Mahmoud Haddara

• Ph.D.
• Memorial University of Newfoundland

Health monitoring of infrastructures is one of the essential modern services for civil engineering structures. A design of a Structural Health Monitoring (SHM) system that allows a continuous assessment of the structure’s integrity is required to increase safety, and to optimize operational and maintenance costs. Nowadays, non-destructive technique...

Ensuring the integrity of subsea process components is one of the primary business objectives of the oil and gas industry. Leak detection system (LDS) is one type of system used to safeguard reliability of a pipeline. Different types of LDS use different technologies for detecting and locating leaks in pipelines. One technology, which is gaining wi...

Failure of Leak Detection System (LDS) to detect pipeline leakages or ruptures may result in drastic consequences that could lead to excessive financial losses. To minimize the occurrence of such failure, the functionality of the LDS and the integrity of the pipeline should be assessed on a priority basis. This paper presents an integrated risk-bas...

Insuring the integrity of subsea process component is one of the primary business objectives for oil and gas industry. One of the systems used to insure reliability of a pipeline, is the Leak Detection System (LDS). Different leak detection systems use different technologies for detecting and locating leaks that could result from pipelines. One tec...

Leak Detection Systems play a major role in enhancing reliability and operability of oil and gas pipelines. They have the functional capabilities to detect, locate and quantify leaks before they can cause drastic effects to environment and operation. The performance of Leak Detection Systems is typically affected by three different failures that ha...

Most of the rules for predicting the crack width of reinforced concrete structures, in existing building codes, are based on the statistical results obtained for normal strength concrete (NSC) members with normal concrete cover. Therefore, these rules need to be adjusted for high strength concrete (HSC) members with thick concrete cover. This paper...

The current building codes provide calculation techniques to estimate crack spacing for regular building members (beams and slabs). Thick members are commonly used for offshore platforms and containment structures for nuclear power structures. The results have proven that it is necessary to modify the equations used for the crack spacing prediction...

The objective of this paper is to estimate the sample size required to assess the maximum pit size over an entire asset that is subject to pitting corrosion. The Bayesian updating approach and the extreme value method are integrated into a single proposed framework to estimate the sample size. The extreme value method is used to predict the maximum...

Purpose The purpose of this paper is to develop a risk‐based integrity model for the optimal replacement of offshore process components, based on the likelihood and consequence of failure arising from time‐dependent degradation mechanisms. Design/methodology/approach Risk is a combination of the probability of failure and its likely consequences....

The present chapter presents the basic concepts associated with Risk-based Inspection and Maintenance (RBIM) philosophy and their application in maintenance planning aiming at controlling power plant equipment degradation. The basic steps of the method are described, such as inspection sampling, inspection planning and maintenance activity selectio...

Cracking of cylindrical shafts is an important area for research, since the changes observed in their vibration characteristics even during large-sized cracking are much smaller than those observed for rectangular beams; hence early identification of crack existence becomes essential to prevent sudden failures in rotating shafts. In this paper expe...

In this study, experimental and analytical investigations are carried out on an overhanging cylindrical shaft carrying a propeller at the cantilever end, in order to identify the crack existence in shafts using the mechanical impedance approach. Also the experimental study uses the modal analysis software, LMS Test Lab TM, for measuring and analyzi...

In this paper experimental and numerical investigations are carried out to identify the presence of a crack in a cylindrical overhanging shaft with a propeller at the free end. In the experimental study, cracks of different depths are located at the (un-cracked) maximum bending moment position. Shaft response parameters for lateral (using an accele...

This paper proposes a methodology to estimate the required sample size to assess, with a specified precision, the localized corrosion of process components. The proposed methodology uses the extreme value and bootstrap methods. The results of estimated sample size ensure that the predicted maximum localized corrosion with the extreme value method i...

A Bayesian approach-based method is proposed for calculating the minimum size of a sample to assess, with a specified precision, the integrity of process components suffering from general corrosion. The proposed method ensures that the error in the posterior estimate of the mean does not exceed a pre-defined acceptable margin of error at a specifie...

In this paper the requisite foundational numerical and experimental investigations that are carried out, to model the “uncracked and cracked” shaft and to identify its bending and torsional vibration responses, are reported. The cylindrical shaft used in this experimental study is continuous over two spans (with a cantilever span carrying a propell...

An experimental program was undertaken to test the feasibility to detect the occurrence of structural damage using a modified mode shape difference technique. The vibration response of a steel beam fixed at one end and hinged at the other was obtained for the intact and damage conditions. Modal analysis was performed to extract the frequencies and...

The punching shear strength of two way slabs without shear reinforcement and without unbalanced moment transfer is estimated using both neural networks and new simplified punching shear equations. An artificial neural network (ANN) was used to predict the punching shear strength of internal slab–column connections. Neural network analysis is conduc...

Offshore structures are subjected to wind loads, wind generated wave excitations, and current forces. In this paper we focus on the wind generated wave excitations as the main source for the external forces on the structure. The main objective of the paper is to provide a tool for using deck acceleration measurements to predict the value of the for...

The objective of this work is to investigate the possibility of using the longitudinal strain on the surface of a pipe to determine the inception of dangerous free spanning. The long term objective is to develop an online monitoring technique to detect the development of dangerous free spanning in subsea pipelines. This work involves experimental s...

On-line identification of cracks occurring in large structures has attracted the attention of many researchers. Identification becomes difficult when there is no easy access available for investigators to employ conventional nondestructive evaluation techniques. In this paper, a scheme is presented for identifying the crack location and its extent...

In this paper, the mα-tangent method is implemented in conjunction with elastic modulus adjustment procedure (EMAP) and an algorithm has been proposed for limit load estimation. This technique is applied to a number of ship structure components possessing different kinematic redundancies. Specifying spatial variations in the elastic modulus, numero...

Limit loads for ship structure components are determined in this paper based on a single linear elastic finite element analysis by invoking the concept of kinematically active reference volume in conjunction with the mα-tangent method. The method enables rapid determination of lower bound limit loads for ship structure components by taking their ki...

Stress corrosion cracking (SCC) problems are routinely observed in boiling water reactor (BWR) units. Nickel-based alloy welds are commonly used in BWR units; the nickel content of the material improves resistance to stress corrosion cracking. However, stress corrosion cracking is still a problem for these welds. When a crack is detected, a decisio...

Offshore jacket structures are composed of tubular members. As offshore structures go deeper into the ocean, the water pressure on these tubular elements is increased. This paper discusses the effect of external and internal pressure on the buckling behavior of the circular cross section tubular elements or pipes. The linear and nonlinear buckling...

There is a need for accurate modeling of mechanisms causing material degradation of equipment in process installation, to ensure safety and reliability of the equipment. Degradation mechanisms are stochastic processes. They can be best described using risk-based approaches. Risk-based integrity assessment quantifies the level of risk to which the i...

This paper discusses the damage detection in offshore jacket platforms subjected to random loads using a combined method of random decrement signature and neural networks. The random decrement technique is used to extract the free decay of the structure from its online response while the structure is in service. The free decay and its time derivati...

A simple method is used to predict damping and natural frequencies of a fixed offshore platform subjected to wind-generated random waves using its stationary response. The method also predicts the reaction forces and bending moment at the foundation of the platform. The method uses the random decrement signature as a tool to identify the parameters...

The random decrement technique is an averaging technique that can be used to extract the free decay response of a structure from its stationary random vibratory response. The free decay response can then be used to identify the vibratory characteristics of the structure. The main advantage of the technique is that the identification of the paramete...

This paper describes a parametric identification tool for predicting the hydrodynamic forces acting on a submarine model using its motion history. The tool uses a neural network to identify the hydrodynamic forces and moments; the network was trained with data obtained from multi-degree-of-freedom captive maneuvering tests. The characteristics of t...

The deterioration of a gas processing asset has a major impact on the continuous operation of the facility. Risk based integrity modeling renders a framework to quantify the risks posed by an ageing asset and hence to protect the human life, financial investment and the environment from the consequences of its likely failure. In risk based integrit...

In this paper, the dynamic response of a scale model of a jacket offshore structure is investigated both theoretically and experimentally. The experiments were conducted both in air and in water. The in-water experiments were done in the towing tank of Memorial University to simulate the realistic operating conditions. The model was subjected to ra...

This paper describes a method to identify the parameters of the dynamic model of a fixed offshore platform subjected to wind-generated random waves using its stationary response. The structure is modeled as a single degree of freedom system. The parameters identified are the damping coefficient, the natural frequency, and the excitation. In additio...

The objective of this paper is to select the optimum non-destructive inspection (NDI) technique and its associated in-service inspection interval for welded components subjected to cyclic loading fatigue. The objective function (total cost) is formulated as a function of the decision variables (controllable) and the condition of the inspected asset...

The deterioration of the condition of process plants assets has a major negative impact on the safety of its operation. Risk based integrity modeling provides a methodology to quantify the risks posed by an aging asset. This provides a means for the protection of human life, financial investment and the environmental damage from the consequences of...

This paper presents a risk-based methodology to estimate optimal inspection & maintenance intervals which maximize a system's availability. The methodology is comprised of two steps: availability modeling, and risk-based inspection & maintenance calculations. The methodology is easy to apply, and needs readily available data. The approach can be fu...

This paper describes a scheme for identifying damage on a cross stiffened plate of a tanker ship model. Two damage locations were investigated. One was located at the intersection between the longitudinal and the bulkhead. The other was located at the intersection between the longitudinal and the web frame. The amplitude of a function containing th...

A method is developed to predict the time series of the wave exciting moment per unit virtual mass moment of inertia using the stationary random roll response. The estimated variance and autocorrelation function of the excitation are compared with those obtained using numerically generated data. The agreement is excellent. The method was also appli...

A parametric identification method for the estimation of hydrodynamic derivatives embedded in the nonlinear steering equations for ship maneuvering in calm seas is presented. The models developed for identification involve determination of constant, "low-frequency" hydrodynamic derivatives. The method is robust, noniterative, and computationally li...

In this paper we discuss the results of experimental and numerical studies carried out for monitoring the integrity of a 1/20th model of the side shell of a ships structure, using its vibration responses. The model was tested for different crack development scenarios under random exciting force having a dominant spectral frequency much lower (appro...

Process plants deal with hazardous (highly flammable and toxic) chemicals at extreme conditions of temperature and pressure. Proper inspection and maintenance of these facilities is paramount for the maintenance of safe and continuous operation. This article proposes a risk-based methodology for integrity and inspection modeling (RBIIM) to ensure s...

The unexpected failures, the down time associated with such failures, the loss of production and, the higher maintenance costs are major problems in any process plant. Risk-based maintenance (RBM) approach helps in designing an alternative strategy to minimize the risk resulting from breakdowns or failures. Adapting a risk-based maintenance strateg...

A new frequency domain system identification method for estimation of hydrodynamic derivatives embedded in linear steering equations for ship maneuvering in calm seas is presented. The frequency domain multiple input-single output models developed for identification involves determination of constant, 'zero-frequency' hydrodynamic derivatives. The...

This paper discusses recently proposed methodology for the design of an optimum maintenance management program. The methodology is based on integrating a reliability approach and a risk assessment strategy to obtain an optimum maintenance schedule. The method is called risk-based maintenance (RBM). First, the likely equipment failure scenarios are...

The increasing complexity of oil and gas installations and operations, along with growing public awareness to ensure higher levels of safety, has put great pressure on the designers and operators to find innovative solutions to ensure safe as well as economically viable operation. Risk-based inspection and maintenance helps in finding such solution...

This paper discusses a methodology for the design of an optimum inspection and maintenance program. The methodology, called risk-based maintenance (RBM) is based on integrating a reliability approach and a risk assessment strategy to obtain an optimum maintenance schedule. First, the likely equipment failure scenarios are formulated. Out of many li...

Early identification of cracks in complex structures is desirable for the safety of operation and economy of maintenance of the structure. Monitoring of the vibration response of structures is a well-known technique for crack identification. As the complexity of the structure increases manual inspection becomes difficult and the use of on-line moni...

The overall objective of the maintenance process is to increase the profitability of the operation and optimize the total life cycle cost without compromising safety or environmental issues. Risk assessment integrates reliability with safety and environmental issues and therefore can be used as a decision tool for preventive maintenance planning. M...

A description was given to a time-domain technique for real-time estimation of wave-induced vertical bending moment from ship motion measurements. The estimated values can be compared with those obtained from the strain gauge readings to ensure the validity of hull response monitoring systems. Artificial neural networks were used to model the time-...

The main objective of this work is to investigate the effects of the damping level as well as different excitation forms on the overall prediction of the hydrodynamic parameters in the equations describing the coupled heave and pitch motions for an Underwater Robotic Vehicle (URV) sailing near the sea surface in random waves. The response of an und...

Visual inspection of large and complex structures such as a ship is difficult and costly due to problems of accessibility. In this paper, a neural network technique is developed for identifying the damage occurrence in the side shell of a ship’s structure. The side shell is modeled as a stiffened plate. The input to the network is the autocorrelati...

Random roll responses measured during the sea trials of two Canadian Coast Guard search and rescue vessels have been analysed using an innovative approach. This approach comprises the use of a combination of the random decrement technique, a neural network algorithm and mathematical modelling. Roll characteristics are found to vary randomly. Estima...

A time-domain technique for estimating wave-induced ship hull bending moment from ship motion measurements is presented. This technique is developed to improve hull response monitoring systems. Artificial neural networks are used to model the time-domain relationship between the wave-induced vertical bending moment and the coupled heave and pitch m...

A method for the identification of the damping, restoring, and coupling parameters in the equations describing the coupled heave and pitch motions for an underwater robotic vehicle (URV) sailing near sea surface in random waves using only its measured responses at sea is presented. The random decrement equations are derived for the URV performing c...

A description is given of a time-domain technique for real-time estimation of a wave-induced vertical bending moment from ship motion measurements. The estimated values can be compared with those obtained from the strain gauge readings to ensure the validity of Hull Response Monitoring Systems. Artificial neural networks are used to model the time-...

When structural damage occurs, the dynamic characteristics of the structure changes correspondingly. This can be used to detect damage occurrence. In this paper, an autocorrelation function was utilized to identify damage in the side shell of ship structures using a combination of experimental and numerical studies. A stiffened plate was used to mo...

Most of the damage in ship structures occurs in the side shell, especially in the connection between the longitudinal and transverse members. The purpose of this study is to apply the random decrement technique for identifying the damage in the longitudinal using a combination of experimental and numerical studies. The side shell was modeled as a s...

A review of the available methods for the calculation of wind loads on ships and offshore structures is presented. Based on the review, four methods were selected and implemented in order to carry out a comparative study of the wind loads on ships. Namely, the ahead force, the side force and the yawing moment were calculated and compared. A large t...

Time domain simulation techniques are becoming a widely accepted tool for the evaluation of controllability and manoeuvring performance of conventional surface ships. Different simulation packages are available on a commercial basis. The accuracy of predictions obtained using these models are largely dependent on the level of accuracy in estimating...

This paper outlines a procedure for the derivation of the differential equations describing the free response of a heaving and pitching ship from its stationary response to random waves. The coupled heave–pitch motion of a ship in random seas is modelled as a multi-dimensional Markov process. The partial differential equation describing the transit...

The dynamic response of flat horizontal plates vibrating in air and under water has been investigated experimentally and analytically. The effect of the boundary conditions and the depth of submergence of the plates has been studied. Excellent agreement was obtained between the analytical solution and the experimental results. An approximate expres...

The objective of the work reported here is to ensure that ice-capable ships are both safe and economical. It is largely based on research conducted over the past two decades. The present methodology allows the designer to calculate a bow plating thickness which will resist local ice loads and be cost-effective. Full-scale data for the MV Canmar Kig...

The main objective of this paper is to present the application of the random decrement technique to nonlinear ship roll motion. The validity, accuracy and reliability of the method are investigated using model experimental and full-scale ship test data. The predicted natural frequency obtained using either the random decrement or autocorrelation fu...

An extensive experimental program has been carried out to estimate roll damping parameters for three models of fishing vessels having different hull shapes and moving with forward speed. Roll damping parameters are determined using a novel method. This method combines the energy method and the modulating function method. The effect of forward speed...

The lift force and turning moment acting on a model towed obliquely to the direction of motion have been measured. Two models were used; one of them was tested fitted with and without a rudder. These measurements were used to determine the magnitude of the lift coefficient and the point of application of the transverse force acting on the model. Th...

The concept of the random decrement has been used successfully in the damping identification of linear systems. The formulation of the random decrement existing in the literature is based on the assumption that the dynamic system is linear. Thus, one can use the principle of superposition in formulating the equation for the random decrement. In thi...

The results of an extensive experimental program to study the roll damping characteristics of a warship model are reported. The simple free decay curves obtained for a towed as well as a self-propelled nine metre model, fitted with and without bilge keels, rudder and propellers, were analysed using an energy approach. A new nondimensionalisation sc...

The determination of roll damping for non-standard hull shapes continues to be an important but difficult problem. For small fishing vessels with deep skegs and hard chines the problem is particularly difficult. In order to develop and judge suitable analytical, semi-empirical, and numerical techniques for the prediction of roll damping, the author...

An extensive experimental program for measuring, recording and analyzing free roll decay curves for three models representative of small fishing vessels was carried out. One of the objectives of this program is to study the form of the roll damping moment. The results indicate that a linear plus linear angle dependent form fits best the experimenta...

The free vibration of a rotating ship propeller blade is studied using an iterative scheme based on Galerkirís method. The blade is idealized as a cantilever beam with variable cross section of airfoil shape. The effects of pitch angle, shear deflection, rotary inertia and speed of rotation are studied. Agreement with results available in the liter...

This report presents the results of an experimental program carried out in the IMD towing tank to investigate the roll damping characteristics of a 9m destroyer hull model.

The angle dependence of the roll damping moment is investigated by analysing experimentally obtained free roll decay records. Two ship models were used with and without bilge keels, also results with forward speed were obtained. The analysis indicate strong angle dependence and explains why the quadratic and cubic velocity dependent damping moments...

The eigen value problem describing the transverse vibration of a propeller-tail shaft system in two perpendicular planes is formulated modelling the propeller as a rotor. Forward and reverse whirl speeds are calculated. These are found to have distinct values for a large propeller/shaft mass ratio. For small propeller/shaft mass ratio the two frequ...

The paper looks at various forms for the roll damping moment of ships and introduces two techniques to identify the parameters of the various models together with a methodology for their evaluation. The emphasis in the paper is on the possibility of using complete portions of roll decay curves rather than decrement curves derived from the peak valu...

Recent instances of marine crankshaft failure were attributed to secondary resonance which is a consequence of variable inertia. More insight into the secondary resonance producing mechanism may be gained by considering the effect of connecting rod obliquity. In this work an analytical method for the study of the effect of variable inertia, taking...

A general stochastic model for rolling motion in realistic environment has been formulated and analyzed. The model recognizes the well known nonlinearities of rolling motion, the stochastic time variations in the transverse stability and the nonstationary character of the excitation. The probability density function for the amplitude of the motion...

Different forms of rolling damping moment are considered. The effect of the difference in form on the rolling response of the ship is investigated. Results indicate that, within the range and scatter of available experimental data, damping moment form has little or no effect on the rolling response.

A nonlinear second order ordinary differential equation in yaw rate is used to study the directional stability of a surface ship when the ship moves with randomly varying forward speed. Randomly varying forward speed may be caused by surge motion in random following (or oblique) waves. A stability criterion is developed and stability loss is found...

The nonlinear equation of rolling motion in random oblique seas is analyzed considering parametric excitation caused by transverse stability variation in realistic seaway. Use of Bogoliubov-Mitropolsky's method of slowly varying parameters together with Stratanovich-Khasminsky's stochastic averaging is made to obtain an equation describing the vari...

The flow in a non-uniform clearance between the impeller shroud and the wear ring of a centrifugal pump was studied. Expressions for the pressure distribution and axial thrust was obtained. The case when these two variables are random functions is also considered. Extreme values for the pressure are estimated. (from authors' abstract)

The deterministic approach to the construction of mathematical models for solving the problem of load fluctuation in hydro-electric power plants has been the subject of considerable investigation. Means of mitigating adverse effects, by use of surge tanks or otherwise, has received equal attention.In fact, the load demand on an electric power plant...

An analytical method for the study of transient behavior as well as the stationary solution of nonlinear ship motion in random waves is presented. The problem of rolling motion of a ship traveling in oblique random waves is considered for the purpose of illustrating the method. The presence of nonlinear damping and restoration terms of general form...

Nondestructive techniques are based on the comparison of the static and dynamic behaviors of intact structures and their behavior in later times. The techniques are based on detection of any damage or deterioration through the structural behavior. One of the effective methods used in damage detection is based on the dynamic response of the structur...

Presents the results of an extensive experimental program carried out in the towing tank of Memorial University of Newfoundland. Free roll decay curves were obtained for three ship models of length approximately 1.5 m. These models represent fishing vessels under 25 m in length. They are all of similar dimensions but have varying hull forms ranging...

This report presents the results of an experimental program carried out in the IMD Clearwater Towing Tank to investigate the roll damping characteristics of a 9m warship hull form.

An alternative method for the prediction of a ship's dynamic bending stresses at sea is presented and examined in this paper. The method uses a ship's heave and pitch motion to determine the dynamic bending moment at a point along the ship's length. This can be combined with the known still water bending moment, and known ship sectional properties...

This paper describes the results of an extensive experimental program carried out to study the effects of forward speed on the roll damping of a warship model. The roll decay records were analysed using the energy approach and a new nondimensionalization scheme was used.