Blind watermarking plays a significant role in copyright protection and information hiding.To enhance the security of watermark image information,a dual encryption method is proposed,which combines block shuffling wit...Blind watermarking plays a significant role in copyright protection and information hiding.To enhance the security of watermark image information,a dual encryption method is proposed,which combines block shuffling with Logistic chaos encryption using two sets of random numbers as keys.This dual encryption technique is applied to blind watermark images,utilizing a combination of discrete wavelet transform(DWT)and discrete cosine transform(DCT)as the embedding method.First,the watermark image is divided into small blocks,which are shuffled and rearranged using one set of random numbers as the key,while recording the shuffling sequence of block positions.Subsequently,the shuffled blocks are reassembled into an image,and another set of random numbers is used as the key for Logistic chaos encryption,rendering the watermark image chaotically invisible.Then,a double DWT is applied to the carrier image,followed by a DCT,allowing the encrypted watermark image to be embedded.This achieves the concealment of the blind watermark.Experimental results demonstrate that this method exhibits robustness,excellent invisibility,and secrecy.展开更多
具有模块化多电平结构的串联开关直流变压器(direct current transformer, DCT)在使用传统单移相控制时,存在中压侧全桥换流时阀串支路产生电流尖峰的问题,器件承受额外的电流应力。基于该新型DCT的工作原理与电流波形,提出一种基于中...具有模块化多电平结构的串联开关直流变压器(direct current transformer, DCT)在使用传统单移相控制时,存在中压侧全桥换流时阀串支路产生电流尖峰的问题,器件承受额外的电流应力。基于该新型DCT的工作原理与电流波形,提出一种基于中压侧全桥换流移相的阀串支路电流优化调制方法。文中对阀串支路的电流应力进行详细分析,结合电路可靠工作移相角范围,确定中压侧全桥换流移相角最优值的计算方法,从而确立优化控制策略。该优化控制策略独立于原有的功率控制环路运行,不改变DCT功率传输状态,不影响功率的调节控制,易于投入实际应用。仿真与样机实验的结果验证了该优化控制策略降低电流应力的有效性,同时样机实验结果显示效率得到提升。综合原理分析与效果验证可知,该优化控制策略对设备的安全运行与器件选型具有借鉴意义。展开更多
在车辆起步过程中,发动机输出转矩波动会导致离合器接合不稳定,从而影响整车动力传动系统的平顺性。双质量飞轮(dual mass flywheel,DMF)可减小发动机转矩波动对离合器及整车动力传动系统的影响。针对起步过程离合器接合不稳定影响整车...在车辆起步过程中,发动机输出转矩波动会导致离合器接合不稳定,从而影响整车动力传动系统的平顺性。双质量飞轮(dual mass flywheel,DMF)可减小发动机转矩波动对离合器及整车动力传动系统的影响。针对起步过程离合器接合不稳定影响整车平顺性的问题,以双离合器自动变速器(dual clutch automatic transmission,DCT)车辆为研究对象,研究了DMF的刚度、阻尼和初级与次级飞轮惯量比对DCT车辆起步过程离合器接合稳定性的影响,并建立了以离合器黏滑比和整车冲击度为目标函数的多目标优化模型,利用遗传算法对模型进行优化,得到了使离合器接合稳定性提高且整车冲击度明显降低的DMF最优参数组合。展开更多
基金supported by the National Natural Science Foundation of China(No.52066010)the Key Research and Development Program of Gansu Province(No.20YF8GA039)。
文摘Blind watermarking plays a significant role in copyright protection and information hiding.To enhance the security of watermark image information,a dual encryption method is proposed,which combines block shuffling with Logistic chaos encryption using two sets of random numbers as keys.This dual encryption technique is applied to blind watermark images,utilizing a combination of discrete wavelet transform(DWT)and discrete cosine transform(DCT)as the embedding method.First,the watermark image is divided into small blocks,which are shuffled and rearranged using one set of random numbers as the key,while recording the shuffling sequence of block positions.Subsequently,the shuffled blocks are reassembled into an image,and another set of random numbers is used as the key for Logistic chaos encryption,rendering the watermark image chaotically invisible.Then,a double DWT is applied to the carrier image,followed by a DCT,allowing the encrypted watermark image to be embedded.This achieves the concealment of the blind watermark.Experimental results demonstrate that this method exhibits robustness,excellent invisibility,and secrecy.
文摘具有模块化多电平结构的串联开关直流变压器(direct current transformer, DCT)在使用传统单移相控制时,存在中压侧全桥换流时阀串支路产生电流尖峰的问题,器件承受额外的电流应力。基于该新型DCT的工作原理与电流波形,提出一种基于中压侧全桥换流移相的阀串支路电流优化调制方法。文中对阀串支路的电流应力进行详细分析,结合电路可靠工作移相角范围,确定中压侧全桥换流移相角最优值的计算方法,从而确立优化控制策略。该优化控制策略独立于原有的功率控制环路运行,不改变DCT功率传输状态,不影响功率的调节控制,易于投入实际应用。仿真与样机实验的结果验证了该优化控制策略降低电流应力的有效性,同时样机实验结果显示效率得到提升。综合原理分析与效果验证可知,该优化控制策略对设备的安全运行与器件选型具有借鉴意义。
