Collopy, Hallie (University of New Orleans) | Yu, Xiaochuan (University of New Orleans) | Li, Yi (University of New Orleans) | Hagimoto, Ken (University of New Orleans) | Meng, Haozhan (University of New Orleans) | Arbeiter, Scott (University of New Orleans)
The Space-X company has introduced a reusable first stage rocket that lands on a floating barge. In the event that the first stage rocket falls off the platform, investigation of where it will land on the seafloor in case its sensors are waterlogged is necessary to increase efficiency in the salvage operation. This paper mainly investigates the landing position of a model rocket through a model experiment. The University of New Orleans Towing Tank facility is used to release a model first stage Falcon 9 rocket at initial drop angles from 0° to 90°. The landing location is recorded and compared with the results derived from the 2D module of numerical simulation tool “DROBS” that solves equations of motion for dropped cylinders. The focus of this paper is to experimentally determine the effects of initial conditions on the landing position of this rocket model.
Dropped objects are among the top ten causes of fatalities and serious injuries in the oil and gas industry (DORIS, 2016). Objects may accidentally fall down from platforms or vessels during lifting or any other offshore operation. The accurate prediction of the landing points of the dropped objects may protect underwater structures and equipment from being damaged. In this paper, the authors propose a three-dimensional (3D) theory to numerically simulate the dynamic motion of a dropped cylindrical object under the water and to investigate the influence of the longitudinal center of gravity (LCG) on the motion. A numerical tool called Dropped Objects Simulator (DROBS) has been further developed on the basis of this 3D theory. It is initially applied to a dropped cylinder with its center of gravity at the center of volume (cylinder #1, LCGD0) falling from the surface through calm water. The calculated trajectories match very well with both the experimental and numerical results published in Aanesland (1987). Then DROBS is further utilized to simulate two dropped cylinders with positive LCG (cylinder #2) and negative LCG (cylinder #3), respectively. The simulated results from DROBS show better agreement with the measured data than the numerical results given in Chu et al. (2005). This comparison again validates and indicates the effectiveness of the DROBS program. Finally, the simulation is applied to investigate the effects of varying LCGs on the trajectory and landing points. The newly developed DROBS program can be used to simulate the distribution of the landing points of dropped cylindrical objects in order to predict risk-free zones for offshore operations.
Dropping tools and equipment into the sea during a lifting operation or any other offshore operation is unfortunately a fairly common event. Table 1 states probabilities according to DNV (2010). Dropped Objects Register of Incidents & Statistics (DORIS, 2016) lists dropped objects as one of the top 10 causes for fatalities and serious injury in the oil and gas industry.
DNV (2010) proposed specific rules about the risk assessment of pipeline protection. In its recorded simplified method, the probability of object excursions on the seabed is assumed to be normally distributed. However, we still lack specialized techniques to predict the trajectory of dropped objects and the subsequent likelihood of striking additional structures and equipment as well as the consequences of such impacts (ABS, 2010). Therefore, the trajectory dynamics of objects falling into the water and their landing points is of interest for the protection of oil and gas production equipment resting on the seabed.
Cao, Yu (Shanghai Ocean University, University of New Orleans) | Yu, Xiaochuan (University of New Orleans) | Liu, Ziyan (Institute of Ship Design and Research) | Xiang, Gong (University of New Orleans) | Ruan, Weidong (Zhejiang University)
In this paper, the new procedures to assess the bending performance of offshore unbonded flexible risers have been proposed. The multilayer bending responses derived from time-domain global dynamic analysis, instead of the traditional local model analysis, may be adopted in the assessment. This can help to save the computation time and increase the accuracy. In addition, the effects of bending hysteresis behavior are considered in the flexible risers’ global dynamic analysis and nonlinear collapsed hypothesis loop model is assumed in order to calculate the bending damage. Further, the sensitivity analysis is also carried out to examine the influence of various design parameters, such as critical curvature, slip stiffness and etc. The purpose of this research is to tentatively propose new assessment procedures to standardize the dynamic response analysis of flexible pipes in offshore engineering, which could be part of guidelines accepted by various class societies.
The offshore steel risers’ in-service may undergo severe corrosions. An effective way to alleviate the problem is to use unbounded flexible risers (Kyriakides and Corona, 2007). Due to the harsh environment, the safety issue seems to hinder its wide application in offshore engineering (Kardomateas and Simitses, 2005). Unbonded flexible pipes have been employed since the 1970s by the offshore oil and gas industry to transfer oil and gas from offshore wells to floating units (or between floating units), inject water or gas in offshore wells, or control and monitor them. When these pipes are used to transport fluids from the seafloor to production or drilling facilities (or from these facilities to the seafloor), they are called flexible risers. As illustrated in Fig. 1, the typical structure of unbounded flexible risers is mainly made of several steel and plastic concentric layers with low bending stiffness but relatively high radial and longitudinal stiffness. Three types of metallic layers are turned out to mainly withstand the imposed structural loads (Berge et al., 1992): inner carcass mainly provides strength against external hydrostatic pressure and crushing loads during installation operations; pressure sheath provides resistance against the hoop stress caused by internal pressure; tensile armors provide strength against the axial stress caused by internal pressure and by external load. Feret and Bournazel (1987) based on experimental tests, proposed the first model that presented the bending behavior of unbonded flexible risers.
This paper presents an extended method to simulate the coupled dynamics of top tensioned risers (TTRs) connected to Tension Leg Platforms. Coupling between TTR and TLP occurs at the tensioner system and the riser guides.
In this paper, a new TTR model that considered effects from tensioner system and riser guide is integrated into existing CABLE3D and COUPLE codes. Tensioner system is consisted of 4 tensioners each of which is treated as a linear spring and acting as concentrated force on TTRs. The motion of TLP is transmitted to TTRs through upper deck and riser guides. The vertical friction between TTRs and upper deck or riser guides is neglected. Results for several applications of up-dated CABLE3D and COUPLE are presented. First, a single TTR under harmonic excitation at the fairlead is analyzed. Corresponding TTR tensions and motions are obtained in time domain. Then a TLP with 9 TTRs and 12 Tendons is treated as a global system exposed to wind and waves.
Risers, such as top tension riser (TTR) and steel catenary riser (SCR), are usually used associated with TLP to secure the oil/gas transportation work so the coupling effects between TLP and risers are needed to be taken into consideration. Chen (2006) used COUPLE to calculate coupled dynamic analysis of a mini TLP with tendon and the riser system. The computation of the force interactions between each individual riser and the corresponding attaching point on the TLP is obtained at each time step. But if TTR is considered, generally, there are two kinds of support to provide top tension for TTR: buoyancy can and tensioner system. Huang (2013) has developed a new module in CABLE3D and COUPLE to consider such dynamic effects on both of them on a Truss spar. In his work, individual tensioner cylinder is treated as a linear spring while buoyancy can is modeled as constant buoyancy force. In TLP, the tensioner system is more popular and more widely utilized.
In this paper, the static and dynamic simulation of a TTR connected to TLP through a tensioner system and with a keel riser guide at near surface have been successfully achieved by extending CABLE3D's capabilities based on Huang (2013) . Firstly, the excitation on the TLP in the dynamic simulation is assumed to be a harmonic motion. Then the dynamic analysis of the TLP coupled with the TTRs and tendon systems is performed. The updated CABLE3D has been integrated into existing COUPLE. The main purpose of this study is to simulate TTR line tensions and TLP’s motions by using this extended model, and to show its capability in current and future research work.
Significant hydrodynamic interactions occur when transferring cargo at sea between a large cargo ship and a smaller amphibious. The motion response calculation between multiple bodies as well as the response control is a great concern for US Navy. The Deep Water Stable Craneship (DWSC) spar allows safe cargo transfer under a wide range of sea environments, because the DWSC spar is a very stable platform with a small waterplane. Further, the Dynamic Positioning (DP) system may be installed to minimize the motions of this spar.
In this paper, the hydrodynamic coefficients of the multibody floating systems are firstly calculated using the hydrodynamic software WAMIT. The motion Response Amplitude Operators (RAOs) for the multiple bodies are obtained and compared with the RAOs of the single body. Then, a new scheme to calculate the motion responses of multibody floating systems is proposed, in which the equations of motion (EOM) of multibody floating system are re-organized into standard state-space format, using the constant coefficient approximation and the impulse response function (IRF) method. In the IRF method, use the trapezoidal rule to expand the convolution term. Further, the Ordinary Differential Equation (ODE) solvers in MATLAB can be directly employed to solve this state-space model. The ideal DP system has been incorporated in the motion response control of multibody floating system. Especially, the innovative representation of EOM in the state-space format makes it easy to apply various controllers. In this example, the modified Linear Quadratic Regulator (LQR) Method is utilized to calculate the feedback force due to the thrusters of DP system.
Cargo-transfer and underway replenishment are essentially important in long-term naval operations. The Office of Naval Research (ONR) initiated a technology development program in 2007 called STLVAST (Small to Large Vessel At-Sea Transfer). The goal of this program is to develop ‘enabling capabilities’ in the realm of logistic transfer (i.e. stores, equipment, vehicles) between a large transport vessel (e.g., the USNS Bob Hope) and a smaller T-craft ship, using a Deep Water Stable Crane (DWSC) spar between them. The DWSC spar consists of two entities, a catamaran craneship and a detachable spar. In this paper, a new numerical scheme to simulate time-domain motion responses of floating systems has been successfully proposed and applied to the motion response control of the DWSC spar. The equation of motions using the Impulse Response Function (IRF) is initially discretized into a new state-space model, where the first order and second order waves loads transfer functions are calculated from WAMIT. Two time steps affect the construction of this state-space model: the time step Δτ used to estimate the IRF, and simulation step Δt. The LQR method is selected in this study. Firstly, the effects of both time step on the controlling efficiency is studied. Then various weighting factors (Q,R) for the LQR controller are further considered to study the robustness of the LQR method. INTRODUCTION The Cargo-transfer and underway replenishment are essentially important in the long-term naval operations. The Office of Naval Research (ONR) initiated a technology development program in 2007 called STLVAST (Small to Large Vessel At-Sea Transfer). The goal of this program is to develop ‘enabling capabilities’ in the realm of logistic transfer (i.e. stores, equipment, vehicles) between a large transport vessel (e.g., the USNS Bob Hope) and a smaller T-craft ship, using a Deep Water Stable Crane (DWSC) spar between them.
Huang, Liqing (Ocean Engineering Program, Civil Engineering Department, Texas A&M University) | Zhang, Jun (Ocean Engineering Program, Civil Engineering Department, Texas A&M University) | Yu, Xiaochuan (Ocean Engineering Program, Civil Engineering Department, Texas A&M University) | Randall, Robert E. (Ocean Engineering Program, Civil Engineering Department, Texas A&M University) | Wilde, Bob (Intermoor Inc)
Yu, Xiaochuan (Ocean Engineering Program / Department of Civil Engineering, Texas A&M University) | Kang, Hooi-Siang (Ocean Engineering Program / Department of Civil Engineering, Texas A&M University) | Huang, Liqing (Ocean Engineering Program / Department of Civil Engineering, Texas A&M University) | Xie, Yonghe (School of Naval Architecture and Civil Engineering, Zhejiang Ocean University) | Zhai, Qiang (Department of Mechanical Engineering, University of Wisconsin Milwauke) | Chen, Guojian (School of Naval Architecture, Ocean and Civil Engineering, Shanghai Jiao Tong University)