| In order to meet the performance requirement of mechanical strength and fluid dynamics,30%~40% of ship hull plates usually have a complex curvature distribution,which needs to be repeatedly processed by skilled workers using oxyacetylene flame as heat source.This method has low production efficiency and generates a large amount of carbon dioxide and noise.However,electromagnetic heating method has abundant advantages,including easy control of heat source,clean environment,high heating efficiency,etc.,and can solve the problems that the oxyacetylene flame itself is difficult to avoid.Therefore,this dissertation mainly studies the forming process for ship hull plate through using electromagnetic heating method.During electromagnetic heating process for ship hull plate,maximum temperature of upper surface may be excessively high due to concentrated heat source resulting from skin effect,thereby causing degradation of mechanical material properties.Otherwise,maximum temperature of bottom surface may be considerably low,that is,the heating depth is small and cannot produce sufficient deformation.In view of the proposed problems above,this dissertation firstly develops a double-circuit and water-cooled inductor with opposite-direction current and gap(ODIG inductor).In order to achieve the movement of inductor,the model of ODIG inductor is dynamically moved and the air model MA around it is dynamically reestablished.Hence,a mutuallycoupled multi-physics numerical analysis algorithm is developed and the corresponding finite element model is established based on ANSYS,then the reliability verification is carried out through building an experimental device platform.The effects of technological process parameters on characteristic shape parameters(Tum,b and h)of temperature field and deformation(?z and ?z)are investigated.The dimensionless predictions of characteristic shape parameters(Tum,b and h)of temperature field,and the intelligent prediction model of deformations are established,respectively.Finally,based on the previous method,the heating performances for three different inductors are compared with each other and composite quality indicator F of characteristic shape parameters of temperature field is proposed to optimize the parameters of ODIG inductor.The main research contents of this dissertation are as follows:1.Firstly,this dissertation develops a double-circuit and water-cooled inductor with opposite-direction current and gap(ODIG inductor)to improve heating depth and deformation for ship hull plate.The mathematical models of electromagnetic field,temperature field and deformation field using ODIG inductor as heat source are deduced in detail.Then the boundary conditions of each physics model are analyzed,the mutuallycoupled methods among different physics fields are investigated,and the solution methods of the models above are discussed.It can be concluded that analytic solution cannot be obtained.Then the method through dynamically moving the ODIG inductor model and reestablishing the air model MA around it is proposed,thus the moving mutually-coupled electromagnetic-thermal algorithm is developed.This can solve the problem of tremendous mesh model using moving material characteristics method of inductor.Considering the temperature-dependent characteristics of electromagnetic and thermal materials,the mutually-coupled electromagnetic-thermal finite element model is established by ANSYS and the obtained transient temperature field is employed as the load to establish coupled thermal-structural finite element model.Finally,analysis of examples for electromagnetic,temperature and deformation field are carried out,respectively.It can be concluded that the heat generation rate distribution can be regarded as two semi-ellipsoids.The space between the front and rear coil can promote heat conduction among thickness direction.The front coil acts as a preheating and the rear coil can be regarded as reheating to improve heating depth.In addition,the deformation along heating line path tends to be steady.2.Experimental device platform for ship hull plate fabricated by moving electromagnetic heating method is firstly established and the corresponding performance parameters are introduced in detail.Meanwhile,a CNC human-computer interaction system is developed by C++,and the function,operation flow and parameter setting of each module are presented.Then two different sizes of plates are taken as research object to validate the reliability of the proposed finite element model through comparing with the temperature profiles of measurement points(C1,R1,S1;C2,R2,S2)and the transverse bending deformation distribution at different X-axis position obtained from experiment research.It can be concluded that the proposed multi-physics finite element model above has sufficient reliability,and the deformations for two different sizes of plates are considerably consistent.3.Characteristic shape parameters of temperature field,including maximum temperature Tum,heating width b and depth h,are proposed to evaluate thermal deformation for ship hull plate fabricated by moving electromagnetic heating method.Hence,the effects of several technological parameters,including gap g between inductor and plate,moving speed v,peak Ip and frequency f of current source,and thickness H of steel plate on characteristic shape parameters(Tum,b and h)of temperature field for ship hull plate are studied through using the proposed mutually-coupled electromagnetic-thermal finite element model in the previous chapter.Then a five-level multi-factor orthogonal test research scheme is constructed to analyze and obtain four principal influence factors through employing multivariate variance analysis,including g,Ip,v and f.The dimensionless regression prediction models for characteristic shape parameters(Tum,b and h)of temperature field are established,respectively.It can be concluded that the models can efficiently predict the parameters(Tum,b and h)under different process parameter schemes and thus prevent degradation of material mechanical properties and increase heating depth.Meanwhile,it can also contribute to planning the appropriate combination of process parameters for the next phase.4.Effect of gap g between inductor and plate,moving speed v,peak Ip and frequency f of current source,and thickness H of steel plate on transverse deformation(transverse bending angle ?z and shrinkage deformation ?z)for ship hull plate by electromagnetic heating method are analyzed through using the proposed mutually-coupled multi-physics finite element model in the previous chapter.The gap g between inductor and plate,moving speed v,current peak Ip,thickness H of steel plate and heating length L are taken at 5 levels,respectively,to perform full level test and 200 groups are randomly selected as test scheme.Finally,deformation properties(?z and ?z)at 5 different positions Lm along heating direction are obtained to construct intelligent prediction model.Consequently,it can also provide support to plan combinations of technological parameters and thus contribute to developing intelligent forming equipment for the next phase.5.On the basis of the previous research,two other inductors with different structures from ODIG inductor,including single-circuit inductor(SC inductor)and double-circuit and water-cooled inductor with opposite-direction current and no gap(ODING inductor),are firstly introduced.Then the corresponding mutually-coupled multi-physics finite element models for each inductor are established,respectively.Therefore,heat generation rate and characteristic shape parameters(Tum,b and h)of temperature field are compared with those obtained from ODIG inductor to verify the perfect performance of ODIG inductor developed in Section 2.1.Finally,an innovative method employed for constructing composite quality indicator F of characteristic shape parameters(Tum,b and h)of temperature field is proposed to optimize structure parameters of ODIG inductor.The obtained combination of inductor parameters is compared with those through using transverse deformation(?z and ?z),respectively.It can be concluded that only characteristic shape parameters(Tum,b and h)of temperature field are needed to achieve the optimization of inductor parameters,and deformations(?z and ?z)are not required.In other words,only electromagnetic-thermal analysis is required to obtain the characteristic shape parameters(Tum,b and h)of temperature field without time-consuming thermal elastoplastic analysis.This proposed method can also be employed to optimize the parameters of other structural inductor. |
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