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  09/26/2023, 16:00 pm (UTC+8) 

  Speaker: Prof. CHEN, JIA-LIN (Julie) (National Cheng Kung University / Taiwan) (CV)

Title:  The transport process of density currents over steep slopes and its implications for subsea cable breaks 

Abstract: 

Tropical cyclone-induced density currents may cause various nvironmental hazards, such as breaks in subsea cables and pipelines. This study aimed to simulate the formation and transport processes of sediment-laden density currents using the Reynolds-Averaged Navier Stokes model. The simulated velocity and excess density of density currents were validated using measurements from laboratory experiments. The model was then applied to simulate the flow field and transport processes of density currents in the Gaoping Submarine Canyon (GPSC), where approximately 17 cable-break events were recorded from 2006-2015. The inflow concentration required for the occurrence of density currents was approximately 21 g/L, which was much lower than the conventional threshold (40–45 g/L) or the critical internal Froude number for the occurrence of density currents. The analysis revealed that the local Richardson number determines the critical state for the occurrence of the density current. The velocities of density currents and estimated distributed load were approximately proportional to the inflow concentration when the inflow concentration exceeded a critical value. The estimated distributed load on cables also increased with river discharge and settling velocities of sediment particles. This study suggested that environmental factors and inflow conditions should be considered for optimal cable design.

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10/12/2023, 16:00 (GMT+8)

Speaker: Prof. Anawat Suppasri (Tohoku University / Japan) (CV)

Title: Recent developments in tsunami hazard and risk assessment

Abstract:   

Indonesia has experienced several tsunamis triggered by seismic tsunami (the 2004 Indian Ocean tsunami) and non-seismic tsunami (the 2018 Sulawesi tsunami and the 2018 Sunda Strait tsunami). These tsunamis damaged or destroyed coastal buildings and infrastructure and caused considerable loss of life.  In addition, the volcanic eruption of the Hunga Tonga–Hunga Haʻapai generated not only the local tsunami around Tonga areas but also distant tsunamis to many locations in the world including damaging tsunami along the Pacific coast of Japan. This presentation introduces you to our latest research findings on hazard and risk assessment conducted in Tsunami Engineering Laboratory, Tohoku University, Sendai, Japan including 1) numerical simulations of non-seismic tsunamis (the 2018 Sulawesi tsunami, the 2018 Sunda Strait tsunami and the 2022 Tonga tsunami), 2) fragility functions of damaged buildings from both seismic and non-seismic tsunamis, loss functions of facilities in port industries which are examples of visualization of vulnerability data and important for recovery and reconstruction process and damage mechanism of aquaculture rafts and 3) impact from sea level rise. Two-layer model and three dimensional slope stability analysis methods were applied to the classical tsunami simulation to increase accuracy of the estimated landslide of the 2018 tsunamis in Indonesia. Numerical simulation of tsunami including air-water coupling effect was added to the model to reproduce the 2022 Tonga tsunami. We assessed the empirical tsunami fragility to the buildings inventory of tsunami tsunamis. We also developed loss functions by quantifying damage criteria and downtime for different port industries based on not only the 2011 earthquake but also other earthquakes until 2021. Our simulation shows how we quantify the sea-level-rise impact on tsunami hazards in terms of both flow depth and inundation area. These information on both hazard and vulnerability will be useful for improving accuracy of tsunami risk assessment as well as input information for decision making during emergency response. The presentation will end by sharing the current situation of mismatch between scientific information related to tsunami risk provided by researchers and the response of local stakeholders.