Summary of Research 2000, Department of Mechanical Engineering

The views expressed in this report are those of the authors and do not reflect the official policy or position of the Department of Defense or U.S. Government.This report contains project summaries of the research projects in the Department of Mechanical Engineering. A list of recent publications is also included, which consists of conference presentations and publications, books, contributions to books, published journal papers, and technical reports. Thesis abstracts of students advised by faculty in the Department are also included

Numerical Analysis of Local and Global Hydroelastic Response of Wetdeck Slamming Events on Multihull Vessels

Catamarans operating in a large sea state encounter slamming events on the wetdeck that may lead to structural failure. Wetdeck slamming is a non-linear process which involves complex free-surface topology, high-velocity water jets, and breaking waves interacting with the bow and deck-hull geometry. The slamming process generates large pressures and loads that are time dependent and concentrated in space. The structure responds in a coupled manner to the complex fluid loading. Common approaches to design for the limiting slamming loads include analytical models or segmented model tests. Analytical slamming models assume a linear free-surface, prescribed velocities, and simplified geometries. These simplified assumptions make it difficult to apply to realistic cases. Experimental model tests capture slamming loads by using segmented models attached to a backspline. It is difficult to scale results to full-scale and to recreate model scale conditions that lead to the limiting load cases. A high-fidelity fluid-structure interaction solver is used to study a simplified impact problem and slamming on a catamaran. The canonical problem is a flat plate impacting a curved water surface. A detailed analysis is conducted on the simple flat plate showing the influence of boundary conditions, structural non-linearities, and the relative impact velocities. A new adaptive inertial under-relaxation scheme is developed for solving the artificial added mass instabilities due to the segregated coupling of the CFD and FEA models. Catamaran slamming simulations compare the influence of global loads on the local wetdeck structure. The full field data provided by the numerical solver is used visualization of flat wetdeck slamming loads. Careful evaluation of existing impact models are presented and recommendations for reduced order modeling of maximum stress during wetdeck slamming are provided.PHDNaval Architecture & Marine EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/147495/1/grahmatt_1.pd

Piezoelectric Wafer Active Sensor Embedded Ultrasonics in Beams and Plates

ABSTRACT—In this paper we present the results of a sys-tematic theoretical and experimental investigation of the fun-damental aspects of using piezoelectric wafer active sensors (PWASs) to achieve embedded ultrasonics in thin-gage beam and plate structures. This investigation opens the path for sys-tematic application of PWASs for in situ health monitoring. After a comprehensive review of the literature, we present the principles of embedded PWASs and their interaction with the host structure. We give a brief review of the Lamb wave principles with emphasis on the understanding the particle motion wave speed/group velocity dispersion. Finite element modeling and experiments on thin-gage beam and plate spec-imens are presented and analyzed. The axial (S0) and flex-ural (A0) wave propagation patterns are simulated and ex-perimentally measured. The group-velocity dispersion curves are validated. The use of the pulse-echo ultrasonic technique with embedded PWASs is illustrated using both finite element simulation and experiments. The importance of using high-frequency waves optimally tuned to the sensor–structure in-teraction is demonstrated. In conclusion, we discuss the ex-tension of these results to in situ structural health monitoring using embedded ultrasonics. KEY WORDS—Piezoelectric wafers, piezoelectric sensors, active sensors, in situ diagnostics, structural health monitor-ing, piezoelectrics, ultrasonics, elastic waves, P-waves, S-waves, shear waves, axial waves, flexural waves, Rayleig

Strength and hydrodynamic performance of a multihull vessel

PhD ThesisThe use of catamarans as an alternative to more conventional monohull high speed vessels for transport, naval and offshore applications is on the increase. This uprising trend is a direct consequence of the global demand for commercially and militarily efficient vessels that offer high speed, potential for improved Sea-keeping at speed, relatively low hydrodynamic resistance in waves and a more useable deck area. The configuration and hull geometry of catamarans are very critical to achieve improved sea-keeping and other hydrodynamic performances. The Round Bilge hull form is one of the most prominent hull geometries in use for the design of displacement-type multi-hull vessels. An alternative hullform series to the Round Bilge, catamarans, named the Deep-V Catamaran series (DVC), has been developed recently at Newcastle University. Early studies on the DVC concept based on this series indicate that the hull form may have better resistance performance than the Round Bilge. However, other important characteristics of this concept such as the motions and wave-induced load response characteristics are still unknown. There is also a lack of understanding of the general hydrodynamic characteristics of the DVC concept in comparison to the Round Bilge hull form. This study contributes to the understanding of the motions and wave induced load response characteristics of the DVC concept. It is also intended to advance the structural design methodology of the DVC concept and its subsequent application as better alternative to the Round Bilge hull form. The study involved the experimental and numerical investigations of the motions and wave-induced load response characteristics of the DVC concept by using a prototype model of “The Princess Royal” which is the current research vessel of Newcastle University. The experimental studies involved the motions and wave-induced response measurements in regular waves at both zero and forward speed conditions. The results obtained were validated using alternative potential flow-based numerical codes in frequency domain. The benchmark study indicates that the numerical codes are capable of producing acceptable results. A comparative study using a representative model of the Round Bilge hull form with the DVC model was conducted in order to establish a direct basis for the comparison of the motion and hydrodynamic load performances. The results obtained from this comparison reveal that the DVC may have better sea-keeping characteristics and is less sensitive to wave loads than the Round Bilge hull concept in critical heading conditions. A further comparison of the experimentally validated numerical predicted loads with those obtained using the International Association of Classification Societies (IACS) approach was completed. The study confirms that the IACS approach over predicts the loads by up to 40% in Beam Seas and Quartering Seas when other components of IACS rules are not considered. A simplified structural analysis of the DVC model using the Finite Element Method was also completed to demonstrate the effects of the predicted loads on the strength of the hull structure with emphasis on the cross-deck structure, which is the most sensitive structural element of the vessel. Overall, the study highlights the promising characteristics of the DVC concept in comparison to the Round Bilge hull form and provides data required for the preliminary design of catamarans using this concept

Design of an automated on-car brake lathe

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2001.Includes bibliographical references (p. 91-92).An on-car brake lathe resurfaces disk-brake rotors by rotating them "in place" and making a light cut along the surface of the disk. The primary goal of this thesis is to develop an automated cutting head for an on-car brake lathe. The new cutting head must produce a surface finish that matches or exceeds that of the current (manual) cutting head. Pro-Cut International, a leading manufacturer of on-car brake lathes, developed functional requirements and cost constraints for the automated cutting head. Technical challenges include design and fabrication of low-cost precision linear bearings and actuators with dynamic stiffness sufficient to suppress chatter. During this thesis, two prototype cutting heads were designed, manufactured, and tested. The first prototype employed modular linear bearings, and produced unacceptable surface finish due to chatter. Cutting-tip vibration measurements combined with modal testing showed that chatter was caused by low structural stiffness of the modular bearing rails. A second prototype employing a unitary ground bearing system produced an acceptable surface finish of 70 [mu] -inch at 0.015" depth of cut per side. The key components of this design can be extruded and sliced to form the assembly, thereby meeting cost constraints.by Andrew Kirk Wilson.S.M

Design and validation of a non-linear passive-selective compliant hydrofoil using shape-memory alloys

Traditionally, sailboats relied on the Archimedes principle to move on the water surface. This method has been used and successfully proven for many thousands of years, with the earliest known depiction found on an Egyptian clay and dating from 3100 B.C. Nowadays, boats can fly by the means of hydrofoils, allowing great performance and efficiency when moving on the water surface. While hydrofoils are efficient in a defined spectrum because of their fixed geometry, this work presents a solution to increase the efficiency in a larger range of operation by proposing a non-linear compliant structure solution based on a AClass sailing catamaran. The objective of this work is to provide a proof of concept of a structure capable of adapting its geometry depending on the load case to which it is submitted to maximize the righting moment and the lift to drag ratio in different sailing conditions. To comply with the A Class rules, this geometrical change must be done passively. To begin, the load case validation and evaluation is performed for the boat take-off and maximum speeds using a custom designed hydrofoil geometry. The thesis then presents the developed tools and Finite Element Model allowing to determine analytically the performance of the Hydrofoil and its morphing and structural capabilities combining traditional CFRP composites and Shape Memory Alloys (SMA). As a final step, the validation of the morphing concept calculations on a 1:1 scale specimen to determine the real-case application and integration constraints is presented. Finally, an example of a full-cycle calculation process for an AClass catamaran with a morphing Hydrofoil is presented, to achieve a preliminary design concept

Efficient Modeling of an Array Antenna and Requirements for Maritime Mobile Reception of Meteorological Satellite Imagery

Wireless communication is an integral part of safety at sea. Direct broadcasts from public weather satellites on L- and X-band provide real-time weather observations and weather product dissemination to end users. These high-bandwidth broadcasts offer enhanced data throughput and require accurate pointing of high-gain antennas. An electronically-steered array antenna can provide high gain and rapid beam steering without moving parts, suitable for deployment on small vessels offshore. Figures of merit, such as array antenna gain and input impedance, vary with the beam steering angle as a consequence of mutual coupling between array elements. The electromagnetic design of an electronically-steered array antenna is more complex than a parabolic dish or a fixed broadside array, requiring an iterative development process and a computationally efficient method of simulating the array. This work addresses the validation of an efficient method for array simulation, a necessary first step in the design process of a deployable array. Starting with a small L-band subarray, a Fourier windowing method is applied to approximate the scan-dependent behavior of an electronically-steered array from an efficient numerical model in a periodic unit cell. Results are validated against experimental measurements of hardware prototypes and explicit numerical models of the subarray. The iterative design of antenna elements in an array environment and construction of a full-size array are left for future work

Efficient Modeling of an Array Antenna and Requirements for Maritime Mobile Reception of Meteorological Satellite Imagery

Wireless communication is an integral part of safety at sea. Direct broadcasts from public weather satellites on L- and X-band provide real-time weather observations and weather product dissemination to end users. These high-bandwidth broadcasts offer enhanced data throughput and require accurate pointing of high-gain antennas. An electronically-steered array antenna can provide high gain and rapid beam steering without moving parts, suitable for deployment on small vessels offshore. Figures of merit, such as array antenna gain and input impedance, vary with the beam steering angle as a consequence of mutual coupling between array elements. The electromagnetic design of an electronically-steered array antenna is more complex than a parabolic dish or a fixed broadside array, requiring an iterative development process and a computationally efficient method of simulating the array. This work addresses the validation of an efficient method for array simulation, a necessary first step in the design process of a deployable array. Starting with a small L-band subarray, a Fourier windowing method is applied to approximate the scan-dependent behavior of an electronically-steered array from an efficient numerical model in a periodic unit cell. Results are validated against experimental measurements of hardware prototypes and explicit numerical models of the subarray. The iterative design of antenna elements in an array environment and construction of a full-size array are left for future work

Numerical Computation of Transient Response of 2D Wedge Impact

The diverse applications of advanced marine craft ascribed to their high speed and technological advancements has led to the use of stronger and lighter metals in such crafts. High speed, in effect also increases slamming loads as higher speed increases frequency of wave encounter while operating in waves. The present study is limited to wedge impact models. Fundamentally, the study is thus about two-dimensional (2D) wedge impact in water. In an attempt to predict the structural response to impact hydrodynamic force, a beam element based finite element (FE) computer program is written and the results of the code are presented in the thesis. A computational tool is developed to predict the transient elastic response of a 2D wedge under impact force using two different numerical methods. Both explicit and implicit numerical schemes have also been studied in order to apply to the present work. Explicit forth order Runge-Kutta (RK4) method and implicit Newmark-b (NB) method have been used in the present work. Coupling effects between excitation and response are ignored in the present numerical computations. Both the numerical schemes are validated using simple static solution and also modal expansion technique

LHA(R): Amphibious Assault Ships For The 21st Century

Amphibious assault ships such as the current LHA and LHD classes are an essential element of the country's ability to exert influence anywhere in the world. The current amphibious assault ships represent the most capable amphibious ships in the world. The LHA 1 class ships are aging, however, with most reaching the end of their expected service lives between 2011 and 2015. It is not feasible to extend the service life of the LHA 1 class due to the rapid technological advances that have taken place during their lifetime. Most have already used their entire growth margin in areas such as combat systems and topside weights. The evolving combat systems and aircraft requirements will only exacerbate these matters. The best solution is to replace the LHA. As the US faces a future with uncertain threats, it is necessary to field a flexible force. In order to make the amphibious forces flexible, selective offload capability must be considered. This allows Marines to access the equipment and vehicles they need for any given operation at any time. A second change that adds a great deal of flexibility is the addition of more ships. Currently, an Amphibious Ready Group (ARG) consists of three ships, an LHA or LHD, an LSD, and an LPD. Replacing the LHA with two ships has several advantages, ranging from increasing the selective offload capability of the ARG to optimally distributing assets among the ships. Most importantly, though, is the ability of the ARG to exert influence over a greater geographic area. In this study, four different options were considered for the future ARG: a. LPD 17, LSD 41, modified LHD 8 plus complement ship variants b. LPD 17, LSD 41, two small LHD variants (2 ships with same hull) c. LPD 17, LSD 41, two new design variants d. LPD 17, LSD 41, single ship LHA(R) variants After modeling a number of variants representing each option, an Overall Measure of Effectiveness (OMOE) and a total lifecycle cost was calculated. Analysis of these variants showed that the variants in Option (a) have a higher OMOE and a relatively lower cost than other options. This study now focuses on the complement ship to a modified LHD 8. A comparison of hull forms, including catamarans, surface effect ships, hydrofoils, trimarans, monohulls, semi-planing monohulls, led to the selection of a trimaran, primarily for its ability to transport equipment at a high speed over a long range. In order to keep the size (and cost) of the ship down, the ship will not carry any landing craft. The nominal amphibious lift capacity of the trimaran complement ship i