Philip J. Valent

Evaluation and quantification of randomness in free-fall trajectories of instrumented cylinders

As part of a field experiment designed to contribute to the Navys effort to improve its capability to model and predict depth of burial of anti-ship mines in mud seafloors, the trajectory, velocity and orientation of a 1,100-kg cylinder were observed during 21 free-fall trials in a field setting. Extreme values and distribution of linear and angular velocity components as well as orientation throughout the water column and, in particular, on impact with the sediment are described. The findings indicate that a critical depth (of about 4 m, for the cylinder configuration tested) appears to exist beyond which the influence of the release conditions is insignificant. All the different nose shapes tested resulted in similar mean values of velocities and orientations. Cylinders with chamfered noses appear to possess the highest variability in these parameters, complicating the mine burial modeling effort. Periodic nature in the variation of several parameters was observed and its changes with cylinder geometry presented. Overall implications on the impact burial prediction analysis of heavy, cylindrical shapes are discussed.

Spatial variability in selected geotechnical property measurements from three sedimentary provinces in the Venezuela Basin

Abstract Relatively undisturbed surficial sediment samples from three sedimentary provinces (pelagic, turbidite dominated and hemipelagic) in the Venezuela Basin were examined for spatial variability in water content and undrained shear strength. A miniature vane shear apparatus boring method which minimized sample disturbance was used to determine variability of sediment shear strength directly within individual box-core samples. The variability of water content and sediment shear strength was also determined from subsamples (61 mm ID cores) collected from replicate box cores at each province. Sediments at the turbidite site yielded a higher average lateral coefficient of variation in water content and sediment shear strength (both methods of measurement) than sediments from the pelagic and hemipelagic sites. Vertical coefficients of variation were consistently higher than lateral coefficients of variations for all measured parameters. Between box-core variability in sediment shear strength was less than within box-core variability reflecting differences in measuring techniques and sample disturbance rather than actual differences. Biological activity, primarily compaction by burrowing polychaetes, maintains steep gradients of decreasing water content and increasing shear strength in the upper 100–200 mm of sediments at all three sites. The biologically controlled gradients and the occasional deposition of turbidites results in much higher vertical compared to lateral variability of some sediment geotechnical properties on scales of tens of millimeters (within box cores) and kilometers (between box cores collected at the same site).

Mine burial by scour: preliminary results from the Gulf of Mexico

Mine burial experiments were conducted on fine and coarse sandy sediments, in 13 to 15-m water depths, 15 km off Indian Rocks Beach, West-Central Florida. Experimental sites were chosen based on extensive acoustic (side scan, chirp and multibeam) surveys and sediment samples collected by USF. Four acoustic (NRL and OMNI Technologies) and six optical (FWG) cylindrical mines were deployed during January-March 2003. The extensive sediment (USF and NRL) data combined with predictions from NOAA wave buoys operating offshore of Tampa, FL during these experiments is used to predict burial by waveinduced scour (VIMS). Extensive wave and current data collected with bottom mounted tripods is compared to physical oceanographic model predictions. Time-dependent scour measured using the optical and acoustic mines, characterized by sector scan sonar (USF), ROV video (USF), and diver photographs/observations (USF and NRL) is compared to model predictions.

Engineering concepts for the placement of wastes on the abyssal seafloor

The Naval Research Laboratory (NRL), with industry and academic participation, has completed a study of the concept of isolating industrial wastes (i.e., sewage sludge, fly ash from municipal incinerators, and dredged material) on the abyssal seafloor. This paper presents results of the technical and economic assessment of this waste management concept. The results of the environmental impacts portion of the study are presented in a companion paper. The technical assessment began with identification of 128 patents addressing waste disposal in the ocean. From these 128 patents, five methods for transporting wastes through the water column and emplacing wastes within an easily monitored area on the abyssal seafloor were synthesized for technical assessment. In one method waste is lowered to the seafloor in a bucket of 190 m3. In a second method waste is pumped down to the seafloor in pipes, 1.37 m in diameter and 6100 m in length. In a third method waste is free-fallen from the ocean surface in 380-m3 geosynthetic fabric containers (GFCs). In the fourth and fifth methods, waste is carried to near the seafloor in GFCs transported in (a) a 20,000 metric ton displacement (loaded), unpowered, unmanned submersible glider, or (b) a 2085 metric ton displacement (loaded) disk-shaped transporter traversing to and from the seafloor much like an untethered elevator. In the last two methods the transporter releases the GFCs to free-fall the last few hundred meters to the seafloor. Two reliability analyses, a Fault Tree Analysis (FTA), and a Failure Modes, Effects, and Criticality Analysis (FMECA), showed that the free-fall GFC method posed the least overall relative risk, provided that fabric container and transporter designs eliminate the potential for tearing of the containers on release from the surface transporter. Of the five methods, the three GFC methods were shown to offer cost-effective waste management options when compared with present-day waste management techniques in higher-priced areas, such as the New York–New Jersey area. In conclusion, the abyssal seafloor waste isolation concept is technically feasible and cost-effective for many waste sources.

Strain-Rate Dependence of Strength of the Gulf of Mexico Soft Sediments

Many marine civil engineering applications require knowledge and understanding of the behavior and strength properties of soft cohesive marine sediments under high strain-rate conditions, typically encountered during impact penetration events of sediment probes and other objects as a result of free fall through the water column. To investigate these effects, a series of variable rotational rate vane shear tests was performed on a sample of Gulf of Mexico marine mud, using a precision rheometer and spanning the rotational rate range of 0.25-1000 r/min. A wide range of water contents from 55% to 95% (liquidity index: 1.5-3.3) was examined as a primary influence on the response of a particular saturated silty clay material. Nonlinearities in the behavior of this soil were analyzed, and applicability and precision of various models were examined. A modified rate equation is suggested yielding good correlation with experimental data at all water contents and all rotational rates explored. A testing schedule for a complete material constant derivation procedure is outlined.

A probabilistic approach for mine burial prediction

Predicting the degree of burial of mines in soft sediments is one of the main concerns of Naval Mine CounterMeasures (MCM) operations. This is a difficult problem to solve due to uncertainties and variability of the sediment parameters (i.e., density and shear strength) and of the mine state at contact with the seafloor (i.e., vertical and horizontal velocity, angular rotation rate, and pitch angle at the mudline). A stochastic approach is proposed in this paper to better incorporate the dynamic nature of free-falling cylindrical mines in the modeling of impact burial. The orientation, trajectory and velocity of cylindrical mines, after about 4 meters free-fall in the water column, are very strongly influenced by boundary layer effects causing quite chaotic behavior. The models convolution of the uncertainty through its nonlinearity is addressed by employing Monte Carlo simulations. Finally a risk analysis based on the probability of encountering an undetectable mine is performed.

Adaptation and improvement of ASW tactical decision aid design to mine warfare tactical decision aid

Summary form only given. In this presentation, the adaptation of a tactical decision aid (TDA) designed for Anti Submarine Warfare (ASW) to one used for Mine Warfare is discussed. Previous work at the Naval Research Laboratory established a TDA, namely GRASP for the ASW role. Recently at NRL work has been done to extend the TDA model to Mine Warfare. Specifically this presentation examines search path algorithms for the two TDAs. Comparisons will be shown between various search path algorithms for environmentally influenced mine detection: GRASP, edge covering, and greedy algorithms for limited time searches and searches for minimal confidence of detection. Oceanic environmental parameters relevant to designing tactical decision aids for mine detection will be noted. In conclusion this presentation discusses how extensively detailed must the environmental survey be in order to make search path analysis sensitive to the data.