Relocation Of Vessels Research Articles

Vessel relocation strategy for multiple steel catenary riser fatigue damage mitigation

In previous work, the vessel relocation methodology for a single steel catenary riser (SCR) was developed to extend the fatigue life of the SCR touchdown zone (TDZ). The method was developed considering symmetrical vessel relocation programs, where the vessel offsets about the nominal station in all directions is equal. However, in actual field applications, the production platform hosts multiple SCRs of different azimuth, cross-section geometry and global configurations. Also, the symmetrical relocation consideration eliminates the potentials of exploring non-symmetrical relocation patterns that may be suitable candidate solutions. These considerations add complexity to the problem since, for example, each of the SCR may have unique optimum relocation programs (ideal solutions), but one global optimum solution is required. In this work, we extend the symmetrical relocation method and apply the index matching technique to solve the multi-objective optimisation problem. The non-symmetrical relocation of this methodology for multiple SCRs is demonstrated by comparing the global optimum solutions with those of the no-relocation case. The developed approach can be applied to new and existing SCRs for life extension purposes.

Vessel relocation solution for steel catenary riser touch down fatigue management

This work is focused on developing a formal optimisation approach to the vessel relocation program for steel catenary riser (SCR) touch down zone (TDZ) fatigue management. Vessel relocation is the planned repositioning of the vessel within the acceptable limit of the riser design to help spread and reduce the fatigue damage over the SCR TDZ. There is a need to obtain an optimum vessel relocation program that best reduces the SCR TDZ fatigue damage. Hence, the facility operator will need to know the optimum combination of the following: the number of stations along the relocation axis, the distance limits for the relocation, and the relocation axis direction. The constraints on the problem are imposed by the stress utilisation, TDZ compression and top tension. The index-matching optimisation technique is applied to solve the optimisation problem. To demonstrate the approach's suitability, we consider a single SCR hosted by a production platform. The fatigue damage responses of the SCR with the optimum vessel relocation programs are compared with those without vessel relocation. The results obtained indicate that a considerable fatigue reduction can be achieved through a well-planned and optimum vessel relocation program.

A dynamic multi-objective location-allocation model for search and rescue assets

This paper presents a dynamic multi-objective mixed integer linear programming model to optimize the location and allocation of search and rescue (SAR) boats and helicopters to enhance the performance of maritime SAR missions. Our model incorporates simulated incident scenarios to account for demand uncertainty and allows relocation of vessels seasonally. We define three objectives as responding to incidents within a critical time, generating a balanced workload distribution among vessels of various types, and minimizing costs associated with operations and vessel relocations. Implementing a goal programming approach, we solve the problem for various objective function term weights and compare the performance of each solution with respect to 10 different metrics. Using historical incident datasets for the Aegean Sea, we show that the proposed model and solution approach can significantly improve the SAR performance and provide decision support for planners in developing effective and efficient resource location-allocation schemes.

Short-term intermittent parathyroid hormone (1-34) administration increased angiogenesis and matrix metalloproteinase 9 in femora of mature and middle-aged C57BL/6 mice.

What is the central question of this study? We sought to assess the effects of intermittent parathyroid hormone (1-34) administration on bone angiogenesis, the redistribution of bone marrow blood vessels, and matrix metalloproteinase9 as a function of advancing age in mice. What is the main finding and its importance? Short-term (i.e. 10 days) intermittent parathyroid hormone (1-34) administration increased the number of small (≤29-µm-diameter) bone marrow blood vessels and augmented matrix metalloproteinase9. These changes occurred before alterations in trabecular bone. Given the rapid response in bone angiogenesis, this investigation highlights the impact of intermittent parathyroid hormone (1-34) administration on the bone vascular network. Intermittent parathyroid hormone (PTH) administration augments bone, stimulates the production of matrix metalloproteinase9 (Mmp9) and relocates bone marrow blood vessels closer to osteoid seams. Discrepancies exist, however, regarding bone angiogenesis. Given that Mmp9 participates in cellular homing and migration, it might aid in blood vessel relocation. We examined the influence of short-term intermittent PTH administration on angiogenesis, Mmp9 secretion and the distance between blood vessels and bone. Mature (6- to 8-month-old) and middle-aged (10- to 12-month-old) male and female C57BL/6 mice were divided into three groups: control (CON), and 5 (5dPTH) and 10days (10dPTH) of intermittent PTH administration. Mice were given PBS (50µlday-1 ) or PTH(1-34) (43µgkg-1 day-1 ). Frontal sections (5µm thick) of the right distal femoral metaphysis were triple-immunolabelled to identify endothelial cells (anti-CD31), vascular smooth muscle cells (anti-αSMA) and Mmp9 (anti-Mmp9). Vascular density, Mmp9 density, area and localization, and blood vessel distance from bone were analysed. Blood vessels were analysed according to diameter: 1-29, 30-100 and 101-200µm. Trabecular bone microarchitecture and bone static and dynamic properties were assessed. No main effects of age were observed for any variable. The density of CD31-labelled blood vessels 1-29 and 30-100µm in diameter was higher (P<0.05) and tended (P=0.055) to be higher, respectively, in 10dPTH versus 5dPTH and CON. Mmp9 was augmented (P<0.05) in 10dPTH versus the other groups. Mmp9 was closer (P<0.05) to blood vessels 1-29µm in diameter and furthest (P<0.05) from bone. In conclusion, bone angiogenesis occurred by day10 of intermittent PTH administration, coinciding with augmented Mmp9 secretion near the smallest blood vessels (1-29µm in diameter).

Technical Solutions for Common Problems in TEVAR:

Thoracic endovascular aortic repair (TEVAR) is rapidly emerging as an important treatment option for several indications, and it would not be unreasonable to predict that endograft treatment may well become the predominant form of therapy for many, if not the majority, of patients. However, several unresolved issues remain, and the need for further improvements and technological refinements will not cease any time soon. Ranking high among these issues are the challenges related to endovascular access and aortic branch management, which constitute the main focus of this review. Achieving safe and successful endovascular access for introduction and deployment of the stent-graft device is a crucially important and often challenging step during TEVAR, but arterial injury has been, and continues to be, an all-too-common occurrence to this day. A clear understanding of the relevant issues and available technical solutions can go a long way toward preventing such catastrophes. A preponderance of thoracic aortic pathologies tend to develop adjacent to or within the branched segments. It is therefore not surprising that branch management issues have risen to the top of the entire TEVAR field. Debranching and vessel relocation techniques have added a whole new dimension to the therapy because they can expand or create suitable landing zones proximally and distally, thereby broadening the applicability of endograft technologies to a much larger number of patients.

Visceral vessel relocation techniques

It has been more than a decade since the first implantation of a thoracic stent graft was reported, and only recently has the first device been approved by the Food and Drug Administration. Even though the technology has been approved by the Food and Drug Administration for 5 years for infrarenal aneurysmal repair, devices for use in the thoracic aorta are considered first generation and are limited by constraints similar to those that infrarenal devices are subject to. Additionally, complicated devices that allow for fenestration or branched designs are lacking or are only in the initial phases of development. Providing adequate distal fixation and accomplishing aneurysm exclusion with an appropriate sealing region is the most challenging task in many patients. Almost all infrarenal devices require 1.5 cm of aortic neck length to provide adequate fixation and seal for aneurysmal exclusion. Additional length is needed in the thoracic aorta, however, given its larger size; 2.0 to 3.0 cm is generally thought to be sufficient. Some experts rely on a ratio calculation and target a fixation length of 0.75 times the aortic diameter as a minimal acceptable length. It is also crucial that the aortic walls be fairly parallel and free of significant calcification and thrombus. Although isolated thoracic aortic lesions can still meet these requirements, many thoracic aortic processes involve the entire descending thoracic aorta and end at, or near, the crus of the diaphragm or in the visceral section. In these cases, obtaining adequate fixation can be problematic. The angle of the descending thoracic aorta also plays a major role in the migration of thoracic stent grafts, possibly causing a cephalad migration of the caudal aspect of the device. It can also make precise deployment rather difficult; many times it is necessary to deploy an additional distal extension. Implanting the device in a region where significant angulation exists can jeopardize the durability of the endovascular repair. Finally, most stent graft deployment mechanisms are designed for precise proximal placement with minimal or no control over the distal attachment site or landing zone. Therefore, accurate deployment near the celiac artery becomes more challenging. Given the aforementioned issues,

Thoracic Aortic Stents: a Combined Solution for Complex Cases

Objectives: the combination of endovascular and standard surgical techniques may facilitate the management of complex aortic disease although the long-term durability of this approach needs to be confirmed. Design: a retrospective review of our experience in the treatment of patients with complex aortic pathology using a combined endovascular and surgical approach. Materials and methods: between 1998 and 2001, 27 patients with thoracic aortic aneurysm underwent stent-graft implantation. Eight required combined endovascular and surgical procedure because of complex pathology. In 3 cases, combined repair was carried out for a concomitant abdominal aortic aneurysm or aorto-iliac-femoral occlusive disease. In the other 5 cases, vessel relocation was performed to obtain safe landing zones: left subclavian artery to left carotid artery translocation in 3 patients, celiac trunk to superior mesenteric artery translocation in one and aorto-celiac-mesenteric bypass grafting in one. Results: one of the 8 patients died on 12th post-operative day of intestinal bleeding and bowel infarction. No neurological sequelae were reported. The other patients are currently well at 11 months mean follow-up time. Conclusions: simultaneous surgical and endovascular procedure is a feasible and may be a valuable adjunct to the treatment of complex aortic and peripheral vessel anatomy.

Repair of coexistent infrarenal and thoracoabdominal aortic aneurysm: Combined endovascular and open surgical procedure with visceral vessel relocation

J Thorac Cardiovasc Surg 2002;124:184-5