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Distribution Statement A: Approved for Public Release; Distribution Unlimited<br />

Dr. Alexander <strong>Gray</strong> 1 , Brian Cuneo 2 , Dr. Nickolas Vlahopoulos 2 , Dr. David Singer 2<br />

1 NAVSEA Carderock, 2 University of Michigan<br />

The Rapid Ship Design Environment –<br />

Multi-Disciplinary Optimization of a U.S. Navy Frigate<br />

ABSTRACT<br />

Early-stage design decisions directly impact the<br />

ultimate quality and cost of a design. The goal<br />

of the U.S. Navy’s Rapid Ship Design<br />

Environment (RSDE) is to enhance early-stage<br />

ship design by utilizing higher fidelity design<br />

and analysis tools, earlier in the ship design<br />

process to intelligently search for an optimal<br />

ship design. In the RSDE, Multi-disciplinary<br />

optimization (MDO) will be utilized to link<br />

existing ship synthesis and analysis tools to<br />

create a design system capable of providing<br />

intelligent decision support. Knowledge is<br />

necessary to make intelligent decisions. RSDE<br />

applies MDO routines in such a way as to<br />

facilitate design space exploration (DSE) and<br />

utilization of design of experiments (DOE). By<br />

using a mixture of gradient and non-gradient<br />

based, discrete and continuous MDO<br />

methodologies, the RSDE will be capable of<br />

representing the inherent uncertainty of earlystage<br />

ship design requirements and design<br />

values. The use of DSE and uncertainty<br />

representation together will allow for a shift<br />

from the classical, point-based, design-spiral<br />

approach, towards a modern set-based design<br />

(SBD) approach for early-stage ship design.<br />

The focus of this paper will be the MDO<br />

capabilities within the RSDE.<br />

To date, a ship analysis Use Case has been<br />

developed to test the current RSDE MDO<br />

capabilities. The goal of the initial Use Case<br />

was to test the ability of RSDE to handle<br />

continuous design variables while developing a<br />

robust, optimal hullform. The MDO algorithms<br />

1<br />

utilized two discipline optimizations,<br />

minimizing lifetime power requirements and<br />

maximizing the percent time operational.<br />

Preliminary results have shown the MDO<br />

algorithms to be capable of reaching an optimal<br />

solution within the boundary of the stated Use<br />

Case. The RSDE will act as a foundation for the<br />

continued growth and development of a SBD<br />

capability for the U.S. Navy and will aid the<br />

workforce in producing more robust ship<br />

designs, reducing the need for costly late-stage<br />

design changes.<br />

INTRODUCTION<br />

As budgets continue to decrease and<br />

shipbuilding costs increase, it has become<br />

increasingly important to design ships that<br />

perform well for multiple mission scenarios.<br />

Designing these multi-mission, flexible, and<br />

highly robust ships requires a paradigm shift in<br />

the methodologies utilized for the ship design<br />

process itself. To successfully implement a<br />

change in design theology, the paradigm shift<br />

must begin as early-on as the concept design<br />

phase. Designers can no longer afford to follow<br />

the traditional design spiral approach, Fig. 1, of<br />

fixing a few key design parameters early-on and<br />

then immediately searching for a single feasible<br />

solution, entirely dependent on the initially<br />

selected key design values, to meet the design<br />

objectives.<br />

Historically, the point-based design method has<br />

resulted in a struggle to maintain a feasible<br />

design during detailed design, which in turn has


Distribution Statement A: Approved for Public Release; Distribution Unlimited<br />

led to compromised design objectives, costly<br />

late-stage design fixes, and sub-optimal ship<br />

designs balancing on the edge of feasibility.<br />

Fig. 2 shows a general description of how costs<br />

steadily increase throughout the life-cycle of a<br />

naval design project.<br />

Fig. 1 Classic Design Spiral for Point-Based<br />

Design [Evans 1959]<br />

Fig. 2 Design and Construction Life-Cycle<br />

Costs [Keane and Tibbitts 1996]<br />

Recently, the U.S. Navy has expressed interest<br />

in utilizing set-based design (SBD) to facilitate<br />

the necessary paradigm design shift [Kassel,<br />

Cooper, and Mackenna 2010; Eccles 2010;<br />

Doerry and Steding 2009; Sullivan, 2008;<br />

Singer, Doerry, and Buckley, 2010]. Set-based<br />

design is a design theory that encourages<br />

exhaustive investigation of a set of solutions and<br />

sets of design values during early-stage design.<br />

Bernstein [1998], provides an excellent<br />

2<br />

description of the intricate details of the SBD<br />

process and applications of SBD in industry.<br />

One key aspect of SBD theory is the intentional<br />

delay of early-stage design decisions until<br />

design trade-offs are fully understood, allowing<br />

for a gradual narrowing of the design space<br />

through the elimination of infeasible and less<br />

desirable design solutions [<strong>Gray</strong> 2011].<br />

Although paradoxical, research has shown that<br />

the SBD method of delaying decisions reduces<br />

costs by investing more resources up-front to<br />

perform DSE [Ward et al. 1995] . The benefits<br />

of the up-front time investment are an increase<br />

in knowledge and a decrease in uncertainty,<br />

enabling designers to make well-informed earlystage<br />

design decisions. Fig. 3, illustrates the<br />

changes in design knowledge and uncertainty<br />

over time and the points at which key earlystage<br />

decisions are made for the point-based and<br />

set-based design methods.<br />

Fig. 3 Key Decision Points for Point-Based<br />

and Set-Based Design Methods<br />

The influence of SBD theory on the design<br />

process is shown in Fig. 4. The figure illustrates<br />

how through the set-based practice of the<br />

delaying of design decisions, there is a parallel<br />

delay of committed costs, as well as a shift in the<br />

strength of managerial influence over the life of<br />

the project.<br />

The drawback of the SBD process is that many<br />

designers and engineers are so accustomed to<br />

utilizing the point-based design approach that<br />

the switch to a design method that relies upon


Distribution Statement A: Approved for Public Release; Distribution Unlimited<br />

the communication of information using sets of<br />

design values and solutions can be extremely<br />

difficult. Liker et. al., discuss the need for the<br />

development of design tools to, “facilitate a<br />

proper exchange of information”, including setbased<br />

information [1996]. This is where a<br />

design tool such as the rapid ship design<br />

environment (RSDE) comes into play.<br />

Fig. 4 Influence of Set-Based Design on the<br />

Design Development Process<br />

With the current push in the Navy to utilize SBD<br />

practices, and with the overall goal of RSDE in<br />

mind, a move to an integrated design framework<br />

is necessary. Fig. 5 shows the overall structure<br />

of the RSDE, within this framework various<br />

technologies are being developed in parallel.<br />

One part of the RSDE architecture currently<br />

undergoing testing is the Multi-Disciplinary<br />

Optimization (MDO) capability using the data<br />

structure provided by the Leading Edge<br />

Architecture for Prototyping Systems (LEAPS).<br />

Within the RSDE environment the ability to use<br />

MDO can help designers and functional design<br />

groups develop a better understanding of the<br />

design space. By identifying optimum values<br />

within a design space, the designers can narrow<br />

their search for preferred solutions, while also<br />

3<br />

gaining information about the space, all without<br />

requiring premature design decisions.<br />

Fig. 5 RSDE Hierarchy<br />

The MDO capabilities being developed for the<br />

RSDE will allow for rapid searching of design<br />

spaces while considering multiple design goals<br />

at the same time. Along with analyses tools<br />

compatible with LEAPS, the MDO abilities<br />

provides automated design space exploration<br />

using models that can contain both continuous<br />

and discrete design variables.<br />

Rapid Ship Design Environment<br />

SBD practice places an emphasis on making the<br />

right decisions the first time, as early decisions<br />

impact all subsequent design decisions, as well<br />

as the ultimate cost, delivery, produce-ability,<br />

and robustness of a design. To facilitate the<br />

SBD process, tools are needed to aid designers<br />

in generating information on design space tradeoffs<br />

during early-stage design and promoting<br />

communication of the information in a set-based<br />

manner [Liker, et. al., 1996].<br />

The Rapid Ship Design Environment (RSDE) is<br />

being developed by NAVSEA-Carderock under<br />

the CREATE-Ships Rapid Design Integration<br />

(RDI) program. RSDE is designed to harness<br />

physics based design tools to provide designers<br />

with a methodology to intelligently explore the<br />

design space and analyze design trade-offs.<br />

Specifically RSDE will utilize, the Advanced<br />

Ship and Submarine Evaluation Tool (ASSET)


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for design [ASSET 2012] and LEAPS for the<br />

aggregation of design data [LEAPS, 2012].<br />

In addition to the DOE capabilities of the RSDE,<br />

a decision support toolkit (DST) is being<br />

developed to provide information about the<br />

design space. The DST is designed to provide<br />

users with an array of multi-disciplinary<br />

optimization (MDO) methods, including<br />

gradient and non-gradient based methods for use<br />

with both discrete and continuous design<br />

variables. Some of the non-gradient based<br />

methods include the use of genetic algorithms<br />

and fuzzy logic methods. As a whole, the RSDE<br />

and the MDO methods provided by the DST<br />

should help to move the Navy towards meeting<br />

the goals outlined in the memorandum by<br />

Admiral Sullivan [2008], Commander of the<br />

Naval Sea Systems Command. The memo<br />

expressed a desire for ever more sophisticated<br />

design and analysis tools capable of facilitating<br />

advanced design methods.<br />

To support MDO in early-stage ship design, a<br />

decision support toolkit (DST) has been jointly<br />

developed by NAVSEA Carderock, Michigan<br />

Engineering Service, and the University of<br />

Michigan. The DST provides several methods<br />

of performing design optimization with the<br />

intent of providing information that can be used<br />

to make intelligent, informed design decisions.<br />

Currently the MDO portion of the DST contains<br />

optimization methods capable of performing<br />

discipline level and system level (MDO)<br />

optimizations using both discrete and continuous<br />

design variables.<br />

Four optimization methods have been developed<br />

within the DST to this point, one utilizing a<br />

gradient based algorithm called NEWSUMT<br />

[Miura and Schmit 1979], two using genetic<br />

algorithms referred to as the RGA [Deb, Dhiraj,<br />

and Ashish 2001] and NSGA2 [Deb et al. 2000]<br />

optimizers, and one fuzzy logic system [Mendel<br />

2001]. The remainder of this paper discusses the<br />

4<br />

work that has been completed on the MDO<br />

portion of the DST and an initial Use Case that<br />

was specifically developed to validate the<br />

performance of the discipline and system level<br />

MDO algorithms for continuous design<br />

variables.<br />

Multi-Disciplinary Optimization<br />

The desire for more cost effective ship designs<br />

has led to a push for multi-functional, multimission,<br />

robust ship design solutions. As a<br />

result, ship designs are now heavily influenced<br />

by multiple stakeholders each representing<br />

unique design disciplines, where each discipline<br />

has its own unique design goal(s). In these types<br />

of multi-disciplinary design environments, the<br />

unique goals of each discipline evoke a constant<br />

struggle for controlling influence of design<br />

parameters. MDO involves the attempt to use<br />

mathematical methods to develop an optimized<br />

solution for all participating design disciplines,<br />

while simultaneously taking into consideration<br />

the often competing and conflicting design goals<br />

of each discipline. MDO has been successfully<br />

used in many industries that involve the design<br />

of complex engineering systems including<br />

power generation [Wang and Singh 2006],<br />

aerospace [Kuan et al. 2010; Vlahopoulos,<br />

Zhang, and Sbragio 2011], automotive [H. M.<br />

Kim et al. 2002], and naval architecture<br />

[Hannapel and Vlahopoulos 2010; H. Y. Kim<br />

and Vlahopoulos 2012].<br />

The unique design goals of each design<br />

discipline result in equally unique discipline<br />

level optimization solutions. A discipline level<br />

optimization is defined as an optimization that<br />

considers the design goals of a single design<br />

discipline only, regardless of other disciplines.<br />

As an example, the optimization of a ship’s<br />

weight would likely result in different optimal<br />

solutions for the Stability, Resistance, and<br />

Survivability design disciplines. Applying an<br />

MDO to optimize the ship weight from a system


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level perspective, simultaneously considering<br />

the design goals of the all three unique<br />

disciplines, would likely result in yet another<br />

distinct optimal ship weight. Fig. 6 shows<br />

theoretical results of the discipline level, and<br />

system level (MDO) optimizations for a ship’s<br />

weight.<br />

Fig. 6 Example Results for Optimization of<br />

Ship Weight at the Discipline Levels and<br />

MDO System Level<br />

When the system level MDO solution is<br />

compared to the solution of a discipline level<br />

optimization, the MDO solution may appear to<br />

be sub-optimal compared to that one discipline.<br />

Consider the comparison of the Resistance<br />

discipline optimization versus the MDO result;<br />

Fig. 6. The higher weight of the system level<br />

MDO solution is due to the necessary<br />

compromises and design trade-offs the MDO<br />

makes to satisfy the added design disciplines of<br />

Stability and Survivability. The MDO develops<br />

a solution that is optimal when accounting for all<br />

discipline level design goals. As a result, the<br />

MDO solution may not be optimal for any one<br />

discipline, but it is optimal from a systems<br />

engineering viewpoint.<br />

A multi-level optimization approach is used in<br />

the DST to support MDO; Fig. 7. The bottom<br />

level of the MDO consists of individual<br />

discipline level optimizations. The discipline<br />

level optimizers pass information to the top,<br />

system level, optimization algorithm which<br />

combines the information to determine a single<br />

MDO result. The system level MDO result is<br />

5<br />

then passed back to the discipline level<br />

optimizers to influence the optimization search<br />

process. The swapping of information between<br />

the discipline levels and system level continues<br />

in an iterative fashion until the system level<br />

convergence criteria are met. Fig. 7 shows a<br />

diagram of the general operating procedure for<br />

the multi-level MDO approach.<br />

Fig. 7 Multi-Level, MDO Algorithm Search<br />

Process Diagram<br />

To date, two system level algorithms for use in a<br />

multi-level MDO problem have been<br />

implemented in the DST. Both algorithms were<br />

developed by Dr. Nick Vlahopoulos at<br />

University of Michigan and can be found in<br />

references [Hannapel and Vlahopoulos 2010]<br />

and [H. Y. Kim and Vlahopoulos 2012]. The<br />

system level algorithm used in the Use Case is<br />

described in [H. Y. Kim and Vlahopoulos 2012]<br />

and summarized below. This MDO system level<br />

algorithm scales each discipline by a Plausible<br />

Reduction Range (prr) to weight each discipline<br />

evenly. The prr for each discipline is calculated<br />

by finding the maximum difference between the<br />

discipline’s objective function optimum ( )<br />

,where are the design variable values for<br />

the optimum of discipline and the discipline<br />

objective value at the optimal design variable<br />

values of all other disciplines ( ). Show in<br />

equation 1.<br />

( ( ) )<br />

(1)<br />

During each iteration of the MDO, the current<br />

values of the design variables are used as<br />

starting points for each of the discipline level


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optimizations. The optimal values from each<br />

discipline are then located, communicated back<br />

to the system level optimizer, and used in the<br />

system level objective function shown in<br />

equation 2.<br />

( )<br />

(∑ ( ) )<br />

(2)<br />

The system level objective function<br />

represents the distance from the discipline<br />

optimum ( ) to the discipline value,<br />

( ), at the current design variable value(s) x,<br />

scaled by the . The system level optimization<br />

formulation is shown in equation 3.<br />

( )<br />

(3)<br />

In equation 3, represents the system<br />

level inequality constraints, which include any<br />

system level constraints, as well as all discipline<br />

level constraints. represents the system<br />

level equality constraints, which again contain<br />

all system and discipline level constraints.<br />

and are the lower and upper<br />

bounds of the variables, which take into account<br />

all system and discipline level bounds. The<br />

system level constraints and bounds consider all<br />

disciplines to ensure that the final optimum point<br />

is feasible for all disciplines involved.<br />

MDO Use Case Definition<br />

The goal of the first Use Case for the MDO<br />

portion of the DST was to demonstrate the MDO<br />

algorithms using all continuous variables. Use<br />

Case 1 (UC-1) conducts an optimization on the<br />

hydrodynamic performance of a surface<br />

combatant based on the hullform of the Oliver<br />

Hazard Perry (FFG 7). The hullform was<br />

optimized with respect to two design disciplines,<br />

minimizing the lifetime power requirements of<br />

6<br />

the ship, and maximizing the average percent<br />

time operational. Each discipline was subject to<br />

various constraints to ensure hydrostatic stability<br />

and feasible designs. The MDO formulation<br />

used 11 continuous design variables, which were<br />

inputs to the LEAPS Hullform Transformation<br />

Utility (HFT). The design variables listed in<br />

Tabel 1. Are all shape factors (SF) used by the<br />

HFT.<br />

Table 1: Design Variable List<br />

Design Variable<br />

Length<br />

Depth<br />

Beam<br />

Longitudinal Fullness Forward<br />

Longitudinal Fullness Aft<br />

Vertical Fullness Above WL<br />

Vertical Fullness Below WL<br />

Transverse Fullness<br />

Hullform Angle Bow<br />

Hullform Angle Stern<br />

Hullform Angle port/starboard<br />

The SF design variables manipulate the hull in<br />

multiple ways and all have values that range<br />

from -1 to 1. The parent hull is found when all<br />

SFs are set equal to zero. The dimensional SF<br />

(Length, Depth, and Beam) correspond to the<br />

respective values on the bounding box around<br />

the ship hull. The longitudinal fullness factors<br />

control what percentage of the ship hull fills the<br />

bounding box forward and aft of midships. The<br />

vertical fullness factors control what percentage<br />

of the ship hull fills the bounding box above and<br />

below the waterline, and the transverse fullness<br />

factor controls the port and starboard fullness<br />

with respect to the bounding box. The bow and<br />

stern angle controls the angle of the front and<br />

end of the bounding box respectively. Finally,<br />

the port/starboard angle controls the angles of<br />

the sides of the bounding box (see Hull Transfer<br />

Utility [2012] for more information). Fig. 8,<br />

shows pictures of the baseline hullform and<br />

transformed hullform utilizing SFs. In the


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optimization process the HFT is called to<br />

automatically shape the hullform for further<br />

7<br />

design analyses.<br />

Fig. 8 Demonstration of the Use of Shape Factors in the Hullform Transfer Utility<br />

The first of the two design disciplines attempts<br />

to minimize the lifetime power requirements of<br />

the ship. The lifetime power requirements are<br />

based on the KW-hours required to overcome<br />

the ships resistance at the speed profile given in<br />

Table 2. The ship was given an assumed ship<br />

time at sea of 4000 hours per year, and a ship<br />

service life of 30 years.<br />

Table 2: Speed Profile<br />

Ship Speed (knots) Time at Speed (%)<br />

10 50<br />

15 30<br />

20 15<br />

25 3<br />

30 2<br />

The analysis of the ship resistance at each speed<br />

was calculated using the LEAPS Total Ship<br />

Drag (TSD) program, which predicts the total<br />

ship resistance based on the methods described<br />

in, “Rapid Resistance Evaluation of High-Speed<br />

Ships” [Metcalf et al]. For each hull form<br />

analyzed by the optimizer, the resistance<br />

characteristics are found for each of the speeds<br />

listed in Table 2, with the results used in<br />

Equation 4. In Equation 4, N is the total number<br />

of speeds, TDi is the total drag at speed i in N,<br />

and Vi is the velocity at speed i in m/s. The<br />

number is converted to KW-hrs giving the<br />

objective function for the lifetime power<br />

minimizer, SLP.<br />

(∑<br />

)<br />

(4)<br />

The second discipline attempts to maximize the<br />

percent time operational (PTO) of the ship. The<br />

PTO is a function of the ship mission. For UC-<br />

1, the ship was assumed to be operational if it<br />

could launch and recover a helicopter. Table 3<br />

shows the upper limits on four motions which<br />

must be satisfied to complete helicopter<br />

operations.


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Table 3: Upper Limits on Motions for<br />

Helicopter Operations<br />

Motion Operational<br />

Limit<br />

Roll 8 [degrees]<br />

Pitch 3 [degrees]<br />

Vertical Acceleration 0.4 [g]<br />

Horizontal Acceleration 0.4 [g]<br />

To find the average PTO, the hullform was<br />

tested in a variety of sea states based on<br />

historical data to give a yearly wave profile in<br />

multiple locations. The analysis was conducted<br />

using the LEAPS Ship Motions Program (SMP).<br />

SMP calculates the ships motions using methods<br />

described in [Conrad 2005]. Using all of the<br />

yearly wave profiles available the resultant ship<br />

motions were inspected with respect to<br />

maximum pitch and roll values, and the vertical<br />

and horizontal acceleration at the helicopter<br />

deck. The helicopter deck was assumed to be<br />

located at 90% of the ship’s length overall. The<br />

average PTO was calculated to give the<br />

objective function value.<br />

For UC-1 both disciplines were subject to the<br />

same constraints. The constraints were designed<br />

to ensure that the ship was hydrostatically stable.<br />

The longitudinal center of buoyancy (LCB) was<br />

constrained to be within 0.5% of the length<br />

water line (LWL) to the longitudinal center of<br />

gravity (LCG). The ship GMT had to be greater<br />

than 10% of the beam (B). The final constraint<br />

for hydrostatics ensured that the weight of the<br />

ship was equal to the displacement .<br />

Additional constraints were used to simplify<br />

calculations. The vertical center of gravity<br />

(VCG) was constrained to be equal to 57% of<br />

the ship depth. The LCG was required to be 51%<br />

of the ship LWL. The weight of the ship was<br />

calculated based on the hull volume by using a<br />

ship density factor of 0.4 MT/m 3 . The final set<br />

of constraints ensured that the displacement of<br />

8<br />

the ship was between 4000 and 7000 metric<br />

tonnes. All constraints are shown in equations<br />

5-13.<br />

Due to limitations in the analysis software, for<br />

UC-1, genetic algorithm solvers were used for<br />

the optimization process. Different combinations<br />

of design variables caused irregular shapes<br />

which would fail to run in the analysis tools.<br />

This would lead to discontinuities in the design<br />

space, which would cause gradient based<br />

optimization solvers to give sub-optimal results.<br />

For all results presented below, the NSGA-II<br />

solver was used for both system and discipline<br />

level optimization solvers.<br />

Results<br />

(5)<br />

(6)<br />

(7)<br />

(8)<br />

(9)<br />

(10)<br />

(11)<br />

(12)<br />

(13)<br />

Although an exhaustive search of the design<br />

space has not been completed, the MDO portion<br />

of the DST displayed promising results. Using<br />

the NSGA-II solver, the DST was successfully<br />

run to pre-determined stopping criteria to select<br />

the “optimal” solution. When the MDO finished<br />

running, the results indicated an improvement in<br />

the objective function, showing that the process<br />

was moving in the correct direction towards an<br />

optimal solution.


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To analyze the optimization processes, first the<br />

parent hullform was optimized with respect to<br />

each of the individual disciplines. The parent<br />

hullform is shown in Fig. 9. The principal<br />

dimensions and values for lifetime power and<br />

PTO of the parent hullform are shown Table 4.<br />

Fig. 9 Parent Hullform (FFG 7)<br />

Table 4: Parent Hull Principle Dimensions<br />

and Objective Function Values<br />

LOA 127.63 [m]<br />

B 13.85 [m]<br />

T 5.07 [m]<br />

D 9.15 [m]<br />

L/B 9.22<br />

B/T 2.73<br />

B/D 1.51<br />

Lifetime Power 1,353,502 [kW-hr]<br />

PTO 32.2 [%]<br />

The results of the individual optimizations are<br />

shown below in Fig. 10 and Table 5 for the<br />

lifetime power minimization, and Fig. 11 and<br />

Table 6 for the average PTO maximization.<br />

Due to the shape factors used, some of the final<br />

hull forms seem unconventional. The use of the<br />

HFT is one aspect that makes this optimization<br />

problem unique, as most early stage design<br />

optimization processes are limited to only using<br />

parametric equations for analyses, or can only<br />

stretch/shrink a hull using parametric<br />

transformations. Even with the unique hull<br />

shapes, the trends that are shown follow a naval<br />

architect’s intuition to the individual optimums.<br />

In the case of the hullform that was optimized<br />

for lifetime power, the hull grew longer,<br />

approached the minimum displacement, and the<br />

9<br />

beam decreased. The average PTO<br />

maximization resulted in a hull with a greater<br />

displacement, and a very full ship under the<br />

waterline.<br />

Fig. 10 Lifetime Power Minimization<br />

Optimized Hullform<br />

Table 5: Lifetime Power Minimization<br />

Optimized Dimensions and Objective<br />

Function Values<br />

LOA 144.5 [m]<br />

B 13.4 [m]<br />

T 4.8 [m]<br />

D 8.9 [m]<br />

L/B 10.78<br />

B/T 2.79<br />

B/D 1.51<br />

Lifetime Power 1,211,480 [kW-hr]<br />

PTO 28.9 [%]<br />

Fig. 11 PTO Maximization Optimized Hullform<br />

Table 6: PTO Maximization Optimized<br />

Principal Dimensions and Objective Function<br />

Values<br />

L 123.9 [m]<br />

B 23.5 [m]<br />

T 7.9 [m]<br />

D 11.9 [m]<br />

L/B 5.27<br />

B/T 2.98<br />

B/D 1.98<br />

Lifetime Power 3,299,331 [kW-hr]<br />

PTO 45.8 [%]


Distribution Statement A: Approved for Public Release; Distribution Unlimited<br />

The ship was then optimized considering both<br />

disciplines’ objectives simultaneously using the<br />

in the complete MDO process. The results are<br />

shown in Fig. 12 and Table 7.<br />

Fig. 12 MDO Optimized Hullform<br />

Table 7: MDO Optimized Principal<br />

Dimensions and Objective Function Values<br />

L 172.5 [m]<br />

B 16.0 [m]<br />

T 3.95 [m]<br />

D 8.6 [m]<br />

L/B 10.78<br />

B/T 4.05<br />

B/D 1.86<br />

Lifetime Power 1,739,142 [kW-hr]<br />

PTO 41.2 [%]<br />

The results observed for the MDO showed<br />

improvement in the objective function for that<br />

process. When comparing the MDO results to<br />

the original hullform, the equal weighting of the<br />

disciplines is visible. The lifetime power<br />

requirements of the ship increased, while the<br />

PTO increased by a larger percentage than the<br />

percent increase of the lifetime power. When<br />

compared to the original parent hullform, the<br />

MDO optimized hullform experienced a 28.0%<br />

increase in lifetime power while the PTO was<br />

increased by 28.5%. Note that for lifetime<br />

power, a percent increase indicates a less<br />

favorable condition, whereas a percent decrease<br />

indicates a more favorable design, one using less<br />

power than the comparable hullform.<br />

The tradeoffs made by the MDO solution are<br />

also shown in comparing the solution to the<br />

lifetime power and PTO optimized solutions.<br />

The lifetime power for the MDO solution<br />

increased by 28.0% from parent hull, while the<br />

lifetime power optimized solution was able to<br />

10<br />

achieve a 10.2% decrease from the parent hull.<br />

However, the lifetime power optimized solution<br />

experienced a 10.5% decrease in PTO. The PTO<br />

of the MDO hull increased by 28.5% from the<br />

parent hull, while the PTO optimized hull form<br />

was able to increase by 42.2% from the parent<br />

hull. Table 8 shows the change in lifetime power<br />

and PTO for the MDO solution when compared<br />

to the parent and optimized hullform types using<br />

a percent error formula.<br />

Table 8: Percent Error of MDO, Lifetime Power<br />

Optimized, and PTO Optimized Solutions versus<br />

Parent Hullform<br />

Parameter Parent/<br />

Lifetime<br />

MDO<br />

Parent/<br />

LTP<br />

Parent/<br />

PTO<br />

Power (+)28.0% (-)10.2% (+)143%<br />

PTO (+)28.5% (-)10.5% (+)42.2%<br />

Conclusions<br />

The current status of the MDO capabilities<br />

within the DST show promising results even<br />

given the current limitations. The optimization<br />

algorithms have given correct results to test<br />

problems with known analytical solutions. In<br />

UC-1, the algorithms did move toward improved<br />

solutions, and in all optimizations, the objective<br />

function improved. Additionally, UC-1<br />

demonstrated how competing and conflicting<br />

design goals force a MDO solution to make<br />

design compromises that result in performance<br />

characteristics that are sub-optimal when<br />

compared to individual performance based<br />

optimizations. However, the results of the MDO<br />

solution are optimal when looking at the<br />

performance of the ship from a combined multidisciplinary<br />

systems view.<br />

Currently, improvements are being completed to<br />

allow for faster more complete optimization<br />

runs. A second use case is also being developed<br />

to test more capabilities of the DST. Use Case 2


Distribution Statement A: Approved for Public Release; Distribution Unlimited<br />

will test the DST’s ability to handle discrete<br />

design variables and will add an additional<br />

mission specific discipline, a high speed transit<br />

scenario.<br />

As the DST continues to grow capabilities, the<br />

overall goal is to integrate the DST into the<br />

RSDE. Within RSDE, the MDO capabilities can<br />

help lead engineers to regions of the design<br />

space with higher preferences. This can help for<br />

communicating preferences between design<br />

groups and facilitate the narrowing of the design<br />

space for SBD.<br />

References<br />

ASSET. 2012. “Ship Systems Integration and<br />

Design - ASSET.” Accessed October 12.<br />

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e/pub/who/departments/asset.aspx .<br />

Bernstein, Joshua I. 1998. “Design Methods in<br />

the Aerospace Industry: Looking for<br />

Evidence of Set-Based Practices”.<br />

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Motion Program Users Manual. West<br />

Bethesda.<br />

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Meyarivan. 2000. A Fast and Elitist Multi-<br />

Objective Genetic Algorithm-NSGA-II.<br />

Kanpur.<br />

Doerry, N. Capt. USN, and M Steding. 2009.<br />

Ship Design Manager Manual.<br />

Eccles, T.J. Commander Naval Sea Systems<br />

Command. 29 Sept. 2010. Ship Design and<br />

Analysis Tool Goals. Ref. COMNAVSEA<br />

memo 9000 Ser 05T/015.<br />

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Evans, J. H. 1959. “Basic Design Concepts.”<br />

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Journal 711 (4): 672–678.<br />

<strong>Gray</strong>, Alexander Westley, “Enhancement of Set<br />

Based Design Practices Via Introduction of<br />

Uncertainty Through the Use of Interval<br />

Type 2 Modeling and General Type 2<br />

Fuzzy Logic Agent Based Methods”.<br />

University of Michigan, 2011.<br />

Hannapel, Shari, and Nickolas Vlahopoulos.<br />

2010. “Introducing Uncertainty in<br />

Multidiscipline Ship Design.” Naval<br />

Engineers Journal 122 (2) (June 7): 41–52.<br />

doi:10.1111/j.1559-3584.2010.00267.x.<br />

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3584.2010.00267.x.<br />

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Surface Warfare Center, Carderock<br />

Division, 2012.<br />

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G.J. Delagrammatikas, N.F. Michelena,<br />

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and Chang Xinlong. 2010. “MDO


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k/pub/who/departments/leaps.aspx<br />

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Author Biographies<br />

Alexander <strong>Gray</strong> graduated with his Ph.D. in<br />

Naval Architecture and Marine Engineering<br />

(NA&ME), from the University of Michigan in<br />

2011. He now works as an engineer at<br />

NAVSEA, Carderock. He holds master’s<br />

degrees in Industrial operations engineering and<br />

NA&ME, as well as bachelor’s degrees in<br />

Mechanical and Aerospace engineering. His<br />

research interests include fuzzy logic,<br />

optimization, and set-based design theory.<br />

Brian Cuneo is a Ph.D. Candidate at the<br />

University of Michigan in the department of<br />

Naval Architecture and Marine Engineering. He<br />

has earned a BSE and MEng in the same major<br />

from the University of Michigan. Brian is<br />

currently a Research Assistant working with<br />

NAVSEA Carderock Division on a Naval<br />

Design Optimization Project. His current<br />

research is on developing a heuristic method of<br />

Multi-Disciplinary Design Optimization using<br />

methodologies from Hierarchical Fuzzy Logic<br />

Controllers.<br />

Nick Vlahopoulos is a Professor in the<br />

Department of Naval Architecture and Marine


Distribution Statement A: Approved for Public Release; Distribution Unlimited<br />

Engineering at the University of Michigan. He<br />

joined the University of Michigan in 1996 after<br />

working in the Industry for seven years. He has<br />

graduated 15 Ph.D. students, published 70<br />

journal papers and over 80 conference papers.<br />

The areas of his research are: numerical methods<br />

in structural-acoustics, and design of complex<br />

systems.<br />

David J. Singer is an Assistant Professor in the<br />

Department of Naval Architecture and Marine<br />

Engineering (NAME) at the University of<br />

Michigan. Dr. Singer obtained a B.S.E. degree<br />

in NAME, M.Eng. degree in Concurrent Marine<br />

Design, M.S.E. degree in Industrial and<br />

Operations Engineering and a PhD in NAME,<br />

all from the University of Michigan.<br />

13

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