Optimal Geometry Design Research Articles

Optimal and fast sensor geometry design method for TDOA localisation systemswith placement constraints

The sensor geometry design problem of time difference of arrival (TDOA) localisation systems based on Cramer-Rao bound is studied. Sensor placement constraints are considered, which means the available placement area is limited. This makes sensor geometry design a sensor selection problem. In two-dimensional (2D) TDOA localisation or 3D TDOA localisation on the earth surface, sensor selection can be implemented through solving a fractional integer programming problem. However, traditional fractional integer programming methods are either suboptimal or too time consuming. For this reason, a new method named path-varying sphere decoding is proposed in two steps. In step one, the programming problem is relaxed into two sphere decoding (SD) subproblems. Solving these subproblems leads to the optimal solution, and the required computational complexity is much less than those of traditional optimal methods. In step two, the structure of the cost function is explored. This makes it possible to calculate the path-varying upper-bound of a quadratic function. Thus the quadratic function constraint used in one SD subproblem becomes tighter and the calculation speed is enhanced. Theory analyses and simulation results show that the proposed method is not only optimal but also much faster than traditional optimal methods when solving large-scale programming problems.

Electrical, Thermal, and Mechanical Characterization of eWLB, Fully Molded Fan-Out Package, and Fan-Out Chip Last Package

Fan-out (FO) packages are widely used in handheld, mobile consumer, and Internet of Things (IoT) devices due to the facility they provide for a greater I/O density and the integration of multiple components in a single package. Various types of FO package are available, including embedded wafer-level BGA (eWLB), fully molded (FM), and a flip-chip-based structure referred to as a fan-out chip-last package (FOCLP). In this paper, ANSYS simulations are performed to examine the warpage, extreme low- $k$ (ELK) interconnect stress and board-level solder joint reliability of the various package types. The validity of the simulation model is confirmed by comparing the numerical results for the warpage of the eWLB and FM packages with the experimental observations. Further simulations are then performed to investigate the heat dissipation performance and electrical crosstalk properties of the three packages. Taguchi experiments are conducted to examine the effects of eight control factors [namely, the inclusion (or otherwise) of a backside laminate film, the board thickness, the joint standoff distance, the ball joint diameter, the under bump metallurgy (UBM) diameter, the joint pitch, the die thickness, and the Cu pillar height] on the thermomechanical reliability of the FM package under accelerated thermal cycling testing. Finally, the Taguchi analysis results are used to determine the optimal geometry design of the FM package.

A note on optimal design of contact geometry in fretting wear

A two-parametric geometry optimization problem for a symmetrical punch with compound curvature in frictionless contact with and an elastic half-plane is considered. An almost constant pressure distribution is sought for by means of least-square method. Another sub-optimal solution, which equalizes the three local maximum peaks (one at the center, and two at either side of the contact interval), is constructed using an asymptotic modeling approach and compared with the exact solution known in the literature.

Optimal Design of Rotor Slot Geometry to Reduce Rotor Leakage Reactance and Increase Starting Performance for High-Speed Spindle Motors

This paper proposes optimal designs of three closed rotor slots geometries for reducing the rotor leakage reactance and increasing the starting performance of high-speed spindle motors. The optimal designs were developed using the response surface methodology and Finite Element Method (FEM). Three closed rotor slot geometries, namely closed, round, and oval were investigated through FEM calculation and validated by experimental measurement for improving starting performance parameters such as starting current, starting torque, magnetic flux linkage in starting condition, and efficiency. In this study, a starting performance analysis, including the alternative equivalent circuit method and flux linkage FEM analysis, was employed. The results show that among the three slot geometries, the optimal design of the circular closed rotor slot produces the lowest rotor leakage reactance and the highest magnetic flux linkage, starting torque, and efficiency. A comparison between the simulation and experimental results validated the accuracy of the proposed model with percentage error being approximately 8%.

Optimal design of rotor geometry in interior permanent magnet machine

Optimal design of rotor geometry in interior permanent magnet machine

Optimal Design of Isothermal Sloshing Vessels by Entropy Generation Minimization Method

In this manuscript, the optimal design of geometry for a forced sloshing in a rigid container based on the entropy generation minimization (EGM) method is presented. The geometry of the vessel considered here is two dimensional rectangular. Incompressible inviscid fluid undergoes horizontal harmonic motion by interaction with a rigid tank. The analytical solution of a fluid stream function is obtained and benchmarked by Finite element results. A parameter study of the aspect ratio, amplitude, and frequency of the horizontal harmonic motion is performed. As well, an analytical solution for the total entropy generation in the volume is presented and discussed. The total entropy generation is compared with the results of the Reynolds-Averaged Navier–Stokes (RANS) solver and the Volume-of-Fluid (VOF) method). Then, the effect of parameters is studied on the total entropy generated by sway motion. Finally, the results show that, based on the excitation frequency, an optimal design of the tank could be found.

Multi‐objective optimization design of plate‐fin vapor generator for supercritical organic Rankine cycle

Supercritical organic Rankine cycle (SORC) is an improved ORC architecture with lower exergy destruction and better heat source utilization when compared with a subcritical one. The accurate design of its vapor generator is of critical importance due to the fact that heat transfer performance significantly affects thermal efficiency, power output, and size of the overall system. This paper aims to develop a mathematical model of the SORC vapor generator using plate-fin heat exchanger. The finite volume method is applied to deal with the properties' variation problem of the supercritical fluids. Multi-objective optimization is employed by the nondominated sorting genetic algorithm II to find the optimum geometry design. The objective functions are the number of entropy production units, annual cost, and volume. For a specific SORC system, an optimum vapor generator is designed using the developed model. Parametric studies are conducted to assess the effect of geometry parameters on the vapor generator performance. The off-design performance of the vapor generator is also evaluated under different mass flow rates and different heat source inlet temperature conditions.

Multimaterial multijoint topology optimization

SummaryIn this paper, a methodology that solves multimaterial topology optimization problems while also optimizing the quantity and type of joints between dissimilar materials is proposed. Multimaterial topology optimization has become a popular design optimization technique since the enhanced design freedom typically leads to superior solutions; however, the conventional assumption that all elements are perfectly fused together as a single piece limits the usefulness of the approach since the mutual dependency between optimal multimaterial geometry and optimal joint design is not properly accounted for. The proposed methodology uses an effective decomposition approach to both determine the optimal topology of a structure using multiple materials and the optimal joint design using multiple joint types. By decomposing the problem into two smaller subproblems, gradient‐based optimization techniques can be used and large models that cannot be solved with nongradient approaches can be solved. Moreover, since the joining interfaces are interpreted directly from multimaterial topology optimization results, the shape of the joining interfaces and the quantity of joints connecting dissimilar materials do not need to be defined a priori. Three numerical examples, which demonstrate how the methodology optimizes the geometry of a multimaterial structure for both compliance and cost of joining, are presented.

Multiobjective design optimization of stent geometry with wall deformation for triangular and rectangular struts.

The stent geometrical design (e.g., inter-strut gap, length, and strut cross-section) is responsible for stent-vessel contact problems and changes in the blood flow. These changes are crucial for causing some intravascular abnormalities such as vessel wall injury and restenosis. Therefore, structural optimization of stent design is necessary to find the optimal stent geometry design. In this study, we performed a multiobjective stent optimization for minimization of average stress and low wall shear stress ratio while considering the wall deformation in 3D flow simulations of triangular and rectangular struts. Surrogate-based optimization with Kriging method and expected hypervolume improvement (EHVI) are performed to construct the surrogate model map and find the best configuration of inter-strut gap (G) and side length (SL). In light of the results, G-SL configurations of 2.81-0.39 and 3.00-0.43mm are suggested as the best configuration for rectangular and triangular struts, respectively. Moreover, considering the surrogate model and flow pattern conditions, we concluded that triangular struts work better to improve the intravascular hemodynamics. ᅟ Graphical abstract.

Optimum shape and length of laterally loaded piles

This study deals with optimum geometry design of laterally loaded piles in a Winkler\'s medium through the Fully Stressed Design (FSD) method. A numerical algorithm distributing the mass by means of the FSD method and updating the moment by finite elements is implemented. The FSD method is implemented here using a simple procedure to optimise the beam length using an approach based on the calculus of variations. For this aim two conditions are imposed, one transversality condition at the bottom end, and a one sided constraint for moment and mass distribution in the lower part of the beam. With this approach we derive a simple condition to optimise the beam length. Some examples referred to different fields are reported. In particular, the case of laterally loaded piles in Geotechnics is faced.

Optimizing three-dimensional point spread function in lensless holographic microscopy

In a number of previous studies on light focusing, the asymmetric axial intensity distribution with intensity peak shifted away from the paraxial focal plane was demonstrated for lenses working with a low Fresnel number. Here, the axial asymmetry of the three-dimensional point spread function (PSF) and the aberration effects are examined in a magnified phase-shifting holographic imaging achieved by the mismatch of reference and reconstruction waves. In the analysis, an optimal combination of experimental parameters and the range of applicable lateral magnifications are found for which the axial asymmetry of the PSF is not apparent and the aberration effects are acceptable. The focal shift and the axial asymmetry of the PSF and the effects of holographic aberrations are evaluated by approximate quantitative criteria whose validity is verified in exact numerical models and experiments. The optimal design of in-line holographic geometry is demonstrated by reconstructing the three-dimensional PSFs and the image of the resolution target recorded in the experimental setup using a spatial light modulator.

Effect of modulation p-doping level on multi-state lasing in InAs/InGaAs quantum dot lasers having different external loss

The influence of the modulation p-doping level on multi-state lasing in InAs/InGaAs quantum dot (QD) lasers is studied experimentally for devices having various external losses. It is shown that in the case of short cavities (high external loss), there is an increase in the lasing power component corresponding to the ground-state optical transitions of QDs as the p-doping level grows. However, in the case of long cavities (small external loss), higher dopant concentrations may have an opposite effect on the output power. Based on these observations, an optimal design of laser geometry and an optimal doping level are discussed.

A Design Approach for Coaxial Magnetic Gear and Determination of Torque Capability

This paper presents a time saving methodology for design and sizing the magnetic gear sets. Some new design parameters similar to mechanical gears are defined to calculate the torque capacity based on these. Finite element analysis is extensively used to calculate the variation of gear set torque capacity due to changes in different geometric parameters of a set. Different design curves are obtained by which the design and sizing of the gears can routinely be accomplished. Optimal performance of magnetic gear wasn’t the main target of this research and just this method helps gear designers to decide on parameters such as scale of gears, magnet thickness, stack length and pole pair numbers and come up with a close to optimum geometry design

Comparative Study on Various Geometrical Core Design of 300 MWth Gas Cooled Fast Reactor with UN-PuN Fuel Longlife without Refuelling

Nuclear power has progressive improvement in the operating performance of exiting reactors and ensuring economic competitiveness of nuclear electricity around the world. The GFR use gas coolant and fast neutron spectrum. This research use helium coolant which has low neutron moderation, chemical inert and single phase. Comparative study on various geometrical core design for modular GFR with UN-PuN fuel long life without refuelling has been done. The calculation use SRAC2006 code both PIJ calculation and CITATION calculation. The data libraries use JENDL 4.0. The variation of fuel fraction is 40% until 65%. In this research, we varied the geometry of core reactor to find the optimum geometry design. The variation of the geometry design is balance cylinder; it means that the diameter active core (D) same with height active core (H). Second, pancake cylinder (D>H) and third, tall cylinder (D<H). The reflector radial-axial width is 50 cm. The power is 300 MWth. First calculation, we calculate survey parameter for UN-PuN fuel with fissile contain from Plutonium waste LWR for each geometry. The minimum power density is around 72 Watt/cc, and maximum power density 114 Watt/cc. After we calculate with various geometry core, when we use the balance geometry, the k-eff value flattest and more stable than the others.

Theoretical analysis on the collapse of dumbbell-shaped tubes

Thin-walled round tube systems are widely used in impact protection. However, in these systems, additional installation time and cost is required to constrain the tubes and prevent their splashing under impact loadings. To address this problem, a self-locked system comprised of thin-walled dumbbell-shaped tubes was recently proposed, which can prevent lateral splash from impact loadings without the presence of any constraints on the boundary or between the tubes. This paper provides a theoretical analysis on the deformation and collapse of dumbbell-shaped tubes under quasi-static lateral loads. A plastic hinge model is developed to estimate the force-displacement relationship, deformation efficiency and specific energy absorption of the dumbbell-shaped tube, and besides, an elastic solution is derived to describe the mechanical response of the dumbbell-shaped tube at small deformation. The theoretical models are validated by both finite element method (FEM) simulation and experiments. Based on the theoretical analysis, the effects of the geometry of the dumbbell-shaped tube on energy absorption are studied, and the optimal geometry design of the tube is discussed. The relation between each geometry parameter and energy absorption properties is summarized in a table, which provides important reference for designing dumbbell-shaped tubes in practical applications.

Semi-analytical model for quasi-double-layer surface electrode ion traps

To realize scale quantum processors, the surface-electrode ion trap is an effective scaling approach, including single-layer, double-layer, and quasi-double-layer traps. To calculate critical trap parameters such as the trap center and trap depth, the finite element method (FEM) simulation was widely used, however, it is always time consuming. Moreover, the FEM simulation is also incapable of exhibiting the direct relationship between the geometry dimension and these parameters. To eliminate the problems above, House and Madsen et al. have respectively provided analytic models for single-layer traps and double-layer traps. In this paper, we propose a semi-analytical model for quasi-double-layer traps. This model can be applied to calculate the important parameters above of the ion trap in the trap design process. With this model, we can quickly and precisely find the optimum geometry design for trap electrodes in various cases.

Optimal design of thread geometry and its performance in friction stir spot welding

As the main factor significantly influencing the material flow behavior during friction stir spot welding (FSSW), tool geometry plays an important role on the weld quality. In this study, a tool with a half-threaded pin aiming to enhance the material flow at the lap interface but induces lower heat input was successfully put forward and manufactured. Using alclad 2A12-T4 aluminum alloy as the research object, the FSSW processes using tools with half-threaded pin and full-threaded pin were investigated by experimental and simulation methods. Compared with the full-threaded pin, peak temperature during welding using the half-threaded pin is lower than that using the full-threaded pin. The half-threaded pin was beneficial for attaining bigger bonding width at the lap interface, which resulted from the higher material flow velocity. Cross tension failure load of the welds using the half-threaded pin is bigger than that using the full-threaded pin, which agrees with the different bonding widths. Fracture morphologies directly prove bigger bonding width on the weld using the half-threaded pin.

Computational Fluid Dynamics Based Optimal Design of Guiding Channel Geometry in U-Type Coolant Layer Manifold of Large-Scale Microchannel Fischer–Tropsch Reactor

A microchannel Fischer–Tropsch reactor retaining high heat and mass transfer performance requires uniform flow distribution on the coolant side to induce isothermal condition for controllable and sustainable operation. The present work improved the flow performance of a large-scale layer of over 100 channels by introducing an extremely simple guiding fin in the inlet and outlet rectangular manifolds. Case studies with three-dimensional computational fluid dynamics (CFD) were carried out where the upper and bottom lengths of the guiding fin were the main geometric variables. Then the optimization work was conducted to estimate the performance of the optimal design. The robustness for the proposed geometry was tested with varying the flow rate, fluid type, and temperature. The result showed that the proposed design can retain uniform distribution over a wide operation range (500 ≤ ReGF ≤ 10800).

An optimal fracture geometry design method of fractured horizontal wells in heterogeneous tight gas reservoirs

In this work, the unified fracture design (UFD) is extended for the first time to the fractured horizontal wells in heterogeneous closed box-shaped tight gas reservoirs. Utilizing the direct boundary element method and influence function, the dimensionless fracture productivity index is obtained and expressed in the function of proppant volume and fracture geometry at the pseudo- steady state. With the iterative method, the effectively propped permeability, k fe, is corrected using the in-situ Reynolds number, N Re. The goal of this paper is to present a new UFD extension to design the proppant volume and the optimal fracture geometry. The results show that there exists an optimal proppant volume for a certain reservoir. The small aspect ratio (y e/x e) and high permeability reservoirs need short and wide fractures to diminish the non-Darcy effect. On the contrary, long and narrow fractures are required for the large aspect ratio and low permeability reservoirs. A small proppant volume is prone to creating long fractures, while a relatively large proppant volume creates wide fractures. The new extension can be used to evaluate the previous fracture parameters and design the following fracture parameters of the fractured horizontal well in heterogeneous tight gas reservoirs, with the non-Darcy effect taken into account.

Cramér–Rao bound and statistical resolution limit investigation for near-field source localization

In this paper, we investigate the performance analysis for near-field source localization in terms of the mean square error and resolvability. We first derive and analyze non-matrix, closed-form expressions of the deterministic Cramér–Rao bound for two closely spaced, time-varying near-field sources in the context of linear arrays. Numerical simulations confirm the validity of the obtained expressions. Using these expressions and based on Smith's criterion, we discuss the behavior of the statistical resolution limit with respect to some features of interest, namely, the correlation factor, the central frequency, the minimum resolution limit boundary and the array geometry. Finally, to avoid the complexity of the optimal geometry design procedure, we propose a fast, nearly optimal, array design scheme to enhance the capacity of resolvability under given constraints (e.g., number of sensors and array aperture).