Julie Chalfant

Analysis of various all-electric-ship electrical distribution system topologies

As advances in technology mature, the need is evident for a coherent simulation of the total electric-drive ship to model the effect of new systems on the overall performance of the vessel. Our laboratory has been developing an integrated architectural model in a physics-based environment which analyzes ship variants using a standard set of metrics, including weight, volume, fuel usage and survivability. This paper discusses advances in the model including the use of operational scenarios, incorporation of a survivability metric, and streamlining the performance of model. The model is employed herein to compare two possible distribution system topologies: a ring bus and a breaker-and-a-half. The ring bus is heavier and larger but more survivable. Fuel usage is equivalent in the two variants.

Early-Stage Design for Electric Ship

One of the truisms of ship design is that the decisions of greatest impact are made in the early stages of design when the least information and the greatest uncertainty are present. In response to this, ongoing efforts in developing ship design tools are directed toward making more information available sooner and pushing decision points later. The integrated nature of electric ship in which performance of support systems directly affects performance of primary mission systems compounds this concern; design and simulation of support systems are needed earlier, and collaborative design among multiple engineering disciplines is required in the process. This paper reviews the Navy ship design process and recent developments in ship design tools to illuminate the areas in which further development is necessary.

Adding simulation capability to early-stage ship design

The Navys early-stage ship design tools do not currently include an inherent simulation capability. Under Navy direction, the Electric Ship Research and Development Consortium (ESRDC) has worked to develop a simulation tool that can be used to determine functionality of ship systems at the early stages of design. This paper describes the current capabilities of the simulation tool and the process and status of the efforts to integrate this tool with the Navys design tools.

Design of a notional ship for use in the development of early-stage design tools

In this paper, current early-stage design tools are used to produce a notional ship that includes leading-edge weapons and sensors. These new systems stress the capabilities of current design tools and demonstrate the need for tools that can address the increasingly integrated, powerful and heat-producing nature of future payloads. The data produced in this process are shown to be the required input to new design tools under development, thus establishing the link between the existing state of the art and tools that provide more advanced capability necessitated by advances in ship system technology. A framework for a semi-automated template-based system arrangement tool is then presented.

System-level analysis of chilled water systems aboard naval ships

A thermal management simulation tool is required to rapidly and accurately evaluate and mitigate the adverse effects of increased heat loads in the initial stages of design in all-electric ships. By reducing the dimension of Navier-Stokes and energy equations, we have developed one-dimensional partial differential equation models that simulate time-dependent hydrodynamics and heat transport in a piping network system. Besides the steady-state response, the computational model enables us to predict the transient behavior of the cooling system when the operating conditions are time-variant. As a demonstration case, we have performed a thermal analysis on a realistic naval ship.

Notional all-electric ship systems integration thermal simulation and visualization

This work presents a simplified mathematical model for fast visualization and thermal simulation of complex and integrated energy systems that is capable of providing quick responses during system design. The tool allows for the determination of the resulting whole system temperature and relative humidity distribution. For that, the simplified physical model combines principles of classical thermodynamics and heat transfer, resulting in a system of three-dimensional (3D) differential equations that are discretized in space using a 3D cell-centered finite volume scheme. As an example of a complex and integrated system analysis, 3D simulations are performed in order to determine the temperature and relative humidity distributions inside an all-electric ship for a baseline medium voltage direct current power system architecture, under different operating conditions. A relatively coarse mesh was used (9410 volume elements) to obtain converged results for a large computational domain (185m×24m×34m) containing diverse equipment. The largest computational time required for obtaining results was 560 s, that is, less than 10 min. Therefore, after experimental validation for a particular system, it is reasonable to state that the model could be used as an efficient tool for complex and integrated systems thermal design, control and optimization.

Mathematical formulation and demonstration of a dynamic system-level ship thermal management tool

Abstract This paper presents the mathematical formulation and unique capability of a system-level ship thermal management tool, vemESRDC, developed to provide quick ship thermal responses in early design stages. The physical model combines principles of classical thermodynamics and heat transfer, along with appropriate empirical correlations to simplify the model and expedite the computations. As a result, the tool is capable of simulating dynamic thermal response of an entire ship, characterized by intricate thermal interactions within a complex ship structure, within an acceptable time frame. In this work, vemESRDC is demonstrated through three case studies in which transient thermal responses of an all-electric ship to different ship operation modes, weather conditions, and partial loss of cooling are investigated. The analysis examines particularly the following: (1) the required cooling capacities to maintain each ship component within its design limit; (2) equipment temperature variations with respect to partial cooling loss in battle mode; and (3) the assets of installing seawater heat exchangers to pre-cool deionized freshwater before chillers. For the notional all-electric ship conceived and assessed in this work, the results verify the capability of vemESRDC to capture dynamic thermal interactions between shipboard equipment and their respective surroundings and cooling systems, e.g., the tool provides practical insights into pulse load cooling strategy, and different solutions are obtained for distinct weather conditions. In addition to the case studies performed in this work, vemESRDC can be employed to conduct diverse studies based on which concrete ship thermal management strategies can be formulated in early design stages.

Comprehensive system-level thermal modeling of all-electric ships: Integration of SMCS and vemESRDC

In this paper, we present the integration effort of two complementary thermal simulation tools: vemESRDC and System-level design of Marine Cooling Systems (SMCS), developed at Florida State University Center for Advanced Power Systems and Massachusetts Institute of Technology Sea Grant, respectively. We integrated these tools into a cohesive whole and expanded its overall capabilities, allowing the user to design a ship cooling system using the state-of-the-art methods and to study the impact of design decisions at the early design stages. The integration was numerically verified by solving a simple problem comprised of nine volume elements with internal heat generation and a cooling network. It was construed from the simulation results that SMCS-vemESRDC integration enhanced the design flexibility as well as reliability of the tool, in evaluating ship cooling network designs and promoting effective thermal management strategies.

Volume element model mesh generation strategy and its application in ship thermal analysis

We present a hexahedral mesh generation strategy for the volume element model.The proposed mesh generation strategy is applied in ship thermal analysis.Highly accurate representations of the ship geometry can be achieved.Plausible ship thermal solutions are obtained using a coarse independent mesh.The strategy enhances the overall computational efficiency of the VEM. This paper introduces a mesh generation strategy devised and implemented for the volume element model (VEM), and elaborates key contributions of the strategy in enhancing the VEM as a prominent tool in ship thermal modeling and simulation. The VEM mesh generation strategy employs ray crossings and ray- triangle intersection algorithms developed in previous studies, and constructs sufficiently accurate geometric representations of the whole ship within permissible time frame using hexahedral meshes. In addition, this work demonstrates the strategys practicality in thermal analysis of a notional all-electric ship, which is characterized by intricate structures and multiple internal components, i.e., thermal loads. Ship thermal solutions obtained in this assessment verify the proposed mesh generation strategys ability to improve the overall computational efficiency of the VEM, by allowing it to obtain plausible thermal solutions with respect to time and space using a coarse independent mesh.

Modular IPS machinery arrangement in early-stage naval ship design

Electrical power demands for naval surface combatants are projected to rise with the development of increasingly complex and power intensive combat systems. This trend coincides with the need to achieve maximum fuel efficiency at both high and low hull speeds. A proposed solution to meet current and future energy needs of conventionally powered naval surface combatants is through the use of an Integrated Power System (IPS), which is seen as the next evolution in naval ship design. In an effort to enhance the relationship between new-concept designs and historically-based ship design processes, this paper focuses on a novel approach of incorporating IPS at the earliest stage of the design process as part of assessing system-level tradeoffs early within the ship design process. This paper describes a methodology for the systematic design and arrangement of an IPS machinery plant to meet a desired power generation level. In conjunction with the methodology development, a hierarchical process and design tool were produced to assist in rapid development and evaluation of various IPS arrangements. The result of this process, through several case studies, provides insight into equipment selection philosophy, the initial sizing of the ships machinery box, and the initial definition of electrical zones.