Ph.D. - Civil and Environmental Engineering

Permanent URI for this collection


Recent Submissions

Now showing 1 - 10 of 10
  • Item
    A Statistical Dynamic Modulus Model of Hot Mix Asphalt Using Joint Estimation and Mixed-Effects Accounting for Effects of Confinement, Moisture and Additives
    ([Honolulu] : [University of Hawaii at Manoa], [December 2016], 2016-12) Corrales, Jose
    With the implementation of mechanistic-empirical pavement design methods, dynamic modulus (|E*|) has become the predominant characteristic of Hot Mix Asphalt (HMA) used as the elastic modulus in the computation of stresses and strains in pavement structures. The predictions of |E*| obtained with the Witczak models currently used in the Mechanistic Empirical Pavement Design Guide (MEPDG) do not account for some HMA characteristics such as polymer modified binders, fibers, confinement and aging effects related to climatic conditions. Therefore, development of models more representative of local materials and conditions are desirable. In this study, a predictive model for dynamic modulus of HMA was developed taking into consideration several HMA characteristics and testing conditions. 6821 observations of 257 mix specimens from three different laboratory datasets, two from Hawaii and one from Costa Rica, were used to estimate the model parameters. All three data sets contain information about some variables in common such as air voids, binder content, and gradation; however, some datasets contain mix characteristics and testing conditions not available in other datasets such as confinement level, available only in the Hawaiian datasets, and the number of freeze-thaw cycles, available only in the Costa Rican dataset. Important characteristics observed from these datasets include confinement, number of freeze-thaw cycles, binder modifiers (SBS polymers) and mixture additives (e.g. fibers and anti-stripping agents), all of which together with other commonly used variables were found to have statistically significant effects. The model was developed by using joint estimation and mixed-effects techniques. Joint estimation allowed the identification of model parameters available from only some of the databases and the determination of bias parameters. It also resulted in more efficient parameter estimates. The mixed-effects approach was used to account for unobserved heterogeneities between samples. Using these approaches, together with proper consideration of heteroscedasticity, allowed the estimation of a comprehensive statistical predictive model that satisfies closely all the regression assumptions and that provides accurate values of |E*| for Hawaiian and Costa Rican conditions for any combination of temperature and frequency. These can be used to generate the |E*| inputs that the MEPDG needs to compute |E*| master curves.
  • Item
    Harvesting Energy from Ambient Vibrations
    ([Honolulu] : [University of Hawaii at Manoa], [August 2016], 2016-08) Zhang, Hui
    In vibratory energy harvesting, the energy flow generally goes through three stages: the external vibration energy is firstly coupled into the device as kinetic energy, which is partially converted to electricity through electromechanical conversion unit (such as electromagnetic, piezoelectric, and electrostatic), then the generated electricity is applied to the electrical load circuit. The process of such energy flow indicates that the energy coupled in the first stage determines the maximum available energy converted to electricity, while the electricity delivered to the load depends on the characteristics of electrical load circuits. Note that the first stage for coupling energy is achieved by device dynamics. To best understand vibratory energy harvesting, the effects of device dynamics and electrical load circuits on energy harvesting performance are investigated in this dissertation. For the effects of device dynamics, we do the study from four areas: parametric oscillator/device, global resonance, the roles of excitation, and dynamics outside the potential well. At first, we investigate the potential of using a nonlinear parametric oscillator/device to harvest energy. In such device, the excitation appears as a parameter of the dynamical system. Such parameterization of the excitation provides a cross-frequency energy transfer in the excitation, resulting in modifying the frequency content of the excitation, i.e. modulation of the excitation, which enables the device into the orbits of higher-order subharmonic oscillations more easily. A device with a pendulum-type architecture is proposed and used as an illustrative example. The further investigation in device dynamics has proved that for a nonlinear device, there exists a generalized, global resonance condition which requires matching of all of the frequencies between the device and the excitation. Under global resonance, the device performance is optimized with the maximum energy harvesting efficiency, but its corresponding displacement is not the largest because the amplitude of global resonance response is strongly correlated with the fundamental frequency supported by a nonlinear potential well (e.g. potential function). Such results suggest that traditionally relying only on increasing the device response in nonlinear systems can be misleading. The global resonance condition also shows that damping of the device and modulation of the excitation play critical roles in facilitating the frequency match required for resonance. According to the global resonance condition, it is revealed that the potential of nonlinear device in harvesting energy from multi-frequency vibrations benefits from multiple frequency match, not from the wider bandwidth obtained from single-frequency response. To harvest energy from multi-frequency vibration using non- linear devices, a device-design concept based on global resonance is thus proposed. When the global resonance condition is satisfied, the instantaneous power of the excitation is always non-negative, resulting in the maximum device performance. Conversely, when the condition is not satisfied, the excitation does negative work for a duration per cycle, leading to the reduction of the energy harvested. During such duration, the excitation actually takes energy back from the device, acting as a sink. The extent to which the excitation behaves as a sink determines the energy harvesting performance. We find that instantaneously changing device response to ensure the velocity in phase with the excitation can reduce the behavior of the excitation as a sink, resulting in dramatic increase of the energy harvested. Based on our findings, it has shown that an active method based on manipulating the roles of excitation would be more promising in bringing vibration energy harvesting to fruition. Although the responses of a device are usually constrained by its potential well, it is possible for the dynamics of a pendulum-type device to escape from the potential well. Here, we also investigated the possibility of utilizing the dynamics outside the potential well of a device for harvesting energy from vibrations. A pendulum-type device is used as an example. Results show that when the device dynamics is outside the potential well and stays in stable orbits of period-one rotations, the harvested energy is proportional to the energy level of the orbit, neither depending on the natural frequency of the device nor on the intensity of the excitation. For the effects of electrical load circuits, we consider three types of non-resistive loads, such as a resistive load with a rectifier, a resistive load with a rectifier and a regulating capacitor, and a simple charging circuit consisting of a rectifier and a storing capacitor. Numerical results suggest that when the harvested energy is to be stored in capacitors, the ultimate voltages across capacitors are the same as the open- circuit voltage of the device minus the rectifier drop. For charging loads, therefore, the amount of stored energy is determined by the capacitance and the device performance under open circuit. Moreover, a larger capacitor is beneficial for an electromagnetic harvester, but not for a piezoelectrical harvester.
  • Item
    HCM Analysis of the Potential Impacts of Driverless Vehicles on the Quality of Flow of Freeways and Intersections
    ([Honolulu] : [University of Hawaii at Manoa], [May 2016], 2016-05) Shi, Liang
    Autonomous or self-driving vehicles, popularly called “driverless cars” (DLC), are capable of navigating themselves through freeways and intersections without any human intervention. It is believed that DLC can bring about tremendous changes to our daily life, including safety, traffic efficiency, environment and community. By 2020 various companies will release their DLC models designed with different levels of automation. Traffic will be mixed with vehicles driven by human drivers and DLC, which cause uncertainties in the magnitude of impacts of DLC and their traffic shares. The Highway Capacity Manual (HCM) was modified to analyze the future impact of DLC on traffic flow operations. A review of the HCM parameters that might be directly affected by DLC is presented in this study. These parameters were modified to include the features of DLC: the technical capability which is quantified by the car-following headway of DLC, and the proportion of DLC in the traffic stream. Case studies were conducted to estimate the effects of DLC on the quality of traffic flow on a basic freeway segment, freeway weaving segment, signalized intersection, all-way stop-controlled intersection and roundabouts. For each case study, a sensitivity analysis was provided to evaluate the potential impacts of DLC with different technological capabilities under various traffic demands and proportions. The results from all case studies reflect the commonality of DLC impacts. DLC are able to maintain constant speed at a shorter car-following distance, which can smooth the traffic flow. For DLC that are connected with infrastructure and other DLC, the car-following distance will become shorter. With more connectivity built between DLC and infrastructure, the road space and delay will be saved by platooning. If in the future all vehicles are driverless cars, capacity of the road will be doubled or tripled. This means every road lane is capable of serving twice as many vehicles at no cost to the city. But if in the future there is only 1% of DLC in traffic, traffic flow will not improve. If the portion of DLC reaches 5%, congestion will improve by 5% if they are regular DLC, or by 12% if they are connected DLC. In the latter scenario, traffic flow can begin to improve in a noticeable way. However, if DLC are designed to drive conservatively, they will cause more delays than humans do.
  • Item
    Evaluation of the SRICOS-EFA Method for Predicting Scour in Hawaiian Rivers
    ([Honolulu] : [University of Hawaii at Manoa], [May 2016], 2016-05) Rahimnejad, Reza
    Nearly 60% of bridge failures in the country are due to scour. The Hawai‘i Department of Transportation (HDOT) has a vested interest in the integrity of bridges and their foundations during heavy floods. It is known that many of the older existing bridges in Hawai‘i were not designed for scour. Therefore, it is critical to have an accurate assessment of their scour potential. In addition, it is also critical to obtain accurate scour predictions when designing new bridges. An underestimate of the scour depth could lead to potential risk of bridge failure while an overestimate can increase the cost of the new bridge construction unnecessarily. In Hawai‘i, scour calculations are traditionally performed based on the Richardson and Davis equation (1995) where the only soil parameter required is the mean particle size, D50. Using this method for cohesive soils is known to lead to overestimated scour depths since the scour depth is inversely proportional to D50, and cohesive soils have very small particle size. Inter-particle electrical forces exist in cohesive soils which cause cohesive soils to erode slower than granular soils. The SRICOS (Scour Rate In COhesive Soils) method accounts for the time-dependent nature of scour in silts and clays. It requires erodibility testing on soil samples using an Erosion Function Apparatus (EFA) and will generally result in smaller scour depths that can lead to savings in bridge construction. The main objectives of this research were to: (1) Obtain undisturbed soil samples from 5 water channels on the island of Oahu to perform EFA and soil testing; (2) Propose a method to define the critical shear stress and evaluate factors affecting its magnitude; (3) Develop a model to predict an EFA curve for a cohesive soil in Hawai‘i based on some common soil parameters; and (4) Examine the applicability of the Pocket Erodometer Test (PET) to Hawai‘ian cohesive soils. The main contributions from this research are summarized as follows: A cohesive soil was reconstituted in the laboratory under 4 different consolidation pressures resulting in 4 different water contents, void ratios, unit weights and consolidation stresses and then tested using the EFA. It was found that the critical shear stress increased with decreasing water content, decreasing void ratio, increasing unit weight and increasing consolidation stress. That the soils can be considered normally consolidated also suggests that the critical shear stress increases with undrained shear strength. The mathematical properties of the EFA curves for 33 cohesive soil samples were studied. Based on these curves, it was found that by plotting the log of the shear stress versus the scour rate, the curves approximate a hyperbola very closely. It is also proposed that the critical shear stress be estimated as the intercept of the hyperbola on the shear stress axis with some constraints. A model was developed to predict an EFA curve using common soil parameters and the hyperbolic model. Three parameters are needed to fully define this hyperbola. Four explanatory variables (soil parameters) are required to define the three hyperbolic model parameters. They include water content, liquid limit, plasticity index and activity, all of which are easily measured in the laboratory. Use of this model in the SRICOS EFA method to estimate scour depth can result in less scour and in significant foundation cost savings. Scour depths at five water channel sites were estimated using HEC-18 and the SRICOS EFA method. It was found that the SRICOS method always resulted in lower scour depths than HEC-18. The PET was used to derive the erosion categories for 33 cohesive soil samples from the five water channel locations and then compared to those from the EFA. It was found that the current PET erosion criterion that separates the medium and high erodibility categories should be increased from 15 to 28 mm to increase the reliability of the method. With this revised criterion, the reliability of the PET for Hawai‘i soils and for soils that were used to develop this criterion improved. It was also found that Briaud et al.’s (2012) erodibility criteria based on soil classification is not very reliable.
  • Item
    Implementation of Structural Health Monitoring System to Indirectly Recover Building and Bridge Displacements
    ([Honolulu] : [University of Hawaii at Manoa], [May 2016], 2016-05) Bell, Michael
    An internal model based method is used to estimate the structural displacements under ambient excitation using only acceleration measurements. Strain measurements are incorporated to expand the method to single span concrete bridges subjected to moving vehicle loads. The structural response is assumed to remain the linear range for the duration of the loading. The excitation is assumed to be with zero mean and relatively broad bandwidth such that at least one of the fundamental modes of the structure is excited and dominates in the response. Using the structural modal parameters and partial knowledge of the load, their respective internal models can be established. These internal models can then be used to form an autonomous state-space representation of the system. It is shown that structural displacements, velocities, and accelerations are the states of such a system, and it is fully observable when the measured output contains structural accelerations only. Reliable estimates of structural displacements are obtained using the standard Kalman filtering technique. These displacement estimates can be used to determine the moment demand and provide insight into whether this demand is exceeding the capacity of the bridge. The effectiveness and robustness of the proposed method has been demonstrated and evaluated via numerical simulations of an eight-story lumped mass model along with a simply supported single span concrete bridge subjected to a moving traffic load. Experimental data of a three-story frame excited by ground accelerations from an actual earthquake record is also used. Lastly, field data from an inverted arch concrete bridge is analyzed as proof of concept for deployment of a structural health monitoring system for the purpose of displacement estimations.
  • Item
    Low Cost Soil-Based Biological Treatment for Water Reclamation
    ([Honolulu] : [University of Hawaii at Manoa], [August 2015], 2015-08) Kim, Lavane
    Water reclamation is a strategy of moving toward sustainable management of freshwater and environmental protection. Treated wastewater has been widely recognized as a potential source of water for landscape and agricultural irrigation, industrial cooling, surface replenishment, groundwater recharge, portable and non-portable use for the past decades. However, concerns about pathogenic organisms and trace organic contaminants in reclaimed water remaine. Low-cost treatment methods show promise in reducing these contaminants in wastewater, but more investigation of these technologies is still needed to improve the efficiency for renewable and sustainable water reclamation. This study presents the soil based filter as a treatment means to remove bacteria in agricultural and domestic effluents for water reclamation. An improved soil filter by ferric oxide based materials integrated with native soil protozoa bacterivory was efficient to eliminate E. coli in swine wastewater. Under anaerobic environment, the microbial iron reduction (MIR) process was very efficient in inactivating E. coli cells. The ferrous production in MIR process was identified as a mechanism for E. coli inactivation under the anaerobic condition. Inactivated bacterial cells were used by the MIR community as an electron donor to drive the MIR process. The anaerobic-aerobic two-stage slow sand filter was a robust system for water reclamation. High removal efficiencies of carbon substrates, trace organic compounds, and microbial contaminants were obtained in this study. The iron oxide coated sand and MIR biofilm provided adsorptive surfaces to retain bacterial cells passing through the filter media. The integration of anaerobic iron coated sand filter and aerobic sand filtration removed not only ferrous production but also improved the overall performance of the treatment system in removing bacteria. This dissertation has shown that the filters packed by iron-rich porous media provided technical and economic feasibilities to remove microbial contaminants in water reclamation. This knowledge could further improve our understanding of the fate and transport of fecal bacteria in the subsurface and sedimentary environments. Future work can be explored for the removal of pathogens enhanced by the mechanisms discovered in this study in engineering processes, such as storm water bio-retention facilities, aquifer artificial recharge, and low-cost soil based water reclamation.
  • Item
    Testing Segregation and Other Rheological Properties of Self-Consolidating Concrete (SCC)
    ([Honolulu] : [University of Hawaii at Manoa], [August 2015], 2015-08) Bahrami Jovein, Hamed
    Self-consolidating concrete (SCC) is a new type of high performance concrete that flows under its own weight, passes through intricate geometrical configurations, and fills the formwork without vibration and consolidation. Compared with normal concrete mixes, the composition and the rheological properties of SCC should be closely controlled in order to satisfy the fresh property requirements simultaneously. Moreover, the segregation resistance of self-consolidating concrete (SCC) is more sensitive to small variations of its properties. Segregation refers to movement of coarse aggregate relative to the mortar. Static segregation occurs when the concrete is at rest and the coarse aggregate sinks in the mortar. Dynamic segregation occurs when the concrete is flowing and the coarse aggregate lags behind the mortar. To study segregation and design an SCC mix, which is robust against small variations in raw materials, it is critical to be able to quickly quantify static and dynamic segregation and stability robustness. In this study, a modified Segregation Probe is introduced as a simple and fast method for testing static segregation and stability robustness of fresh concrete. On the other hand, Flow Trough was developed to measure dynamic segregation. It was found that mixture properties, such as higher paste volume, lower superplasticizer percentage by weight of cement, lower slump flow, smaller aggregate size, better gradation, and higher aggregate packing density may improve robustness and dynamic stability. The effects of various aggregate properties on SCC rheology were investigated. It was found that lower superplasticizer dosage, higher aggregate volume, higher fine aggregate to coarse aggregate ratio, smaller aggregate size and lower aggregate packing density may increase yield stress of SCC mixture. Aggregate size had insignificant effect on plastic viscosity. Mixtures with Low slump flow (slump flow value less than 580 mm (23 in) in this study) exhibited anti-thixotropy manner, while mixtures with higher slump flow showed thixotropy manner.
  • Item
    Source and Fate of Fecal Indicator Bacteria in Tropical Soil, Sand, and Seawater Environments
    ([Honolulu] : [University of Hawaii at Manoa], [May 2015], 2015-05) Zhang, Qian
    Fecal contamination of coastal recreational water can adversely impact public health and economic well-being of many coastal communities. Enterococci and E. coli are common fecal indicator bacteria (FIBs) used in water quality monitoring and regulation. This dissertation investigates the source and fate of FIBs in Hawaii’s tropical soil, sand and seawater environments. Since Hawaii’s soils are known to contain high levels of E. coli that can serves as alternative sources to waterways, the second chapter of this dissertation investigated the survival of soil E. coli strains under desiccation stress. The soil E. coli strains showed significantly higher desiccation resistance than a laboratory reference strain and several strains isolated from wastewater, and the de novo synthesis and accumulation of trehalose was identified as an important mechanism for soil E. coli desiccation resistance. Since beach sand is often reported to contain high levels of FIBs while beach erosion or replenishment activities can abruptly affect beach sand abundance, the third chapter investigated the contribution of beach sand to the decay of FIBs in beach systems. The presence of subtidal sand significantly enhanced the decay of E. faecalis in beach microcosms, and the indigenous microbiota of the subtidal sand was largely responsible for the decay enhancement. To further understand the fate of FIBs in beach systems, the fourth chapter determined the decay patterns of FIBs in beach sand and seawater separately and compared them to the overall microbial community dynamics. Biphasic decay patterns of FIBs and other fecal bacteria were observed in both beach sand and seawater, while the decay rates in beach sand were significantly smaller than that in seawater, providing a kinetic explanation to the observed high abundance of FIBs in beach sand. In the fifth chapter, microbial communities in beach sand and seawater microcosms contaminated by municipal wastewater were tracked using next-generation sequencing of the 16S rRNA gene amplicons, and the exogenous nutrients in the wastewater appeared to determine the microbial community dynamics to a significant extent. Based on results presented, conclusions and recommendations were also made in the sixth chapter of the dissertation.
  • Item
    Impact Response Based on Timoshenko Beam Theory
    ([Honolulu] : [University of Hawaii at Manoa], [May 2015], 2015-05) Khowitar, Eid
    The elastic impact of a translating flexible pole is studied herein. Three scenarios are considered: 1) transverse impact against a rigid stop, 2) longitudinal impact against a flexible column and 3) transverse impact against a flexible column. Based on Timoshenko beam theory, an analytical solution method using mode superposition for the coupled spring-pole or column-pole system is presented. Any physical set of boundary conditions can be accommodated for the pole and the column. For all cases involving axial impacts, the maximum initial impact force is governed by the local shear deformation in the column and the axial deformation in the pole. However, for transverse impacts, the maximum initial impact force is governed by the local shear deformation in the pole and the column. A simple formula for the maximum initial force is derived and shown to be quite accurate. In no case is the total mass of the pole significant to the initial peak force. Indeed, based on Euler-Bernoulli beam theory the initial impact force is unbounded as the spring stiffness increases whereas Timoshenko beam theory has a clear limiting value for the initial impact force. The impact duration depends on the wave propagation in the pole or the column. In addition, the energy transfer between kinetic energies and strain energies reveals both the initial dependence on shear deformation and the transfer of the associated energy to bending energy. The energy exchange also shows the importance of the inertia of the column in absorbing a significant part of the initial kinetic energy of the pole. It is shown that the moment of inertia has a negligible effect on the impact force, which is an interesting conclusion because some structural finite element codes use a lumped mass matrix that includes translational masses but not rotational inertias. For transverse impact, multiple impacts are considered, and the whole collision event is divided into contact phases and separation phases. It is shown that for all cases the maximum contact force occurs during later contact phases and its value can reach up to 1.6 times the peak force in the first contact phase. The impact duration of the first contact phase depends on the shear wave in the pole or the column according to the mass and wave speed ratios. The total impulse on the pole ranges between 1.5-1.8 times the initial momentum of the pole, depending on the stiffness of the column. The energy exchange during the multiple impacts, while it can be complicated, reveals that for relatively stiff columns the sum of the translational kinetic and bending strain energies of the pole constitutes approximately 90% of the total energy. In all cases considered, relatively little net energy has been transmitted to the column at the time of final separation. For axial impact, multiple impacts depend on the relative stiffness of the column and the pole, and also on the inertia of the pole. Hence, the entire collision event for the stiffest column is characterized by a single impact. However, for the most flexible column all cases involve multiple impacts. For the case of single impact, most of the kinetic energy of the pole is transferred into axial strain energy in the pole. However, for the multiple impacts, most of the kinetic energy of the pole is transferred into bending energy in the column. The maximum impact force reaches up to 1.9 times the initial peak force and the total impulse reaches up to 1.9 times the initial momentum of the pole. For all cases, the duration of the entire collision event depend mainly on the wave propagation in the pole. The impact force and duration depend on the type of impact as well as the end boundary conditions of the column. For all cases, the axial impact yields larger impact force than that for the transverse impact according to the stiffness of the column with similar boundary conditions of the column. The stiffer the column, the larger is the impact force and the smaller the impact duration. In addition, free end column yields the smallest impact force and duration. However, pin-end column gives the largest impact duration and fixed-end column gives the largest impact force. The dynamic amplification factors for shear force and bending moment depend mainly on the stiffness of the column and the inertia of the pole. Cases involving stiffer column and larger pole inertia yield higher dynamic amplification factors. In addition, the dynamic amplification factors significantly increase for cases involving multiple impacts and always reach their maximum values at later impacts.
  • Item
    Submerged Breakwater Modeling and Coral Reef Ecological Analyses for Harbor Protection
    ([Honolulu] : [University of Hawaii at Manoa], [May 2015], 2015-05) Foley, Michael
    This dissertation provides insight into the previously unexplored option of using submerged breakwater structures to provide harbor protection while simultaneously providing ecological and recreational value as coral reefs. Chapter 1 provides background on the concept of multifunctional reefs and how they can be used to protect the Kahului Harbor on the island of Maui, Hawai‘i. In Chapter 2, a numerical wave response model was developed to determine how a multifunctional reef of various dimensions and orientations would influence the wave energy inside the Kahului Harbor. The numerical model results were validated with a physical scale wave response model as discussed in Chapter 3. Further numerical modeling to explore the effect of various reef shapes are discussed in Chapter 4. In Chapter 5, the costs and benefits of various coastal engineering technologies for the design and construction of the submerged breakwater structure were considered. In Chapter 6, the relationship between substrate characteristics and coral colonization was investigated through coral recruitment experiments and study of field conditions in order to develop the biological information needed in the ecological engineering of the artificial coral reef. The significant findings from this dissertation research are summarized in Chapter 7. The Kahului Commercial Harbor 2030 Master Plan recommends modernizing Maui’s only commercial harbor to accommodate projected growth in cargo and passenger traffic. The planned $345.1 million in harbor developments include the West Breakwater Harbor Development, which requires the dredging of an expanded turning basin and the construction and extensions to the west and east breakwaters to allow vessels to berth without risk of surge. Previously, the Kahului Harbor 2025 Master Plan proposed similar breakwater extensions and developments. A U.S. Army Corps of Engineers study modeled the effects that the proposed developments would have on the wave energy in the Kahului Harbor. The study indicated that none of the configurations of the breakwater extensions were ideal for reducing the wave energy in the harbor. The study especially argued against the landward extension of the west breakwater due to the likelihood that the structure would increase wave oscillations inside the harbor. The updated 2030 Master Plan proposed similar breakwater extension configurations that are likely to also create surge problems inside the harbor. The modernization plan will also have a significant impact on the marine habitat and recreational activates in the Kahului Harbor area. A portion of the coral reef inside the harbor will be removed by the dredging of an expanded turning basin. This reef is of significant value to the Maui community because of its environmental and recreational value. The reef forms three popular surfing waves that are within close proximity to large residential areas, schools, and the community college. The destruction of the surfing resource is likely to cause negative social and cultural impacts in the community. The modernization plan has been publicly protested by community organizations opposed to the removal of the reef. This dissertation research introduces the concept of a multifunctional reef as a means to at least partially mitigate the significant impacts of the modernization of the Kahului Harbor. A multifunctional reef is an engineered structure that alters the bathymetry of the sea floor to supplement the benefits that naturally occurring reefs provide to a coastal area or partially mitigate reef damage. Benefits of building a multifunctional reef include coastal protection, marine habitat, and a venue for recreational activities such as surfing, fishing and diving. The proposed multifunctional reef located on the ocean side of the Kahului Harbor’s east breakwater would serve two primary functions. First, a sophisticated reef design would shoal and refract approaching waves before they enter the harbor, thereby reducing the amount of wave energy that disturbs harbor operations. In this sense, the multifunctional reef will function as a coastal engineering structure known as a submerged breakwater, so the terms are used interchangeably in this dissertation. Second, the multifunctional reef would provide significant ecological value by being specifically designed to provide habitat for coral reef species. This function is commonly known in marine biology as an artificial reef, so the multifunctional reef is also referred to as such in this document. A numerical modeling investigation was conducted to evaluate the installation of a submerged breakwater near the entrance of the Kahului Harbor. The breakwater is intended to improve the harbor’s tranquility and, thereby, increase the harbor’s operational days. The objective of the numerical modeling investigation was to propose the optimal location, orientation and dimensions for the layout of a submerged breakwater outside the Kahului Harbor. To this end, the wave characteristics in the vicinity of the harbor were analyzed and the model was used to investigate the wave transformation as they propagate towards shore. The tranquility conditions at various locations along the harbor approach channel and inside the harbor basin were evaluated using phase-resolved nearshore wave modeling. The model results for tranquility inside the harbor and along the approach channel under existing conditions versus conditions in the presence of a submerged breakwater were compared. Based on a comprehensive wave data analysis, the numerical study used a predominant wave direction of 17.5° (east from north), wave height of 1 meter (m), and a wave period of range 4 to 18 seconds (s). The study considered the orientations of a submerged breakwater with respect to the geographic north that varied from 105° to 150° in steps of 15°. The length, breadth and depth of submergence of the proposed breakwater in the model was varied from 100m to 150m, 7m to 21m, and 1m to 5m, respectively, and the results for the wave transmission coefficient inside the harbor and along the approach channel were calculated for each case. The investigation critically reviewed and compared the results obtained from all the combinations of orientation, length, breadth and depth of submergence of the breakwater structure. The results of the numerical model investigation indicated that the optimal Kahului Harbor submerged breakwater will have a length of 100m, width of 15m, submergence depth of 1m, orientation of 135°, and be placed 280m offshore from the existing eastern breakwater. A submerged breakwater of this design was found to reduce the average wave diffraction coefficient (kD) by 38% in the harbor basin and increase kD along the approach channel by 4% for long-period waves (T=11 to 18 seconds). For short-period waves (T= 4 to 10 seconds), the reduction in the average kD was found to be 0.9% and 16% along the approach channel and within the basin, respectively. A scale physical model study on the wave penetration into the Kahului Harbor was carried out in a 15m wide, 17m long and 1m deep wave basin at the Department of Ocean Engineering, IIT Madras, India. The objective of the physical modeling exercise was to validate the results of the numerical modeling in terms of how the tranquility inside the Kahului Harbor is increased by placing a submerged breakwater structure offshore of the harbor entrance. The submerged breakwater location, orientation and size defined by the results of the numerical model were reproduced in the physical model basin. The bathymetry of the area was also carefully reproduced in the physical model. The conclusions drawn from this physical model study showed that there was a statically significant agreement between the results of the physical and numerical models, and that construction of the submerged breakwater can be expected to cause an average reduction in wave transmissions of between 3% and 15% in the navigation channel and between 20% and 35% in the harbor basin. Additional numerical modeling was carried out to determine how other options for the submerged breakwater design shape affect the ability of the structure to attenuate wave energy propagating into the harbor basin while simultaneously providing secondary functions of enhanced marine habitat and surfing recreation resources. The wave response of the additional submerged breakwater concepts were investigated using the CGWAVE finite-element model interfaced with the Surface-water Modeling System (Version 11.1). Three designs were investigated: the IIT Madras reef concept developed in a previous numerical modeling study, and two new concepts, reef alternative 1 and 2. The reef alternative 1 concept consisted of a shore-connected reef, linked by a sloping spur from the existing east breakwater head which descends to the reef crest elevation of -1m (MLLW). The reef alternative 2 concept is completely submerged and located offshore of the existing east breakwater head like the IIT Madras reef. Unlike the Madras reef, reef alternative 2 has a chevron-shape footprint and shallow slope on the offshore face (4:1, horizontal to vertical). Based on the results of the calculated wave height responses, this numerical study found that out of the three alternative configurations, reef alternative 1 demonstrates the highest degree of effectiveness in reducing average wave heights within the harbor. The model results also showed that the IIT Madras reef and concept reef alternative 2 each provided average wave height reductions within the central and eastern portions of the harbor, but in the vicinity of the harbor mouth, these two designs produced increased average wave heights. These two designs also increased the wave heights at the tip of the existing east breakwater, while alternative 1 showed a reduction in wave heights all along the breakwater. The results of this analysis indicated that while alternative 1 is most beneficial, all three of the studied reef designs are effective at reducing average wave heights within the harbor area. This dissertation also reviewed and analyzed the design alternatives for the installation of the submerged breakwater at the Kahului Harbor. The submerged breakwater size and location as defined by the results of the numerical and physical modeling studies informed how the structure should be constructed in the field. The conceptual designs of rubble-mound, caisson, floating and geotextile-tube breakwater structures were considered in this analysis to develop perspective on the suitably of these various design options. The analysis considered aspects of each option in terms of hydrodynamic performance, structural design stability, construction logistics and procedure, execution time, and rough cost. The results of this exercise concluded that compared to other alternatives, using geotextile tubes seems to be the less attractive alternative, because it would result in extended execution time and significant increases to project costs. For the given site-specific depth of installation (~15m) of the proposed breakwater layout, a caisson-type breakwater would be the most efficient alternative. A prefabricated concrete caisson structure is easier to install and more cost-effective because it requires a smaller body width and less material. The prefabricated caisson approach also fits the five-month window for installation dictated by the local wave climate. While the numerical and physical modeling studies showed how the structure can be expected to mitigate operational problems caused by wave energy entering the harbor, the question remained of how a large marine structure can be designed to provide coral reef habitat in order to increase recreational and environmental value of the project. There is limited information on how the design of coastal structures can be manipulated to enhance the ecology of targeted coral communities. The relationship between substrate characteristics and coral colonization was investigated through coral recruitment experiments and study of field conditions in order to develop the biological information needed in the ecological engineering of the submerged breakwater. Three concrete compositions that differed by the use of basalt, limestone, or recycled aggregates were tested in field and laboratory experiments to determine the impact of each substrate on the recruitment of juvenile hermatypic corals. The concrete test plates were deployed in three environments for a period of about one year, after which the coral recruits on each plate were identified and counted. The field trials at two sites of different depths showed no significant difference in the average number of coral recruits on the concrete mixed with basalt, limestone and recycled aggregate (60 ± 9, 83 ± 17 and 76 ± 14, respectively). However, the laboratory results versus field results showed significant differences in coral recruitment between the laboratory tanks, deep water, and shallow water field tests environments (86 ± 11, 135 ± 15 and 4 ± 1, respectively). These results highlight the importance of environmental site conditions for the development of coral reef habitat. When designing the submerged breakwater for coral reef ecology, effort should be spent on enhancing the environmental conditions at the site so that they are favorable for recruitment and growth of hermatypic corals. A field study was conducted in the vicinity of proposed artificial reef site at Kahului Harbor in order to relate the topographic features of the surrounding environment to the levels of live coral coverage. These data provide information on what types of communities will develop on the proposed submerged breakwater. The benthic zone was surveyed using a drop camera system and by SCUBA divers who recorded in-situ observations. Of the area surveyed, the highest density of coral coverage (>90% cover on 60% of the area) was found on an adjacent natural reef area that was characterized by spur and groove geomorphology with a high degree of macro- and micro-topographic complexity. In contrast, sparse coral cover was discovered on the concrete armor units of the existing east breakwater structure. No live coral cover was observed on the sand and carbonate rubble substrate at the proposed artificial reef location. The high coral coverage on the adjacent natural reef suggests that the artificial coral reef design should emulate the natural spur and groove structure with regards to topographic complexity on multiple scales, orientation with wave direction, and water depth.