Entire Design Life Research Articles

Modified asphalt-rubber green pavement (MARGPave) mixtures: Product development and performance assessment

The major objective of this study was to develop “Modified Asphalt-Rubber Green Pavement (MARGPave)” mixtures with dense- and gap-graded aggregate structures to accomplish performance attributes superior to the conventional asphalt-rubber mixtures. The scope encompassed production of one conventional dense-graded, one dense-graded MARGPave, one gap-graded MARGPave, and one gap-graded asphalt-rubber mixtures using the Superpave mix design, conduct of stiffness modulus tests, moisture sensitivity, and fatigue evaluation at varying temperature-frequency combinations, which generated over 300 data points. The dense-graded MARGPave mix exhibited three times higher fatigue life and increased durability than the conventional dense-graded mix. The gap-graded MARGPave mix had lower modulus at all temperatures by more than 50% than the dense-graded MARGPave mix due to 2% higher asphalt content and rubber inclusions. Likewise, the modulus of gap-graded MARGPave mix was higher than gap-graded asphalt-rubber mix across all temperatures and frequencies, indicative of the elastic nature of the MARGPave mix due to higher rubber content. Higher modulus at higher temperatures and lower modulus at lower temperatures were concurrently displayed by dense-graded MARGPave mix, which indicated that the material would be resistant against rutting and low-temperature thermal cracking, thereby able to outperform conventional materials with insignificant rate of change of viscosity with increasing temperatures, and the presence of rubber particles that would render the mix the necessary additional resilience to endure the mix performance for the entire design life. It is noteworthy that the procedure of blending asphalt binder, aggregates, and the modified asphalt-rubber product that replaces some portions of fine aggregates helped create MARGPave mixtures that was found akin to the semi-dry process technology. It is envisioned that the indigenously developed MARGPave mixtures will be best suited as a roadway construction and maintenance strategy that supports the engineering use of end-of-life tires, encouraging the waste-to-wealth concept.

Demonstration of a prototype design synthesis capability for space access vehicle design

ABSTRACTThe early conceptual design (CD) phase of space access vehicles (SAVs) is the most abstract, innovative and technologically challenging phase of the entire aerospace design life cycle. Although the design decision-making during this phase influences around 80 percent of the overall life cycle cost, it is the most abstract and thus least understood phase of the entire design life cycle. The history of SAV design provides numerous examples of project failures that could have been avoided if the decision-maker had had the capability to forecast the potential risks and threats correctly ahead of time during the conceptual design phase. The present study addresses this crucial phase and demonstrates a best-practice synthesis methodology prototype to advance the current state of the art of CD as applied to SAV design. Developed by the Aerospace Vehicle Design (AVD) Laboratory at the University of Texas at Arlington (UTA), the Aerospace Vehicle Design Synthesis process and software (AVDS) is a prototype solution for a flight vehicle configuration–flexible (generic) design synthesis capability that can be applied to the primary categories of SAVs. This study focusses on introducing AVDS, followed by the demonstration and verification of the system’s capability through a sizing case study based on the data-rich Boeing X-20 Dyna-Soar spaceplane.

Fatigue damage assessment of mooring lines under the effect of wave climate change and marine corrosion

Fatigue is one of the major failure modes of offshore structures typically operating continuously for 20–30 years at sea. Gradually varying factors, such as wave climate change and marine corrosion, can contribute significantly to the fatigue damage assessment during the entire design life; however, these factors are generally ignored. This study aims to propose a new fatigue damage assessment method, wherein the effects of wave climate change and marine corrosion on the fatigue damage assessment of mooring lines are considered by introducing a reasonable model into the hull/mooring system coupled dynamics. The fatigue damage of the mooring lines used for a semi-submersible platform is assessed in the time domain using the proposed method. The results indicate that wave climate change and marine corrosion have a significant influence on the distribution of the mooring lines’ tension ranges and fatigue damage assessment. When the effects of both wave climate change and marine corrosion are ignored, the cumulative fatigue damage during the entire design life is underestimated by up to 35%. Thus, it can be concluded that a design without the consideration of the gradually varying factors poses significant security risks.

Aeromechanical Response of a Distortion-Tolerant Boundary Layer Ingesting Fan

Boundary layer ingestion (BLI) is a propulsion technology being investigated at NASA by the Advanced Aircraft Transportation Technology (AATT) Program to facilitate a substantial reduction in aircraft fuel burn. In an attempt to experimentally demonstrate an increase in the propulsive efficiency of a BLI engine, a first-of-its-kind subscale high-bypass ratio 22″ titanium fan, designed to structurally withstand significant unsteady pressure loading caused by a heavily distorted axial air inflow, was built and then tested in the transonic section of the GRC 8′ × 6′ supersonic wind tunnel. The vibratory responses of a subset of fan blades were measured using strain gages placed in four different blade pressure side surface locations. Response highlights include a significant response of the blade's first resonance to engine order excitation below idle as the fan was spooled up and down. The fan fluttered at the design speed under off operating line, low flow conditions. This paper presents the blade vibration response characteristics over the operating range of the fan and compares them to predicted behaviors. It also provides an assessment of this distortion-tolerant fan's (DTF) ability to withstand the harsh dynamic BLI environment over an entire design life of billions of load cycles at design speed.

Hull Structure Integrity Management in Floating Structures–FSO Puteri Dulang Case

This paper highlights the key differences in practices employed in managing hull structure integrity of permanently moored floating offshore structures as against sailing vessels which are subject to periodic dry docking. During the design phase, the structural integrity management over the life of a sailing vessel is primarily taken into account by means of Class prescribed Nominal Design Corrosion Values which are added to minimum scantling requirements calculated based on strength and fatigue criteria. In contrast, for permanently moored offshore installations like FPSOs, FSOs etc. the hull structure integrity over the entire design life of the asset is a key design consideration both for new buildings and conversions. Analytic methods and tools (primarily those developed by Class Societies) are available to evaluate the strength requirements (based on yielding, buckling and ultimate strength criteria) and fatigue life of the hull structure. Typically three levels of analysis with increasing degree of complexity and analysis time are used to predict the structural response and fatigue life of the Hull during design phase. The degree of detailed analysis required needs to be determined in light of the expected optimization in terms of savings in scantlings for new building or for steel renewal requirements in case of conversions.

Probabilistic modelling of the bond deterioration of fully-grouted rock bolts subject to spatiotemporally stochastic corrosion

Developing predictive models for quantitative assessment of the deterioration of rock bolts exposed to corrosive environments is essential for rational planning of maintenance activities for anchorage structures. This article presents a probability-based computational model for predicting the time-dependent deterioration of bond capacity of corroding rock bolts due to the attack of chlorides. The inherent stochastic nature involved in the corrosion and degradation process is identified and simulated. A method is developed based on fundamental Mohr–Coulomb theory to evaluate the effect of corrosion on the bond strength due to a failure mode involving splitting of grout cover. Parameters affecting both strength and stress state at the bolt–grout interface are quantitatively related to the degree of corrosion. Integrating the realised corrosion stochastic process and the developed bond loss evaluation method, a computational algorithm based on Monte Carlo simulation is presented for evaluating the bond deterioration in a probabilistic framework. The presented model is used in an illustrative example to show its capability to trace the evolution, throughout the entire design life, of several representative performance indicators of rock bolts as a structure unit or of the interested location within the anchor length.

Seismic Damage Analysis of Aged Concrete Gravity Dams

The design of a concrete gravity dam must provide the ability to withstand the seismic forces for which nonlinear behavior is expected. The nonlinear seismic response of the dam may be different due to aging, as the concrete gets degraded because of environmental factors and mechanical loadings. The present study investigates the evolution of tensile damages in aged concrete gravity dams, which is necessary to estimate the safety of existing dams towards future earthquake forces. The degraded material properties of the concrete with age, subjected to environmental factors and mechanical loadings, are determined introducing an isotropic degradation index. A concrete damaged plasticity model, which assumes both the compressive and tensile damage, is used to evaluate the nonlinear seismic response of the dam. Results show that the peak maximum principal stresses reduced at the neck due to aging effects in the concrete. It is observed that the neck region is the most vulnerable region to initiate damage for all cases of aged dams. The results show that there are severe damages to the structure at higher ages under seismic loadings. The proposed method can ensure the safety of dams during their entire design life considering the environmental factors and mechanical loadings affecting the materials as they age.

Environmental policy for long-life pavements

This article uses life-cycle assessment to evaluate the role of long-life pavements in achieving environmental goals. The success of such pavements in reducing environmental impacts over their life cycle hinges on their ability to serve their intended purpose for their design life. Those pavements that do serve for their entire design life offer extreme longevity at only a marginal environmental cost. However, the return on the initial environmental investment occurs after many decades of use and is often beyond conventional analysis periods. Evolving performance expectations and demand create uncertainty regarding the ability of long-life pavements to reach environmental goals because time-dependent factors, such as technology shifts and functional obsolescence, affect their ability to serve for their entire design life.

Equivalent constant rates for performance-based seismic assessment of ageing structures

Analytical, closed-form solutions are derived for the computation of equivalent constant rates of limit-state exceedance for structures under seismic loads whose capacity is degrading with time. Seismic guidelines currently designate constant, time-independent probabilities or mean annual frequencies of exceedance that are assumed to remain invariable for the entire design life. These are at odds with the time-dependent, ever-increasing exceedance rates of ageing structures. Based on the concept of social equity and discounting of societal investments, the equivalent constant rate provides a basis for judging the safety of structures with time-dependent capacity by allowing comparisons with the code-mandated rates of limit-state exceedance. Starting from the simple SAC/FEMA solution and assuming a power-law degradation of capacity with time and a linear change in the combined epistemic and aleatory variability of capacity, we provide general solutions for the equivalent constant rate and for the limiting case of the average rate over the design life of the structure. The solutions are formulated both in the demand-based and in the intensity-based format, the latter being suitable for all limit-states, even close to global collapse. By using a 7-story reinforced concrete building as an example, we demonstrate the accuracy and the practicality of these approximations for the assessment of an existing structure.

Phenomena of reverse momentum pulse and fluid leak after poison injection in the shut down system of PHWR

The primary function of the shut down system in a nuclear reactor is to terminate any reactivity transient occurring in the core during its entire design life. Normally there is more than one system, which are independent and diverse in its mode of operation. They consist of quick acting mechanisms like dropping of safety rods by gravity, poison injection, etc. Typically in liquid poison injection system wherein high flow velocities are involved, there is significant fluid structure interaction associated with cyclic shock transients in the system. One such phenomenon has been captured and analyzed to understand the dynamics involved in the loop. The trends of loop pressure and vibration indicated presence of more than two pressure transients after complete injection of poison. The first transient arrived after 1.44 s and the second after 0.75 s. The reverse pressure pulses that manifested in the loop as a result of fast injection of fluid has been mathematically characterized by solving basic fluid balance equations. Possibility of ball lifting due to momentum pulse is also discussed.

Reliability and feedback of multiple hop wireless networks

This paper analyzes fault-tolerance over the entire design life of a class of multiple-hop wireless networks, where cooperative transmission schemes are used. The networks are subject to both node failure and random channel fading. A node lifetime distribution is modeled with an increasing failure rate, where the node power consumption level enters the parameters of the distribution. A method for assessing both link and network reliabilities projected at the network’s design life is developed. Link reliability is enhanced through use of redundant nodes. The number of redundant nodes is restricted by the cooperative transmission scheme used. The link reliability is then used to establish a re-transmission control policy that minimizes an expected cost involving power, bandwidth expenditures, and packet loss. The benefit and cost of feedback in network operations are examined. The results of a simulation study under specific node processing times are presented. The study quantifies the effect of loop closure frequency, acknowledgment deadline, and nodes’ storage capacity on the performance of the network in terms of network lifetime, packet loss rate, and false alarm rate. The study concludes that in a network where energy is severely constrained, feedback must be applied judiciously.

FAULT TOLERANCE OF MULTIHOP WIRELESS NETWORKS

This paper analyzes fault-tolerance over the entire design life of a class of multiple-hop wireless networks subject to both node failure and random channel fadings. It also examines the benefit and cost of feedback in network operations. A node lifetime distribution is modeled with an increasing failure rate, where the node power consumption level enters the parameters of the distribution. A method for assessing both link and network reliabilities projected at the network's design life is developed. The link reliability is then used to allocate active nodes to clusters using dynamic programming for maximizing the network's fault-tolerance, and to establish a re-transmission control policy that minimizes an expected cost involving power, bandwidth expenditures, and packet loss.

Breaking away from the conventional ‘usability lab’: the Customer-Centered Design Group at Tektronix, Inc.

Abstract The conventional usability lab is primarily responsible for testing prototypes and products to determine if customers will accept a new design. Often this testing comes too late in the development cycle to allow major design or product changes to occur. In the Customer-Centered Design Group at Tektronix Labs, the usability lab is a small part of our group's involvement in the entire design life cycle of a Tektronix product. We work with design groups to bring the benefits of a usability lab to all phases of design, beginning with understanding our customer's current system and work processes to assessing the competitor's strengths and weaknesses to simulating and evaluating design alternatives. Our ‘lab’ is often on the road; meeting with customers where they work, working with design teams to simulate and prototype designs, and evaluating designs with our customers. To keep in touch with customers and to keep product development focused, we feel a usability group must break down the barriers inh...