Can Elmar Balas

A statistical riverine litter propagation model.

A statistical riverine litter propagation (RLP) model based on importance sampling Monte Carlo (ISMC) simulation was developed in order to predict the frequency distribution of certain litter types in river reaches. The model was preliminarily calibrated for plastic sheeting by a pilot study conducted on the River Taff, Wales (UK). Litter movement was predominantly controlled by reach characteristics, such as vegetation overhang and water-course obstructions. These affects were modeled in the simulations, by utilizing geometric distributions of river reaches in the time domain. The proposed model satisfactorily simulated the dosing experiments performed at the River Taff. It was concluded from the preliminary calibrations that, the RLP model can be efficiently utilized to portray litter propagation at any arbitrarily selected river site, provided that the stream flows and reach characteristics are calibrated by representative probability distributions of similar sections. Therefore, the RLP model can be considered as a new statistical technique that can predict litter propagation in river sections.

A SENSITIVITY STUDY FOR THE SECOND ORDER RELIABILITY-BASED DESIGN MODEL OF RUBBLE MOUND BREAKWATERS

The reliability-based risk assessment and structural design model (REBAD) (Balas, 1998) introduced in this paper, is a worthwhile tool in the preliminary design of maritime structures which are portrayed by vast failure consequences and significant resource expenditures. REBAD model in which the Second-Order Reliability Method (SORM) is utilized together with a cost-optimization algorithm, is implemented to Mersin yacht harbor which is constructed near the city of Mersin located on the Turkish coast of Mediterranean Sea. SORM is established on a more correct approximation of the failure surface than the first-order method. The failure mode probability is predicted by approximating the failure surface by a quadratic surface with the identical curvature at the design point. First, REBAD is implemented to the main breakwater by utilizing the Hudson failure function to determine the size of armor units, then failure mode response functions were obtained for the fixed exceedance probability of several damage levels. Combining with the hydraulic model study carried out by Ergin and Özhan (1994) and REBAD outcome, the trunk section of main breakwater and design functions were determined. The second order reliability-based sensitivity study was also carried out to systematically compare limit state equations of Hudson and Van der Meer. Authors concluded that, Van der Meer failure function is a more reliable design function for this case study which illustrated the affect of uncertainties encountered in Turkey on the design practice of rubble mound breakwaters. Since REBAD enabled the first application of reliability-based design practice for coastal structures in Turkey, it is the commencement for the development of a national reliability-based design standard of maritime structures.

Application of multivariable generalized predictive control to a packed distillation column

Abstract The present work deals with the application of Multivariate Generalized Predictive Control (MGPC) systems to a packed distillation column. The steady-state and dynamic behaviour of the system have been simulated using two film plug flow model. The model solutions have been obtained employing orthogonal collocation on finite element. The Jacobi polynomials within the finite element procedure was tested to determine the phase flow rates, the liquid and vapour composition profiles and the temperature profiles. All the theoretical results were compared with experimental data obtained from a pilot-plant packed distillation column distilling methanol-water mixture. Decoupling and MGPC control of overhead and/or bottom compositions were examined. Perturbation in feed composition and, reflux ratio and the reboiler heat duty were utilized as the disturbance and the manipulated variables respectively. Performance of these systems was tested by using an integral square of error (ISE and IAE) criterion.

Reliability-Based Risk Assessment of Rubble Mound Breakwaters Under Tsunami Attack

ABSTRACT In the reliability-based risk assessment, the second order reliability index (βII) method and the Conditional Expectation Monte Carlo (CEMC) simulation were utilised in order to analyse the safety levels of Haydarpasa Port main breakwater, Sea of Marmara, Turkey. The failure probability was forecasted in the βII method by approximating the Hudson performance surface with a second-degree polynomial having an equal curvature at the design point where the design and structural parameters were taken into consideration. In the past, applications of reliability-based risk assessment methodology in Turkey for design conditions, only wave characteristics, tidal range, storm surge, wave set-up and the structural system parameters were included. Tsunami risk was not considered a major design parameter and was not included in the computations. In this study, a structural stability criterion in coastal engineering is suggested to achieve a common definition of reliability including the tsunami risk. The model introduced in this study is a practical technique for reliability-based risk assessment of breakwaters subject to tsunami risk. In order to determine the occurrence probability under design conditions, which is a function of storm waves, tidal range, storm surge and tsunami height, the CEMC simulation was interrelated with the βII method. From the reliability-based risk assessment model applied to Haydarpasa port as a pilot study in Turkey it was found that, inclusion of the tsunami risk increases the failure risk of the structure, and as lifetime of the structure increases, the impact of tsunami risk on the failure mechanism is more important. For Haydarpasa port main breakwater, tsunami was not the key design parameter when compared to storm wave, however, in places with great seismic activity, tsunami risk may be very significant depending on the occurrence probability and the magnitude of the tsunami.

Environmental risk assessment; a case study of the Colhuw Beach revetment on the Glamorgan Heritage Coast, Wales

A newly constructed coastal revetment at Colhuw Beach in the Glamorgan Heritage Coast, Wales, UK, was analysed using a recently developed environmental risk assessment package (ERA). Conflict with Heritage Coast conservation objectives is apparent and the act of building such a structure is questioned for a location where maintenance ofnatural beauty is an axiom of the coastal management philosophy. The likelyhood of revetment related environmental consequences of significant magnitude was analysed using estimated probability values derived from Bayesian theory. The damaging impact of the structure on the natural environment is out of all proportion to the level of storm protection afforded to the site. Analyses, such as carried out via ERA, would have shown planners, engineers and environmentalists, the inadequacies of such an investment and management strategy. The ERA approach can help to introduce greater clarity and consistency into decision making processes.

Fuzzy system analysis of beach litter components

Tourist beaches on the southern coast of Turkey are surveyed in order to facilitate a standardised fuzzy approach to be used in litter prediction and to assess the aesthetic state of the coastal environment for monitoring programs. During these surveys the number of litter items on beaches were counted and recorded in different categories. The main source of litter on beaches was determined as “beach users”. A fuzzy system was developed to predict the classification of the beaches, since uncertainty was generally inherent in beach work due to the high variability of beach characteristics and the sources of litter categories. This resulted in effective utilization of “the judgment and knowledge of beach users” in the evaluation of beach gradings.

A computational risk assessment model for breakwaters

In the reliability-risk assessment, the second order reliability index method and the Conditional Expectation Monte Carlo (CEMC) simulation were interrelated as a new Level III computational approach in order to analyse the safety level of the vertical wall breakwaters. The failure probabilities of sliding and overturning failure modes of the Minikin method for breaking wave forces were forecasted by approximating the failure surface with a second-degree polynomial having an equal curvature at the design point. In this new computational approach, for each randomly generated load and tide combination, the joint failure probability reflected both the occurrence probability of loading condition and the structural failure risk at the limit state. This new approach can be applied for the risk assessment of vertical wall breakwaters in short CPU durations of portable computers.

Rubble Mound Breakwaters Under Tsunami Attack

In the past applications of risk assessment for coastal structures; only wave characteristics, tidal range, storm surge, wave set-up, surf beat, and structural system parameters were considered, but the tsunami risk could not be incorporated to the reliability based design in the literature. The reliability model REBAD introduced in this study primarily enabled the risk assessment of breakwaters subject to tsunami risk. The Second-Order Reliability Method (SORM) was applied to determine the safety of Haydarpasa Port, Sea of Marmara, Turkey. The failure probability was forecasted by approximating the Van der Meer failure surface with a second-degree polynomial having an equal curvature at the design point. Inclusion of tsunami risk that has an extended return period when compared to storm waves, increased the failure risk of the structure in its lifetime. For Haydarpasa port main breakwater, the failure risk of the structure was not sensitive to the tsunami occurrence. However, in places with great seismic activity, tsunami risk may be very significant depending on the occurrence probability, and the magnitude of the tsunami.