ارزیابی رویکردهای ترکیبی برای تعریف دیتوم در پایش شبکه های ژئودتیکی کلاسیک

نوع مقاله: مقاله پژوهشی

نویسندگان

1 دانشجوی کارشناسی ارشدگرایش ژئودزی، دانشکده مهندسی نقشه برداری و اطلاعات مکانی، پردیس دانشکده های فنی، دانشگاه تهران

2 استادیاردانشکده مهندسی نقشه برداری و اطلاعات مکانی، پردیس دانشکده های فنی، دانشگاه تهران

3 دانشیاردانشکده مهندسی نقشه برداری و اطلاعات مکانی، پردیس دانشکده های فنی، دانشگاه تهران

10.22131/sepehr.2020.44579

چکیده

تجزیه و تحلیل رفتار سازه‌های مهندسی از جمله فعالیت­های مهم در ژئودزی است چرا که هرگونه ارزیابی نادرست از جابجایی‌ها، می‌تواند تاثیرات مرگباری داشته باشد. برای یافتن میزان تغییر شکل ایجاد شده در یک سازه بر اثر عوامل مختلف، ابتدا باید به برآورد جابجایی نقاط آن سازه پرداخت. بدین منظور از دو روش مقاوم[1]  و غیرمقاوم[2]  که بر نتایج سرشکنی مشاهدات اپک‌ها استوار هستند، استفاده می‌شود. روش حداقل سازی نرم [3]L1 و سرشکنی تکراری وزن­دار دو اپک زمانی[4]، از جمله روش­های مقاوم هستند که با حداقل سازی نرم اول و دوم، بردار جابجایی را محاسبه می­کنند. تجزیه و تحلیل جابجایی‌ها بر حسب میزان دخالت نقاط در محاسبات، به دو گروه تک نقطه‌ای و ترکیبی[5] تقسیم می‌شوند. در روش‌های تک نقطه‌ای تعیین دیتوم در پایش شبکه­های ژئودتیک کلاسیک، روش سرشکنی همزمان دو اپک زمانی[6] ، به عنوان روش بهینه در نظر گرفته می‌شود. یکی از مشکلات اساسی این روش‌ها وابستگی شدید آن­ها به هندسه‌ی شبکه است که مانع از کشف همه‌ی نقاط ناپایدار و افزایش میزان خطا در محاسبات خواهد شد. در این تحقیق، استفاده از روش‌های ترکیبی به عنوان جایگزین مناسبی برای این روش‌ها معرفی می‌گردد. تفاوت این روش­ها با روش­های تک نقطه­ای، در بررسی تمامی نقاط شبکه­ی ژئودتیک بشکل یک­جا و کشف نقاط ناپایدار در بین آن­ها است. هدف این تحقیق بررسی موفقیت روش‌های ترکیبی در جهت کشف نقاط ناپایدار و مقایسه‌ی موفقیت آن‌ها با روش سرشکنی همزمان دو اپک زمانی و انتخاب روش بهینه می‌باشد. در این راستا بر مبنای مشاهدات یک شبکه شبیه‌سازی شده و ایجاد حالت‌های مختلف جابجایی، بهترین روش انتخاب گردید سپس روش پیشنهادی بر روی مشاهدات واقعی سد جامیشان، واقع در جنوب غرب شهرستان سقز، واقع در کرمانشاه، پیاده‌سازی شد. با وجود توانایی روش سرشکنی همزمان دو اپک زمانی در کشف نقاط ناپایدار، این روش برخلاف روش زیرنمونه چندگانه تفاضلات طولی[7]، نتوانسته است همواره تمامی نقاط ناپایدار را تشخیص دهد. روش زیرنمونه چندگانه با تفاضلات داده­های طولی، با درصد 100 به 70، 100 به 87.5 و 100 به 87.5، در مقابل روش سرشکنی همزمان دو اپک زمانی، توانست موفقیت بهتری را بدست آورد. بنابراین روش زیرنمونه چندگانه تفاضلات طولی به عنوان بهترین روش انتخاب شده است.



[1] Robust


[2] Non-robust


[3] Minimum norm L1


[4] Iterative Weighted Simultaneous of Two Epochs (IWST)


[5] Combinatorial methods


[6] Simultaneous Adjustment of Two Epochs (SATE)


[7] Multiple Sub Sample distance difference

کلیدواژه‌ها


عنوان مقاله [English]

Evaluation of combinatorial methods used for datum definition in classical geodetic network monitoring

نویسندگان [English]

  • Zahra Banimostafavi 1
  • Saeed Farzaneh 2
  • Mohammad Ali Sharifi 3
1 Msc. Student of geodesy, Department of surveying and geomatics engineering, Faculty of Engineering, University of Tehran, Iran
2 Assistant professor, Department of surveying and geomatics engineering, Faculty of engineering, University of Tehran, Iran
3 Associate professor, Department of surveying and geomatics engineering, Faculty of engineering, University of Tehran, Iran
چکیده [English]

Extended Abstract:
Introduction
Nowadays, engineering structures face many threats. Natural and human activities can result in deformation and displacement of dams, bridges, and towers. As a result, any crack in the body of these structures is important and may have dangerous consequences. To prevent catastrophes, the behavior of these structures should be monitored permanently during the construction phase and after opening.Nowadays,thebehavior of engineering structures such as dams, power plants, and towers is considered to be especially important. Three different methods are usually used to measure such behavior: classical, satellite and precise instruments.
 
Materials and methods
Modern equipment is considered to be a crucial factor in controllingpossible changes and preventing human errors. Therefore, different sensors are installed in the structure to measure tensile and shear flexibility during the construction phase. Moreover, data received from these sensors is analyzed permanently during the service life to ensure sustainability of the structure. These tools make internal analysis of these structures possible. Analyzing the behavior of engineering structures is considered to be one of the most important tasks in the field of geodesy. Inaccurate analysis of displacements can have deadly effects. Various methods are used to measure such displacements, which are divided into two categories: robust and non-robust methods based upon the results of the epoch adjustment. To find deformations, a geodetic network should be defined in the first step. If two epochs are not measured in the same datum, the results will not be reliable. Displacement can be measured in two ways: Absolute and Relative. In the absolute method, some points are considered to be stable, while in the relative network, all points are considered to be unstable, and the problem is solved based upon this hypothesis. The method of relative network is used in the present study. Regarding network geometry, displacement analysis is performed using two methods:single and combinatorial. Moreover, displacement analysis is divided into two categories of robust and non-robust methods. Iterative Weighted Similarity Transformation (IWST)and Minimum L1 norm are among robust methods which calculate the matrix of displacement by minimizing the first and second norm. Global Congruency Test (GCT) is a non-robust statistical method used to determine unstable points in geodetic networks. Robust and GCT are among classical methods used to discover unstable points in geodetic networks, while Simultaneous Adjustment of Two Epoch (SATE(is a new method used to achieve this purpose. Combinatorial methods are also considered to be a suitable alternative method used for detecting unstable points in a geodetic network. In our previous study, “evaluation of single-point methods used fordetecting displacement in classical geodetic networks”, single-point methods of detecting unstable points were investigated and the SATE method was selected as the optimal method. Unlike single-point methods, these methods examine all points of the geodetic network simultaneously to discover unstable points.
 
Results and discussion
The strong dependence of these methods on the network geometry makes discovery of all unstable points impossible. Combinatorial methods are considered to be a suitable alternative method used to detect all unstable points in the geodetic network. These methods does not have a strong dependence on scale and the network geometry. Multiple Sub Sample and M-split methods are classified in this category. These methods can detect unstable points efficiently. The present study takes advantage of simulated datato evaluate combinatorial methods such as Multiple Sub Sample (MSS) Angles, MSS-distance difference, and M-split and compare them with the SATE method with the aim of choosing the optimal method. Then, unstable points in the real network of Jamishan dam in Kermanshah Province will be discovered using the identified optimal method.
 
Conclusion
The present study identifies the best method between single and combinatorial methods. The best method can detect most unstable points and has the lowest dependence on geometry, scale and other factors influencing the results.According to the results, Multiple Sub Sample with distance difference is selected as the best method.

کلیدواژه‌ها [English]

  • Multiple Sub Sample
  • M-split
  • Combinatorial methods
  • Simultaneous Adjustment of Two Epochs
  • Unstable points
  • Monitoring networks
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