Hull Model Research Articles

Efficiency of Primary Health Services in the Greek Public Sector: Evidence from Bootstrapped DEA/FDH Estimators.

Strengthening primary healthcare (PHC) is vital for enhancing efficiency and improving access, clinical outcomes, and population well-being. The World Health Organization emphasizes the role of effective PHC in reducing healthcare costs and boosting productivity. With growing healthcare demands and limited resources, efficient management is critical. Background/Objectives: Building on this point, this study aimed to evaluate the efficiency of PHC units across Greece, focusing on Health Centers (HCs) and Local Health Units (ToMYs). The objective was to assess their efficiency levels and identify factors contributing to observed inefficiencies. This study explores a novel research area by being the first to assess the efficiency of restructured primary healthcare facilities in Greece, utilizing 2019 data-the first year operational data became available for the newly established ToMY facilities following recent healthcare reforms. Methods: We applied a comprehensive suite of non-parametric methods, including Data Envelopment Analysis (DEA) under variable, constant, increasing, and decreasing returns to scale (VRS, CRS, IRS/NDRS, DRS/NIRS) assumptions, along with the Free Disposal Hull (FDH) model, all oriented toward output maximization. Efficiency scores were refined using bootstrapping to calculate 95% confidence intervals, and efficient units were ranked via the super-efficiency model. Outliers were identified and removed through the data cloud algorithm. For the first time at this scale, the final sample included the vast majority of PHC facilities in Greece-234 Health Centers and 94 Local Health Units-with inputs categorized into three human resource types: medical, nursing/paramedical, and administrative/other staff. Outputs encompassed scheduled visits, emergency visits, and pharmaceutical prescription visits. This diverse and comprehensive application of DEA methods represents a novel approach to evaluating PHC efficiency in Greece, with potential relevance to broader healthcare contexts. Results: The analysis revealed significant inefficiencies and differences in technical efficiency between HCs and ToMYs. HCs could nearly double their outputs (VRS score: 1.92), while ToMYs could increase theirs by 58% (VRS score: 1.58). Scale efficiency scores were closer, with HCs slightly more aligned with their optimal scale (1.17 vs. 1.20 for ToMYs). Conclusions: There is significant potential to improve efficiency in PHC, with variations depending on unit characteristics and regional differences. This evaluation provides a foundation for policymakers to identify areas for improvement and enhance the overall performance of healthcare services in Greece.

Coordinate Transformation Techniques for Improved Co-Simulation in the Maritime Industry

Abstract Co-simulation is the modular and flexible coupling of stand-alone simulation models. It promises to help unlock the maritime industry’s digitalization potential, but the correct and efficient handling of coordinate systems between models is one of the unsolved challenges that stand in the way of wide-spread adoption. Here, we give a brief introduction to the problem and describe what makes it especially difficult for co-simulations. We introduce a few of the most common models and provide a list of coordinate systems and reference frames used in maritime co-simulations. Focusing on hull and gangway models, we explore general solution approaches and provide practical advice for how to handle coordinate systems in co-simulations using a vessel–gangway simulation case for illustration.

Numerical simulation and experimental study of the dynamic characteristics of a gas turbine rotor system with beam sea and head sea excitation

Vibration analysis is crucial for studying rotor dynamics. The gas turbine rotor system is subjected to complex alternating loads during navigation, resulting in vibrations transmitted to the bearings that alter the system’s dynamic characteristics. Based on the similarity law of the wave resistance test, a hull model was established. Beam sea and head sea tests were conducted in the towing pool to measure the acceleration response at the key positions. A finite element model of the turbine rotor system was established, and the test data were imported into the model after wavelet noise reduction and resampling to calculate the vibration response at the front and rear bearing points. The vibration responses transmitted to different locations and directions caused by beam sea and head sea conditions were analyzed. A comparison and analysis were conducted on the acceleration responses in various locations and directions under beam sea or head sea conditions. The equivalent von Mises stress distribution of the gas turbine rotor system under beam sea and head sea loads was obtained. The vibration transfer model was verified for accuracy and can be used to quickly analyze the vibration response of bearings under wave load transfer. This study provides a theoretical basis and reference for enhancing the stability of the gas turbine rotor system.

Impact of correlation between interest rates and mortality rates on the valuation of various life insurance products

AbstractIn this paper, we question the traditional independence assumption between mortality risk and financial risk and model the correlation between these two risks, estimating its impact on the price of different life insurance products. The interest rate and the mortality intensity are modelled as two correlated Hull and White models in an affine set-up. We introduce two building blocks, namely the zero-coupon survival bond and the mortality density, calculate them in closed form and perform an investigation about their dependence on the correlation between mortality and financial risk, both with theoretical results and numerical analysis. We study the impact of correlation also for more structured insurance products, such as pure endowment, annuity, term insurance, whole life insurance and mixed endowment. We show that in some cases, the inclusion of correlation can lead to a severe underestimation or overestimation of the best estimate. Finally, we illustrate that the results obtained using a traditional affine diffusive set-up can be generalised to affine jump diffusion by computing the price of the zero-coupon survival bond in the presence of jumps.

Hydrodynamic features specific to the dynamic movements of an underwater glider

The purpose of this study was to show the influence of the underwater glider's motion on its hydrodynamic coefficients. The proposed drone was based on a scaled-down geometry of the DARPA suboff bare hull model that was equipped with wings and fins. A series of Computer Fluid Dynamics simulations were performed using the ANSYS Fluent software. It was shown that with the increase of the drone's rotational velocity, the detachment of flow on the wings was delayed, and thus, the overall lift was increased. The hysteresis present in the characteristics of hydrodynamic properties during pitching movement had higher amplitude with increased pitching frequency. It was concluded that the parameters of the underwater glider's motion can have a significant influence on its hydrodynamic properties.

Developing a predictive method based on the vibration behavior of a naval ship hull model using hybrid fuzzy meta-heuristic algorithms

Ships are complex structures composed of various components with exclusive dynamic behaviors and natural frequencies, so assessing their vibration behavior is essential. Some situations in practical applications could alter the ship's dynamic characteristics and cause significant changes in its vibration behavior. Since the ship's mass is one of the most important dynamic parameters in determining vibration behavior, local mass change can lead to changes in its dynamic characteristics and must be considered. This study aims to develop a method to predict the effect of the location and magnitude of mass change on the ship hull's vibration behavior. It would be feasible to enhance the dynamic behavior and reduce undesirable noises by locating the mass change on the ship hull. In this regard, experimental and numerical modal analysis is performed on a scaled model of a naval ship hull. The baseline FE model is used to calculate the variation in frequencies of the model caused by different local mass change scenarios. Using these measurements a fuzzy system is generated and optimized by Genetic and Particle Swarm Optimization algorithms. Finally, the efficiency of the fuzzy-PSO is validated by different mass change scenarios foreseen on the physical model of the ship hull.

Auto Finance in the Electric Vehicle Transition

Financing cost differentials tilt the calculus for households toward electric vehicles (EVs). Using 85 million observations on U.S. auto loans, we study households’ credit risk by engine type, seek to uncover the sources and ask if credit risk differentials are being priced. We find that EV borrowers default 29% less relative to internal combustion engine vehicle (ICEV) borrowers with a back-of-the-envelope value of $1,457 in lender savings. To disentangle selection from expost exposure to differential costs of running an EV, we implement a differential shock exposure by treatment model of Borusyak and Hull (2023). Do lenders passalong these savings to borrowers? EV borrowers pay 2.2 percentage point lower interest rate, the equivalent of $2,711 in foregone payments. This lower rate is only for captive (manufacturer-based) lenders, not for bank and nonbank lenders, suggestive of policy and strategic motives by manufacturers, not a passing along of credit risk value. Another $1,457 is probably not being priced to households. Finally, we find that the ABS market knows, at least partially, allowing for less in loan loss reserves buffering the ABS, reflecting $233 in savings for the ABS issuer.

Numerical analysis of wave slamming on the David Taylor Model Basin 5415 ship model

This paper employs the user-defined function method to define the boundary and analyzes the effects of various ship speeds, wave parameters, and bow structural loads on deck and hull motion responses. When the ship has a wave slamming phenomenon, the water body's height, its response to the slamming load on the deck and superstructure, and hull motion improve the seakeeping performance of the hull model. Analysis of simulation results reveals that peak slamming loads generally increase with higher speeds and wave heights. As speed increases, results oscillate irregularly, affecting the nonlinearity of the slamming load. Additionally, when the wave slamming occurs, the slamming load near the superstructure of the bow model is relatively small. Finally, the numerical modeling method is used to modify the bow area structure, and the simulation analysis is carried out under different incident waves and speeds. The influence of the drift angle on the superstructure is discussed, and beneficial suggestions are provided for the future studies of waves on deck.

Numerical study of hydrodynamic drag effects of streamwise riblet structures on SUBOFF bare hull model

This study performs a full-scale numerical simulation on meter-scale underwater vehicles (UWVs) with micrometer-scale V-type streamwise riblet structures, focusing on hydrodynamic drag using the SUBOFF model. The periodic simulation along the azimuthal direction enables the full-scale analysis. Two main scenarios are discussed: (1) effect of riblet structure size on drag at a constant maneuvering speed and (2) effect of maneuvering speed on drag for representative riblet cases. In scenario (1), the average wall shear stress at the central region of the body exhibited significant reduction of approximately 50%. However, owing to larger effective area at the central surface of the body fixed with riblets, the friction drag may either decrease or increase depending on the riblet size. Consequently, R100 case showed maximum total drag reduction of ∼3%, whereas R500 case showed maximum increase in drag of ∼3%, where R100 and R500 indicate riblet-applied SUBOFF models with riblet heights of 100 and 500 μm, respectively. In scenario (2), friction drag in riblet-applied region exhibited smaller variations in R100 case, showing universal drag reduction effect at all speeds. In contrast, R500 case showed significant variations, with drag increments ranging from minimum of 1% to maximum of 12% at all speeds.

Estimating hydrodynamic performances of the designed leisure boats: a study considering hull shape and dimension variations

Abundant marine natural resources make Indonesia have potential in the field of marine tourism. Karimunjawa is one of the regions that still relies on marine tourism as the main sector in supporting the economy. Unfortunately, the existing modes of marine tourism transportation are dominated by traditional ships that have low performance, safety, and comfort. Therefore, infrastructure development is needed by developing a leisure boat design that has stability and good ship movement so that tourists are comfortable and safe on the trip. This study focuses on optimizing the hydrodynamic characteristics of leisure boats with variations in hull shape and hull dimensions adjusted to the characteristics of waters in Karimunjawa. The research was conducted by designing and analyzing 16 variations of hull models based on 5 reference ships. The regression approach is carried out on the dimensions of the reference ship to obtain variations in ship dimensions, then variations in hull shape include deep v, shallow v, flat bottom and round bottom. Each model variation is tested for resistance, stability, and seakeeping to determine the hydrodynamic performance of each model. Multi Attribute Decision Making (MADM) calculations are carried out afterwards to get the best tourist hull design. Then a sensitivity analysis was carried out on each variation to determine the influence of variations in dimensions and hull shape. The results showed the Deep V D model as the best model based on MADM calculations and hull shape variations had a significant influence on the hydrodynamic performance of the ship. It is hoped that this model can help the development of safe and comfortable tourist boats in accordance with the characteristics of the waters in Karimunjawa.

Free disposal hull models of multicomponent technologies

AbstractFree disposal hull (FDH) is a nonparametric model of production technology based on the single assumption of free disposability of all inputs and outputs. In this paper, we consider multicomponent production technologies in which every decision making unit (DMU) consists of several parallel component processes that can in principle operate independently of each other, provided they have sufficient resources. An example is universities viewed as DMUs, with their departments or groups of departments viewed as component processes. Each component process uses its own set of inputs and an unknown part of the shared inputs in order to produce its own set of outputs and an unknown part of the shared outputs. We allow combinations of component processes taken from different DMUs in order to construct new hypothetical DMUs, and refer to the resulting model of technology as the multicomponent FDH (MFDH) model. We further develop a larger, and mathematically nontrivial, variant of MFDH for the case in which we can specify certain bounds on the proportions in which shared inputs and outputs are allocated to component processes. We use an illustrative example in the context of universities to demonstrate the increasing discriminatory power of the new MFDH models over the standard FDH models in the multicomponent setting.

Matching of propulsion system components for a planing hull model

ABSTRACT This study specifies propellers for a main engine and transmission system to reach 20 knots for a vessel of certain dimensions. Propeller designs for 16-20 knots were examined using Fn and speed-resistance prediction. Twenty-four propeller variants are created with a 110 kW main engine and varied reduction rates. Twelve propellers that meet design specifications are CFD analysed. The data show that the P6 propeller consistently generates the most thrust and the P3 the least. Margins of error analysis show that propellers P4, P7 and P9 are closest to performance charts' values. As the advance ratio exceeds thresholds, open water diagram-CFD solver error rates rise. As long as advance ratios are followed, the P4 propeller produces reliable results, limiting error rates. Future studies should include propellers at different speeds further propellers, engines and transmissions. For researchers, professionals and mariners interested in ship propulsion design and effectiveness, this article is crucial.

Analyzing the performance of hull and water jet propeller under mooring conditions: effects of shallow water depths and varying inflow speeds

PurposeWater jet propulsion is widely used in various military and civilian fields due to its advantages of simple structure and high propulsion efficiency. The process of mooring involves utilizing specially designed equipment to secure a ship at a designated berth. During the process of water jet propulsion, the single propeller operates within a complex and turbulent three-dimensional flow. Hence, studying the coupling between the water jet propeller and the hull is critical to comprehending the characteristics of the device and the distribution of the flow field in detail.Design/methodology/approachFirstly, we conducted computational fluid dynamics (CFD)-based self-propulsion calculations to evaluate the interaction between the hull and the propeller. We subsequently analyzed the propeller's performance and the forces acting on the hull to understand how the presence or absence of the hull influenced the water jet propeller. Finally, we performed calculations and analysis of the cavitation characteristics of the coupling between the hull and the water jet propeller, considering different rotational speeds and water depths at the bottom of the pool.FindingsThe study demonstrated that the presence of the hull boundary layer under the hull-propeller coupling condition led to reduced uniformity of propeller inlet flow and lower efficiency of the propulsion pump. However, it also increased the bias toward low-flow conditions. Additionally, increasing the impeller speed led to a gradual increase in the cavitation volume within the water jet propeller, resulting in a gradual decrease in the propeller's performance.Originality/valueThis research provides the technical support required for effective design and operation of water jet propulsion systems. This paper involves studying and analyzing the performance and flow field of the coupling between the hull and propeller under mooring conditions with a specified hull model.

Exact simulation of the Hull and White stochastic volatility model

We show how to simulate exactly the asset price and the variance under the Hull and White stochastic volatility model. We derive analytical formulas for the Laplace transform of the time integral of volatility conditional on the variance level at the endpoint of the time interval and the Laplace transform of integrated variance conditional on both integrated volatility and variance. Based on these results, we simulate the model through a nested-conditional factorization approach, where Laplace transforms are inverted through the (conditional) Fourier-cosine (COS) method. Under this model, our approach can be used to generate unbiased estimates for the price of derivatives instruments. We propose some variants of the exact simulation scheme for computing unbiased estimates of option prices and sensitivities, a difficult task in the Hull and White model. These variants also allow for a significant reduction in the Monte Carlo simulation estimator's variance (around 93-98%) and the computing time (around 22%) when pricing options. The performances of the proposed algorithms are compared with various benchmarks. Numerical results demonstrate the faster convergence rate of the error in our method, which achieves an O(s−1/2) convergence rate, where s is the total computational budget, largely outperforming the benchmark.

A Framework for Structural Analysis of Icebreakers during Ramming of First-Year Ice Ridges

This paper presents a framework for structural analysis of icebreakers during ramming of first-year ice ridges. The framework links the ice-ridge load and the structural analysis based on the physical characteristics of ship–ice-ridge interactions. A ship–ice-ridge interaction study was conducted to demonstrate the feasibility of the proposed framework. A PC-2 icebreaker was chosen for the ship–ice interaction study, and the geometrical and physical properties of the ice ridge were determined based on empirical data. The ice ridge was modeled by solid elements equipped with the continuous surface cap model (CSCM). To validate the approach, the simulated ice resistance was computed using the Lindqvist solution and in situ tests of R/V Xuelong 2. First, the local ice-induced pressure on the hull shell was determined based on numerical simulations. Subsequently, the local ice pressure was applied to local deformable sub-structural models of the PC-2 icebreaker hull by means of triangular impulse loads. Finally, the structural response of sub-structural models with refined meshes was computed. This case study demonstrates that the proposed framework is suitable for structural analysis of ice-induced stresses in local hull components. The results show that the ice load and the structural response obtained based on the four first-year ice-ridge models show obvious differences. Furthermore, the ice load and corresponding structural response increases with the width of the ridge and with increasing ship speed.

Active control of target sound fields using structural-acoustic brightness applied to a ship model's acoustic signature.

This manuscript presents a method for reproducing sound fields actively by using a vibrating submerged structure as the field reproduction source, with the target sound field to be reproduced defined in the frequency domain using the acoustic brightness approach. To balance the predetermination of a mono- or multi-zone target sound pressure field and the control effort required, singular value decomposition of the structural-acoustic system matrix is proposed. The dependency of the radiation efficiency into the target zone on the singular modes representing source and pressure modes is investigated using a wavenumber-domain approach. Furthermore, a feedforward control principle is adopted for adaptive sound-field reproduction with mode matching from the least squares perspective. Finally, an experiment is reported that involve synthesizing a tonal target underwater acoustic signature of a model of a fast attack craft (scale 1:8) at a measurement facility at Lake Plön in Germany. The results show that with the structural-acoustic brightness approach structural modes with radiation coupling into the target zone are excited and related pressure modes exhibit individual focus in the direction of hydrophones in use. Finally, a predetermined narrowband sound pressure field is actively reproduced at the hydrophone positions using inertial actuators and accelerometers on the ship model's hull.

Pygmy Blue Whale Home Ranges and Their Overlaps with Indonesian and Australian Marine Protected Areas: Comparison between a-LoCoH and BBMM Methods

Information on the distribution of marine migratory species is lacking, and for a long time, these species have been overlooked in the designation of Marine Protected Areas (MPAs). This study analysed the home range of pygmy blue whales (PBWs) from western Australia to eastern Indonesia to be able to assess the overlap with current MPAs. In this study, data from 11 individual PBWs tagged in the Perth Canyon were used. Two home range methods, adaptive Local Convex Hull (a-LoCoH) and Brownian Bridge Movement Model (BBMM), were performed and compared to identify core use areas and connections between these areas (i.e., migration corridors). By assessing the relative properties and visually inspecting the home ranges, 90% BBMM (home range and migration corridor) and 50% BBMM (core use area) are chosen as the best results, because they cover the connected core-use areas to a large extent. The home ranges that were covered by current MPAs were only 2% in Indonesia and 16% in Australia. Important migration corridors without current protection are in the east Savu Sea, south of Timor Island, and wider Banda Sea. It is noteworthy that comparing methods is relevant to be able to choose the most suitable method for the data used and the goal of this study. The limited overlap between the calculated home ranges and the MPAs of the Indonesian waters articulates the importance of in-depth scientific studies to be able to evaluate, implement and develop marine conservation planning.

Leisure Boat Concept Design: Study on the Influence of Hull Form and Dimension to Increase Hydrodynamic Performance

The tourism sector contributes significantly to the economic growth of the community and the country. Labuan Bajo has the potential for marine tourism, which is famous for foreign classes. The separation of the islands in Labuan Bajo requires transportation to support tourist activities to tourist destinations. One type of transportation to support the needs of marine tourism is leisure boats or recreational boats. The leisure ship must have standards of comfort, security for passenger safety, and efficient operational costs. It is necessary to have infrastructure in the form of a leisure ship that functions optimally, so research on the hull’s hydrodynamic characteristics is essential. This research aims to observe the influence of hull form variables and primary size on the hydrodynamic characteristics of the ship. The research method was the simulation method to determine the response of the hull model variation to the environmental conditions tested. Simulation testing using Maxsurf software based on resistance, stability, and seakeeping criteria. The MADM method analysis results showed that the Deep V Hull model variation had the highest score of 0.787. In the sensitivity analysis calculation, the hull form variable significantly affected resistance and stability testing with R square values of 0.6008 and 0.5930. Meanwhile, the size variable had more influence on seakeeping testing, especially roll motion, with an R square value of 0.4081.

Study on the flooding characteristics of damaged barges with dynamic explosive deformation

Dynamic explosion in a compartment damages the structure, resulting in flooding and even sinking of the ship. To study the flooding characteristics of damaged compartments and floating states of the hull under deformation of the bulkhead caused by explosion, the damage effects on a single compartment and multiple compartments under dynamic explosion are illustrated. Then, the flooding characteristics are analyzed for single compartment models with two types of damage modes and one multi-compartment asymmetric damage model. The results indicate that the deflection of the bulkhead increases the capacity of the compartment, resulting in variations in the flooding process of damaged compartments. Compared with the single models without deflection deformation, the final flooding quantity of the two types of models with deflection deformation increased by 62.49% and 65.48%. The difference in flooding characteristics led to deviation in the six-degree-of-freedom motion of the two types of hull models. Significantly, the amplitude of heave in the models with deflection deformation under the two types of asymmetric damage modes increased by 60% and 66% compared to that of the models without deflection deformation, and the pitch increased by 66% and 50%. Nevertheless, in the multi-compartment models, there were no distinct differences in the flooding process and six-degree-of-freedom motion. These results can support the rapid assessment of the unsinkability of ships in explosive environments.

Pricing and hedging of longevity basis risk through securitisation

AbstractPension funds and insurers face difficulties in hedging their longevity risk, which is the uncertainty of how long their clients will live. A possible solution could be using longevity-linked securities to transfer some of this risk to other parties. However, these securities may not match the actual mortality rates of the insurer’s clients, resulting in a potential loss due to basis risk. In this paper, we measure this basis risk through the pricing of a longevity derivative under Solvency II. We also compare this method with other common pricing methods in finance. We explore and evaluate different hedging strategies for insurers, using a multi-population model derived from a two-dimensional Hull and White model that captures the dynamics of mortality over time.