The Steel Catenary Riser (SCR) is often the preferred riser concept in deep and ultra deepwaters when it is proven to be a feasible riser solution. One of the first tasks in any front end engineering study is to assess the feasibility of SCRs for the applicable design criteria and the floating system of interest. A number of SCRs have been installed worldwide over the years and SCR technology is gradually becoming mature. However, the expanding needs of the offshore industry tend to continuously push the limits of SCR technology. Engineers are often asked to assess the feasibility of SCRs outside the limits of what has been done to-date. SCR feasibility is controlled by fatigue in the touch-down zone. The purpose of this paper is to describe some recent studies on pragmatic ways to enhance fatigue performance of SCRs. These studies include a number of insightful sensitivity analyses and innovative solutions which can help SCR engineers throughout the industry. 1.0 Introduction A recent survey [1] indicates that there are more than seventy Steel Catenary Risers (SCRs) in operation connecting both import and export lines to fixed and floating platforms, and at least eighty additional SCRs are in the planning and fabrication stages. This indicates the growing maturity of SCR technology. However, design challenges remain, and a combination of larger vessel motions, lower water depth, larger pipe diameter and/or degradation of the fatigue S-N curve due to sour service application can result in conventional SCRs being found to be infeasible for a project. It is generally considered a greater challenge to suspend SCRs from vessels with relatively higher motions, such as semi-submersibles and FPSOs. In the present paper, attention is focused on SCRs attached to semi-submersible vessels, although much of the findings are general enough to be applicable to other floating platform types also. The schematic of a typical SCR is shown in Figure 1. In general, fatigue performance, especially in the Touchdown Zone (TDZ), poses a greater challenge to SCR design than strength response. In instances where low fatigue life in the TDZ of the SCR poses seemingly insurmountable difficulties, instead of switching to an entirely different riser concept, it may be possible to add enhancements to the basic SCR configuration in order to achieve acceptable performance. This paper discusses the factors that control the fatigue response of SCRs suspended from floating production systems. Solutions to the TDZ fatigue problem using currently available techniques/technologies are presented, along with the results of sensitivity studies. 2.0 Factors Controlling SCR TDZ Response Typically, the water depth, SCR diameter, pressure requirements, soil properties and environmental conditions are fixed by specific project requirement. All other factors are open to variation, especially in the early "system selection" phase of a project. References [2,3,4,5] provide interesting insights on the effects of soil nonlinearities, self trenching and incorporating K-C number dependent hydrodynamic coefficients, each of which can impact (and, for the most part, improve) the calculated fatigue life at the TDZ significantly. These are general topics on which research has been done, and continues to be performed. This paper will not address these issues. Instead, this paper will concentrate on fundamental aspects related to response and feasibility enhancement of SCRs attached to Semi-FPS vessels.

It is shown in this paper that a semisubmersible-FPS can be used as a dry tree platform in ultra-deep water Gulf of Mexico when designed with Compliant Vertical Access Risers (CVARs). The Technical feasibility of the proposed dry tree semi concept is demonstrated by an example application in 8,000 ft water depth. Riser extreme response, interference and fatigue have been analyzed. Installation schemes have been considered. It is concluded that the proposed dry tree semi concept is technically feasible and that it can provide an attractive lower cost solution for dry trees in the ultra-deep parts of the Gulf of Mexico. Introduction Dry tree platforms have been used in the Gulf of Mexico in water depths up to 5,400 ft. Studies have shown that it becomes expensive to extend the application of conventional dry tree platform concepts (TLPs and Spars) to ultra-deep water depths such as 8,000 or 10,000 ft. We propose an alternate dry tree platform concept to provide operators with the benefits of direct access to wells from lower cost floating systems such as the semisubmersible-FPS (henceforth 'semi- FPS'). Dry tree wells are tied back to the semi-FPS using Compliant Vertical Access Risers (see Figure 1). The CVAR is attached rigidly to the semi-FPS (see Figure 2) via a flexjoint or a tapered stress joint avoiding the need for flexible jumpers and simplifying deck layout. Unlike a Spar or a TLP, there is no relative motion between the riser top and the vessel in operation, simplifying access to the dry trees and well access during workovers. At the sea floor the CVAR is attached to the wellhead in much the same manner as a Top Tensioned Riser (TTR). The CVAR, like Spar or TLP TTRs, has the benefit that the riser is vertical at its top and bottom - permitting vertical access. TTRs obtain their compliancy by virtue of relative motion at their tops which is accommodated by tensioner or buoyancy can stroke. CVARs obtain their compliancy from excess riser length. Since the buoyancy is distributed approximately in the middle portion of the riser CVARs have the characteristic shape shown in Figure 1. Background The idea of the CVAR dates back (at least) to 1988 when a patent was awarded to Pearce et al [1] for a flexible riser and associated equipment that could be used to obtain vertical access to a subsea well. (The patent belongs to Halliburton/KBR.) KBR carried out a number of early studies in the late 1980s and early 1990s on the feasibility of using CVARs as production and workover risers from floating production systems in 3,000 to 6,000 ft depths. Brinkmann and Whooley [2] describe the use of CVARs with a Spar (also known as Deep Draft Caisson Vessel or DDCV) in 4,800 ft of water in the Gulf of Mexico. However, a study on this subject has not been reported so far.

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The analysis of thermoelastic wave propagation in continuum solids at micro/nano-seconds is especially significant for ultrafast heating technologies, where strain relaxation effects will increase significantly. In most cases, it is commonly accompanied by a relatively small strain-rate; however, this is questionable in the environment of transient thermal wave propagation under the ultrafast heating case. The present work is dedicated to constitutive modelling of a novel generalized thermoelasticity model by introducing an additional strain-rate term associated with a relaxation time parameter in the Lord-Shulman (LS) thermoelasticity with the aid of an extended thermodynamics framework. As an application, the newly developed model is applied to a half-space one-dimensional problem which is traction free at one end a time-dependent thermal shock is imposed at the same end to analyze transient responses of thermodynamic field variables (temperature, displacement, strain and stress). The inclusion of strain-rate in the LS model eliminates the possible propagating jump discontinuities of the strain and stress fields at the wavefront. The current work is expected to be useful in the mathematical modelling and numerical simulation of thermoelastic processes under an ultrafast heating environment.