Dispersion of Axisymmetric Longitudinal Waves in A Bi-Material Compound Solid Cylinder Made of Viscoelastic Materials

The paper studies the dispersion of axisymmetric longitudinal waves in the bi-material compound circular cylinder made of linear viscoelastic materials.The investigations are carried out within the scope of the piecewise homogeneous body model by utilizing the exact equations of linear viscoelasto-dynamics.The corresponding dispersion equation is derived for an arbitrary type of hereditary operator and the algorithm is developed for its numerical solution.Concrete numerical results are obtained for the case where the relations of the constituents of the cylinder are described through fractional exponential operators.The influence of the viscosity of the materials of the compound cylinder on the wave dispersion is studied through the rheological parameters which indicate the characteristic creep time and long-term values of the elastic constants of these materials.Dispersion curves are presented for certain selected dispersive and non-dispersive attenuation cases under various values of the problem parameters and the influence of the aforementioned rheological parameters on these curves is discussed.As a result of the numerical investigations,in particular,it is established that in the case where the rheological parameters of the components of the compound cylinder are the same,the viscosity of the layers’materials causes the axisymmetric wave propagation velocity to decrease.

Numerical Prediction of Form Factor and Wave Interference of A Trimaran for Different Outrigger Positions

Trimaran hydrodynamics have been an important research topic in recent years.Trimarans have even been chosen for naval surface combatants.In this case,investigation of a trimaran with different outrigger positions is important and necessary for better hydrodynamic performance.This paper focuses on the numerical investigation of trimaran hydrodynamics.The trimaran model used in this study is a 1/80 scale high-speed displacement frigate-type concept developed by the Center for Innovation in Ship Design(CISD)at Naval Surface Warfare Center,Carderock Division(NSWCCD).The numerical simulations were conducted for different outrigger positions at low and moderate Froude numbers by using commercial CFD software solving URANS equations.A verification and validation study was carried out for the numerical method in one configuration and one ship velocity.The existing experimental results for the trimaran resistance in the literature were used for validation.Five different outrigger positions were analyzed and the form factor of each configuration was calculated by the Prohaska method.The total resistance was decomposed to its components using the form factor.The interference factor was calculated for each configuration in terms of total resistance,residual resistance and wave resistance.Also,wave profiles using the longitudinal wave cuts in different locations were obtained both numerically and experimentally.It was concluded that the outrigger position had different effects on the interference,total resistance and wave profile at different Froude numbers.It was also shown that the CFD results were in good agreement with the experimental data in all configurations.In conclusion,this study presents the results of interference effects for different trimaran configurations in terms of wave resistance in addition to the total resistance and residual resistance.The numerical method was validated not only with the total resistance test data but also the longitudinal wave profiles along the hull.

Emphasizing the importance of using cold-ironing technology by determining the share of hotelling emission value within the total emission

Considering the number of deaths due to air pollution,it is clear that it poses a great danger to public health.Sources that cause air pollution can be divided into two groups:natural resources(such as desert storms,fires and volcanic eruptions)and artificial sources(residences,industrial sector and motor vehicles),which cause a much higher rate of air pollution than natural resources.It is known that air pollutants originating from ships and port operations have an important share among vehicle sourced pollutants.Considering the emissions from both ships and operational reasons and their proximity to human habitats,it is obvious that port regions are important points in terms of emissions harmful to human health.The use of cold-ironing technology in ports instead of providing the energy needed from ship auxiliary machinery during the hotelling period at the port is the most effective method used to reduce the amount of ship-sourced emissions in the port area.On the other hand,it is seen that the number of ports where cold-ironing technology is used,which is extremely effective in reducing emissions harmful to human health,is quite limited.In this context,the share of the emission amount during the hotelling period in the total emission amount in the port area was calculated according to ship type and duration of hotelling in the port,and the importance of the use of cold-ironing technology in reducing the port-originated emissions was emphasized.