ABSTRACT

This paper describes the procedures used and sample information obtained in conducting field measurements of wave pressures acting on Dubai Petroleum Company's Khazzan No.3 storage vessel during March of 1973.

One of the major concerns in designing marine structures is determining dynamic wave loads. CBI decided during the design phase of the Dubai type tanks that a full scale investigation of the wave forces acting on a structure of this size would provide much needed information, to establish the credibility of the potential wave force theory applied to large structures.

A novel feature of the instrumentation setup enabling installation, calibration and recovery of the recording transducers is described.

INTRODUCTION

Since the concept of the submerged oil storage tank, Chicago Bridge & Iron Company has been engaged in an extensive program involving theoretical and model simulation studies to determine wave forces on various marine structures. In addition to investigating a number of basic shapes, CBI has also conducted extensive studies of the Dubai Khazzan type subsea oil storage vessels.

One of the major concerns in the design of most marine structures is determining the forces acting on a structure caused by dynamic wave activity.

The present trend toward larger structures and deeper waters have created an even more vital need for field information of wave loads. CBI has developed a potential wave force theory which predicts both the incident and scattered potential pressures and thus forces on bodies of revolution. In order to enhance the credibility of potential theory and its correlation to various model data, a full-scale investigation of ocean wave pressures was conducted on the Dubai Khazzan No. 3 storage tank in the Arabian Gulf.

This field test involved the recording of dynamic pressures acting on both the external and internal portions of the tank surfaces. The analysis of the information brought back from Dubai consists of comparisons between these measured pressures and those calculated using potential theory No attempt has been made to analyze the measured pressure data in depth as the main purpose of this report is to show that this field data acquisition system is both feasible and accurate.

CONCEPTUAL DESIGN AND SCOPE OF STUDY

It was decided at an early stage that both inside and outside pressure measurements should be made, and that only direct measurements of the pressures would suffice as second order information such as strain would involve higher inaccuracies.

Figure 1 shows the selected locations which resulted in a total of 24 outside and T inside measurement locations. The main problem encountered with projects of this nature is the inaccessibility of the equipment once it is installed. Consider for example a pressure transducer mounted in location 328-3. In addition to being subject to corrosion, 70 psig pressure and marine fouling; salvaging of the transducer would require a dive to 150 ft depth and repair of the underwater cable would be virtually impossible.

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