| 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 |
