of a cylinder simulations in two-dimension. Free decay simulations show that the natural frequency decrease with the increasing draft of the caisson. Maximum response amplitudes occur in the range of 10<Vr <13 for the draft Dp=0.1m. The resonance occurs when the crossflow response frequency f y is very close to the natural frequency f n. The inline/crossflow response frequency increases as the draft increases at the same reduced velocity V r. The response frequency in the inline direction is double of that in the crossflow direction. Eight-shaped trajectories are observed. The maximum displacements in the crossflow direction increase as the drafts increase.

Course-Keeping Performance of a Container Ship with Various Draft and Trim Conditions under Wind Disturbance

IMO presented the standard for ship’s manoeuvrability which every ship is recommended to satisfy. Although it specifies a full load and even keel condition as the condition at which the standard applies, practically, ships are operated under various loading conditions of cargo. From this viewpoint, the authors have conducted manoeuvring tests of a container ship under five loading conditions with different combinations of the draft and trim, and one of the authors established the manoeuvring mathematical model of the ship for each condition so far. This study focuses on the course-keeping performance of the same ship under these loading conditions under wind disturbance. It is the aim of this study to discuss both the influences of loading condition and wind condition simultaneously on the check helm and attitude of the ship while maintaining the target course. For this purpose, the arrangement of containers and their weight distribution were designed as exact as possible. For example, the ship with a trim by bow, which is commonly preferred for fuel efficiency, needs to have a larger check helm for course keeping, especially under the condition of wind disturbance diagonally from behind. This kind of knowledge would be useful for safe navigation.

Sea state estimation based on the motion data of a moored FPSO using neural networks: An evaluation with multiple draft conditions

Useful information for offshore systems can be obtained by monitoring sea state parameters, but the accurate estimation of the on-site wave condition is challenging. This paper deals with motion-based wave estimation using neural networks. The main novelty of this contribution is the evaluation of the performance of the data-driven inference system with motion data from different draft conditions. The study is based on the simulated motions of a Floating Production Storage and Offloading (FPSO) unit with multiple loadings, subjected to typical sea conditions observed offshore the Brazilian coast. The inference models were trained to estimate two independent sets of wave related parameters, corresponding to modal wave statistics, which were post processed to identify single and double-peaked sea states. Results showed that estimation errors were quite similar along the evaluated drafts, with an overall good agreement between estimations and reference values. However, a limitation of the method regarding less frequent sea conditions was observed, even when significant wave response is induced. Also, an analysis of the robustness of the estimation models with respect to a draft variation of ± 0.5 m was carried out considering the global wave statistics, presenting small average deviations compared to the expected values.

Effect of Applied Geotextile and Compost on Chemical Properties of Sandy and Clay Soils and Sorghum Productivity under Draught Conditions.

Effect of Applied Geotextile and Compost on Chemical Properties of Sandy and Clay Soils and Sorghum Productivity under Draught Conditions.

Experimental study on the propulsion performance of a partially submerged propeller

The present study concerns an open water performance of a partially submerged propeller. To investigate the free surface effects on the propulsion performance, the force and moment were measured, and the ventilation phenomena were visualized with respect to submergence ratios and advance coefficients. The thrust loss in heavy load conditions due to ventilation at the suction side of the propeller blade was observed. The extent of the ring-shaped ventilation phenomena increased as the advance coefficients decreased, resulting in thrust loss. Using the underwater camera and the fast Fourier transform results of the thrust, the ventilation phenomena were classified into five types. Also, the shaft excitation force of the propeller was analyzed. The shaft-bearing load was approximately 100% greater than the propeller weight in the ballast draft condition. A larger load was applied to the shaft due to the movement of the thrust eccentricity near the free surface.

Experimental studies on the effects of draft condition, current heading and mooring stiffness on vortex-induced motions of a Tension-Leg Platform

The paper presents experimental studies on the effects of draft conditions, current headings and mooring stiffnesses on the Vortex-Induced Motion (VIM) responses of a Tension-Leg Platform (TLP) with four circular columns. The nominal transverse and yaw amplitudes, and the corresponding spectra obtained by fast Fourier Transform (FFT) and continuous wavelet transform (CWT) are analyzed to examine the characteristics of the motion responses. Four current headings in the range of 0° to 45° are adopted in the model test. The results show that the maximum response amplitude in both transverse and yaw directions are achieved at 0° current incidence. For the transverse response, the maximum nominal amplitude decreases and the lock-in range narrows as the current heading increases. The spectral analyses for the transverse and yaw motions at 0° current heading show that the dominant peak frequencies increase as the reduced velocity increases. It is observed that the low-frequency spectral peak of the in-line motion amplitude spectra increases as reduced velocity increases. A color band or a ribbon concentrates stably around the frequency of f<0.05 in the wavelet analysis. It is primarily caused by the initial acceleration of the model in the towing tank. The absolute values of correlations between the spring tensions and the transverse motion of the platform are much larger than those between the spring tensions and the in-line or yaw motions. Moreover, it is found that the VIM trajectories of the TLP are primarily always along the direction perpendicular to the current heading.

Analysis of FPSO station keeping characteristics

Nowadays with increasing production and exploration activities offshore, the FPSO system has been widely adopted globally because of its unique design system and adaptability to these offshore environmental conditions. This research project aims to provide the station-keeping characteristics of an FPSO in the West African region, by analysing an FPSO with spread mooring design for multiple load cases, different offset, multiple draught conditions and environmental loads, all acting simultaneously and dynamically on the coupled FPSO system. Static and dynamic analysis were conducted using the Orcaflex software to establish the station-keeping characteristics, the recommended practices by DNV for mooring and global performance analysis were utilized for the mooring lines in the static analysis to obtain the primary equilibrium position before the dynamic analysis was conducted and to estimate a dynamic response of the risers in dynamic analysis. The effective tension of the static and dynamic analysis results for the different draught and environmental conditions shows that the far offset had the maximum effective tension, with the fully laden effective tension been the maximum effective tension of the entire simulation. The increase in effective tension as the loading of the FPSO tanks increased caused a reduction in the bending moment radius and thereby reducing the curvature of mooring lines and riser bends. But it was the near offsets that had the minimum bending radii as expected, however, from the analysis the draught conditions provided the largest responses to the multiple loading cases when compared with the changes in the offset positions.

Study on the Relationship Between Ship Resistance and Trim, Supported by Experimental and Software-Based Analysis

In this study, towing tank experiments have been carried out for a container ship under different trim-draft conditions. Experimental results have been interpreted together with the results of the Holtrop method used in both Maxsurf and Orca to identify reactions to changing trim conditions. The study has shown that towing tank experiment findings differ from other relevant findings. The ship shows different resistance characteristics under different trim conditions, but generally the least resistance without trim. In addition, the total resistance change at ship design speed was found to be up to 18% higher in the trim by aft condition. We believe that study findings will help better understand the constantly changing resistance variable depending on draft, speed, and trim conditions.

Numerical trim and draft optimization of a twin-screw modern surface combatant with inverted bow

Trim optimization is an effective tool that the International Maritime Organization recommends (IMO) to increase marine vessels' economic efficiency. This paper comprehensively evaluated the effect of the initial trim and draft on various resistance and hydrodynamic propulsion components of the fully appended ONR tumblehome model. In this regard, a complete set of resistance, double-body, and self-propulsion tests were simulated in the computational fluid dynamics (CFD) environment for different initial trim and draft conditions in constant displacement. The validation of the results with the available experimental data demonstrated an excellent agreement among them. The analysis result revealed that for this model, trim by fore reduced the total resistance, increased the thrust of the propellers, and thus increased hydrodynamic propulsive efficiency.

A study on the dynamic motion of floating fibers in the double apron drafting process

Double apron drafting is an important unit in yarn spinning; the motion of fibers during the double apron drafting zone directly determines the quality of the final yarn. In this research, we sought to study how the motion of the fibers and the irregularities introduced during the double apron drafting process were affected by the processing settings and fiber properties. The fiber acceleration point under different drafting conditions was investigated using the tracer fiber technique. The results showed that both the drafting parameters as well as the input sliver properties have a certain influence on the fluctuation of fiber acceleration points, but the difference is small. In addition, the irregularity caused by the fluctuation of the fiber acceleration point during the drafting process (CVFAP) was also calculated under the same drafting conditions based on the irregularity of the input sliver and that of the spun yarn. By comparing the relationship between the CVFAP and fiber acceleration point fluctuation, it was found that the trend of the change between the two is in fairly good agreement. This is consistent with theoretical research and practical experience, and it can prove the accuracy of the fiber acceleration point test results from another aspect as well. Studying the dynamic motion of floating fibers during the double apron drafting process sheds light on the correlation between spinning conditions and yarn quality, which can provide a reference for process optimization.

Activity-based evaluation of ship pollutant emissions considering ship maneuver according to transportation plan

Ships that use fossil fuels produce pollutant emissions that significantly affect air quality, global climate change, disruption of marine ecosystems, loss of coastline, and devastation of human health. Thus, it is important to manage maritime pollutant emissions. The first step to manage marine pollutant emissions is to precisely evaluate the emitted quantities. This paper presents the construction of a new approach to evaluate pollutant emissions of CO2, SOX, NOX, HC, CO, and PM using an activity-based approach by simulating an autopiloted ship for a transportation plan. The evaluated pollutant emissions were analyzed according to the fuel type, draft condition, and command speed. The evaluated emissions using the suggested approach were compared with those using a simplified approach, which shows the benefit of using LNGF for CO2, SOX, and CO in comparison to HFO. Potential drawbacks for NOX, HC, and PM emissions were also recognized for some conditions.

Heat Exchange in Staggered Threaded Pipe Banks with Similar Developed Surface Patterns under Natural Draft Conditions

Helical pipes with similar developed surface patterns efficiently operate under forced convection conditions. The available literature describes their essential advantages over the tubes of a round-ribbed profile and the possibility of their application as a heat-exchanging section for the air-cooling unit. However, the peculiarities of the operation of such units require checking an opportunity for the use of helical pipes with similar developed surface patterns under natural draft conditions. The purpose of the research is to get new data on the flow structure in the intertube space of the staggered banks of such pipes under natural draft conditions. These data are required for the in-depth analysis of the appropriateness of the use of such pipes for “dry” air cooling systems. The methods of investigation included the use of the academic licensed software package ANSYS Student for numerical computations. It was established that the heat exchange in ribbed pipes under natural draft conditions is specified first of all by the parameters of the staggered bank (longitudinal and transversal pitches of the arrangement of pipes in the bank) and the geometric parameters of the pipes, in particular the pitch between the humps and the dents on the tube surface that form its helical surface. Design ratios were suggested for the determination of the averaged heat exchange in the staggered banks of the single-thread helical pipes with similar developed surface patterns. It was shown that the pitch characteristics of the banks have the greatest effect on the similarity equation. A preliminary validation was carried out for the methods adopted for the design of helical pipes and the known methods used for the computation of the staggered banks of smooth cylindrical pipes. The obtained research data can be used for the evaluation of the intensification of the heat exchange and for the flow analysis in order to increase the efficiency of the heat-exchange equipment.

운항조건에서 11,000TEU 컨테이너선의 소요마력 저감을 위한 트림변화 연구

In this paper, the effect of trim variation on the required power of 11,000TEU container ship was investigated under conditions considering the actual operation speed and draft. For each draft condition, the effective power (PE) and delivered power (PD) trends were investigated with changes in trim and ship speed. At this time, the displacement volume was fixed same as the value of the even trim condition and the both sinkage at the fore and after perpendicular are confirmed. The test ship speeds were determined by considering the operating speed. Both numerical and experimental methods were used to analyze the effects of trim variation. Numerical analysis results were used for evaluating the resistance performance, and the self-propulsion performance was estimated using experimental data obtained from model test.

Comparison of a decade’s data between LST and NDVI data for agricultural drought analysis in Rayalaseema region, AP, India

Drought is an extreme weather condition that disturbs agricultural production by raising the temperatures and altering precipitation patterns. As agriculture in India heavily depends on monsoon, any changes in these patterns will severely affects its agricultural economy. Rayalaseema is one of such regions which was hit by sever draught conditions in past few decades. The region depends on the traditional agricultural economy; thus, not only production but also the life of the common man is influenced by the impact of drought on agriculture. The purpose of this study is to investigate vegetation stress in the Rayalaseema region with the help of normalised difference vegetation index (NDVI) values and land surface temperature (LST) for the years 2011 and 2019. To measure both NDVI and LST, satellite data is used. A clear interdependency between LST and NDVI was observed and it was found to be a negative correlation between them. The correlation values for 2011 and 2019 between LST and NDVI were found to be -0.44577, -0.80447 respectively. The influence of rain fall data was also discussed in the study to explain the increase in NDVI values during the last quarter of 2019.

Theoretical analysis on hydrodynamic performance for a dual-chamber oscillating water column device with a pitching front lip-wall

For the sake of extracting wave energy over a broader range of wave frequencies, dual-chamber OWC devices are more beneficial than the single-chamber one. In this paper, the concept of a dual-chamber OWC device with a pitching front lip-wall is proposed and by utilizing the matched eigenfunction method along the adjacent interfaces, present theoretical model developed under the framework of potential flow theory can be numerically solved. To determine the optimal turbine parameters combination of front and rear chamber for the optimal wave power extraction efficiency, a numerical method of successive approximation is employed. Parameters, including lip-wall drafts, installed location of mid lip-wall and angle spring stiffness are changed to explore effects on the hydrodynamic performance. It is found that when the device is designed with an asymmetry structure configuration, i.e., narrow front but wide rear, is more desirable and the optimal breadth ratio is 3:7. There exists a medium lip-wall draft condition which can satisfy stable operation and efficient performance simultaneously by including the pitching motion of front lip-wall. In addition, a relatively smaller spring stiffness (within the range of 105) is more recommended as the pitching motion of lip-wall can be adequately utilized to obtain a more satisfactory energy efficiency curve.

Experimental Investigation on Resistance Reduction for Multiple Service Conditions of Container Ship Bulbous Bow Optimization

Yin, X.; Huang, L.; Lu, Y.; Zou, J., and Wan, L., 2021. Experimental investigation on resistance reduction for multiple service conditions of container ship bulbous bow optimization. Journal of Coastal Research, 37(3), 634–643. Coconut Creek (Florida), ISSN 0749-0208.In this article, the main objective is to implement an experimental investigation on resistance reduction within a hydrodynamic container ship design procedure for bulbous bow form optimization under multiple service conditions. One container ship was used as a parent ship, and using different bulb characteristic parameters as design variables, a new hull form with an optimized bulbous bow was developed to satisfy the economical requirement of slow steaming for the modern container vessel. Through the conduction of ship-model resistance tests in both design and scantling drafts covering a wide speed range, the experimental results of various resistance component values were monitored and compared between the original and optimized ship. The results show that the hydrodynamic performance of the optimized hull form is improved, especially at lower speeds, and the total resistance reduction per unit displacement in full scale reaches 30%∼40% and then decreases gradually with the increase of Froude number under design draft conditions in contrast to the original hull, suggesting the evolved hull form optimization method is valuable. In addition, the bulbous bow optimization method is proved more practical and effective than the traditional optimization process, which is only based on a contractually specified design condition. On the basis of the comparison and analysis of test results, the influence of the bulbous bow characteristic parameters on the resistance performance is further studied. The presented work is of high reference value for the hydrodynamic optimization design of modern container vessels.

Flow structure definition in the bundles of flat-oval tubes with incomplete finning under conditions of natural draft

The expediency of using dry cooling systems for technological products is considered. The expediency of using flat-oval tubes with incomplete finning as heat exchange surfaces of air coolers is shown. The transfer of the operating mode of air coolers to the operating mode with the fans turned off during a certain time of the year is substantiated. Installation of an additional exhaust tower can lead to energy savings for the fan drive up to 55 %. The technique of numerical modeling and experimental study of the flow structure in a package of flat-oval tubes with incomplete finning under natural draft conditions is presented. Experimental studies and computational fluid dynamics (CFD) – modeling of the flow structure and averaged velocity fields in a package of flat-oval tubes with incomplete finning under natural draft conditions are carried out. The obtained numerical and experimental distributions of velocities and temperatures near the surface of the tubes and in the wake behind them give an idea of the features of the flow around the tubes and the effect of the flow structure on the intensity of their heat transfer. It was found that the hydrodynamic flow pattern in a stack of flat-oval tubes according to the results of CFD modeling corresponds to the classical concepts of hydrodynamics. The absence of a part of the finning in the aft part of flat-oval tubes with incomplete finning, where the formation of the aft circulation zone is observed, is substantiated. The verification of the CFD-modeling data and the data of the experimental study on the determination of the average velocities and temperatures in the flow behind the pack of flat-oval tubes with incomplete finning is carried out. The verification results indicate that the average numerical simulation error does not exceed 18 %. It is shown that to determine the optimal, from the point of view of heat transfer, geometric parameters of a number of flat-oval tubes under natural draft conditions, it is advisable to use CFD modeling