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Prof. Dagang Zhao
Harbin Engineering University

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Research Keywords & Expertise

0 Marine Engineering
0 Ocean Engineering
0 Ship Dynamics
0 hydrodynamic Simulation
0 Hydrodynamic testing

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Journal article
Published: 06 October 2020 in Ocean Engineering
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With the implementation of an energy efficiency design index, energy-saving devices (ESDs) have received increasing research interest. In this study, experimental and numerical analyses were performed on a 25-m long ore carrier model to investigate the working mechanism of ESDs comprising a pre-swirl stator and a rudder bulb. The interactions between the hull, propeller, rudder, and ESDs were observed to have a positive effect on the propulsion performance of the large-scale ship model. To elucidate the effects, self-propulsion tests were conducted at sea to determine the thrust and torque coefficients. The sliding mesh method was used to perform numerical simulations of the large-scale ship model for unsteady multiphase flows with different inflow speeds. The wake field at the stern and the pressure distribution on the vessel surface were analysed to investigate the energy-saving mechanism. The results showed that ESDs can effectively ameliorate the propeller slipstream and have a positive interference effect on the large-scale hull. The average gain of the ESDs relative to no-ESDs was up to 3%.

ACS Style

Yu-Min Su; Jian-Feng Lin; Da-Gang Zhao; Chun-Yu Guo; Hang Guo. Influence of a pre-swirl stator and rudder bulb system on the propulsion performance of a large-scale ship model. Ocean Engineering 2020, 218, 108189 .

AMA Style

Yu-Min Su, Jian-Feng Lin, Da-Gang Zhao, Chun-Yu Guo, Hang Guo. Influence of a pre-swirl stator and rudder bulb system on the propulsion performance of a large-scale ship model. Ocean Engineering. 2020; 218 ():108189.

Chicago/Turabian Style

Yu-Min Su; Jian-Feng Lin; Da-Gang Zhao; Chun-Yu Guo; Hang Guo. 2020. "Influence of a pre-swirl stator and rudder bulb system on the propulsion performance of a large-scale ship model." Ocean Engineering 218, no. : 108189.

Journal article
Published: 04 October 2020 in Journal of Marine Science and Engineering
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In marine environments, ships are bound to be disturbed by several external factors, which can cause stochastic fluctuations and strong nonlinearity in the ship motion. Predicting ship motion is pivotal to ensuring ship safety and providing early warning of risks. This report proposes a real-time ship vertical acceleration prediction algorithm based on the long short-term memory (LSTM) and gated recurrent units (GRU) models of a recurrent neural network. The vertical acceleration time history data at the bow, middle, and stern of a large-scale ship model were obtained by performing a self-propulsion test at sea, and the original data were pre-processed by resampling and normalisation via Python. The prediction results revealed that the proposed algorithm could accurately predict the acceleration time history data of the large-scale ship model, and the root mean square error between the predicted and real values was no greater than 0.1. The optimised multivariate time series prediction program could reduce the calculation time by approximately 55% compared to that of a univariate time series prediction program, and the run time of the GRU model was better than that of the LSTM model.

ACS Style

Yumin Su; Jianfeng Lin; Dagang Zhao; Chunyu Guo; Chao Wang; Hang Guo. Real-Time Prediction of Large-Scale Ship Model Vertical Acceleration Based on Recurrent Neural Network. Journal of Marine Science and Engineering 2020, 8, 777 .

AMA Style

Yumin Su, Jianfeng Lin, Dagang Zhao, Chunyu Guo, Chao Wang, Hang Guo. Real-Time Prediction of Large-Scale Ship Model Vertical Acceleration Based on Recurrent Neural Network. Journal of Marine Science and Engineering. 2020; 8 (10):777.

Chicago/Turabian Style

Yumin Su; Jianfeng Lin; Dagang Zhao; Chunyu Guo; Chao Wang; Hang Guo. 2020. "Real-Time Prediction of Large-Scale Ship Model Vertical Acceleration Based on Recurrent Neural Network." Journal of Marine Science and Engineering 8, no. 10: 777.

Research article
Published: 01 September 2020 in Journal of Marine Science and Application
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The hydrodynamic performance of a three-dimensional finite-length rotating cylinder is studied by means of a physical tank and numerical simulation. First, according to the identified influencing factors, a hydrodynamic performance test of the rotating cylinder was carried out in a circulating water tank. In order to explore the changing law of hydrodynamic performance with these factors, a particle image velocimetry device was used to monitor the flow field. Subsequently, a computational field dynamics numerical simulation method was used to simulate the flow field, followed by an analysis of the effects of speed ratio, Reynolds number, and aspect ratio on the flow field. The results show that the lift coefficient and drag coefficient of the cylinder increase first and then decrease with the increase of the rotational speed ratio. The trend of numerical simulation and experimental results is similar.

ACS Style

Wei Wang; Yuwei Wang; Dagang Zhao; Yongjie Pang; Chunyu Guo; Yifan Wang. Numerical and Experimental Analysis of the Hydrodynamic Performance of a Three-Dimensional Finite-Length Rotating Cylinder. Journal of Marine Science and Application 2020, 19, 388 -397.

AMA Style

Wei Wang, Yuwei Wang, Dagang Zhao, Yongjie Pang, Chunyu Guo, Yifan Wang. Numerical and Experimental Analysis of the Hydrodynamic Performance of a Three-Dimensional Finite-Length Rotating Cylinder. Journal of Marine Science and Application. 2020; 19 (3):388-397.

Chicago/Turabian Style

Wei Wang; Yuwei Wang; Dagang Zhao; Yongjie Pang; Chunyu Guo; Yifan Wang. 2020. "Numerical and Experimental Analysis of the Hydrodynamic Performance of a Three-Dimensional Finite-Length Rotating Cylinder." Journal of Marine Science and Application 19, no. 3: 388-397.

Journal article
Published: 16 June 2020 in Ocean Engineering
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In recent years, under the advocacy of ITTC, large-scale model test technology has garnered significant attention from researchers all over the world. Increasingly sophisticated test equipment and a large amount of experimental experience have promoted the development and improvement of test technology. Here, a 25 m long bulk carrier model was built as the research object. The self-propulsion test about propulsion performance in real sea environment was conducted in the coastal waters of northern China. The manoeuvrability test proved that the designed ship model integrated system was reliable. The effects of complex wake field environments on the propulsion performance were studied using the equal thrust and equal torque methods. The results indicated that the complex wake field environment causes the torque to increase by 2%–11%, and the thrust loss ranges from 3 to 15%. When the propeller was operated at a high rotating speed, the torque and thrust in the oblique wave tended to decrease by 1–3% compared to the propulsion performance in the head wave. In addition, the more severe sea state caused the propeller torque to decrease and the thrust to increase.

ACS Style

Chun-Yu Guo; Xiang-Hai Zhong; Da-Gang Zhao; Chao Wang; Jian-Feng Lin; Ke-Wei Song. Propulsion performance of large-scale ship model in real sea environment. Ocean Engineering 2020, 210, 107440 .

AMA Style

Chun-Yu Guo, Xiang-Hai Zhong, Da-Gang Zhao, Chao Wang, Jian-Feng Lin, Ke-Wei Song. Propulsion performance of large-scale ship model in real sea environment. Ocean Engineering. 2020; 210 ():107440.

Chicago/Turabian Style

Chun-Yu Guo; Xiang-Hai Zhong; Da-Gang Zhao; Chao Wang; Jian-Feng Lin; Ke-Wei Song. 2020. "Propulsion performance of large-scale ship model in real sea environment." Ocean Engineering 210, no. : 107440.

Journal article
Published: 30 May 2020 in Journal of Marine Science and Engineering
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As a new testing technology, large-scale ship model tests on the sea are advantageous in addressing the scale effect in ship models and in simulating ship navigation conditions. In this study, the uncertainty of a ship model propulsion test on the sea was analyzed using the Monte Carlo method, and the influence of the test environment was quantified. We used a 25 m-long ship model for the propulsion performance test. Based on the procedure recommended by the International Standardization Organization (ISO), several tests were conducted on the Yellow Sea (the northwestern part of the East China Sea). The results demonstrate that the wind and waves in the environment are the two factors that have the greatest influence on the test accuracy. This study will aid the development of sea trials, and the analysis method used in the propulsion test is also suitable for many complex ship tests.

ACS Style

Guangli Zhou; Yuwei Wang; Dagang Zhao; Jianfeng Lin. Uncertainty Analysis of Ship Model Propulsion Test on Actual Seas Based on Monte Carlo Method. Journal of Marine Science and Engineering 2020, 8, 398 .

AMA Style

Guangli Zhou, Yuwei Wang, Dagang Zhao, Jianfeng Lin. Uncertainty Analysis of Ship Model Propulsion Test on Actual Seas Based on Monte Carlo Method. Journal of Marine Science and Engineering. 2020; 8 (6):398.

Chicago/Turabian Style

Guangli Zhou; Yuwei Wang; Dagang Zhao; Jianfeng Lin. 2020. "Uncertainty Analysis of Ship Model Propulsion Test on Actual Seas Based on Monte Carlo Method." Journal of Marine Science and Engineering 8, no. 6: 398.

Journal article
Published: 07 January 2020 in Ocean Engineering
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In this study, we developed a comprehensive test system for ship-model testing in actual wind, wave, and current flow environments. The resistance and propulsion performance of a 25-m-long ship model were analysed, and corresponding correction methods were developed to determine the performance in actual sea conditions. The effects of an energy-saving device on the ship performance under actual sea conditions were assessed using this platform. The proposed methodology and technique are reliable and promising, and can provide a basis for the development of new ship testing techniques.

ACS Style

Jianfeng Lin; Da-Gang Zhao; Chun-Yu Guo; Yu-Min Su; Xiang-Hai Zhong. Comprehensive test system for ship-model resistance and propulsion performance in actual seas. Ocean Engineering 2020, 197, 106915 .

AMA Style

Jianfeng Lin, Da-Gang Zhao, Chun-Yu Guo, Yu-Min Su, Xiang-Hai Zhong. Comprehensive test system for ship-model resistance and propulsion performance in actual seas. Ocean Engineering. 2020; 197 ():106915.

Chicago/Turabian Style

Jianfeng Lin; Da-Gang Zhao; Chun-Yu Guo; Yu-Min Su; Xiang-Hai Zhong. 2020. "Comprehensive test system for ship-model resistance and propulsion performance in actual seas." Ocean Engineering 197, no. : 106915.

Journal article
Published: 31 May 2019 in Water
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In this study, particle image velocimetry was used to measure the fine flow-field characteristics of an L-type podded propulsor in various working conditions. The flow-field details at different cross-sections between the propeller and the inclined bracket were compared and analyzed, allowing for more intuitive comparison of the flow-field characteristics of L-type podded propulsors. The interference mechanisms among the propeller, pod, and bracket of the L-type podded propulsors at different advance coefficients, deflection angles, and deflection directions were investigated in depth. The results of this study can serve as reference material and provide technical support for the design and practical shipbuilding application of L-type podded propulsors. Therefore, the results have theoretical significance and practical engineering value.

ACS Style

Dagang Zhao; Chunyu Guo; Tiecheng Wu; Wei Wang; Xunbin Yin. Hydrodynamic Interactions between Bracket and Propeller of Podded Propulsor Based on Particle Image Velocimetry Test. Water 2019, 11, 1142 .

AMA Style

Dagang Zhao, Chunyu Guo, Tiecheng Wu, Wei Wang, Xunbin Yin. Hydrodynamic Interactions between Bracket and Propeller of Podded Propulsor Based on Particle Image Velocimetry Test. Water. 2019; 11 (6):1142.

Chicago/Turabian Style

Dagang Zhao; Chunyu Guo; Tiecheng Wu; Wei Wang; Xunbin Yin. 2019. "Hydrodynamic Interactions between Bracket and Propeller of Podded Propulsor Based on Particle Image Velocimetry Test." Water 11, no. 6: 1142.

Journal article
Published: 27 May 2019 in Journal of Marine Science and Engineering
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In this study, the self-propulsion performance of a ship model with double-L-type podded propulsors was predicted. Additionally, a conversion method for the performance of a full-scale ship was established based on the correction method published by the International Towing Tank Conference (ITTC) for the scaling effect of a single podded propeller and research reports on pod tests conducted by different ship research institutes. The thrust deduction and wake fraction of the ship were also analyzed. Furthermore, the self-propulsion performance of a full-scale ship with double L-type pods was determined, the full- and model-scale ships compared in terms of their flow fields and pressure charts, and the influence of the scaling effect analyzed. In addition, the calculation results were compared with the conversion results of a full-scale ship, and the reliability of the method adopted for the performance estimation of a full-scale ship with double podded propulsors was verified. The findings reported herein can provide statistics and technical support for the design of L-type podded propulsors and their application in full-scale ships, which are of theoretical significance and practical value in the engineering domain.

ACS Style

Dagang Zhao; Chunyu Guo; Jianfeng Lin; Zuotian Zhang; Xue Bai. Prediction of Self-Propulsion Performance of Ship Model with Double L-Type Podded Propulsors and Conversion Method for Full-Scale Ship. Journal of Marine Science and Engineering 2019, 7, 162 .

AMA Style

Dagang Zhao, Chunyu Guo, Jianfeng Lin, Zuotian Zhang, Xue Bai. Prediction of Self-Propulsion Performance of Ship Model with Double L-Type Podded Propulsors and Conversion Method for Full-Scale Ship. Journal of Marine Science and Engineering. 2019; 7 (5):162.

Chicago/Turabian Style

Dagang Zhao; Chunyu Guo; Jianfeng Lin; Zuotian Zhang; Xue Bai. 2019. "Prediction of Self-Propulsion Performance of Ship Model with Double L-Type Podded Propulsors and Conversion Method for Full-Scale Ship." Journal of Marine Science and Engineering 7, no. 5: 162.

Journal article
Published: 20 February 2019 in Journal of Marine Science and Engineering
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In this study, the Reynolds-averaged Navier–Stokes (RANS) method and a model experimental test in a towing tank are used to investigate the unsteady hydrodynamic performance of L-type podded propulsion under different oblique flow angles and advance coefficients. The results show that the load of the operative propeller increases with oblique flow angle and the bracket adds resistance to the pod due to the impact of water flow, leading to a reduced propeller thrust coefficient with increased oblique flow angle. Under a high advance coefficient, the speed of increase of the pressure effect is higher than that of the viscosity effect, and the propeller efficiency increases with the oblique flow angle. The nonuniformity of the inflow results in varying degrees of asymmetry in the horizontal and vertical distributions of the propeller blade pressure. Under high oblique flow angle, relatively strong interference effects are seen between venting vortexes and the cabin after blades, leading to a disorderly venting vortex system after the blade. The numerical simulation results are in good agreement with the experimental values. The study findings provide a foundation for further research on L-type podded propulsors.

ACS Style

Wei Wang; Dagang Zhao; Chunyu Guo; Yongjie Pang. Analysis of Hydrodynamic Performance of L-Type Podded Propulsion with Oblique Flow Angle. Journal of Marine Science and Engineering 2019, 7, 51 .

AMA Style

Wei Wang, Dagang Zhao, Chunyu Guo, Yongjie Pang. Analysis of Hydrodynamic Performance of L-Type Podded Propulsion with Oblique Flow Angle. Journal of Marine Science and Engineering. 2019; 7 (2):51.

Chicago/Turabian Style

Wei Wang; Dagang Zhao; Chunyu Guo; Yongjie Pang. 2019. "Analysis of Hydrodynamic Performance of L-Type Podded Propulsion with Oblique Flow Angle." Journal of Marine Science and Engineering 7, no. 2: 51.