Damage Diagnosis of Bolt Loosening via Vector Autoregressive - Support Vector Machines

Developments in engineering techniques have concentrated on how to build better solutions for engineering structures in order to main the integrity and to reduce the costs in operations. Since the last two decades, advances in computational power have allowed machine learning algorithms to be applied as a powerful tool in anomaly detection problems, classification as well as in regression analysis. The objective of this study is to detect the damage using the vector auto regression model VAR coupled with support vector machines SVM . A base excited three storey manufactured from an aluminium is investigated in a lab medium for various structural states. Accelerometers are fastened to the each corner of structure's floor to collect time series data. Damage simulation scenarios in structure are performed by releasing the bolt load which cause the nonlinear effects. Once the sensors' measurements are collected for each state and organized to represent the appropriate scenario's label, they are processed in VAR model to obtain feature vectors such as residuals and VAR parameters. Then, SVM with optimal kernels are implemented on those features to classify and locate the damage. The results demonstrate that the VAR residuals shows a significant performance over VAR parameters once they are used as features in SVM technique. Moreover, it is also found that detection performance rises as the number of damage increases

Theoretical and experimental ımprovement of the effect of the diaphragm springs form used in the clutch system on the fatigue strength and mechanical characteristics

Kuru kavramalı debriyaj sistemlerinde yer alan debriyaj baskısının alt bileşeni olan diyafram yay formu, performans ve ömür parametreleri açısından büyük bir role sahiptir. Bu çalışmanın amacı, diyafram yay geometrik formunu ömür parametresi açısından optimize etmektir. Önce, diyafram yayı kuvvet-yer değiştirme ilişkisi deneysel, teorik ve sonlu elemanlar yaklaşımıyla incelenmiştir. Sonra mekanik özelikleri karakterize etmek için diyaframda kullanılan 50CrV4 malzemesine sahip numuneler için çekme ve yorulma testleri gerçekleştirilmiştir. Elde edilen veriler sonlu elemanlar yönteminde kullanılarak simülasyon ve optimizasyon çalışmaları yapılmıştır. Yapılan optimizasyon çalışmalarında diyafram yaya etki eden gerilme değerlerini düşürmek ve yorulma ömrünü arttırabilmek için deney tasarımı yöntemiyle 149 adet dizayn noktası oluşturulmuştur. Yanıt yüzeyi metoduyla optimum diyafram yay tasarımı belirlenmiş ve nihai tasarım belirlenen amaç optimizasyonuyla doğrulanmıştır.Diaphragm spring which is a subcomponent of the clutch cover in dry clutch systems has an important role in performance and life parameters. The main aim of this study is to optimize the geometrical form of this diaphragm spring in terms of life parameter. Initially, the force-displacement relationship has been investigated using the experimental, theoretical and computational approaches. Then, tensile and fatigue tests have been performed for the 50CrV4 specimens used in diaphragm spring to characterize the mechanical properties. The characterized results have been used in the finite element method to perform simulation and optimization tasks. In order to reduce the stress values affecting the diaphragm spring and increase the fatigue life, 149 design points have been created with the design of experiment method. The optimum diaphragm spring design has been determined using the response surface method, and its ultimate design was verified by the specified goal optimization

Birden çok cıvata gevşemesinin veri tabanlı istatistiki örüntü tanıma teknikleriyle tespiti

The main objective of this research is to diagnose single or multiple bolt loosening for a system exposed to environmental and operational uncertain conditions by implementing both vector auto regressive (VAR) model alone and VAR model coupled with singular value decomposition (SVD), Mahalanobis distance and principal component analysis (PCA). The research has been deployed on a three-storey system constructed with aluminum members in the laboratory medium. The damage simulation scenarios in system have been performed by loosening the frame bolts on each floor which cause the nonlinear effects. The system's ground storey has been excited with an electromagnetic shaker vibrating at band limited random frequencies. Accelerometers are attached to each edge of the floor to acquire the dynamic response of the structure and use their signals for damage diagnosis. The accelerometers' measurements were collected for eight loosening cases. Once these measurements have been processed and evaluated in statistical pattern recognition algorithms, their performance results have been compared and presented via tables and ROC curves. It is obtained from ROC curves that the VAR model coupled with PCA technique has the highest diagnosis performance score in terms of area under curve (AUC) and optimum true positive rate (TPR). The approach it has been followed here demonstrates that the individual sensor that is most affected by the loosening can be identified which could be implemented to detect the bolt loosening

Ağsız yöntemlerle yapısal analiz

Farklı tiplerdeki kısmi diferansiyel denklemlerin çözümünde sayısal çözümleme yöntemlerinin uygulanması son yirmi yıldır oldukça ilgi uyandırmaktadır. Kısmi diferansiyel denklemlerin sayısal çözümü iki temel kısmı oluşturur. Denklem veya bilinmeyen fonksiyon yaklaşık olarak çözülür. Zayıf veya güçlü form, yaklaşık formatta türetilen denkleme yerleştirilerek bilinmeyen fonksiyon belirlenir. Bilinmeyen fonksiyon tam olarak kararlaştırılması için sınır koşulları uygulanır. Nümerik metodun doğruluk ve verimliliği bu iki kısmın doğruluk ve verimliliğine bağlıdır. Son on yıl boyunca çeşitli ağsız yöntemler (EBG,DPH,N M,AYPG gibi) farklı mühendislik problemlerine uygulanarak başarılı bir şekilde geliştirilmiştir. Bu çalışmada yeni ve son zamanlarda çok kullanılan nümerik metodlardan ağsız eleman bağımsız Galerkin ve radyal nokta interpolasyon yöntemi, elastik katı cisimler mekaniği problemlerine uygulanmıştır. Bu metodların çözümünde hareketli en küçük kareler prosüdürü ve radyal nokta interpolasyon yöntemi şekil fonksiyonları kullanılmıştır. Ayrıca şekil fonksiyonları bir ve iki boyutlu çözüm bölgelerine uygulan p x-y-z koordinat sisteminde çizdirilmiştir. Bu tezde katı cisim mekaniği problemi olarak bir ucu ankastre, diğer ucu da zorlanmaya maruz bırakılan iki boyutlu lineer, elastik bükülebilir kiriş incelenmiştir. Yaklaşık denklem çözümü için araştırmacılar tarafından önerilip kullanılan radyal nokta interpolasyon yöntemi ve eleman bağımsız Galerkin gibi farklı teknikler, doğruluk ve verimlilik bakımından sonlu elemanlar yöntemi ve analitik çözümle karşılaştırılmıştır. Ayrıca verimli olan metodun bulunmasında kirişin değişik kesitlerinde gerilme ve yer değiştirme değerleri incelenmiştir. Sonuç olarak radyal nokta interpolasyon metodu ve eleman bağımsız Galerkin yöntemlerinin doğruluk ve verimliliği sonlu elemanlar yöntemine göre daha iyi olduğu kararına varılmıştır. Ayrıca radyal nokta interpolasyon yöntemi ile eleman bağımsız Galerkin yöntemiyle elde edilen sonuçlar karşılaştırıldığında, eleman bağımsız Galerkin yönteminin seçilen kiriş problem için daha hassas sonuçlar verdiği görülmüştür

Meshfree Methods and Their Classification

Many meshless methods have been developed and improved remarkably during the last two decades. In this study, some fundamental information about meshless methods which are new and popular numerical methods in recent years is given. Meshless methods are compared with the finite element method in terms of the solution procedures proposed and used by researchers in engineering problems. Meshless methods are classified in terms of their properties and some popular types of these methods are described

Finite element analysis of the Anterior Drawer Test for foot Ankle

European Biotechnology Congress -- SEP 28-OCT 01, 2011 -- Istanbul, TURKEYWOS: 000295310800495European Biotechnol Themat Network Asso

Damage diagnosis of a laminated composite beam and plate via model based structural health monitoring techniques

WOS: 000392927000002In this study, model based damage identification algorithms were applied for a delaminated composite beam and plate. Initially, natural frequencies of healthy and delaminated beam were measured via experimental modal analysis. Next, the natural frequencies obtained by experimental method were verified with the finite element analysis. Once the validation has been fulfilled, the next step was to apply the finite element analysis to extract the mode shapes. Then, the curvatures mode shapes were obtained from the mode shapes, and these parameters were used in the gapped smooth method (GSM) and strain energy method (SEM) to detect the location and size of the delamination. The damage diagnosis technique for composite plate was evaluated for two cases. In the first case, it was assumed that the initial health information of a structure is known. However, the information of an undamaged structure may not be available during the diagnosis process for some circumstances. Therefore, the diagnosis was conducted by evaluating the curvatures of damaged structure using surface fit techniques in order to predict the initial status for the second case. Both of the two damage detection algorithms were evaluated for these two cases. The results show that, the delamination of laminated composite beam and plate could be predicted non-destructively by employing the data obtained from experimental or numerical technique in model based SHM approach for laboratory conditions