A Thermal-Solid–Fluid Method for Topology Optimization of Structures with Design-Dependent Pressure Load

For the topology optimization of structures with design-dependent pressure,an intuitive way is to directly describe the loading boundary of the structure,and then update the load on it.However,boundary recognition is usually cumbersome and inaccurate.Furthermore,the pressure is always loaded either outside or inside the structure,instead of both.Hence,the inner enclosed and outer open spaces should be distinguished to recognize the loading surfaces.To handle the above issues,a thermal-solid–fluid method for topology optimization with design-dependent pressure load is proposed in this paper.In this method,the specific void phase is defined to be an incompressible hydrostatic fluid,through which the pressure load can be transferred without any needs for special loading surface recognition.The nonlinear-virtual thermal method(N-VTM)is used to distinguish the enclosed and open voids by the temperature difference between the enclosed(with higher temperature)and open(with lower temperature)voids,where the solid areas are treated as the thermal insulation material,and other areas are filled with the self-heating highly thermally conductive material.The mixed displacement–pressure formulation is used to model this solid–fluid problem.The method is easily implemented in the standard density approach and its effectiveness is verified and illustrated by several typical examples at the end of the paper.

海上水下爆炸的爆炸压力测量

Blast pressure measurements of a controlled underwater explosion in the sea were carried out.An explosive of 25-kg trinitro-toluene(TNT)equivalent was detonated,and the blast pressures were recorded by eight diferent high-performance pressure sensors that work at the nonresonant high-voltage output in adverse underwater conditions.Recorded peak pressure values are used to establish a relationship in the well-known form of empirical underwater explosion(UNDEX)loading formula.Constants of the formula are redetermined by employing the least-squares method in two diferent forms for best ftting to the measured data.The newly determined constants are found to be only slightly diferent from the generally accepted ones.

Experimental Study on Seepage Characteristics of a Soil-Rock Mixture in a Fault Zone

A mixture of fault gouge and rubble taken out from a fault zone is used to prepare a S-RM(Soil-Rock Mixture)sample with rock block proportions of 20%,30%,40%,50%,60%and 70%,respectively.A GDS triaxial test system is used accordingly to measure the seepage characteristics of such samples under different loading and unloading confining pressures in order to determine the variation law of the permeability coefficient.The test results show that:(1)The permeability coefficient of the S-RM samples decreases as the pressure increases,and the decrease rate of this coefficient in the initial stage of confining pressure loading is obviously higher than in the semi-late period;(2)The permeability coefficient at different confining pressure levels presents a common trend as the rock block proportion is increased,i.e.,it decreases first then it increases(the permeability coefficient of the sample with rock block proportion 40%being the smallest,70%the largest);(3)In the stage of confining pressure unloading,the recovery degree of the permeability coefficient grows with the increase of rock block proportion(the recovery rate of S-RM sample with rock block proportion 70%reaches 50.2%);(4)In the stage of confining pressure loading and unloading,the sensitivity of the permeability coefficient to the rock block proportion displays the inverse“Z”variation rule(when rock block proportion reaches 60%,the sensitivity is highest);(5)In the stage of confining pressure loading,the relationship between the permeability coefficient and confining pressure can be described by an exponential relationship.

Analysis of flow response to fluctuation of rotational speed in a radial impeller

By discretizing the convection terms with AUSM+-up scheme in the rotating coordinate system,a finite volume analysis code based on multi-block structured grids was developed independently so as to realize the numerical solving of internal flow fields of turbomachineries.Taking an unshrouded radial impeller with the working fluid of water vapour as the research object,the flow response to the fluctuation of rotational speed was calculated.By comparing the surface pressure profiles and velocity contours calculated by the code and commercial software respectively,the accuracy of flow solver was verified.The analysis of flow response data indicates that,as the working condition shifts closer towards the surge boundary,the response of flow parameters such as mass flow and aerodynamic torque will be more nonsynchronous with the fluctuation of rotational speed,and also the influence of density variation on mass flow variation will be smaller.Moreover,the transient variation region of working condition performance will deviate farther away from the steady performance curve as the working condition approaches the surge boundary.Compared to the working conditions with small mass flows,the distribution characteristics of pressure difference load on the blade surface vary little under large mass flow conditions.The reduction of fluctuation amplitude of rotational speed exerts no influence on abating the hysteresis of flow response.

The development and application of an inviscid inverse method

A two-dimensional inviscid inverse method is developed,verified and applied inthis paper.The method solves the Euler equation in absolute reference frame by a cell-centeredfinite volume method,and the hybrid Runge-Kutta method ls used for time integration.Different from the direct method,the inverse method imposes a unique"transpiration"boundary condition on the blade surfaces.The inputs of inverse method are pressure loadingand blade tangential thickness distribution along the blade chord.During the time marchingprocess,the blade shape is periodically updated.When the solution is converged,the bladeshape will be stabled.In the paper,the principle of the inverse method is described in detail.Then the developed inverse method is verified against a consistence test:recover an axialcompressor cascade from a different start.Finally,to demonstrate the powerful capability ofthe method,it is used to redesign the cascade,and final results give an improved aerodynamicperformance.