"EXTRA!" Using the Newsvendor Model to Optimize War Reserve Storage

17 USC 105 interim-entered record; under review.The article of record as published may be found at https://doi.org/10.22594/dau.21-865.28.04The United States Marine Corps (USMC) Installation and Logistics Command requested a study for determining appropriate inventory levels of war reserve materiel to meet future operational needs under surge demands in uncertain environments. This study sought to explore a potential approach by using the common newsvendor model, but modified for a military scenario. The authors' novel version of this core concept considers the purchase and storage costs of an item and proposes an intangible cost function to capture the consequences of a shortage. Further, they show a sample application of the model using a ubiquitous military item-the BA-5590/U battery. The output of the model provides USMC with a new tool to optimize inventory levels of a given item of interest, depending on scenario inputs.USMC Installation and Logistics Command, Logistics Plans and Operations (Maritime and Geo-Prepositioning Programs) (LPO-2

Multidisciplinary experiment using steep regular waves to determine ship operating conditions that avoid capsize

The article of record as published may be found at http://dx.doi.org/10.1007/s41939-018-0012-1This paper explores using steep regular waves to identifying safe operating conditions that avoid capsize. The data is from a multidisciplinary experiment using an autonomous scale-model running a proportional-derivative controller in aft of beam steepregularwaves.Thetestexploredrelativewaveheadingsfrom15◦to75◦andspeedsfrom0.1to0.4Froudenumber.This effort analyzes the resultant ship trajectories to determine if the model obtained the desired operating conditions during each run. For slow speeds, safe operating conditions could not be identified since the requested headings could not be achieved. For moderate speeds, most requested headings could be achieved. At the highest speeds, only relative wave headings closer to beam seas could be explored as the model capsized in stern quartering waves. Results show that wavelength and wave steepness have minimal effects on the model’s ability to achieve a desired heading. Finally, only a limited number of runs are required to verify a safe operating condition since capsizes appear to be consistently repeatable. This research highlights the usefulness of using steep regular waves for capsize testing but also some of its limitations

The application of controlled variable magnetic eddy current damping to the study of vortex-induced vibrations

A powerful variable magnetic eddy current damping system has been constructed and utilized in an experimental study of vortex-induced vibrations (VIV). This damping system allows us to impose precise values of nearly ideal viscous damping over a wide range of damping values of interest. This new damping system offers improvements over previously utilized damping methods. Unlike most studies of VIV, where the damping cannot be independently controlled, we are able to impose our system damping independent of the other system parameters. Also, because the system only requires that a thin conductive plate be attached to the oscillating system, the overall mass of the system does not increase dramatically and still allows the investigation of very low mass systems. Finally, the system can operate in a steady-state fashion, supplying a constant damping value for an extended period of time, or in a transient fashion, where the damping value is intentionally varied over time. With this damping system, we have systematically explored both steady and transient damping effects on VIV behavior and provide a brief overview of some sample results

Phase-locking of laminar wake to periodic vibrations of a circular cylinder

17 USC 105 interim-entered record; under review.The article of record as published may be found at https://doi.org/10.1103/PhysRevFluids.6.034401Phase synchronization between the vortex shedding behind a two-dimensional circular cylinder and its vibrations is investigated using the phase-reduction analysis. Leveraging this approach enables the development of a one-dimensional, linear model with respect to the limit-cycle attractor of the laminar wake, which accurately describes the phase dynamics of the high-dimensional, nonlinear fluid flow and its response to rotational, transverse, and longitudinal vibrations of the cylinder. This phase-based model is derived by assessing the phase response and sensitivity of the wake dynamics to impulse perturbations of the cylinder, which can be performed in simulations and experiments. The resulting model in turn yields the theoretical conditions required for phase-locking between the cylinder vibrations and the wake. We furthermore show that this synchronization mechanism can be employed to stabilize the wake and subsequently reduce drag. We also uncover the circumstances under which the concurrent occurrence of different vibrational motions can be used to promote or impede synchronization. These findings provide valuable insights for the study of vortex-induced body oscillations, the enhancement of aerodynamic performance of flyers, and the mitigation of structural vibrations by synchronizing or desynchronizing the oscillatory motions of a body to the periodic wake.We gratefully acknowledge the support from the U.S. Air Force Office of Scientific Research Grant No. FA9550-16-1-0650) and the Army Research Office (Grant No. W911NF-19-1-0032

Investigation of unsteady hydrodynamic loads on a UUV during near surface operations

CRUSER Funded ResearchFY17 Funded Research ProposalCRUSER has funding to support NPS Faculty research focused on any aspect of unmanned systems/robotics related research.  Researchers are selected based upon presentations at our spring Technical Continuum (TechCon) or our annual Call for Proposals.  Proposals that support concepts from our current innovation thread are encouraged, but all research related to unmanned systems or robotics will be considered.Consortium for Robotics and Unmanned Systems Education and Research (CRUSER

The Effects of Cross-Sectional Geometry on Wave-Induced Loads for Underwater Vehicles

The article of record as published may be found at http://dx.doi.org/10.1109/JOE.2020.3023320This article investigates the role that cross-sectional geometry plays on the magnitude and phase of wave-induced linear loads experienced by an underwater vehicle operating near the surface. A towing tank with wave making capabilities is used to measure the wave-induced forces and moments on various cross-sectional shapes experimentally. These are compared to predictions we made using a framework that can handle non-body-of-revolution geometries. In many cases, our experimental results were the opposite of the theoretical predictions. For instance, according to the predictions, for long wavelengths, the aspect ratio of a rectangle should not influence the linear heave force. However, we found that the heave force was proportional to the planform area of the rectangle. This study is a systematic investigation of the effects that changing the cross-sectional shape from a body-of-revolution to either a square, rectangular, or asymmetric shape, has on the wave-induced loads.Consortium for Robotics and Unmanned Systems Education and Research (CRUSER)Department of the Navy, Office of Naval Researc

On the Accuracy of an Analytical Solution to Model Wave-Induced Loads on an Underwater Vehicle in Real-Time

The article of record as published may be found at http://dx.doi.org/10.1115/1.4049119The accuracy of an existing analytical solution for modeling the linear, first-order wave-induced loads on a fully submerged body is investigated. The accuracy is assessed for the situation where the underlying theoretical assumptions are met, and the sensitivity of the accuracy to these assumptions is also explored. The accuracy was quantified by comparing the analytical solutions to experimental measurements from a tow tank with wave generation capability. The assessment showed that when all the assumptions are met, the heave and surge forces are predicted quite accurately but the pitch moment is overpredicted. The results also showed that the deeply submerged assumption is met as long as the body does not cause a disruption of the passing wave on the free surface. The slenderness and end face curvature assumptions are also quite relaxed and the curvature assumption only affects the pitch moment accuracy. The most stringent assumption appears to be the body-of-revolution assumption which can cause all three loads to be predicted poorly. The analytical solution appears to be accurate over a large parameter space and could be incorporated as a wave disturbance model into a virtual environment used to develop control and autonomy of unmanned underwater vehicles.K.I. Yeager was sponsored by ONR, and then in the Research Participant Program sponsored by the Oak Ridge Institute for Science and Education (ORISE).Unmanned Systems Education and Research (CRUSER) project sponsored by the Department of the Navy, Office of Naval Research

Upgrades to and Current Research Efforts Involving the Tow Tank Facility at the Naval Postgraduate School

The 30th American Towing Tank Conference, West Bethesda, Maryland, October 2017The Naval Postgraduate School has added wave making capability to the existing small tow tank that resides on campus. A new collaborative research effort between the Systems Engineering and Mechanical and Aerospace Engineering Departments is underway that utilizes this new capability. The aim of this new effort is to understand and predict the unsteady hydrodynamic loads experienced by a submerged vehicle operating near the surface. The tow tank was originally built around 1970 but only had the capability of testing models at slow speed in calm water. Even with this limited capability, a number of interesting studies were conducted in the facility including measuring the drag on a towed hydropower turbine and examining the forces due to collisions between floating iceequivalent objects and a composite plate. The new wave making capability in the tow tank is provided by a vertical plunging wedge that was modeled off of the sediment tank wavemaker at the United States Naval Academy. The wedge rides on a pair of vertical rails with the oscillation amplitude and frequency controlled by a linear actuator and electric motor. A variable angle wave absorbing beach is planned for the opposite end of the tank. An additional component of this modernization effort is the creation of a numeric tow tank, using ANSYS CFX, which can simulate the wave dynamics in the tank. This allows complementary numerical and experimental components of future research efforts. The current experimental effort involves characterizing the performance of the wavemaker and quantifying the wave environment throughout the tank. The wedge to wave amplitude transfer function has been determined over the relevant amplitude and frequency space. The uniformity of a wave crest has also been examined. For the numeric tow tank work, the wedge motion has been duplicated and the simulated wave elevation and propagation down the tank are being compared to experimentally measured results.2017The Research and Sponsored Programs Office at the Naval Postgraduate School provided funding for this effort as part of the institutionally funded Research Initiation Pro- gram for new faculty members (J.T. Klamo). The Consor- tium for Robotics and Unmanned Systems Education and Research (CRUSER) also provided funding for the current research (J.T. Klamo and Y.W. Kwon).The Research and Sponsored Programs Office at the Naval Postgraduate School provided funding for this effort as part of the institutionally funded Research Initiation Pro- gram for new faculty members (J.T. Klamo). The Consor- tium for Robotics and Unmanned Systems Education and Research (CRUSER) also provided funding for the current research (J.T. Klamo and Y.W. Kwon)