ObjectivesAiming at application of digital twin technology to marine power system (MPS), this paper investigates technology route being adopted to implement digital twin in the design process of MPS, which it exhibit features of high integration and full life-cycle development. MethodsA research of digital twin technical system is done in accordance with the characteristics of MPS development, making use of a set of advantages of digital twin, such as virtual reality fusion and real-time interaction, iterative operation and optimization, and all-element, all-process data-driven,etc. ResultsThe structures of digital twin technology top-level system framework, platform construction system, key technology system and digital twin model construction system are constructed.ConclusionsThe results of this study can provide quantitative support for the demonstration applications and practices of MPSs based on digital twin technology systems.

ObjectivesIn order to realize the digitalization, networking and intellectualization of ship steam power systems, this paper puts forward an application system based on a digital twin model.MethodsThe "four-dimensional thought model" of a ship steam power system based on a digital twin is proposed, covering the four dimensions of physical object, process element, life cycle and virtual space. The "five order system model" of the whole life cycle of the power system is then established, including five typical stages: concept demonstration, system design, general assembly and construction, trial run, and operation and maintenance. Advanced technologies such as big data, internet of things, cloud computing, artificial intelligence and model-based system engineering are introduced, and the overall digital twin "seven-layer architecture model" of a ship steam power system is formed, composed of the physical layer, interface layer, data layer, model layer, scheduling layer, function layer and application layer.ResultsThe verification results of the virtual design analysis and test platform of the ship steam power system show that the digital twin system framework can effectively support the system's scheme design, operation analysis and test scheme evaluation, and realize interaction and cooperation between the physical space and virtual space throughout the whole life cycle of the ship.ConclusionsThe results of this study can provide valuable references for the overall digital design of ship steam power systems.

ObjectivesTo address the unstable power output of photovoltaic systems on the mobile platforms of ships and power fluctuations caused by surge loading/unloading, an energy management strategy involving a photovoltaic hybrid energy storage system based on optimal power distribution is proposed.MethodsIn view of the shortcomings of the traditional limit management method, the filter time constant is adaptively adjusted according to the different zones of the charged state of the supercapacitor, thereby realizing the optimal power distribution of the hybrid energy storage system. Meanwhile, the control strategy and working mode of each converter are analyzed.Results The Matlab simulation results and engineering test results show that the energy management scheme and converter control strategy can effectively improve the overcharge or over-discharge problem of hybrid energy storage systems, not only ensuring the stability of the DC bus voltage, but also improving the dynamic response and coordination of the system.ConclusionsThe results of this study can provide references for the energy management of photovoltaic systems on mobile platforms.

ObjectivesDue to many disadvantages in obtaining the fault type data of large marine diesel engine through bench testing or real ship, the numerical calculation of diesel engine fault simulation is particularly important, which is of great significance to the construction of diesel engine fault troubleshooting and data-driven intelligent fault diagnosis systems.MethodsBased on AVL BOOST software and bench test data, the diesel engine simulation model was established to verify that the simulation model meets the accuracy requirements under four load conditions. Based on the model of full load condition, the control variable method was used to simulate the typical faults of a diesel engine, such as combustion start angle, single cylinder stoppage and crankcase gas escape, and the calculated data results were analyzed.ResultsThe results show that, the maximum combustion pressure in the cylinder increases by 17.4% when the start angle of combustion is advanced by 5°. After No.1 cylinder is stopped, the effective fuel consumption rate increases by nearly 15%. Compared with different cylinders, the change range of the characteristic parameters of No.2, No.3 cylinders is small. With the increase of effective piston channeling air clearance, the characteristic parameters basically show a linear expansion trend. When the channeling air clearance is 0.04 mm, some characteristic parameters drastically increase, such as the fuel consumption rate increasing by nearly 40%.ConclusionsThe results obtained by the simulation can be used as an important basis for the recognition of fault states and diesel engine intelligent fault diagnosis system construction, to explore a new approach for marine diesel engine intelligent fault diagnosis technology.

ObjectivesRegarding transonic flow occurring at the throat of the stator blades of axial flow turbines at high subsonic and transonic speeds, it is will need a long period of time to have 3D reseach and to obtain the characteristic parameters. Therefore, an cost-effective approach for predicting turbine characteristic is required.MethodsThe existing loss models are integrated to predict turbine characteristics via one-dimensional programming and verify them via three-dimensional numerical simulation.ResultsThe results show that the relative error of the isentropic stage-temperature ratio is 11.53%, that of the stage-expansion ratio is 11.77% and that of the reaction degree is 14.23%. Whether transonic phenomena occur at the static blade is judged accurately. The adiabatic index of the outlet temperature of the rotor blade is used to estimate the characteristics of the single-stage turbine accurately. ConclusionsWithin the range of acceptable error, this method allows the fast and accurate prediction of transonic turbine characteristics, thus reducing calculation time.

Objectives To meet the use requirements of a steam-powered system in different working conditions, it is necessary to study the design of the condensate water distribution and pipeline optimization.MethodsUsing the Flowmaster software, a simulation model of a ship's condensate water system was created. The pressure and flow rate in the condensate water system were studied in different working conditions of the steam-powered system. Based on this, two optimal design suggestions, reducing the installation height of the water tank and adjusting the system pipeline connection, were presented.ResultsThe calculation results showed that the maximum storage capacity is 0.128 (normalization result) when the openings of the throttle valve and circulation valve are 30% and 45% respectively, in reduced working conditions. Moreover, when the throttle valve opening is less than 13%, the condensate water system will not be able to store water. The maximum storage capacity was 0.404 (normalization result) when the openings of the throttle valve and the circulation valve were 90% and 18% respectively, in increased working conditions. The distribution coordination of the system was also better. Two optimization designs can effectively improve the condensate water distribution in reduced working conditions.ConclusionsThe research results can provide a reference for the optimal design of the actual ship's condensate water system.

ObjectivesTo address the impact of non-zero sideslip angle and input saturation on the heading control of a surface ship, a method based on a backstepping control algorithm is proposed.Methods The actual sideslip angle is obtained through the relative velocity, and heading angle error is amended using the sideslip angle. A pre-filter is used to minimize the impact of speed change when the heading alters. Hyperbolic tangent and Nussbaum functions are introduced to approximate the input constraint, an adaptive law is designed to estimate approximation errors and disturbances in the yaw direction, and a command filter is proposed to simplify the design of the backstepping controller. The stability of the control system is proved by Lyapunov's theory.ResultsThe simulation results show that the proposed controller can effectively reduce the heading output error of a surface ship while simultaneously maintaining a small control input torque.ConclusionsThe study results can provide reference for the heading control design of surface ships.

In view of the development demand and challenge for the naval ship technology, this paper briefly analyzes the necessity and urgency of developing the application engineering of composite structures, from the perspective of the overall ship performance, integrated stealthiness, and integrated logistics support. Taking the application of submarines in western navies as examples, this paper summarizes the development approaches of the application of composite structures in naval ships, and puts forward and expounds upon three "integrated" technical features of the application engineering of functional composite structures. Moreover, a discussion is included to emphasize the definitions concerning overall and structural design technology of naval ships, as well as their connotation and composition of key technology. This paper concludes with the recommendation that the top-level design should be constructed as soon as possible, in the meantime, enhancing the capability of basic design research and establishment of standardization systems in response to the future development requirements demanded of Chinese naval ships in this field.

ObjectivesThe hydrodynamic performance under different bailer conditions based on numerical and experimental methods was investigated. MethodsThe hydrodynamic performance of the seaplane with different displacements under different speeds was studied using an experimental method, and the viscous flow field of the seaplane under three conditions（without bailer, bailer closed, bailer lowered) at different speeds was computed.ResultsThe results show that at the same displacement the total resistance and heave amplitude of the seaplane increase, the trim angle decreases, when the speed increases; with displacement increases, the total resistance, trim angle and heave amplitude of the seaplane increase; while the bailer lowers, the total resistance and heave amplitude of the seaplane increase, the trim angle decreases; the effect on the hydrodynamic performance is not obvious as the bailer closes. ConclusionsThe results of this paper are of great significance to the optimal design of water pumping systems of the seaplane.

ObjectivesAs many factors influence decision-making in the course of warship water reuse scheme optimization, and such factors cannot be fully quantified and sequenced, it is necessary to build a scientific and reasonable optimization evaluation model.MethodsBased on the grey analytic hierarchy process (AHP) and Delphi method, an evaluation index system for warship water reuse schemes with a hierarchical structure is constructed for the first time. The grey evaluation method of whitening weight function is used to quantify the evaluation elements and carry out the comprehensive evaluation of different schemes.ResultsThe calculation results show that the obtained comprehensive evaluation results are reasonable, and the consistency test of the total hierarchical ranking meets the index requirements.ConclusionsBased on expert judgment, grey analytic hierarchy process can comprehensively adopt opinions from all aspects, reduce the arbitrariness and subjectivity of judgment, and improve the scientificity and rationality of scheme selection. It is suitable for optimal decision-making of multi-schemes and multi-objectives water reuse system design for warship.

ObjectivesAiming at problems such as low accuracy, low efficiency and even a lack of algorithms in the calculation of moving spaces in existing virtual assembly and maintenance, and combined with the actual needs of the virtual assembly and maintenance of the ship, this paper puts forward a method for quickly and accurately calculating parts in a moving space for the purpose of spatial collision verification.MethodsBased on the intersection detection algorithm of a hierarchical bounding box and triangular patches, we improve the transformation method of the box and triangular patches in a moving space, then obtain the interference distance according to the method of dichotomy and increment, thus proposing an algorithm for spatial collision verification and distance verification. Finally, CATIA secondary development technology is used to design and develop a rapid space verification module that can verify the rationality and accuracy of the algorithm.ResultsThe examples show that in models of different levels of complexity with more than 2 000 parts, the calculation time of spatial collision is less than 100 ms and that of spatial distance is about 0.5 s. ConclusionsThis algorithm can have a significant auxiliary effect on the design of ships when designers consider assembly and maintenance space, thus effectively reducing the ship design cycle, production cycle and maintenance cycle.

Objectives In order to improve the performance of traditional absorbing materials, a high-absorptivity broadband absorber is designed.MethodsThe absorber consists of a resistive film, dielectric substrate and metal ground plate. The element unit of the resistive film is composed of a Jerusalem cross unit and outer square loop.ResultsThe simulated results indicate that the absorption of the designed absorber is more than 90% in the frequency range of 2.9–5.1 GHz, and an absorptivity peak of 99.4% can be achieved. Absorption performance can also be maintained in wide-angle cases and polarization-insensitive cases. ConclusionsThe absorber proposed in this paper has significance for the design and application of broadband absorbers.

ObjectivesSubmarine construction is a multi-procedural coupled process. With the development of modular construction mode, its "outfitting" in a broad sense includes the whole process of material forming, structure building, equipment piping system manufacturing, installation and painting, in the design phase, precisely allocated top-level submarine outfitting plan can effectively influence the submarine construction process and ensure the overall functional performance.MethodsWith a focus on submarine outfitting between pressure and non-pressure hulls, the precision allocation process is suggested, the connotations and scope of the application of the precision allocation method based on the dimensional chain are discussed, and finally the key elements between pressure and non-pressure hulls and their precision control objects are identified according to the dimensional chain principle, and any unknown precision items throughout the outfitting process are allocated.ResultsThe allocation value of unknown precision items in the list of key outfitting items is obtained to meet construction precision requirements.Conclusions A precision allocation process and method, including materials, structures, equipment, and installation, is formed, which can be used to guide the processes and process designs of submarine outfitting.

ObjectivesIn order to develop a computation method for the corrugated core panel bending issue and solve the bending deflection and stress of such panels, an equivalent stiffness method is proposed. MethodsFirst, the middle cores of these sandwich panels are taken as equivalent to orthotropic elastic materials, then the equivalent elastic modulus of the cores are solved by Castigliano's theorem and the integral stiffnesses of the sandwich panels are calculated by laminated plate theory. According to the solved integral stiffness constants, the distribution of bending deflection is achieved by solving the orthotropic plate bending equilibrium equations, and stress distribution is derived by adopting Hooke's law.ResultsIt is validated that the stiffness error evaluated by this proposed method is -6.98% compared with the method in literature(Ref.[7]), the maximum error of deflection is -2.01% and stress is 3.63%, which correspond with the FEM results.ConclusionsThis proposed method for calculating integral stiffness through layered accumulation not only avoids the complicated derivation of applying the method of Ref.[7] completely, but also satisfies calculation precision when computing the bending issue.

ObjectivesFor the ship structures subjected to pulse loading such as explosion or slamming, research on the "saturated impulse" phenomenon shows that designing hull structures with maximum loading amplitude and total impulse is unreasonable. Hence, exploring the application of saturated impulse in engineering is necessary.MethodsThe concept and development of the saturation phenomenon are first summarized. Then, taking a cabin internal explosion as a typical example, the loading curve and structural response characteristics are analyzed by FEM. Following that, the complex blast loadings are equivalent to the rectangular pressure pulse loadings of the saturated equivalent method, and the response of structures under the equivalent loadings are calculated by theoretical and numerical methods.Results The results show that the saturated impulse phenomenon exists in a wide array of cabin explosions due to the existence of quasi-static overpressure. In practical engineering problems, the explosion loading will produce large plastic deformation (usually more than 10 times the plate thickness), with an error of less than 10% between the analysis results and the numerical simulation results, by using the equivalent method based on saturated impulse.ConclusionsBy studying the cabin internal explosion saturation phenomenon, the results of the plastic dynamic response of the structure can be given more accurately, and repeated complex nonlinear numerical calculations can be reduced in structural optimization, so as to carry out the anti-impact design of the hull structure more effectively.

ObjectivesIn order to study the damage characteristics of a typical cabin explosion load on stiffened plates, the explosion load in a cabin is divided into the initial explosion shock wave load and quasi-static air pressure load, finite element analysis software LS-DYNA is used to simulate and calculate the damage characteristics of fixed stiffened plates under the explosive load.MethodsIn this paper, the deformation characteristics of the stiffened plate under the same impulse and peak load are simulated, and the damage characteristics of the stiffened plate under the initial explosion shock wave load, quasi-static air pressure load and the combined action of the two loads are analyzed.ResultsThe results show that when the impulse acting on the stiffened plates is equal and the load action time is less than 0.05 times the vertical first-order natural vibration period, the final deflection value of the stiffened plates is near the maximum value. When the load peaks are equal, there is a saturation impulse value, after which the loading time no longer affects the final deformation of the stiffened plates.ConclusionsThe final deformation of stiffened plates under an explosion load in a cabin is not a simple superposition under the action of two loads; the combined effect of the two loads enhances their damage.

Objectives A simulation of steel/polyurea composite structures under close-range air blast loading was conducted, in order to study the improvement mechanism and analyze the influence of the polyurea backing layer on the blast-resistant performance of steel plates.MethodsThe deformation/failure process and energy absorption mechanism of steel/polyurea composite structures under close-range air blast load-ing were numerically investigated, and the rationality and effectiveness of the numerical investigation were verified by related experiments. On this basis, the influence of the thickness matching and strength matching between the front steel plate and the back polyurea layer on the deformation/failure and energy absorption of the structure were analyzed.ResultsThe results show that the polyurea layer had two caving phenomena under blast loading, and the kinetic energy of the fragment was dominant in the total absorption energy of the polyurea layer. With the increase of the thickness matching between steel plate and polyurea layer, the deformation of the steel plate initially decreased, and then increased. With the increase of strength matching, the deformation of the front plate, and the energy absorption ratio of polyurea decreased monotonically. The kinetic energy of the fragment produced by caving was the main energy absorption mode of the polyurea layer. Under conditions of constant overall surface density, the steel/polyurea composite structure has the optimal thickness matching of anti-explosion performance. The increase of strength matching will decrease the energy absorption ratio of the polyurea layer, and the overall blast-resistant capacity will be improved.Conclusions The research in this paper serves as a valuable reference for the future study of the blast resistance capacity of polyurea-coated 304 stainless steel plates.

ObjectivesDue to the aging and illegal operation of crane equipment during hoisting operations on offshore platforms, dropped object accidents are the most prevalent type of accident, of which the dropping of slender rod-like objects such as drill collars and casings is the most common. Due to the small contact area and high velocity, the failure of the partial-plate structure is often caused, which requires attention.MethodsThis paper studies the specific deformation mechanism of a deck under the impact of dropped slender rods at different impact angles while considering the influence of the impact angle on damage to the deck. A new deformation model is proposed for decks subject to impact loads at different impact angles. Based on this new deformation model, a prediction method which considers the influence of the impact angle is obtained on the basis of the plastic mechanics theory.ResultsThe results show that a small impact angle will cause great structural damage and deformation, as well as high structural energy absorption. According to the structural response, the impact angle can be divided into four angle intervals. The energy absorption curves obtained from the analytical method and simulation are similar in value and change trend.Conclusions When a rod-like structure hits a deck at a certain angle, the shape of the plastic deformation area of the deck changes with the depth of the collision. The analytical results of the deformation characteristics of the deck at each stage can provide valuable references for the preliminary structural design and assessment of the crashworthiness of the deck structures of offshore platforms.

ObjectivesIn order to solve the problems of the local buckling effect and obvious structural response and buckling failure force caused by high concentrated load, a meshless numerical method is proposed to simulate the problem.MethodsBased on discrete nodes in the problem domain, this method establishes a compact support function and uses the weighted residual method to establish a discrete equation of the system displacement field. Then uses the moving least square method to construct the shape function of the discrete nodes to finally obtain the approximation function of the displacement function. Finally, combined with the simplified buckling evaluation method, the eigenvalues of the buckling equation are effectively solved to reduce the order, and a more accurate buckling load factor is obtained.Results The effectiveness of the proposed method is verified by the comparison between the proposed method and the traditional calculation method through the demonstration of an example. The calculation results of the proposed method also have a higher degree of agreement with the original structure.ConclusionBy analyzing the characteristics of meshless numerical analysis of perforated plate beam, a new method is provided for the analysis of various shapes of honeycomb plate beam structure.

ObjectivesA plate forming technique during ship construction will not only influence the cost and scheduling of fabrication, but also the accuracy of its formation will influence hydrodynamic performance and operating costs.MethodsIn order to cope with such problems as low efficiency and poor accuracy during double-curvature plate forming, induction heating was used to provide an advanced heating source for plate bending with a typical sail shape. By using advanced thermal elastic plastic finite element (TEP FE) analysis and elastic FE analysis on the moment of bending, the mechanical response during plate bending was then represented, and the computed results strongly correlate with the measurements. Moreover, the plate forming process parameters' mechanism of influence was also clarified, and a method using linear approximation with an iterative bisection was proposed to obtain the line heating position and moving speed of the induction heating coil during induction heated plate formation, while the planned processing parameters were also validated and confirmed using a numerical analysis.ResultsThe computed out-of-plane bending deformation within the planned parameters well agrees with the target bending deformation.ConclusionsThe engineering application of the plate bending method using linear approximation with iterative bisection has also been confirmed, which provides new solution for process parameter optimization during plate bending with induction heating.