Experimental and numerical determination of the shoreline motion during the run-up of tsunami waves on a plain beach

Master's Thesis , 2014 , 84 Pages , Grade: 1.7

Geography / Earth Science - Oceanography

Within this master thesis the behaviour of long periodic waves during their run-up on a plain beach was investigated via physical and numerical modelling. In the experimental part, for seven leading depression, non-breaking sine waves with surf similarity parameters between 3.1 and 15.6 the wave velocity, wave height and run-up on a plain beach were determined. In addition, the motion of the initially still shoreline, i.e. run-up/ run-down process, run-up/ run-down velocity, wave acceleration, maximum run-up and maximum run-up velocity, was determined via two high-speed cameras. Comparison of the aforementioned characteristics with the theory revealed good agreement; deviations can mostly be attributed to experimental performance.
For wave generation a new volume driven wave generator was used. Long waves are generated by a pair of high capacity pumps under control of a proportional-integral-derivative controller (PID-controller). While rotating clockwise or counterclockwise water is pumped into the propagation section or extracted from it. Thereby, waves of arbitrary length can be generated.
Using the relatively new strategy of observing the shoreline motion via optical measurements gave a comparatively exact shoreline position during wave run-up. In contrast, determination of the shoreline position during run-down was less exact due to missing evidence indicating the distinct position of the shoreline. In general, the experimentally determined shoreline position agreed with the theoretical approach. The maximum run-up/ run-down occurred for waves with surf similarity parameters between 3 and 6 (interval in which transition from breaking to non-breaking occurs). The magnitude of the theoretical breaking point increased for decreasing wave non-linearity A/h. For surf similarity parameters greater equal of the theoretical breaking point and for increasing surf similarity parameters the normalized run-up and magnitude of normalized run-down decreased. The maximum run-up/ run-down was proportional to wave non-linearity, i.e. the normalized run-up and magnitude of normalized run-down decreased with increasing wave amplitude as predicted by theory. The agreement of experimental and theoretical maximum run-down/ run-up depended on tuning of the PID controller and the resulting actual curve. For longer waves suboptimal tuning of the PID controller resulted in riding waves.

Inhaltsverzeichnis (Table of Contents)

• Introduction
  • Motivation
  • General Information on Tsunamis
  • Scope of the Thesis
  • Outline of the Thesis
• Literature Review
  • Long Wave Generation Techniques
    • Piston-type Wave Generation
    • Dam Break Analogy
    • Vertical Sea Bed Motion
    • Pneumatic Wave Generation
  • The Brier Score
  • The Shoreline Motion of Long Sinusoidal Waves
  • Breaking Criterion for Sinusoidal Waves
  • Optical Measurements of Long Wave Run-up
• Experimental Setup
  • Description of Instruments
    • The Wave Flume
    • The Wave Gauges
    • The Velocity Meter
    • The Pressure Sensors
    • The High Speed Cameras
  • Performance of Physical Experiments
  • Data Processing
    • Processing of Time Series
    • Image Processing
    • Derived Quantities: Position, Velocity and Acceleration of the Shoreline
• Wave Generation
  • Introduction
  • The Pump-driven Wave Generator
  • The Controller Scheme
  • Summary
• Results Of Physical Experiments
  • Time Series
    • Comparison Reference and Actual Curve, Brier Score
    • Time Series of Wave Gauges
    • Time Series of EMS Sensor
    • Time Series of Pressure Sensors
  • Run-up and Run-down of Long Waves
  • Maximum Run-up and Run-down
  • Shoreline Velocity During Run-up and Run-down
  • Maximum Shoreline Velocity During Run-up and Run-down
  • Wave Acceleration During Run-up and Run-down
  • Summary
• Numerical Model Test
  • Introduction
  • Description of the Numerical Model
  • Results of the Numerical Model Study
    • Evolution of SSH During Propagation
    • Numerical Shoreline Location and Maximum Run-Up
  • Summary
• Summary and Outlook

Zielsetzung und Themenschwerpunkte (Objectives and Key Themes)

This master thesis aims to investigate the motion of the shoreline during the run-up of tsunami waves on a plain beach. The study combines both experimental and numerical approaches to achieve a comprehensive understanding of this phenomenon. The key themes explored in this work are:

• Experimental and numerical determination of shoreline motion during tsunami wave run-up
• Analysis of the influence of wave characteristics on shoreline motion
• Development and application of a numerical model to simulate shoreline motion
• Comparison of experimental and numerical results to assess the accuracy of the numerical model
• Evaluation of the applicability of the findings for coastal engineering applications

Zusammenfassung der Kapitel (Chapter Summaries)

• Chapter 1: The introduction provides an overview of the motivation behind the thesis and introduces the general characteristics of tsunamis. It also outlines the scope of the thesis and its structure.
• Chapter 2: This chapter reviews relevant literature, focusing on long wave generation techniques, the Brier score for evaluating forecast accuracy, the shoreline motion of long waves, and breaking criteria for sinusoidal waves. It also discusses optical methods for measuring long wave run-up.
• Chapter 3: This chapter details the experimental setup used in the study, including descriptions of the wave flume, wave gauges, velocity meter, pressure sensors, and high-speed cameras. It also discusses the data processing techniques employed.
• Chapter 4: This chapter focuses on the wave generation process, introducing the pump-driven wave generator and the controller scheme used to generate waves with specific characteristics. It also provides a summary of the wave generation methodology.
• Chapter 5: This chapter presents the results of the physical experiments, including time series analyses, run-up and run-down measurements, maximum run-up and run-down values, shoreline velocity and acceleration, and a summary of the key findings.
• Chapter 6: This chapter describes the numerical model used in the study and presents the results of the numerical model study, focusing on the evolution of sea surface height during propagation and the comparison between numerical and experimental shoreline locations.

Schlüsselwörter (Keywords)

This master thesis focuses on the experimental and numerical investigation of shoreline motion during the run-up of tsunami waves on a plain beach. Key areas of research include wave generation techniques, shoreline motion dynamics, run-up and run-down processes, numerical modeling, and data analysis. This work aims to provide valuable insights into the complex interplay of wave characteristics and shoreline motion, ultimately contributing to improved understanding and prediction of tsunami impacts on coastal areas.

• College: University of Hamburg (Institute of Oceanography Hamburg)
• Course: Physical Oceanography
• Grade: 1.7
• Author: Ulrike Drähne (Author)
• Publication Year: 2014
• Pages: 84
• Catalog Number: V280860
• ISBN (eBook): 9783656743804
• ISBN (Book): 9783656743774
• Language: English
• Tags: experimental