Spatial and temporal scales at which processes modulate genetic diversity over the landscape are usually overlooked, impacting the design of conservation management practices for widely distributed species. We examine processes shaping population divergence in highly mobile species by re-assessing the case of panmixia in the iconic olive ridley turtle from the eastern Pacific. We implemented a biophysical model of connectivity and a seascape genetic analysis based on nuclear DNA variation of 634 samples collected from 27 nesting areas. Two genetically distinct populations largely isolated during reproductive migrations and mating were detected, each composed of multiple nesting sites linked by high connectivity. This pattern was strongly associated with a steep environmental gradient and also influenced by ocean currents. These findings relate to meso-scale features of a dynamic oceanographic interface in the eastern tropical Pacific (ETP) region, a scenario that possibly provides different cost–benefit solutions and selective pressures for sea turtles during both the mating and migration periods. We reject panmixia and propose a new paradigm for olive ridley turtles where reproductive isolation due to assortative mating is linked to its environment. Our study demonstrates the relevance of integrative approaches for assessing the role of environmental gradients and oceanographic currents as drivers of genetic differentiation in widely distributed marine species. This is relevant for the conservation management of species of highly mobile behaviour, and assists the planning and development of large-scale conservation strategies for the threatened olive ridley turtles in the ETP.
Some fairly radical changes to the naval ship design process occurred during the 1970s. The decade of the 80s has also witnessed a steady stream of changes. One of the most significant was the establishment of the Ship Characteristics Improvement Board (SCIB) in the Office of the Chief of Naval Operations (OpNav), and the resulting influence on the dialog between the military requirements decision makers and the Navy's ship designers. Other changes have occurred for which the impacts are less clear. These include establishment of the chief engineer of the Navy (ChEng) position, creation of the Space and Naval Warfare Systems Command (SpaWar) and OpNav's “Revolution at Sea” initiative. This paper will describe and discuss these and other changes, and comment on the resultant impact. The authors will attempt to present a global view of the total pattern of changes and try to discern if we are on a path of revolution, or merely normal evolution.
The U.S. Navy has experimented with many approaches to design and build its ships. Using an existing design as the “parent” design, also referred to as “modified-repeat” design, is on its face an attractive option. Many acquisition executives, program managers and some ship design engineers believe that a design based on a parent has fewer technical risks than a new “clean sheet of paper” design and therefore the time and cost to design and build it will be reduced. They assume early in the ship acquisition program that “the design is mature”” and because of that fewer problems will be encountered in completing the design and savings will thus be accrued. Yet, a number of naval ships based on a parent design have in fact experienced unanticipated cost and schedule growth during construction as well as technical problems during their in-service life. The authors will examine some of these ship designs which were based on an existing design and/or prototypes and highlight the fallacies of such beliefs and assumptions. The authors will also briefly describe the development and use of more physics-based design tools during early stage design that can reduce the risks of a new clean sheet ship design through design space exploration and actual design maturation. The authors are convinced from our experience on over fifty major naval ship designs that much of the unbudgeted and unnecessary growth in the costs to produce naval ships can be attributed to poor design decisions during early concept design. Achieving a truly mature or stable ship design earlier in the design process is critical for ensuring successful ship design, acquisition, construction, and in-service outcomes.
In the summer of 2005, the lead ship of the LPD 17 Class was delivered to the US Navy. The LPD 17 is a highly capable amphibious assault warship, designed as a total ship system, which will provide significantly improved warfighting capabilities to support US Marine Corps and joint operations. Potential ship capabilities were initially explored as LX Concept Studies (1989–1990) and the final ship took form in the 1990s as Preliminary, Contract, and Detail Design progressed. Fabrication of the lead ship began in June 2000 and the LPD 17 was launched in July 2003. Currently, three ships have been delivered to the US Navy and five are under construction. The LPD 17 was the last contract design developed in‐house under the leadership of the Naval Sea Systems Command (NAVSEA) ship design group utilizing NAVSEA's highly experienced ship design workforce. Many new and innovative concepts and approaches were introduced into the LPD 17 design and acquisition process. The LPD 17 was the first surface ship design to experience the benefits of Total Ship Systems Engineering, Integrated Product and Process Development (IPPD), Navy–Shipbuilder Integrated Product Teams (IPTs) collocated at the shipyard, and an Integrated Product Data Environment (IPDE). Such dramatic changes created many opportunities, hurdles, and even some pain. The Navy's Center for Innovation in Ship Design (CISD) championed a systems engineering case study of the LPD 17 ship design addressing all phases from requirements determination through detail design. This paper provides a retrospective of what occurred in order to document best ship design practices and lessons learned and to determine how the naval ship design process can be further improved. These lessons learned and best design practices will help transmit accumulated intellectual capital to other shipbuilding programs and future design leaders. The construction and delivery of ships is at a stage that provides a logical benchmark from which to make assessments. For example, the Secretary of the Navy recently received the US Marine Corps initial impressions of the LPD 17 Operational Evaluation (OPEVAL): “The Right Ship, The Right Size, The Right Capabilities.” Although a number of ship design process innovations contributed to a sound Contract Design technical package, it is now common knowledge that the LPD 17 lead ship was over budget and late. The authors conclude that the most significant best practice, or lesson learned in the case of LPD 17, is that there must be a tightly integrated, seamless, collaborative design‐build approach between the Navy and the Shipbuilder(s) throughout the whole design‐build process starting at the very beginning of ship design. There are new ship design projects like MPF(F) and CG(X) that could benefit from the innovations, best practices, and lessons learned of the LPD 17 Ship Design: leading a sea change toward collaborative product development.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.