Shahrin, Muhammad I. (Universiti Teknologi Malaysia) | Abdullah, Rini A. (Universiti Teknologi Malaysia) | Sa’ari, Radzuan (Universiti Teknologi Malaysia) | Mustaffar, Mushairry (Universiti Teknologi Malaysia) | Jeon, Seokwon (Seoul National University)
Bench blasting is the most common method of rock excavation in productive quarries. Properties of the rock mass and the discontinuities are factors that influence rock fragmentation but cannot be controlled. In this study, the remote sensing techniques known as Terrestrial Laser Scanning (TLS) and Close Range Photogrammetry (CRP) using Unmanned Aerial Vehicles (UAV) have been utilised to generate 3-dimensional (3D) models of rock surfaces using Topcon ScanMaster and Agisoft Photoscan software. From the data obtained, rock mass can be classified using rock mass rating (RMR) and geological strength index (GSI); the blastability index (BI) is then obtained for blast design. A 3D model of the blasted rock surface is established based on pre and post-point cloud data. It can be concluded that the TLS and CRP methods, using UAV, can be used as complementary methods when classifying the rock mass and establishing the 3D finite element model of a quarry face.
The aim of blasting is to extract the largest possible quantity of rock at minimum cost in the safest manner possible whilst minimising side effects like flyrock, noise and ground vibration. Mackenzie (1966) mentioned that blasting is the cheapest way to fragment rock. Rock fragmentation has been the subject of much research because of its direct effects on the costs of drilling and blasting as well as the efficiency of the subsystems, such as loading, hauling and crushing in mining operations (Goodman &; Shi, 1985; Dershowitz, 1993; Faramarzi et al., 2013). In order to get good fragmentation during blasting, geometrical information such as discontinuities in the rock mass, needs to be clearly identified as this can help when designing the blasting pattern etc. Adhikari &; Gupta (1989) mentioned that rock mass properties are important parameters in a blast design and understanding the influence of geological discontinuities and the physico-mechanical properties of the rock is fundamental.
Characterisation of the rock mass requires the gathering of information through geological fieldwork, conventionally being collected manually using a compass-clinometer and a tape measure. The conventional methods are simple and effective, however the collection of data via fieldwork can be a hazardous, time consuming process and data quality may be affected by the user’s level of experience (Slob et al., 2010). Tannant (2015) highlights some of the drawbacks of hazard assessment of rock faces, such as: (i) safe access to the rock face to carry out geological mapping often does not exist, (ii) it is difficult to measure the orientation and geometry of large geological structures such as faults by simply measuring an orientation where a scanline crosses the fault, and (iii) mapping with a compass at the base of a steep slope exposes people to the risk of harm from rock falls.
Blasting is commonly used energy to fragment the rock mass in mining, quarry and civil engineering projects. The aim of blasting in mining and quarry projects is to obtain the maximum yield with desired fragmentation in a safer manner with minimum side effects such as ground vibration, fly rock and noise. The parameters influencing blast results can be categorized to blast design parameters, explosive charge characteristics, properties of rock mass and intact rock. There are many rock fragmentation models were developed by previous researchers and each model incorporate with different blast design and rock mass parameters. The complexities and uncertainties involves are strong arguments for developing a more robust model by incorporating computerized numerical models based on first principles. However, in recent years with the aid of computer technology, some researchers have tried to develop the models based on the numerical method for the prediction of particle size of fragmentation. This review paper presents a framework for selecting the appropriate prediction blasting models on rock fragmentation in quarry blasting parameters which have significant influence on rock fragmentation.
In mining and quarrying operation, the aim of blasting is to extract the largest possible quantity of rock at minimum cost in a safer manner with minimum side effects happens. Blasting operation is carried out to provide quality and quantity requirements of production. Assessment of each blast is necessary to keep the aim of the blast is achieved. The blast results can be desired fragmentation and unwanted results such as ground vibration, fly rock and noise. Back-break and toe formation also consider as undesirable results.
A fly rock incident was reported on July 2013, where a factory worker was killed while 10 others were injured after being hit by rock debris from blasting at nearby quarry located in Johor, the incident also damaged 18 cars and 14 factories along the road, Mohamad et al. (2013).
Rock fragmentation has been the concern of many research works because it is considered as the most important aspect of production blasting, since it effects on the costs of drilling, blasting and the efficiency of all the subsystems such as loading, hauling and crushing in mining operations (Faramarzi et al., 2013).
In addition, Adhikari & Gupta (1989) mentioned that rock mass properties are important parameters in a blast design and understanding the influence of geological discontinuities and physicomechanical properties of rock is fundamental to obtain optimum fragmentation. Finally, this paper is limited to previous methods of prediction blasting models on blast results in quarry and mine. The blast results focus on rock fragmentation, flyrock, backbreak and ground vibration. The methods included empirical method, mechanistic method and numerical method.
Offshore structures are exposed to random wave loading in the ocean environment and hence the probability distribution of the extreme values of their response to wave loading is required for their safe and economical design. Due to nonlinearity of the drag component of Morison’s wave loading and also due to intermittency of wave loading on members in the splash zone, the response is often non-Gaussian; therefore, simple techniques for derivation of the probability distribution of extreme responses are not available. However, it has recently been shown that the short-term response of an offshore structure exposed to Morison wave loading can be approximated by the response of an equivalent finite-memory nonlinear system (FMNS). Previous investigation shows that the developed FMNS models reduce the computational effort but the predictions are not very good for low intensity sea states. Therefore, to overcome this deficiency, a modified version of FMNS models is referred to as MFMNS models is used to determine the extreme response values which improves the accuracy but is computationally less efficient than FMNS models. In this paper, the 100-year responses derived from the long-term probability distribution of the extreme responses from MFMNS and FMNS models are compared with corresponding distributions from the CTS method is investigated with the effect of current to establish their level of accuracy. The methodology for derivation of the long-term distribution of extreme responses (and the evaluation of 100-year responses) is discussed. The accuracy of the predictions of the 100-year responses from MFMNS and FMNS models will then be investigated.
For an offshore structure, wind, wave and gravitational forces are all important sources of loading. The dominant load, however, is normally due to wind-generated random waves. Probabilistic properties of the loading and the resulting responses are therefore required for risk-based design of these structures. The major obstacle in the probabilistic analysis of the response due to wave and current loading, is the nonlinearity of the drag component of Morison's wave loading (Morison, J.R. et al., 1950) which results in non-Gaussian probability distributions for both loading and response (Borgman, L.E., 1967; Tickell, R.G., 1977; Burrows, R., 1979 and Eatock Taylor, R. et al., 1981). The problem is further compounded by current and by intermittent loading on members in the splash zone, which have a significant effect on the statistical properties of response (Tung, C.C., 1995 and Liaw, C.Y. et al., 2003).
Linear random wave theory (LRWT) is frequently used to simulate water particle kinematics at different nodes of an offshore structure from a reference surface elevation record. However, it is well known that LRWT leads to water particle kinematics with exaggerated high-frequency components in the vicinity of mean water level (MWL). To avoid this problem, empirical techniques such as Wheeler and vertical stretching methods are frequently used to provide a more realistic representation of the wave kinematics in the near surface zone. Previous investigation shows that these two different methods of simulating water particle kinematics on the probability distribution of extreme responses could be significant leading to uncertainty as to which method should be used. Modified version of LRWT; effective node elevation and effective water depth methods are introduced which would significantly reduce the computational effort for evaluation of water particle kinematics in the near surface zone. While the offshore industry recognizes that different methods of simulating water particle kinematics lead to different responses, no systematic investigation has been conducted to investigate the effect of this on the probability distribution of the extreme responses. Thus, in this paper, the more efficient time simulation (ETS) method has been used to compare the magnitude of the 100-year responses derived from different methods. First, these methods and their differences are reviewed. Then, the ETS method will be used to calculate the 100-year responses from different methods are compared and the design implications will be commented on.
Offshore structures are used worldwide in a variety of water depths and environments and for a variety of functions. However, their primary use is for extracting oil and gas from the bottom of the sea. These structures must be designed to withstand a variety of loads such as the gravitational load, earthquake load together with wind and wave forces during their intended service life. However, the dominant load is generally due to wind-generated random waves. Morison's equation (Morison et al, 1950) is frequently used to calculate wave hydrodynamic loads on the cylindrical members of an offshore structure from wave-induced water particle kinematics. It can therefore be concluded that accurate estimation of wave-induced water particle kinematics is a key step for accurate prediction of wave loads on the structure.
Wellbore streaming current and their applicability in the location of subsurface sand bodies were discovered in 1931 and the usefulness of this measurement has persisted to the present day. Through the endeavor of many researchers, knowledge and understanding of streaming potential (SP) have slowly evolved from the original mere recognition of its existence to its present-day quantitative use in many applications such as Enhanced Oil Recovery (EOR), water flooding, intelligent wells, etc. The spontaneous potential acts to maintain overall electroneutrality when a separation of electrical charge occurs in response to gradients in pressure (Electrokinetic), chemical composition (Electrochemical), or temperature (Thermoelectric). In spite of it being discovered 70 years ago, unfortunately little work has been done to find measurable value especially for thermoelectric coupling coefficient. Many researchers attempt to generate a universal model for SP. They attributes the limitations (if any) of their model to the scarce availability of accurate estimation for coupling coefficient. This study measures the value of thermoelectric coupling coefficient for five rock samples saturated with 0.01M (NaCl) saline brine. The study takes account of temperature dependant electrode effect. The result shows value of 0.2 mV/K, which is in a good match with most of the published data. It was also found that there is no strong correlation between the thermoelectric coupling coefficient and porosity. The measured thermoelectric values are considered insignificantly small compared to the electrokinetic effect in the system.
Significant and dangerous drilling problem is created when suddenly facing massive lost returns. Consequently, conventional means of controlling the well through circulation down the drill pipe and returning up the annulus becomes impossible. Due to their heterogeneous nature, carbonate rocks typically present drilling challenges. In M offshore field it is common to encounter tight formations, highly fractured rocks, and vugular textures. Accordingly, alternate means of controlling the well and safely drilling ahead must be used.
This paper reviews and discusses the application of mud cap drilling (MCD) which was used to drill a well in a highly fractured formation offshore Iran in Persian Gulf. The target formation in 12 ¼? section of an appraisal well of Iran's M gas field shared with Saudi Arabia was a carbonate reef. This section contains highly fractured rocks and dissolution channels created by large caverns that partially collapsed with later sedimentation. When these dissolution channels were penetrated by the well path, the formation completely yielded to any small amount of pressure overbalance and complete loss of returns was experienced. Seismic analysis was not successful in clearly identifying these areas. All wells drilled into the target reservoir had the potential for this loss. All attempts at curing this lost circulation with conventional techniques failed. The logical way of approaching the problem and achieving total depth was to drill with MCD technique.
PETRPARS has recently implemented a MCD solution on one well offshore Persian Gulf, Iran, which experienced total losses. Once total losses are encountered, a series of procedures are executed that result in converting the well from a conventional drilling operation to a MCD operation. While drilling Well M03, PETROPARS encountered total lost in Surmeh and Neyriz formations from 7904 to 10184 feet. The consequent actions include trying to cure losses with lost-circulation materials, cementing, waiting on mud materials and enduring other drilling problems associated with massive losses encountered in the lower portion of the well. Full penetration of these formations requires the use of a MCD and consequently well cost was minimized due to application of this method. A comparison for the cost of drilling mud in 12 ¼? section in well M03 shows 43.7% reduction when drilling shifted to MCD technique.
This paper discusses the operational and technical problems encountered including well control, optimizing mud composition and usage, and formation evaluation on an appraisal well which was drilled on this field. The geology, lithology and causes of loss also will be discussed at this paper.
Soom, E. Mat (Petronas Carigali Sdn Bhd) | Husain, M. K. Abu (Petronas Carigali Sdn Bhd) | Zaki, N. I. Mohd (Universiti Teknologi Malaysia) | Nor, M. N. K. Mohd (Petronas Carigali Sdn Bhd) | Ayob, M. S. (Petronas Carigali Sdn Bhd) | Najafian, G. (The University of Liverpool)
Malaysia is the second largest oil and gas producer in Southeast Asia. The majority of jacket platforms in Malaysia have exceeded their design life with various types of underwater structure irregularities. Therefore, it is essential to address the reliability of the jacket platforms in Malaysia due to ageing and increasing environmental loading. Global Ultimate Strength Assessment (GUSA) methodology was established to support detailed reassessment applied in managing safety, integrity analysis and reliability by evaluating the ageing and existing platform loading. It is a tool for the high-end analysis of structures for risk based assessment and has been accepted by most of the major marine operators in the offshore industry. The main purposes of this analysis are to manage the structure’s risk level over its remaining service life and to initiate cost efficient inspection or mitigation actions, if required. Probabilistic models which are derived from structural reliability methods with the result from pushover analysis, are used to determine the annual probability of failure of the structure over its remaining service life. The outcome of these analyses can efficiently assist in understanding the structure failure mechanism and correctly define relevant type of mitigations required. In this paper, the reassessment of an ageing platform over 30 years old, still in production is presented to demonstrate GUSA capability to perform life extension evaluation. Due to the demand to prolong the production for a further 25 years, it has been evaluated in design level analysis in early stage. With the major modifications such as extension deck for multipurpose pump and outboard conductors have given rise to overstressed and fatigue issues.
Quen, Lee Kee (Universiti Teknologi Malaysia) | Abu, Aminudin (Universiti Teknologi Malaysia) | Muhamad, Pauziah (Universiti Teknologi Malaysia) | Kato, Naomi (Osaka University) | Sahekhaini, Asnizah (Universiti Terknologi Malaysia) | Abdullah, Hanida (Universiti Terknologi Malaysia)
The proposed paper investigates experimentally the effectiveness of strakes in suppressing the vortex-induced vibration (VIV) of a long flexible cylinder by varying the pitch, height and the number of helix of the strakes, which differ from the previous studies that only focus on short rigid cylinder. The experiment was conducted in towing tank with constant velocity under subcritical Reynolds number () by using a Poly Vinyl Chloride cylinder with aspect ratio of 162. CCD cameras were installed to capture the amplitude vibration and the frequency responses in both in-line (IL) and cross-flow (CF) directions while the fluctuation of tension was measured by using tension load-cell. The theoretical laminar boundary layer thickness around a circular cylinder was calculated and was used as a benchmark in deciding the height of strakes for the experiment.
The purpose of present study is to identify the optimum configuration of helical strakes that can be implemented on a long flexible riser with low mass ratio.
The experimental result shows the helical strakes perform well in mitigating the VIV. Significant VIV mitigation is found for the strakes with a certain height which is larger than the laminar boundary layer thickness. However, its effectiveness in suppressing the vibration amplitude of flexible cylinder is far smaller than the rigid cylinder. Varying the pitch of strakes influents the occurrence of lock-in region and prevent the switch of frequency into higher mode. Previous study stated that pitch of 15D is as effective as 5D for a rigid cylinder. However, it does not work on a flexible cylinder. Changing the height of strakes narrows the lock-in region and contributes most in suppressing the vibration of cylinder. Also, it is surprising to find that two-helical strakes perform slightly better than three-helical strakes in lower velocity range. The hydrodynamic forces of cylinders are still in the process of analysing.
The information presented in this paper will shed some light on the effectiveness of strakes with different configurations and suggest the appropriate dimension of strakes in term of pitch, height and the number of helix of the strakes as currently the available resources are limited.
Jamei, S. (Universiti Teknologi Malaysia) | Maimun, A. (University of Technology Malaysia) | Ghazanfari, S.A. (Universiti Teknologi Malaysia) | Tofa, M. (Universiti Teknologi Malaysia) | Ahmed, Y.M. (Universiti Teknologi Malaysia)
Many researchers have studied on the flow around a steel riser for the vibration and fatigue analyses that are the principal challenges in riser design and fabrication. It is a demand to enhance our knowledge about vortex-induced vibration effects (VIV) on the risers in deep-water for oil extraction.
VIV is the main factor to predict the long life of the risers. In this study, the fatigue estimation of steel riser in deep water will be numerically investigated, and then design parametric study respect to some design parameter such as mass ratio and aspect ratio of riser will be done.
The motion of the riser and flow pattern around it will be examined in detail. This fluid structure interaction (FSI) problem will be solved by commercial code ANSYS. Reynolds-averaged Navier-Stokes equations (RANS) and some turbulent models will be employed in computational fluid dynamics (CFD) for force calculation and finite element (FM) method will be used for structural analysis. For validation purpose, the numerical results will be compared with other research works. Next, the effect of design parameter on vibration and fatigue life of steel riser will be explored.
Hopefully, new findings of the current study can be useful for riser research and design.
Tofa, M. Mobassher (Universiti teknologi Malaysia) | Maimun, Adi (University of Technology Malaysia) | Ahmed, Yasser M. (Marine Technology Centre, Faculty of Mechanical Engineering, Universiti Teknologi Malaysia Skudai 81310, Malaysia) | Jamei, Saeed (Universiti Teknologi Malaysia) | Khairuddin, N.M. (Universiti Teknologi Malaysia)
Study of vibrations due to vortex shedding(VIV) in the wake of a cylinder that is exposed to a current is very important, especially for marine risers which are used to extract oil and gas from sea bed. The phenomenon of vortex induced vibration(VIV) has been one of the major concerns for hydrodynamic researchers due to its potential ability to cause severe fatigue damage, the hydrodynamics of VIV is a very complex subject to be dealt with. Though there are numbers of research papers about VIV simulation of a circular cylinder, most of them were related to 2D flow and lower Reynolds number. 3D numerical simulation of vortex induced vibration at high Reynolds number can be very challenging.
Successful 3D simulation can be useful for designing effective VIV suppression devices.
Suitable mesh and turbulence model are important to get desired results, analyzing computational time and resources are crucial before starting such projects. In this paper turbulence model such as DES and LES are used at three dimensional VIV simulation for a Reynolds number Re=104, results from CFD are compared with existing experimental results. A comparison was drawn between these two turbulence models in terms of result accuracy and computation time.
Hopefully discussion of this paper can be helpful for any future project that would deal with VIV simulation.