Modelling of waste dispersion in coastal area | |
| Author | Lan, Chin-wu |
| Call Number | AIT Diss. no. WA-86-02 |
| Subject(s) | Hydrodynamic--Mathematical models Hydraulics |
| Note | A dissertation submitted in partial fulfilment of the requirements for the Degree of Doctor of Engineering, School of Engineering and Technology |
| Publisher | Asian Institute of Technology |
| Series Statement | Dissertation ; no. WA-86-02 |
| Abstract | Two-dimensional plane-view mathematical models are developed to describe hydrodynamic circulation and substance dispersion in coastal areas. In this study the field of major concern is water pollution created by dumping dredging waste into the shallow coastal area. Due to the shallowness of the coastal area where waste dispersion occurs the two-dimensional plane- view models with conservative substance dispersion are selected for this study. As the flow characteristics are nearly uniform in the vertical direction, the convection and dispersion in horizontal direction are more predominant than the vertical convection and dispersion. However, the three-dimensional flow characteristics of the non-uniform velocity distribution in the vertical direction are considered in the effective shear stress terms which occur as a byproduct of the vertical integration of convective inertial and surface stress terms in the momentum equations. In the Dispersion Model, provision is made to take into account indirectly the rate of deposition due to the vertical dispersion. The mathematical models are based on the conservation of momentum and mass equations, and derived by integrating the three-dimensional equations over the flow depth. The assumption and limitation inherent in the derivation are clearly noted to ensure proper application of the model. The treatments of boundaries and boundary conditions are given particular attention. For example, the boundary condition of the dispersion model is specified to make the model more flexible. The solution of the formulated problem is achieved by using numerical techniques. For spatial discretization, the finite element method is chosen because of its larger flexibility in grid layout and better treatment of boundary conditions. The time integration schemes are also approached by the finite element method. The stability and accuracy of the time integration schemes for some simplified cases are analyzed by mathematical and numerical methods. For different characteristics of the governing equations, the different time integration schemes shou 1 d be considered respective 1 y and in here, several time integration schemes are discussed . In this study, two different time integration schemes are chosen to be applied for the Hydrodynamic Model and Dispersion Model. Under the Hydrodynamic Model, triangular elements with linear interpolation functions are used in finite element formulation . A weighting function by which the mass matrix is made to be diagonal is deduced on the two - dimensional simplex element. It forms in the lumped mass matrix finite element equation. The split- time combined with two - step explicit scheme is used for time integration. The split- time technique, in which water depths and flow velocities are computed separately at alternating time steps, can reduce the number of unknown variables and the size of element matrix. This will reduce the computer time and storage. At each alternating step the two-step explicit scheme is used, which makes the model more stable and is highly accurate. The combination of the lumped mass matrix method and the above time integration scheme will make the model effective in terms of computer time and storage. Additionally, it can simplify the node numbering technique and programmability. For the Dispersion Model, the triangular elements with linear interpolation functions are - iii - used for spatial discretization too, while the formulation is based on the Galerkin's weighted residual method and the trapezoidal rule is employed for time integration. The model is shown to be unconditionally stable. The developed models are verified against several known analytical solutions of the simple geometric problems to ensure the validity of t hese models and to test their accuracy and stability. The sensitivity of some parameters in the model are tested too. The verification tests show satisfactory results. Some more numerical experiments have been performed to approve the conclusions of the theoretical derivation and have shown good agreements. Finally, the developed Hydrodynamic Model and Dispersion Model are applied to a real world system. The simulated results of the Hydrodynamic Model applied to the East Coast of Phuket in Southern Thailand are compared with the field measurements which have been carried out recently. It shows good agreement. The simulated results obtained from the Hydrodynamic Model are used to provide the water depth and flow velocity inputs to the Dispersion Model. Comparing the computed concentration against the field measurement data shows that there are some scatter, but their trends are similar. In order to obtain some more useful information of the dispersion processes in the application study area, there are several cases have been considered in this study. |
| Year | 1986 |
| Corresponding Series Added Entry | Asian Institute of Technology. Dissertation ; no. WA-86-02 |
| Type | Dissertation |
| School | School of Engineering and Technology |
| Department | Other Field of Studies (No Department) |
| Academic Program/FoS | Water Resources Research Engineering (WA) |
| Chairperson(s) | Suphat Vongvisessomjai ; |
| Examination Committee(s) | Tawatchai Tingsanchali ;Gupta, Ashim Das ;Worsak Kanok-Nukulchai ;Wang, Tsan-Wen ;Vries, M. De ; |
| Scholarship Donor(s) | Republic of China; |
| Degree | Thesis (Ph.D.) - Asian Institute of Technology, 1986 |