Unit Load Devices Research Articles

Experimental simulation of temperature non-uniformity in a loaded container along air cargo supply chain: Mango case study

The cooling time of mango boxes (initial temperature 19 °C) at different positions in a Unit Load Device (ULD) located in a test room of 6 °C was monitored. Plaster mangoes were used due to the high perishability of real mangoes. The influence of box designs (closed and top-open) on the cooling time were studied. Both box designs showed shorter Half-cooling time (HCT) at the bottom than at the top. Closed boxes exhibited more uniform temperatures in the ULD. Heat transfer in closed boxes was primarily conduction, while natural convection played a significant role in top-open boxes. Then, the ULD was exposed to variable ambient temperatures to simulate real conditions in an air cargo supply chain. The results demonstrate that the critical step is the airport tarmac; after 2 h for example, the temperature at the top rose to 50 °C (with external air at 32 °C), resulting in a 10 °C increase in the mangoes in the top box.

Experimental study of air cargo temperature variations and its impact on mango quality

An air cargo supply chain for fresh mango was investigated from Thailand to France. Measurements of air temperature, air relative humidity, and fruit (peel) temperature were conducted using thermo-hygrometer data loggers in cartons. In a Unit Load Device (ULD) containing 148 cartons, twenty-seven instrumented cartons were placed at different positions to observe spatial and temporal temperature variations during 12 h cruising. At the destination, mango quality attributes were assessed at different time-points during 15-day storage at 16.1 °C and 21.6 °C. Throughout the supply chain, fruit temperatures ranged from 16.6 °C to 30.5 °C. During cruising, fruit temperatures in upper cartons remained almost constant, whereas base carton temperatures continuously decreased from 26.1 °C to 18.1 °C. Because of a short cruising period in comparison to a storage duration at the destination and proper ambient temperature condition during the experiment, carton position in the ULD had no discernible impact on fruit quality during storage. Fruit stored at 16.1 °C preserved superior fruit quality compared to 21.6 °C storage. For the same storage temperature, better quality of fruits stored in Thailand demonstrated the impact of air shipment on product degradation. The measured temperature and relative humidity evolutions were used as input parameters of a mass loss evolution model. A comparison with the measured data exhibited good agreement (RMSE < 1.8 % mass loss). Considering 10 % mass loss as a critical value, this model allows an estimation of the product shelf life based on a supply chain scenario.

LOADING OPERATION EFFICIENCY FOR INTERNATIONAL AIR EXPRESS AT A SPOKE AIRPORT

Loading operation efficiency at airports plays an indispensable role in international air express service performance. The authors comprehensively examined the priorities of factors that affect loading operation efficiency for air express services at Taoyuan International Airport in Taiwan. The reviewed results from surveying practical experts using a rank pair-wise comparison (RPC) revealed that load factor and load planning consistently ranked higher and more crucial among 15 elements regardless of flight properties. Long-haul services to the North American hub were most concerned with inventory control of unit load devices (ULDs). Regional feeder services attached importance to the ground operations workforce as well. Feeder services for cross-continental deliveries additionally focused on the arrangement of apron bays. The authors used the TOPSIS, i.e., technique for order preference by similarity to ideal solutions, to evaluate flights by three freighter types. Considering that the studied company performed more consistently on the top crucial factors, the sub-criteria that belong to the negative subset and are affected by the external units played a dominant role in these evaluated flights.

A Combinatorial Optimization Approach for Air Cargo Palletization and Aircraft Loading

The current air cargo loading plan handles the Air Cargo Palletization Problem (ACPP) and the Aircraft Weight and Balance Problem (WBP) separately, which has an impact on the optimization of the payload and the aircraft’s center of gravity (CG). Thanks to improvements in computer processing power, the joint combinatorial optimization of ACPP and WBP is now feasible. Three integer linear programming models are proposed: a Bi-objective Optimization Model (BOM), a Combinatorial Optimization Model (COM), and an Improved Combinatorial Optimization Model (IOM). The objectives of the models are the maximum loading capacity and the lowest CG deviation from a specified target CG. The models also consider a wide range of restrictions in the actual packing and stowage procedures, such as volume, weight, loading position, aircraft balance, and other aspects of aircraft and unit load devices. Four scenarios with various conditional metrics for three models are solved for the B777F aircraft using Gurobi. The results of the computations demonstrate that the BOM has the fastest solution speed, but the CG deviation is the largest, and in several cases the CG deviation results are unacceptable. The COM has the longest solution time, which is difficult to tolerate in practice. Despite taking a little longer to solve computationally than the BOM, the IOM offers the best optimization solution.

A Hybrid Framework for Real-Time Dispatching of Airline Unit Load Devices under Demand Variations

This study is devoted to a new research topic in real-time airline operations, the redispatching of unit load devices (ULDs) under demand variations. We develop a new hybrid framework to solve the problem of ULD redispatch following the time-sequence decision-making required by airlines. The hybrid framework is developed by integrating techniques including the probability distribution technique to simulate different types of operational demand, the adjustable number of stages which is needed to meet the requirements of a decision-making process following a time sequence and the time pressure characteristic of real operations, and the scenario tree and probability rule approaches which are aimed and representing all possible demand scenarios for a stage, while the network flow technique is applied to represent the movement and location of ULDs at each airport over time and is used for the development of the associated mathematical model and the simulation. We performed a simulation of 2,000 cases based on different operational days and types of operational demand. The results show that this hybrid framework is able to achieve stability and also a small variability of both ULD operating costs and solution times, which could allow the airline to save on ULD operating costs, under demand variations in real-time operations.

The ground handler dock capacitated pickup and delivery problem with time windows: A collaborative framework for air cargo operations

We study a typical problem within the air cargo supply chain, concerning the transportation of standard Unit Load Devices (ULDs) from freight forwarders’ to ground handlers’ warehouses. First, ULDs are picked up by a set of available trucks at the freight forwarders’ premises within a time window. Next, they are delivered to the ground handlers, also within a time window, and discharged according to a Last In First Out (LIFO) policy. Due to space constraints, ground handlers have limited capacity to serve the trucks and waiting times may arise, especially in case freight forwarders do not coordinate their operations. Therefore, in this paper we consider a cooperative framework where this transportation is coordinated by a central planner. The goal of the planner is to find a proper routing and scheduling that minimizes the sum of the transportation and waiting times at the ground handlers’ warehouses, while satisfying the capacity of the trucks. We propose two mathematical formulations, one based on the routing and the other based on the packing aspect of the problem. To solve large instances of the problem, an Adaptive Large Neighborhood Search algorithm is also developed. With numerical experiments, we compare the performances of the two models and the metaheuristic, and we quantify the benefits of the proposed framework to reduce waiting times.

Unit load device reassignment following temporary airport closures

In this study, a reassignment model is developed for helping airline planners in reassigning unit load devices (ULDs), which include containers and pallets, to flights after temporary airport closures. The objective of the model is to minimise the system cost, which includes total weighted delay time and the total penalty for leftover ULDs. To test the model's efficiency and applicability, several problem instances of different scales are randomly generated based upon data from an airline in Taiwan. The sensitivity of results is analysed. The results show that as weight capacity increases, more ULDs can be assigned and average ULD delays increase. The approved ULD's quantity per flight increases, while the number of un-assigned ULD and average ULD delay time may decrease. Also, as the ULD weight increases, fewer ULDs can be assigned, and average ULD delay time may increase. The results show the usefulness of the proposed model for actual operations.

Unit load device reassignment following temporary airport closures

Unit load device reassignment following temporary airport closures

A simulation approach for aircraft cargo loading considering weight and balance constraints

Air cargo transport is a growing industry in parallel with the growth in world trade and e-commerce. The global air cargo transport traffic getting busier, the importance of timely loading with minimum error is increasing. Therefore, digitalization of the air cargo loading process is needed. Assignment of Unit Load Devices (ULDs) to the specific positions on the freighter is performed by loadmasters by manual or semi-manual methods. This study aims to design a simulation model, which performs the ULD assignment automatically by simulating the loading process performed by the experienced loadmasters under the weight and balance constraints. The SEMMA (sample, explore, modify, model, assess) model is used while generating the simulation model. Fifty real-world loading orders were used to assess the performance of the model. The ULD assignment process by the simulation model and the loadmasters using semi-manual loading were compared with regard to time and center of gravity performance indicators. The results demonstrated that the simulation model can load all the given sets of ULDs, as efficiently as a loadmaster with a similar center of gravity in a shorter period of time. In conclusion, the proposed simulation model provides an efficient solution to the ULD assignment problem. However, the base model generated may be improved to address various real-world scenarios

How Blockchain and IoT-Based Decentralized System Solves ULD Rental Problem of Airlines

This study is devoted to ULD (Unit Load Device) rental among airlines and air cargo terminals at airports through data exchange. When airlines want to rent their partner airline's ULD, they use it after receiving data through its ULD inventory management system. This paper proposes a de-centralized ULD rental solution by combining blockchain technology and IoT (Internet of Things). The airline that wants to rent a partner airline's ULD checks the available inventory information before use and pays the amount according to the time of service. In addition, the smart contract specifies the remittance status to activate IoT on the ULD. Airlines that supply ULDs for partner airlines first create inventory information to provide services. Airlines that want to rent ULDs can check availability and remit rental costs according to usage time in cryptocurrency. The ULD rental service ends when the usage time is over. This ULD rental solution allows all airlines rent out their ULDs to partner airlines in real-time. Also, when a specific airport runs out of its own ULD, it is possible to overcome the difficulties of inventory shortage by renting the inventory of partner air-lines.

Intermodal Humanitarian Logistics Using Unit Load Devices.

Intermodal freight transportation facilitates today’s global trade. The benefits of intermodal freight transportation have been studied and are more observable in commercial logistics; however, the potential benefits of humanitarian logistics have not been thoroughly investigated. This research aims to present a resilient transportation framework by modeling intermodal transportation utilizing interoperable loading devices during disaster responses. We developed an integer programming model based on a time–space network by considering route and vehicle availabilities that are allowed to change with time. We consider vehicles with varying capacities in three transportation modes (i.e., ground, maritime, and air). The contribution of this study is threefold: (1) Two compatible unit load devices are proposed for humanitarian logistics; (2) a mathematical model that includes integer variable representation for vehicle fleets in different transportation modes is developed; and (3) intermodal transportation is compared with single-mode transportation using a real-life dataset. Our main results are as follows: In terms of cost, intermodal transportation is effective when demand occurs in consecutive periods and response time is short. Inventory is held more in intermodal transportation when it is cost-effective to use transportation modes with large capacities. Thus, the benefits of the responsiveness of intermodal transportation outweigh the costs of mode interchange and inventory holding for sudden-onset disasters where quick responses are needed within a short time.

Optimization approach to the aircraft weight and balance problem with the centre of gravity envelope constraints

The aircraft weight and balance problem (WBP) defined in terms of selecting unit load devices (ULDs) from an available set and allocating them to specified positions in cargo holds. It is critical to aircraft safety as well as operational efficiency and profit. It is an NP-hard problem combining characteristics of the knapsack problem and generalized assignment problems, as well as complex practical constraints. A mixed integer programming model is constructed to maximize the total payload and minimize the center of gravity (CG) deviation by considering the constraints of positions, weights, balance etc. In contrast to prior studies using a constant delta to limit CG deviation, a new set of CG envelope constraints is proposed based on the variation in actual CG under different statuses and precise describing CG. A linearizing strategy is further designed to simplify the nonlinear CG envelope constraints. The proposed model can be solved using commercial optimization software within a few seconds and maintain the CG within the designated CG envelope in all test instances; in contrast, the other (CG deviation-based) method may result in flight hazards in some scenarios.

Airline unit load device dispatch and scale in short-term operations involving skypooling – A new sharing economy in airline industry

The skypooling is a free platform for the sharing of unit load devices (ULD), which contributes a new sharing economy by allowing airlines to exchange ULDs and coordinate ULD delivery services. The akypooling aids airlines to match their requirements for the two ULD sharing operations. However, such matching is not always successful. The matching success rate naturally affects skypooling performance and generates a gap between the expected and available numbers of ULDs for the two ULD sharing operations. We design two achievement rates for ULD sharing operations, which represent the likelihood of meeting ULD dispatch requirements in actual operations, as well as devising. We develop a novel ULD sharing model and a solution algorithm to handle the problem. The model is developed by combining the network technique utilized in Operations Research with the binomial distribution utilized in Statistics. The solution algorithm comprises a three-stage iterative evolutionary process. We obtain that the carrier decrease the number of ULDs utilized each week by 7% by the two ULD sharing operations. Different instances exemplifying optimistic, normal, and pessimistic situations are examined to understand the ultimate implications and applications of the new technique for airline operations.

Real-Time Location-Positioning Technologies for Managing Cart Operations at a Distribution Facility

In this paper, we propose an RFID-based location-positioning platform for managing cart operations at vast and fast-moving distribution facilities. Our work was motivated by a real-world problem in a large airmail center. Our system requires that each cart is affixed with an active RFID tag, and RFID readers are installed at multiple locations of the facility. The locations of the tagged carts are determined by the estimated angles of arrival communication signals between the readers and the tags and the signal strengths, and the information about their positions are stored in the platform continuously. This platform enables the users to locate tagged objects in real time, thereby saving staff members a significant amount of time from searching for the right carts in the highly dynamic environment. Consequently, the mail facility can benefit from the increased efficiency. Furthermore, the system is also able to reduce the chance of having a delay in delivering mail bags to unit load device (ULD) area and misplacements of mail bags to ULDs. We further analyze the the huge amount of historical data collected from the RFID infrastructure of the airmail center for the cart movements within the facility and observed previously unrecognized operational issues. We also discuss some of the challenges and problems faced in this project. We believe that this application can bring huge benefits to businesses and organizations along supply chains by effectively anticipating the increasing demand for logistics services in the age of electronic retailing.

Influence of venting on the response of scaled aircraft luggage containers subjected to internal blast loading

This paper concerns the mitigation of damage in aircraft luggage containers subjected to internal blast loading. It reports findings of experimental and computational work on the influence of venting on the blast response of scaled unit load devices. The internal geometry of the structure was based on a 1:6 scale version of the commonly used LD-3 unit load device. To simplify the problem, only the face closest to the aircraft primary structure could deform whilst the other walls were kept rigid. Small, spherical, charges of PE4 plastic explosive were detonated inside the scaled structures. The fully confined blast tests exhibited the highest permanent displacements and were the only tests to produce rupture of the target plate. Introducing venting reduced the target plate displacement significantly. Computational simulations were developed using LS-Dyna to provide additional insight into the blast loading and its interaction with the structure beyond what could be measured experimentally. Venting appeared to have no effect on the pressure peak, but it was effective at removing the late-time pressure reflections. The influence of the side venting was slightly obscured in the experiments due to boundary pulling-in effects at higher charge masses, but the simulations showed that venting from two sides was slightly more effective in reducing target plate deformation than single-sided venting. The paper demonstrates the potential benefit of using LD-3 ULDs unit load device with canvas sides (rather than solid ones) and venting lengthwise along the aircraft body to redirect the loading away from vulnerable locations.

Scheduling personnel for the build-up of unit load devices at an air cargo terminal with limited space

This paper addresses the preparation of unit load devices (ULDs) at an air cargo terminal. This process is difficult to plan for many airlines, which face the challenge of assigning a limited number of workers to a limited number of workspaces available for preparing the ULDs, while respecting the requirements imposed by an existing flight schedule. During the preparation of ULDs, the objectives are to comply with the flight schedule, not to exceed the available space at the terminal, and to minimize the maximum workforce employed over time. To support airlines in realizing efficient ULD preparation processes, this paper proposes a mixed-integer linear programming model as well as a generalized set partitioning reformulation of this problem. Based on the latter formulation, we develop different heuristic strategies, some of which are shown to solve this NP-hard problem to near-optimality in a matter of merely 10 s, decisively outperforming a simple rule of thumb frequently used in practice. We also investigate the inherent trade-off between workforce and space utilization.

Optimization of shielding to reduce cosmic radiation damage to packaged semiconductors during air transport using Monte Carlo simulation

BackgroundCosmic ray-induced particles can lead to failure of semiconductors packaged for export during air transport. This work performed MCNP 6.2 simulations to optimize shielding against neutrons and protons induced by cosmic radiation Methods and materialsThe energy spectra of protons and neutrons by incident angle at the flight altitude were determined using atmospheric cuboid model. Various candidates for the shielding materials and the geometry of the Unit Load Device Container were evaluated to determine the conditions that allow optimal shielding at all sides of the container. ResultsIt was found that neutrons and protons, at the flight altitude, generally travel with a downward trajectory especially for the particles with high energy. This indicated that the largest number of particles struck the top of the container. Furthermore, the simulation results showed that, among the materials tested, borated polyethylene and stainless steel were the most optimal shielding materials. The optimal shielding structure was also determined with the weight limit of the container in consideration. ConclusionsUnder the determined optimal shielding conditions, a significantly reduced number of neutrons and protons reach the contents inside the container, which ultimately reduces the possibility of semiconductor failure during air transport.

Freighter Loading Efficiency at Airports for International Air Express

Loading efficiency of freighters plays an indispensable role for the service performance of international air express companies. This study examined the priorities of factors to affect freighter loading efficiency at Taoyuan International airport (TPE) with an analytic hierarchy process (AHP). Unit load device (ULD) inventory control, load factor and load plan were ranked top 3 from 15 factors by practical experts. This study used the technique for order preference by similarity to ideal solution (TOPSIS) to evaluate 26 flights of MD11 freighters operated by an international air express company at TPE. The results revealed that the performance ranges between the best and worst flights were obvious.

Unit Load Devices (ULD) Demand Forecasting in the Air Cargo for Optimal Cost Management

Unit Load Devices (ULD) Demand Forecasting in the Air Cargo for Optimal Cost Management

Airline unit load device dispatching considering service level and violation days

The purpose of this research is to consider the dispatching and scale problem of airline unit load devices (ULDs) with consideration of service levels and violation days. A service level is specified to control the number of days that the ULD safety stock requirement can be violated. The network model and solution algorithm are developed with parallel computing. We find that our solutions are an improvement over the current solutions employed by the studied carrier from 31.89% to 33.01% for different safety stock levels. We also conclude that the studied carrier should set the service level to 90% as the general standard for stations considering the tradeoff between the number of ULDs required and the violation days.