Modeling of Fatigue Wear of Viscoelastic Coatings

A new model for studying the kinetics of fatigue wear of a viscoelastic coating bonded to a rigid substrate is proposed. The fatigue mechanism is due to the cyclic interaction of the coating with a rough counterbody, which is modeled by a periodic system of smooth indenters. The study includes the solution of the problem of sliding contact of the indenter at a constant velocity along the viscoelastic coating, the calculation of stresses taking into account the mutual effect, and study of the process of damage accumulation in the material. The calculation of the damage function of the surface layer was carried out using the reduced stress criterion. Assuming the possibility of summation of accumulated damage, two processes were considered: delamination of surface layers of the coating and continuous fracture of the surface by the fatigue mechanism. The effect of the sliding velocity and viscoelastic properties of the material on the damage accumulation and the coating wear rate was analyzed. Two types of load, constant and stochastically varying, were used in modeling and analysis. It was found that the rate of fatigue wear of the coating increased and then became constant.

Noise Measurements and Mitigation for a Foil Assisted Catamaran

Noise control recommendations and mitigation approaches for a foil-assisted catamaran become very sensitive when it comes to weight tradeoff. While weight control on a fast marine craft is critical, it reaches the uppermost limit when it comes to a foil-assisted catamaran. A foil-assisted catamaran is very sensitive to weight growth as well as the Longitudinal Center of Gravity (LCG) of the vessel in terms of reaching foil-assisted planing speeds. An increase in weight leads to a slow pre-planing speed which does not generate sufficient foil lift to transition the vessel into full planing speed. Whereas incorrect LCG of the vessel leads to wrong foil attack angle and thus leading to insufficient foil lift. This paper covers design philosophy, risk management, onboard measurements, weight management, mitigation approaches, and recommendations associated with the design of a 61 ft foil-assisted catamaran designed to reach 38+ knots and meet specific noise criteria limits at the maximum cruising speed as well as other operational conditions. An initial solution was applied, and the noise reduced at intermediate design speeds, however, at design cruising speeds the noise levels still exceeded the limits. Further computational analyses and mitigation methods such as insulation, mass-loaded vinyl, joiner barriers, viscoelastic coatings, trim adjustment, and floating floors were implemented on a trial-and-error basis to minimize the overall weight added to the vessel while achieving vessel design speed.

On the Dispersion and Attenuation of Guided Waves in Tubular Section with Multi-Layered Viscoelastic Coating — Part I: Axial Wave Propagation

Guided modes admissible in elastic hollow pipes are derived to establish their dispersion and attenuation characteristics in the presence of multi-layered viscoelastic coatings. Longitudinal waves propagating in the axial direction in response to displacement continuity boundary conditions signifying perfect interfacial bonds are evaluated against a baseline uncoated tubing. Viscoelastic bitumen and epoxy are coating materials applied to improve pipeline reliability. The impact of viscoelastic coating layers on wave dispersion and attenuation are investigated by incorporating complex material properties in the characteristic equation. The real and complex roots of the corresponding characteristic equation are determined, allowing the phase velocity and attenuation dispersion to be depicted as functions of the propagation frequency. The effects of varying attenuation parameter and coating thickness are also examined. Viscoelastic protective materials are found to have a substantial impact on the propagation and attenuation of longitudinal waveguide modes.

Guided Wave Propagation in Tubular Section With Multi-Layered Viscoelastic Coating: Part I — Axial Waves

Propagating waves physically admissible in a tubular section are derived to establish their dispersion characteristics in response to the presence of multi-layered viscoelastic coatings. Longitudinal waves that propagate in the axial direction are studied. To characterize the hollow cylinder with coating layers, wave dispersion and attenuation are studied using the “global matrix” technique. Since each layer is considered to be perfectly bonded to each other, displacement and strain continuity are imposed as the interfacial boundary conditions. Viscoelastic coating materials such as bitumen and epoxy serve to improve pipeline reliability, but they also dampen and dissipate wave energy. The viscoelastic materials are studied as well. By replacing the real material constants with complex material constants in the characteristic equation, the impact of the viscoelastic coatings on wave dispersion is established. Bisection method is followed to find the real and complex roots of the three characteristic equations derived. Roots thus obtained are manipulated to allow the phase velocity and attenuation dispersion to be plotted against frequency. The dispersion of phase velocity and wave attenuation for coated pipes are evaluated against a baseline model which is the bare, uncoated tubing to establish the propagation characteristics of the guided shear and longitudinal waves in the presence of multiple coating layers. The effects of increasing attenuation parameter and coating thickness are also investigated.

Guided Wave Propagation in Tubular Section With Multi-Layered Viscoelastic Coating: Part II — Circumferential Waves

Propagating waves physically admissible in a tubular section are derived to establish their dispersion characteristics in response to the presence of multi-layered viscoelastic coatings. Shear and longitudinal waves along the circumferential direction were investigated. To characterize the hollow cylinder with coating layers, wave dispersion and attenuation are studied using the “global matrix” technique. Since each layer is considered to be perfectly bonded to each other, displacement and strain continuity are imposed as the interfacial boundary conditions. Viscoelastic coating materials such as bitumen and epoxy serve to improve pipeline reliability, but they also dampen and dissipate wave energy. The viscoelastic materials are studied as well. By replacing the real material constants with complex material constants in the characteristic equation, the impact of the viscoelastic coatings on wave dispersion is established. Bisection method is followed to find the real and complex roots of the three characteristic equations derived. Roots thus obtained are manipulated to allow the phase velocity and attenuation dispersion to be plotted against frequency. The dispersion of phase velocity and wave attenuation for coated pipes are evaluated against a baseline model which is the bare, uncoated tubing to establish the propagation characteristics of the guided shear and longitudinal waves in the presence of multiple coating layers.