پیش بینی موقعیت رسوبگذاری در ناحیه سواش سواحل ماسه ای به روش سطح پاسخ

نویسندگان
محمدرضا مطلبی زاده 1
مهدی شفیعی فر 2
مسعود قدسیان 2
1 دانشجوی دکتری دانشگاه تربیت مدرس
2 استاد دانشکده مهندسی عمران و محیط زیست، دانشگاه تربیت مدرس
چکیده
ناحیه سواش، بعنوان محدوده‌ی انتهایی ناحیه داخلی شکست، مناطق و سازه‌های ساحلی را تحت تاثیر قرار می‌دهد. عملکرد سواش تحت تاثیر امواج ورودی از ناحیه شکست، هندسه بستر ساحلی و اندرکنش سفره زیرزمینی-دریا است. در تحقیقات گذشته برای طراحی آزمایش‌ها از روش «هر بار یک عامل» استفاده شده است و تاثیر کیفی پارامترهای ارتفاع و پریود موج منظم، تراز آب سمت دریا، تراز سفره زیر زمینی، و شیب ساحل بر تغییرشکل ساحل مورد بررسی قرار گرفته است. در تحقیق حاضر، برای ساحل ماسه‌ای انعکاسی با قطر متوسط mm8/0، آزمایش‌ها به روش «سطح پاسخ مرکزی» طراحی شده اند و تاثیر کمّی و متقابل پارامترهای ارتفاع و پریود موج نامنظم، ترازهای آب سمت دریا و پشت ساحل، و شیب ساحل؛ بر موقعیت شروع رسوبگذاری سواش بررسی شده است. نتایج حاصل از روش سطح پاسخ مرکزی نشان داد تراز آب زیر زمینی در ساحل، تاثیر معناداری بر موقعیت شروع رسوبگذاری سواش ندارد و افزایش ارتفاع موج منجر به جابجایی سریع این موقعیت به بالای ساحل می‌شود. موقعیت شروع رسوبگذاری سواش با زیاد شدن شیب ساحل به بالای ساحل حرکت می‌کند و برعکس با بالا آمدن تراز آب سمت دریا این موقعیت به سمت پایین ساحل جابجا می‌شود. اندرکنش قابل توجهی بین میزان تاثیر ارتفاع و پریود موج بر موقعیت شروع رسوبگذاری سواش وجود دارد. در ضمن بین تراز آب سمت دریا و ارتفاع موج اندرکنش کمی وجود دارد.

کلیدواژه‌ها

عنوان مقاله English

Sedimentation Position Prediction in the Swash Zone of Sandy Beaches using Response Surface Method

نویسندگان English

mohammadreza motalebizadeh 1
Mehdi Shafieefar 2
masoud ghodsian 2
1 PhD student of Hydraulic, Faculty of Civil and Environmental Eng., Tarbiat Modares University
2 Prof., Coastal Engineering. Faculty of Civil and Environmental Eng., Tarbiat Modares University
چکیده English

Reflective beaches requires a combination of lower waves, longer periods and particularly coarser sands. They are typically steep in beach profile with a narrow shoaling and surf zone, composed of coarse sediment. Coarser sediment allows percolation during the swash part of the wave cycle, thus reducing the strength of backwash and allowing material be deposited in the swash zone
The Swash zone, as extreme area of inner surf zone, influences coastal area and coastal structures. It defined as the part of the beach between the minimum wave run-down and maximum wave run-up. It constitutes a beach area where waves dissipate or reflect their remaining energy after traveling towards the shore. The role of Swash zone is influenced by incoming waves from surf zone, the geometry of beach face and the interaction between beach groundwater and surf zone.
The review of Laboratory researches indicated that wave height and period, beach slope, grain size distribution of beach material, still water level (SWL), beach groundwater level, the hydraulic conductivity of beach influence on the evolution of sand beaches. In a few laboratory researches, experiments is designed with One Factor At a Time method (OFAT) and the qualitative effect of parameters of regular wave height and period, SWL and beach groundwater level, and beach slope are investigated on nearshore evolution.
In this research, experiments are designed using Central Composite Design (CCD) of Response Surface Method (RSM). CCD is a type of response surface design that present very good predictions in the middle of the design space. Important properties and features of CCD are orthogonality, rotatability and uniformity. The quantitative effects and interactions of irregular wave height and period, beach groundwater level and SWL, and beach slope on beach profile evolution is examined in a sandy beach by 50 experiments designed with CCD. The experiments are carried out in laboratory flume in Faculty of Civil and Environmental Engineering, Tarbiat Modares University with high accuracy. The experimental setup is designed to simulate varying beach groundwater level and SWL and course sand (d50=0.8mm) is selected for beach material. Analysis of hydrodynamic data of the experiments indicated that the type of breaking waves is plunging wave and the hydrodynamic status of the swash zone is intermediate condition. The starting position of swash sedimentation (SWS) is extracted from mean of the beach profiles evolution.
By analyzing of experiments' SWS using CCD, a cubic model is suggested with %95 confidence level and predicted R-squared of 0.86. The results of model revealed that groundwater level has no significant effect on SWS. Wave height is the most influential factor affecting SWS and increasing wave height result to this position moves to upper beach rapidly. In addition, increasing beach slope causes the movement of SWS toward the beach. Increasing sea level lead to the displacement of SWS toward the sea.
This model indicated that the effect of wave height on SWS depends on wave period strongly and there is significant interaction between them. In addition, there is slightly interaction between the SWL and wave height and these variables influence on the role of each other in SWS.

کلیدواژه‌ها English

sandy beaches
swash zone
Response surface method
laboratory model
starting position of swash sedimentation

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مهندسی عمران مدرس
دوره 17، شماره 3
مرداد و شهریور 1396
صفحه 183-184