Corrosion Margins for Redundant Ship Structures

2018 ◽  
Author(s):  
Yordan Garbatov ◽  
C. Guedes Soares
Keyword(s):  
Differential Equation ◽  
Degradation Process ◽  
Step Function ◽  
Order System ◽  
Safety Factors ◽  
Ship Structures ◽  
Degradation Model ◽  
Corrosion Depth ◽  
First Order ◽  
Partial Safety Factors

The work presented here analyses the structural corrosion degradation of two sets of corrosion depth measurements collected with a one-decade difference. The corrosion degradation process is associated to a first order system, subjected to a sudden disturbance, where a step function is used as an input to define the solution of the differential equation of this system leads to the exponential corrosion degradation model as developed earlier. Corrosion margins of redundant ship structures with serious consequences of failure are derived and several conclusions related to the new trend in the ageing structures are presented and discussed. Partial safety factors with respect to the corrosion environment and corrosion margins are developed that can be used in the design, avoiding a complex probabilistic analysis.

Analysis of the Partial Safety Factor Method Using Probabilistic Techniques

2010 ◽  
Author(s):  
B. A. Lindley ◽  
P. M. James
Keyword(s):  
Probabilistic Method ◽  
Probability Of Failure ◽  
Safety Factors ◽  
First Order Reliability Method ◽  
First Order ◽  
Target Probability ◽  
Reliability Method ◽  
Input Parameters ◽  
Partial Safety Factors ◽  
Hand Calculation

Partial Safety Factors (PSFs) are scaling factors which are used to modify the input parameters to a deterministic fracture mechanics assessment in order to consider the effects of variability or uncertainty in the values of the input parameters. BS7910 and SINTAP have adopted the technique, both of which use the First Order Reliability Method (FORM) to derive values for PSFs. The PSFs are tabulated, varying with the target probability of failure, p(F), and the Coefficient of Variance (COV) of the variable. An accurate assessment of p(F) requires a probabilistic method with enough simulations. This has previously been found to be time consuming, due to the large number of simulations required. The PSF method has been seen as a quick way of calculating an approximate, conservative value of p(F). This paper contains a review of the PSF method, conducted using an efficient probabilistic method called the Hybrid probabilistic method. The Hybrid probabilistic method is used to find p(F) at a large number of assessment points, for a range of different PSFs. These p(F) values are compared to those obtained using the PSF method. It is found that the PSF method was usually, and often extremely, conservative. However there are also cases where the PSF method was non-conservative. This result is verified by a hand calculation. Modifications to the PSF method are suggested, including the establishment of a minimum PSF on each variable to reduce non-conservatisms. In light of the existence of efficient probabilistic techniques, the non-conservatisms that have been found in the PSF method, coupled with the impracticality of completely removing these non-conservatisms, it is recommended that a full probabilistic assessment should generally be performed.

Reliability-Based LRFD Criteria for Unstiffened Panel of Ship Structures

2013 ◽  
Author(s):  
Yong Bai ◽  
Miao-hua Qian
Keyword(s):  
Limit State ◽  
State Equation ◽  
Safety Factors ◽  
Ship Structures ◽  
Future Design ◽  
Practical Project ◽  
Safety And Reliability ◽  
Partial Safety Factors ◽  
Factor Design ◽  
Load And Resistance Factor

It is of significance to do the research of safety and reliability for ship structures, especially for marine structures because of the poor conditions and high risks, future design for ship structures will move toward a more rational and probability-based design. This paper chooses the unstiffened panel of ship structures as the research subject. Based on the MATLAB software, this paper develops the procedures and calculates one limit state equation of the panel, derives partial safety factors (PSF) for the Load and Resistance Factor Design (LRFD) of the panel under different reliability index levels. The PSF may provide a reference for the practical project design.

A General Approximate Solution for Stretching Problems in Viscous Fluid

2015 ◽  
Vol 70 (9) ◽  
pp. 781-786
Author(s):  
Saleem Asghar ◽  
Mudassar Jalil ◽  
Ahmed Alsaedi
Keyword(s):  
Differential Equation ◽  
Approximate Solution ◽  
Boundary Value Problem ◽  
Analytic Solution ◽  
Boundary Value ◽  
Skin Friction Coefficient ◽  
Order System ◽  
First Order ◽  
Exponential Stretching ◽  
Special Cases

AbstractIn this study, we propose a boundary value problem that contains two arbitrary parameters in the differential equation and show that the results of a number of existing stretching problems (linear, power law, and exponential stretching) are the special cases of the proposed boundary value problem. A two-term analytic asymptotic solution of this problem is developed by introducing a small parameter in the differential equation. Interest lies in the finding of rare exact analytical solutions for the zeroth and first order systems. Surprisingly, only a two-term closed form of analytical solution shows an excellent match with the existing literature. The solution for second-order system is found numerically to improve the accuracy of the approximate solution. The generalised analytic solution is tested over a number of stretching problems for the velocity field and skin friction coefficient showing an excellent match. In conclusion, various stretching problems discussed in literature are special cases of this study.

scholarly journals Gradient Structures Associated with a Polynomial Differential Equation

Mathematics ◽  
2020 ◽  
Vol 8 (4) ◽  
pp. 535 ◽  
Author(s):  
Savin Treanţă
Keyword(s):  
Differential Equation ◽  
Order System ◽  
Mathematical Framework ◽  
Special Significance ◽  
First Order ◽  
System Method ◽  
Polynomial Differential Equation ◽  
The Cauchy Problem ◽  
Finite Set ◽  
Kernel Representation

In this paper, by using the characteristic system method, the kernel of a polynomial differential equation involving a derivation in R n is described by solving the Cauchy Problem for the corresponding first order system of PDEs. Moreover, the kernel representation has a special significance on the space of solutions to the corresponding system of PDEs. As very important applications, it has been established that the mathematical framework developed in this work can be used for the study of some second-order PDEs involving a finite set of derivations.

An Adjustment of Reference Tracking PID Controllers for a First-order System with a Dead Time

2016 ◽  
Vol 136 (5) ◽  
pp. 676-682 ◽  
Author(s):  
Akihiro Ishimura ◽  
Masayoshi Nakamoto ◽  
Takuya Kinoshita ◽  
Toru Yamamoto
Keyword(s):  
Dead Time ◽  
Order System ◽  
Pid Controllers ◽  
Reference Tracking ◽  
First Order
Sign in / Sign up

Export Citation Format

Share Document