## Further Development and Optimiza tion of the Ballast-Free Ship Design Concept

Final Report

Michael G. Parsons Arthur F. Thurnau Professor Emeritus Professor Emeritus of Naval Architecture and Marine Engineering Phone: 734-945-2886; FAX: 734-936-882; e-mail: parsons@umich.edu

Miltiadis Kotinis Assistant Professor, Mechani cal Engineering, Old Dominion University Phone: 757-683-5939; FAX: 757-962-5097; e-mail: mkotinis@odu.edu

October 30, 2008

Department of Naval Architecture and Marine Engineering University of Michigan 2600 Draper Road Ann Arbor, MI 48109-2145

This report represents th e results of research conducted by the authors and does not necessarily represent the views or policies of the Great Lakes Maritime Research Institute. This report does not contain a standard or sp ecified technique. The authors and the Great Lakes Maritime Research Institute do not endorse products or manufacturers. Trade or manufacturers’ names appear herein solely because they are considered essential to this report.

Research funded in part by the Great Lakes Maritime Research Institute. This study was supported by the U.S. Maritime Administration

Grant # DTMA1-G-06-005

### Table of Contents

page

1. Introduction 1

2. Background 2

2.1 Development of the Seaway-sized Bulk Carrier 4

2.2 Arrangement and Design of Inlet and Outlet 6

3. Numerical Investigation 8

3.1 External Flow 8

3.2 Internal Flow 15

4. Experimental Investigation 16

5. Potential Economic Impact s of the Research Results 20

6. Dissemination of Study Results 22

7. References 25

### List of Tables

page

Table 2.1: Main Particulars of the Ballast-Free Bulk Carrier 5

Table 2.2: Characteristics of the Ballast-Free Bulk Carrier Model in Ballast Condition 5

Table 3.1: Grid Independence Study 10

Table 3.2: Drag Coefficients and Form Factor 10

Table 3.3: Nominal Axial Wake Fraction 14

Table 4.1: Form Factor Comparison 17

Table 4.2: Characteristics of the MHL No. 20 and No. 23 Propellers 17

Table 4.3: Propulsion Test Results – Balla st Condition at 15.5 Knots 18

### List of Figures

page

Figure 2.1: Schematic of the Ballast-Free Ship Concept 2

Figure 2.2: Typical Seaway-size Bu lk Carrier (left); Ballast-Free Concept Bulk Carrier (right) 3

Figure 2.3: Bow View of the Seaway-sized Bulk Carrier Model 5

Figure 2.4: Stern View of the Seaway-sized Bulk Carrier Model 5

Figure 2.5: Location of Forward Ballast Trunk Inlet 6

Figure 2.6 : Location of Two Ballast Trunk Discharges Investigated 7

Figure 3.1: Bow Grid Detail of the Ballast-Fr ee Bulk Carrier in Ballast Condition 8

Figure 3.2: Stern Grid Detail of the Ballast-Fre e Bulk Carrier in Ballast Condition 8

Figure 3.3: Bow Pressure Coefficient Contours of the Ballast-Free Bulk Carrier (baseline no trunk flow case) 9

Figure 3.4: Stern Pressure Coefficient Contours of the Ballast-Free Bulk Carrier (baseline no flow case), Outlet Locations Shown for Reference 9

Figure 3.5: Stern Pressure Coefficient of the Ballast-Free Bulk Carrier (discharge Sta. 17 – 90 min) 11

Figure 3.6: Stern Pressure Coefficient of the Ballast-Free Bulk Carrier (discharge Sta. 19 – 90 min) 11

Figure 3.7: Stern Pressure Coefficient of the Ballast-Free Bulk Carrier (discharge Sta. 17 – 120 min) 11

Figure 3.8: Stern Pressure Coefficient of the Ballast-Free Bulk Carrier (discharge Sta. 19 – 60 min) 12

Figure 3.9: Axial Velocity Contours in the Propeller Plane (baseline no trunk flow case) 12

Figure 3.10: Axial Velocity Contours in the Propeller Plane (discharge Sta. 17 – 90 min) 13

Figure 3.11: Axial Velocity Contours in the Propeller Plane (discharge Sta. 19 – 90 min) 13

Figure 3.12: Axial Velocity Contours in the Propeller Plane (discharge Sta. 17 – 120 min) 14Figure 3.13: Axial Velocity Contours in the Propeller Plane (discharge Sta. 19 – 60 min) 14

Figure 3.14: Computational Model of Double Bottom Ballast Trunk Structure 15

Figure 4.1: Ballast-Free Bulk Carrier Total Resistance 16

Figure 4.2: Ballast-Free Bulk Carrier Effective Power 17

Figure 4.3: Stock Propeller Open Wa ter Characteristics and Ship Thrust Requirement 19

Figure 5.1: Order of Magnitude Economics Compar ing a Typical Bulk Carrier with

Filtration and UV Treatment with Ballast-Free Bulk Carrier 21Executive Summary

The initial investigation of the Ballast-Free Ship concept demonstrated the feasibility of the concept though a thorough examina tion of various design aspects. The effectiveness of the concept, in terms of eliminating the transport of foreign ballast water from ships operating in the ballast condition, was also demonstrated by u tilizing Computational Fluid Dynamics (CFD)

software to simulate the flow in the double bottom ballast trunks of the vessel. Nevertheless, this initial investigation did not succeed in showing th e full cost-effectiveness of the concept. The main reason was a significant fuel penalty that resulted from an increased power requirement found in the initial hy drodynamic testing of a non-optimized discharge configuration on an existing, higher-speed vessel with a non-optimum propeller.

The ongoing GLMRI sponsored research pr oject has undertaken further hydrodynamic investigation of the Ballast-Free Ship concept; both experimental and numerical. The experimental investigation was performed by ut ilizing the Seaway-size bul k carrier model that was designed and built as part of th e initial phase of this project. Resistance and propulsion tests were performed with this model in the towing tank of the University of Michigan Marine Hydrodynamic Laboratory in January 2007. The initia l numerical investigations were performed utilizing the commercial CFD software FLUENT ®

.

The computational results were utilized both as guidance for the experiment al setup and also to corroborate the experimental result s. Specifically, the selection of the trunk flow inlet and outlet locations utilized in the towing tank experi ments was guided by the numerical results. The

ballast trunk flow inlet was located in the cente r of the bulbous bow. Two different locations were tested for the water discharge: one at the level of the upper part of the propeller disk close to Station 17 (near the forward engine room bul khead, full scale) and one lower close to Station 19 (near the aft engine room bulkhead).

The experiments in the towing tank consisted of detailed resistance and propulsion testing with and without the ballast trunk flow. The analysis of the model test da ta revealed that the experimental results were in good agreement with the numerical results. Overall, discharging water at the stern of the model slightly incr eases ship resistance, but proper design of the discharging arrangements can ove rcome this negative effect. A nother source of modest ship

resistance increase is the trunk inlet at the bow. Given the limited positive-pressure region at the

bow of the full form bulk carrier under consideration, an inlet location other than that currently utilized will probably result in a significant reduction in the av ailable pressure differential, without providing a noteworthy benefit in terms of ship resistance.

Nonetheless, the proper water discharge at the ster n of the vessel can have a favorable effect on the propulsion characteristics fo r the Seaway-size bulk carrier design investigated. The reduction in powering requirements, relative to the initial unmodified design, at an assumed ballast speed of 15.5 knots was fo und in the January 2007 experi ments to be 7.3% for water discharge close to Station 17 and 2.1% for wate r discharge close to St ation 19. The gain in overall propulsive efficiency outweighs the increase in ship resistance. The large power decrease of 7.3% was, however, suspect leading to a dditional work during inthe current year.Additional numerical work was performed du ring the past year using the Star-CCM+ ® CFD

software that includes the v 2 -f turbulence modeling that has been found to be more effective for fuller hull forms as in the Seaway-sized bulk carrier under consideration. Additional modelscale experiments were also undertaken in the to wing tank of the University of Michigan Marine Hydrodynamic Laboratory in July 2008. These e xperiments utilized improved methods for the resistance testing and this provi ded more consistent results and higher total resistance increases

with the use of the Ballast-Free trunk flow than found in the January 2007 experiments. With the discharge at Station 19, the resistance increase in the ballast condition at 15.5 knots was found to be 2.44% full scale. With the discharge at St ation 17, the resistance increase at the ballast

condition at 15.5 knots was found to be 4.61%.

When the required propulsion power was determ ined, it was found to d ecrease by 1.63% from the unmodified case with the preferred discharge at Station 17. This results from a change in the propeller operating poin t and changes in the flow over the stern due to the ballast trunk flow introduction into the boundary laye r so that it increases the flow into the upper part of the propeller disk. This results in increases in the propeller operating efficiency and also the hull efficiency that are large enough to offset the increase in the tota l resistance measured without the propeller. These results confirm the requi red power decrease found in the January 2007 experiments, but show that those results were unrealistically high.

In order to investigate the econom ic benefit of the aforementione d propulsive improvements, an operating scenario for the grain trade to Europe was adopted for the Ballast-Free bulk carrier. The change in the Required Freight Rate (RFR) w ith respect to an alternative filtration and UV ballast treatment system was estimated. The net savings would be about $1.00 per tonne of cargo for the Ballast-Free bulk carrier with the wate r discharged close to Station 17. The overall ship design would also benefit from placement of the water discharge near the forward engine room bulkhead. A different operating scenario coul d result in even lower savings. Nevertheless, cost-effectiveness combined with a numerically-demonstrated foreign-ballast-elimination capability confirms the Ballast-Free Ship concept will be a viable alternative to more costly ballast treatment systems. Even though the cu rrent project focuses on a smaller Seaway-size bulk carrier, the concept should also be applicable to other new- construction ships of different types and sizes.1 1. Introduction

The Ballast-Free Ship Concept was inve nted (US Patent #6,694,908 2004) and initially investigated (Kotinis et al. 2004, Kotinis 2005, Ballast Water News 2004) at the University of Michigan as a way to minimize the risk of the further introduction of nonindigenous aquatic species into the Great Lakes and other coastal waters by ships arri ving in the ballast condition. Even though the feasibility of the concept was de monstrated, the initial analysis was limited by its required comprehensive research scope and limited associated budget. Thus, it was only feasible to support model testing that utilized an ex isting model. Although the vessel type of greatest interest for the Great Lakes nonindigenous aquatic speci es introduction problem is theSeaway-sized bulk carrier, the best available model was of a relatively finer, higher-speed bargecarrying Lighter Aboard Ship (LASH) vessel. The results with this finer model indicated a significant 7.4% power penalty with the us e of the Ballast-Free Ship concept.

The first year of GLMRI sponsored research (P arsons and Kotinis 2006) supported the design of a typical Seaway-sized bul k carrier and the constr uction of a scaled mode l to be utilized in subsequent towing tank experiments. This mo del was designed, construc ted, and delivered in 2006. The goal was to use this model to optim ize the location of the Ballast-Free trunk discharges in order to reduce or eliminate th e propulsion power increa se observed with the modified LASH model. Experimental and nu merical hydrodynamic investigations, combined with an optimization procedure, were expected to lead to a design solution that could offer a net required power reduction and savings in Required Fr eight Rate (RFR) relative to alternate ballast water treatment methods and approaches.

In the second year of GLMRI sponsored rese arch (Parsons and Kotinis 2007), the hydrodynamic aspects of the Ballast-Free Ship concept were further investigated both experimentally and numerically. Part of the numerical inve stigation, including discharge location design optimization, was reported in a paper presented at the 9 th International Conference on Numerical Ship Hydrodynamics (Kotinis and Parson s 2007a). The experimental hydrodynamic investigation, supported by the Computational Flui d Dynamics (CFD) analysis and an economic analysis, was presented at the Annual Societ y of Naval Architects and Marine Engineers (SNAME) Meeting in November 2007 (Kotinis and Parsons 2007b). This work showed a significant 6.3% net required power reduction that need ed further confirmation.

In the current year of GLMRI sponsored rese arch, the hydrodynamic aspect of the BallastFree ship concept was further investigated both numerically and experimentally. The BallastFree bulk carrier model, utilized in prior phase s of the investigation, was employed as the investigated model hull. The numerical part was performed using the Star-CCM+ ®
commercial CFD software. Various aspects of the flow were examined; the appropriate locations for the inlet/outlet, the form factor as a function of flow rate, the nominal wake, and

the internal trunk flow. The experimental investigation wa s performed in July 2008 in the Marine Hydrodynamics Laboratory (MHL) towing ta nk of the University of Michigan. The qualitative effect of the water suction and discharge on the resi stance of the bulk carrier model was determined and the results were extrapolated to full scale. Furthermore, the effect on propulsion and the economics was also examined utilizing a second pr opeller of the same diameter as the one utilized in the previous year experiments (Kotinis and Parsons 2007b).2 2. Background

The initial Sea Grant supported development of th e Ballast-Free Ship Concept was reported in a paper before the Annual Meeting of the Societ y of Naval Architects and Marine Engineers (SNAME) in Washington, DC, in October 2004 (Kotin is et al. 2004). Overa ll, the investigation of the Ballast-Free Ship Concept has shown that it provides a viable altern ative to the addition of costly ballast water treatment systems in orde r to meet the evolving performance requirements for ballast water treatment. The concept essentially eliminates the transport of foreign ballast

water . This should be more effect ive than current treatment me thods in reducing the potential

for the further introduction of nonindigenous aquatic sp ecies into the Great Lakes and coastal waters. Furthermore, it should be equally effect ive as international re quirements extend below the 50 micron range (IMO 2004).

The traditional approach to ballast operations, since the introduction of steam machinery, has

been the use of water ballast to increase the we ight of the vessel in the light cargo condition. A paradigm shift in thinking here views the ballas t condition as a change of buoyancy rather than an addition of weight in order to get the vessel to its safe ballast drafts. Such a shift in thinking

led to the invention of the Ballast-Fr ee Ship Concept (US Patent #6,694,908 2004).

In this concept, the traditional ballast tanks are replaced by longit udinal, structural ballast trunks that extend beneath the cargo region of the ship below the ballast draft. A schematic of this concept is shown in Fig. 2.1.

Figure 2.1: Schematic of the Ballast-Free Ship Concept

The arrangement of a conventional Seaway-size bulk carrier is show n on the left in Fig. 2.2; the arrangement of an equal grain capacity Ballast- Free Ship Concept Seaway-size bulk carrier is shown for comparison on the right. In this ex ample, the three ballast trunks per side are

connected to the sea thro ugh a plenum at the bow and a second plenum at the stern. These trunks3 are flooded with seawater to reduc e the buoyancy of the vessel in th e ballast conditio n in order to get the vessel down to its ballast drafts. Since there is a natu ral hydrodynamic pressure differential created between the bow region and the stern region of a ship due to its motion through the water, a slow flow is induced in th ese open ballast trunks. This ensures that the ballast trunks are always filled with slowly-movi ng “local seawater.” This should ensure that there is no transport nonindigenous aquatic species across the globe. Therefore, the vessel becomes foreign “ballast-free” fr om the traditional viewpoint.

When the ballast voyage is completed, the ballast trunks can be isolated from the sea by valves and then pumped dry using conve ntional ballast pumps . The need for costly ballast water treatment equipment or ballast water treatment chemicals would, thus, be eliminated. This approach would also be equally effective for bi ota smaller than 50 microns. During the full load condition or any condition where ballast is not n ecessary, the outer four ballast trunks would be segregated utilizing valves at ea ch of the cargo hold bulkheads. This is needed to provide the vessel adequate damage survivability under current IMO requirements.

Figure 2.2: Typical Seaway-size Bulk Carrier (left); Ballast-Free C oncept Bulk Carrier (right)

In order to provide ad equate intact stability, equivalent damage surviv ability, equivalent cargo capacity, etc., the entire vessel design needs to be developed to support this concept of ballast operations as illustrated in Fig. 2.2. Thus, it is not feasible for back fit and is suitable only for new construction. The ship requ ires a higher tank top in order to locate enough ballast trunk4 volume below the ballast draft and requires a greater hull depth in or der to maintain the vessel’s capacity to carry light cargos, such as grain. The Ballast-Free Ship Concept also includes features to minimize the buildup of sediment within the ballast trunks and f acilitate their required cleaning; i.e., easier to clean 2.4 m high ballast tr unks and the elimination of the lower part of the

floors next to the shell.

As noted, the initial research on the development of the Ballast-Free Ship Concept was limited by its required comprehensive research scope and limited associated budget. For budgetary reasons, it was only feasible to support model tes ting that utilized an existing model. Although the vessel type of greatest interest for the Great Lakes nonindigenous aquatic species introduction problem is the Seaway-size bulk carrie r, the best available model was of a relatively finer, higher-speed barge-carrying Lighter Aboard Ship (LASH) vessel. This existing model was

modified to utilize a more c onventional stern, but th e model test results were not directly applicable to the Seaway-size bulk carriers studied in detail in the rest of the research effort.

The initial model tests had to be limited to a single system design for the existing model. There was no opportunity to optimize the hydrodynamic design of the system to minimize the economic impact of the Ballast-Free Ship Concep t design. The initial model tests using the

modified LASH vessel hull showed that the specific ballast intake and discharge locations and

method tested resulted in a m odest 2.2% increase in resistan ce, but a more significant 7.4% increase in the required propulsion power. This specific result assumed a change in the ballast water within the ballast trunks once every two hour s, which would meet the environmental intent of the Ballast-Free Ship Concept. The large powe r increase could result in an undesirable engine size increase and would certainly result in an important fuel cost penalty. In that investigation, it was concluded that further hydrodynamic optimizati on could eliminate most, if not all, of this significant added power requirement.

This undesirable power penalty motivated the GLMRI sponsored research effort that has designed a Seaway-sized bulk carrier, produced a 5 m precision scale m odel of that vessel, undertaken Computational Fluid Dynamics (C FD) analyses of this design, and conducted hydrodynamic testing of the model in the Univ ersity of Michigan Marine Hydrodynamics Laboratory (MHL). The primary goa l of this research has been the optimization of the ballast trunk intake and discharge configurations in orde r to provide a required power reduction rather than an increase, if feasible.

2.1 Development of the Se away-sized Bulk Carrier

The Ballast-Free bulk carrier model, which was designed and built during the initial GLMRI sponsored phase of this project (Parsons and Ko tinis 2006), was tested at the University of Michigan Marine Hydrodynamics Laboratory (MHL) in January of 2007 in year two. The main particulars of the ship are shown in Table 2.1. The characteristics of th e model in the ballast condition are presented in Table 2.2. The bow and the stern of the constructed model are shown in Figs. 2.3 and 2.4, respectively. All of the initial tests were carrie d out at the ballast drafts at

which the Ballast-Free trunks would be in use.5 Table 2.1: Main Particulars of the Ballast-Free Bulk Carrier

Table 2.2: Characteristics of the Ballast-Free Bulk Carrier Model in the Ballast Condition

Figure 2.3: Bow View of the Seaway-sized Bulk Carrier Model

Figure 2.4: Stern View of the Seaway-sized Bulk Carrier Model Waterline length (m) 195.5 Maximum beam (m) 23.76 Depth to main deck (m) 16.00 Full-load draft (m) 10.70

Block coefficient C B 0.835

Geometric scale ratio λ 37.92 Waterline length (m) 5.00 Maximum beam (m) 0.627 F.P. draft @ 40% DWL (m) 0.113 A.P. draft @ 70% DWL (m) 0.198 Wetted surface area (m 2 ) 5.346 2.2 Arrangement and Design of Ba llast Trunk Inlet and Outlets

A full-scale diameter of approxima tely 1 m was chosen for the plena inlet and outlet to ensure a smooth inflow and outflow without imposing severe constraints on the stru ctural arrangements. The corresponding inlet/outlet diamet er at model scale is approxima tely 2.6 cm. The flow rate in the longitudinal trunks was calculated assuming a full-scale volume of ballast water equal to 18,500 m 3 . This value was obtained from similar ships, under the assumption of flooding both the normal ballast tanks and a central cargo hold for a heavy weather ballast condition. Assuming an exchange time of 90 min and utilizing Froude scaling, the internal flow rate at model scale is Q

m = Q

s λ -5/2 = 3.9·10 -4 m 3 /s. Using the continuity equation and assuming a symmetrical plenum about the centerplane, the average discharge fluid speed is 0.382 m/s.

The selection of the inlet location was based pr imarily on providing a pressure differential capable of sustaining a steady tru nk (internal) flow. In addition to this, the inlet must be adequately submerged to avoid ai r ingestion and interaction with the free surface and the bowgenerated wave system. An important design cons traint is the low forward draft in the ballast

condition. It was decided to locate the water inlet right on the face of the bulbous bow in the area around the stagnation point to take advantage of the hi gh positive pressure in this region. Therefore, the center of the water inlet was place d at approximately 25% of the design waterline (DWL) above the keel as shown in Fig. 2.5.

Figure 2.5: Location of Forward Ballast Trunk Inlet

In order to investigate the effect of the water discharge on the flow at the stern, two different discharge locations were selected; one close to Station 17 and one close to Station 19 as shown in Fig. 2.6. Station 17 is approxima tely at the location of the forward engine room bulkhead in the full-scale ship; Station 19 is approximately at the aft engine room bul khead. The discharge at Station 17 was located high at a bout the 45% DWL and the discha rge at Station 19 was located

lower at about the 30% DWL. Th e flow was discharged at abou t 10 degrees to the local hull surface. In this way, the effect on the boundary layer flow, as well as the effect on propeller inflow, could be investigated in a systematic manner.

The choice of the discharge locat ions investigated was based on the results of a numerical CFD investigation. These results are presented in the next section. If trunk flow rate maximization7 were the only criterion, the water outlet should be lo cated in an area with high suction pressure to maximize the pressure differential. On the othe r hand, when the propeller operation is taken into account, the real objective should be to minimize the ship’s power requirement subject to achieving adequate ballast trunk flow.

Figure 2.6: Location of Two Ballast Trunk Discharges Investigated8 3. Numerical Investigation

3.1 External Flow

The numerical investigation of the flow around the Ballast- Free Concept bulk carrier model was performed using the Star-CCM+ ® CFD software during the r ecent year. A predominantly hexahedral grid, detail s of which are shown in Figs. 3.1 and 3.2, was utilized. Star-CCM+ ®

was used instead of FLUENT ® , as used in the previous wor k, because the turbulence could be simulated using the v 2 -f turbulence model, which has been more successful in predicting the wake characteristics of full hull shapes. The bou ndary layer flow was resolved all the way to the solid boundary (hull), as one of the goals was the successful pred iction of the mixing between the boundary layer flow and the wa ter discharge at th e stern. The v 2 -f turbulence model is theoretically valid th roughout the flow domain wit hout the need for turbulence damping functions in the viscous sublayer. Therefore, the mesh was created to provide the required refinement close to the hull.

Figure 3.1: Bow Grid Detail of the Ballast-Fr ee Bulk Carrier in Ballast Condition

Figure 3.2: Stern Grid Detail of the Ballast-Fre e Bulk Carrier in Ballast Condition9 The positioning of the water inlet at the bow of the Ballast-Free bulk carrier was established using the earlier CFD results. A plot of the Star-CCM+ ® pressure coefficient distribution, at the ballast drafts and speed, is shown in Fig.3.3. The magenta is the highest pressure, while the blue-greens and blues represent a negative pr essure. The high block coefficient of this hull form limits the region of positive pressure at the bow and, consequently, the alternatives for the bow inlet position. It was decided to place the inlet right on the tip of the bulb to ensure that there would be an adequate pressu re differential to drive the trunk flow. This configuration was utilized in bo th sets of towing tank testing (J anuary 2007 and July 2008) as

well as in the numerical hydrodynamic investigations.

Figure 3.3: Bow Pressure Coefficient Contours of th e Ballast-Free Bulk Carrier (baseline no trunk flow case)

Two discharge locations at the st ern of the vessel were tested as shown on the model. These two locations are shown in Fig. 3.4 together with the pressure co efficient contours at the stern

of the Ballast-Free bulk carrier while in ballast draft and speed, but with no trunk flow. There is a relatively flat suction pressure region ne ar Station 17, which could provide a steadier internal (trunk) flow. As not ed, the selected discharge loca tion in this region offers an

additional benefit as it would be close to the forward engine room bulkhead, thus, obviating the need for extending the trunks through th e engine room. During the experimental investigation in January 2007, both these disc harge locations provided a reduction in the propulsive requirements, leading to savings in the Required Freight Rate (RFR). The better

Station 17 location was further i nvestigated in 2008 to confirm the very la rge required power improvement (-7.3%) found in the 2007 tests.

Figure 3.4: Stern Pressure coefficient Contours of the Ballast-Free Bulk Carrier (baseline no flow case), Ou tlet Locations Shown for Reference10 Prior to deriving conclusions based on the num erical results, a grid convergence study was

carried out in order to obtain a grid-independent solution. The investigation was performed in model scale (geometric scale factor of 37.92) in order to be able to perform direct comparisons with the experimental results. The grid convergence was evaluated by comparing the pressure, friction, and total drag co efficients of systematically refined grids.

Given the unstructured nature of the generated grids, a system atic refinement was performed mainly in the area close to the hull (and w ithin the boundary layer) setting a goal for an approximate grid refinement ratio of √ 2.

The ballast speed in full scal e was assumed to be 15.5 knots. The computational model did not include a free surface; theref ore, the results do not include wave drag and can be utilized directly for the form factor calculation. An additional assumption pertains to the trunk flow speed. This was computed utilizing an exchange time for the ballast wate r of 90 min, which is equivalent to a model scale flow rate of 6.1 gpm, assuming that th e flow is scaled to maintain Froude number similarity, in a manner si milar to the external flow scaling.

The model-scale simulations were run on a PC equipped with a quad-core 2.66 MHz processor and 8 GB of RAM running in 64-bit Windows Vista. A full-scale simulation of the flow has not been successful thus far, as the near-wall meshing requirements to allow for the flow mixing cannot be handled appropriately by the currently utili zed grid generator.

As shown in Table 3.1, the solution in the fine grid can be considered grid-independent. Subsequently, this grid was utiliz ed in all simulations. The results in Table 3.2 re veal that the pressure drag coefficient is lower when the internal flow is simulated. It can be postulated that the major contribution to the pressure coe fficient reduction comes from the placement of

the water suction at the tip of the bulbous bow, which causes a significant pressure relief in this region producing a form drag reduction. The pressure coeffi cient contours at the stern with discharge near Stations 17 and 19 ar e shown in Figs. 3.5 and 3.6, respectively.

Table 3.1: Grid Independence Study

Grid (# of cells) Baseline case

C P C F C T Coarse (581,162) 0.960e-3 3.225e-3 4.185e-3 Medium (815,402) 0.937e-3 3.366e-3 4.303e-3 Fine (1,176,085) 0.936e-3 3.377e-3 4.313e-3

Table 3.2: Drag Coefficients and Form Factor

C P C F C T Form

Factor

Baseline no trunk flow case 0.936e-3 3.377e-3 4.313e-3 0.315 Discharge at St. 17 – 90min 0.906e-3 3.375e-3 4.281e-3 0.306 Discharge at St. 19 – 90min 0.921e-3 3.378e-3 4.299e-3 0.31111 Figure 3.5: Stern Pressure Coefficient of the Ballast-Free Bulk Carrier (discharge Sta. 17 – 90 min)

Figure 3.6: Stern Pressure Coefficient of the Ballast-Free Bulk Carrier (discharge Sta. 19 – 90 min)

Additional runs were performed to investigate the flow rate effect on the resistance. Specifically, runs were made for an exchange time of 120 min, and thus, a slower water discharge, and also an exchange time of 60 mi n leading to higher discharge velocities. The first, slower case was investigated using the di scharge location near Station 17 as this is a relatively higher pressure region which is less li kely to provide a high exchange rate. The computed pressure drag coefficient has a valu e of 0.884e-3 and the fric tion drag coefficient has a value of 3.375e-3. The computed pressu re drag coefficient value corresponds to a substantial reduction compared to the 90-min wa ter exchange case with discharge from the same location. The resulting form factor value is 0.299. The pressure coefficient contours at the stern of the vessel in this case are shown in Fig. 3.7.

Figure 3.7: Stern Pressure Coefficient of the Ballast-Free Bulk Carrier (discharge Sta. 17 – 120 min)12 The case with discharge near Station 19 was fu rther investigated usin g a higher flow rate corresponding to a ballast exchange time of 60 min. The ma jor consequence of the increased flow rate is a significantly higher pressure drag coefficient, which diminishes the benefits obtained through the bow water suction. The com puted values of the pressure and friction drag coefficients are 0.932e-3 and 3.379e-3, respectively. The corresponding form factor value is 0.315. The pressure coefficient contours at the stern of the vessel in this case are shown in Fig. 3.8.

Figure 3.8: Stern Pressure Coefficient of the Ballast-Free Bulk Carrier (discharge Sta. 19 – 60 min)

The discharge effect on the nominal hull wake was studied by computing the nominal wake fraction. The corresponding values for each of the aforementioned cases are listed in Table 3.3. Plots of the axial velocity at the propeller plane are show n in Figs. 3.9 through 3.13. The results reveal that a faster discharge flow provides a more uniform wake, even though, as pointed out earlier, this leads to higher pressure drag. On the other hand, the discharge at Station 19 provides a more homogeneous, but slower, wake at lower radii.

Figure 3.9: Axial Velocity Contours in the Prope ller Plane (baseline no trunk flow case)13 Figure 3.10: Axial Velocity Contours in the Prope ller Plane (discharge Sta. 17 – 90 min)

Figure 3.11: Axial Velocity Contours in the Prope ller Plane (discharge Sta. 19 – 90 min)14 Figure 3.12: Axial Velocity Contours in the Prope ller Plane (discharge Sta. 17 – 120 min)

Figure 3.13: Axial Velocity Contours in the Prope ller Plane (discharge Sta. 19 – 60 min)

Table 3.3: Nominal Axial Wake Fraction

w H Baseline no trunk flow case 0.405 Discharge at St. 17 – 90min 0.402 Discharge at St. 19 – 90min 0.438 Discharge at St. 17 – 120min 0.408 Discharge at St. 19 – 60min 0.42715 3.2 Internal Flow

The trunk flow was simulated by utilizing the co mputational model of th e initial investigation of the Ballast-Free ship concep t (Kotinis et al. 2004). The domain of the internal flow

consists of the trunks in si x cargo holds connected via sluice gates. The double bottom structures were modeled as accurately as possi ble, as shown in Fig. 14 . Due to the center plane symmetry, only half of the domain wa s modeled. Even though the inlet location has changed since the initial investigation, it was decided to utilize the original configuration in order to compare the effect of the turbulence mo del on the calculations. The turbulence model

utilized in this case was the v 2 -f model within Star-CCM+ ® . The objective was to compute the time required to flush the existing water inside the trunks. The pressure differential was set equal to 0.50. The concentration of the wate r that enters the trunk s through the pressure inlet (‘new water’) was monitored and utilized as the stopping criterio n. Specifically, three

new water concentration levels for the entire array of ballast trunks were considered: 95%, 99%, and 99.9%. The respective recorded times were 85.0, 108.5, and 139.4 minutes. All these times are slightly lower than those obtained earlier using FLUENT ® (Kotinis et al. 2004).

Figure 3.14: Computational Model of Doubl e Bottom Ballast Trunk Structure16 4. Experimental Investigation

The flow around the Ballast-Free Ship was tested experimentally in the towing tank of the MHL in July 2008. A different stock propeller wa s utilized in an attempt to validate the results obtained in January 2007 and also inve stigate the performan ce of a propeller with different characteristics (blade sections, pitch, and expanded area ratio). In addition to this, the resistance tests utilized updated MHL testing equipment that provided a more reliable prediction of the trunk flow on the vessel resistance. Finally, the vessel wa s also tested in the full load condition. The latter provided more accu rate input in the Balla st-Free Ship powering investigation.

Plots of the International Towing Tank Conferen ce (ITTC 1978) extrapolat ed ship resistance and effective power are shown in Figs. 4.1 and 4.2, respectively. Recall that effective power is the power equivalent of this total resistance obtained without a prope ller so these show the same results. Even though there is some overlap in the error bands, there is a clear trend that the flow discharge increases the vessel's resi stance. This trend was not obvious in results from the previous (January 2007) investigation. With discharg e at Station 19, the resistance increase at the ballast speed of 15.5 knots is 2.44%. The corresponding increase for Station

17 is 4.61%. The form factor values were al so computed for each case. The experimental results were found to be in relatively good agr eement with the numerical results. The CFD results, however, over predict th e form factor in all cases.

500 550 600 650 700 750 800 850 900

14.0 15.0 16.0 17.0 Ship Speed (knots)RTs(kN) baseline

St.19

St.17

Figure 4.1: Ballast-Free Bulk Carrier Total Resistance17 3,000 4,000 5,000 6,000 7,000 8,000

14.0 15.0 16.0 17.0 Ship Speed (knots)Effective Power (kW) baseline

St.19

St.17

Figure 4.2: Ballast-Free Bulk Carrier Effective Power

Table 4.1: Form Factor Comparison

CFD Experiment

Baseline no trunk flow case 0.315 0.303 Discharge at St. 17 – 90min 0.306 0.283 Discharge at St. 19 – 90min 0.311 0.283

The model was also tested in the full load cond ition at the speed that corresponds to the full scale design speed of 14.5 knots. The ex trapolated effective power was 7,114 hp, only slightly higher than the eff ective power in the ballast condi tion at 15.5 knots (7,042 hp). This

validates the selection of the vesse l speed in the ba llast condition.

The characteristics of the No. 20 stock propeller used in the 2008 testing and the No. 23 stock propeller used in the 2007 te sting are listed in Table 4.2.

Table 4.2: Characteristics of the MHL No. 20 and No. 23 Propellers

Characteristic MHL No. 20 MHL No. 23 Number of blades, Z 4 4 Diameter (m) 0.159 0.158 Hub diameter (m) 0.032 0.031

Pitch-diameter ratio 0.80 1.08 Expanded area ratio 0.40 0.5518 The propulsive performance was evaluated at the ballast speed. The discharge at Station 17 resulted in reduced powering requirements, compared to the ba seline no trunk flow case, even though the reduction was significantly lower than that observed in the January 2007 testing for the discharge at this same location. Part of this change resulted from the higher, and more accurately determined total resistance change (4.6% in July 2008 vs. 2.7% in January 2007). These propulsion test results are summarized in Table 4.3.

Table 4.3: Propulsion Test Results - Ballast Condition at 15.5 knots

Baseline No Trunk

Flow Case Discharge at St. 17 – 90min Exchange Open water efficiency η O 0.487 0.522

Wake fraction w 0.345 0.268

Thrust deduction t 0.287 0.167 Hull efficiency η H = (1 – t)/(1 – w) 1.088 1.138
Relative rotative efficiency η R 1.013 0.959
Behind propeller efficiency η P = η O η R 0.493 0.501 Advance coefficient J = V(1-w)/nD 0.478 0.533 Propulsive efficiency η D = η O η H η R 0.536 0.570 Change in propulsive e fficiency base +6.34% Delivered power P D (kW) 9,794 9,634 Change in required power base -1.63%

The total resistance R T is related to the developed power P D needed at the input to the propeller by the following:

P D = R T V/1000 η D kW (1)

where η D is the product of the propeller open water efficiency η O ; the relative rotative efficiency η R , which corrects this to the behind the hull condition; and the hull efficiency η H that is related to the wake fraction w and the th rust deduction t as shown in Table 4.3 (Parsons 2003). When the ballast trunk flow is introduced into the upper part of the propeller disk, all of these components cha nge. With the added flow the wa ke fraction w changes downward as the flow becomes closer to vessel speed. With the acceleration of the stern flow, the propeller accelerates the flow less also reducing the thrust deduction t. The net e ffect is an important increase in the hull efficiency η H . With a faster propeller in flow, the advance coefficient J operating point of the propeller increases as the propeller a ssumes a new operating point to supply the greater ship total resistance. Th is results in an increase in the open water efficiency η O and behind the hull propeller efficiency η P . With both η H and η P increasing, the overall propulsive efficiency η D increases. This increa se is large enough (6.34%) to

overcome the total resistance increas e (4.61%), i.e. 1.0461/1.0634 = 0.9837, the 1.63% reduction in required power measured.

The fact that we didn't observe a similar reduc tion in powering requireme nts can be partially

attributed to both the increase in measured resist ance and the use of a different stock propeller.19 The stock propeller utilized in July 2008 has blade sections with very low camber values; therefore, the propeller blades ne ed to work at relatively high angles of attack to produce the required thrust and, thus, has lo wer open water efficiency. The propeller utilized in January 2007 (MHL #23) was able to demonstrate signi ficantly better performance at the ballast condition in all cases (with and w/o discharg e). The open water diagrams of the two propellers with the ship requirements in fu ll load are shown in Fig. 4.3 for comparison.

0.000 0.100 0.200 0.300 0.400 0.500 0.600 0.700 0.800

0.000 0.200 0.400 0.600 0.800 1.000 1.200

Advance Coefficient J #23 Kt

#23 eta0

#20 Kt

#20 eta0
Kt, ship

Figure 4.3: Stock Propeller Open Water Character istics and Ship Thrust Requirement

There is also evidence that the Station 17 discha rge experimental data that produced the large required power reduction (-7.3%) in the January 2007 experiments may have contained faulty data. When the direction of the change in w, t, J, η O , and η R (but not η H and η D ) are compared

between the baseline and the ballast flow cas es found in the January 2007 tests with the discharge at Station 17 they are opposite to the direc tion of the changes found for the other tests as illustrated in Fig. 4.3. The direction of the changes found in the January 2007 tests with the discharge at Station 19 and the Ju ly 2008 tests with the discharge at Station 17 were consistent. This flawed data appears to be a third reason for very large required power reduction found in that January 2007 test with the discharge at Stat ion 17. The results for this case as reported in Kotinis and Parsons 2007b appear to have been in error.20 5. Potential Economic Impact of the Research Results

The economic impact of the Ballast-Free Ship concept on the capital a nd operating cost of a typical Seaway-sized bulk carrier was estimated in a manner similar to that used in the initial investigation of the concept (Kot inis et al. 2004). The results for the water discharge close to Station 17 are presented in Fig. 5.1. A realistic scenario was a dopted for the economic analysis: a Handy-sized bulk carrier transporting grain fr om the upper Great Lakes (e.g. Duluth, Thunder Bay) to ports in Northern Europe and occasiona lly transporting steel into the Great Lakes. A North Atlantic voyage route be tween Rotterdam and Montreal, entering the Great Lakes through the St. Lawrence Seaway while in a ballast condition, is assumed.

A conservative assumption is that the 1.6% reduction in the requi red power of the Ballast Free bulk carrier will not be enough to permit a change in the main engine; thus, no propulsion machinery capital cost reduction was included. Fo reign new construction, typical of Korea, was

assumed for the calculation of the hull steel and ot her construction costs. The eliminated ballast water treatment system was assumed to consist of automatic backflush filtration as a primary

treatment combined with UV irradiation for a sec ondary treatment. The es timated cost of this treatment equipment was based upon a stud y commissioned by the Great Lakes Ballast Technology Demonstration Projec t (Hurley et al. 2001).

The net savings in terms of the Δ RFR with the ballast trunk water di scharge close to Station 17 is estimated to be about $1.00 per tonne of cargo. This is relative to a typical 2008 grain freight rate to Europe of about $100 per tonne and an annual cargo capacity for this vessel of 168,000 tonnes if it were only involved in this trade. Thes e savings are relative to the use of filtration primary and UV secondary ballast water treatment when ballast water exchange is no longer permitted in the future.21Figure 5.1:Order of MagnitudeEconomics Comparing a Typical Bulk Carrierwith Filtration and UV Treatment withBallast-Free Bulk Carrier22 6. Dissemination of Study Results

During this past year, the project worked with University of Michigan New Services (Jim Erickson) to prepare a 5 min video and news re lease describing the Ballast-Free Ship concept and the testing sponsored by GLMRI. This was featured on the University website and a parallel article has appeared in The University RECORD , the in-house UM newspaper. The video has also been included on YouTube. The news spot has been picked up or utilized for articles by numerous organiza tions including the following:

UPI Washington Post

WWJ radio in Detroit

The Naval Architect of RINA Mechanical Engineer of ASME

Technish Weekblad in Denmark Surveyor , to be published by the American Bureau of Shipping

Discover magazine

Polish Newsweek magazine Estuary of the San Francisco Estuary Project

Conservation

Business Week

Prism of the American Associati on for Engineering Education Frontiers of Ecology Ingenioren , Denmark Scandinavian Shipping Gazette Ballast Exchange Newsletter Inventique

Parsons was interviewed for a spot that appeared on National Public Radio’s Environmental Report. A short invited article authored by Parsons and Kotinis appeared in the May

environmental issue of Maritime Reporter . A short invited article by Parsons appeared in the

2008 Yearbook of Maritime Technology published by the Scandinavian Shipping Gazette. A short article by Parsons and Kotinis has also been submitted for inclusion in a fall 2008 issue of Great Lakes/Seaway Review . The support of GLMRI has been mentioned whenever feasible.

Parsons has been contacted informally by three parties (two U.S. and one Korean) concerning opportunities and interest in participating in the commercialization of the Ballast-Free Ship

concept.

The following publications during the past year were related to this funded research:

• Kotinis, M. and Parsons, M. G., “Hydrodynamic Optimization of the Ballast-Free Ship Concept” Transactions SNAME, 115 , 2007. This paper received the ABS/Captain Joseph H. Linnard Prize for the Best Pape r presented before the society in 200723 • Parsons, M. G. and Kotinis, M., “ Recent Testing Indicates the Ballast-Free Ship Concept can also Provide Fuel Savings ,” Maritime Reporter , May 2008.

• Parsons, M. G., “An alternativ e solution to ballast water treatment: the Ballast-Free Ship concept,” 2008 Yearbook of Maritime Technology

, Scandinavian Shipping Gazette , 2008.

• Parsons, M. G. and Kotinis, M., “Ballast-Fr ee Ship Concept Testing Shows a Potential Fuel Savings,” to appear in Great Lakes/Seaway Review , fall 2008.

The following presentations during the past year were related to this funded research:

• Kotinis, M. and Parsons, M. G., “Hydrodynamic Optimization of the Ballast-Free Ship Concept” to be presented at the Society of Naval Architects and Marine Engineers Annual Meeting, Ft. Lauderdale, FL, Nov. 2007.

• Parsons attended and presented a summary of this project at the GLMRI Affiliates Meeting, September 23, 2008, in Superior, WI.

• Kotinis and Parsons will present a paper on the re sults of the project at the meeting of the

Great Lakes and Great Rivers of SNAM E in Ann Arbor, MI, on November 13, 2008.

The results of the funded research were reviewed in the following class:

• It is understood that the results of this invest igation were reviewed in the graduate class NA570 Advanced Marine Design at the Universi ty of Michigan in the Winter Semester

2008.25 7. References

Ballast Water News 2004 "The Ballast -Free Ship - Fact or Fancy?" Ballast Water News , Global Ballast Water Management Program, IMO, 17 , April-June.

Hurley, W. L. JR., Schilling, S. S. JR. and M ackey, T. P. 2001 “Contract Designs for Ballast Water Treatment Systems on Containership R. J. Pfeiffer and Tanker Polar Endeavor ,” SNAME/ ASNE Marine Environmental Engine ering Technical Symposium, Arlington, VA, May 31-June 1 (CD).

IMO 2004 “International Convention for the Control and Management of Ships’ Ballast Water & Sediments,” Diplomatic Conference, February, London.

ITTC 1978 “15 th International Towing Tank Conference, 3-10 September 1978, The Hague, The Netherlands”, Netherlands Ship Model Basin, Wageningen.

Kotinis, M., Parsons, M. G., Lamb, T. and Sirvie nte, A. 2004 “Development and Investigation of the Ballast-Free Ship Concept,” Transactions SNAME, 112 , pp. 206-240.

Kotinis, M. 2005 “Development and Investigatio n of the Ballast-Free Ship Concept,” Ph.D. Dissertation, University of Michigan, Department of Naval Architecture and Marine Engineering.

Kotinis, M. and Parsons, M. G. 2007a “Numerical Investigation of the Flow at the Stern of a

Ballast-Free Bulk Carrier Model” Proceedings of the 9 th Int. Conference in Numerical Ship Hydrodynamics, Aug.

Kotinis, M. and Parsons, M. G. 2007b “Hydrodynamic Optimization of the Ballast-Free Ship Concept” Transactions SNAME, 115 , pp. 50-67.

Parsons, M. G. 2003 “Parametric Design,” Ch. 11 in Lamb, T. (ed.), Ship Design and
Construction, SNAME, Jersey City, NJ.

Parsons, M. G. and Kotinis, M. 2006 “Seaway -Sized Bulk Carrier Model for Hydrodynamic Optimization of Ballast-Free Ship Desi gn,” GLMRI Annual Report, October 2.

Parsons, M. G. and Kotinis, M. 2007 “Hydrodynamic Optimization Testing of Ballast-Free Ship Design,” GLMRI Annual Report, October 30.

U. S. Patent #6,694,908 2004 “Ballast Free Ship Syst em,” U. S. Patent and Trademark Office, Washington, DC.