A consideration of the structural design of a large-scale floating structure

The land area of Japan, especially flat land, is very small compared with its economic size. Large-scale floating structures are one solution to satisfy the demand for space by utilizing the ocean. This paper presents a general view of the dynamic response characteristics of large-scale floating structures, pontoons and semi-submersibles. For example, it is shown that the natural frequencies of eigenmodes are higher than the natural frequency of heaving motion. The response of the outer framework of a structure is shown to be generally larger than the response of the central part. Within the limits of our present understanding of the general dynamic response characteristics of such structures, the design and analysis of semi-submersible, large-scale floating structures is discussed. For a pontoon-type large-scale floating structure, a type whose perimeter structure has been modified to become lighter and more rigid is proposed. With this modification, the dynamic response of the whole structure is imporved.     

Active control for installation of underwater structures

The trend towards deepwater development requires a new approach to underwater installation of offshore structures. The present method using crane vessels has some drawbacks in operations at more than 2000 m depth. The natural period of the coupled system of the rigged structure and the crane vessel becomes longer, so that it is no longer possible to manipulate the cranes to achieve the desired positioning accuracy. This paper examines the application of an active control technique for underwater installations as one of the solutions to the present problems. An active control technique also has the advantage that it can deal with the structural flexibility which allows the structure to be large and light-weight. This structural flexibility imposes problems of suppressing the elastic responses and securing the stability of the control system. In this paper, anH _∞ controller combined with a low authority control/high authority control (LAC/HAC) feedback controller is designed for cases where structural flexibility cannot be ignored. A robust model-following controller is examined for cases where the structure can be treated as rigid. In order to confirm the control algorithm and verify the possibility of the active control installation method, basin tests are executed using two types of neutrally buoyant flexible models with ultrasound ranging systems and thrusters.     

Rationale for utilizing 3PL in supply chain management: A shippers' economic perspective

In this paper we first propose a conceptual framework for evaluating 3PL (third-party logistics) utilization in SCM (supply chain management), in which it is assumed that shippers may enjoy advantages derived from four contributory sources of 3PL specialization: scale, know-how, searching ability, and IT skills. It is also supposed that shippers may particularly benefit from 3PL when facing uncertain business environments. We also apply principal–agent relationships to shippers and 3PL providers. Further, we see enhancing “agency efficiency” as important to obtaining the benefits of 3PL utilization. We also look at the role of 3PL provider selection, the “hold-up” problem under incomplete contracts, and asset ownership. After that we briefly discuss the utilization of 3PL and environmental concerns. These are the main points that we consider related to 3PL utilization. The main contribution of this study is to identify discussion points from models and theories, such as contract theory, that relate to the utilization of 3PL in SCM.