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Cerebras' CS-1 computer is a refrigerator-sized machine that contains the largest computer chip ever made. For certain classes of problems in high-performance computing, all supercomputers have an unavoidable, and fatal bottleneck: Memory bandwidth. That is the argument made this week by one startup company at SC20, a supercomputing conference that takes place in a different city each year, but this year is being held as a virtual event given the COVID-19 pandemic. The company making that argument is Cerebras Systems, the artificial intelligence computer maker that contends its machine can achieve speed in solving problems that no existing system can. "We can solve this problem in an amount of time that no number of GPUs or CPUs can achieve," Cerebras's chief executive officer, Andrew Feldman, told ZDNet in an interview by Zoom.
This study presents a dual-functional system, which is a submerged fluid-filled semi-circular piezoelectric membrane for breakwater and wave energy converter. The mixed Eulerian-Lagrangian method is used to simulate the fully nonlinear waves, deformation of the membrane and variation of voltage on the load . The simulation found that the variation frequency of the strain in the piezoelectric membrane is 2 times of the wave. There exists an optimum resistance of the load that can give the maximum electrical output power. The maximum electrical output power of the piezoelectric membrane occurs as the transmission coefficient of the wave approaches its minimum value.
The utilization of wave energy has been studied by many scholars for several decades. Most of studies focused on the wave energy converter (WEC) with higher wave energy extraction efficiency. This study presents a submerged fluid-filled piezoelectric membrane WEC , which is called SFPMWEC in the following section. Compared with traditional WECs, the wave energy extraction efficiency of SFPMWEC is lower. However, the construction cost of SFPMWEC is much lower than traditional WECs. Other advantages of SFPMWEC are easier maintenance and deployment, non-intrusion and cost sharing with breakwaters. As breakwaters, a submerged fluid-filled flexible membrane has been studied by some scholars. Ohyama et al (1989) had done experiments to study transmission and reflection waves over a submerged bottom-mounted fluid-filled membrane . Phadke and Cheung (1999,2001) studied the response of fluid-filled membrane in linear gravity waves by boundary element method (BEM) coupled with finite element method (FEM). The geometric nonlinearity due to the larger deformation of the membrane is considered in the work of Phadke and Cheung (2003). Das (2009) assumed small amplitude of surface waves and membrane deflection and used the threedimensional, coupled boundary element and finite element model to study the response of a bottom mounted fluid-filled membrane in a wave flume. Liu and Huang (2019) used the mixed EulerianLagrangian method to simulate the fully nonlinear interaction of waves and the submerged fluid-filled flexible membrane. These studies show that the submerged fluid-filled flexible membrane breakwater can reduce the transmission waves greatly at resonance of the membrane system. The resonance of the membrane system means that the maximum response of the membrane occurs as the natural frequency of the membrane system equal to the frequency of the incident wave. Therefore, it is possible to use a submerged fluid-filled piezoelectric membrane as both breakwater and WEC.
The objective of this study is to design and optimize the layout of the offshore wind farms to maximize the power at a specific location. The energy production of the downstream wind turbines decreases because of the reduced wind speed and increased level of turbulence caused by the wakes formed by the upstream wind turbines. Therefore, the overall power efficiency is lowered due to the wake interference among wind turbines. This paper focuses on using the application of a Gaussian-based wake model and different optimization algorithms like the differential evolution particle swarm optimization (DPSO). The Gaussian wake model uses an exponential function to evaluate the velocity deficit, in contrast to the Jensen wake model that assumes a uniform velocity profile inside the wake. The layout optimization framework has been created for the energy production in order to provide reference for specific conditions and constraints at the Gulf of Maine and other typical projects in the future.
With the growing requirement of energy and environmental protection, the sustainable energy like wind energy has been significantly concerned in recent years. In this case, the investigations about wind farm optimization have been concerned by lots of researchers. In wind farms, one of the most critical power reduction is caused by the wake and turbulence from the blades of previous turbines. Generally, this phenomenon would drop the power production and mechanical performance of turbines. The layout optimization of wind farms according to the wake has been an essential concern for both onshore and offshore wind energy applications.
Figure 1 indicates the annual average offshore wind speeds (m/s) in the United States. From this diagram, the Gulf of Maine have one of the greatest wind energy potential on the east coast. The Gulf of Maine locates very close to the cities such as Portland and Boston with magnificent electricity requirement. So, it is considerably valuable to investigate how to develop wind power in the Gulf of Maine.
Zhang, Hengming (College of Shipbuilding Engineering, Harbin Engineering University) | Zhou, Binzhen (School of Civil Engineering and Transportation, South China University of Technology / College of Shipbuilding Engineering, Harbin Engineering University) | Zang, Jun (University of Bath) | Sun, Ke (College of Shipbuilding Engineering, Harbin Engineering University)
This paper aims to investigate the wave resonance in the WECbreakwater gap of a dual-body hybrid system using the Star-CCM+ software. The effects of the narrow gap wave resonance on the performance of the dual-body hybrid system and the forces on the breakwater are studied. The influence of the WEC motion and the gap width of the hybrid system on the wave elevations are analyzed. Results reveal that the wave resonance in the WEC-breakwater gap significantly improves the wave energy extraction performance of the hybrid system, but has little impact on the wave attenuation performance of the hybrid system.
The high construction cost and low extraction performance of the Wave Energy Converters (WECs) reduce the economic competitiveness of the wave energy, which constrains the development of the commercialscale wave power operations. Combining WECs with the breakwater can provide an effective solution to make the wave energy economically competitive and promote the development of WECs and floating breakwaters (Mustapa et al., 2017; Zhao et al., 2019).
One of the widely studied integrated WEC-breakwater system is Oscillating-Buoy (OB) type WECs integrated with floating breakwaters, which mainly includes the single-floater integrated system (Ning and Zhao, 2016; Madhi et al., 2014; Zhang et al., 2020a) and the dual-body hybrid system (Zhao and Ning, 2018; Ning et al., 2019; Reabroy et al., 2019). The existence of the gap between two floaters of the dual-body hybrid system is one of main differences comparing with the singlefloater integrated system. The wave surface in the gap between two structures oscillates and the wave response amplitude can reach the maximum under certain wave frequency, which is called wave resonance in the narrow gap. The wave resonance in the gap between two floaters of the dual-body hybrid system can significantly affects the performance of the WEC. Thus, it is essential to study the influence of the gap wave resonance on the performance of the hybrid system.
Zhang, Zhigang (School of Mechatronics Engineering, Harbin Institute of Technology) | He, Guanghua (School of Mechatronics Engineering, Harbin Institute of Technology / School of Ocean Engineering, Harbin Institute of Technology / Shandong Institute of Shipbuilding Technology) | Liu, Shuang (School of Mechatronics Engineering, Harbin Institute of Technology) | Luan, Zhengxiao (School of Mechatronics Engineering, Harbin Institute of Technology) | Mo, Weijie (School of Mechatronics Engineering, Harbin Institute of Technology)
The effects of circumferential location-defects on the cloaking phenomenon for water waves are investigated. The cloaking condition means the absence of scattered waves radiating to infinity; that is, the cloaked structure appears invisible to a far-field observer. To accurately study this type of wave-structure-interaction problem, the higher-order boundary element method combined with wave interaction theory is adopted. Both the scattered wave energy and the wave drift forces are calculated and analyzed for the different defect cases of cylinders.
The cloaking phenomenon, originally proposed for electromagnetic waves (Pendry et al., 2006), is an effective method to protect the structure in waves. Here, cloak means no scattered waves radiate to infinity and the vertical cylinder appears invisible to the far-field observer. For water waves, the scattering cancellation method is a typical way to cloak a structure in waves.
Porter (2011) firstly proposed cloaking a vertical cylinder in shallow water by designing the topography in the region surrounding this cylinder, based on the scattering cancellation method. In order to obtain the proper topography, an optimization method was introduced to minimize the scattered wave energy of the vertical cylinder while the mild-slope equation was taken as the governing equation. Then, Newman (2012) confirmed the results obtained in Porter (2011) using a three-dimensional boundary element method. The reduction of the wave drift force on the vertical cylinder was found by Porter and Newman (2014); this puts forward a practical application of the cloaking phenomenon in ocean engineering.
However, the method associated with changing topography is effective only for shallow water. To cloak a structure in deep water, Newman (2013, 2014) proposed attaching surrounding truncated cylinders or a continuous ring. It was validated that the scattered wave energy and wave drift force of the structures can be significantly reduced to almost zero with the cloaking configuration. Following Newman’s works, Iida et al. (2014, 2015) numerically and experimentally confirmed the reduction of wave drift force by cloaking phenomenon. It was found that the wave drift force acting not only on the whole structure but also on the inner cylinder can be significantly reduced to almost zero. Read et al. (2016) performed further experimental research of the cloaking phenomenon for a circular cylinder surrounded by a circumferential array of eight cylinders to investigate the potential interferences that may affect the measurements. Zhang et al. (2017) demonstrated a periodic quasicloaking phenomenon with varying distances between the inner and the outer cylinders. Subsequently, Zhang et al. (2019a) experimentally and numerically investigated the wave elevation in the vicinity of the inner cylinder and the wave drift force on the inner cylinder under a series of different wave directions. It was found that the wave drift forces acting on the inner cylinder are closely related to the corresponding wave pattern.
Wang, Hai-Yang (Marine Design and Research Institute of China) | Cheng, Hao (College of Shipbuilding Engineering, Harbin Engineering University) | Sun, Shi-Li (College of Shipbuilding Engineering, Harbin Engineering University) | Xia, Yi-Mei (Marine Design and Research Institute of China) | Cai, Si-Yuan (Marine Design and Research Institute of China)
In this paper, extreme value of the section load on a ship navigating in irregular waves is predicted and analyzed. Design sea state method is introduced to determine the limit sea conditions and cruising sea conditions. The load of the ship navigating these sea conditions are calculated by the COMPASS-WALCS software. An extreme value analysis method of the irregular load is put forward to give the most possible extreme value and design extreme value. The rationality of the extreme value analysis method is verified by comparison with experiment data. Finally, the numerical calculation results and the test results are comprehensively compared and analyzed.
Ships navigate and work under different sea conditions throughout their service life, and they are subjected to wave force during most of its service time. The wave force in rough sea will bring great danger to ship structure. Therefore, it is of great significance to predict the maximum wave load during service time to design ship structure. The sea condition is random and thus the wave load is also random. To determine the maximum wave load, the probability method of extreme value analysis is usually adopted. In present paper, both the numerical result of wave load and experimental data is used as the input of the extreme value analysis. In summary, the numerical methods for solving wave load are developed from two-dimensional slice theory to three-dimensional theory, from linear to nonlinear theory, from rigid body boundary conditions to hydro-elastic boundary conditions. The three-dimensional potential flow theory with hydro-elastic boundary conditions is adopted here to predict the irregular random wave load on ship and this is realized by utilizing the COMPASS-WALCS software.
After obtaining the irregular random wave loads in time domain, the extreme value in long term and short term need to be predicted through probability method. The ship structure need to be designed strong enough to resist this extreme load. To predict the extreme value within a certain period of time, the probability density function need to be fitted from the time history curve of wave load. For linear wave load, the spectral analysis method is most often used and the load is assumed to conform to the Rayleigh distribution. While the nonlinear wave load is assumed to follow the Weibull distribution, its probability density function is fitted through statistical analysis of peak load in histogram. Based on the probability density functions of different sea conditions, the short-term and long-term prediction will be performed, and the short-term analysis lasts for a few hours and long-term analysis several years. Ren and Dai (1997) , Qin (2003), Xu (2008), Li et al. (2013) and Tang (2014) have given reasonable short-term and long-term forecasting methods for nonlinear loads. Chen and Shen (1996) compared the long-term value of wave bending moment with the design load. Gu et al. (1998) studied the influence of sea state on long-term prediction. IACS (1992) also stipulated the conditions for long-term extreme value analysis in the direct calculation of wave load. Luo (2016) investigated the extreme value of wave loads of a flat ship. Jiao et al. (2019) carried research on short-term prediction of wave loads and slamming loads based on experimental data of a ship.
Liu, Zhiqiang (Computational Marine Hydrodynamics Lab (CMHL), State Key Laboratory of Ocean Engineering. School of Naval Architecture, Ocean and Civil Engineering, Shanghai Jiao Tong University) | Liu, Xinwang (Computational Marine Hydrodynamics Lab (CMHL), State Key Laboratory of Ocean Engineering. School of Naval Architecture, Ocean and Civil Engineering, Shanghai Jiao Tong University) | Wan, Decheng (Computational Marine Hydrodynamics Lab (CMHL), State Key Laboratory of Ocean Engineering. School of Naval Architecture, Ocean and Civil Engineering, Shanghai Jiao Tong University)
To improve the ship hull optimization efficiency and take full advantage of the non-linear fitting capability of neural networks and the fast random search capability of genetic algorithms, the Wigley hull optimization based on artificial network and genetic algorithm is investigated in the present paper. The in-house hull form optimization software OPTShip-SJTU is firstly applied to obtain a series of new hull form and to calculate these hull resistances. Then a surrogate model of 3-layer BP neural network is constructed based on the sample data and a genetic algorithm is used to optimize the design of the Wigley ship with the total resistance minimum as the optimization objective function. During the calculation of hull hydrodynamics, potential flow solver NMShip-SJTU combined with ITTC formula is adopted to efficiently obtain the total resistance of the Wigley hull. The verification is also carried out to ensure the reliability of the optimization result. The results show that the resistance performance of the Wigley hull can be improved by designing the hull form reasonably. Besides, the form of bow bulbous is essential for the decreasing of total resistance according to the parameters sensitivity analysis. The design method—artificial network and the genetic algorithm can accurately work out the minimum resistance hull form and can be taken as a practical and efficient design tool.
With the implementation of the green ship and Ship Energy Efficiency Design Index (EEDI), how to reduce fuel consumption and carbon emission becomes the focus of the attention of shipyards and ship owners. One way to alleviate this problem is to optimize ship-shape curves. Based on the original ship, the ship-shape curves are optimized to reduce the wave-making resistance of the hull, and the ship-shape line also can be optimized with multiple objectives considering the ship's 6-DOF motion index.
The method of combining neural networks and genetic algorithm is used widely in different fields. Wang, Han, Sun, and Guo (2020) combined the elliptic basis (EBF) neural network approximation model and genetic algorithm to optimize the KP505 propeller, obtained the optimal design scheme theoretically and improved the optimization efficiency. Zeng, Ding, and Tang (2010) used the BP neural network and genetic algorithm to establish a new method for the optimal design of ship propeller based on the original map design method. Koushan (2003) used the genetic algorithm and neural networks to optimize the resistance and wave-making of a high-speed ship, and the optimization effect was obvious. Xu, Zhou, and Wang (2017) used the neural networks and genetic algorithm to optimize the ship's mooring system, and the optimization result is well. Yan, Liu, Xu, and Feng (2013) used the BP neural network and genetic algorithm to obtain the seaworthiness layout of trimaran ships with different layouts at different speeds. Wang, Lu, and Wang (2020) applied neural network and genetic algorithm to the airfoil optimization, optimized FFAW3- 301 airfoil have better aerodynamic performance. The optimization results showed that the optimization method was feasible. Lv, and Wang (2018) use the RBF neural network and genetic algorithm to optimize the strength of the ship hull after the broken. Chen and Ye (2009) firstly used the genetic algorithm to optimize the weights of the neural network, and then used the optimized neural network to predict the resistance of series 60 ship types. The neural network is simple and fast to calculate the resistance of ships, which can be applied to the calculation of ship resistance. Lin, Chen, Luo, and Wang (2019) analyzed a large number of data collected during the operation of a bulk cargo ship and used BP artificial neural network for training under the condition of considering fuel consumption. The fuel consumption rate optimization model is based on the neural network and the genetic algorithm is established. Xu (2012) used the BP neural network to optimize the layout of the trimaran with static water resistance as the target. From above all, we can realize that the BP neural network surrogate model is applied in optimization. But for hull optimization, it doesn’t been applied for the wide hull.
Wang, Tiange (Shandong Provincial Key Lab of Ocean Engineering, Ocean University of China) | Zhang, Min (Shandong Provincial Key Lab of Ocean Engineering, Ocean University of China) | Ji, Hao (China Renewable Energy Engineering Institute ) | Liao, Qichen (Key Laboratory of Far-shore Wind Power Technology of Zhejiang Province, POWERCHINA Huadong Engineering Corporation Limited )
In this paper, the damage identification of offshore floating platform mooring system is investigated. Firstly, based on the change of the axial stiffness of the mooring line, different damage severities of the mooring system are simulated and the static analysis of the platform and mooring system are calculated under a series of sea states. The Radial Basis Function (RBF) neural network is applied for damage identification to deal with the complex behavior of floater and mooring system. The numerical results show that RBF neural network has a good performance on damage identification of mooring lines.
Mooring line is the key component of offshore floating system as providing the station keeping function. During the service life, damages of the mooring system are unavoidable as a result of the action of various loads including operational and environmental forces. The structural health monitoring (SHM) system is very necessary to ensure the safety of the structures, lower the maintenance cost and prolong the service lives. A SHM system is defined as the process of implementing a damage detection strategy for engineering infrastructure related to aerospace, civil and mechanical engineering (Farrar and Sohn, 2000).
For damage detection of offshore structures, Mangal
The emergence of artificial neural networks has greatly improved this situation. The neural network has a good nonlinear mapping ability, and converts the inverse problems such as damage identification and positioning of the engineering structure into the positive problem. The earliest use of neural networks for structural damage identification was the Venkatasubramanian and Chan of Purdue University in the United States. In 1989, they first used neural networks for damage identification of large structures (Venkatasubramanian and Chan, 1989).
Dai, Huiling (Harbin Engineering University) | Lang, Jicai (Harbin Engineering University) | Pang, Fuzhen (Harbin Engineering University / Yantai Research Institute and Graduate School of Harbin Engineering University) | Wang, Yu (Harbin Engineering University)
A new polar ice-breaking method based on resonance theory was proposed and the mechanism was studied. Taking the infinite scale flat ice of 2m thickness in the polar region as an example, it is simplified as an elastic rectangular plate. Under the excitation of ice-breaking load, the vibration characteristic analysis of ice and numerical simulation of ice-breaking process are carried out, and the stress variation trend and failure mode of the ice with different excitation frequency, excitation position and excitation quantity are discussed. Results show that, when the excitation frequency is close to the natural frequency of ice, the resonance effect will be stimulated, which will lead to a significant enhancement of stress at the peak or trough of vibration mode. For the pre-breaking position, the effective directional ice-breaking can be realized by selecting the appropriate vibration mode, excitation position and excitation quantity. This paper verifies the feasibility and directivity of the polar resonance ice-breaking method, which provides reference for further research on the new polar ice-breaking equipment.
With the continuous promotion of polar scientific investigation and the upsurge of polar resource exploitation, methods of polar ice-breaking and ice-area channel opening have become a hot research issue (Bai, 2020). At present, relatively mature methods are excessively dependent on the weight of icebreaker and have high cost efficiency ratios. Therefore, the exploration of new polar ice-breaking methods with high capability has always been favored by researchers. In the actual icebreaking process, it is found that icebreaker and ice constitute a complex vibration system. Based on this, resonance ice-breaking method gradually comes into people's view.
Resonance ice - breaking method was first applied in road, aviation and other fields. In terms of road ice-breaking, Wang (2011) carried out the ice-breaking test by cutters and found that it is more efficient to break the ice with the same thickness by vibration method than static pressure method. Wan (2015) established the double-deck plate model on Kelxin foundation and derived the deformation and stress solutions under constant load and simple harmonic load, indicating that the deformation and stress of the plate under simple harmonic load are greater than those under constant load. Zhang, Li and Luan (2019) applied the resonant ice-breaking mechanism to the design of road de-icing devices. In aviation field, piezoelectric resonance deicing is used widely. Kandagal and Venkatraman (2005) used piezoelectric elements to find the resonant mode of cantilever plate in low frequency band, and selected the mode with the maximum shear stress for excitation, and finally obtained a good de-icing effect. Bai, Zhu, Miao, Li and Zhang (2014) took a planar aluminum plate as the research object, and explored the relationship among piezoelectric plate size, vibration mode and de-icing shear stress. They proposed a reverse mode that the vibration mode could be selected according to the freezing position, so as to design of piezoelectric plate size and layout. Villeneuve, Harvey, Zimcik, Aubert and Perron (2015) used a piezoelectric actuator to activate the resonant frequency of the plate, and drew a conclusion that the maximum displacement under given vibration mode can be obtained by locating the actuator at the ventral point and activating it synchronously with the ventral point. The result was applied to the structure of helicopter rotor blades.
Li, Liang (China Ship Scientific Research Center (CSSRC) national key laboratory on ship vibration & noise, Jiangsu Key laboratory of Green Ship technology ) | Liu, Dengcheng (China Ship Scientific Research Center (CSSRC) national key laboratory on ship vibration & noise, Jiangsu Key laboratory of Green Ship technology ) | Wu, Shen (China Ship Scientific Research Center (CSSRC) national key laboratory on ship vibration & noise, Jiangsu Key laboratory of Green Ship technology )
When the ship sail in the brash ice channel, it’s inevitable that the propeller will collide with brash ice due to its suction action. In order to study the propeller hydrodynamic performance changes under the brash ice impacting, the CFD and DEM coupling methods is adopted in this paper to simulate the propeller-ice-water coupling interaction near the free surface by taking the INSEAN E1619 propeller as research object. The free surface is captured using VOF model and the propeller rotation motion is realized by overset grid method. Both the brash ice motion and propeller hydrodynamics is obtained through the calculation. The results show that the brash ice distributing regularly on the free surface are speeding forward because of the suction action of the propeller. When the brash ice move close to the propeller plane, they show posture changes such as ups and downs, rotation and rolling. Parts of brash ice finally are involved into the underwater and collide with the blade, then bounce off rapidly. The propeller efficiency drops a little in the ice-water condition compared with open water condition. However the fluctuations of the propeller thrust and torque rise sharply which are unfavorable for propeller vibration and noise performance. The collision area mainly focus on the propeller tip and leading edge. It is suggested that these areas should be strengthened specially in consideration of suffering frequent ice collision.
The area and thickness of the arctic icecap continue to drop for the past few years. As a result, it provide more convenience for the commercial navigating through the arctic route. Although the commercial ship sailing in the polar region is assisted to enter into or depart from the harbor by the ice-breaker, after that the ship have to pass through the brash ice channel or the channel with the thin ice layer which is formed that year on its own. So in order to make sure that the selected main engine and propelling system can satisfy the requirements of polar navigation, the ship performance in the brash ice condition should be paid great attention to in the design stage of ship.