Offshore support and naval vessels operate in complex and hazardous environments facing the risk of impact from falling objects, collisions and projectiles. Accurate impact localization is essential to guarantee safety of the individuals, the environment and the asset.

This thesis explores the feasibility of impact localization on steel plates and stiffened panels by utilizing the information carried by the stress waves generated during impacts. These waves propagate along the surface of the structure as Guided Ultrasonic Waves (GUW). The inherent time reversibility and spatial reciprocity properties of the wave equations allow the use of Time Reversal (TR) process of the recorded wave signals to localize impacts.

The study combines experimental testing with an analytical framework. Small scale controlled impact experiments were performed in the Structures Laboratory at TU Delft while large scale tests were conducted onboard a Shoalbuster vessel at DAMEN Shipyards in Gorinchem, allowing the assessment of the scalability and robustness of the method. Acoustic Emissions (AE) were generated through Pencil Lead Breaks (PLBs) and instrumented hammer impacts. TR was implemented virtually in the frequency domain using an analytical propagation formulation that models dispersion and wave amplitude decay due to geometric spreading. The novelty of the present research lies in extending the analytical TR framework from plates to stiffened panels by removing the effect of stiffeners in back-propagation. This is achieved by introducing a scalar Transmission Coefficient (Tc) into the analytical model.

In the small scale experiments two configurations were tested, a plate and a stiffened plate with a stiffener located at the midspan, both measuring 400 x 400 mm². The average localization error for the plate ranged from 11 to 15 mm, while stiffened panel tests showed slightly higher errors in the order of 12 to 23 mm, depending on the impact type. Larger errors were observed for the instrumented hammer impacts. In the large scale tests, a 7500 x 2000 mm² area was monitored. Localization accuracy decreased due to increased structural complexity, including variable plate thickness, multiple stiffeners, and high acoustic noise from parallel steel work activity. A mean localization error of 662 mm was achieved, demonstrating the method’s scalability and potential for real world application.

These results confirm that TR of GUW is a feasible method for impact localization across different scales. The developed methodology shows potential for extension to composite materials and towards a complete impact identification framework that includes impact severity estimation, contributing to the development of integrated Structural Health Monitoring (SHM) systems capable of detecting, localizing, and quantifying structural impacts.

Fiber Reinforced Composite (FRC) materials are gaining great popularity in marine structures because of their excellent strength-to-weight ratio, low density, and provided freedom in the design process. However, the use of FRC materials comes along with relatively large uncertainties in material properties and structural integrity after manufacturing and during its use. In this research a new in-situ non-destructive stiffness assessment methodology is proposed. This methodology is based on a coupling principle between the laminate structural stiffness properties and the ultrasonic guided wave characteristics of FRC materials. In the methodology, a range of possible stiffness properties is defined based on the structural information available for a structure of interest. The average relation between this stiffness range of interest and corresponding wave characteristics is described using a set of coupling coefficients which are determined using numerical simulations. For this, a batch of reference laminates is constructed that covers the entire stiffness range of interest. Input for the system are the group velocities of the zeroth-order symmetric and antisymmetric guided wave modes, measured on the structure of interest. The potential of the proposed methodology is evaluated using a numerical feasibility study based on numerical simulations. Good results were obtained for different test scenarios, varying in the amount of structural information available on the structure of interest. Thereafter, the in-situ application of the methodology has been examined in an experimental setup. Good measurement and analysis times were achieved by using a compact measuring device that is capable of recording the wave signal in five directions simultaneously. A reliable accuracy assessment of the in-situ application of the methodology was, however, difficult to obtain due to the lack of reliable reference studies. Therefore, in future research reliable reference information should be gathered. Additionally, a next step for future research should focus on decreasing the amount of information available on the structure of interest.