共查询到20条相似文献,搜索用时 93 毫秒
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为解决目前侧入式导光板网点优化设计中存在经验式手动优化繁琐、且很难达到一个高均匀效果的问题,提出了一种基于模糊优化理论的网点自动优化设计方法。网点形状采用锥形结构,为使目标面上各处的光能分布主要由其正下方网点的散射光贡献,分析了其半顶角与网点位置的关系,并使得网点半顶角仅由其位置决定。以网点半径为主要优化参数,通过隶属度函数将网点结构模糊化,并自定义评价函数来解模糊化实现均匀照明。进而,采用动态数据交换(DDE)技术将Matlab与TracePro进行联立,通过Matlab语言与Scheme语言混编控制TracePro自动进行数据交换、光线追迹与模糊优化。导光板网点优化设计实例仿真结果表明,优化后均匀度达到92.17%,光能利用率达到70.37%,全程实现自动优化,无需任何手动调节。 相似文献
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大口径主镜轻量化结构参数的优化设计 总被引:1,自引:0,他引:1
针对空间遥感器中大口径主镜的轻量化结构设计引入了基于Kriging近似模型的多目标遗传优化方法,以2 m口径SiC主镜为例对其轻量化结构参数进行了优化设计。采用拉丁超立方法对优化参数进行试验设计,建立了Kriging模型,并用多目标遗传算法迭代求得了最优解。优化后得到了质量为243 kg的2 m口径SiC主镜,其面形精度达到了25.7 nm PV,4.7 nm RMS,轻量化率为84%。试验结果验证了此优化设计方法的可行性,为大口径主镜的轻量化结构参数优化设计提供了借鉴和参考。 相似文献
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大流量贯流式水轮机转轮叶片由轮毂至轮缘形状变化很大,流动特征变化亦非常明显,采用代表半径处能量平均的一元设计将不能满足要求。为了使转轮叶片设计达到更细致的优化设计目标,非常有必要进行二元的转轮叶片翼型优化设计。本文提出将一元能量概念及技术扩张至二元能量收支的新概念。研究中由CFD三维数值解析结果求得叶片进出口二元能量收支状况并对其进行评价及控制,为转轮叶片翼型优化设计提供依据。研究结果表明,二元能量收支方法对优化设计具有实际意义,用此方法设计的贯流式水轮机效率比一元设计提高了0.5%。 相似文献
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Assaad Alsahlani 《Journal of sound and vibration》2011,330(12):2721-2732
The dynamics of a vibrating string subjected to a constraint at one boundary is investigated in this paper. The constraint is applied by a scabbard that moves a small distance along the mean position of the string. The scabbard is moved instantaneously such that the position and the velocity of the string outside the scabbard is unaffected immediately after application of the constraint, whereas the length of the string covered by the scabbard is brought to rest. The constraint is removed by moving the scabbard back to its original position and the change in energy of the string is investigated for different values of scabbard travel distance and time of application of the constraint. Analytical and numerical simulation results are first provided for the string vibrating in the first mode, and then for a more general case where the string has arbitrary initial conditions. The results show that the energy of the string can increase or decrease depending on the time of application of the constraint for a given distance of travel of the scabbard. This provides the opportunity for active control of vibration of the string through direct physical interaction, using the scabbard as an actuator. A simple feedback control strategy is proposed and numerical simulation results are presented. These results indicate that although removal of the constraint does not change the energy of the string, the effectiveness of the control strategy depends on the time of removal of the constraint. 相似文献
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Assaad Alsahlani Frank B. Mathis Ranjan Mukherjee 《Journal of sound and vibration》2012,331(20):4395-4405
A new method for the control of string vibration is presented. The method relies on application and removal of a constraint at one point on the string close to one of its boundaries. Application of the constraint temporarily results in two vibrating strings, one of which is significantly shorter in length than the other. The vibration of the shorter length string decays rapidly due to high damping and results in reduction in the overall energy of the system. Removal of the constraint does not change the energy of the system but allows the constraint to be applied repeatedly for vibration suppression. A mathematical model of the cycle of constraint application and removal is presented and multiple cycles of constraint application and removal are simulated. Experiments were performed with a coiled extension spring which behaves like a lightly damped string. Simulation and experimental results match well with each other and demonstrate the efficacy of the simple control strategy. 相似文献
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Optimum processor theory successfully accounts for earlier pitch data by including the constraint that component tones in a complex stimulus are estimated as successive harmonics. This constraint gives the paradoxical prediction that a periodic complex tone comprising nonsuccessive harmonics cannot evoke periodicity pitch corresponding to its period. Most published data from pitch-shift experiments imply the necessity for this constraint. New periodicity pitch experiments on pitch shift and musical interval recognition were performed which prove that the theoretical constraint is not generally true. New and old data are reconciled by replacing the maximum likelihood estimation of the theory with maximum posterior probability estimation and removing the successive harmonic constraint. Periodicity pitch is estimated by optimizing the match between the aurally measured frequencies of stimulus components and a general harmonic template over some a priori expected pitch range. The new, more general, formulation reduces in many experimental situations to the successive harmonic constraint as a special case. 相似文献
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The free energy as a function of the reaction coordinate (rc) is the key quantity for the computation of equilibrium and kinetic quantities. When it is considered as the potential of mean force, the problem is the calculation of the mean force for given values of the rc. We reinvestigate the PMCF (potential of mean constraint force) method which applies a constraint to the rc to compute the mean force as the mean negative constraint force and a metric tensor correction. The latter allows for the constraint imposed to the rc and possible artefacts due to multiple constraints of other variables which for practical reasons are often used in numerical simulations. Two main results are obtained that are of theoretical and practical interest. First, the correction term is given a very concise and simple shape which facilitates its interpretation and evaluation. Secondly, a theorem describes various rcs and possible combinations with constraints that can be used without introducing any correction to the constraint force. The results facilitate the computation of free energy by molecular dynamics simulations. 相似文献
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Both projectable and non-projectable versions of Horava-Lifshitz gravity face serious challenges. In the non-projectable version, the constraint algebra is seemingly inconsistent. The projectable version lacks a local Hamiltonian constraint, thus allowing for an extra scalar mode which can be problematic. A new formulation of non-projectable Horava-Lifshitz gravity, naturally realized as a representation of the master constraint algebra studied by loop quantum gravity researchers, is presented. This yields a consistent canonical theory with first class constraints. It captures the essence of Horava-Lifshitz gravity in retaining only spatial diffeomorphisms (instead of full space-time covariance) as the physically relevant non-trivial gauge symmetry; at the same time the local Hamiltonian constraint needed to eliminate the extra mode is equivalently enforced by the master constraint. 相似文献
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Paul T. Allen Lars Andersson Alvaro Restuccia 《Communications in Mathematical Physics》2011,301(2):383-410
In this paper we consider the classical initial value problem for the bosonic membrane in light cone gauge. A Hamiltonian
reduction gives a system with one constraint, the area preserving constraint. The Hamiltonian evolution equations corresponding
to this system, however, fail to be hyperbolic. Making use of the area preserving constraint, an equivalent system of evolution
equations is found, which is hyperbolic and has a well-posed initial value problem. We are thus able to solve the initial
value problem for the Hamiltonian evolution equations by means of this equivalent system. We furthermore obtain a blowup criterion
for the membrane evolution equations, and show, making use of the constraint, that one may achieve improved regularity estimates. 相似文献
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With the development of wireless communication, free-space optical (FSO) communication is becoming a highly promising technology. In this paper, we consider the covert FSO communication between two legitimate peers in the presence of an external warden. We establish a system model under a nonnegativity constraint, a peak optical intensity constraint, an average optical intensity constraint and a covertness constraint. For the considered system, the optimal input signal is shown to follow a uniform distribution. Based on the optimal input signal and covertness constraint, we obtain an upper bound that should be satisfied by the transmitter’s peak optical intensity, which provides a basis for the transmitter to set the transmit optical intensity. We also derive the upper bound of maximum amount of information transmitted covertly, which reveals the fundamental performance limit of covert FSO communication. Finally, we verify the theoretical analysis by numerical simulations. 相似文献
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气象数值预报中,由于分析过程引入初始非平衡,从而引起虚假快波振荡,重力波控制弱约束把资料分析过程和初始化过程结合在一起,通过数字滤波弱约束在极小化过程中实现对分析场的平衡约束,克服非平衡问题. 以2008年初的一次南方雨雪天气为研究个例,进行了数字滤波弱约束的同化试验和预报试验,结果表明,数字滤波弱约束4D-Var能充分控制快波振荡的出现和初始调整现象,使得到的分析场不仅能更好的逼近观测,而且能更好地与模式动力相协调. 预报检验的结果表明,在同化过程中施加数字滤波弱约束,能有效滤除由于地形或观测资料等因素
关键词:
变分同化
初始非平衡
数字滤波
弱约束 相似文献
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辐射测温技术随着辐射测量传感器技术的进步而不断进步,已经由单波长测温发展到多波长和多波段测温,由点温测量发展到二维甚至三维温度场测量。但是在辐射测温更精确反演方面,却很难克服因发射率未知性而引起的模型构建误差。发射率行为难以确定并极大地影响了测温精度,急需发展一种具有通用性,不受发射率具体行为限制,具有较高稳定性的辐射测温方法。双波长测温适用于发射率具有灰体行为的物体温度测量,一系列的发射率补偿算法和波长选择方法均未能很好地实现通用性测量,往往直接单色测量可能误差比比色法更小。多波长测温得到广泛应用,但并不是波长越多越好,发射率模型仍然具有较大局限性。提出了发射率直接限定算法和发射率松驰限定算法来反演温度。在发射率限定条件相同时,这两种方法是等价的。发射率松驰限定算法基于最小二乘算法和松驰因子进行真温求解。推导了松驰限定法的误差传递公式,发现在保证测量信号强度的前提下,λT越小温度误差越小;发射率行为对温度相对误差具有重要影响,在相同的λT条件下,发射率随波长变化越大,在限定区间上覆盖越均匀,测量误差越小。但从直接限定算法可以看出所测波长数越多,测量误差越小。两种方法均可以看出,减少限定区间长度也可以显著地提高测量精度。 相似文献
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José W. Maluf 《General Relativity and Gravitation》1996,28(11):1361-1376
In the teleparallel equivalent of general relativity the integral form of the Hamiltonian constraint contains explicitly theadm energy in the case of asymptotically flat space-times. We show that such expression of the constraint leads to a natural and straightforward construction of a Schrödinger equation for time-dependent physical states. The quantized Hamiltonian constraint is thus written as an energy eigenvalue equation. We further analyse the constraint equations in the case of a space-time endowed with a spherically symmetric geometry. We find the general functional form of the time-dependent solutions of the quantized Hamiltonian and vector constraints. 相似文献